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+metadata, and any other content or labor, has been confirmed to be
+in the PUBLIC DOMAIN IN THE UNITED STATES.
+
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+Project Gutenberg (https://www.gutenberg.org) public repository for
+eBook #60143 (https://www.gutenberg.org/ebooks/60143)
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-The Project Gutenberg EBook of Prairie Peak and Plateau, by 
-John Chronic and Halka Chronic
-
-This eBook is for the use of anyone anywhere in the United States and most
-other parts of the world at no cost and with almost no restrictions
-whatsoever.  You may copy it, give it away or re-use it under the terms of
-the Project Gutenberg License included with this eBook or online at
-www.gutenberg.org.  If you are not located in the United States, you'll have
-to check the laws of the country where you are located before using this ebook.
-
-Title: Prairie Peak and Plateau
-       A Guide to the Geology of Colorado
-
-Author: John Chronic
-        Halka Chronic
-
-Release Date: August 21, 2019 [EBook #60143]
-
-Language: English
-
-Character set encoding: UTF-8
-
-*** START OF THIS PROJECT GUTENBERG EBOOK PRAIRIE PEAK AND PLATEAU ***
-
-
-
-
-Produced by Stephen Hutcheson and the Online Distributed
-Proofreading Team at http://www.pgdp.net
-
-
-
-
-
-
-  STATE OF COLORADO
-  John A. Love, _Governor_
-
-  DEPARTMENT OF NATURAL RESOURCES
-  T. W. Ten Eyck, _Executive Director_
-
-  COLORADO GEOLOGICAL SURVEY
-  John W. Rold, _State Geologist and Director_
-  A. L. Hornbaker, _Mineral Deposits Geologist_
-  Richard H. Pearl, _Ground Water Geologist_
-  William P. Rogers, _Engineering Geologist_
-  Antoinette M. Ray, _Secretary_
-
-MISSION OF THE COLORADO GEOLOGICAL SURVEY
-
-The Colorado Geological Survey was legislatively re-established in
-February 1969 to meet the geologic needs of the citizens, governmental
-agencies, and mineral industries of Colorado. This modern legislation
-was aimed at applying geologic knowledge toward the solution of today’s
-and tomorrow’s problems of an expanding population, mounting
-environmental concern, and the growing demand for mineral resources.
-
-SPECIFIC LEGISLATIVE CHARGES:
-
-  “Assist, consult with, and advise state and local governmental
-          agencies on geologic problems.”
-  “Promote economic development of mineral resources.”
-  “Evaluate the physical features of Colorado with reference to present
-          and potential human and animal use.”
-  “Conduct studies to develop geologic information.”
-  “Inventory the state’s mineral resources.”
-  “Collect, preserve and distribute geologic information.”
-  “Determine areas of geologic hazard that could affect the safety of or
-          economic loss to the citizens of Colorado.”
-  “Prepare, publish, and distribute geologic reports, maps, and
-          bulletins.”
-
-
-
-
-                                PRAIRIE
-                                PEAK and
-                                PLATEAU
-
-
-                   A GUIDE TO THE GEOLOGY OF COLORADO
-
-                      _by John and Halka Chronic_
-
-[Illustration: Relief image of Colorado]
-
-                 COLORADO GEOLOGICAL SURVEY BULLETIN 32
-                                  1972
-
-               Available from Colorado Geological Survey
-                          1845 Sherman Street
-                         Denver, Colorado 80203
-                              Price—$2.00
-
-
-                            ACKNOWLEDGMENTS
-
-This guidebook was written at the request of the Colorado Geological
-Survey to fulfill a long-felt need for a popular account of the state’s
-geology and its relationship to Man.
-
-The authors wish to thank those of their colleagues who have assisted at
-various times in the preparation of this book. John Rold, Colorado State
-Geologist, and William Weber, of the University of Colorado Museum
-staff, made many helpful suggestions concerning the manuscript. John
-Schooland, vice president of the Colorado Historical Society, generously
-provided several pictures of early mining activities in Colorado.
-Permission to reproduce drawings and paintings of fossils and
-reconstructions of past environments was granted by the American Museum
-of Natural History and the University of Colorado Museum. Drawings,
-maps, and diagrams are largely the work of Robert Maurer, who also
-designed the cover and title page.
-
-[Illustration: Tilted dark red sedimentary rocks of the
-Pennsylvanian-Permian Maroon Formation are well exposed in the cliffs of
-Maroon Bells, southwest of Aspen. (Photo courtesy Hydraulic Unlimited
-Mfg. Co.)]
-
-
-                                CONTENTS
-
-
-                                                                   _Page_
-  Introduction                                                          1
-  I Colorado’s Three Provinces                                          3
-      The Prairies                                                      8
-      The Peaks                                                        10
-          Front Range                                                  11
-          Wet Mountains                                                16
-          Sangre de Cristo Range and Spanish Peaks                     17
-          Park Range and Rabbit Ears Range                             19
-          Gore Range                                                   20
-          Tenmile and Mosquito Ranges                                  21
-          Sawatch Range                                                22
-          Elk Mountains and West Elk Mountains                         24
-          San Juan Mountains                                           25
-          Uinta Mountains                                              26
-      The Plateaus                                                     28
-  II Geologic History of Colorado                                      32
-      Precambrian Era                                                  33
-      Paleozoic Era                                                    38
-          Cambrian Period                                              39
-          Ordovician Period                                            40
-          Silurian Period                                              42
-          Devonian Period                                              42
-          Mississippian Period                                         43
-          Pennsylvanian Period                                         44
-          Permian Period                                               48
-      Mesozoic Era                                                     51
-          Triassic Period                                              51
-          Jurassic Period                                              52
-          Cretaceous Period                                            56
-      Cenozoic Era                                                     59
-          Tertiary Period                                              59
-          Quaternary Period                                            68
-  III Geology and Man in Colorado                                      74
-      Gold, Silver, and Other Metals                                   77
-          Boulder County                                               79
-          Central City and Idaho Springs                               80
-          Georgetown, Empire, and Silver Plume                         81
-          Leadville                                                    82
-          Breckenridge                                                 83
-          Fairplay                                                     84
-          Silverton                                                    85
-          Ouray                                                        87
-          Aspen                                                        88
-          Creede                                                       89
-          Cripple Creek                                                90
-          Climax                                                       91
-      Radium, Uranium, and Vanadium                                    93
-      Oil, Natural Gas, and Oil Shale                                  94
-      Coal                                                             96
-      Construction Materials                                           97
-          Sand, Gravel, and Clay                                       97
-          Stone                                                        99
-          Lime and Gypsum                                             101
-      Gems                                                            102
-      Water                                                           103
-          Surface Water                                               103
-          Groundwater                                                 105
-          Caves                                                       106
-          Springs                                                     109
-      Environmental Geology                                           111
-  Glossary                                                            114
-  Suggested Reading                                                   119
-  Index                                                               121
-
-
-                                 ILLUSTRATIONS
-
-
-                                                                   _Page_
-  Colorado’s three geologic provinces                                   2
-  Pikes Peak, seen from the Garden of the Gods                          4
-  Rock classification (chart)                                           5
-  Stratigraphic column (chart)                                          7
-  Jurassic rocks in Colorado (map)                                      9
-  East face of Longs Peak                                              11
-  Rocky Mountain National Park (east-west profile)                     12
-  Big Thompson Canyon, west of Loveland                                13
-  Red Rocks Amphitheater, west of Denver                               14
-  Colorado Springs area (map and cross section)                        15
-  Joint systems in Precambrian rocks, Boulder Canyon                   15
-  Spanish Peaks, southwest of Walsenburg                               18
-  Hahn’s Peak, north of Steamboat Springs                              19
-  Gore Range from the east                                             20
-  Aspen Mountain geology (map)                                         23
-  Mt. Sopris, south of Glenwood Springs                                24
-  Ouray, in the San Juan Mountains                                     25
-  Steamboat Rock, Dinosaur National Monument                           27
-  Grand Hogback, near Rifle (block diagram)                            28
-  Mt. Garfield, near Grand Junction                                    30
-  Precambrian-Cambrian unconformity south of Ouray                     34
-  Geologic map of Colorado                                             35
-  Black Canyon of the Gunnison National Monument                       36
-  Precambrian-Cambrian unconformity, Glenwood Canyon                   38
-  Cambrian fossils                                                     39
-  Ordovician fossils                                                   41
-  Devonian fossils                                                     43
-  Mississippian fossils                                                44
-  Pennsylvanian paleogeography (map)                                   45
-  Fountain Formation northwest of Denver                               45
-  Pennsylvanian fossils                                                46
-  Contorted Pennsylvanian rocks near Gypsum                            46
-  Balanced Rock, Garden of the Gods                                    48
-  Permian reptile tracks                                               49
-  The Flatirons, near Boulder                                          50
-  Colorado National Monument                                           51
-  Morrison Formation, west of Denver                                   53
-  Dinosaur bones, found near Morrison                                  54
-  Dakota Sandstone hogback                                             56
-  Cretaceous fossils                                                   57
-  Wolford Mountain, north of Kremmling                                 60
-  Eohippus, the “Dawn Horse”                                           61
-  Golden and South Table Mountain                                      62
-  Devil’s Staircase, near Spanish Peaks                                63
-  Green River oil shale, west of Rifle                                 64
-  Florissant Fossil Beds National Monument                             65
-  Pawnee Buttes, north of Fort Morgan                                  66
-  Fossil mammals, northeastern Colorado                                67
-  Glacial lakes in Rocky Mountain National Park                        68
-  Arapaho Glacier, west of Boulder                                     70
-  Pleistocene mastodons                                                72
-  Great Sand Dunes National Monument                                   73
-  Colorado Mineral Belt (map)                                          78
-  Sluicebox mining in early Colorado                                   81
-  Early-day Leadville                                                  82
-  Gold dredge, Fairplay                                                84
-  Silverton, in the San Juan Mountains                                 86
-  Abrams Mountain, south of Ouray                                      87
-  Creede and its mines (map)                                           89
-  Cripple Creek, near Pikes Peak                                       90
-  Climax molybdenum mine (cross section)                               91
-  Rampart Range quarry, near Colorado Springs                          98
-  Yule Marble quarry, near the town of Marble                          99
-  Lyons Sandstone quarry                                              100
-  University of Colorado Museum                                       100
-  Colorado-Big Thompson Project (cross section)                       103
-  San Luis Valley (cross section)                                     105
-  Cave of the Winds, near Manitou                                     107
-  Mesa Verde cave and Indian dwellings                                108
-  Glenwood Hot Springs                                                109
-
-
-
-
-                        PRAIRIE PEAK and PLATEAU
-
-
-
-
-                              Introduction
-
-
-Gold was discovered in the bed of the South Platte River in 1858.
-Prospectors flocked to Colorado as they had flocked only a few years
-before to California. They worked the sands and gravels of Cherry Creek,
-Clear Creek, Boulder Creek, and California Gulch. Exhausting the placer
-sands of the stream bottoms, they moved higher to mine gold-bearing
-veins at Central City and Blackhawk. Mining camps sprang into existence
-overnight, each heralding some new “strike,” each populated by a new
-rush of fortune seekers. As lower areas were mined out, prospectors
-moved yet higher—to Breckenridge, Gold Hill, and Empire, Aspen,
-Leadville, and Cripple Creek. Silver was found as well as gold, then
-iron, and later tungsten and molybdenum. The metallic ring of mining
-tools echoed from Colorado’s peaks. Fortunes were made here. Legends
-were born.
-
-Prospectors and miners were not, however, the first people interested in
-the rocks of Colorado. Earlier, bands of nomadic Cheyenne and Arapaho
-Indians had searched Colorado’s hills for flint for arrowheads and
-brightly colored clays for warpaint. Cliff-dwelling Pueblo Indians in
-southwestern Colorado sought clay for their pottery and fossil seashells
-for the magic of their medicine men. And from farther to the southwest,
-Navajo tribesmen came to Colorado for turquoise.
-
-From clay to gold, much of Colorado’s wealth has come from her
-mountains. But after the rush to the mines, as veins were mined out and
-placers worked over, as values and prices changed, her population sought
-the riches of the prairies: fertile lands for agriculture, and in the
-rock layers below, black gold—vast accumulations of oil and natural gas.
-The tablelands and plateaus west of the mountains yield their wealth,
-too. Here are valley farms, fed often by irrigation water, and ranch
-country. Here is more oil, and in some areas precious metals and
-uranium.
-
-In recent years Colorado’s prairies, peaks, and plateaus have brought
-new meaning to all America: the state now provides an attractive
-playground for state residents and their visitors. Campgrounds, streams,
-lakes, and high trails beckon in summer; barren slopes deep in winter
-snow attract the skier. More and more, those who live in Colorado and
-those who visit her seek to understand these mountains and hills and
-prairies, to learn of her geologic origins and her far distant past. For
-tourist and resident, casual visitor, ski enthusiast, Sunday picnicker,
-for all those who have met Colorado and enjoyed her, this book is
-written.
-
-[Illustration: Topographically, scenically, and geologically, Colorado
-can be divided into the three provinces shown here.]
-
-  PLATEAUS
-    UINTA MTS.
-    GREEN RIVER BASIN
-    Yampa River
-    Steamboat Springs
-    UINTA BASIN
-    White River
-    WHITE RIVER PLATEAU
-    ROAN PLATEAU
-    Glenwood Springs
-    Colorado River
-    Grand Junction
-    GRAND MESA
-    Gunnison River
-    UNCOMPAHGRE PLATEAU
-    Dolores River
-    PARADOX BASIN
-    MESA VERDE
-  MOUNTAINS
-    NORTH PARK
-    RABIT EARS RANGE
-    PARK RANGE
-    MIDDLE PARK
-    GORE RANGE
-    FRONT RANGE
-    ELK MTS.
-    Aspen
-    SAWATCH RANGE
-    Leadville
-    MOSQUITO RANGE
-    Fairplay
-    SOUTH PARK
-    WEST ELK MTS.
-    Gunnison
-    Salida
-    WET MTS.
-    SANGRE DE CRISTO RANGE
-    SAN LUIS VALLEY
-    Rio Grande
-    Alamosa
-    SAN JUAN MTS.
-    Ouray
-    Silverton
-    Durango
-    MESA DE MAYA
-  PLAINS
-    Fort Collins
-    South Platte River
-    Denver
-    GREAT PLAINS
-    Colorado Springs
-    Arkansas River
-    WET MT. VALLEY
-    HUERFANO PARK
-    La Junta
-    Walsenburg
-
-
-
-
-                                   I
-                       Colorado’s Three Provinces
-
-
-Scenically, Colorado is divided into three provinces: the Plains or
-Prairies on the east, the Rocky Mountains bisecting the state from north
-to south, and the Colorado Plateaus on the west. There are a number of
-local variations of course, but by and large the provinces are clearly
-defined. These three divisions will form the basis for our discussion of
-the geology of Colorado, for the scenic differences are almost exactly
-paralleled, and usually controlled, by differences in geologic
-structure.
-
-The Plains rise gently from an elevation of about 3350 feet at the
-eastern border of the state to 5000 feet where they meet the mountains
-150 miles further west.
-
-Two major rivers cross the Colorado Plains: the South Platte River,
-flowing northeastward from the Denver region, and the Arkansas River,
-which leaves the mountains at Canon City south of Colorado Springs and
-travels eastward across the southern portion of the state. Tributaries
-of these two main river systems have etched the prairie surface, so that
-much of eastern Colorado has a gently rolling, hilly appearance.
-
-The Mountains rise abruptly along a north-south line at about 105° west
-longitude. They reach elevations of over 14,000 feet at Pikes Peak,
-Mount Evans, Longs Peak (all visible from far out on the plains), and
-fifty other peaks further west. The ranges of the Colorado Rockies form
-rank upon rank of ridges and peaks, roughly north-south in trend, about
-100 miles across from east to west, extending from the northern to the
-southern border of the state. Here, in mountain springs and lakes, are
-born the rivers of Colorado: the Platte, the Arkansas, the Yampa, the
-Colorado. Crags and cliffs tower above tree-covered slopes, the rocks
-always a dominant part of the landscape. The continental divide runs
-through the state along the summit ridges. West of the divide, all
-streams flow to the Colorado River and the Pacific; east of it, streams
-flow into the Mississippi or the Rio Grande, and thence to the Gulf of
-Mexico.
-
-West of the highest ranges, the country flattens out once more into the
-Plateaus, which extend across western Colorado, southern Utah, and
-northern Arizona. Here, the predominant land forms are flat-topped mesas
-and deep canyons. Redrock walls shimmer in the brilliance of the western
-sun, offset by deep purple shadows sometimes hiding ancient cliff
-dwellings. Fragrance of pine and juniper mingles with the pungency of
-sage. Narrow tracks lure the explorer. Despite the canyons, water is
-scarce except along major river systems, for this is the beginning of
-the desert west.
-
-The scenic and geologic division of the state into three north-south
-strips is not everywhere clearly defined. In southwestern Colorado, the
-San Juan Mountains and the complicated uplifts surrounding Ouray and
-Silverton are out of key with either mountain or plateau. They are best
-considered part of the Mountain Province, however, although they extend
-it far to the west. Other exceptions to these divisions occur also. The
-Mountain Province is interrupted by four broad high-altitude valleys:
-North Park, Middle Park, South Park, and the San Luis Valley. The Uinta
-Mountains jut into the northwest corner of Colorado from adjacent Utah.
-And the Paradox, Uinta, and Green River Basins protrude into the Plateau
-Province, modifying its topographic character.
-
-[Illustration: Pikes Peak rises to an elevation at 14,110 feet. Composed
-of Pikes Peak Granite, the mountain is almost surrounded by younger
-sedimentary rocks, including those of the Garden of the Gods, in the
-foreground. (Floyd Walters photo)]
-
-Before discussing the geologic nature of the three provinces, let us
-review briefly two sets of geologic terms. The first set has to do with
-the rocks themselves—What kind of rock is that?—but serves also to tell
-something about the origin of the rocks. The second set is concerned
-with time—When was that rock formed? Is it older or younger than
-adjacent rock? How does it relate, time-wise, to geologic events in
-other parts of the world?
-
-These two sets of terms are presented in the charts that follow. If you
-are unfamiliar with geologic terminology, refer to these charts as often
-as you need to while you read this book, as well as to the glossary on
-pages 114-118.
-
-  Geologists divide rocks into three main groups, depending on their
-  modes of origin.
-
-  _Igneous rocks_ originate from molten material, cooling deep below the
-  surface of the earth (intrusive igneous rocks) or flowing out and
-  hardening at the surface (extrusive igneous rocks).
-
-  _Sedimentary rocks_ are formed from broken or dissolved bits of other
-  rock, washed by wind and water and deposited as layers of fragments or
-  as chemical precipitates. They often contain fossil plants or animals.
-
-  _Metamorphic rocks_ are pre-existing rocks (igneous or sedimentary)
-  changed by heat, pressure, or chemical action.
-
-  Examples of these three classes of rocks are given in the accompanying
-  figure. Many varieties of all three classes occur in Colorado.
-
-  Class         Example       Occurrence in Colorado
-
-  Sedimentary   Sandstone     Plains, plateaus, flanks of mountain
-                              areas
-                Shale
-                Conglomerate
-                Limestone
-  Igneous       Extrusive:    Volcanic areas such as San Juan
-                   Basalt     Mountains, Spanish Peaks
-                Intrusive:    Pikes Peak, Longs Peak, and most
-                   Granite    central mountain areas
-                   Diorite
-  Metamorphic   Marble        Mountain areas
-                (from
-                limestone)
-                Quartzite
-                (from
-                sandstone)
-                Gneiss
-                (from
-                granite or
-                sandstone)
-                Schist
-                (from shale
-                or basalt)
-
-  Geologists arrange rocks in their chronologic sequence by studying the
-  fossils and minerals which they contain. The age of some rocks can be
-  determined with reasonable precision from ratios of radioactive
-  minerals and their fission products. The relative age of others can be
-  determined from their position, the fossils enclosed in them, and many
-  minor details of their structure.
-
-  The _stratigraphic column_ shown opposite may be thought of as a
-  calendar by which geologic events in Colorado can be arranged in their
-  proper order and related to events in the rest of the world.
-  Mississippian and Pennsylvanian Periods are American divisions;
-  elsewhere this time interval is known as the Carboniferous Period.
-  Other time terms are in worldwide use.
-
-  In the generalized geologic map of Colorado which accompanies Chapter
-  II, rocks are identified by the era in which they were formed. A more
-  detailed geologic map can be obtained from the U.S. Geologic Survey
-  map distribution center in the Federal Building, Denver.
-
-[Illustration: Stratigraphic Column]
-
-  ERA Period  Millions  Distinctive fossils       Events in Colorado
-              of years
-                 ago
-
- CENOZOIC
- (Age of Mammals)
-    Quaternary          Modern types of       Development of present
-                        animals and plants    topography; glaciation in
-                                              mountains
-                     3
-    Tertiary            Mammals, flowering    Uplift and mountain
-                        plants                building
-                    70
- MESOZOIC               Dinosaurs and other
- (Age of Reptiles)      reptiles
-    Cretaceous                                Submergence, then uplift
-                   135
-    Jurassic                                  Desert, then submergence
-                   180
-    Triassic                                  Widespread floodplains
-                                              and deserts
-                   225
- PALEOZOIC
- (Age of Fishes)
-    Permian             First reptiles        Widespread floodplains
-                                              and deserts
-                   270
-    Pennsylvanian       Swamp and forest      “Ancestral Rocky
-                        plants                Mountains”
-                   310
-    Mississippian       Reef corals, sharks   Partial submergence
-                   350
-    Devonian            Armored fish, first   Probable submergence
-                        insects
-                   400
-    Silurian            Corals and shellfish  Probable submergence
-                   440
-    Ordovician          First fish            Submergence
-                   500
-    Cambrian            First hard-shelled    Gradual encroachment of
-                        animals               sea from west
-                   570
- PRECAMBRIAN          “Lipalian Interval”     Erosion to almost flat
-                                              surface or peneplain
-                        Primitive             Alternate episodes of
-                        soft-bodied marine    mountain building and
-                        organisms             erosion
-            3,600 plus
-
-
-                              THE PRAIRIES
-
-Beneath the flat prairies of eastern Colorado, sedimentary rocks form a
-series of layers. Those near the surface are among the youngest rocks in
-Colorado. We know this from the fossils they bear, fossils of large
-mammals such as the hairy mammoth, which lived in early Quaternary time,
-the bison, and many smaller mammals living today.
-
-The layers below—sandstones, shales, and limestones—become progressively
-older as one goes deeper. Most of them were formed originally on the
-bottoms of shallow seas that covered this part of North America several
-times during the history of the continent. In most places the layers are
-horizontal or nearly so, but westward, as they approach the mountains,
-they bend upward, gently at first and then more steeply. At the very
-edge of the mountains, where they were dragged upward when the mountains
-rose, their eroded edges appear at the surface.
-
-The entire sequence of flat-lying rocks can be studied where they are
-exposed along the mountain front or where streams and rivers have
-dissected them. They are also known from cuttings and cores of oil and
-water wells. Some parts of Colorado’s eastern plains have been drilled
-so intensively in the search for oil and gas that we know a great deal
-about the subsurface sedimentary rock and can even make maps showing the
-distribution and character of the individual rock layers. From such
-maps, the history of the region can be deduced. We know, for example,
-that the area around Denver has subsided more in the past than has the
-area near La Junta or Lamar; it is called the Denver Basin because of
-its past history and not because it is a basin at present.
-
-Although the plains of Colorado appear flat, they really slope gently
-eastward. The rock layers near the surface slope eastward also, but the
-deeper rock layers may not.
-
-Near the western edge of the Plains Province, hills and valleys are
-formed by differential erosion of hard and soft rock layers. Some hills,
-such as Castle Rock, are topped with resistant sandstone; others, like
-Mesa de Maya south of Trinidad and Table Mountain near Golden, are
-capped with layers of basalt. Close to the mountains flat-topped
-foothills result from partial dissection of former erosion surfaces as
-the mountains, stabilized for a time, rose again, or as climatic cycles
-changed. Examples of these dissected erosion surfaces can be seen north
-and south of Boulder.
-
-Far east of the mountain front, near the northern border of Colorado,
-remnants of another, higher prairie surface stand as Pawnee Buttes.
-Torrential erosion—spring floods and summer thunderstorms—has deeply
-furrowed the prairie surface here and left these buttes as lonely
-sentinels.
-
-[Illustration: This map shows the distribution, character, and thickness
-of certain Jurassic rocks in Colorado. These rocks are deeply buried
-beneath the plains and are known there only from well samples. They have
-been eroded from most mountain areas. They come to the surface along the
-edges of the mountains and in the deeply incised canyons of the Plateau
-Province.]
-
-  PRECAMBRIAN ROCKS
-  PALEOZOIC ROCKS
-  JURASSIC ROCKS
-    SANDSTONE
-    SHALY SANDSTONE
-    SANDY SHALE
-    SHALE
-  JURASSIC ROCKS COVERED WITH VOLCANICS OR NEVER DEPOSITED.
-
-What lies below the sedimentary layers of the plains? The sedimentary
-rocks are 5,000 to 10,000 feet thick. They lie on an almost horizontal
-surface of much, much older rock, the Precambrian or “basement” rock.
-This is igneous and metamorphic rock, much crumpled and folded, the
-roots of long gone mountains which were beveled and leveled to an almost
-flat surface or _peneplain_ perhaps a billion years ago.
-
-We know little of the ancient basement rocks below the sedimentary
-layers of the plains, for few wells penetrate this deep. What we do know
-indicates that they are similar to rocks of the mountain masses to the
-west, and are composed of granite, schist, and gneiss. They probably are
-not rich in valuable minerals, however, for the mineral-rich veins of
-the mountains came about as a result of uplift of the mountain areas.
-
-
-                               THE PEAKS
-
-Most of the individual ranges making up the Rocky Mountains in Colorado
-are the result of highly localized movements of the crust as the entire
-region was thrust upward from below. These movements broke the deep,
-massive igneous and metamorphic rocks of the Precambrian basement, and
-bent the more flexible Paleozoic and Mesozoic layered rocks above them
-until they arched upward in a series of corrugations. The mountains thus
-formed are known to geologists as _faulted anticlines_.
-
-As the mountains rose, they were of course attacked by the forces of
-erosion. The sedimentary layers were completely stripped from the crests
-of many of the uplifts, so that Precambrian rocks were exposed. It is
-these rocks which form the summits of the highest peaks of Colorado. As
-with all rules, there are exceptions: the Spanish Peaks are volcanic,
-and the crest of the Sangre de Cristo Range is composed of sedimentary
-rocks.
-
-The trend of most of the ranges in Colorado is north-south, swinging to
-northwest-southeast near the southern end. Surprisingly, in the
-northwestern corner of the state there is an east-west trending range,
-the Uinta Mountains.
-
-Fifty or more mountain ridges in Colorado have been named as separate
-ranges. Of these, the most prominent, frequently visited ones will be
-discussed here.
-
-
-                              Front Range
-
-The easternmost range of the Rocky Mountains is the longest continuous
-uplift in the state. It is a relatively simple faulted anticline
-extending from Canon City northward to the Wyoming border, where it
-splits into two ridges, the Medicine Bow Mountains and the Laramie
-Range.
-
-[Illustration: Longs Peak challenges technical climbers with its
-2000-foot vertical east face, the Diamond. This magnificent cliff is the
-result of glacial action and freezing and thawing in homogeneous but
-fractured granite. The small remnant of ice and snow at the lower left
-is all that remains of the glacier. The flat summit may be part of an
-ancient erosion surface formed toward the end of Precambrian time. (Jack
-Rathbone photo)]
-
-Along the highest portion of the range, from Pikes Peak to Rocky
-Mountain National Park, the Paleozoic and Mesozoic sediments formerly
-draped over the top of the range have long since been washed away,
-leaving only the gneiss, granite, and schist of the mountain core. The
-almost flat tops of Longs Peak, Mt. Evans, and Pikes Peak, and the
-rolling upland traversed by Trail Ridge Road in Rocky Mountain National
-Park are thought to be remnants of the 600-million-year-old erosion
-surface that once existed at the top of the Precambrian rocks, and that
-still exists below the sedimentary rocks of the Plains Province. This
-surface, formed near sea level, has been raised 12,000 to 14,000 feet
-within the Mountain Province.
-
-Throughout most of its length, the Front Range displays some of the most
-striking high-altitude scenery in the world. Particularly accessible
-areas, well worthy of visits, are Rocky Mountain National Park, Berthoud
-and Loveland Passes, Mt. Evans, and Pikes Peak. In these areas the
-Precambrian rocks can be seen and studied, and the effects of glaciation
-observed.
-
-The granite, gneiss, and schist of the mountain core are shattered and
-broken into blocks of various sizes. The breaks between the blocks are
-called _joints_ if there is no apparent displacement between adjacent
-blocks, and _faults_ where there is obvious displacement. The joints
-frequently appear in parallel arrays or sets; there may be two or more
-intersecting sets, giving a cross-hatched appearance to large exposures.
-
-[Illustration: East-west profile across Rocky Mountain National Park,
-through Grand Lake and Longs Peak, showing the inferred position of the
-original surface of the anticlinal uplift of the Front Range. This
-diagram is generalized, and faults are not shown. (USGS Bull. 730a)]
-
-  Restoration of surface which emerged from Cretaceous sea
-  Restoration of Dakota sandstone
-  MIDDLE PARK
-  _Grand Lake_
-  Longs Peak
-  Foothills
-  GREAT PLAINS
-  Sedimentary rocks
-  Granite and schist
-  Sedimentary rock of plains
-  _South Platte R._
-
-[Illustration: Big Thompson Canyon, west of Loveland on U.S. highway 34,
-is carved in almost vertical layers of Precambrian metamorphic rocks.
-Gently dipping Late Paleozoic and Mesozoic sedimentary rocks of the
-Fountain, Lyons, Lykins, and Morrison Formations can be seen in the
-distance, capped by the Cretaceous Dakota Sandstone. (Floyd Walters
-photo)]
-
-The Precambrian rocks vary from place to place. Several irregular masses
-of granite, called _batholiths_, make up portions of the range.
-Batholiths are large intrusions of molten rock that cooled slowly at
-great depth. The minerals in them form distinct crystals, often quite
-large. The Pikes Peak Granite and the Boulder Creek Granite are
-examples. Highly contorted and banded gneiss and schist are well exposed
-elsewhere, particularly in the Idaho Springs-Central City-Black Hawk
-region.
-
-Along the flanks of the Front Range, the eroded edges of the sedimentary
-rocks which once covered the range are exposed. These rocks are usually
-tilted sharply against the mountains, as at Garden of the Gods, Denver’s
-Red Rocks Park, and the Flatirons near Boulder. The Rocky Mountain
-Association of Geologists has erected a plaque explaining the geology of
-the Red Rocks area; look for it about half a mile northeast of the Red
-Rocks Amphitheater. Tilted layers of Paleozoic and Mesozoic sandstones
-form hogback ridges along the mountain front, and stand out clearly on
-aerial photographs.
-
-In some areas, particularly near Boulder, Coal Creek, and Golden, the
-tilting of the sedimentary layers has been so extreme that the layers
-are upside down. Basement rocks may even be thrust out above them.
-
-[Illustration: Sandstones and conglomerates of the Pennsylvanian
-Fountain Formation dip steeply toward the plains along the eastern edge
-of the Rockies. Near Denver, erosion has carved these rocks into a
-natural amphitheater, now the site of Red Rocks Amphitheater.
-Precambrian granite forms the hill in the background. (Jack Rathbone
-photo)]
-
-Further north, near Loveland and Lyons, as well as further south at
-Colorado Springs, irregularities in the uplift have caused abrupt breaks
-in the generally smooth eastern edge of the range. Folds and faults in
-these areas trend northwest, cutting across and offsetting the mountain
-front.
-
-[Illustration: South of Colorado Springs, between Fort Carson and the
-NORAD installation in Cheyenne Mountain, Mesozoic rocks are faulted
-against the mountain front. Paleozoic rocks are deeply covered by as
-much as 3000 feet of Mesozoic sediments. They come to the surface about
-10 miles further south.]
-
-  RAMPART RANGE
-    Garden of the Gods
-    Ute Pass Fault
-  MANITOU SPRINGS
-  PIKES PEAK MASSIF
-  CHEYENNE MOUNTAIN
-    COLORADO SPRINGS
-  CROSS SECTION
-    Ute Pass Fault
-    Rampart Fault
-      Tertiary
-      Mesozoic
-      Paleozoic
-      Precambrian
-
-[Illustration: West of Boulder, several intersecting sets of joints
-pattern the Precambrian rocks above Boulder Creek. (John Chronic photo)]
-
-The west margin of the Front Range is not as sharply defined as the
-eastern margin. Prominent faults edge North, Middle, and South Parks,
-however. The northern end of the range merges with the Medicine Bow
-Mountains, where dips of sedimentary rocks seldom exceed 30 to 40
-degrees. At its southern end, the Front Range plunges into the plains,
-although a southwest-trending ridge connects it with the Wet Mountains.
-
-Within the Precambrian core of the Front Range, many economic mineral
-deposits have been found. These are discussed in Chapter III. Glacial
-features of the Front Range are discussed in Chapter II in the section
-on the Quaternary Period.
-
-
-                             Wet Mountains
-
-The Wet Mountains are the easternmost range of the Rockies south of
-Canon City. Their crest has a distinct northwest-southeast trend, with
-the north end offset about 25 miles westward from the south end of the
-Front Range. The Canon City Embayment lies at the junction between the
-ranges.
-
-Though smaller and lower than the Front Range, the Wet Mountains include
-many pleasant and easily accessible recreation areas and a number of
-attractive streams and reservoirs. Greenhorn Peak, the summit of the
-range, is 12,334 feet high. It is formed of Precambrian granite, as is
-most of the crest of the range.
-
-The structure of the eastern side of the Wet Mountains is similar to
-that of the Front Range, except that there are more faults in the
-sedimentary layers. The southern end plunges southeastward into the
-plains. On the western side, westward-dipping sediments are completely
-submerged in Cenozoic lava flows and debris from the mountains. Ore
-minerals very like those of the Front Range occur near Silver Cliff, but
-they have so far proved to be of little economic importance.
-
-
-                Sangre de Cristo Range and Spanish Peaks
-
-The Sangre de Cristo Mountains are visible from many parts of
-southeastern Colorado as a jagged, sawtoothed, snow-crested ridge on the
-western skyline. They extend about 150 miles from the Arkansas River
-near Salida southward into New Mexico.
-
-Few mountain ranges form so impassable a barrier as the Sangre de
-Cristos. Only at La Veta Pass does a highway cross the range. However,
-old wagon roads, passable now by jeep or on foot, once existed across
-Hayden, Music, Mosca, and Whiskey Creek Passes.
-
-Often no more than twenty miles wide, the central portion of the range
-is composed largely of red Late Paleozoic sediments like those exposed
-in the Garden of the Gods and Red Rocks Park. These rocks are
-intricately folded and faulted, but not metamorphosed. They include
-sandstones, shale, conglomerates, and fossil-bearing limestones. The
-northern end of the range is formed of Precambrian igneous and
-metamorphic rocks.
-
-Just west of La Veta Pass, Sierra Blanca stands as an outpost of the
-range where its continuity is interrupted and its structure changed.
-Huge blocks of Precambrian granite were here pushed upward and thrust
-westward to form a cluster of peaks, several of which are over 14,000
-feet in elevation.
-
-Many prominent rock glaciers are present in the Sangre de Cristo
-Mountains. They are composed of fragments of rock, lubricated by snow
-and ice, creeping almost imperceptibly down the steep flanks of the high
-peaks. One of these rock glaciers can be seen on the slope of Mt. Mestas
-east of La Veta Pass; others are visible from Great Sand Dunes National
-Monument.
-
-South of La Veta Pass, an igneous intrusion along the axis of the range
-changes the character of the Sangre de Cristos. This intrusion is harder
-and has weathered more slowly than the rest of the range, and forms a
-group of prominent peaks known as the Culebra Range.
-
-On the west flank of the Sangre de Cristo Range, east of Villa Grove, a
-prominent iron-mineralized area can be seen. Here the ghost mine of
-Orient marks the site where iron ores were mined in the early days of
-the Colorado Fuel and Iron Company. Nearby, an abrupt terrace along the
-edge of the valley marks the position of a fault. Recent gravels are
-involved in this fault, indicating that movement has taken place here
-within the last few hundred years. A number of hot springs occur along
-the base of the mountains nearby.
-
-The Spanish Peaks, not structurally related to the Sangre de Cristos,
-are visible from La Veta Pass highway. These two peaks represent a pair
-of Cenozoic volcanoes, now deeply eroded and much reduced from their
-former height. Numerous dikes radiating from the bases of these peaks
-represent fissures which were filled with lava as the peaks formed.
-
-The Great Sand Dunes, close to the Sangre de Cristo Mountains north of
-Sierra Blanca, are discussed in Chapter II in the section on the
-Quaternary Period.
-
-[Illustration: Spanish Peaks, south of Colorado Springs and southwest of
-Walsenburg, are twin mountains of volcanic and intrusive rock, the roots
-of Tertiary volcanoes greatly worn down and reshaped by erosion. This
-view looks southeast from near La Veta Pass, on U.S. Highway 160. (Jack
-Rathbone photo)]
-
-
-                    Park Range and Rabbit Ears Range
-
-Bordering the western side of North, Middle, and South Parks, another
-long north-south trending ridge extends from the Wyoming border toward
-the center of Colorado. The northern part of this ridge, forming the
-western boundary of the main mountain mass in the state, is called the
-Park Range.
-
-The structure of the Park Range is similar to that of the Front Range: a
-huge linear corrugation in the earth’s crust, bounded by faults. Because
-this area has fewer resistant sedimentary rock layers above the
-Precambrian basement rocks, it is not prominently edged with upturned
-sedimentary layers.
-
-[Illustration: Hahn’s Peak, a highly eroded laccolith of rhyolite
-porphyry, lies on the west side of the Park Range, along the eastern
-margin of the Plateau Province. Placer gold was discovered here in 1865,
-but the bedrock source of the gold was never found. (Jack Rathbone
-photo) A geologic section shows the structure of the area.]
-
-  TERTIARY
-  RED BEDS
-  JURASSIC
-  DAKOTA
-  MANCOS
-  DAKOTA
-    Hahn’s Peak
-  PORPHYRY
-  MANCOS
-  DAKOTA
-  PORPHYRY
-  JURASSIC
-  RED BEDS
-  RE-CAMBRIAN
-
-[Illustration: Hahn’s Peak]
-
-The range is crossed by Rabbit Ears Pass in the north; Gore Pass near
-Kremmling marks its southern end. Mt. Zirkel (12,180 feet) and Flattop
-Mountain (12,118 feet) are the two high points of the range; these and a
-number of unnamed peaks over 11,000 feet high are upward-faulted blocks
-of Precambrian granite.
-
-A rough ridge of volcanic country joins the Park Range with the Front
-Range and effectively separates North Park and Middle Park. This is the
-Rabbit Ears Range, named for a double-eared knob of Precambrian granite
-near Rabbit Ears Pass on U. S. highway 40. Many Tertiary volcanic
-features, including dikes and lava flows, can be seen along this ridge,
-which is also traversed by Colorado state highway 125 between Granby and
-Walden via Willow Creek Pass.
-
-
-                               Gore Range
-
-The Gore Range lies south of Gore Pass, along the Park Range trend. The
-ridge of this range is low for about 15 miles south of Kremmling, but
-the southern part of the range forms a spectacular high cluster of peaks
-with many relatively inaccessible and rugged summits. Many of the peaks
-in this remote country are as yet unnamed; the area has been set aside
-as the Gore Range-Eagle’s Nest Wilderness Area. The Colorado River cuts
-directly across the northern part of the Gore Range just west of
-Kremmling, in a steep-walled canyon that is one of the wild scenic spots
-of Colorado.
-
-[Illustration: The southern part of the Gore Range, viewed from the
-east, shows Precambrian granite and metamorphic rocks rising above
-Cretaceous shale hills. The nearly horizontal crest of the range
-probably represents the Precambrian erosion surface. (Jack Rathbone
-photo)]
-
-The Gore Range is, like the Front Range, a faulted anticline with
-Precambrian rocks at its core. The red sedimentary rocks on the west
-flank of the range, visible at Vail Pass and Vail ski area, are of the
-same age as those in Red Rocks Park near Denver and the Garden of the
-Gods near Colorado Springs. Paleozoic rocks are absent on the east flank
-of the range, having been eroded from that area before Mesozoic
-deposition. South of the Colorado River and north of the Wilderness
-Area, Mesozoic rocks extend over the crest of the range.
-
-The south end of the Gore Range is marked by Tenmile Gorge (U. S.
-highway 6 between Frisco and Vail Pass). This gorge is a glacial valley,
-carved during the Ice Age by a glacier more than 1,000 feet thick, along
-a weak faulted zone in the range. A fault surface can be seen on the
-east side of the valley.
-
-From Vail Pass, or from the top of the Vail ski lift, other evidences of
-glaciation can be seen—cirques and U-shaped valleys—testifying to the
-former presence here of many large valley glaciers.
-
-
-                      Tenmile and Mosquito Ranges
-
-With scarcely a break, the Park Range-Gore Range structure continues
-southward into the Tenmile and Mosquito Ranges. These high ridges
-separate South Park from the upper Arkansas Valley, and include a
-cluster of very high peaks, Quandary, Mt. Lincoln, Mt. Democrat, and Mt.
-Bross, all over 14,000 feet in elevation.
-
-Structurally, both the Tenmile Range and the Mosquito Range are highly
-asymmetrical anticlines, gentle on the east and steeply faulted on the
-west. Paleozoic sedimentary rock layers containing many fossils cover
-large portions of the higher parts of these ranges, but two of the
-highest peaks, Mt. Bross and Mt. Lincoln, are capped by the Lincoln
-Porphyry, a Tertiary intrusive, while Quandary Peak is Precambrian
-granite.
-
-These mountains are highly mineralized, and have been extensively
-explored and mined. The Climax Molybdenum Corporation operates an
-especially large mine at Climax, and the New Jersey Zinc Company has a
-large underground mine and mill at Gilman, on the western slopes of
-Tenmile Range.
-
-Buffalo Peaks, two highly eroded volcanic mountains near the south end
-of Mosquito Range, are extrusions of lava and ash which have buried the
-axis of the Mosquito uplift. They are major volcanoes related to a group
-of small volcanic cones near Antero Junction, in South Park.
-
-South of Buffalo Peaks, near Trout Creek Pass, the Mosquito Range loses
-altitude rapidly and merges with the rough country called the Arkansas
-Hills. Cinder cones, dikes, and other evidences of Tertiary volcanic
-activity can be seen between Trout Creek Pass and Salida.
-
-
-                             Sawatch Range
-
-Bordering the Arkansas River valley on the west, the Sawatch Range
-includes Colorado’s highest mountain, Mt. Elbert (14,417 feet). With
-several other 14,000-foot summits, this range is the highest in the
-state. One group of peaks, known as the Collegiate Range (Mts. Harvard,
-Yale, Columbia, and Princeton) forms a particularly imposing vista from
-U. S. highway 24 between Trout Creek Pass and Buena Vista. The
-Independence Pass highway (Colorado 82) between Leadville and Aspen
-penetrates the heart of the Sawatch high country.
-
-The Sawatch Range as a whole is about 100 miles long (north to south)
-and 40 miles wide. It is a great faulted anticline intruded by igneous
-rocks. The high area north of Leadville shows that the Sawatch and
-Mosquito Ranges are in reality one huge dome with a slight sag in the
-middle. The ranges, though, are sharply separated topographically by the
-deep valley of the Arkansas River. Precambrian rocks are near the
-surface between the ranges, hidden only by a thin cover of stream
-gravels. Near Leadville, some complexly faulted Paleozoic limestones lie
-in the sag between the ranges.
-
-At Mt. Princeton Hot Springs there is evidence of repeated faulting and
-igneous activity. The rocks are strongly altered by hot water coming to
-the surface through fissures and cracks.
-
-On the west side of the Sawatch range, the old mining towns of Tincup
-and Aspen grew up where limestone and sandstone layers, broken and
-crumpled as the Sawatch Range rose, were mineralized by solutions rich
-in gold and silver. The Aspen Mining District was studied extensively by
-geologists of the U.S. Geological Survey, and their maps show almost
-unbelievable complexity in the faulting of the rock layers which exist
-there.
-
-The north end of the Sawatch Range plunges under shales and sandstones
-along the Eagle River east of Wolcott. Gypsum in the sediments here has
-acted like putty: the layers of rock in which it was deposited have
-become peculiarly crumpled, making the area along the Eagle River
-(visible from U. S. Interstate 70) between Avon and Edwards hummocky and
-irregular. Vegetation is unusually sparse here because of gypsum in the
-soil.
-
-About midway between Edwards and Wolcott, the Eagle River suddenly
-changes direction and flows northward for about a mile before resuming
-its former westward course. This sudden change is caused by a sharp
-north-south fold in the sedimentary rocks on the northwestern flank of
-the Sawatch Range. A magnificent series of roadcut and hillside
-exposures along the highway here illustrates the close relation between
-rock layers and river course. Within about a mile, the highway cuts
-through rocks of Pennsylanian, Permian, Triassic, Jurassic, and
-Cretaceous age, spanning a geologic time interval of more than 200
-million years.
-
-The south end of the Sawatch Range, at Monarch Pass, contains steeply
-dipping Late Paleozoic limestones and coal beds. The coal has been mined
-on a small scale; the limestone is now quarried for use as a flux in
-iron smelters at Pueblo.
-
-  [Illustration: The area below the Aspen Mountain ski lift is highly
-     complex geologically. It is particularly well known because of
-       extensive prospecting and mining activity in the region.]
-
-
-                  Elk Mountains and West Elk Mountains
-
-The Elk Mountains and West Elk Mountains appear to be westward
-continuations of the Sawatch Range. Structurally, however, they are not
-faulted anticlines like most of the other ranges in Colorado, but are
-composed of a series of layers of Paleozoic sediments thrust westward
-over one another. These rocks, often crumpled and highly metamorphosed,
-are cut by numerous sills, dikes, and other intrusions, many of which
-have caused mineral enrichment locally.
-
-At Maroon Bells, in the canyon of Maroon Creek, and at Redstone on the
-Crystal River, these metamorphosed sediments are well exposed. Here, red
-sandstones and shales have been altered to quartzites and slate. At
-Marble, metamorphism of a thick limestone bed has produced white marble
-of great beauty, known as Yule Marble. This decorative stone was
-quarried extensively until about 1940. It was used in the Lincoln
-Memorial and several other monumental structures; in the town of Marble
-it has been used for the doorsteps of log cabins! The largest block
-quarried, for the Tomb of the Unknown Soldier in Arlington National
-Cemetery, measured 14 by 7.4 by 6 feet in the rough, and weighed 56
-tons.
-
-[Illustration: Mt. Sopris, south of Glenwood Springs, is an igneous
-intrusion. (Jack Rathbone photo)]
-
-Crested Butte, at the south end of the Elk Mountains, is a small
-intrusive igneous mass called a _laccolith_. Hard and resistant to
-erosion, it stands over 2,000 feet above the adjacent valley floor.
-
-
-                           San Juan Mountains
-
-The San Juan Mountains are the most extensive range in Colorado, and
-also the most heterogeneous. Covering more than 10,000 square miles of
-the southwestern part of the state, these mountains are formed mostly of
-Tertiary volcanic rocks, the result of repeated outpourings of lava and
-ash from a cluster of volcanoes. Water-laid gravels composed of volcanic
-sand and pebbles are interlayered with basalts and ash beds; the total
-thickness of these beds reaches many thousands of feet.
-
-[Illustration: The mining town of Ouray, now also a tourist haven and
-summer resort, nestles below Pennsylvanian sedimentary rocks of Ouray
-Canyon. At the north end at town can be seen the Ouray Hot Springs
-swimming pool. Gold, silver, lead, and zinc are still mined in this
-area. (Jack Rathbone photo)]
-
-The widespread volcanic activity which formed most of the range began in
-mid-Tertiary time and continued for several million years. A few
-Quaternary volcanic flows are known in the region, but there is no
-active volcanism there at present.
-
-The western side of the main range, including some of the highest peaks,
-consists primarily of uplifted and faulted Paleozoic sedimentary layers.
-These layers, highly dissected by erosion, can be seen near Ouray, at
-Molas Lake, and at Durango. Large patches of Precambrian granite and
-metamorphic rocks protrude through the sediments, as in the Needle
-Mountains; they indicate that this part of the range is a faulted
-anticline like many other Colorado ranges.
-
-Early Cenozoic glacial deposits occur in some parts of the San Juans.
-These are unusual features, as glaciation of this age is unknown
-elsewhere in Colorado.
-
-Three small ranges rise just west of the San Juans: the San Miguel,
-Rico, and La Plata Mountains. Each consists of several small masses of
-Tertiary igneous rock intruded into Paleozoic conglomerates, shales, and
-limestones.
-
-Mineralization has been intense in the San Juans; most of it took place
-during the Late Tertiary volcanic period. Rich veins penetrate
-Precambrian gneiss and granite, and Paleozoic limestones are often
-enriched also. Several mines are still active near Ouray, Silverton,
-Telluride, and Rico.
-
-
-                            Uinta Mountains
-
-The eastern end of Utah’s Uinta Mountains extends into Colorado. Unlike
-other ranges in Colorado, these mountains trend east-west. Structurally,
-the range is a faulted anticline. It is quite asymmetrical, however, and
-is tilted and folded upward on the south, and overturned or
-thrust-faulted on the north. Steeply dipping Mesozoic and Paleozoic
-sediments on the south side of the range, sparsely vegetated and often
-thrown into spectacular folds, are a prominent feature of northwest
-Colorado scenery.
-
-In Colorado the crest of the Uintas reaches an elevation of about 8,500
-feet. It consists of Precambrian rocks, but these are not the igneous
-and metamorphic rocks that characterize the Precambrian core of other
-Colorado mountains. They are easily recognized as sediments—dark red
-conglomerates, sandstones, and mudstones—virtually unmetamorphosed
-though they were deposited nearly a billion years ago. Called the Uinta
-Mountain Formation, these rocks are found only in this part of Colorado
-and adjacent areas of Utah. They are probably related to similar
-Precambrian rocks found in Montana and Canada.
-
-At the east end of the Uintas two isolated uplifts, Cross Mountain and
-Juniper Mountain, are faulted blocks of Paleozoic rocks standing like
-islands in a sea of Cenozoic valley fill. They are the last outposts of
-the Uinta anticlinal pattern as it wanes toward the southeast.
-
-Dinosaur National Monument, a Uinta Mountain tourist attraction,
-encompasses a vast area of wilderness on both sides of the Yampa River
-in Colorado. Here many of the features of the east end of the Uinta
-Mountain structure can be seen. A unique display of the world’s largest
-fossils can be visited in the Utah portion of the Monument.
-
-[Illustration: At their confluence in Dinosaur National Monument, the
-Yampa and Green Rivers have carved Late Paleozoic sandstone into the
-precipitous cliffs of Steamboat Rock. (William C. Bradley photo)]
-
-
-                              THE PLATEAUS
-
-The western quarter of Colorado is a region of flat-lying Paleozoic,
-Mesozoic, and Cenozoic sedimentary rocks which have not been bent up
-into mountains except in a few isolated instances. This area lies more
-than a mile above sea level, however, and because of the gradient such
-an elevation affords, it is deeply sculptured. The Colorado River and
-its tributaries have sliced into the plateau surface, separating it into
-many isolated tablelands or mesas. Some are capped with sedimentary
-rock, others with Tertiary basalt.
-
-[Illustration: The Grand Hogback is a good example of the type of
-geologic structure known as a _monocline_. The hogback ridge is formed
-by differential erosion, where soft layers wear away more easily than
-hard layers.]
-
-Simple folds and faults have given the mesas different elevations. Thus
-the average elevation of the White River Plateau is 11,000 feet, that of
-the Roan Plateau 9,500 feet, and that of Mesa Verde only 7,000 feet.
-West of Durango the plateaus dip gently southward, as can be seen at
-Mesa Verde. Igneous intrusions and extrusions have altered plateau
-topography in some areas. West of Mesa Verde, for instance, an intrusive
-stock forms a prominent dome in the Southern Ute Indian Reservation.
-
-West of the northern Colorado mountains, and north and west of the White
-River Plateau, a rolling upland extends from Colorado into Utah and
-Wyoming. It is interrupted by the Uinta Mountains and a number of
-smaller related uplifts such as Juniper Mountain and Cross Mountain.
-South of the Uinta axis the area is known as the Uinta Basin.
-
-The northern part of this area is structurally the south edge of the
-Green River or Washakie Basin in Wyoming. The Rangely anticline, in the
-northeastern corner of the Uinta Basin, is one of Colorado’s richest oil
-fields; it is discussed in Chapter III.
-
-Although surfaced with much younger sediments than the rest of the
-Plateau Province, this area is structurally similar. On the whole,
-sedimentary layers are relatively flat-lying, and where they are
-uplifted they are deeply sculptured by streams and rivers. The
-sedimentary rocks in this region contain uranium and placer gold in
-addition to great oil and gas deposits. The southeastern part of the
-Uinta Basin, usually called the Piceance Basin, is the site of a great
-deposit of oil shale (see Chapter III). The term “basin” may here seem
-unusual to the casual observer, for the oil shales occur on the Roan
-Plateau at places well over 10,000 feet in elevation. However, the
-entire region was basin-like—lower than the surrounding ranges—for many
-millions of years, and during Tertiary time thousands of feet of valley
-and lake deposits were laid down in it.
-
-The White River Plateau, north of Glenwood Springs, is composed of
-almost horizontal Paleozoic sedimentary rocks that fold downward sharply
-along its south and west edges. The fold is 135 miles long and is
-clearly marked by the Grand Hogback, the eroded edge of hard Cretaceous
-and early Cenozoic rock layers. Shale and coaly layers involved in the
-same fold have eroded more readily, leaving the resistant sandstone as a
-prominent ridge.
-
-The Uncompahgre Plateau, southwest of Grand Junction, is structurally
-very like the White River Plateau. Its features can be well observed in
-Colorado National Monument. It has been elevated several thousand feet
-more than the Book Cliffs and Grand Valley areas to the north. Sharp
-folding and faulting near the Colorado River at the north boundary of
-the National Monument show that differential movement between the two
-regions was sharp and localized.
-
-A series of northwest-trending anticlines along the Utah border in
-southwestern Colorado are of special geologic interest. They represent
-peculiar structures in which salt and gypsum have played a major part.
-These minerals were deposited in thick layers late in Paleozoic time;
-subsequently they were covered by thousands of feet of sand, shale, and
-limestone. Because of their low density and high plasticity they have
-since crept upward along weak spots in the overlying sediments, often
-contorting these rocks as they moved. Breaking through to the surface,
-the salt and some of the gypsum washed away more rapidly than the
-surrounding rock, leaving long faulted troughs such as Gypsum Valley and
-Paradox Valley. In most of these structures the gypsum can still be
-seen, although the more soluble salt has eroded away. Oil wells in this
-part of Colorado and in adjacent parts of southeast Utah have penetrated
-thousands of feet of evaporites, including pure salt, gypsum, and
-potassium salts.
-
-[Illustration: In the arid climate of the Colorado Plateaus, ledges of
-well-cemented sandstone stand out sharply from slopes of shale or
-mudstone. The Mesa Verde and Mancos Formations, Cretaceous in age, form
-the slopes and top of Mt. Garfield near Grand Junction (Jack Rathbone
-photo)]
-
-The peculiar weathering characteristics of flat-lying sedimentary rocks
-in an arid climate are well demonstrated in Colorado National Monument,
-Mesa Verde National Park, and elsewhere in the Plateau Province. Those
-fortunate enough to make a river trip through the Yampa or Green River
-Canyons in northwestern Colorado or on the rivers of eastern Utah and
-northern Arizona will have an unusually fine opportunity to observe
-close at hand the weathering and erosion in this area. Resistant
-sandstone and limestone layers break into sheer cliffs, often many
-hundreds of feet high, while the softer layers of mudstone and shale
-form gentle slopes and terraces. Vast arching caves often develop where
-resistant layers are undermined—caves sometimes containing ancient
-Indian dwellings.
-
-
-
-
-                                   II
-                      Geologic History of Colorado
-
-
-Astronomical and geologic evidence indicates that the earth was probably
-formed as an immense blob of molten rock, held together and shaped into
-spherical form by its own gravity. It may even have been gaseous at
-first, cooling gradually to a molten state. After hundreds of millions
-of years it became cool enough to begin to harden.
-
-As the surface cooled, a crust formed, and lay like a blanket over the
-liquid mass beneath. Convection currents—large-scale boiling
-movements—stirred the molten interior, thrust portions of the crust
-upward, and sucked other portions downward to be remelted. Some of the
-lighter components, such as compounds of silicon and oxygen and
-hydrogen, accumulated on the surface like froth on a kettle: the
-continents were born. With further cooling the atmosphere and oceans
-came into being.
-
-Something can be told of the age of the continents. Measurements of
-radioactivity in the most ancient rocks exposed at the surface today
-indicate that the oldest known continental rock is between three and
-four billion years old. Since the continents were formed, they have been
-bent and shifted and broken by the pressures exerted against them by
-convection in the interior. Parts of the continents at times have been
-submerged below the level of the sea, even as they are today. Other
-portions, lifted above sea level, were immediately attacked by the
-wearing-down processes of erosion. The battle between mountain-building
-forces and erosion has been a continuous one ever since the crust was
-formed. Even now earthquakes give testimony to continued crustal
-movement, storms still sweep across the continents and wash mud and
-frost-loosened rocks into churning torrents, rivers still deposit great
-floodplains and deltas, sediments accumulate slowly but persistently
-upon the bottoms of the seas.
-
-
-                            PRECAMBRIAN ERA
-
-Only part of the earth’s very early history is represented in Colorado,
-where the oldest known rocks are the gneisses and schists of the Idaho
-Springs Formation, at least 1,800,000,000 years old. These rocks appear
-to be the remains of ancient sediments, folded and metamorphosed into
-vast mountain areas long before recognizable life inhabited the earth.
-
-Precambrian rocks in Colorado are on the whole very poorly known. They
-have, however, been studied in detail in the Front Range west of Denver
-and Boulder, where they have been intensively explored for valuable
-minerals. The lack of fossils in the oldest rocks makes their close
-correlation difficult, but from studies of radioactive minerals
-contained in these rocks, and of the relationships of the rock units
-themselves, we can list them in order of their relative ages.
-
-Note that the rock sequence given below reads chronologically from
-bottom to top—a logical pattern in geology since younger rocks,
-especially those of sedimentary origin, normally lie above older ones.
-Recent studies indicate that the sequence may be much more complex than
-shown here.
-
-   (youngest) Silver Plume Granite:  light pinkish gray, fine-grained
-                                     granite.
-                Pikes Peak Granite:  pink, coarse-grained granite.
-             Boulder Creek Granite:  dark gray, faintly banded
-                                     granodiorite.
-              Coal Creek Quartzite:  light gray quartzite with grains
-                                     ranging in size from fine sand to
-                                     boulders, with some interbedded
-                                     schist.
-        Swandyke Hornblende Gneiss:  dark gray to black, strongly banded
-                                     gneiss.
-  (oldest) Idaho Springs Formation:  gray to black schist and gneiss.
-
-From a sequence such as this, it is possible to reconstruct some
-features of Colorado’s early history. The first chapter of which we have
-a record is the deposition of the Idaho Springs Formation, probably as
-an accumulation of mud, sand, and limy mud in an ancient sea. Swandyke
-deposition followed—the sediments were iron-rich, perhaps derived from
-ancient volcanic materials. The original Coal Creek sediments were sands
-and gravels, some of them quite coarse and therefore indicative of
-near-shore deposition. The schist layers suggest that muds must have
-been deposited also.
-
-[Illustration: South of Ouray, Cambrian sandstones of the Sawatch
-Formation lie almost horizontally across the vertical Precambrian
-metamorphic rocks. (Jack Rathbone photo)]
-
-Together these three formations represent some 40,000 feet of
-sedimentary layers. Deposition of such a great thickness of mud, sand,
-and lime must have taken a very long period of time. Details of the
-geography of the continent during that period have of course been
-obscured by later events, when these rocks were subjected to repeated
-uplift, crumpling, folding, various degrees of remelting and
-recrystallization, and erosion. But the ancient sediments must have been
-derived from even more ancient highlands, either folded and faulted
-mountains or volcanoes, and probably were deposited under water in broad
-expanses of sea that covered portions of the continent.
-
-[Illustration: Geologic map of Colorado. Geologic maps show the age of
-rocks appearing at the surface, disregarding soil cover. A more detailed
-geologic map of Colorado may be obtained from the U.S. Geological Survey
-at the Federal Center in Denver.]
-
-  PRECAMBRIAN
-  PALEOZOIC
-  MESOZOIC
-  CENOZOIC SEDIMENTS
-  CENOZOIC VOLCANICS
-    Yampa River
-    White River
-    Fort Collins
-    South Platte River
-    Glenwood Springs
-    Denver
-    Colorado River
-    Grand Junction
-    Aspen
-    Gunnison River
-    Colorado Springs
-    Gunnison
-    Salida
-    Dolores River
-    Rio Grande
-    Arkansas River
-    La Junta
-    Walsenburg
-    Alamosa
-    Durango
-
-The Boulder Creek, Pikes Peak, and Silver Plume Granites cut through the
-metamorphic rocks, and are therefore younger. They represent pulses of
-molten rock forced upward from deep within the crust, probably during
-three separate episodes of mountain building. As each set of mountains
-was formed, it was worn down, perhaps to low rolling hills, perhaps to
-flat plains almost at sea level, and partially or entirely covered with
-thick layers of sediment. Each time, another mountain building episode
-followed, with new intrusions of granite and new metamorphism of the
-pre-existing rocks.
-
-Each succeeding period of metamorphism and mountain building further
-changed the nature of the rocks involved, complicating the patterns of
-folding and faulting, adding recrystallization to recrystallization,
-until the oldest of the rocks bore little trace of their original
-sedimentary nature. In general, the rocks that are oldest were most
-altered by the repeated metamorphism, while the younger rocks were less
-altered.
-
-[Illustration: The Black Canyon of the Gunnison River is one of the
-state’s deep and spectacular chasms. Canyon walls are of Precambrian
-gneiss intruded by many dikes and highly fractured by later uplifts. The
-flat upper surface of the Precambrian rocks represents an ancient plain
-on which, during Jurassic time, the dinosaur-bearing Morrison Formation
-was deposited. (John Chronic photo)]
-
-The Precambrian Era ended with a long period of erosion, a period known
-to geologists as the Lipalian Interval. During this time, over almost
-the entire world there was no mountain building. The land lay sleeping,
-subject only to the forces of erosion. The last mountains were flattened
-nearly to sea level. Slow, sluggish streams and rivers carried sand and
-mud toward the oceans—oceans in which perhaps primitive, soft-bodied
-organisms, with no hard parts to be preserved as fossils, were beginning
-to evolve.
-
-On the continents, the time of intense metamorphism was over; most rocks
-of later eras are preserved today in pretty much their original state.
-The boundary between the Precambrian and later rocks is normally well
-defined. It is visible at many places in Colorado: in Williams Canyon
-near Colorado Springs, in Glenwood Canyon, near Red Rocks west of
-Denver, just west of La Veta Pass, at the top of Royal Gorge and the
-Black Canyon of the Gunnison. At most of these localities it is a
-smoothly beveled surface, with highly contorted Precambrian rocks below
-it and flat-lying Paleozoic sediments above it. Near Red Rocks and La
-Veta Pass, the same relationship prevails, but the entire contact, and
-the rocks above and below it, have been steeply tilted by the uplift of
-the present mountains.
-
-In portions of western North America, deposition late in Precambrian
-time has left a series of flat-lying rocks between the contorted
-Precambrian and later Paleozoic sediments. These rocks can be seen in
-northwestern Colorado, where they form the dark red sedimentary core of
-the Uinta Mountains.
-
-
-                             PALEOZOIC ERA
-
-Geologists have divided the second great era of geologic time into units
-called Periods. The rocks deposited during a Period are called Systems,
-but more often than not it is convenient to discuss them in terms of
-easily recognized units of rock, called Formations. Formations are named
-after areas in which they are well exposed.
-
-The stratigraphic column given in Chapter I shows the Periods and
-Systems in their correct order, and gives the age in years for each, as
-determined by radioactivity methods. As you read, refer as often as
-necessary to this column.
-
-The geologic map on page 35 will help you locate areas where the rocks
-discussed in the text are exposed, and will greatly facilitate your
-understanding of the geology of the state.
-
-[Illustration: The Cambrian Sawatch Sandstone lies almost horizontally
-on Precambrian granite in Glenwood Canyon. In the foreground is the
-Colorado River. (Jack Rathbone photo)]
-
-
-                            Cambrian Period
-                      (500-570 million years ago)
-
-The first fossiliferous rocks in Colorado were deposited during the
-Cambrian Period, at a time when over much of the world the seas were
-creeping in across wide, level plains formed during the Lipalian
-Interval. Colorado was not covered by these seas until quite late in the
-Cambrian Period. Beach deposits progressively younger in age suggest
-that the sea invaded from the west, and spread slowly eastward,
-inundating most of the central part of the state but not the extreme
-north or south.
-
-The beach deposits, now called the Sawatch Sandstone because they are
-well exposed in the Sawatch Range, are composed mostly of fine quartz
-sand. They are colored with glauconite, a green mineral, and hematite, a
-dark red mineral, so that the rock has a variegated appearance. The post
-office at Manitou is built of this red and green rock, and good
-exposures of it exist in Williams Canyon near Manitou, along U. S.
-Highway 24 northwest of Manitou, near Red Cliff and Minturn, and in
-Glenwood Canyon.
-
-The sea which crept over Colorado at this time contained small
-conical-shelled mollusks, brachiopods, and trilobites. Their shells can
-occasionally be found in Cambrian rocks in Williams Canyon and in the
-Sawatch and Mosquito Ranges. At two localities unusual fossils called
-graptolites have been found in thin Upper Cambrian shales overlying the
-Sawatch Sandstone.
-
-[Illustration: These fossils can occasionally be found in Cambrian rocks
-in central Colorado.]
-
-
-                           Ordovician Period
-                      (440-500 million years ago)
-
-The sea deepened and widened as the Ordovician Period began, and a
-series of limestones and dolomites was deposited, either on top of the
-Sawatch Sandstone or, where the Sawatch had not been deposited, directly
-on the Precambrian. These rocks are now called the Manitou Formation.
-
-The fossils in these rocks are much more varied than those in the
-Sawatch Sandstone: snails, echinoderms, sponges, cephalopods,
-brachiopods, and trilobites are common. The Ordovician sea must have
-teemed with life, as many rocks deposited at this time are more than
-half composed of animal remains. In addition to hard-shelled animals
-which formed fossils, there were probably abundant soft-bodied animals
-such as jellyfish and worms, which left no record of their presence.
-
-After deposition of the Manitou Formation, the seas receded slightly. A
-new series of sands was deposited above the Manitou in central Colorado.
-These now form the Harding Sandstone, a formation of unusual interest
-because it contains remains of the earth’s earliest known vertebrates,
-primitive jawless fish called Agnathids. In places in the Harding
-Sandstone there are dense accumulations of the tiny polygonal armor
-plates from these fish. Although no whole fish have been found, we can
-reconstruct their appearance by comparing individual plates or groups of
-plates with later, better known relatives.
-
-Also present in great quantities in the Harding Sandstone are conodonts,
-peculiar tiny brown tooth-like fossils. Relationships of the conodonts
-are unknown; they may be parts of the Agnathids, or perhaps they
-represent some entirely different group of animals, with no living
-relatives.
-
-After deposition of the sands of the Harding Sandstone, the sea deepened
-locally and the Fremont Limestone, a massive gray crystalline limestone
-containing many marine fossils, was deposited. Mollusks (some quite
-large), brachiopods, and corals contributed their shells to the Fremont
-Limestone. The chain coral _Catenipora_ and the horn coral
-_Streptelasma_ may often be used to identify the formation.
-
-The Fremont Limestone was deposited very late in the Ordovician Period.
-Probably the seas were much more extensive then than present deposits
-indicate; subsequent erosion has at several times erased the evidence in
-uplifted areas.
-
-[Illustration: These Ordovician fossils can be found in the Manitou
-Formation in the Colorado Springs area.]
-
-[Illustration: The earliest known fish remains come from the Ordovician
-Harding Sandstone of central Colorado. These fragments of the protective
-plates have been magnified about five times.]
-
-[Illustration: Corals and coral-like organisms occur in the Ordovician
-Fremont Limestone.]
-
-
-                            Silurian Period
-                      (400-440 million years ago)
-
-Until very recently, no Silurian rocks or fossils were known in
-Colorado, and it was thought that seas did not extend into the state
-during this period. However, a few years ago good Silurian corals and
-brachiopods were discovered near the northern edge of the state. They
-occur in broken blocks and patches of Silurian limestone, mingled with
-blocks of other sedimentary rocks and, oddly enough, with volcanic
-material.
-
-What seems to have happened here is that sedimentary layers of Silurian
-age _were_ present over northern Colorado at one time. During some
-subsequent period of volcanism, volcanic lavas penetrated these
-sediments from below. Near the volcanic tubes, broken, angular fragments
-of the surrounding sedimentary rocks were sometimes carried upward or
-downward by the motion of the lava.
-
-Much later, both the volcanic outpourings (if the lavas ever reached the
-surface) and the sediments were stripped away by erosion, probably at a
-time when mountains were rising in the area. Only the deep portions of
-the tubes that fed the volcanoes were preserved. These tubes are called
-diatremes, and thanks to the blocks of sedimentary rock in them we know
-that there were indeed seas in Colorado during Silurian time, seas
-containing the abundant life of a shallow marine environment very much
-like that existing at the same time in Illinois, Iowa, and Indiana.
-
-
-                            Devonian Period
-                      (350-400 million years ago)
-
-As far as we know now, Colorado was just a little above sea level during
-most of Devonian time. Early and Middle Devonian deposits are lacking.
-Late in the period, however, Colorado was widely inundated once more.
-Embayments of a western sea covered most of the central part of the
-state and an area in southwestern Colorado around Ouray.
-
-Deposits formed in these embayments have been given several names.
-Chaffee Formation is the name most commonly used in central Colorado;
-Ouray Formation identifies rocks of the same age in southwest Colorado.
-The Chaffee Formation has been subdivided into two well defined units,
-the Parting Sandstone or Quartzite, and the Dyer Dolomite or Limestone.
-Many ore deposits are associated with these rock units—notably deposits
-of lead and zinc. The Parting Sandstone is frequently so well cemented
-with silica that it is actually a quartzite; thin shale beds or
-“partings” make it easy to recognize. It frequently contains remains of
-fossil fish and distinctive beds of algae.
-
-The Dyer Dolomite contains brachiopods and bryozoans, mollusks and
-corals. Some of the best fossil hunting in Colorado is in Dyer beds
-around the White River Plateau, where the fossils frequently weather out
-of the rock as almost perfect specimens.
-
-[Illustration: These Devonian brachiopods come from the White River
-Plateau in western Colorado.]
-
-
-                          Mississippian Period
-                      (310-350 million years ago)
-
-The sea continued to cover most of Colorado after the end of the
-Devonian Period, well into Mississippian time. Mississippian rocks are
-characteristically thick, massive gray limestones collectively called
-the Leadville Limestone. This unit is well known as the host rock for
-many Colorado ore deposits, notably those around the town of Leadville.
-
-During Mississippian time the western sea, warm and rich in organisms,
-covered much of North America. Brachiopods and corals flourished, as did
-many other forms of life. The seas during part of this time extended
-completely across Colorado to merge with seas that covered the
-midwestern part of the United States.
-
-Over all this vast area, as well as southwest into Arizona, the gray,
-massive, fossiliferous Mississippian limestone is remarkably uniform and
-easily recognized, although it is called by different names in different
-areas.
-
-Late in Mississippian time, the Colorado area rose slightly and the sea
-in which the Leadville Limestone was deposited receded. An interval of
-erosion followed. The surface of the limestone was dissolved and pitted,
-tunnels and caves formed where running water etched deep into the rock,
-and a reddish soil formed on the surface and in the hollows. This
-portion of the limestone, which in some places also contains pebbles of
-chert, is named the Molas Formation. Part of the Molas may be
-Pennsylvanian in age.
-
-[Illustration: Mississippian fossils from western Colorado show that
-seas covered much of the state about 330 million years ago.]
-
-
-                          Pennsylvanian Period
-                      (270-310 million years ago)
-
-As the Pennsylvanian Period began, the Colorado area continued to rise.
-Earliest deposits of this age are fine-grained black shales and
-sands—the Glen Eyrie Formation along the southern Front Range and the
-Belden Formation in west central Colorado. Then, through millions of
-years, mountain-building took place. Some areas rose more than others,
-so that formerly flat-lying marine sediments were bent and broken, and a
-series of high mountain ridges and deep basins were formed. Geologists
-sometimes call these the Ancestral Rocky Mountains.
-
-Although the pattern of the mountains changed repeatedly, the Ancestral
-Rockies consisted principally of two large ranges. One range roughly
-paralleled the present Front Range, but lay thirty to fifty miles
-further west. The other extended from the San Luis Valley northwest
-toward Colorado National Monument, including the area around the Black
-Canyon of the Gunnison and the present Uncompahgre Plateau. Coarse
-sediments washed off both sides of both ranges, and accumulated as
-alluvial fans and valley fill along the mountain margins. These exist
-today as the Fountain Formation of the eastern Front Range, the Minturn
-Formation between the ancient uplifts, and the Hermosa Formation west of
-the western uplift.
-
-[Illustration: This paleogeographic map reflects the distribution of
-land and sea during the early part of the Pennsylvanian Period and shows
-where coarse sediments derived from the Ancestral Rockies were
-deposited.]
-
-  FOUNTAIN FORMATION
-  MINTURN FORMATION
-  HERMOSA FORMATION
-
-[Illustration: West of Denver, the main line of the Denver & Rio Grande
-Railroad tunnels beneath steeply dipping sandstones and conglomerates of
-the Fountain Formation. (Jack Rathbone photo)]
-
-[Illustration: Corals, brachiopods, and fusulinid Foraminifurida can be
-found in the Pennsylvanian Minturn Formation at many places in the
-Mountain and Plateau Provinces.]
-
-[Illustration: In western Colorado, where vegetation is sparse, rock
-structures are clearly defined. This photograph shows beds of the
-Pennsylvanian Minturn Formation sharply folded, probably as a result of
-the deformation of gypsum in underlying layers. (Jack Rathbone photo)]
-
-In the Flatirons near Boulder, Red Rocks Park near Denver, and the
-Garden of the Gods near Colorado Springs we see well exposed examples of
-the Fountain Formation. The Minturn Formation is visible along the Eagle
-River west of Wolcott, and along Gore Creek near Vail. The Hermosa
-Formation forms striking red cliffs north of Durango. In the Sangre de
-Cristo Mountains area, exceptionally great and rapid deposition took
-place, and the Minturn Formation is very thick.
-
-In west central Colorado, near the towns of Eagle and Gypsum, a large
-basin formed. In it, gypsum and other salts were deposited as arms of
-the sea were cut off from the main marine area. The unusual appearance
-of the hills along the Eagle River, especially north of U. S. Highway
-24, is caused by the presence of gypsum in the bedrock.
-
-In a similar manner, the Paradox Basin was formed in southwestern
-Colorado. Thousands of feet of gypsum, salt, and potash were deposited
-here, probably also precipitated in restricted arms of the sea. These
-minerals, the so-called evaporites, have since significantly controlled
-development of the landscape in Gypsum Valley and other parts of this
-region. (See The Plateaus in Chapter I and the section on Gypsum in
-Chapter III).
-
-Between the mountain masses and their surrounding alluvial deposits,
-shallow seas repeatedly invaded the lowland areas of the state. Marine
-fossils in some parts of the Minturn Formation bear witness to as many
-as twenty marine cycles. Strangely, the Pennsylvanian Period appears to
-have been cyclical in other parts of the United States as well, for
-marine sediments are found alternating with nonmarine sediments in
-Pennsylvania, Illinois, Kansas, Nebraska, and New Mexico. In middle
-Pennsylvanian time, general uplift occurred in Colorado, and almost the
-entire state was above sea level for the rest of the period.
-
-
-                             Permian Period
-                      (223-270 million years ago)
-
-By the end of the Pennsylvanian Period, the mountains of the Ancestral
-Rockies had been almost entirely removed by erosion, and the deep basins
-were filled with sediments. Colorado was once more a great plain,
-sloping gently to the northeast. In eastern Colorado, a shallow sea
-gradually dried up, leaving some thin limestone and gypsum beds along
-its margin. The western shore of this sea was edged with beaches and
-sand dunes, preserved as the Lyons Sandstone. The buildings of the
-University of Colorado, as well as many homes and other structures in
-the Boulder-Denver area, are faced with this beautiful salmon-colored
-sandstone.
-
-[Illustration: Balanced Rock, in the Garden of the Gods northwest of
-Colorado Springs, is an erosional remnant of iron-rich conglomerate and
-sandstone. It remains while the rest of the surrounding layers are gone
-because it is harder and more completely cemented together by silica.
-The rock is part of the Late Paleozoic Fountain Formation. (John Chronic
-photo)]
-
-In the western part of the state, Permian deposits consist mostly of
-shales and sandstones. The red color of these rocks, and the complete
-absence of fossils in them, suggest that the environment in which they
-were deposited was not marine, but was a vast, level mudflat subject to
-alternating wet and dry periods. The shales and sandstones collectively
-are called the Maroon Formation, named for Maroon Bells, near Aspen,
-where they are dramatically exposed in the mountain cliffs.
-
-[Illustration: Tracks of Permian reptiles called _Laoporus
-coloradoensis_ occur in the Lyons Sandstone near Lyons. These are about
-life size.]
-
-During part of Permian time, a shallow sea extended from Idaho, Utah,
-and Wyoming into the northwest corner of Colorado. In this sea was
-deposited the Phosphoria Formation, a highly phosphatic limestone
-containing only rare, poorly preserved molluscan fossils.
-
-As the Paleozoic Era ended, Colorado was still flat and low-lying. By
-this time land plants and animals had evolved, but if vegetation grew in
-the Colorado area, or animals roamed it, they left few fossil remains.
-Tracks of early reptiles have been found in the Lyons Sandstone. Dune
-sandstones here and in adjacent areas suggest that desert conditions may
-have prevailed, in which case Colorado would have been very similar,
-scenically and climatically, to Sahara regions today.
-
-[Illustration: Dark red Pennsylvanian and Permian conglomerates form the
-Flatirons that overlook the University of Colorado campus at Boulder.
-University buildings are faced with Permian Lyons Sandstone quarried
-along the foothills of the northern Front Range. (University of Colorado
-photo)]
-
-
-                              MESOZOIC ERA
-
-The Mesozoic Era, popularly known as the Age of Reptiles or Age of
-Dinosaurs, is divided into three periods. The climate of the entire
-earth appears to have been warmer then than it is at present, perhaps
-because of a different distribution of land and sea areas, or because
-continental areas were not as high and mountainous as they are just now.
-Colorado was a rather low land area for most of the first two Mesozoic
-periods; then a vast sea covered the entire state for the remainder of
-the era.
-
-[Illustration: The pink cliffs of Colorado National Monument are made of
-Wingate and Entrada Sandstones. Underlying them, in the valley bottom,
-Chinle shales form steep red slopes. (William C. Bradley photo)]
-
-
-                            Triassic Period
-                      (180-225 million years ago)
-
-Saharan conditions continued to prevail in western North America during
-the early part of the Mesozoic Era. In central Colorado, the lowest
-Mesozoic deposits are the Triassic Lykins Formation, a series of soft,
-bright red sandstones and shales. Where the Lykins is exposed along the
-Front Range, its bright red color identifies it. Because of its
-softness, it is often less prominent than adjacent rock layers in the
-mountain foothills. The Lykins Formation includes some evaporites,
-apparently derived from Permian evaporites washed into the Triassic
-ponds and lakes which existed occasionally in this region.
-
-Over almost the entire state, the rocks deposited at this time are very
-similar. Formation names may differ—Lykins, Moenkopi, Chinle, Ankareh,
-Wingate—but the rocks are almost universally fine-grained sandstones and
-shales with a red or pink color. They represent ancient coastal plain,
-dune, or delta deposits. Toward the western edge of the state they
-coarsen, and contain layers of conglomerates similar to the Triassic
-conglomerates of northern Arizona and Utah. These suggest that
-mountain-building was taking place west of here at that time.
-
-There are virtually no fossils known from Triassic rocks in Colorado,
-although some fossil palm fronds have been found west of the San Juan
-Mountains, in the southwestern corner of the state.
-
-
-                            Jurassic Period
-                      (135-180 million years ago)
-
-During the Jurassic Period, Colorado was still a low, flat desert area
-with intermittent streams flowing eastward over the surface of older
-sediments. The Navajo Sandstone, formed from dune sands, was deposited
-in the western part of the state. Streams flowing eastward from Utah
-brought fine sediments—silts and muds—to western Colorado, forming what
-is now the Carmel Formation. Near Canon City, coarse gravels bear
-witness to local uplift in Jurassic time. Both these gravels and the
-Carmel Formation were overlain by more dune sands, now hardened into the
-Entrada Sandstone.
-
-In Late Jurassic time the Colorado area, which had been predominantly
-desert since Permian time, appears finally to have been submerged once
-more. Fine calcareous muds of the Curtis Formation, containing
-ammonites, belemnites, and other marine shellfish, show us that a
-shallow sea transgressed from the west over the wind-blown sands. This
-sea was, geologically speaking, of short duration—only a few million
-years. Bounded on almost all sides by desert, it seems to have dried up,
-depositing the gypsum that is now present in a thin layer along the
-Front Range between Denver and Canon City in the Ralston Formation.
-
-At about this time, however, the climate underwent a major change.
-Deposits above the Ralston indicate an increasingly moist environment,
-the environment in which the Morrison Formation was deposited over most
-of Colorado and parts of the adjacent states of Kansas, Arizona, Utah,
-and Wyoming. The Morrison Formation is exposed in many places, and is
-characteristically composed of layers of fine, limy mud, brightly
-colored in streaks of red, brown, green, and blue. In most areas it is
-so soft that it becomes soil-covered; it is well exposed only in
-roadcuts or where it is protected from erosion by a “caprock” of harder
-sediments or lava. Spectacular outcrops can be seen in new roadcuts
-along U. S. Interstate highway 70 just west of Denver.
-
-[Illustration: In this roadcut along U. S. Interstate 70 west of Denver,
-Jurassic and Cretaceous rocks are unusually well exposed in the Dakota
-hogback. Green and purple shales represent the dinosaur-bearing Morrison
-Formation. The Cretaceous Dakota Group forms the eastern, higher half of
-the cut. Black layers are carbon-rich clays of the South Platte
-Formation, frequently quarried locally for ceramic uses. (John Chronic
-photo)]
-
-Fossil dinosaur bones occur in great numbers in the Morrison Formation
-near the towns of Morrison and Canon City and at several other places in
-Colorado. Those at Canon City have been quarried extensively, and are
-now mounted in a number of museums in the United States. At Dinosaur
-National Monument, in eastern Utah and northwestern Colorado, many
-excellent remains have been found; those in Utah can be seen in place in
-the rock in a striking exhibit at the National Monument.
-
-[Illustration: In an old painting, a paleontologist contemplates fossil
-bones found near Morrison. The date is 1877. The bones are those of the
-70-foot dinosaur _Apatosaurus_, more commonly known as _Brontosaurus_,
-shown below in reconstruction.]
-
-[Illustration: Apatosaurus]
-
-Some of the dinosaurs known from the Morrison Formation reached 80 feet
-in length. Both plant-eating and meat-eating types are known. In
-addition to the bones themselves, gastroliths or gizzard stones can
-frequently be found; these highly polished stones were as essential to
-dinosaur digestion as gravel is to a chicken or a caged canary.
-
-Along with the dinosaur fossils are found abundant remains of water
-plants called charophytes. These plants formed tiny spiralled balls of
-calcite as part of their reproductive activities; both the little balls
-and the stalks of the plants themselves occur in many parts of the
-state. In western Colorado, near Grand Junction, silicified shells of
-freshwater snails can also be found in the Morrison.
-
-Early in the 1900s vanadium, radium, and uranium were discovered in
-Jurassic sandstones and mudstones of western Colorado. Extensive mining
-in this area has revealed that these elements often become concentrated
-by groundwater in organic material such as fossil plant stems or
-dinosaur bones. The search for radioactive minerals has thus brought to
-light many ancient fossil accumulations.
-
-
-                           Cretaceous Period
-                       (70-135 million years ago)
-
-Early in Cretaceous time, marine conditions once more prevailed in
-Colorado. This is indicated by a marked change in rock types from beach
-and near-shore deposits to true marine sediments.
-
-[Illustration: Between the Front Range and the Plains the Cretaceous
-Dakota Formation forms a hogback ridge which can be traced for 200 miles
-or more. The well-cemented sandstone resists erosion, and so remains as
-a ridge when softer layers are stripped away. (Jack Rathbone photo)]
-
-The sandstones derived from beach sands sometimes include coarse pebbles
-of chert which can be traced to sources in Permian rocks of Utah and
-Nevada. Occasionally the beach and near-shore deposits include marine
-shells like oysters, indicating that there were brackish and salt water
-lagoons and marshes along the shore. The Dakota Formation represents the
-beach of the transgressive or advancing sea. This formation contains oil
-in eastern Colorado, Nebraska, and Wyoming; the oil itself may have been
-derived from decay of organic materials in swamps behind the beaches and
-bars.
-
-As the sea deepened in eastern Colorado, finer sediments were deposited.
-These included the black muds of the Benton Shale, and the Niobrara
-Limestone, a shallow-water deposit containing abundant shells of clams
-(_Inoceramus_ and _Ostrea_) and ammonites and tiny one-celled animals
-called Foraminiferida. Above the Benton and Niobrara Formations lie the
-fine gray muds of the Pierre Shale. Several thousand feet thick, the
-Pierre contains occasional beautifully preserved ammonite shells as well
-as bones from fossil fish and swimming reptiles.
-
-[Illustration: Cretaceous rocks in Colorado are rich in fossil
-pelecypods. Each of the fossils illustrated above may grow to a much
-larger size than shown.]
-
-[Illustration: Shales of the Laramie Formation contain many recognizable
-plant fossils.]
-
-The rocks deposited in western Colorado at this time are markedly
-different from those deposited in eastern Colorado. In the east,
-deposits are fine and very limy, containing abundant shells and little
-in the way of coarse debris. In the west, sandstones of the Mesa Verde
-Formation dominate, and coal beds suggest marshy or swampy conditions
-inshore from the ancient ocean. This is just the pattern we would expect
-from a low-lying region bordering a shallow sea, a region similar
-perhaps to the southeastern Atlantic and Gulf coasts of the United
-States today.
-
-Toward the end of the Cretaceous Period, the sea receded from Colorado.
-Beaches and bars of the retreating sea left a sandstone layer which now
-outcrops prominently east of the Front Range as the Fox Hills Sandstone.
-Above lie interbedded sands and coals, the Laramie Formation. The
-presence of coal above beach sands shows that the coal swamps moved
-eastward as the sea retreated.
-
-The exact age of the shoreline deposits and coal beds varies from place
-to place in such a way as to indicate that the sea withdrew slowly and
-irregularly. In general the shore moved eastward, but there are
-localities such as North Park where deposition lasted much longer than
-elsewhere. In some places no real beach was formed at the ancient strand
-line.
-
-In western Colorado, the end of Cretaceous time is marked by coarser
-beds, indicating an increased rate of uplift in Utah. Conglomerates were
-deposited in the beds of the McDermott Formation, now visible along the
-Animas River south of Durango.
-
-
-                              CENOZOIC ERA
-
-It is characteristic of earth history that the younger the rocks are,
-the more we know about them. This is because younger rocks lie near the
-surface, have not been disturbed as much by mountain building processes
-as have older rocks, and have not been affected as strongly by repeated
-erosion. Many of the events of the Cenozoic Era are documented in detail
-in the geology of Colorado, and these events have intimately influenced
-the scenery as we see it today.
-
-The Cenozoic is the Age of Mammals. How it happened that mammals
-triumphed over reptiles is one of the mysteries of geology. Some
-scientists think that climatic changes—dropping temperatures and
-increases in rainfall—swung the balance in favor of the warm-blooded
-mammals. Others believe that cosmic ray bombardment during some unusual
-astronomical event may have destroyed many surface-living dinosaurs,
-while small burrowing mammals (as well as many small reptiles) were able
-to survive. Still others maintain that the superior intelligence and
-regulated body temperatures of mammals enabled them to win out in the
-battle for survival without the aid of climatic or cosmic change.
-
-The names Tertiary and Quaternary, used for the two Cenozoic Periods,
-are holdovers from early studies in geology in which rocks were divided
-into Primary (very hard, crystalline rocks such as igneous and
-metamorphic rocks), Secondary (well consolidated layered rocks),
-Tertiary (layered rocks which are not fully cemented but which are
-nevertheless fairly well consolidated), and Quaternary (sediments in
-which the grains have not become cemented together).
-
-
-                            Tertiary Period
-                        (3-70 million years ago)
-
-During the first part of the Tertiary Period, uplift began in earnest in
-Colorado and adjacent states. This uplift was part of the great Laramide
-Orogeny that built the Rocky Mountain chain from Alaska to New Mexico.
-The entire area rose above the level of the sea, and mountains were
-thrust up in a great series of north-south ranges that extended unbroken
-almost the length of the continent. Between the ranges, thick layers of
-gravel and sand, derived from the surrounding highlands, were deposited
-in intermontane basins. Occasional freshwater limestones and shales
-indicate the presence of lakes.
-
-In Colorado, many details of the formation of the Rockies stand out in
-bold relief. The Front Range moved upward sharply, mostly as a linear
-block broken or faulted along both edges. Paleozoic and Mesozoic
-sediments along the margins of the block were steeply tipped and in some
-places even overturned, while in some localities Precambrian rocks were
-thrust out over the younger sediments.
-
-Just east of the Front Range, especially in the area around Denver, the
-land remained lower and was the site of thick deposits of gravel and
-sand eroded from the range. The Denver Formation, the Arapahoe
-Conglomerate, and the Dawson Arkose are more than 2,000 feet thick in
-this area. These are delta and river sediments, all varying a great deal
-from place to place. Individual layers of sand or gravel are not
-continuous over extensive areas, but some, such as the Castle Rock
-Conglomerate, are very prominent locally.
-
-[Illustration: On Wolford Mountain, just north of Kremmling, Precambrian
-granite lies on top of Cretaceous shale. The older rocks were thrust up
-and over younger rocks during the Laramide Orogeny. The position of the
-fault shows clearly because trees prefer the granite soil above the
-fault to the shale below. (Jack Rathbone photo)]
-
-Along the eastern margin of the Front Range west of Castle Rock and
-Sedalia, rocks deposited at this time are now folded steeply, indicating
-that the mountains continued to rise even as basin sediments were being
-deposited.
-
-In southern Colorado, the Sangre de Cristo and Wet Mountains were also
-formed as upthrust blocks. Between them, the Huerfano Basin and
-adjoining Raton Basin received particularly rapid alluvial deposition.
-In the Raton Basin, quantities of vegetation were deposited in swamps
-and marshes, forming the thick coal beds which can now be seen in road
-cuts west of Trinidad and along the Raton Pass highway. Huerfano Basin
-deposits contain some of the earliest known horse remains, skeletons of
-a tiny four-toed horse called _Hyracotherium_ (formerly known as
-_Eohippus_).
-
-[Illustration: Bones of _Hyracotherium_, the “dawn horse,” have been
-found northwest of Walsenburg in Early Tertiary sediments of the
-Huerfano Basin. (C. R. Knight painting, courtesy American Museum of
-Natural History)]
-
-Other rising ranges provided material for alluvial deposition in North
-Park, Middle Park, South Park, and the San Luis Valley. Layers of basalt
-and volcanic peaks show that as the mountains rose, the crust cracked
-and allowed lava to rise to the surface in great quantities. Tertiary
-basalts are very much part of the Colorado landscape: some can be seen
-west of Granby, others in Table Mountains east of Golden. Near Boulder,
-Valmont Dike was intruded, though lava may not have reached the surface
-in that area. Spanish Peaks in southern Colorado, Mesa de Maya, the
-Rabbit Ears Range, Grand and Battlement Mesas, and many other volcanic
-features were formed at this time.
-
-[Illustration: The town of Golden nestles between the Front Range and
-South Table Mountain. Tertiary basalt capping South Table Mountain
-covers beds of the Denver Formation. It thins to the right, or south,
-indicating that its source was probably to the north or northwest.
-Buildings in the right foreground are the Colorado School of Mines.
-(Jack Rathbone photo)]
-
-[Illustration: A series of almost vertical dikes radiate from West
-Spanish Peak. Surrounding sediments are Tertiary. Weathering and erosion
-along sets of joints in the largest dike have shaped it into the
-“Devil’s Staircase.” (Jack Rathbone photo)]
-
-Most of the rich mineral deposits of Colorado are thought also to have
-been formed during the early part of the Tertiary Period. Solutions rich
-in gold, silver, zinc, lead, copper, and sulfides of iron seeped into
-joints and faults in the crust as the mountains were pushed upward. Ore
-minerals crystallized out, sometimes in veins in the ancient Precambrian
-igneous and metamorphic rocks, sometimes in Paleozoic sediments. These
-are further discussed in Chapter III.
-
-[Illustration: The Eocene Green River Formation includes great
-thicknesses of oil shale, an untapped petroleum reserve containing
-perhaps three trillion barrels of oil. The richest part of the oil shale
-is a dark brown layer called Mahogany Ledge, visible here on cliffs just
-west of Rifle. If placed in a campfire, fragments of this shale release
-enough oil to burn with a yellow, smoky flame. (Jack Rathbone photo)]
-
-Further to the north and west, the Uinta Mountains rose. They are a
-fault-block range, but they lie at right angles to the general
-north-south trend of the Rocky Mountains. South of them the Uinta Basin,
-one of the largest of the intermontane basins, received shaly deposits
-in a great lake which existed here for probably several million years.
-The lake extended over some 100,000 square miles, and during its
-existence great quantities of tiny organisms lived in its waters. Oily
-material from these organisms was deposited in the mud of the lake
-sediments, particularly in the eastern end of the basin, there to remain
-trapped in a great oil-shale deposit. Fossil fish, crayfish, algae, and
-many forms of insect and plant life have been found as fossils in these
-lake shales.
-
-West of Pikes Peak, another lake formed, dammed by a lava flow from a
-nearby volcanic field. Fine volcanic ash falling into this lake
-preserved the trunks and leaves of many plants as well as abundant
-insects, fish, and occasional mammal bones. These are now protected and
-exhibited in Florissant Fossil Beds National Monument. The fossil
-plants, among them redwoods, poplar, hackberry, and pine, suggest a
-climate warmer than the present one, and have been taken to indicate
-that regional uplift to the present altitude had not yet occurred.
-
-Another rich deposit of fossil insects and plants occurs near Creede.
-Other lake deposits in South Park contain ash layers with fossil algae
-and snails.
-
-[Illustration: Large petrified trunks of redwoods and other trees can be
-seen at Florissant Fossil Beds National Monument, west of Colorado
-Springs. (John Chronic photo)]
-
-In southwestern Colorado, extensive Tertiary lava flows, ash falls, and
-river deposits form the eastern part of the San Juan Mountains, the
-largest volcanic area in the state. Mineral collectors are attracted to
-this region by the many excellent localities for agate and other
-siliceous stones.
-
-Still another center of Tertiary volcanism was located in what is now
-Rocky Mountain National Park. Specimen Mountain, northwest of Trail
-Ridge, was an active volcano about 30 million years ago, shedding ash
-and lava over much of northern Colorado. The rhyolite which now caps the
-hill west of Iceberg Lake, on Trail Ridge Road, was derived from this
-volcano, but is now separated from it by the deep glaciated valley of
-the Cache la Poudre River and Milner Pass.
-
-Volcanic ash at times drifted far eastward and blanketed the surface of
-the plains, burying specimens of many animals and plants. The White
-River Formation, extending from northeast Colorado northward into South
-Dakota, is formed of such drifting ash. Many now-extinct mammals have
-been excavated from this formation.
-
-Sometime after the mid-Tertiary episode of violent volcanic activity,
-Colorado was uplifted to its present altitude. This was a general
-uplift, raising the plains and plateau areas as well as the mountains.
-The uplift was not an abrupt process, but continued for perhaps ten
-million years. It raised the entire state 3,000 to 5,000 feet above its
-previous level.
-
-[Illustration: Pawnee Buttes, about 40 miles north of Fort Morgan, rise
-like castles from the eastern Prairie Province. Remnants of Oligocene
-and Miocene sedimentary rock that once covered much of northeastern
-Colorado and adjacent states, they contain jaws, teeth, and other bones
-of primitive mammals. (Department of Highways photo)]
-
-During the remainder of the Tertiary Period, Colorado was the site of
-erosion rather than deposition. However, some stream material was
-deposited in the mountain valleys, and on the prairies wind-blown and
-stream-borne sands were spread thinly, interlayered with impure
-limestones deposited in ponds and lakes. In the San Luis Valley,
-deposition was probably more continuous than elsewhere, as the exit from
-the valley was blocked by volcanic flows. The deposits in this valley,
-sands and clays of the Santa Fe and Alamosa Formations, form a great
-artesian basin. The rich agricultural development of the valley is made
-possible by water wells tapping these formations.
-
-[Illustration: Remains of many now-extinct mammals have been found in
-Tertiary sedimentary rocks of northeastern Colorado, in the general area
-of Pawnee Buttes. Those illustrated are _Oreodon_ from Oligocene strata
-and a “giraffe-camel” (_Oxydactylus_) from Miocene rocks.]
-
-
-                           Quaternary Period
-                    (3 million years ago to present)
-
-The most significant feature of the Quaternary Period in Colorado, as
-elsewhere in the northern hemisphere, is the evidence of glaciation.
-During the first part of the Quaternary Period, known as the Pleistocene
-Epoch, great continental glaciers covered most of Canada and much of
-northern United States. The ice sheets did not extend southward as far
-as Colorado, but large valley glaciers developed in many of the mountain
-ranges of the state and left their traces in many mountain valleys.
-
-[Illustration: Mills and Jewel Lakes, in Rocky Mountain National Park,
-occupy small glacier-gouged basins in Glacier Gorge. The flat-topped
-peak at the upper left is Longs Peak, elevation 14,256 feet; Pagoda
-Mountain is in the center of the skyline. Bedrock in this area is
-Precambrian granite, gneiss, and schist at the Front Range “core.” (Jack
-Rathbone photo)]
-
-The conditions leading to Pleistocene glaciation are not fully
-understood. Climatic changes may have been initiated by a decrease in
-solar radiation, changing patterns of ocean currents, reduction of solar
-heating by volcanic dust, or an increase in general elevation of the
-land. As the climate became cooler and moister, snowfall increased in
-the north and at high altitudes. In areas where winter snowfall exceeded
-summer melting, glaciers developed.
-
-In Colorado, glaciers formed along the crests of the Front Range, the
-Sawatch Range, the Elk Mountains and West Elk Mountains, the Sangre de
-Cristo and Mosquito Ranges, the San Juan Mountains, and the Park and
-Gore Ranges. Glaciation in Colorado was selective: in many places
-elevation was sufficient for glaciation, but snowfall apparently was not
-great enough. Where they did occur, the glaciers extended down to
-elevations of about 8,000 feet. There, temperatures became mild enough
-to melt the ice.
-
-The mountain glaciers have left many tell-tale signs of their presence.
-Valleys above 8,000 feet are U-shaped, their upper ends bounded by
-horseshoe-shaped, steep-walled cirques. In the lower portions of the
-valleys, at elevations just above 8,000 feet, lie long lines of glacial
-debris known as moraines: terminal moraines forming crescents across the
-valleys to show where melting glaciers dropped their rocky loads;
-lateral moraines along the sides of valleys; medial moraines where
-glaciers from two valleys met. Terminal moraines, often forming
-effective barriers across the present streams, may act as dams, creating
-lakes such as Grand Lake in Rocky Mountain National Park.
-
-There were at least three distinct glacial episodes in Colorado. This is
-known because careful studies of glacial debris in moraines reveal three
-different degrees of rock weathering. All three stages can be seen in or
-near Rocky Mountain National Park. The oldest is represented by a
-moraine about three miles west of Estes Park, where the Big Thompson
-River traverses a wide U-shaped valley before entering its narrow,
-unglaciated canyon. The next oldest is represented in terminal moraines
-further up the valley, at Aspenglen campground. The youngest is shown in
-a prominent terminal moraine about one mile west of the park entrance in
-Horseshoe Park.
-
-A large lateral moraine separates Hidden Valley from the south side of
-Horseshoe Park, and an almost equally large lateral moraine is present
-on the north side of this valley. At Moraine Park, both sides of the
-valley are edged with lateral moraines also.
-
-Studies in Rocky Mountain National Park have revealed many other details
-of glaciation in this area. These are described in Park Service
-brochures and guidebooks, in the museum at Park headquarters, and in
-informative roadside signs.
-
-[Illustration: A line of hikers approaches Arapaho Glacier, west of
-Boulder. Movement of the glacier is evidenced by the crevasses apparent
-just below the snowfield in the dirty gray glacial ice. (H. H. Heuston
-photo)]
-
-Several small glaciers are still present in the Colorado mountains, all
-in sheltered cirques above 11,000 feet. These may be remnants of the
-former larger glaciers, or new glaciers formed after a long warming
-episode. A hike to one of these glaciers is a rewarding experience for
-anyone interested in geology. Some of the more accessible are St. Mary’s
-Glacier west of Denver, Arapaho Glacier west of Boulder (the Boulder
-Chamber of Commerce sponsors a festive hike to Arapaho Glacier every
-August), and Tyndall Glacier in Rocky Mountain National Park.
-
-The Ice Age brought drastic changes also to the landscape below 8,000
-feet elevation. Heavily loaded with glacial debris, mountain streams
-disgorged coarse sands and gravels along the mountain front and in the
-intermontane basins. As the glaciers melted after each period of
-expansion, the swollen streams cut deeply into their former deposits and
-into much older rocks as well. Royal Gorge, the Black Canyon of the
-Gunnison, and many of the deep, colorful canyons of the Plateau Province
-were cut or at least deepened by these waters. The canyons along the
-east face of the mountains—Big Thompson, Boulder, Clear Creek, and
-others—were also deepened and sharpened by the rushing ice-fed torrents.
-
-On the prairies, rivers dumping their loads of sand covered the older
-rocks. Sand dunes developed along the river channels. Bones and huge
-tusks of hairy mammoths were sometimes buried in these soft deposits;
-now they are occasionally revealed as the dune and river sands are
-washed or blown away by continuing erosion.
-
-About 20,000 years ago, man arrived in Colorado. Soon after this, the
-water supply of the valleys diminished greatly, and erosion slowed down
-correspondingly. The climate gradually became semiarid to arid. Many
-features of the natural scene were much as they must have been a century
-ago, without the highways, dams, and television aerials of today.
-Buffalo and many smaller types of game roamed the plains and foothills;
-deer, elk, and bighorn sheep were plentiful in the mountains. Nomadic
-tribes camped and hunted in both mountain and prairie. In the western
-part of the state, homes could be built in the shelter of great caves,
-as at Mesa Verde, and game could be supplemented with corn and squash
-planted on plateau surfaces.
-
-Several features of Colorado scenery changed with increasing aridity.
-The glaciers of course were gone or nearly gone. Streams were no longer
-the violent torrents they had been. Many mountain lakes, filled with
-sediment and vegetation, became instead mountain meadows. And the once
-fertile intermontane valleys became deserts.
-
-[Illustration: During the last Ice Age, elephant-like mastodons roamed
-Colorado. As present-day erosion removes sediments, bones, teeth, and
-tusks are frequently exposed, especially in the Prairie Province. (C. R.
-Knight painting, courtesy American Museum of Natural History)]
-
-[Illustration: Mastodon]
-
-On the eastern side of the San Luis Valley, the Great Sand Dunes
-developed at this time. These dunes nestle against the Sangre de Cristo
-Range, where strong southwesterly winds blowing across the wide valley
-tend to funnel toward Mosca and Music Passes. These winds lift loads of
-sand from the lightly vegetated valley floor, and drop it as they rise
-over the mountains. Where the sand is dropped, the dunes have formed.
-They rise to about 700 feet above the valley floor, and cover about
-forty square miles. The low rainfall of the area, seven to eight inches
-per year, keeps vegetation from creeping over the dunes and makes them a
-most distinctive feature of Colorado, a lesson in geology in the making.
-
-                            * * * * * * * *
-
-Geologic processes in Colorado now seem to be much reduced from what
-they were a few thousand years ago. Reduction in rainfall has led to
-reduced erosion. Mountain-building, having reached a climax in Tertiary
-time, has declined markedly. However, we find evidence that volcanism
-has occurred within the last few thousand years and faulting within the
-last few hundred, and Colorado streams rise after sudden mountain storms
-to approximate the violent torrents of glacial times. Colorado’s
-scenery, fashioned during some three billion years of earth history, is
-ever changing.
-
-[Illustration: The Great Sand Dunes of Colorado were formed during
-Pleistocene and Recent time by deposition of quartz sand lifted from
-unconsolidated alluvial deposits in the San Luis Valley. The highest of
-the dunes rises 700 feet above the adjacent valley floor. (John Chronic
-photo)]
-
-
-
-
-                                  III
-                      Geology and Man in Colorado
-
-
-Colorado’s first permanent settlers arrived in 1858, when gold was
-discovered in river sands near what is now the city of Denver. The
-ensuing gold rush, coming ten years after the rush to California,
-rivalled it in fury and brought sudden wealth to lucky miners and the
-adventurous merchants who grubstaked them. Several hundred mining towns
-or “camps” sprang into existence almost overnight, their sites
-determined by the geology of the mountain areas. The cities of Denver,
-Boulder, and Golden were established as milling and shipping centers for
-the products of the mines. In 1876 the now-wealthy area, previously part
-of Kansas Territory, became the State of Colorado.
-
-For more than a hundred years Colorado’s minerals—products of her long
-and diverse geologic history—have influenced her development in many
-ways. The state’s early wealth, stemming from bonanzas in gold and
-silver, is evidenced by palatial homes, hotels, and public buildings
-constructed during the first few decades of mining activity. Some of
-these are still standing—the opera houses at Central City and Aspen,
-Central City’s famous Teller House, and the Grand Imperial Hotel at
-Silverton are examples.
-
-Many of the stories and legends of Colorado’s gold camps are recounted
-in _Stampede to Timberline_, by Muriel Sibell Wolle, delightfully
-illustrated with sketches of old mining towns as they appear today.
-_Mining in Colorado_, published by the U. S. Geological Survey, also
-makes fascinating reading, as it contains many historical anecdotes and
-eyewitness accounts of gold-rush days.
-
-Development of the metal-mining areas in Colorado followed a definite
-sequence. Placer gold was usually discovered first. Recovery of placer
-gold was followed by mining of gold from veins or “lodes.” Although at
-first only native gold was mined, gold-bearing compounds such as
-telluride were soon recognized as an additional source, especially at
-Gold Hill, Cripple Creek, and of course the camp that came to be known
-as Telluride. As gold sources were depleted, silver, first produced as a
-byproduct, became of prime interest. Lead and zinc were in turn
-byproducts of silver mining. Other metals, notably copper, vanadium,
-tungsten, and iron, were produced later. Molybdenum is the
-Johnny-come-lately of the state’s mining industry, but is now the chief
-metal produced. A uranium boom in the 1950s brought a short rush to
-western Colorado and new vigor to the economy.
-
-Oil was discovered near Canon City in 1862. The nearby Florence field
-and a small, shallow field near Boulder preceded much greater
-discoveries in the Denver Basin, the Uinta Basin, and southwest
-Colorado. Oil reservoirs, confined to areas of sedimentary rock, are
-found primarily in the Prairie and Plateau Provinces of the state, and
-recovery of the oil has done much to distribute population to these
-areas.
-
-Coal is also restricted to sedimentary rock areas. Coal production in
-Colorado has waxed and waned with the years, but has provided fuel for
-export, for the railroads, for the manufacture of electric power, and
-for many of the state’s industries.
-
-A good picture of present mineral production in Colorado can be obtained
-from the following summary for 1971, prepared by the Colorado Bureau of
-Mines:
-
-                        Product                Value
-
-               Molybdenum                    $105,389,456
-               Petroleum                       90,494,459
-               Sand and gravel                 32,842,503
-               Coal                            30,251,443
-               Natural gas                     18,695,225
-               Uranium                         18,048,692
-               Vanadium                        15,863,554
-               Cement                          13,377,520
-               Zinc                            13,310,787
-               Lead                             6,582,025
-               Tungsten                         6,360,020
-               Limestone and dolomite           5,397,570
-               Silver                           4,198,054
-               Fluorspar                        3,887,210
-               Copper                           3,875,976
-               Stone                            1,961,279
-               Gold                             1,832,791
-               Clay                               962,986
-               Iron                               880,047
-               Pumice                             309,370
-               Tin                                278,862
-               Gypsum                             253,856
-               Pyrites                            142,640
-               All others                       1,091,927
-                  Total                    ($376,288,252)
-
-Colorado is now the nation’s leading producer of molybdenum, tin, and
-vanadium, and second in output of tungsten. In oil production it ranked
-twelfth among the states in 1968, but ninth in reserves, with
-420,000,000 barrels of proven reserves on 1 January 1969. An as yet
-untapped source of oil lies in the oil shales of western Colorado.
-
-As part of the natural environment, water plays a major role in man’s
-activities. Water problems in Colorado revolve mainly around the best
-use of runoff in a state whose major catchment basins are across the
-continental divide from her largest population centers and most fertile
-farm land. Groundwater, closely related to surface water distribution
-and movement, is a geological problem, and in Colorado as in other
-states many government and private geologists serve farm and industrial
-communities in the search for usable supplies.
-
-
-
-
-CAUTION: Old mines are dangerous! They may contain water or deadly
-gases, or be on the verge of collapse. Keep away from abandoned prospect
-pits and mine shafts. WARN AND WATCH YOUR CHILDREN.
-
-
-                     GOLD, SILVER, AND OTHER METALS
-
-Colorado’s placer and lode sources of gold, which gave first impetus to
-the series of mining booms in the state, were fantastically rich. Summit
-and Lake Counties, for instance, each produced more than $5,000,000 in
-placer gold between 1859 and 1867. During the same nine-year period,
-more than $9,000,000 in lode gold was produced from Gregory Gulch, a
-tiny canyon between Central City and Black Hawk. Other districts
-rivalled or surpassed these figures.
-
-Early in the game it was recognized that almost all the deposits
-occurred along what came to be known as the “mineral belt,” a
-fifty-mile-wide zone extending southwest from the Boulder region. Most
-of the metals mined in the state come from this belt, but there are
-three notable exceptions: Cripple Creek, Silver Cliff, and western
-Colorado vanadium and uranium districts. In the first few years of the
-Colorado rush, gold ores and placer gold were discovered only in the
-northeastern part of the mineral belt. Gradually the belt was found to
-extend further and further southwest: Tincup was discovered in 1861,
-Silverton in 1870, Lake City in 1871, and Telluride in 1875. Aspen, on
-the western edge of the belt, was not discovered until 1879, perhaps
-because the area was difficult of access and lacked the easily
-recognizable native gold.
-
-In the northeast part of the mineral belt, gold and other minerals occur
-in veins in Precambrian granite and gneiss. In the Leadville and Aspen
-areas, ores are associated with altered Paleozoic limestones. At the
-southwest end of the mineral belt, in the San Juan Mountains, ore veins
-are found near or in Tertiary volcanic rocks. Native gold, gold-bearing
-compounds, and other metallic ores in these veins originated where
-mineral-rich solutions from deep within the earth penetrated fissures
-and joints in the surrounding rock. Regardless of the age of the host
-rock, almost all the ores of Colorado were deposited in the early or
-middle Tertiary Period, about 35 to 70 million years ago.
-
-Gold and silver are no longer mined extensively in Colorado, although
-any summer Sunday will see weekend operators panning near mountain
-streams or trundling rock from one-man mines. The recent rise in the
-price of silver has encouraged many miners to reopen old shafts. The
-most active mines in the state today are those producing molybdenum,
-lead, zinc, and vanadium. (Vanadium, although a metal, usually occurs in
-Colorado with radioactive minerals, and so is discussed with them rather
-than with the metals.)
-
-[Illustration: The Colorado mineral belt extends from Boulder County on
-the northeast to San Juan County on the southwest. Almost all of the
-prominent mining districts in Colorado lie along this belt. Cripple
-Creek and Silver Cliff, however, lie far to the east of the general
-trend.]
-
-    Telluride
-    Denver
-    Colorado Springs
-    Alamosa
-  BOULDER
-    Ward
-    Gold Hill
-    Boulder
-    Nederland
-  GILPIN
-    Central City
-    Black Hawk
-  JEFFERSON
-    Golden
-  CLEAR CREEK
-    Empire
-    Georgetown
-    Silver Plume
-    Idaho Springs
-  SUMMIT
-    Breckenridge
-  EAGLE
-  PITKIN
-    Aspen
-  GUNNISON
-    Tincup
-  CHAFFEE
-  PARK
-    Climax
-    Alma
-    Como
-    Fairplay
-  TELLER
-    Cripple Creek
-  FREMONT
-  OURAY
-    Ouray
-    Camp Bird
-    Ironton
-  SAN JUAN
-    Silverton
-  HINSDALE
-    Lake City
-  LA PLATA
-    Durango
-  MINERAL
-    Creede
-  CUSTER
-    Silver Cliff
-
-All told, some 430 metal mining districts have been established as legal
-entities in the state of Colorado. Each of these districts had the right
-to draw up its own regulations concerning prospecting, claims, and
-mining rights, within a framework established by the Federal government.
-Only a few of the districts ever became really significant producers.
-The geology and history of several of the leading areas are presented in
-the pages that follow.
-
-
-                             Boulder County
-
-Gold Run, near Gold Hill, was the scene of one of the earliest strikes
-in Colorado. Gold was found here in December 1858, and was sluiced from
-stream sands and mined from veins early in 1859. Active placer mining
-lasted only about a year, however, and lode mining dropped off rapidly
-as near-surface oxidized ores were worked out. When a smelter was
-erected at Black Hawk in 1868, and sulfide ores could be treated, there
-was a revival of activity. In 1869 the Caribou and Poorman mines near
-Nederland were discovered; they quickly became the most active mines in
-the county. The Ward district opened soon after.
-
-In 1872, a gold-silver telluride called petzite was found in veins at
-Gold Hill. Renewed prospecting in this area resulted in location of
-mines near Sunshine, Salina, and Magnolia. During the years that
-followed, new mines appeared almost as fast as old ones were depleted.
-In 1892, the peak year, more than $1,000,000 in gold and silver was
-produced; total production has been about $25,000,000.
-
-In 1900, a black mineral common in the Nederland area was recognized as
-ferberite, an ore of tungsten, and a new rush to the area started.
-During the next eighteen years Boulder County was the main tungsten
-producer in the United States; about 24,000 tons of tungsten trioxide,
-worth $23,000,000, were produced here. The ore was found in nearly
-vertical veins six inches to three feet thick, in a lenticular area
-about nine miles long extending from Nederland northeast to Arkansas
-Mountain, four miles west of Boulder.
-
-Boulder County is characterized by an abundance of small mines. Old
-shafts, pits, and mine buildings can be found throughout the central
-part of the county. Little mining is done here today; many of the towns
-that once peppered these hills have fallen into decay or disappeared
-entirely.
-
-
-                     Central City and Idaho Springs
-
-The Central City-Idaho Springs area was the principal metal mining
-region in the state until the late 1880s. In 1858, rich placer deposits
-were discovered in gravels and river terraces along both forks of Clear
-Creek. Exploration upstream led to discoveries of rich oxidized quartz
-veins at Central City, Black Hawk, and Idaho Springs. These veins, which
-generally trend northeast-southwest, extend through the mountains in a
-zone about six miles long and three miles wide between the two forks of
-Clear Creek.
-
-The ores filled a multitude of cracks and fissures in the Precambrian
-bedrock. The veins are usually less than five feet thick, and are almost
-vertical and often clustered in zones up to thirty feet wide. The
-position of one of the vein systems may be seen clearly between Black
-Hawk and Central City—the ore-bearing rock has been mined out, but a
-series of collapsed tunnels marks the line where the veins crossed the
-valley. A monument here commemorates the discovery of Gregory Gulch, one
-of the richest localities in the state.
-
-Several rich veins were mined in both directions—southwest from Central
-City and northeast from Idaho Springs—until the mines met. The Argo
-tunnel, marked by dilapidated buildings and extensive dumps on the north
-side of Idaho Springs, connected the two districts; it was completed in
-1904.
-
-The “Patch,” a deep crater-like hole on Quartz Hill, about one mile
-southwest of Central City, is an intriguing feature in this area. It was
-produced by glory-holing, a mining technique in which a deep tunnel is
-deliberately caved by blasting, so that ores above the tunnel can be
-removed. This glory hole was dynamited below an irregular mass of highly
-broken rock where many ore-rich veins converged. After the caving, ores
-were taken out through the remaining part of the tunnel.
-
-The principal ore minerals of Central City and Idaho Springs are native
-gold, pyrite, sphalerite, galena, chalcopyrite, and tennantite.
-Prospecting for uranium was carried out during the 1950s but no uranium
-was ever mined here.
-
-The area has produced almost $200,000,000 worth of gold, silver, lead,
-zinc, and copper. A few mines still operate seasonally or on a small
-scale, but tourists, many of them riding Jeeps across the mountainous
-terrain to visit mines and ghost towns, are often more visibly active
-than the mines.
-
-
-                  Georgetown, Empire, and Silver Plume
-
-A few miles southwest of Idaho Springs, another mining area had a
-similar, though less productive, history. In 1859, placer and lode gold
-were discovered near what is now Georgetown. Placer mining dominated
-here between 1859 and 1863. Gravel and crushed rock from decomposed
-quartz and sulfide veins were washed through sluiceboxes in the same way
-as placer gravel, gold being caught in riffles or gunny sacking on the
-bottoms of the troughs. The veins were found to be decomposed to depths
-of about 40 feet; below this the gold occurred closely associated with
-sulfides such as pyrite, sphalerite, galena, and chalcopyrite, from
-which it could not easily be separated. However, smelters were developed
-in 1866 for treatment of these sulfides, and gold, silver, lead, and
-copper were recovered. Gradually, as the gold was worked out, silver and
-lead became the important products of the mines.
-
-[Illustration: Sluicebox mining was a common sight near the early gold
-camps, where primary recovery was from placer deposits or decomposed
-quartz and sulfide veins. (State Historical Society of Colorado photo)]
-
-
-                               Leadville
-
-Placer gold was discovered in 1859 in California Gulch, about seven
-miles north of the present town of Leadville. The rush that followed was
-short but sweet; the camp was called Oro—gold! About $5,000,000 was
-produced from the placer mines within two years, though by 1861 the area
-was all but deserted, for the easily won placer gold was gone.
-
-[Illustration: Early-day Leadville sprawled among its mine dumps at an
-elevation of 10,200 feet. The Sawatch Range, in the background,
-contained many smaller mining communities, now deserted. Mt. Massive,
-the state’s second highest peak, forms the crest of the continental
-divide here. (State Historical Society of Colorado photo)]
-
-In 1875 a smelter was erected a few miles downstream from Oro to process
-cerussite—silver-rich lead carbonate—that occurred in the placer sands.
-For years this mineral had been considered a nuisance because, being
-much heavier than sand, it tended to separate out with the gold. The new
-town of Leadville sprang up near the smelter and shortly afterward more
-lode deposits were discovered south of the placer workings. From $63,000
-in 1875, production climbed to $2,500,000 in 1878 and more than
-$15,000,000 in the peak year of 1882.
-
-Geologically, the ores of this district occur as Tertiary replacements
-and veins in Ordovician, Devonian, and Mississippian limestones. The
-“Blue” or Leadville Limestone, of Mississippian age, contains the
-richest ore. Ore deposits were formed after the limestones had been
-faulted and cracked extensively by mountain-building movements; the ores
-themselves probably crystallized from molten or gaseous materials
-involved in related igneous intrusions. River gravels and glacial debris
-mask the true nature of the lode deposits, but studies in the mines show
-that the fault systems along which ores are deposited trend north or
-north-northeast.
-
-The Leadville district is now experiencing its third mining boom as a
-newly recognized lead-zinc orebody is being developed. Production is
-expected to reach 700 tons of ore per day by 1971. Total production of
-gold, silver, lead, zinc, and copper in the district has reached
-$500,000,000.
-
-
-                              Breckenridge
-
-Breckenridge was also discovered in 1859, with placer gold the first
-attraction. The placers gave out in 1862 after about $3,000,000 in gold
-had been recovered. Earliest attempts to mine the rich silver and lead
-veins of the district were in 1869.
-
-As at Leadville, the sedimentary rocks of the area were intruded by
-granitic masses in Tertiary time, but here the sedimentary rocks are
-mostly Pennsylvanian sandstones and shales. These rocks were badly
-faulted and broken during the intrusion, and the ores were deposited as
-the granitic material cooled. The lode deposits occur mostly in small
-veins well hidden by surface sands and gravels. Some of the veins
-yielded exceptionally beautiful crystallized wire and flake gold,
-specimens of which are on display at the Colorado School of Mines
-library in Golden and in the Denver Museum of Natural History.
-
-Dredging for alluvial gold was attempted in 1898 in the Breckenridge
-district, but this method of extracting gold was not successful until
-1905. A number of dredges operated between 1910 and 1925. These floating
-behemoths shovel up gold-bearing gravels from the bottom and one side of
-the pond on which they float, sort out the gold in giant sluiceboxes,
-and spew out the leftover gravels in great arc-shaped heaps that can be
-seen near Breckenridge and Fairplay and in a number of other valleys in
-Colorado. They depend for their operation on a plentiful supply of water
-and a shallow water table, but they can sift through quantities of
-gravel at relatively low cost. All told, about $7,000,000 in gold has
-been dredged from this district.
-
-
-                                Fairplay
-
-[Illustration: This gold dredge, still floating in its pond just south
-of Fairplay, operated from 1941 to 1952. With chains of buckets like
-those in the foreground, it dug gravel 70 feet below water level,
-carving a 35-foot bank above water level; in effect it mined to a depth
-of 105 feet. This dredge extracted nearly 115,000 ounces of gold from
-about 33 million cubic yards of gravel (John Chronic photo)]
-
-Another gold field discovered in 1859 was in the northwest corner of
-South Park, along the headwaters of the South Platte River. Several
-mining camps were established here. After early production of rich
-placer deposits, claims were consolidated and large flumes constructed
-so that gold could be recovered by hydraulic mining. In this type of
-mining, streams of water from high-pressure hoses are directed at gravel
-surfaces. The gravels are washed into long sluiceboxes, where gold is
-caught in riffles. Hydraulic mining continued upstream from Fairplay
-until about 1900.
-
-In 1922 a dredge was constructed near Fairplay to process gravel along
-the South Platte and in the valley floor. An even larger dredge,
-constructed in 1941, operated until 1952, when rising labor costs
-overrode the narrow margin on which it operated. At the time operations
-ceased, the dredge was recovering about six cents in gold for each cubic
-yard of gravel processed.
-
-Placer gold has always been the principal mineral product of the
-Fairplay area, but native gold also occurs in the surrounding mountains
-in quartz veins, and many small mines were developed to extract it.
-Sulfide ores were also mined; they contained silver, lead, and zinc as
-well as gold. In the Mosquito Pass and Horseshoe Amphitheater areas,
-there is renewed activity now because of the recent rise in the price of
-silver.
-
-
-                               Silverton
-
-Gold was discovered in the San Juan Mountains of southwest Colorado in
-1870. The earliest mine, near what is now Silverton, was located by a
-group of prospectors sent out by Governor Pile of New Mexico Territory.
-Since the site was on Ute Indian land, real mining did not begin until a
-treaty allowing it was ratified in 1874.
-
-Production in the Silverton district has been from veins in Tertiary
-volcanic rocks within an elliptical area known as the Silverton
-cauldron. Here the volcanic rocks, part of the several thousand feet of
-lava flows and ash falls of the San Juan volcanic field, were cracked
-and faulted by a second period of igneous activity. Ores formed in the
-cracks and fissures.
-
-In the 1870s the Silverton district was very remote, and difficulties
-with transportation retarded activity there. In 1882, however, a
-narrow-gauge railroad was built connecting Silverton with Durango, and
-the problem of transporting ore out of the isolated mountain valley was
-simplified. The railway still exists; a train makes daily passenger runs
-during the summer—the only remaining operating narrow-gauge line in the
-United States. The track follows the Animas River canyon, whose cliffs
-and crags are dotted with long-abandoned mines, prospect holes, and mine
-buildings, monuments to the tenacity and determination of the men who
-mined here.
-
-Production in this district was more than $22,000,000 in gold and
-$20,000,000 in silver between 1874 and 1923. New activity is evident
-here, as in other silver-rich areas of Colorado, because of recent
-demand for silver, lead, and zinc.
-
-[Illustration: Silverton lies in a remote mountain valley in the San
-Juan Mountains. Silver, gold, lead, and zinc have been mined here since
-1874. Storm Peak, composed of Tertiary volcanic rocks, forms the
-backdrop; the narrow-gauge railroad track is visible in the foreground.
-(Jack Rathbone photo)]
-
-
-                                 Ouray
-
-Ouray was settled in 1875, when gold and silver deposits were found near
-Mount Sneffels. Since 1877, mines in Ouray County have produced over
-$35,000,000 in gold and $32,000,000 in silver. The district is still
-quite active: in 1965, mines in this area produced more than $9,000,000
-in gold, silver, copper, lead, and zinc, about a third of total Colorado
-production of these metals for that year.
-
-[Illustration: A few miles south of Ouray, along Uncompahgre Gorge, an
-old mine clings to the slope below the Million Dollar Highway (U. S.
-550). Abrams Mountain rises in the background. The Precambrian
-Uncompahgre Quartzite outcrops up to about the road level; Miocene
-Sunshine Peak Rhyolite caps the peak. (Jack Rathbone photo)]
-
-A mile north of Ouray a prominent intrusive stock marks the center of
-mining activity closest to Ouray. The richest deposits of the Ouray
-area, however, lie about five miles southwest, near Mount Sneffels and
-Red Mountain Creek. There, several large mines, including the famous
-Camp Bird mine, have operated for many years, extracting ore from
-hundreds of veins that underly the surface. Some of these veins are two
-to four miles long. They are in Tertiary volcanic rocks of the San Juan
-Formation. Quartz and calcite are the common gangue (non-economic)
-minerals, and pyrite, sphalerite, galena, and chalcopyrite are the most
-abundant ores. Most of the silver is in the galena; gold occurs in
-streaks and nodules associated with quartz.
-
-About ten miles south of Ouray, along the “Million Dollar Highway” (U.
-S. 550), the Red Mountain district lies on the northwest edge of the
-Silverton volcanic cauldron. It contains a number of small pipelike
-bodies very rich in silver-copper and silver-lead ores. Following the
-mid-Tertiary volcanism and ore intrusion, surface rocks in this area
-were intensely oxidized: resulting iron oxides now form the gaudy reds
-and yellows of Red Mountain and the slopes near Ironton. This
-alteration, as well as the fact that much of the area is covered with
-fallen rock, stream gravels, or glacial deposits, compounds difficulties
-of locating the small though high-grade ore deposits.
-
-The Idarado Mine, on the east side of U. S. highway 550 near Red
-Mountain, used to produce ores from nearby volcanic pipes; now it
-produces from veins some distance to the northwest. The area is
-honeycombed with tunnels and shafts.
-
-
-                                 Aspen
-
-Silver was found at Castle Creek and on Aspen Mountain in 1879. A group
-of prospectors from Leadville, apparently after examining maps of the
-Geological and Geographical Atlas of Colorado published in 1877,
-explored along the line of Paleozoic limestones encircling the Sawatch
-Range. As they had hoped, they found ores similar to those at Leadville
-in rocks of the same age.
-
-Mining began at Aspen in 1880. Here, as at Leadville, intrusion of
-granite porphyry into or near the Leadville Limestone had broken and
-deformed the layers, and ores were deposited in fissures and as
-replacements during cooling of the intrusions. The intricacy of faulting
-which controls the ore pockets in the limestone is well shown on the map
-of Aspen Mountain in Chapter II.
-
-Glaciation occurred in this area, and glacial deposits cover most of the
-ore bodies and outcrops so that little bedrock is exposed. Mapping was
-accomplished by extrapolating to the surface the bedrock patterns shown
-in mine pits, shafts, and tunnels.
-
-Aspen produced some of the richest silver ores in the world, and thrived
-as a boom town for most of two decades. In 1888 the value of ores
-produced reached over $7,000,000; the next year it topped $10,000,000.
-After the silver crash of 1893 production declined rapidly; the last
-mines were closed in the 1920s. Total production of silver, lead, zinc,
-and copper reached about $100,000,000. There was virtually no gold in
-the ores at Aspen.
-
-
-                                 Creede
-
-[Illustration: Creede and its mines are located in an area of Tertiary
-rhyolite and dacite, light-colored volcanic rocks.]
-
-  Happy Thought Mine
-  Amethyst Mine
-  West Willow Creek
-  AMETHYST FAULT
-  Last Chance Mine
-  Del Monte Mine
-  Commodore Mine
-  Jackpot Mine
-  Coppervein Mine
-  Bachelor Mine
-  BULLDOG MOUNTAIN FAULT
-  Kansas City Star Mine
-  Commodore Tunnel
-  Mustang Tunnel
-  Nelson Tunnel
-  Exchequer Mine
-  SOLOMON FAULT
-  CAMPBELL MOUNTAIN
-  Holy Moses #2
-  Holy Moses Mine
-  Ridge Mine
-  Solomon Mine
-  Monte Carlo Mine
-  Mollie S. Mine
-  East Willow Creek
-  Ramey Tunnel
-  Dora Belle Mine
-  Mammoth Tunnel
-  Homestake Mine
-  Mammoth Mine
-  MAMMOTH MOUNTAIN
-  Nancy Hanks Mine
-  Pipe Dream Mine
-  THE NARROWS
-  Windy Gulch
-  CREEDE
-  Willow Creek
-
-The Creede district ranks as one of the most productive silver areas in
-the United States. It came into being largely as a result of a discovery
-by N.H. Creede in 1889. When exploring in this area, he was reported to
-have exclaimed “Holy Moses!” on examining a rich piece of ore, thus
-giving the name to the mine which initiated the rapid development of the
-district. By the end of 1892 the Holy Moses and nearby mines had
-produced ore valued at more than $4,000,000. The area was so rich that
-it managed to survive 1893’s great decline in the price of silver; by
-1920 almost $42,000,000 in gold, silver, lead, and zinc had been mined
-there.
-
-The ores, silver-bearing galena, sphalerite, native gold, pyrite, and
-chalcopyrite, are in quartz or amethyst veins in faulted and shattered
-Tertiary volcanic rocks. Nearly all the ore deposits lie along a complex
-system of vertical faults, the Amethyst fault zone, which runs more or
-less northwest-southeast through this region. Both the faulting and the
-enrichment of the fault fissures are believed to have taken place in
-mid-Tertiary time, shortly after deposition of the volcanic host rocks.
-
-
-                             Cripple Creek
-
-[Illustration: Cripple Creek, on the flanks of the Pikes Peak massif,
-has produced more than $400,000,000 worth of gold. The Sangre de Cristo
-Mountains are visible in the distance beyond the Arkansas River valley.
-(Jack Rathbone photo)]
-
-In 1890, two sheepherders stumbled on some richly mineralized rocks near
-Cripple Creek. A boom developed immediately, for the rocks contained
-both gold and silver. Since then, the area has produced more than
-2,000,000 ounces of silver and nearly 19,000,000 ounces of gold.
-
-Cripple Creek has produced almost half of all the state’s gold and
-silver. The ores are located in or at the edge of a large mass of middle
-Tertiary volcanic rocks which form an elliptical basin or _caldera_
-several miles across. The caldera, surrounded by Precambrian gneiss and
-granite of the Pikes Peak massif, was probably formed by collapse of a
-volcanic center that had erupted through the older rock. The collapse
-shattered the rocks around the basin margin, and subsequent volcanic
-activity introduced mineral-rich solutions into the many faults and
-fissures produced by the collapse. Tellurides of gold, silver, and
-copper, as well as pyrite, sphalerite, galena, tetrahedrite, and other
-minerals, are characteristic.
-
-
-                                 Climax
-
-[Illustration: At Climax, the ore occurs scattered through the intrusive
-Climax Granite Porphyry and the intruded Idaho Springs Formation.
-Visitors can tour the surface workings during the summer months.]
-
-    Tertiary dikes
-    Shell of Climax stock
-    Core of Climax stock
-    Ore zone
-    Precambrian granite
-    Fault
-    Dykes
-
-Molybdenum now ranks as the number one metal mined in Colorado. Over
-$105,000,000 of “moly” was mined here during 1969, almost all of it from
-the Climax Mine, the world’s largest single source of this metal. The
-Climax deposit is located high on the west slope of Ten Mile Range in
-central Colorado, about 100 miles southwest of Denver. It is in the
-central part of the Colorado mineral belt, near the Mosquito Fault, a
-prominent structural feature which extends about sixty miles along the
-north-south trend of the mountains. Rocks on both sides of this fault
-are intruded by Tertiary granite dikes, sills, and stocks. The Climax
-Mine is in a stock just east of the fault, near the axis of a broad
-anticline in Precambrian metamorphic rocks.
-
-Ore minerals at Climax are molybdenite, huebnerite, and cassiterite;
-pyrite is recovered also for the manufacture of sulfuric acid. The ore
-is very low in metal content, containing only one-third of a percent of
-molybdenum, 0.005% tungsten trioxide, and 0.0001% tin. The great size of
-the ore body and efficient recovery by modern methods make Climax a
-profitable mine, however. Production has risen each year since the mine
-began operation.
-
-Urad Mine near Berthoud Pass is a newly developed near-surface
-molybdenum mine similar to Climax. Nearby at the Henderson Mine the ore
-body is more than half a mile below the surface of the ground.
-
-
-                     RADIUM, URANIUM, AND VANADIUM
-
-Over a large area of the Plateau Province in western Colorado, Mesozoic
-sedimentary rocks are locally stained bright yellow, orange, or green.
-Such staining suggests mineralization, and radioactive compounds were
-recognized here before 1900. At that time, however, there was little or
-no market for them or for the vanadium frequently associated with them.
-When Marie Curie required radium for experiments with her newly
-discovered element, the raw materials were sent from western Colorado;
-by and large, though, production of radium from these ores was
-prohibitively expensive.
-
-In 1905, vanadium was found to be effective in toughening steel. The
-Vanadium Corporation of America was formed to mine the Colorado ore.
-This company mines a rich zone in the Jurassic Entrada Sandstone, where
-vanadinite occurs with carnotite and other uranium ores. In the early
-days of vanadium mining, the uranium ores were discarded with other
-gangue materials; now, of course, uranium is produced from them.
-
-Since 1945, uranium production has been an important Colorado industry;
-in 1969 about $17,500,000 worth was produced. Uranium occurs in the
-state in two very different situations. In the Plateau Province, where
-it was first discovered, it occurs in sedimentary rocks as patches of
-pitchblende, carnotite, and a greenish yellow mineral called
-schroekingerite. It is most abundant in the Triassic Chinle Formation
-and the Jurassic Entrada and Morrison Formations, where it was probably
-deposited by downward movement of rainwater from overlying uranium-rich
-Tertiary volcanic rocks. Concentrations of uranium often occur in or
-near organic matter such as coal, fossil bone, or petrified wood, so
-mines tend to be located along rock layers carrying abundant organic
-material.
-
-Another type of uranium ore is found in the Mountain Province. Veins in
-Precambrian rocks of the Front Range and several other ranges contain
-pitchblende which seems to have been deposited by hot groundwater rising
-through broken and fissured Precambrian rocks. Often exceedingly rich,
-such ore is mined in the manner of most of Colorado’s metals. The
-Schwartzwalder Mine, a few miles northwest of Golden, has produced more
-ore of this type than any other mine in Colorado.
-
-
-                    OIL, NATURAL GAS, AND OIL SHALE
-
-Petroleum and natural gas have been found in large quantities in the
-Prairie and Plateau Provinces in Colorado, as well as in smaller
-quantities in North Park in the Mountain Province. They generally occur
-in porous sandstone and limestone layers, where they have been trapped
-by overlying finer-grained, less permeable layers in or near folds and
-faults.
-
-Several oil and gas seeps were found along the mountain front shortly
-after the arrival of the earliest settlers. Near Canon City, on Oil
-Creek, a plaque commemorates the first production:
-
-  Oil Creek—site of the first oil well in the west—second place in the
-  United States to produce petroleum from wells. In 1862 ... A. M.
-  Cassedy drilled an oil well 50 feet deep. By February, 1863,
-  production was one barrel a day. Later, several thousand gallons of
-  petroleum were produced by primitive methods, and kerosene and
-  lubricating oil were shipped by ox team as far as Denver and Santa Fe.
-
-About twenty miles to the southeast, near Florence, the Cretaceous
-Pierre shales were drilled in 1876. Oil was found in a system of
-intersecting fractures and joints. Some of the early wells in the
-Florence field are still producing, making this Colorado’s oldest and
-longest producing field. It has yielded more than 10,000,000 barrels of
-oil.
-
-Small quantities of oil have been produced near Boulder since about
-1900, also from Pierre sandstones and shales. In this area, wells were
-located by “dowsing” or “witching,” as was fashionable at the time.
-Several old rigs can be seen near Boulder Reservoir. As at Florence, oil
-has been trapped in fractures of otherwise dense and impervious shale.
-Some gas is produced and is used by local farms.
-
-More recently, oil was found far beneath the surface in the northern
-part of the Prairie Province. Here, in the Denver Basin, oil is produced
-from several levels in the Dakota Sandstone. The oil has accumulated in
-lenses of beach sand deposited along the shoreline of the Cretaceous
-sea. The general trend of the shoreline, and of the oil fields, is
-northeast-southwest. The shore appears to have been similar to Georgia’s
-present coastline: a swampy tidal zone separated from open sea by
-lagoons, sandy bars, and clean sand beaches.
-
-Individual oil pools in the Denver Basin are small, but there are many
-of them; they lie nearly a mile below the surface, under much of Morgan
-and Logan Counties and adjacent parts of Nebraska. Exploratory and
-development drilling keeps total oil production at about 50,000 barrels
-a day. Oil and gas produced here is piped to Denver and other Colorado
-cities.
-
-In southeastern Colorado, oil and gas occur in late Paleozoic limestones
-and sandstones similar to those which outcrop at the edge of the Wet
-Mountains. Prospecting by geophysical methods and by drilling has
-revealed several small, rich accumulations, one of which is thought to
-contain about 30,000,000 barrels of oil.
-
-The Rangely field, in northwestern Colorado, is the most productive
-field in the state. Located in the northeastern part of the Uinta Basin,
-it is an outstanding example of an anticlinal field, where oil is
-trapped in a large, gentle dome. The shape of the dome shows up well on
-the surface; rock layers can be seen dipping outward in all directions
-from the town of Rangely. Oil was found by drilling on the crest of the
-dome. At first, oil was produced from fractures in the Cretaceous Mancos
-Shale at less than 1,000 feet depth. Later, deeper drilling showed that
-oil had also accumulated in the Permian Weber Sandstone, at 5,000 to
-7,000 feet. At present this field is producing about 28,000 barrels of
-oil a day, but the figure is dropping each year as the field is
-depleted.
-
-Oil and gas are produced in southwestern Colorado from the eastern edge
-of the Paradox Basin and the northern edge of the San Juan Basin. In the
-Paradox Basin, oil comes from Pennsylvanian limestone mounds or reefs.
-Production in the Colorado part of the basin has been at most a few
-thousand barrels per day; more is produced in adjacent Utah. In the San
-Juan Basin, gas and oil are trapped in thin porous layers of Cretaceous
-and Pennsylvanian sandstone, between impervious layers of shale. Most of
-the production is in New Mexico, although some oil comes from the
-Colorado part of the basin.
-
-The greatest known potential oil resource in the world lies in the oil
-shales of western Colorado. The richest of these shales cover an area of
-1,600 square miles north of the Colorado River, south of the White
-River, and just east of the Colorado-Utah line. The oil shales are part
-of the Tertiary Green River Formation, which extends over much of
-northwest Colorado, northeast Utah, and southern Wyoming. Oily material
-called _kerogen_ is locked in these rocks, too solid to flow out of the
-fine pore spaces of the shale. To free it the shale must be mined,
-finely crushed, and heated until the kerogen converts to liquid oil.
-This is an expensive process, and as yet production of petroleum from
-the oil shale has not been possible at a cost which will compete with
-production of oil and gas from wells. The United States Bureau of Mines,
-as well as a number of oil companies, have sought for more than fifty
-years to discover a less expensive method for extracting oil from the
-shale. No doubt at some time in the future a competitive technique will
-be developed, or a growing shortage of other oil will bring world prices
-to a level with which present production techniques can compete.
-
-Oil and gas production in Colorado is decreasing at present, even though
-great efforts are being made to find new oil pools. Petroleum
-prospecting and wildcat drilling are carried out in as yet unproductive
-basins in the Plateau Province, in intermontane basins such as the San
-Luis Valley, and on the Plains. Known reserves will continue to provide
-the state with significant income for many years to come, and if oil
-shale recovery becomes profitable. Colorado’s hydrocarbons will become
-the most prominent of her commodities.
-
-
-                                  COAL
-
-Coal resources of Colorado amount to about 60 billion tons. Only one per
-cent of this has been mined. Thousands of tons are now being produced
-daily from large mines in central, southern, and northwestern parts of
-the state.
-
-Colorado’s coal deposits were formed during late Cretaceous and early
-Tertiary time, when seas were receding from this region and the land was
-rising. They represent accumulations of leaves and other plant material
-in swamps and flood plains similar to those now found in the delta of
-the Mississippi River and in the swamps of southeastern United States.
-Almost all Colorado coal is bituminous or soft coal.
-
-Coal was recognized early in Colorado history by settlers along the
-mountain front, and was mined west and north of Denver in the 1860s.
-Several large underground mines still operate in this district,
-supplying local power plants, but production does not compare with that
-of the Walsenburg-Trinidad area in southern Colorado or the Hayden area
-in northwest Colorado.
-
-The Walsenburg-Trinidad region, part of the Raton coal field, has
-produced coal since the building of the Santa Fe Railroad in the early
-1870s. For many years coal from these mines moved the Santa Fe trains
-and many of the numerous smaller railroads that served Colorado’s cities
-and mining camps. The location of the mines helped to determine the
-location of the Colorado Fuel and Iron Company smelter in Pueblo. Now,
-most southern Colorado coal is used to produce electric power. Many
-small mines, miles away from the power plant west of Trinidad, are
-deserted.
-
-A large coal-burning power plant has recently been built between Hayden
-and Steamboat Springs, just west of the Yampa River. Here, some of the
-extensive coal deposits can be seen in road cuts along U. S. highway 40.
-Until conversion to diesel fuel became almost universal in North
-American railroads, mines of this district produced coal for
-locomotives.
-
-In the heyday of the gold and silver mines, coal was also mined near
-Coalmont, in North Park, and Como, in South Park. Coal from these areas
-was used for fuel in nearby mining towns and ranches, and for the
-narrow-gauge railroads that penetrated the mountains here.
-
-At Anthracite, near Crested Butte, high-grade anthracite coal was mined
-for a time. Identical in origin with other Colorado coal, the anthracite
-of this region was hardened by heat and pressures from Tertiary igneous
-intrusions forcing their way into local sedimentary rocks during
-post-Cretaceous mountain building.
-
-A multitude of other coal camps are scattered about Colorado: Cokedale,
-Delcarbon, Coaldale, Roncarbo, Carbondale, and Cardiff stand out because
-of their suggestive names. These early small camps are, like their
-metal-mine cousins, largely deserted today.
-
-
-                         CONSTRUCTION MATERIALS
-
-
-                         Sand, Gravel, and Clay
-
-Sand, gravel, and crushed rock rate high among geologic products in
-Colorado; more than $27,000,000 worth of these materials were produced
-in the state in 1969. Highway and construction activities have brought
-recent expansion in the number and size of quarries and gravel pits.
-Increasingly, Coloradoans are insisting that quarries and pits be
-excavated only where they will not mar the natural beauty of the
-landscape, and many old pits are now being filled in. Unfortunately, the
-scars left by some quarries—such as that on the Rampart Range near
-Colorado Springs—are difficult to erase.
-
-Clay of good quality occurs in Cretaceous deposits in many parts of
-Colorado, most frequently in the Dakota or Laramie Formations. In the
-area around Golden, the Coors Porcelain Company for many years mined
-clay for use in pottery and low temperature ceramic ware. Scars from
-this mining can be seen along the mountain front north and south of
-Golden, and deep clefts within the town, just west of Colorado School of
-Mines, testify to the amounts of clay that have been removed. Colorado
-clay is not pure enough to be used in high temperature ceramics, and the
-present use for it is in the manufacture of common tiles and bricks.
-
-A recent development in Colorado is the use of Cretaceous Pierre shales
-in manufacturing lightweight aggregate for building. The shale is mined
-between Golden and Boulder, near Colorado highway 93. In the nearby
-plant, it is pulverized and then heated in a large rotating cylinder
-until the surface of each particle fuses. Then the particles are quickly
-cooled. The resulting product is much like cinder, light in weight and
-yet strong. It can be mixed with cement for use in construction work
-requiring a great strength-to-weight ratio, or made into concrete
-blocks.
-
-[Illustration: Quarrying of Paleozoic limestones and dolomites along the
-east flank of the Rampart Range northwest of Colorado Springs has badly
-defaced a prominent mountain backdrop. Recent seeding efforts by quarry
-operators are returning the exhausted part of the quarry to its original
-lightly vegetated condition, and hopefully, as the quarry is depleted,
-the scar will disappear. (John Chronic photo)]
-
-
-                                 Stone
-
-In Colorado, as in most parts of the world, building stone for local use
-is quarried locally. Two of the state’s stones, however—Yule Marble from
-the Crystal River Canyon, and Lyons Sandstone of the Front Range—have
-been more widely used.
-
-The Yule Marble, or Yule Colorado Marble, was produced by metamorphism
-of Leadville Limestone in an area intruded by the Treasure Mountain
-Granite, thirty-five miles south of Glenwood Springs. This exquisite
-marble, which has graced many famous monuments and buildings (among them
-the Lincoln Memorial and the Tomb of the Unknown Soldier), is known for
-its almost uniform snowy whiteness and regular, fine crystallization.
-Although its beauty, massive character, and uniformity made it a
-sought-after ornamental stone, quarrying was economically marginal
-because of the remoteness of the site. In spite of this, nearly
-$7,000,000 worth of the marble was produced before the quarry closed in
-1940.
-
-[Illustration: Pure white marble was quarried for many years at the Yule
-Colorado Marble Quarry, about three miles southeast of the village of
-Marble. (U. S. Geological Survey photo)]
-
-The Lyons area, north of Boulder, provides pink, hard, even-grained
-sandstone which splits readily into slabs or flagstones. These are used
-in the Denver-Boulder area for sidewalks and patios as well as for
-facing buildings. Quarries owned by the University of Colorado provide a
-constant supply of handsome facing material and flagstone for new
-university buildings, although in recent years the high cost of stone
-construction has limited its use on the campus.
-
-[Illustration: Lyons Sandstone is quarried near Lyons, Colorado. The
-salmon-colored sandstone splits along surfaces defined by slight
-differences in size and arrangement of the sand grains. (John Chronic
-photo)]
-
-[Illustration: Most of the buildings of the University of Colorado are
-faced with Permian Lyons Sandstone, which is widely used for buildings
-and flagstones throughout the Boulder-Denver area. The University
-Museum, shown here, was established in 1902, and contains over a million
-scientific specimens, including many Colorado fossils and minerals.
-Exhibits in the Hall of Earth portray Colorado’s geologic history.
-(Tichnor Bros. photo)]
-
-The Lyons Sandstone was deposited as beach and bar sand along the edge
-of a sea which lay east of the Front Range in Permian time. After
-deposition, the sand was deeply buried and compacted. Now tilted up
-along the Front Range uplift, it comes to the surface along the east
-side of the range. Only between Fort Collins and Boulder does the stone
-have the desirable combination of hardness, thin-beddedness, and color
-which makes it desirable for ornamental use. The pink color of the Lyons
-Sandstone is derived from iron oxides, mostly hematite, disseminated
-between the sand grains. Dendrites (often erroneously called fossil
-ferns or plants) ornament some slabs; they were formed by
-crystallization of manganese dioxide from groundwater as it slowly
-percolated through the rock.
-
-
-                            Lime and Gypsum
-
-Outcrops of the Cretaceous Greenhorn and Niobrara Limestones provide
-most of the cement materials in Colorado. A number of plants along the
-mountain front, including a completely automated and dust-free one near
-Lyons, provide the major population centers with millions of tons of
-cement each year.
-
-Colorado is richly endowed with gypsum, useful in cement and plaster
-manufacture and for ornamental stone and sculpture. Along the eastern
-front of the mountains, gypsum occurs in the Triassic Lykins Formation;
-in the Mountain Province, it is abundant in Pennsylvanian sedimentary
-rocks. Particularly high-quality Pennsylvanian gypsum is quarried at the
-town of Gypsum, west of Eagle.
-
-The Colorado portion of the Paradox Basin, in the Plateau Province,
-contains immense deposits of Pennsylvanian gypsum. Here, rocks near the
-surface have been pushed up into sharp northwest-trending faulted
-anticlines by upward movements of gypsum and salt from depths of several
-thousands of feet. The soluble salt and gypsum cores of these structures
-have been washed away more rapidly than the surrounding layers of
-sandstone and shale, leaving depressions such as Gypsum Valley, Paradox
-Valley, and Sinbad Valley, on the crests of the anticlines. Red and
-yellow Triassic sandstones and shales, especially the Chinle Formation
-and the Wingate Sandstone, dip away from these valleys. Exploratory
-wells indicate that vast masses of salt and gypsum are present beneath
-the surface, and may extend to depths greater than 10,000 feet.
-
-
-                       GEMS AND ORNAMENTAL STONES
-
-More than thirty different gems and ornamental stones are known to occur
-in Colorado. Amazonstone, amethyst, garnet, tourmaline, aquamarine,
-topaz, lapis lazuli, quartz crystal, smoky and rose quartz, sapphire,
-several varieties of agate, zircon, and other attractive stones are
-gathered within the state, mainly in the Mountain Province. Turquoise is
-known at several places in the volcanic area of southern Colorado.
-Alabaster is mined along the northeastern mountain front near Fort
-Collins and Loveland. Localities of interest to gem hunters are
-described in _Colorado Gem Trails and Mineral Guide_, by Richard M.
-Pearl.
-
-Gem Village, in southwestern Colorado on U. S. highway 160 between
-Durango and Pagosa Springs, is a favorite stopping place for tourists
-wishing to see or buy colorful and attractive Colorado stones such as
-petrified wood, agatized dinosaur bones, chalcedony, and jasper.
-
-
-                                 WATER
-
-Although not all aspects of water and water supply are geologic, water
-is an important geologic agent, determining the shape of the surface,
-the distribution of minerals, and the location of caves. Water used in
-Colorado comes entirely from precipitation within the state, as all of
-Colorado’s rivers flow from Colorado outward toward the surrounding
-lower-elevation states.
-
-
-                             Surface Water
-
-[Illustration: A cross section through the Front Range northwest of
-Denver shows the redistribution and use of western slope water in
-eastern Colorado through the Colorado-Big Thompson Project. This project
-has cost about $160,000,000, but it is repaying the investment many
-times over by providing electric power and increasing farm production.]
-
-Moisture carried by prevailing westerly or northwesterly winds falls
-primarily on Colorado’s western slope, although at some times of year
-precipitation may come from the northeast or southeast. West of the
-continental divide, where population is sparse, there is a surplus of
-water. East of the divide, where more than 90 per cent of the population
-lives, water is in desperately short supply. The high and largely
-unpopulated Mountain Province receives by far the greatest proportion of
-precipitation, while agricultural areas of the Prairie and Plateau
-Provinces receive much less. Needless to say, the major problem
-involving water in Colorado is how to move it from areas where it is
-abundant to areas where it is needed.
-
-In many parts of the state, complex water laws and complicated
-irrigation canals and water systems were developed soon after the area
-became settled. Gradually but inevitably, water resources have been
-transferred from the western slope to the eastern. However, such
-transfer must be undertaken with due regard for the rights of downstream
-users, notably California, Arizona, and New Mexico.
-
-One of the largest water movement schemes in the state is the
-Colorado-Big Thompson Project. Water that otherwise would flow into the
-Colorado River is piped from Grand Lake through the Alva B. Adams tunnel
-under the high mountains of Rocky Mountain National Park, and into the
-Big Thompson drainage near Estes Park. It then travels through a series
-of reservoirs and tunnels into the South Platte River basin, where it is
-used for irrigation and household water. The water is pumped up the
-western gradient of this system by electric power produced as it flows
-down the eastern slope. Surplus electric power serves the
-Colorado-Wyoming area.
-
-Another large project is the Denver Water Board’s Dillon Reservoir
-Project, in which western slope water collected at Dillon is pumped
-twenty-three miles under the continental divide through the Harold D.
-Roberts tunnel to the North Fork of the South Platte River for use by
-the city of Denver. The exit point of this tunnel can be seen a few
-miles west of Grant along U. S. highway 285. This project is
-continuously growing as Denver’s water needs mount.
-
-In each of these projects, engineering geologists played a prominent
-part in locating dams and tunnels that would not leak or fail, and that
-could collect and transport a maximum amount of water during the
-high-runoff spring season for distribution through the rest of the year.
-Fortunately for geologists, the tunnels and bores necessary to the
-projects allowed them to learn a great deal about the structure of the
-interior of the high mountains, and helped to improve their
-interpretation of earth history in this most interesting region.
-
-The necessity for storing irrigation water along the eastern mountain
-front has led to the creation of hundreds of new lakes in the region.
-Although water levels vary with the season, many of the lakes provide
-opportunities for water sports and recreation for the burgeoning inland
-population.
-
-Two large dams have recently been built in western Colorado for another
-purpose: to control the flow of water in the Colorado River drainage
-basin. Electric power for western Colorado also comes from these dams.
-One of the dams is on the Gunnison River at Curecanti, upstream from the
-Black Canyon of the Gunnison National Monument, and the other is on the
-Frying Pan River near Ruedi. The latter was completed over the
-objections of geologists, who believed that the extensive gypsum
-deposits underlying the damsite would cause its failure. Cement pumped
-deep into the rocks in the vicinity has so far prevented serious
-rupture.
-
-There is strong resistance by conservation groups to the construction of
-more dams on Colorado River drainage, primarily because the Colorado and
-its tributaries pass through many irreplaceable canyons, some of them
-parts of National Parks and Monuments, that are very much a part of our
-western heritage.
-
-
-                              Groundwater
-
-[Illustration: In the San Luis Valley, runoff from the San Juan and
-Sangre de Cristo Mountains sinks into layers of sand in the Alamosa
-Formation. Flowing along the sand layers toward the center of the
-valley, it provides artesian water for irrigation of valley farmlands.]
-
-  SAN JUAN MOUNTAINS
-  LIMIT OF FLOWING WELLS
-  HUBBARD’S WELL
-  OTTOWAY’S WELL
-  ALAMOSA WELL
-  GEORGE NEWSOM’S WELL
-  CALKIN’S WELL
-  LIMIT OF FLOWING WELLS
-  Moraine
-  Alluvial Slope
-  SANGRE DE CRISTO MOUNTAINS
-  Sands, lava beds, gravels, conglomerates, etc.
-  Alamosa formation
-  Granites
-  WEST
-  SANTE FE FORMATION
-  SANTE FE FORMATION
-  EAST
-
-Groundwater is extremely important to Colorado, especially in the
-Prairie Province and the San Luis Valley. Below these two areas lie a
-number of distinct and productive groundwater aquifers, several of them
-artesian. In Otero County, for example, there are five major aquifers:
-three separate Quaternary gravel deposits, the Cretaceous Dakota
-Sandstone, and the Cheyenne Sandstone Member of the Purgatoire
-Formation, also Cretaceous. All these aquifers are characterized by
-their high porosity and permeability, which allow water to flow rapidly
-through them. Wells in the younger, shallower aquifers produce as much
-as 2,000 gallons per minute; those in the older, deeper aquifers produce
-about eighty gallons per minute, some of it with an artesian “head.”
-
-The San Luis Valley supports intensive agriculture, made possible by a
-great artesian water supply. A thick series of soft interlayered clays
-and sands, the Alamosa Formation, slopes down toward the center of the
-basin from the surrounding mountains. Water entering the sandstone beds
-at the mountain edges flows through the sand layers held there by the
-impermeable clay beds. By the time it reaches the center of the valley,
-it has developed considerable hydrostatic head, and the water rises in
-wells without pumping. Unfortunately, both the irrigation water and the
-soils in the San Luis Valley are highly alkaline. Constant evaporation
-from the irrigated fields has concentrated the alkali near and on the
-surface, rendering some of the land less usable than it was originally.
-
-
-                                 Caves
-
-Colorado has many caves, most of them carved by underground water in
-Paleozoic limestone. The Cave of the Winds at Manitou is the only one in
-the state which has been developed as a tourist attraction. It is in
-highly faulted Ordovician and Mississippian limestone near the mountain
-front, where the faulting, coupled with the high relief, has accelerated
-solution of the rock by allowing groundwater to percolate downward
-rapidly. The cavern was probably carved during the Pleistocene Ice Age,
-when surface water and groundwater were much more abundant than at
-present. Deposition of stalactites and stalagmites has occurred within
-the last few thousand years, as supplies and movement of water have
-decreased.
-
-Spanish Cave, above timberline on Marble Mountain in the Sangre de
-Cristo Range, is probably the nation’s highest limestone cave. It is in
-thick folded and faulted Pennsylvanian reef limestone, at an elevation
-of over 12,000 feet. The cave has many intricate passageways branching
-from its main vertical tubes and channels.
-
-Fulford Cave, south of Eagle, is in the Mississippian Leadville
-Limestone of the northern part of the Sawatch Range. Many other caves
-are situated south of Fulford, near Woods Lake, where the limestone is
-widely exposed and highly dissected.
-
-Fairy Cave, northeast of Glenwood Springs, is the best known of the many
-caverns in the Paleozoic limestones that form the southern flanks of the
-White River Plateau.
-
-[Illustration: In Cave of the Winds near Manitou, Paleozoic limestones,
-cracked and tilted by uplift of the Front Range, have been honeycombed
-by ground water. Calcite stalactites hang from the ceiling, while
-stalagmites grow up from the floor. (Cave of the Winds Company photo)]
-
-In the Plateau Province another type of cave is formed not so much by
-groundwater as by weathering of the flat-lying alternating beds of
-massive resistant sandstone and less resistant, thinly bedded mudstone
-and shale. Where the resistant layers are undermined, great arching
-caves develop. These are best observed at Mesa Verde National Park,
-where many of them once sheltered Indian communities. They can also be
-seen in Colorado National Monument and along the Colorado River and
-several of its major tributaries.
-
-[Illustration: Along the edge at Mesa Verde, caves in Cretaceous Mesa
-Verde sandstone were used for shelter by Indians. Springs near the bases
-of the caves, which provided the Indian communities with water, probably
-contributed to the undermining of the sandstone cliffs. (Colorado
-Department of Highways photo)]
-
-
-                                Springs
-
-The multitudes of mineral and hot springs in Colorado are a fascinating
-and interesting facet of the Mountain Province. Some are located along
-major faults, where the rocks are so broken and shattered that
-groundwater can move freely toward the surface. Colorado Springs,
-Manitou Springs, and Eldorado Springs are on the fault complex that
-forms the east edge of the Front Range. Glenwood, Juniper, Steamboat,
-and Poncha Springs are on well defined faults also.
-
-[Illustration: Glenwood Hot Springs flow from Pennsylvanian shales of
-the Belden Formation, where sedimentary layers are faulted by the sharp
-upward tilting against the south side of the White River Plateau. Behind
-the hotel and on the right can be seen the Mississippian Leadville
-Limestone, cut by the Colorado River. (From a painting by William H.
-Jackson, courtesy of Colorado State Archives and Public Record)]
-
-Many other springs do not seem to be controlled so strongly by faulting,
-but owe their presence to sources of volcanic or magmatic heat which
-exist near to the surface of the ground. Some springs of this type issue
-from Precambrian granite, or Cenozoic volcanic rock, while others flow
-from sedimentary rock layers. Waunita Hot Springs and Pagosa Springs,
-although near volcanic rocks, reach the surface through porous
-sandstones and shales of Cretaceous age. Mt. Princeton Hot Springs comes
-from alluvium but its heat source is the intrusive igneous rock which
-makes up part of the adjacent mountain.
-
-Springs of another general type are also present in Colorado where
-aquifers, generally sandstones, are dissected by erosion. These springs,
-usually not highly mineralized or warm, are most often found in the
-Plateau Province. Such springs are frequent at the bases of the great
-sandstone cliffs of Mesa Verde and Colorado National Monument.
-
-Manitou’s carbonated springs, which attract many tourists, have their
-origin in the arrangement and nature of the rocks through which the
-water flows. Water from the Pikes Peak region, slightly acid from its
-contact with the granitic rock, flows into the Manitou limestone all
-along Ute Pass fault, which extends from Cheyenne Mountain northwest to
-Woodland Park. Descending through channels along the fault, the water
-becomes pressurized. Because of its pressure and its acid content, it
-partly dissolves the calcium carbonate of the limestone, and from then
-on carries carbon dioxide in solution. As the water comes to the surface
-at the low point of the fault exposure, near the west edge of Manitou,
-the pressure is released and the carbon dioxide effervesces, just as a
-bottle of soda water effervesces when the cap is removed.
-
-
-                         ENVIRONMENTAL GEOLOGY
-
-The preceding part of this chapter mentions many ways in which man’s
-destiny in Colorado has been shaped by geologic factors. Early
-Coloradoans settled near gold and silver placers, later ones near mines
-that produced ores of other metals, or in the towns that sprang up
-around the mills and smelters that processed these ores. Our present
-distribution of population is partly a heritage from these first
-settlements, partly a result of later discoveries of oil, gas, and
-radioactive minerals, and partly a response to the state’s extreme
-topographic variation, which controls and delineates agricultural areas
-and transportation routes.
-
-In recent years, man has begun to appreciate the fact that he may
-benefit in other ways from knowledge about geology. A new geology has
-developed—_environmental geology_—which may be defined as the total of
-all geological conditions and influences affecting the life and
-development of man.
-
-Environmental geology is a broad science, concerned not only with the
-location of cities and towns, but with the uses people make of the land
-and its economic products, and with the relationship between the
-geological character of the land and the present and future location of
-roads, dams, bridges, factories, homes, recreation facilities, sanitary
-land fills, and even sewage plants.
-
-Two aspects of environmental geology which are particularly pertinent to
-Colorado’s residents are discussed below.
-
-
-_Landslides_ and slumping rock or earth are a frequent menace to
-Colorado’s development in the Mountain Province. Often activated by
-heavy rains or deep manmade cuts, they can cause—and _have_ caused—much
-damage to roads, buildings, and other works of man.
-
-The flanks of North and South Table Mountains, near Golden, are mantled
-by thick landslide debris; intermittent movement of the individual
-slides has repeatedly affected the railroad, irrigation ditches, and
-roads. As many as six different slides have moved within a single year.
-In one slide area, asphalt road material is estimated to be thirteen
-feet thick; successive layers of pavement have been laid one on top of
-another to keep the street up to grade.
-
-Landslides and landslide-prone areas may not be obvious to the untrained
-eye. Each year buildings and roads are constructed on unsuitable rock
-and soil foundations, in places where some degree of land slip is almost
-inevitable. Building in such areas is risky, but sometimes worth the
-risk; if condition are less than ideal, risks can be reduced by
-specialized types of construction.
-
-
-_Floods_ are a perennial threat to much of the state, because of the
-high relief of the drainage basins and the torrential nature of the
-spring and summer rainfall. Their damaging effects were realized early
-in Colorado’s history, when canyons were used as highways and railroad
-routes.
-
-Colorado’s most expensive flood was probably the flood in the South
-Platte River basin south of Denver in 1965, which caused $508,000,000
-worth of damage and drowned six people. The losses can be attributed to
-man’s failure to realize the significance of the South Platte drainage
-routes and flood plains. Homes, shopping centers, and many other
-buildings occupied—and still occupy, as of 1971—land that has been
-intermittently flooded for many years. The following description of this
-flood, by H. F. Matthai of the U. S. Geological Survey, may help to
-convey some warning to residents or potential residents of the South
-Platte valley and other river valleys in Colorado:
-
-“The morning of June 16 was most pleasant, but conditions changed
-rapidly shortly before noon. A tornado touched ground 15 miles south
-southeast of Denver about 1 p.m. Within the next hour, another unroofed
-30 homes in the little town of Palmer Lake, 40 miles south of Denver.
-About 2 p.m., a dense mass of clouds descended and concealed the top of
-Dawson Butte, 7 miles southwest of Castle Rock; and the little light
-remaining faded until it was dark black and frightening, according to
-some people. A nearby rancher’s wife described the intense quiet as
-awesome, but the calm did not last very long.
-
-“The deluge began, not only near Dawson Butte, but also at Raspberry
-Mountain, 6 miles to the south, near Larkspur. The rain came down harder
-than any rain the local residents had ever seen, and the temperature
-dropped rapidly until it was cold. The quiet was shattered by the
-terrible roar of wind, rain, and rushing water. Then the thudding of
-huge boulders, the snapping and tearing of trees, and the grinding of
-cobbles and gravel increased the tumult. The small natural channels on
-the steep slopes could not carry the runoff; so water took shortcuts,
-following the line of least resistance. Creeks overflowed, roads became
-rivers, and fields became lakes—all in a matter of minutes.
-
-“The flow from glutted ravines and from fields and hillsides soon
-reached East and West Plum Creeks. The combined flow in these creeks
-have been described as awesome, fantastic, and unbelievable; yet none of
-these superlatives seem adequate to describe what actually occurred.
-Large waves, high velocities, crosscurrents, and eddies swept away
-trees, houses, bridges, automobiles, heavy construction equipment, and
-livestock. All sorts of debris and large volumes of sand and gravel were
-torn from the banks and beds of the streams and were dumped, caught,
-plastered, or buried along the channel and flood plains downstream. A
-local resident stated, ‘The banks of the creek disappeared as if the
-land was made of sugar.’
-
-“The flood reached the South Platte River and the urban areas of
-Littleton, Englewood, and Denver about 8 p.m. Here the rampaging waters
-picked up house trailers, large butane storage tanks, lumber, and other
-flotsam and smashed them against bridges and structures near the river.
-Many of the partly plugged bridges could not withstand the added
-pressure and washed out. Other bridges held, but they forced water over
-approach fills, causing extensive erosion. The flood plains carried and
-stored much of the flood water, which inundated many homes, businesses,
-industries, railroad yards, highways, and streets.
-
-“The flood peak passed through Denver during the night, and the
-immediate crisis was over by morning; but those in the inundated areas
-were faced with a Herculean task. The light of day revealed the nature
-of the destruction—mud in every nook and cranny, soggy merchandise,
-warped bowling alleys, drowned animals, the loss of irreplaceable
-possessions, to name a few types. The colossal cleanup job, which would
-take months, began.”
-
-Hydrogeological studies by the U. S. Geological Survey and Corps of
-Engineers give knowledgeable estimates of flood danger for different
-populated areas of the state, and recommend that homes, roads, and other
-structures be placed above likely flood levels.
-
-
-
-
-                                GLOSSARY
-
-
-Alluvial fan. A cone-shaped mass of sediment built by rivers or streams
-    as they issue from mountains onto more level ground.
-
-Alluvium. Stream deposits formed in recent geologic time, composed of
-    sand, gravel, and stones.
-
-Ammonite. One of a large group of extinct mollusks related to the living
-    chambered _Nautilus_. Ammonite shells, usually cone-shaped or
-    coiled, are divided into many chambers by crenellated septa.
-
-Angular unconformity. A surface separating tilted or folded layers of
-    rock from overlying less disturbed layers.
-
-Anticline. An upward fold or elongated arch in rock layers.
-
-Aquifer. A rock layer that is water-bearing.
-
-Artesian water. Groundwater that is under sufficient pressure to rise
-    above the level at which it is encountered in a well. It does not
-    necessarily rise completely to the surface.
-
-Basalt. An extrusive igneous rock, fine-grained and dark colored,
-    composed mainly of calcium-rich feldspar and the black mineral
-    pyroxene.
-
-Basement. A name commonly applied to metamorphic or igneous rocks
-    underlying the sedimentary rock layers.
-
-Batholith. A large body of intrusive igneous rock, 40 square miles or
-    more in outcrop area, which extends downward to an unknown depth.
-
-Bedrock. The solid rock which underlies soil, sand, clay, or other loose
-    surface material.
-
-Belemnite. The cigar-shaped internal shell of an extinct marine mollusk
-    similar to a squid.
-
-Brachiopod. One of a large group of marine shelled animals having two
-    unequal, bilaterally symmetrical shells.
-
-Bryozoa. A large group of tiny colonial marine animals that secrete
-    calcareous or horny coverings in a great variety of shapes.
-
-Caldera. A large basin-shaped depression caused by explosion or collapse
-    around a volcanic center.
-
-Cassiterite. A heavy, brown to brownish black mineral composed of tin
-    and oxygen (SnO₂) that is an ore of tin.
-
-Cephalopod. A marine mollusk with a head surrounded by tentacles. Squids
-    and octupuses belong to this group, as do fossil forms having
-    straight or coiled shells divided into numerous interior chambers.
-
-Chalcopyrite. A reddish-gold colored ore of copper (CuFeS₂).
-
-Cirque. A deep, steep-walled recess in a mountain, caused by glacial
-    erosion at the head of a valley.
-
-Concretion. A nodular or irregular concentration of minerals such as
-    calcite or limonite, formed by precipitation of the mineral from
-    groundwater around a nucleus.
-
-Conglomerate. A rock containing coarse fragments of an older rock,
-    usually as rounded water-worn stones or pebbles.
-
-Conodont. One of a group of tiny dark brown tooth-like fossils thought
-    to be dermal or dental parts of some extinct group of fish.
-
-Diatreme. A volcanic vent or pipe drilled through rocks by the explosive
-    energy of gas-charged molten rock, now containing igneous rock and
-    often altered or unaltered fragments of the surrounding rock.
-
-Dike. A vertical or nearly vertical sheet of igneous rock which cuts
-    across the structure of adjacent rocks.
-
-Diorite. An intrusive igneous rock composed of sodium-rich feldspar and
-    dark minerals, with only small amounts of quartz.
-
-Dip. The angle at which a layer of rock is inclined below the
-    horizontal.
-
-Dome. A roughly circular upfold in which the rock layers dip outward in
-    all directions from the center.
-
-Dowsing. Searching for underground water or ore with a divining rod,
-    usually a forked stick supposed to locate spots where the desired
-    substance may be found under the surface.
-
-Echinoderm. One of a large group of marine invertebrate animals, most of
-    which have pentagonal symmetry and a skeleton of many calcite
-    plates. Many forms are spiny. The group includes starfish and sea
-    urchins.
-
-Evaporite. Chemical sediments precipitated when water (usually sea
-    water) evaporates.
-
-Extrusive rocks. Igneous rocks formed when molten rock material is
-    ejected onto the surface. Synonymous with volcanic rocks.
-
-Fault. A break in the rocks in which there has been displacement of the
-    two sides relative to each other.
-
-Fault block range. A mountain range bounded on two or more sides by
-    faults.
-
-Feldspar. A group of light-colored aluminum silicate minerals that are
-    major constituents of igneous rocks. They contain potassium, sodium,
-    and calcium in differing proportions.
-
-Fold. A bend in rock layers.
-
-Foraminiferida. One-celled marine animals with microscopic, perforated,
-    many-chambered calcium carbonate shells, often called forams.
-
-Fossil. The remains or traces of an animal or plant which has been
-    preserved in the rock.
-
-Fusulinid. One-celled marine animals (forams) with shells which look
-    like a grain of wheat in shape and size, frequently abundant in
-    Colorado Pennsylvanian rocks.
-
-Galena. A heavy gray metallic mineral (PbS), often cubic in form, that
-    is the most important ore of lead.
-
-Gangue. Nonvaluable minerals occurring in veins with ore minerals.
-
-Glaciation. Alteration of the earth’s surface by erosion and deposition
-    by glacier ice.
-
-Glacier. A body of ice originating on land by recrystallization of snow,
-    and showing evidence of movement by flowing.
-
-Gneiss. A coarse-grained metamorphic rock usually banded with streaks of
-    darker, finer-grained rock.
-
-Granite. An intrusive igneous rock consisting essentially of sodium or
-    potassium feldspar and quartz, often speckled with dark-colored
-    minerals.
-
-Graptolite. Extinct marine organisms without known close living
-    relatives, with small black sawblade-like chitinous hard parts
-    preserved as fossils.
-
-Hematite. A steel gray or metallic grayish black or reddish gray mineral
-    (Fe₂O₃) that is an important ore of iron.
-
-Hogback. A sharp-crested ridge formed by a resistant layer of steeply
-    dipping rock.
-
-Huebnerite. A heavy reddish brown mineral (MnWO₄) that is a major ore of
-    tungsten.
-
-Igneous rocks. Rocks formed by solidification from a molten state,
-    either at the surface (extrusive) or below the surface (intrusive).
-
-Intrusive rocks. Igneous rocks formed when molten rock material
-    solidifies without reaching the surface.
-
-Joint. A fracture in the rock, along which no discernible movement has
-    taken place.
-
-Kerogen. Solid bituminous material in oil shales.
-
-Laccolith. A lens-shaped mass of igneous rock intruded into layered
-    rocks.
-
-Lava. Fluid or molten rock such as that which issues from a volcano.
-
-Lode. A rock mass, often a vein, containing valuable minerals.
-
-Massif. A mountainous mass that has relatively uniform geologic
-    characteristics and which may embrace a number of peaks.
-
-Mesa. A flat-topped mountain bounded on at least one side by a steep
-    cliff.
-
-Metamorphic rock. Rock formed by alteration of pre-existing rock,
-    especially by great temperatures and pressures.
-
-Mollusk. Any one of the large group of invertebrate animals which
-    includes the snails, clams, octopuses, squids, and their extinct
-    relatives.
-
-Molybdenite. A soft bluish gray, metallic mineral (MoS₂) that is a major
-    ore of molybdenum.
-
-Monocline. A steplike fold in otherwise horizontal or gently dipping
-    rock layers.
-
-Moraine. An accumulation of unsorted rock material built up by the
-    action of glacier ice.
-
-Native gold. Gold occurring in nature uncombined with other elements.
-
-Peneplain. A land surface worn down by erosion to a nearly flat or
-    broadly undulating plain.
-
-Petzite. A heavy black or steel gray metallic telluride ore of gold and
-    silver (Ag₃AuTe₂).
-
-Placer. A sand or gravel deposit containing particles or nuggets of gold
-    or other heavy valuable minerals.
-
-Plateau. An elevated, comparatively flat surface of land, usually larger
-    than a mesa, sometimes composed of many mesas, and often dissected
-    by deep stream valleys.
-
-Porphyry. An igneous rock, usually intrusive, which contains conspicuous
-    large crystals in a fine-grained matrix.
-
-Pyrite. A brass-yellow metallic mineral (FeS₂) that is an important
-    source of sulfur. It is commonly known as fool’s gold.
-
-Reef. A moundlike limestone structure built in the sea by sedentary
-    organisms such as corals.
-
-Rhyolite. A light-colored volcanic rock with quartz and feldspar as the
-    principal constituents.
-
-Schist. A metamorphic rock characterized by parallel orientation of
-    flat-grained minerals like mica.
-
-Sedimentary rocks. Rocks formed of fragments of other rock transported
-    by wind or water, or formed by precipitation from solution.
-
-Sphalerite. An amber-yellow to black mineral (ZnS) that is an important
-    ore of zinc.
-
-Stalactite. A cylindrical or conical deposit of calcite hanging from the
-    roof of a cavern, formed by evaporation of water droplets containing
-    calcium carbonate.
-
-Stalagmite. Columns or ridges of calcite rising from the floor of a
-    cavern, formed by water containing calcium carbonate dripping from a
-    stalactite.
-
-Stock. A mass of igneous intrusive rock that covers less than 40 square
-    miles, has steep sides, and extends to an unknown depth.
-
-Tennantite. A metallic gray mineral that contains copper, iron, and
-    arsenic, and is an ore of copper.
-
-Tetrahedrite. A brittle, dark gray to black, metallic mineral containing
-    copper, iron, zinc, and silver.
-
-Trilobite. One of a primitive group of extinct marine crustaceans,
-    related to crabs and lobsters, having segmented bodies divided by
-    longitudinal grooves into three lobes.
-
-Unconformity. A surface separating layers of rock, formed by a period of
-    nondeposition or erosion.
-
-Vein. A crack or fissure filled with mineral material, often with
-    valuable ore minerals.
-
-
-
-
-                           SUGGESTED READING
-
-
-There are thousands of scientific articles and books on Colorado
-geology, and many new ones appear each year. Following is a selection of
-books and booklets which we believe will be most useful and interesting
-in extending your knowledge of the state’s geology.
-
-Donnell, John R., editor, 1960, GEOLOGICAL ROAD LOGS OF COLORADO. Rocky
-    Mountain Association of Geologists, Denver. Itineraries for a number
-    of geological trips along Colorado highways and byways.
-
-Eckel, Edwin B., 1961, MINERALS OF COLORADO, A 100-YEAR RECORD. U. S.
-    Geological Survey Bulletin 1114.
-
-Emmons, S. F., Cross, Whitman, and Eldridge, G. H., 1896, GEOLOGY OF THE
-    DENVER BASIN IN COLORADO. U. S. Geological Survey Monograph 27. The
-    classic early treatment of the surface geology around Denver, with
-    many historic illustrations.
-
-Hansen, Wallace R., 1965, THE BLACK CANYON OF THE GUNNISON TODAY AND
-    YESTERDAY. U. S. Geological Survey Bulletin 1191. A readable account
-    of this unusual national monument near Montrose.
-
-Hansen, Wallace R., 1969, THE GEOLOGIC STORY OF THE UINTA MOUNTAINS. U.
-    S. Geological Survey Bulletin 1291. The eastern part of this range
-    is in Colorado.
-
-Henderson, C. W., 1926, MINING IN COLORADO, A HISTORY OF DISCOVERY,
-    DEVELOPMENT AND PRODUCTION. U. S. Geological Survey Professional
-    Paper 138.
-
-Lee, W. T., 1917, THE GEOLOGIC STORY OF THE ROCKY MOUNTAIN NATIONAL
-    PARK, COLORADO. U. S. National Park Service Publication. An old
-    report, not adequately superseded.
-
-Lovering, T. S., and Goddard, E. N., 1950, GEOLOGY AND ORE DEPOSITS OF
-    THE FRONT RANGE, COLORADO. U. S. Geological Survey Professional
-    Paper 223. A comprehensive study of mineral-bearing areas in the
-    Front Range.
-
-Lohman, S. W., 1965, THE GEOLOGIC STORY OF COLORADO NATIONAL MONUMENT.
-    Colorado and Black Canyon Natural History Association, Grand
-    Junction.
-
-Pearl, Richard M., 1956, NATURE AS SCULPTOR: A GEOLOGIC INTERPRETATION
-    OF COLORADO SCENERY. Denver Museum of Natural History Popular Series
-    No. 6, Revised Edition.
-
-Pearl, Richard M., 1969, EXPLORING ROCKS, MINERALS, FOSSILS IN COLORADO.
-    Swallow Press, Revised Edition.
-
-Pearl, Richard M., 1971, COLORADO GEM TRAILS AND MINERAL GUIDE. Swallow
-    Press, 3rd Edition.
-
-Powell, John Wesley, 1876, REPORT ON THE GEOLOGY OF THE EASTERN PORTION
-    OF THE UINTA MOUNTAINS AND A REGION OF COUNTRY ADJACENT THERETO. U.
-    S. Geological and Geographical Survey of the Territories. One of the
-    earliest accounts of geology in Colorado, written by the explorer of
-    the Colorado River and the father of the U. S. Geological Survey.
-
-Rabbit, Mary C., and others, 1969, THE COLORADO RIVER AND JOHN WESLEY
-    POWELL. U. S. Geological Survey Professional Paper 669. A resumé of
-    part of Powell’s work and a good discussion of the geologic history
-    of the entire Colorado River, which begins near Grand Lake.
-
-Richmond, Gerald M., 1965, GLACIATION OF THE ROCKY MOUNTAINS. A part of
-    THE QUATERNARY OF THE UNITED STATES, Princeton University Press. A
-    summary of current knowledge of glaciation in Colorado and
-    surrounding areas.
-
-Rodeck, Hugo G., editor, 1964, NATURAL HISTORY OF THE BOULDER AREA.
-    University of Colorado Museum Leaflet No. 13. Contains articles on
-    geology and biology.
-
-Untermann, G. E., and Untermann, B. R., 1954, GEOLOGY OF DINOSAUR
-    NATIONAL MONUMENT AND VICINITY, UTAH—COLORADO. Utah Geological and
-    Mineralogical Survey Bulletin 42. A detailed study of the eastern
-    Uinta Mountains.
-
-Weimer, Robert J., and Haun, John D., editors, 1960, GUIDE TO THE
-    GEOLOGY OF COLORADO. Geological Society of America, Rocky Mountain
-    Association of Geologists, and Colorado Scientific Society, Denver.
-    A concise summary of many aspects of Colorado geology, this guide
-    includes several geological itineraries and many reference listings.
-
-Wolle, Muriel Sibell, 1949, STAMPEDE TO TIMBERLINE, Sage Books. An
-    excellent account of early mining activity in the state, with many
-    fine drawings of the early settlements.
-
-
-
-
-                                 INDEX
-
-
-                                   A
-  Abrams Mountain, 87
-  Alamosa, 35
-  Alamosa Formation, 67, 105, 106
-  Alma, 78
-  Ancestral Rocky Mountains, 44, 45
-  Animas River, 58, 86
-  Ankareh Formation, 52
-  Antero Junction, 21
-  Anthracite, 97
-  Arapahoe Conglomerate, 60
-  Arapaho Glacier, 70, 71
-  Arkansas Hills, 21
-  Arkansas Mountain, 79
-  Arkansas River, 3, 22, 35, 90
-  Arkansas Valley, 21
-  Aspen, _Front._, 1, 22, 35, 50, 74, 77, 78, 88-89
-  Aspen Mountain, 23, 88
-  Avon, 22
-
-
-                                   B
-  Battlement Mesa, 62
-  Belden Formation, 44, 109
-  Benton Shale, 57
-  Berthoud Pass, 12, 92
-  Big Thompson Canyon, 12, 71
-  Big Thompson River, 69, 103, 104
-  Black Canyon of the Gunnison, 36, 37, 44, 71, 105
-  Black Hawk, 14, 77, 78, 79, 80
-  Blue River, 103
-  Book Cliffs, 29
-  Boulder, 8, 14, 33, 45, 47, 48, 50, 71, 74, 75, 94, 98, 99, 100,
-          101
-  Boulder County, 78, 79
-  Boulder Creek, 1, 15, 71, 103
-  Boulder Creek Granite, 14, 33, 35
-  Boulder Reservoir, 103
-  Breckenridge, 1, 78, 83-84
-  Bross, Mt., 21
-  Buena Vista, 22
-  Buffalo Peaks, 21
-  Building stone, 24, 48, 50, 99-101
-
-
-                                   C
-  Cache la Poudre River, 66, 103
-  Cambrian, 7, 34, 39
-  Camp Bird, 78, 88
-  Canon City, 3, 11, 16, 52, 53, 75, 94
-  Canon City Embayment, 16
-  Carbondale, 97
-  Carboniferous, see Mississippian, Pennsylvanian
-  Cardiff, 97
-  Carmel Formation, 52
-  Carter Lake, 103
-  Castle Creek, 88
-  Castle Rock, 8, 61, 112
-  Castle Rock Conglomerate, 60
-  Cave of the Winds, 106, 107
-  Caves, 31, 106-108
-  Cenozoic (see also Tertiary, Quaternary), 7, 16, 18, 26, 28, 29,
-          59-73, 109
-  Central City, 1, 14, 74, 77, 78, 80
-  Chaffee Formation, 42
-  Cherry Creek, 1
-  Cheyenne Mountain, 14, 15, 110
-  Cheyenne Sandstone, 105
-  Chinle Formation, 51, 52, 93, 101
-  Clay, 75, 97-99
-  Clear Creek, 1, 71, 80
-  Climax, 21, 78, 91-92
-  Climax Granite Porphyry, 91, 92
-  Coal, 23, 75, 96-97
-  Coal Creek, 14, 15
-  Coal Creek Quartzite, 33
-  Coaldale, 97
-  Coalmont, 97
-  Cokedale, 97
-  Collegiate Range, 22
-  Colorado National Monument, 29, 31, 44, 51, 108
-  Colorado River, 3, 20, 21, 28, 29, 35, 39, 103, 104, 105, 108, 109
-  Colorado Springs, 14, 15, 35, 37, 48, 97, 98, 109
-  Columbia, Mt., 22
-  Como, 78, 97
-  Construction materials, 97-102
-  Copper, 74, 75, 80, 81, 83, 89, 91
-  Creede, 65, 78, 89-90
-  Crested Butte, 24, 97
-  Cretaceous, 7, 12, 20, 23, 29, 30, 53, 56-58, 94, 95, 97, 98, 101,
-          105, 108, 110
-  Cripple Creek, 1, 74, 77, 78, 90-91
-  Cross Mountain, 26, 29
-  Crystal River, 24, 99
-  Culebra Range, 17
-  Curecanti, 105
-  Curtis Formation, 52
-
-
-                                   D
-  Dakota Formation, 12, 51, 53, 56, 94, 97, 105
-  Dawson Arkose, 60
-  Dawson Butte, 112
-  Delcarbon, 97
-  Democrat, Mt., 21
-  Denver, 3, 8, 14, 33, 35, 37, 45, 47, 48, 52, 53, 60, 74, 83, 94,
-          96, 99, 100, 104, 112, 113
-  Denver Basin, 8, 75, 94, 95
-  Denver Formation, 60, 62
-  Devonian, 7, 42-43, 83
-  Dillon, 104
-  Dinosaur National Monument, 27, 53, 55
-  Durango, 25, 28, 35, 47, 58, 78, 85, 102
-  Dyer Dolomite, 42
-
-
-                                   E
-  Eagle, 47, 101, 106
-  Eagle River, 22, 47
-  Edwards, 22
-  Elbert, Mt., 22
-  Eldorado Springs, 109
-  Elk Mountains, 24, 69
-  Empire, 1, 78, 81
-  Englewood, 113
-  Entrada Sandstone, 51, 93
-  Environmental geology, 111-113
-  Eocene, 64
-  Estes Lake, 103
-  Estes Park, 69, 104
-  Evans, Mt., 3, 12
-
-
-                                   F
-  Fairplay, 78, 84-85
-  Fairy Cave, 107
-  Flattop Mountain, 19
-  Floods, 112-113
-  Florence, 74, 94
-  Florissant Fossil Beds National Monument, 65
-  Fort Carson, 15
-  Fort Collins, 35, 101, 102
-  Fountain Formation, 12, 14, 45, 47, 48
-  Fox Hills Sandstone, 58
-  Fremont Limestone, 40, 41
-  Frisco, 21
-  Front Range, 11-16, 33, 35, 44, 50, 51, 52, 56, 60, 61, 68, 69,
-          70, 71, 93, 99, 101, 103, 107, 109
-  Frying Pan River, 105
-  Fulford, 107
-  Fulford Cave, 106
-
-
-                                   G
-  Garden of the Gods, 4, 14, 15, 47, 48
-  Garfield, Mt., 30
-  Gas, natural, 1, 28, 75, 94-96
-  Gems, 75, 102
-  Gem Village, 102
-  Georgetown, 78, 81
-  Gilman, 21
-  Gilpin County, 78
-  Glen Eyrie Formation, 44
-  Glenwood Canyon, 37, 39
-  Glenwood Springs, 24, 29, 35, 99, 107, 109
-  Gold, 1, 22, 29, 74, 75, 77-91
-  Golden, 8, 14, 62, 74, 78, 83, 93, 98, 111
-  Gold Hill, 1, 74, 78, 79
-  Gore Creek, 47
-  Gore Pass, 19, 20
-  Gore Range, 20-21, 35, 69
-  Gore Range-Eagle’s Nest Wilderness Area, 20, 21
-  Granby, 20, 62
-  Granby Lake, 103
-  Grand Hogback, 28, 29
-  Grand Junction, 29, 30, 35, 55
-  Grand Lake, 12, 69, 103, 104
-  Grand Mesa, 35, 62
-  Grand Valley, 25
-  Gravel, 75, 97-99
-  Great Sand Dunes National Monument, 17, 18, 73
-  Green River, 27, 103
-  Green River Basin, 4
-  Green River Canyon, 31
-  Green River Formation, 64, 95-96
-  Greenhorn Formation, 101
-  Greenhorn Peak, 16
-  Groundwater, 76, 105-106
-  Gunnison, 35
-  Gunnison, Black Canyon of the, 36, 37, 44, 71, 105
-  Gunnison River, 35, 36, 37, 105
-  Gypsum (mineral), 22, 30, 75, 101-102
-  Gypsum (town), 47, 101
-  Gypsum Valley, 30, 47, 101
-
-
-                                   H
-  Hahn’s Peak, 19
-  Harding Sandstone, 40, 41
-  Harvard, Mt., 22
-  Hayden, 96, 97
-  Hayden Pass, 17
-  Hermosa Formation, 45, 47
-  Hidden Valley, 69
-  Horseshoe Amphitheater, 85
-  Horseshoe Park, 69
-  Horsetooth Reservoir, 103
-  Huerfano Basin, 35, 61
-
-
-                                   I
-  Ice Age, see Pleistocene
-  Iceberg Lake, 66
-  Idaho Springs, 14, 78, 80
-  Idaho Springs Formation, 33, 92
-  Independence Pass, 22
-  Iron, 1, 17, 74
-  Ironton, 78, 88
-
-
-                                   J
-  Jewel Lake, 68
-  Juniper Mountain, 26, 29
-  Juniper Springs, 109
-  Jurassic, 7, 9, 23, 36, 52-55, 93
-
-
-                                   K
-  Kremmling, 19, 20, 60
-
-
-                                   L
-  La Junta, 8, 35
-  Lake City, 77, 78
-  Lake County, 77
-  Lamar, 8
-  Landslides, 111-112
-  La Plata Mountains, 26
-  Laramide Orogeny, 59, 60
-  Laramie Formation, 57, 58, 97
-  Larkspur, 112
-  La Veta Pass, 17, 18, 37
-  Lead, 74, 75, 80, 81, 82, 83, 85, 86, 89
-  Leadville, 1, 22, 77, 78, 82-83
-  Leadville Limestone, 43, 44, 83, 88, 99, 106, 109
-  Lime, 75, 101
-  Lincoln, Mt., 21
-  Lincoln Porphyry, 21
-  Lipalian Interval, 7, 36, 39
-  Littleton, 113
-  Logan County, 95
-  Longs Peak, 3, 11, 12, 68
-  Loveland, 14, 102
-  Loveland Pass, 12
-  Lykins Formation, 12, 51, 52, 101
-  Lyons, 14, 49, 99, 100, 101
-  Lyons Sandstone, 12, 48, 49, 50, 99, 100, 101
-
-
-                                   M
-  Magnolia, 79
-  Mancos Shale, 30, 95
-  Manitou, 39, 106, 107, 110
-  Manitou Formation, 40, 41, 110
-  Manitou Springs, 109
-  Marble, 24, 99
-  Marble Mountain, 106
-  Maroon Bells, Front., 24, 50
-  Maroon Creek, 24
-  Maroon Formation, 50
-  Mary’s Lake, 103
-  Massive, Mt., 82
-  McDermott Formation, 58
-  Mesa de Maya, 8, 35, 62
-  Mesa Verde, 28, 29, 35
-  Mesa Verde Formation, 30, 58, 108
-  Mesa Verde National Park, 31, 71, 108
-  Mesozoic (see also Triassic etc.), 7, 10, 11, 12, 14, 15, 26, 28,
-          51-58, 60, 93
-  Mestas, Mt., 17
-  Middle Park, 4, 16, 35, 61
-  Million Dollar Highway, 87, 88
-  Mills Lake, 68
-  Milner Pass, 66
-  Minturn, 39
-  Minturn Formation, 45, 46, 47
-  Miocene, 66, 67, 87
-  Mississippian, 6, 7, 43-44, 83, 106, 109
-  Moenkopi Formation, 52
-  Molas Formation, 44
-  Molas Lake, 25
-  Molybdenum, 1, 74, 75, 76, 77, 91-92
-  Monarch Pass, 23
-  Morgan County, 95
-  Morrison, 53, 54, 55
-  Morrison Formation, 12, 36, 51, 53, 55, 93
-  Mosca Pass, 17, 73
-  Mosquito Pass, 85
-  Mosquito Range, 21, 22, 35, 39, 69
-  Mountain Province, 3, 4, 10-27, 35, 46, 93, 94, 101, 102, 103,
-          109, 111
-  Mt. Bross, 21
-  Mt. Columbia, 22
-  Mt. Democrat, 21
-  Mt. Elbert, 22
-  Mt. Evans, 3, 12
-  Mt. Garfield, 30
-  Mt. Harvard, 22
-  Mt. Lincoln, 21
-  Mt. Massive, 82
-  Mt. Mestas, 17
-  Mt. Princeton, 22
-  Mt. Princeton Hot Springs, 22, 110
-  Mt. Sneffels, 87, 88
-  Mt. Sopris, 24
-  Mt. Yale, 22
-  Mt. Zirkel, 19
-  Music Pass, 17, 73
-
-
-                                   N
-  Navajo Sandstone, 52
-  Nederland, 78, 79
-  Needle Mountains, 26
-  Niobrara Formation, 57, 101
-  North Park, 4, 16, 35, 58, 61, 94, 97
-
-
-                                   O
-  Oil, 1, 29, 30, 75, 76, 94-96
-  Oil Creek, 94
-  Oil shale, 95-96
-  Oligocene, 66, 67
-  Ordovician, 7, 40-41, 83, 106
-  Orient, 17
-  Oro, 82
-  Otero County, 105
-  Ouray, 4, 25, 26, 34, 42, 78, 87-88
-  Ouray Formation, 42
-
-
-                                   P
-  Pagoda Mountain, 68
-  Pagosa Springs, 102, 109
-  Paleozoic (see also Cambrian etc.), 7, 10, 11, 12, 14, 15, 17, 21,
-          22, 24, 26, 27, 28, 30, 34, 37, 38-50, 60, 64, 77, 95, 98,
-          106, 107
-  Paradox Basin, 4, 47, 95, 101
-  Paradox Valley, 30, 101
-  Park Range, 19-20, 35, 69
-  Parting Sandstone, 42
-  Pawnee Buttes, 9, 66, 67
-  Peak Province, see Mountain Province
-  Peat, 75
-  Pennsylvanian, _Front._, 6, 7, 14, 23, 44-47, 48, 50, 83, 95, 101,
-          106, 109
-  Permian, _Front._, 7, 23, 48-50, 95, 99, 100, 101
-  Petroleum, 1, 29, 30, 75, 76, 94-96
-  Phosphoria Formation, 50
-  Piceance Basin, 29
-  Pierre Formation, 57, 94, 98
-  Pikes Peak, 3, 4, 11, 12, 15, 65, 90, 91, 110
-  Pikes Peak Granite, 4, 14, 33, 36
-  Plains Province, see Prairie Province
-  Plateau Province, 3, 4, 9, 28-31, 35, 46, 71, 75, 93, 94, 96, 101,
-          103, 107, 110
-  Platte River, 3
-  Pleistocene, 7, 8, 25, 59, 68-73, 105, 106
-  Plum Creek, 112
-  Poncha Springs, 109
-  Prairie Province, 3, 8-10, 12, 35, 66, 72, 75, 94, 96, 103, 105
-  Precambrian, 7, 10, 11, 14, 15, 16, 17, 19, 20, 21, 26, 33-37, 40,
-          60, 64, 68, 77, 87, 91, 92, 93, 109
-  Princeton, Mt., 22
-  Pueblo, 23, 97
-  Pumice, 75
-  Purgatoire Formation, 105
-  Pyrites, 75
-
-
-                                   Q
-  Quandary Peak, 21
-  Quaternary, 7, 8, 25, 59, 68-73, 105, 106
-
-
-                                   R
-  Rabbit Ears Pass, 19
-  Rabbit Ears Range, 20, 35, 62
-  Radium, 93
-  Rampart Range, 15, 97, 98
-  Rangely, 29, 95
-  Raspberry Mountain, 112
-  Rattlesnake Reservoir, 103
-  Raton Basin, 61
-  Raton Pass, 61
-  Red Cliff, 39
-  Red Mountain, 88
-  Red Mountain Creek, 88
-  Red Rocks Park, 14, 37, 47
-  Redstone, 24
-  Rico, 26
-  Rico Range, 26
-  Rifle, 64
-  Rio Grande, 35
-  Roan Plateau, 28, 29, 35
-  Rocky Mountain National Park, 11, 12, 66, 68, 71, 104
-  Roncarbo, 97
-  Royal Gorge, 37, 71
-  Ruedi, 105
-
-
-                                   S
-  St. Mary’s Glacier, 71
-  Salida, 17, 21, 35
-  Salina, 79
-  Sand, 75, 97-99
-  Sangre de Cristo Range, 10, 17-18, 35, 47, 61, 69, 73, 90, 105,
-          106
-  San Juan Basin, 95
-  San Juan County, 78
-  San Juan Formation, 88
-  San Juan Mountains, 4, 25-26, 35, 52, 65, 69, 77, 85, 86, 87, 88,
-          105
-  San Luis Valley, 4, 35, 44, 61, 67, 73, 96, 106
-  San Miguel Range, 26
-  Santa Fe Formation, 67, 105
-  Sawatch Range, 22-23, 35, 39, 69, 82, 106
-  Sawatch Sandstone, 34, 39, 40
-  Sedalia, 61
-  Shadow Mountain Reservoir, 103
-  Sierra Blanca, 17, 18
-  Silurian, 7, 42
-  Silver, 22, 74, 77-91
-  Silver Cliff, 16, 77, 78
-  Silver Plume, 78, 81
-  Silver Plume Granite, 33, 35
-  Silverton, 4, 26, 74, 77, 78, 85-86, 88
-  Sinbad Valley, 101
-  Sneffels, Mt., 87, 88
-  Sopris, Mt., 24
-  South Park, 4, 16, 21, 35, 61, 65, 84, 97
-  South Platte River, 1, 3, 35, 85, 103, 104, 112, 113
-  Spanish Cave, 106
-  Spanish Peaks, 10, 18, 62
-  Specimen Mountain, 66
-  Springs, 17, 22, 109-110
-  Steamboat Springs, 97, 109
-  Summit County, 77
-  Sunshine, 79
-  Sunshine Peak Rhyolite, 87
-  Swandyke Gneiss, 33
-
-
-                                   T
-  Table Mountain, 8, 62, 111
-  Telluride, 26, 74, 77, 78
-  Tenmile Gorge, 21
-  Tenmile Range, 21, 91
-  Tertiary, 7, 15, 20, 21, 25, 26, 29, 59-67, 73, 77, 83, 87, 88,
-          89, 90, 91, 92, 93, 95, 96, 97
-  Tin, 75
-  Tincup, 22, 77, 78
-  Trail Ridge Road, 12, 66
-  Treasure Mountain Granite, 99
-  Triassic, 7, 23, 51-52, 93, 101
-  Trinidad, 8, 61, 96, 97
-  Trout Creek Pass, 21, 22
-  Tungsten, 1, 74, 75, 79
-  Tyndall Glacier, 71
-
-
-                                   U
-  Uinta Basin, 4, 29, 64, 75, 95
-  Uinta Mountain Formation, 26
-  Uinta Mountains, 4, 10, 26-27, 29, 35, 37, 64
-  Uncompahgre Gorge, 87
-  Uncompahgre Plateau, 29, 35, 44
-  Uncompahgre Quartzite, 87
-  Urad Mine, 92
-  Uranium, 1, 29, 80, 93
-
-
-                                   V
-  Vail, 21, 47
-  Vail Pass, 21
-  Valmont, 62
-  Vanadium, 74, 75, 93
-  Villa Grove, 17
-
-
-                                   W
-  Walden, 20
-  Walsenburg, 35, 61, 96
-  Ward, 78
-  Water, 76, 103-110
-  Waunita Hot Springs, 109
-  Weber Sandstone, 95
-  West Elk Mountains, 24, 35, 69
-  Wet Mountains, 16, 35, 61, 95
-  Wet Mountain Valley, 35
-  Whiskey Creek Pass, 17
-  White River, 35, 95
-  White River Formation, 66
-  White River Plateau, 28, 29, 35, 43, 107, 109
-  Williams Canyon, 37, 39
-  Willow Creek Pass, 20
-  Willow Creek Reservoir, 103
-  Wingate Formation, 51, 52, 101
-  Wolcott, 22, 47
-  Wolford Mountain, 60
-  Woodland Park, 110
-  Woods Lake, 107
-
-
-                                   Y
-  Yale, Mt., 22
-  Yampa River, 3, 27, 31, 35, 97
-  Yule Marble, 24, 99
-
-
-                                   Z
-  Zinc, 74, 75, 80, 82, 83, 85, 86, 89
-  Zirkel, Mt., 19
-
-
-
-
-                          Transcriber’s Notes
-
-
---Retained publication information from the printed edition: this eBook
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-  _underscores_.
-
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-  underscore and delimited by brackets.
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-
-
-
-
-
-End of the Project Gutenberg EBook of Prairie Peak and Plateau, by 
-John Chronic and Halka Chronic
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-The Project Gutenberg EBook of Prairie Peak and Plateau, by 
-John Chronic and Halka Chronic
-
-This eBook is for the use of anyone anywhere in the United States and most
-other parts of the world at no cost and with almost no restrictions
-whatsoever.  You may copy it, give it away or re-use it under the terms of
-the Project Gutenberg License included with this eBook or online at
-www.gutenberg.org.  If you are not located in the United States, you'll have
-to check the laws of the country where you are located before using this ebook.
-
-Title: Prairie Peak and Plateau
-       A Guide to the Geology of Colorado
-
-Author: John Chronic
-        Halka Chronic
-
-Release Date: August 21, 2019 [EBook #60143]
-
-Language: English
-
-Character set encoding: ISO-8859-1
-
-*** START OF THIS PROJECT GUTENBERG EBOOK PRAIRIE PEAK AND PLATEAU ***
-
-
-
-
-Produced by Stephen Hutcheson and the Online Distributed
-Proofreading Team at http://www.pgdp.net
-
-
-
-
-
-
-  STATE OF COLORADO
-  John A. Love, _Governor_
-
-  DEPARTMENT OF NATURAL RESOURCES
-  T. W. Ten Eyck, _Executive Director_
-
-  COLORADO GEOLOGICAL SURVEY
-  John W. Rold, _State Geologist and Director_
-  A. L. Hornbaker, _Mineral Deposits Geologist_
-  Richard H. Pearl, _Ground Water Geologist_
-  William P. Rogers, _Engineering Geologist_
-  Antoinette M. Ray, _Secretary_
-
-MISSION OF THE COLORADO GEOLOGICAL SURVEY
-
-The Colorado Geological Survey was legislatively re-established in
-February 1969 to meet the geologic needs of the citizens, governmental
-agencies, and mineral industries of Colorado. This modern legislation
-was aimed at applying geologic knowledge toward the solution of today's
-and tomorrow's problems of an expanding population, mounting
-environmental concern, and the growing demand for mineral resources.
-
-SPECIFIC LEGISLATIVE CHARGES:
-
-  "Assist, consult with, and advise state and local governmental
-          agencies on geologic problems."
-  "Promote economic development of mineral resources."
-  "Evaluate the physical features of Colorado with reference to present
-          and potential human and animal use."
-  "Conduct studies to develop geologic information."
-  "Inventory the state's mineral resources."
-  "Collect, preserve and distribute geologic information."
-  "Determine areas of geologic hazard that could affect the safety of or
-          economic loss to the citizens of Colorado."
-  "Prepare, publish, and distribute geologic reports, maps, and
-          bulletins."
-
-
-
-
-                                PRAIRIE
-                                PEAK and
-                                PLATEAU
-
-
-                   A GUIDE TO THE GEOLOGY OF COLORADO
-
-                      _by John and Halka Chronic_
-
-[Illustration: Relief image of Colorado]
-
-                 COLORADO GEOLOGICAL SURVEY BULLETIN 32
-                                  1972
-
-               Available from Colorado Geological Survey
-                          1845 Sherman Street
-                         Denver, Colorado 80203
-                              Price--$2.00
-
-
-                            ACKNOWLEDGMENTS
-
-This guidebook was written at the request of the Colorado Geological
-Survey to fulfill a long-felt need for a popular account of the state's
-geology and its relationship to Man.
-
-The authors wish to thank those of their colleagues who have assisted at
-various times in the preparation of this book. John Rold, Colorado State
-Geologist, and William Weber, of the University of Colorado Museum
-staff, made many helpful suggestions concerning the manuscript. John
-Schooland, vice president of the Colorado Historical Society, generously
-provided several pictures of early mining activities in Colorado.
-Permission to reproduce drawings and paintings of fossils and
-reconstructions of past environments was granted by the American Museum
-of Natural History and the University of Colorado Museum. Drawings,
-maps, and diagrams are largely the work of Robert Maurer, who also
-designed the cover and title page.
-
-[Illustration: Tilted dark red sedimentary rocks of the
-Pennsylvanian-Permian Maroon Formation are well exposed in the cliffs of
-Maroon Bells, southwest of Aspen. (Photo courtesy Hydraulic Unlimited
-Mfg. Co.)]
-
-
-                                CONTENTS
-
-
-                                                                   _Page_
-  Introduction                                                          1
-  I Colorado's Three Provinces                                          3
-      The Prairies                                                      8
-      The Peaks                                                        10
-          Front Range                                                  11
-          Wet Mountains                                                16
-          Sangre de Cristo Range and Spanish Peaks                     17
-          Park Range and Rabbit Ears Range                             19
-          Gore Range                                                   20
-          Tenmile and Mosquito Ranges                                  21
-          Sawatch Range                                                22
-          Elk Mountains and West Elk Mountains                         24
-          San Juan Mountains                                           25
-          Uinta Mountains                                              26
-      The Plateaus                                                     28
-  II Geologic History of Colorado                                      32
-      Precambrian Era                                                  33
-      Paleozoic Era                                                    38
-          Cambrian Period                                              39
-          Ordovician Period                                            40
-          Silurian Period                                              42
-          Devonian Period                                              42
-          Mississippian Period                                         43
-          Pennsylvanian Period                                         44
-          Permian Period                                               48
-      Mesozoic Era                                                     51
-          Triassic Period                                              51
-          Jurassic Period                                              52
-          Cretaceous Period                                            56
-      Cenozoic Era                                                     59
-          Tertiary Period                                              59
-          Quaternary Period                                            68
-  III Geology and Man in Colorado                                      74
-      Gold, Silver, and Other Metals                                   77
-          Boulder County                                               79
-          Central City and Idaho Springs                               80
-          Georgetown, Empire, and Silver Plume                         81
-          Leadville                                                    82
-          Breckenridge                                                 83
-          Fairplay                                                     84
-          Silverton                                                    85
-          Ouray                                                        87
-          Aspen                                                        88
-          Creede                                                       89
-          Cripple Creek                                                90
-          Climax                                                       91
-      Radium, Uranium, and Vanadium                                    93
-      Oil, Natural Gas, and Oil Shale                                  94
-      Coal                                                             96
-      Construction Materials                                           97
-          Sand, Gravel, and Clay                                       97
-          Stone                                                        99
-          Lime and Gypsum                                             101
-      Gems                                                            102
-      Water                                                           103
-          Surface Water                                               103
-          Groundwater                                                 105
-          Caves                                                       106
-          Springs                                                     109
-      Environmental Geology                                           111
-  Glossary                                                            114
-  Suggested Reading                                                   119
-  Index                                                               121
-
-
-                                 ILLUSTRATIONS
-
-
-                                                                   _Page_
-  Colorado's three geologic provinces                                   2
-  Pikes Peak, seen from the Garden of the Gods                          4
-  Rock classification (chart)                                           5
-  Stratigraphic column (chart)                                          7
-  Jurassic rocks in Colorado (map)                                      9
-  East face of Longs Peak                                              11
-  Rocky Mountain National Park (east-west profile)                     12
-  Big Thompson Canyon, west of Loveland                                13
-  Red Rocks Amphitheater, west of Denver                               14
-  Colorado Springs area (map and cross section)                        15
-  Joint systems in Precambrian rocks, Boulder Canyon                   15
-  Spanish Peaks, southwest of Walsenburg                               18
-  Hahn's Peak, north of Steamboat Springs                              19
-  Gore Range from the east                                             20
-  Aspen Mountain geology (map)                                         23
-  Mt. Sopris, south of Glenwood Springs                                24
-  Ouray, in the San Juan Mountains                                     25
-  Steamboat Rock, Dinosaur National Monument                           27
-  Grand Hogback, near Rifle (block diagram)                            28
-  Mt. Garfield, near Grand Junction                                    30
-  Precambrian-Cambrian unconformity south of Ouray                     34
-  Geologic map of Colorado                                             35
-  Black Canyon of the Gunnison National Monument                       36
-  Precambrian-Cambrian unconformity, Glenwood Canyon                   38
-  Cambrian fossils                                                     39
-  Ordovician fossils                                                   41
-  Devonian fossils                                                     43
-  Mississippian fossils                                                44
-  Pennsylvanian paleogeography (map)                                   45
-  Fountain Formation northwest of Denver                               45
-  Pennsylvanian fossils                                                46
-  Contorted Pennsylvanian rocks near Gypsum                            46
-  Balanced Rock, Garden of the Gods                                    48
-  Permian reptile tracks                                               49
-  The Flatirons, near Boulder                                          50
-  Colorado National Monument                                           51
-  Morrison Formation, west of Denver                                   53
-  Dinosaur bones, found near Morrison                                  54
-  Dakota Sandstone hogback                                             56
-  Cretaceous fossils                                                   57
-  Wolford Mountain, north of Kremmling                                 60
-  Eohippus, the "Dawn Horse"                                           61
-  Golden and South Table Mountain                                      62
-  Devil's Staircase, near Spanish Peaks                                63
-  Green River oil shale, west of Rifle                                 64
-  Florissant Fossil Beds National Monument                             65
-  Pawnee Buttes, north of Fort Morgan                                  66
-  Fossil mammals, northeastern Colorado                                67
-  Glacial lakes in Rocky Mountain National Park                        68
-  Arapaho Glacier, west of Boulder                                     70
-  Pleistocene mastodons                                                72
-  Great Sand Dunes National Monument                                   73
-  Colorado Mineral Belt (map)                                          78
-  Sluicebox mining in early Colorado                                   81
-  Early-day Leadville                                                  82
-  Gold dredge, Fairplay                                                84
-  Silverton, in the San Juan Mountains                                 86
-  Abrams Mountain, south of Ouray                                      87
-  Creede and its mines (map)                                           89
-  Cripple Creek, near Pikes Peak                                       90
-  Climax molybdenum mine (cross section)                               91
-  Rampart Range quarry, near Colorado Springs                          98
-  Yule Marble quarry, near the town of Marble                          99
-  Lyons Sandstone quarry                                              100
-  University of Colorado Museum                                       100
-  Colorado-Big Thompson Project (cross section)                       103
-  San Luis Valley (cross section)                                     105
-  Cave of the Winds, near Manitou                                     107
-  Mesa Verde cave and Indian dwellings                                108
-  Glenwood Hot Springs                                                109
-
-
-
-
-                        PRAIRIE PEAK and PLATEAU
-
-
-
-
-                              Introduction
-
-
-Gold was discovered in the bed of the South Platte River in 1858.
-Prospectors flocked to Colorado as they had flocked only a few years
-before to California. They worked the sands and gravels of Cherry Creek,
-Clear Creek, Boulder Creek, and California Gulch. Exhausting the placer
-sands of the stream bottoms, they moved higher to mine gold-bearing
-veins at Central City and Blackhawk. Mining camps sprang into existence
-overnight, each heralding some new "strike," each populated by a new
-rush of fortune seekers. As lower areas were mined out, prospectors
-moved yet higher--to Breckenridge, Gold Hill, and Empire, Aspen,
-Leadville, and Cripple Creek. Silver was found as well as gold, then
-iron, and later tungsten and molybdenum. The metallic ring of mining
-tools echoed from Colorado's peaks. Fortunes were made here. Legends
-were born.
-
-Prospectors and miners were not, however, the first people interested in
-the rocks of Colorado. Earlier, bands of nomadic Cheyenne and Arapaho
-Indians had searched Colorado's hills for flint for arrowheads and
-brightly colored clays for warpaint. Cliff-dwelling Pueblo Indians in
-southwestern Colorado sought clay for their pottery and fossil seashells
-for the magic of their medicine men. And from farther to the southwest,
-Navajo tribesmen came to Colorado for turquoise.
-
-From clay to gold, much of Colorado's wealth has come from her
-mountains. But after the rush to the mines, as veins were mined out and
-placers worked over, as values and prices changed, her population sought
-the riches of the prairies: fertile lands for agriculture, and in the
-rock layers below, black gold--vast accumulations of oil and natural
-gas. The tablelands and plateaus west of the mountains yield their
-wealth, too. Here are valley farms, fed often by irrigation water, and
-ranch country. Here is more oil, and in some areas precious metals and
-uranium.
-
-In recent years Colorado's prairies, peaks, and plateaus have brought
-new meaning to all America: the state now provides an attractive
-playground for state residents and their visitors. Campgrounds, streams,
-lakes, and high trails beckon in summer; barren slopes deep in winter
-snow attract the skier. More and more, those who live in Colorado and
-those who visit her seek to understand these mountains and hills and
-prairies, to learn of her geologic origins and her far distant past. For
-tourist and resident, casual visitor, ski enthusiast, Sunday picnicker,
-for all those who have met Colorado and enjoyed her, this book is
-written.
-
-[Illustration: Topographically, scenically, and geologically, Colorado
-can be divided into the three provinces shown here.]
-
-  PLATEAUS
-    UINTA MTS.
-    GREEN RIVER BASIN
-    Yampa River
-    Steamboat Springs
-    UINTA BASIN
-    White River
-    WHITE RIVER PLATEAU
-    ROAN PLATEAU
-    Glenwood Springs
-    Colorado River
-    Grand Junction
-    GRAND MESA
-    Gunnison River
-    UNCOMPAHGRE PLATEAU
-    Dolores River
-    PARADOX BASIN
-    MESA VERDE
-  MOUNTAINS
-    NORTH PARK
-    RABIT EARS RANGE
-    PARK RANGE
-    MIDDLE PARK
-    GORE RANGE
-    FRONT RANGE
-    ELK MTS.
-    Aspen
-    SAWATCH RANGE
-    Leadville
-    MOSQUITO RANGE
-    Fairplay
-    SOUTH PARK
-    WEST ELK MTS.
-    Gunnison
-    Salida
-    WET MTS.
-    SANGRE DE CRISTO RANGE
-    SAN LUIS VALLEY
-    Rio Grande
-    Alamosa
-    SAN JUAN MTS.
-    Ouray
-    Silverton
-    Durango
-    MESA DE MAYA
-  PLAINS
-    Fort Collins
-    South Platte River
-    Denver
-    GREAT PLAINS
-    Colorado Springs
-    Arkansas River
-    WET MT. VALLEY
-    HUERFANO PARK
-    La Junta
-    Walsenburg
-
-
-
-
-                                   I
-                       Colorado's Three Provinces
-
-
-Scenically, Colorado is divided into three provinces: the Plains or
-Prairies on the east, the Rocky Mountains bisecting the state from north
-to south, and the Colorado Plateaus on the west. There are a number of
-local variations of course, but by and large the provinces are clearly
-defined. These three divisions will form the basis for our discussion of
-the geology of Colorado, for the scenic differences are almost exactly
-paralleled, and usually controlled, by differences in geologic
-structure.
-
-The Plains rise gently from an elevation of about 3350 feet at the
-eastern border of the state to 5000 feet where they meet the mountains
-150 miles further west.
-
-Two major rivers cross the Colorado Plains: the South Platte River,
-flowing northeastward from the Denver region, and the Arkansas River,
-which leaves the mountains at Canon City south of Colorado Springs and
-travels eastward across the southern portion of the state. Tributaries
-of these two main river systems have etched the prairie surface, so that
-much of eastern Colorado has a gently rolling, hilly appearance.
-
-The Mountains rise abruptly along a north-south line at about 105� west
-longitude. They reach elevations of over 14,000 feet at Pikes Peak,
-Mount Evans, Longs Peak (all visible from far out on the plains), and
-fifty other peaks further west. The ranges of the Colorado Rockies form
-rank upon rank of ridges and peaks, roughly north-south in trend, about
-100 miles across from east to west, extending from the northern to the
-southern border of the state. Here, in mountain springs and lakes, are
-born the rivers of Colorado: the Platte, the Arkansas, the Yampa, the
-Colorado. Crags and cliffs tower above tree-covered slopes, the rocks
-always a dominant part of the landscape. The continental divide runs
-through the state along the summit ridges. West of the divide, all
-streams flow to the Colorado River and the Pacific; east of it, streams
-flow into the Mississippi or the Rio Grande, and thence to the Gulf of
-Mexico.
-
-West of the highest ranges, the country flattens out once more into the
-Plateaus, which extend across western Colorado, southern Utah, and
-northern Arizona. Here, the predominant land forms are flat-topped mesas
-and deep canyons. Redrock walls shimmer in the brilliance of the western
-sun, offset by deep purple shadows sometimes hiding ancient cliff
-dwellings. Fragrance of pine and juniper mingles with the pungency of
-sage. Narrow tracks lure the explorer. Despite the canyons, water is
-scarce except along major river systems, for this is the beginning of
-the desert west.
-
-The scenic and geologic division of the state into three north-south
-strips is not everywhere clearly defined. In southwestern Colorado, the
-San Juan Mountains and the complicated uplifts surrounding Ouray and
-Silverton are out of key with either mountain or plateau. They are best
-considered part of the Mountain Province, however, although they extend
-it far to the west. Other exceptions to these divisions occur also. The
-Mountain Province is interrupted by four broad high-altitude valleys:
-North Park, Middle Park, South Park, and the San Luis Valley. The Uinta
-Mountains jut into the northwest corner of Colorado from adjacent Utah.
-And the Paradox, Uinta, and Green River Basins protrude into the Plateau
-Province, modifying its topographic character.
-
-[Illustration: Pikes Peak rises to an elevation at 14,110 feet. Composed
-of Pikes Peak Granite, the mountain is almost surrounded by younger
-sedimentary rocks, including those of the Garden of the Gods, in the
-foreground. (Floyd Walters photo)]
-
-Before discussing the geologic nature of the three provinces, let us
-review briefly two sets of geologic terms. The first set has to do with
-the rocks themselves--What kind of rock is that?--but serves also to
-tell something about the origin of the rocks. The second set is
-concerned with time--When was that rock formed? Is it older or younger
-than adjacent rock? How does it relate, time-wise, to geologic events in
-other parts of the world?
-
-These two sets of terms are presented in the charts that follow. If you
-are unfamiliar with geologic terminology, refer to these charts as often
-as you need to while you read this book, as well as to the glossary on
-pages 114-118.
-
-  Geologists divide rocks into three main groups, depending on their
-  modes of origin.
-
-  _Igneous rocks_ originate from molten material, cooling deep below the
-  surface of the earth (intrusive igneous rocks) or flowing out and
-  hardening at the surface (extrusive igneous rocks).
-
-  _Sedimentary rocks_ are formed from broken or dissolved bits of other
-  rock, washed by wind and water and deposited as layers of fragments or
-  as chemical precipitates. They often contain fossil plants or animals.
-
-  _Metamorphic rocks_ are pre-existing rocks (igneous or sedimentary)
-  changed by heat, pressure, or chemical action.
-
-  Examples of these three classes of rocks are given in the accompanying
-  figure. Many varieties of all three classes occur in Colorado.
-
-  Class         Example       Occurrence in Colorado
-
-  Sedimentary   Sandstone     Plains, plateaus, flanks of mountain
-                              areas
-                Shale
-                Conglomerate
-                Limestone
-  Igneous       Extrusive:    Volcanic areas such as San Juan
-                   Basalt     Mountains, Spanish Peaks
-                Intrusive:    Pikes Peak, Longs Peak, and most
-                   Granite    central mountain areas
-                   Diorite
-  Metamorphic   Marble        Mountain areas
-                (from
-                limestone)
-                Quartzite
-                (from
-                sandstone)
-                Gneiss
-                (from
-                granite or
-                sandstone)
-                Schist
-                (from shale
-                or basalt)
-
-  Geologists arrange rocks in their chronologic sequence by studying the
-  fossils and minerals which they contain. The age of some rocks can be
-  determined with reasonable precision from ratios of radioactive
-  minerals and their fission products. The relative age of others can be
-  determined from their position, the fossils enclosed in them, and many
-  minor details of their structure.
-
-  The _stratigraphic column_ shown opposite may be thought of as a
-  calendar by which geologic events in Colorado can be arranged in their
-  proper order and related to events in the rest of the world.
-  Mississippian and Pennsylvanian Periods are American divisions;
-  elsewhere this time interval is known as the Carboniferous Period.
-  Other time terms are in worldwide use.
-
-  In the generalized geologic map of Colorado which accompanies Chapter
-  II, rocks are identified by the era in which they were formed. A more
-  detailed geologic map can be obtained from the U.S. Geologic Survey
-  map distribution center in the Federal Building, Denver.
-
-[Illustration: Stratigraphic Column]
-
-  ERA Period  Millions  Distinctive fossils       Events in Colorado
-              of years
-                 ago
-
- CENOZOIC
- (Age of Mammals)
-    Quaternary          Modern types of       Development of present
-                        animals and plants    topography; glaciation in
-                                              mountains
-                     3
-    Tertiary            Mammals, flowering    Uplift and mountain
-                        plants                building
-                    70
- MESOZOIC               Dinosaurs and other
- (Age of Reptiles)      reptiles
-    Cretaceous                                Submergence, then uplift
-                   135
-    Jurassic                                  Desert, then submergence
-                   180
-    Triassic                                  Widespread floodplains
-                                              and deserts
-                   225
- PALEOZOIC
- (Age of Fishes)
-    Permian             First reptiles        Widespread floodplains
-                                              and deserts
-                   270
-    Pennsylvanian       Swamp and forest      "Ancestral Rocky
-                        plants                Mountains"
-                   310
-    Mississippian       Reef corals, sharks   Partial submergence
-                   350
-    Devonian            Armored fish, first   Probable submergence
-                        insects
-                   400
-    Silurian            Corals and shellfish  Probable submergence
-                   440
-    Ordovician          First fish            Submergence
-                   500
-    Cambrian            First hard-shelled    Gradual encroachment of
-                        animals               sea from west
-                   570
- PRECAMBRIAN          "Lipalian Interval"     Erosion to almost flat
-                                              surface or peneplain
-                        Primitive             Alternate episodes of
-                        soft-bodied marine    mountain building and
-                        organisms             erosion
-            3,600 plus
-
-
-                              THE PRAIRIES
-
-Beneath the flat prairies of eastern Colorado, sedimentary rocks form a
-series of layers. Those near the surface are among the youngest rocks in
-Colorado. We know this from the fossils they bear, fossils of large
-mammals such as the hairy mammoth, which lived in early Quaternary time,
-the bison, and many smaller mammals living today.
-
-The layers below--sandstones, shales, and limestones--become
-progressively older as one goes deeper. Most of them were formed
-originally on the bottoms of shallow seas that covered this part of
-North America several times during the history of the continent. In most
-places the layers are horizontal or nearly so, but westward, as they
-approach the mountains, they bend upward, gently at first and then more
-steeply. At the very edge of the mountains, where they were dragged
-upward when the mountains rose, their eroded edges appear at the
-surface.
-
-The entire sequence of flat-lying rocks can be studied where they are
-exposed along the mountain front or where streams and rivers have
-dissected them. They are also known from cuttings and cores of oil and
-water wells. Some parts of Colorado's eastern plains have been drilled
-so intensively in the search for oil and gas that we know a great deal
-about the subsurface sedimentary rock and can even make maps showing the
-distribution and character of the individual rock layers. From such
-maps, the history of the region can be deduced. We know, for example,
-that the area around Denver has subsided more in the past than has the
-area near La Junta or Lamar; it is called the Denver Basin because of
-its past history and not because it is a basin at present.
-
-Although the plains of Colorado appear flat, they really slope gently
-eastward. The rock layers near the surface slope eastward also, but the
-deeper rock layers may not.
-
-Near the western edge of the Plains Province, hills and valleys are
-formed by differential erosion of hard and soft rock layers. Some hills,
-such as Castle Rock, are topped with resistant sandstone; others, like
-Mesa de Maya south of Trinidad and Table Mountain near Golden, are
-capped with layers of basalt. Close to the mountains flat-topped
-foothills result from partial dissection of former erosion surfaces as
-the mountains, stabilized for a time, rose again, or as climatic cycles
-changed. Examples of these dissected erosion surfaces can be seen north
-and south of Boulder.
-
-Far east of the mountain front, near the northern border of Colorado,
-remnants of another, higher prairie surface stand as Pawnee Buttes.
-Torrential erosion--spring floods and summer thunderstorms--has deeply
-furrowed the prairie surface here and left these buttes as lonely
-sentinels.
-
-[Illustration: This map shows the distribution, character, and thickness
-of certain Jurassic rocks in Colorado. These rocks are deeply buried
-beneath the plains and are known there only from well samples. They have
-been eroded from most mountain areas. They come to the surface along the
-edges of the mountains and in the deeply incised canyons of the Plateau
-Province.]
-
-  PRECAMBRIAN ROCKS
-  PALEOZOIC ROCKS
-  JURASSIC ROCKS
-    SANDSTONE
-    SHALY SANDSTONE
-    SANDY SHALE
-    SHALE
-  JURASSIC ROCKS COVERED WITH VOLCANICS OR NEVER DEPOSITED.
-
-What lies below the sedimentary layers of the plains? The sedimentary
-rocks are 5,000 to 10,000 feet thick. They lie on an almost horizontal
-surface of much, much older rock, the Precambrian or "basement" rock.
-This is igneous and metamorphic rock, much crumpled and folded, the
-roots of long gone mountains which were beveled and leveled to an almost
-flat surface or _peneplain_ perhaps a billion years ago.
-
-We know little of the ancient basement rocks below the sedimentary
-layers of the plains, for few wells penetrate this deep. What we do know
-indicates that they are similar to rocks of the mountain masses to the
-west, and are composed of granite, schist, and gneiss. They probably are
-not rich in valuable minerals, however, for the mineral-rich veins of
-the mountains came about as a result of uplift of the mountain areas.
-
-
-                               THE PEAKS
-
-Most of the individual ranges making up the Rocky Mountains in Colorado
-are the result of highly localized movements of the crust as the entire
-region was thrust upward from below. These movements broke the deep,
-massive igneous and metamorphic rocks of the Precambrian basement, and
-bent the more flexible Paleozoic and Mesozoic layered rocks above them
-until they arched upward in a series of corrugations. The mountains thus
-formed are known to geologists as _faulted anticlines_.
-
-As the mountains rose, they were of course attacked by the forces of
-erosion. The sedimentary layers were completely stripped from the crests
-of many of the uplifts, so that Precambrian rocks were exposed. It is
-these rocks which form the summits of the highest peaks of Colorado. As
-with all rules, there are exceptions: the Spanish Peaks are volcanic,
-and the crest of the Sangre de Cristo Range is composed of sedimentary
-rocks.
-
-The trend of most of the ranges in Colorado is north-south, swinging to
-northwest-southeast near the southern end. Surprisingly, in the
-northwestern corner of the state there is an east-west trending range,
-the Uinta Mountains.
-
-Fifty or more mountain ridges in Colorado have been named as separate
-ranges. Of these, the most prominent, frequently visited ones will be
-discussed here.
-
-
-                              Front Range
-
-The easternmost range of the Rocky Mountains is the longest continuous
-uplift in the state. It is a relatively simple faulted anticline
-extending from Canon City northward to the Wyoming border, where it
-splits into two ridges, the Medicine Bow Mountains and the Laramie
-Range.
-
-[Illustration: Longs Peak challenges technical climbers with its
-2000-foot vertical east face, the Diamond. This magnificent cliff is the
-result of glacial action and freezing and thawing in homogeneous but
-fractured granite. The small remnant of ice and snow at the lower left
-is all that remains of the glacier. The flat summit may be part of an
-ancient erosion surface formed toward the end of Precambrian time. (Jack
-Rathbone photo)]
-
-Along the highest portion of the range, from Pikes Peak to Rocky
-Mountain National Park, the Paleozoic and Mesozoic sediments formerly
-draped over the top of the range have long since been washed away,
-leaving only the gneiss, granite, and schist of the mountain core. The
-almost flat tops of Longs Peak, Mt. Evans, and Pikes Peak, and the
-rolling upland traversed by Trail Ridge Road in Rocky Mountain National
-Park are thought to be remnants of the 600-million-year-old erosion
-surface that once existed at the top of the Precambrian rocks, and that
-still exists below the sedimentary rocks of the Plains Province. This
-surface, formed near sea level, has been raised 12,000 to 14,000 feet
-within the Mountain Province.
-
-Throughout most of its length, the Front Range displays some of the most
-striking high-altitude scenery in the world. Particularly accessible
-areas, well worthy of visits, are Rocky Mountain National Park, Berthoud
-and Loveland Passes, Mt. Evans, and Pikes Peak. In these areas the
-Precambrian rocks can be seen and studied, and the effects of glaciation
-observed.
-
-The granite, gneiss, and schist of the mountain core are shattered and
-broken into blocks of various sizes. The breaks between the blocks are
-called _joints_ if there is no apparent displacement between adjacent
-blocks, and _faults_ where there is obvious displacement. The joints
-frequently appear in parallel arrays or sets; there may be two or more
-intersecting sets, giving a cross-hatched appearance to large exposures.
-
-[Illustration: East-west profile across Rocky Mountain National Park,
-through Grand Lake and Longs Peak, showing the inferred position of the
-original surface of the anticlinal uplift of the Front Range. This
-diagram is generalized, and faults are not shown. (USGS Bull. 730a)]
-
-  Restoration of surface which emerged from Cretaceous sea
-  Restoration of Dakota sandstone
-  MIDDLE PARK
-  _Grand Lake_
-  Longs Peak
-  Foothills
-  GREAT PLAINS
-  Sedimentary rocks
-  Granite and schist
-  Sedimentary rock of plains
-  _South Platte R._
-
-[Illustration: Big Thompson Canyon, west of Loveland on U.S. highway 34,
-is carved in almost vertical layers of Precambrian metamorphic rocks.
-Gently dipping Late Paleozoic and Mesozoic sedimentary rocks of the
-Fountain, Lyons, Lykins, and Morrison Formations can be seen in the
-distance, capped by the Cretaceous Dakota Sandstone. (Floyd Walters
-photo)]
-
-The Precambrian rocks vary from place to place. Several irregular masses
-of granite, called _batholiths_, make up portions of the range.
-Batholiths are large intrusions of molten rock that cooled slowly at
-great depth. The minerals in them form distinct crystals, often quite
-large. The Pikes Peak Granite and the Boulder Creek Granite are
-examples. Highly contorted and banded gneiss and schist are well exposed
-elsewhere, particularly in the Idaho Springs-Central City-Black Hawk
-region.
-
-Along the flanks of the Front Range, the eroded edges of the sedimentary
-rocks which once covered the range are exposed. These rocks are usually
-tilted sharply against the mountains, as at Garden of the Gods, Denver's
-Red Rocks Park, and the Flatirons near Boulder. The Rocky Mountain
-Association of Geologists has erected a plaque explaining the geology of
-the Red Rocks area; look for it about half a mile northeast of the Red
-Rocks Amphitheater. Tilted layers of Paleozoic and Mesozoic sandstones
-form hogback ridges along the mountain front, and stand out clearly on
-aerial photographs.
-
-In some areas, particularly near Boulder, Coal Creek, and Golden, the
-tilting of the sedimentary layers has been so extreme that the layers
-are upside down. Basement rocks may even be thrust out above them.
-
-[Illustration: Sandstones and conglomerates of the Pennsylvanian
-Fountain Formation dip steeply toward the plains along the eastern edge
-of the Rockies. Near Denver, erosion has carved these rocks into a
-natural amphitheater, now the site of Red Rocks Amphitheater.
-Precambrian granite forms the hill in the background. (Jack Rathbone
-photo)]
-
-Further north, near Loveland and Lyons, as well as further south at
-Colorado Springs, irregularities in the uplift have caused abrupt breaks
-in the generally smooth eastern edge of the range. Folds and faults in
-these areas trend northwest, cutting across and offsetting the mountain
-front.
-
-[Illustration: South of Colorado Springs, between Fort Carson and the
-NORAD installation in Cheyenne Mountain, Mesozoic rocks are faulted
-against the mountain front. Paleozoic rocks are deeply covered by as
-much as 3000 feet of Mesozoic sediments. They come to the surface about
-10 miles further south.]
-
-  RAMPART RANGE
-    Garden of the Gods
-    Ute Pass Fault
-  MANITOU SPRINGS
-  PIKES PEAK MASSIF
-  CHEYENNE MOUNTAIN
-    COLORADO SPRINGS
-  CROSS SECTION
-    Ute Pass Fault
-    Rampart Fault
-      Tertiary
-      Mesozoic
-      Paleozoic
-      Precambrian
-
-[Illustration: West of Boulder, several intersecting sets of joints
-pattern the Precambrian rocks above Boulder Creek. (John Chronic photo)]
-
-The west margin of the Front Range is not as sharply defined as the
-eastern margin. Prominent faults edge North, Middle, and South Parks,
-however. The northern end of the range merges with the Medicine Bow
-Mountains, where dips of sedimentary rocks seldom exceed 30 to 40
-degrees. At its southern end, the Front Range plunges into the plains,
-although a southwest-trending ridge connects it with the Wet Mountains.
-
-Within the Precambrian core of the Front Range, many economic mineral
-deposits have been found. These are discussed in Chapter III. Glacial
-features of the Front Range are discussed in Chapter II in the section
-on the Quaternary Period.
-
-
-                             Wet Mountains
-
-The Wet Mountains are the easternmost range of the Rockies south of
-Canon City. Their crest has a distinct northwest-southeast trend, with
-the north end offset about 25 miles westward from the south end of the
-Front Range. The Canon City Embayment lies at the junction between the
-ranges.
-
-Though smaller and lower than the Front Range, the Wet Mountains include
-many pleasant and easily accessible recreation areas and a number of
-attractive streams and reservoirs. Greenhorn Peak, the summit of the
-range, is 12,334 feet high. It is formed of Precambrian granite, as is
-most of the crest of the range.
-
-The structure of the eastern side of the Wet Mountains is similar to
-that of the Front Range, except that there are more faults in the
-sedimentary layers. The southern end plunges southeastward into the
-plains. On the western side, westward-dipping sediments are completely
-submerged in Cenozoic lava flows and debris from the mountains. Ore
-minerals very like those of the Front Range occur near Silver Cliff, but
-they have so far proved to be of little economic importance.
-
-
-                Sangre de Cristo Range and Spanish Peaks
-
-The Sangre de Cristo Mountains are visible from many parts of
-southeastern Colorado as a jagged, sawtoothed, snow-crested ridge on the
-western skyline. They extend about 150 miles from the Arkansas River
-near Salida southward into New Mexico.
-
-Few mountain ranges form so impassable a barrier as the Sangre de
-Cristos. Only at La Veta Pass does a highway cross the range. However,
-old wagon roads, passable now by jeep or on foot, once existed across
-Hayden, Music, Mosca, and Whiskey Creek Passes.
-
-Often no more than twenty miles wide, the central portion of the range
-is composed largely of red Late Paleozoic sediments like those exposed
-in the Garden of the Gods and Red Rocks Park. These rocks are
-intricately folded and faulted, but not metamorphosed. They include
-sandstones, shale, conglomerates, and fossil-bearing limestones. The
-northern end of the range is formed of Precambrian igneous and
-metamorphic rocks.
-
-Just west of La Veta Pass, Sierra Blanca stands as an outpost of the
-range where its continuity is interrupted and its structure changed.
-Huge blocks of Precambrian granite were here pushed upward and thrust
-westward to form a cluster of peaks, several of which are over 14,000
-feet in elevation.
-
-Many prominent rock glaciers are present in the Sangre de Cristo
-Mountains. They are composed of fragments of rock, lubricated by snow
-and ice, creeping almost imperceptibly down the steep flanks of the high
-peaks. One of these rock glaciers can be seen on the slope of Mt. Mestas
-east of La Veta Pass; others are visible from Great Sand Dunes National
-Monument.
-
-South of La Veta Pass, an igneous intrusion along the axis of the range
-changes the character of the Sangre de Cristos. This intrusion is harder
-and has weathered more slowly than the rest of the range, and forms a
-group of prominent peaks known as the Culebra Range.
-
-On the west flank of the Sangre de Cristo Range, east of Villa Grove, a
-prominent iron-mineralized area can be seen. Here the ghost mine of
-Orient marks the site where iron ores were mined in the early days of
-the Colorado Fuel and Iron Company. Nearby, an abrupt terrace along the
-edge of the valley marks the position of a fault. Recent gravels are
-involved in this fault, indicating that movement has taken place here
-within the last few hundred years. A number of hot springs occur along
-the base of the mountains nearby.
-
-The Spanish Peaks, not structurally related to the Sangre de Cristos,
-are visible from La Veta Pass highway. These two peaks represent a pair
-of Cenozoic volcanoes, now deeply eroded and much reduced from their
-former height. Numerous dikes radiating from the bases of these peaks
-represent fissures which were filled with lava as the peaks formed.
-
-The Great Sand Dunes, close to the Sangre de Cristo Mountains north of
-Sierra Blanca, are discussed in Chapter II in the section on the
-Quaternary Period.
-
-[Illustration: Spanish Peaks, south of Colorado Springs and southwest of
-Walsenburg, are twin mountains of volcanic and intrusive rock, the roots
-of Tertiary volcanoes greatly worn down and reshaped by erosion. This
-view looks southeast from near La Veta Pass, on U.S. Highway 160. (Jack
-Rathbone photo)]
-
-
-                    Park Range and Rabbit Ears Range
-
-Bordering the western side of North, Middle, and South Parks, another
-long north-south trending ridge extends from the Wyoming border toward
-the center of Colorado. The northern part of this ridge, forming the
-western boundary of the main mountain mass in the state, is called the
-Park Range.
-
-The structure of the Park Range is similar to that of the Front Range: a
-huge linear corrugation in the earth's crust, bounded by faults. Because
-this area has fewer resistant sedimentary rock layers above the
-Precambrian basement rocks, it is not prominently edged with upturned
-sedimentary layers.
-
-[Illustration: Hahn's Peak, a highly eroded laccolith of rhyolite
-porphyry, lies on the west side of the Park Range, along the eastern
-margin of the Plateau Province. Placer gold was discovered here in 1865,
-but the bedrock source of the gold was never found. (Jack Rathbone
-photo) A geologic section shows the structure of the area.]
-
-  TERTIARY
-  RED BEDS
-  JURASSIC
-  DAKOTA
-  MANCOS
-  DAKOTA
-    Hahn's Peak
-  PORPHYRY
-  MANCOS
-  DAKOTA
-  PORPHYRY
-  JURASSIC
-  RED BEDS
-  RE-CAMBRIAN
-
-[Illustration: Hahn's Peak]
-
-The range is crossed by Rabbit Ears Pass in the north; Gore Pass near
-Kremmling marks its southern end. Mt. Zirkel (12,180 feet) and Flattop
-Mountain (12,118 feet) are the two high points of the range; these and a
-number of unnamed peaks over 11,000 feet high are upward-faulted blocks
-of Precambrian granite.
-
-A rough ridge of volcanic country joins the Park Range with the Front
-Range and effectively separates North Park and Middle Park. This is the
-Rabbit Ears Range, named for a double-eared knob of Precambrian granite
-near Rabbit Ears Pass on U. S. highway 40. Many Tertiary volcanic
-features, including dikes and lava flows, can be seen along this ridge,
-which is also traversed by Colorado state highway 125 between Granby and
-Walden via Willow Creek Pass.
-
-
-                               Gore Range
-
-The Gore Range lies south of Gore Pass, along the Park Range trend. The
-ridge of this range is low for about 15 miles south of Kremmling, but
-the southern part of the range forms a spectacular high cluster of peaks
-with many relatively inaccessible and rugged summits. Many of the peaks
-in this remote country are as yet unnamed; the area has been set aside
-as the Gore Range-Eagle's Nest Wilderness Area. The Colorado River cuts
-directly across the northern part of the Gore Range just west of
-Kremmling, in a steep-walled canyon that is one of the wild scenic spots
-of Colorado.
-
-[Illustration: The southern part of the Gore Range, viewed from the
-east, shows Precambrian granite and metamorphic rocks rising above
-Cretaceous shale hills. The nearly horizontal crest of the range
-probably represents the Precambrian erosion surface. (Jack Rathbone
-photo)]
-
-The Gore Range is, like the Front Range, a faulted anticline with
-Precambrian rocks at its core. The red sedimentary rocks on the west
-flank of the range, visible at Vail Pass and Vail ski area, are of the
-same age as those in Red Rocks Park near Denver and the Garden of the
-Gods near Colorado Springs. Paleozoic rocks are absent on the east flank
-of the range, having been eroded from that area before Mesozoic
-deposition. South of the Colorado River and north of the Wilderness
-Area, Mesozoic rocks extend over the crest of the range.
-
-The south end of the Gore Range is marked by Tenmile Gorge (U. S.
-highway 6 between Frisco and Vail Pass). This gorge is a glacial valley,
-carved during the Ice Age by a glacier more than 1,000 feet thick, along
-a weak faulted zone in the range. A fault surface can be seen on the
-east side of the valley.
-
-From Vail Pass, or from the top of the Vail ski lift, other evidences of
-glaciation can be seen--cirques and U-shaped valleys--testifying to the
-former presence here of many large valley glaciers.
-
-
-                      Tenmile and Mosquito Ranges
-
-With scarcely a break, the Park Range-Gore Range structure continues
-southward into the Tenmile and Mosquito Ranges. These high ridges
-separate South Park from the upper Arkansas Valley, and include a
-cluster of very high peaks, Quandary, Mt. Lincoln, Mt. Democrat, and Mt.
-Bross, all over 14,000 feet in elevation.
-
-Structurally, both the Tenmile Range and the Mosquito Range are highly
-asymmetrical anticlines, gentle on the east and steeply faulted on the
-west. Paleozoic sedimentary rock layers containing many fossils cover
-large portions of the higher parts of these ranges, but two of the
-highest peaks, Mt. Bross and Mt. Lincoln, are capped by the Lincoln
-Porphyry, a Tertiary intrusive, while Quandary Peak is Precambrian
-granite.
-
-These mountains are highly mineralized, and have been extensively
-explored and mined. The Climax Molybdenum Corporation operates an
-especially large mine at Climax, and the New Jersey Zinc Company has a
-large underground mine and mill at Gilman, on the western slopes of
-Tenmile Range.
-
-Buffalo Peaks, two highly eroded volcanic mountains near the south end
-of Mosquito Range, are extrusions of lava and ash which have buried the
-axis of the Mosquito uplift. They are major volcanoes related to a group
-of small volcanic cones near Antero Junction, in South Park.
-
-South of Buffalo Peaks, near Trout Creek Pass, the Mosquito Range loses
-altitude rapidly and merges with the rough country called the Arkansas
-Hills. Cinder cones, dikes, and other evidences of Tertiary volcanic
-activity can be seen between Trout Creek Pass and Salida.
-
-
-                             Sawatch Range
-
-Bordering the Arkansas River valley on the west, the Sawatch Range
-includes Colorado's highest mountain, Mt. Elbert (14,417 feet). With
-several other 14,000-foot summits, this range is the highest in the
-state. One group of peaks, known as the Collegiate Range (Mts. Harvard,
-Yale, Columbia, and Princeton) forms a particularly imposing vista from
-U. S. highway 24 between Trout Creek Pass and Buena Vista. The
-Independence Pass highway (Colorado 82) between Leadville and Aspen
-penetrates the heart of the Sawatch high country.
-
-The Sawatch Range as a whole is about 100 miles long (north to south)
-and 40 miles wide. It is a great faulted anticline intruded by igneous
-rocks. The high area north of Leadville shows that the Sawatch and
-Mosquito Ranges are in reality one huge dome with a slight sag in the
-middle. The ranges, though, are sharply separated topographically by the
-deep valley of the Arkansas River. Precambrian rocks are near the
-surface between the ranges, hidden only by a thin cover of stream
-gravels. Near Leadville, some complexly faulted Paleozoic limestones lie
-in the sag between the ranges.
-
-At Mt. Princeton Hot Springs there is evidence of repeated faulting and
-igneous activity. The rocks are strongly altered by hot water coming to
-the surface through fissures and cracks.
-
-On the west side of the Sawatch range, the old mining towns of Tincup
-and Aspen grew up where limestone and sandstone layers, broken and
-crumpled as the Sawatch Range rose, were mineralized by solutions rich
-in gold and silver. The Aspen Mining District was studied extensively by
-geologists of the U.S. Geological Survey, and their maps show almost
-unbelievable complexity in the faulting of the rock layers which exist
-there.
-
-The north end of the Sawatch Range plunges under shales and sandstones
-along the Eagle River east of Wolcott. Gypsum in the sediments here has
-acted like putty: the layers of rock in which it was deposited have
-become peculiarly crumpled, making the area along the Eagle River
-(visible from U. S. Interstate 70) between Avon and Edwards hummocky and
-irregular. Vegetation is unusually sparse here because of gypsum in the
-soil.
-
-About midway between Edwards and Wolcott, the Eagle River suddenly
-changes direction and flows northward for about a mile before resuming
-its former westward course. This sudden change is caused by a sharp
-north-south fold in the sedimentary rocks on the northwestern flank of
-the Sawatch Range. A magnificent series of roadcut and hillside
-exposures along the highway here illustrates the close relation between
-rock layers and river course. Within about a mile, the highway cuts
-through rocks of Pennsylanian, Permian, Triassic, Jurassic, and
-Cretaceous age, spanning a geologic time interval of more than 200
-million years.
-
-The south end of the Sawatch Range, at Monarch Pass, contains steeply
-dipping Late Paleozoic limestones and coal beds. The coal has been mined
-on a small scale; the limestone is now quarried for use as a flux in
-iron smelters at Pueblo.
-
-  [Illustration: The area below the Aspen Mountain ski lift is highly
-     complex geologically. It is particularly well known because of
-       extensive prospecting and mining activity in the region.]
-
-
-                  Elk Mountains and West Elk Mountains
-
-The Elk Mountains and West Elk Mountains appear to be westward
-continuations of the Sawatch Range. Structurally, however, they are not
-faulted anticlines like most of the other ranges in Colorado, but are
-composed of a series of layers of Paleozoic sediments thrust westward
-over one another. These rocks, often crumpled and highly metamorphosed,
-are cut by numerous sills, dikes, and other intrusions, many of which
-have caused mineral enrichment locally.
-
-At Maroon Bells, in the canyon of Maroon Creek, and at Redstone on the
-Crystal River, these metamorphosed sediments are well exposed. Here, red
-sandstones and shales have been altered to quartzites and slate. At
-Marble, metamorphism of a thick limestone bed has produced white marble
-of great beauty, known as Yule Marble. This decorative stone was
-quarried extensively until about 1940. It was used in the Lincoln
-Memorial and several other monumental structures; in the town of Marble
-it has been used for the doorsteps of log cabins! The largest block
-quarried, for the Tomb of the Unknown Soldier in Arlington National
-Cemetery, measured 14 by 7.4 by 6 feet in the rough, and weighed 56
-tons.
-
-[Illustration: Mt. Sopris, south of Glenwood Springs, is an igneous
-intrusion. (Jack Rathbone photo)]
-
-Crested Butte, at the south end of the Elk Mountains, is a small
-intrusive igneous mass called a _laccolith_. Hard and resistant to
-erosion, it stands over 2,000 feet above the adjacent valley floor.
-
-
-                           San Juan Mountains
-
-The San Juan Mountains are the most extensive range in Colorado, and
-also the most heterogeneous. Covering more than 10,000 square miles of
-the southwestern part of the state, these mountains are formed mostly of
-Tertiary volcanic rocks, the result of repeated outpourings of lava and
-ash from a cluster of volcanoes. Water-laid gravels composed of volcanic
-sand and pebbles are interlayered with basalts and ash beds; the total
-thickness of these beds reaches many thousands of feet.
-
-[Illustration: The mining town of Ouray, now also a tourist haven and
-summer resort, nestles below Pennsylvanian sedimentary rocks of Ouray
-Canyon. At the north end at town can be seen the Ouray Hot Springs
-swimming pool. Gold, silver, lead, and zinc are still mined in this
-area. (Jack Rathbone photo)]
-
-The widespread volcanic activity which formed most of the range began in
-mid-Tertiary time and continued for several million years. A few
-Quaternary volcanic flows are known in the region, but there is no
-active volcanism there at present.
-
-The western side of the main range, including some of the highest peaks,
-consists primarily of uplifted and faulted Paleozoic sedimentary layers.
-These layers, highly dissected by erosion, can be seen near Ouray, at
-Molas Lake, and at Durango. Large patches of Precambrian granite and
-metamorphic rocks protrude through the sediments, as in the Needle
-Mountains; they indicate that this part of the range is a faulted
-anticline like many other Colorado ranges.
-
-Early Cenozoic glacial deposits occur in some parts of the San Juans.
-These are unusual features, as glaciation of this age is unknown
-elsewhere in Colorado.
-
-Three small ranges rise just west of the San Juans: the San Miguel,
-Rico, and La Plata Mountains. Each consists of several small masses of
-Tertiary igneous rock intruded into Paleozoic conglomerates, shales, and
-limestones.
-
-Mineralization has been intense in the San Juans; most of it took place
-during the Late Tertiary volcanic period. Rich veins penetrate
-Precambrian gneiss and granite, and Paleozoic limestones are often
-enriched also. Several mines are still active near Ouray, Silverton,
-Telluride, and Rico.
-
-
-                            Uinta Mountains
-
-The eastern end of Utah's Uinta Mountains extends into Colorado. Unlike
-other ranges in Colorado, these mountains trend east-west. Structurally,
-the range is a faulted anticline. It is quite asymmetrical, however, and
-is tilted and folded upward on the south, and overturned or
-thrust-faulted on the north. Steeply dipping Mesozoic and Paleozoic
-sediments on the south side of the range, sparsely vegetated and often
-thrown into spectacular folds, are a prominent feature of northwest
-Colorado scenery.
-
-In Colorado the crest of the Uintas reaches an elevation of about 8,500
-feet. It consists of Precambrian rocks, but these are not the igneous
-and metamorphic rocks that characterize the Precambrian core of other
-Colorado mountains. They are easily recognized as sediments--dark red
-conglomerates, sandstones, and mudstones--virtually unmetamorphosed
-though they were deposited nearly a billion years ago. Called the Uinta
-Mountain Formation, these rocks are found only in this part of Colorado
-and adjacent areas of Utah. They are probably related to similar
-Precambrian rocks found in Montana and Canada.
-
-At the east end of the Uintas two isolated uplifts, Cross Mountain and
-Juniper Mountain, are faulted blocks of Paleozoic rocks standing like
-islands in a sea of Cenozoic valley fill. They are the last outposts of
-the Uinta anticlinal pattern as it wanes toward the southeast.
-
-Dinosaur National Monument, a Uinta Mountain tourist attraction,
-encompasses a vast area of wilderness on both sides of the Yampa River
-in Colorado. Here many of the features of the east end of the Uinta
-Mountain structure can be seen. A unique display of the world's largest
-fossils can be visited in the Utah portion of the Monument.
-
-[Illustration: At their confluence in Dinosaur National Monument, the
-Yampa and Green Rivers have carved Late Paleozoic sandstone into the
-precipitous cliffs of Steamboat Rock. (William C. Bradley photo)]
-
-
-                              THE PLATEAUS
-
-The western quarter of Colorado is a region of flat-lying Paleozoic,
-Mesozoic, and Cenozoic sedimentary rocks which have not been bent up
-into mountains except in a few isolated instances. This area lies more
-than a mile above sea level, however, and because of the gradient such
-an elevation affords, it is deeply sculptured. The Colorado River and
-its tributaries have sliced into the plateau surface, separating it into
-many isolated tablelands or mesas. Some are capped with sedimentary
-rock, others with Tertiary basalt.
-
-[Illustration: The Grand Hogback is a good example of the type of
-geologic structure known as a _monocline_. The hogback ridge is formed
-by differential erosion, where soft layers wear away more easily than
-hard layers.]
-
-Simple folds and faults have given the mesas different elevations. Thus
-the average elevation of the White River Plateau is 11,000 feet, that of
-the Roan Plateau 9,500 feet, and that of Mesa Verde only 7,000 feet.
-West of Durango the plateaus dip gently southward, as can be seen at
-Mesa Verde. Igneous intrusions and extrusions have altered plateau
-topography in some areas. West of Mesa Verde, for instance, an intrusive
-stock forms a prominent dome in the Southern Ute Indian Reservation.
-
-West of the northern Colorado mountains, and north and west of the White
-River Plateau, a rolling upland extends from Colorado into Utah and
-Wyoming. It is interrupted by the Uinta Mountains and a number of
-smaller related uplifts such as Juniper Mountain and Cross Mountain.
-South of the Uinta axis the area is known as the Uinta Basin.
-
-The northern part of this area is structurally the south edge of the
-Green River or Washakie Basin in Wyoming. The Rangely anticline, in the
-northeastern corner of the Uinta Basin, is one of Colorado's richest oil
-fields; it is discussed in Chapter III.
-
-Although surfaced with much younger sediments than the rest of the
-Plateau Province, this area is structurally similar. On the whole,
-sedimentary layers are relatively flat-lying, and where they are
-uplifted they are deeply sculptured by streams and rivers. The
-sedimentary rocks in this region contain uranium and placer gold in
-addition to great oil and gas deposits. The southeastern part of the
-Uinta Basin, usually called the Piceance Basin, is the site of a great
-deposit of oil shale (see Chapter III). The term "basin" may here seem
-unusual to the casual observer, for the oil shales occur on the Roan
-Plateau at places well over 10,000 feet in elevation. However, the
-entire region was basin-like--lower than the surrounding ranges--for
-many millions of years, and during Tertiary time thousands of feet of
-valley and lake deposits were laid down in it.
-
-The White River Plateau, north of Glenwood Springs, is composed of
-almost horizontal Paleozoic sedimentary rocks that fold downward sharply
-along its south and west edges. The fold is 135 miles long and is
-clearly marked by the Grand Hogback, the eroded edge of hard Cretaceous
-and early Cenozoic rock layers. Shale and coaly layers involved in the
-same fold have eroded more readily, leaving the resistant sandstone as a
-prominent ridge.
-
-The Uncompahgre Plateau, southwest of Grand Junction, is structurally
-very like the White River Plateau. Its features can be well observed in
-Colorado National Monument. It has been elevated several thousand feet
-more than the Book Cliffs and Grand Valley areas to the north. Sharp
-folding and faulting near the Colorado River at the north boundary of
-the National Monument show that differential movement between the two
-regions was sharp and localized.
-
-A series of northwest-trending anticlines along the Utah border in
-southwestern Colorado are of special geologic interest. They represent
-peculiar structures in which salt and gypsum have played a major part.
-These minerals were deposited in thick layers late in Paleozoic time;
-subsequently they were covered by thousands of feet of sand, shale, and
-limestone. Because of their low density and high plasticity they have
-since crept upward along weak spots in the overlying sediments, often
-contorting these rocks as they moved. Breaking through to the surface,
-the salt and some of the gypsum washed away more rapidly than the
-surrounding rock, leaving long faulted troughs such as Gypsum Valley and
-Paradox Valley. In most of these structures the gypsum can still be
-seen, although the more soluble salt has eroded away. Oil wells in this
-part of Colorado and in adjacent parts of southeast Utah have penetrated
-thousands of feet of evaporites, including pure salt, gypsum, and
-potassium salts.
-
-[Illustration: In the arid climate of the Colorado Plateaus, ledges of
-well-cemented sandstone stand out sharply from slopes of shale or
-mudstone. The Mesa Verde and Mancos Formations, Cretaceous in age, form
-the slopes and top of Mt. Garfield near Grand Junction (Jack Rathbone
-photo)]
-
-The peculiar weathering characteristics of flat-lying sedimentary rocks
-in an arid climate are well demonstrated in Colorado National Monument,
-Mesa Verde National Park, and elsewhere in the Plateau Province. Those
-fortunate enough to make a river trip through the Yampa or Green River
-Canyons in northwestern Colorado or on the rivers of eastern Utah and
-northern Arizona will have an unusually fine opportunity to observe
-close at hand the weathering and erosion in this area. Resistant
-sandstone and limestone layers break into sheer cliffs, often many
-hundreds of feet high, while the softer layers of mudstone and shale
-form gentle slopes and terraces. Vast arching caves often develop where
-resistant layers are undermined--caves sometimes containing ancient
-Indian dwellings.
-
-
-
-
-                                   II
-                      Geologic History of Colorado
-
-
-Astronomical and geologic evidence indicates that the earth was probably
-formed as an immense blob of molten rock, held together and shaped into
-spherical form by its own gravity. It may even have been gaseous at
-first, cooling gradually to a molten state. After hundreds of millions
-of years it became cool enough to begin to harden.
-
-As the surface cooled, a crust formed, and lay like a blanket over the
-liquid mass beneath. Convection currents--large-scale boiling
-movements--stirred the molten interior, thrust portions of the crust
-upward, and sucked other portions downward to be remelted. Some of the
-lighter components, such as compounds of silicon and oxygen and
-hydrogen, accumulated on the surface like froth on a kettle: the
-continents were born. With further cooling the atmosphere and oceans
-came into being.
-
-Something can be told of the age of the continents. Measurements of
-radioactivity in the most ancient rocks exposed at the surface today
-indicate that the oldest known continental rock is between three and
-four billion years old. Since the continents were formed, they have been
-bent and shifted and broken by the pressures exerted against them by
-convection in the interior. Parts of the continents at times have been
-submerged below the level of the sea, even as they are today. Other
-portions, lifted above sea level, were immediately attacked by the
-wearing-down processes of erosion. The battle between mountain-building
-forces and erosion has been a continuous one ever since the crust was
-formed. Even now earthquakes give testimony to continued crustal
-movement, storms still sweep across the continents and wash mud and
-frost-loosened rocks into churning torrents, rivers still deposit great
-floodplains and deltas, sediments accumulate slowly but persistently
-upon the bottoms of the seas.
-
-
-                            PRECAMBRIAN ERA
-
-Only part of the earth's very early history is represented in Colorado,
-where the oldest known rocks are the gneisses and schists of the Idaho
-Springs Formation, at least 1,800,000,000 years old. These rocks appear
-to be the remains of ancient sediments, folded and metamorphosed into
-vast mountain areas long before recognizable life inhabited the earth.
-
-Precambrian rocks in Colorado are on the whole very poorly known. They
-have, however, been studied in detail in the Front Range west of Denver
-and Boulder, where they have been intensively explored for valuable
-minerals. The lack of fossils in the oldest rocks makes their close
-correlation difficult, but from studies of radioactive minerals
-contained in these rocks, and of the relationships of the rock units
-themselves, we can list them in order of their relative ages.
-
-Note that the rock sequence given below reads chronologically from
-bottom to top--a logical pattern in geology since younger rocks,
-especially those of sedimentary origin, normally lie above older ones.
-Recent studies indicate that the sequence may be much more complex than
-shown here.
-
-   (youngest) Silver Plume Granite:  light pinkish gray, fine-grained
-                                     granite.
-                Pikes Peak Granite:  pink, coarse-grained granite.
-             Boulder Creek Granite:  dark gray, faintly banded
-                                     granodiorite.
-              Coal Creek Quartzite:  light gray quartzite with grains
-                                     ranging in size from fine sand to
-                                     boulders, with some interbedded
-                                     schist.
-        Swandyke Hornblende Gneiss:  dark gray to black, strongly banded
-                                     gneiss.
-  (oldest) Idaho Springs Formation:  gray to black schist and gneiss.
-
-From a sequence such as this, it is possible to reconstruct some
-features of Colorado's early history. The first chapter of which we have
-a record is the deposition of the Idaho Springs Formation, probably as
-an accumulation of mud, sand, and limy mud in an ancient sea. Swandyke
-deposition followed--the sediments were iron-rich, perhaps derived from
-ancient volcanic materials. The original Coal Creek sediments were sands
-and gravels, some of them quite coarse and therefore indicative of
-near-shore deposition. The schist layers suggest that muds must have
-been deposited also.
-
-[Illustration: South of Ouray, Cambrian sandstones of the Sawatch
-Formation lie almost horizontally across the vertical Precambrian
-metamorphic rocks. (Jack Rathbone photo)]
-
-Together these three formations represent some 40,000 feet of
-sedimentary layers. Deposition of such a great thickness of mud, sand,
-and lime must have taken a very long period of time. Details of the
-geography of the continent during that period have of course been
-obscured by later events, when these rocks were subjected to repeated
-uplift, crumpling, folding, various degrees of remelting and
-recrystallization, and erosion. But the ancient sediments must have been
-derived from even more ancient highlands, either folded and faulted
-mountains or volcanoes, and probably were deposited under water in broad
-expanses of sea that covered portions of the continent.
-
-[Illustration: Geologic map of Colorado. Geologic maps show the age of
-rocks appearing at the surface, disregarding soil cover. A more detailed
-geologic map of Colorado may be obtained from the U.S. Geological Survey
-at the Federal Center in Denver.]
-
-  PRECAMBRIAN
-  PALEOZOIC
-  MESOZOIC
-  CENOZOIC SEDIMENTS
-  CENOZOIC VOLCANICS
-    Yampa River
-    White River
-    Fort Collins
-    South Platte River
-    Glenwood Springs
-    Denver
-    Colorado River
-    Grand Junction
-    Aspen
-    Gunnison River
-    Colorado Springs
-    Gunnison
-    Salida
-    Dolores River
-    Rio Grande
-    Arkansas River
-    La Junta
-    Walsenburg
-    Alamosa
-    Durango
-
-The Boulder Creek, Pikes Peak, and Silver Plume Granites cut through the
-metamorphic rocks, and are therefore younger. They represent pulses of
-molten rock forced upward from deep within the crust, probably during
-three separate episodes of mountain building. As each set of mountains
-was formed, it was worn down, perhaps to low rolling hills, perhaps to
-flat plains almost at sea level, and partially or entirely covered with
-thick layers of sediment. Each time, another mountain building episode
-followed, with new intrusions of granite and new metamorphism of the
-pre-existing rocks.
-
-Each succeeding period of metamorphism and mountain building further
-changed the nature of the rocks involved, complicating the patterns of
-folding and faulting, adding recrystallization to recrystallization,
-until the oldest of the rocks bore little trace of their original
-sedimentary nature. In general, the rocks that are oldest were most
-altered by the repeated metamorphism, while the younger rocks were less
-altered.
-
-[Illustration: The Black Canyon of the Gunnison River is one of the
-state's deep and spectacular chasms. Canyon walls are of Precambrian
-gneiss intruded by many dikes and highly fractured by later uplifts. The
-flat upper surface of the Precambrian rocks represents an ancient plain
-on which, during Jurassic time, the dinosaur-bearing Morrison Formation
-was deposited. (John Chronic photo)]
-
-The Precambrian Era ended with a long period of erosion, a period known
-to geologists as the Lipalian Interval. During this time, over almost
-the entire world there was no mountain building. The land lay sleeping,
-subject only to the forces of erosion. The last mountains were flattened
-nearly to sea level. Slow, sluggish streams and rivers carried sand and
-mud toward the oceans--oceans in which perhaps primitive, soft-bodied
-organisms, with no hard parts to be preserved as fossils, were beginning
-to evolve.
-
-On the continents, the time of intense metamorphism was over; most rocks
-of later eras are preserved today in pretty much their original state.
-The boundary between the Precambrian and later rocks is normally well
-defined. It is visible at many places in Colorado: in Williams Canyon
-near Colorado Springs, in Glenwood Canyon, near Red Rocks west of
-Denver, just west of La Veta Pass, at the top of Royal Gorge and the
-Black Canyon of the Gunnison. At most of these localities it is a
-smoothly beveled surface, with highly contorted Precambrian rocks below
-it and flat-lying Paleozoic sediments above it. Near Red Rocks and La
-Veta Pass, the same relationship prevails, but the entire contact, and
-the rocks above and below it, have been steeply tilted by the uplift of
-the present mountains.
-
-In portions of western North America, deposition late in Precambrian
-time has left a series of flat-lying rocks between the contorted
-Precambrian and later Paleozoic sediments. These rocks can be seen in
-northwestern Colorado, where they form the dark red sedimentary core of
-the Uinta Mountains.
-
-
-                             PALEOZOIC ERA
-
-Geologists have divided the second great era of geologic time into units
-called Periods. The rocks deposited during a Period are called Systems,
-but more often than not it is convenient to discuss them in terms of
-easily recognized units of rock, called Formations. Formations are named
-after areas in which they are well exposed.
-
-The stratigraphic column given in Chapter I shows the Periods and
-Systems in their correct order, and gives the age in years for each, as
-determined by radioactivity methods. As you read, refer as often as
-necessary to this column.
-
-The geologic map on page 35 will help you locate areas where the rocks
-discussed in the text are exposed, and will greatly facilitate your
-understanding of the geology of the state.
-
-[Illustration: The Cambrian Sawatch Sandstone lies almost horizontally
-on Precambrian granite in Glenwood Canyon. In the foreground is the
-Colorado River. (Jack Rathbone photo)]
-
-
-                            Cambrian Period
-                      (500-570 million years ago)
-
-The first fossiliferous rocks in Colorado were deposited during the
-Cambrian Period, at a time when over much of the world the seas were
-creeping in across wide, level plains formed during the Lipalian
-Interval. Colorado was not covered by these seas until quite late in the
-Cambrian Period. Beach deposits progressively younger in age suggest
-that the sea invaded from the west, and spread slowly eastward,
-inundating most of the central part of the state but not the extreme
-north or south.
-
-The beach deposits, now called the Sawatch Sandstone because they are
-well exposed in the Sawatch Range, are composed mostly of fine quartz
-sand. They are colored with glauconite, a green mineral, and hematite, a
-dark red mineral, so that the rock has a variegated appearance. The post
-office at Manitou is built of this red and green rock, and good
-exposures of it exist in Williams Canyon near Manitou, along U. S.
-Highway 24 northwest of Manitou, near Red Cliff and Minturn, and in
-Glenwood Canyon.
-
-The sea which crept over Colorado at this time contained small
-conical-shelled mollusks, brachiopods, and trilobites. Their shells can
-occasionally be found in Cambrian rocks in Williams Canyon and in the
-Sawatch and Mosquito Ranges. At two localities unusual fossils called
-graptolites have been found in thin Upper Cambrian shales overlying the
-Sawatch Sandstone.
-
-[Illustration: These fossils can occasionally be found in Cambrian rocks
-in central Colorado.]
-
-
-                           Ordovician Period
-                      (440-500 million years ago)
-
-The sea deepened and widened as the Ordovician Period began, and a
-series of limestones and dolomites was deposited, either on top of the
-Sawatch Sandstone or, where the Sawatch had not been deposited, directly
-on the Precambrian. These rocks are now called the Manitou Formation.
-
-The fossils in these rocks are much more varied than those in the
-Sawatch Sandstone: snails, echinoderms, sponges, cephalopods,
-brachiopods, and trilobites are common. The Ordovician sea must have
-teemed with life, as many rocks deposited at this time are more than
-half composed of animal remains. In addition to hard-shelled animals
-which formed fossils, there were probably abundant soft-bodied animals
-such as jellyfish and worms, which left no record of their presence.
-
-After deposition of the Manitou Formation, the seas receded slightly. A
-new series of sands was deposited above the Manitou in central Colorado.
-These now form the Harding Sandstone, a formation of unusual interest
-because it contains remains of the earth's earliest known vertebrates,
-primitive jawless fish called Agnathids. In places in the Harding
-Sandstone there are dense accumulations of the tiny polygonal armor
-plates from these fish. Although no whole fish have been found, we can
-reconstruct their appearance by comparing individual plates or groups of
-plates with later, better known relatives.
-
-Also present in great quantities in the Harding Sandstone are conodonts,
-peculiar tiny brown tooth-like fossils. Relationships of the conodonts
-are unknown; they may be parts of the Agnathids, or perhaps they
-represent some entirely different group of animals, with no living
-relatives.
-
-After deposition of the sands of the Harding Sandstone, the sea deepened
-locally and the Fremont Limestone, a massive gray crystalline limestone
-containing many marine fossils, was deposited. Mollusks (some quite
-large), brachiopods, and corals contributed their shells to the Fremont
-Limestone. The chain coral _Catenipora_ and the horn coral
-_Streptelasma_ may often be used to identify the formation.
-
-The Fremont Limestone was deposited very late in the Ordovician Period.
-Probably the seas were much more extensive then than present deposits
-indicate; subsequent erosion has at several times erased the evidence in
-uplifted areas.
-
-[Illustration: These Ordovician fossils can be found in the Manitou
-Formation in the Colorado Springs area.]
-
-[Illustration: The earliest known fish remains come from the Ordovician
-Harding Sandstone of central Colorado. These fragments of the protective
-plates have been magnified about five times.]
-
-[Illustration: Corals and coral-like organisms occur in the Ordovician
-Fremont Limestone.]
-
-
-                            Silurian Period
-                      (400-440 million years ago)
-
-Until very recently, no Silurian rocks or fossils were known in
-Colorado, and it was thought that seas did not extend into the state
-during this period. However, a few years ago good Silurian corals and
-brachiopods were discovered near the northern edge of the state. They
-occur in broken blocks and patches of Silurian limestone, mingled with
-blocks of other sedimentary rocks and, oddly enough, with volcanic
-material.
-
-What seems to have happened here is that sedimentary layers of Silurian
-age _were_ present over northern Colorado at one time. During some
-subsequent period of volcanism, volcanic lavas penetrated these
-sediments from below. Near the volcanic tubes, broken, angular fragments
-of the surrounding sedimentary rocks were sometimes carried upward or
-downward by the motion of the lava.
-
-Much later, both the volcanic outpourings (if the lavas ever reached the
-surface) and the sediments were stripped away by erosion, probably at a
-time when mountains were rising in the area. Only the deep portions of
-the tubes that fed the volcanoes were preserved. These tubes are called
-diatremes, and thanks to the blocks of sedimentary rock in them we know
-that there were indeed seas in Colorado during Silurian time, seas
-containing the abundant life of a shallow marine environment very much
-like that existing at the same time in Illinois, Iowa, and Indiana.
-
-
-                            Devonian Period
-                      (350-400 million years ago)
-
-As far as we know now, Colorado was just a little above sea level during
-most of Devonian time. Early and Middle Devonian deposits are lacking.
-Late in the period, however, Colorado was widely inundated once more.
-Embayments of a western sea covered most of the central part of the
-state and an area in southwestern Colorado around Ouray.
-
-Deposits formed in these embayments have been given several names.
-Chaffee Formation is the name most commonly used in central Colorado;
-Ouray Formation identifies rocks of the same age in southwest Colorado.
-The Chaffee Formation has been subdivided into two well defined units,
-the Parting Sandstone or Quartzite, and the Dyer Dolomite or Limestone.
-Many ore deposits are associated with these rock units--notably deposits
-of lead and zinc. The Parting Sandstone is frequently so well cemented
-with silica that it is actually a quartzite; thin shale beds or
-"partings" make it easy to recognize. It frequently contains remains of
-fossil fish and distinctive beds of algae.
-
-The Dyer Dolomite contains brachiopods and bryozoans, mollusks and
-corals. Some of the best fossil hunting in Colorado is in Dyer beds
-around the White River Plateau, where the fossils frequently weather out
-of the rock as almost perfect specimens.
-
-[Illustration: These Devonian brachiopods come from the White River
-Plateau in western Colorado.]
-
-
-                          Mississippian Period
-                      (310-350 million years ago)
-
-The sea continued to cover most of Colorado after the end of the
-Devonian Period, well into Mississippian time. Mississippian rocks are
-characteristically thick, massive gray limestones collectively called
-the Leadville Limestone. This unit is well known as the host rock for
-many Colorado ore deposits, notably those around the town of Leadville.
-
-During Mississippian time the western sea, warm and rich in organisms,
-covered much of North America. Brachiopods and corals flourished, as did
-many other forms of life. The seas during part of this time extended
-completely across Colorado to merge with seas that covered the
-midwestern part of the United States.
-
-Over all this vast area, as well as southwest into Arizona, the gray,
-massive, fossiliferous Mississippian limestone is remarkably uniform and
-easily recognized, although it is called by different names in different
-areas.
-
-Late in Mississippian time, the Colorado area rose slightly and the sea
-in which the Leadville Limestone was deposited receded. An interval of
-erosion followed. The surface of the limestone was dissolved and pitted,
-tunnels and caves formed where running water etched deep into the rock,
-and a reddish soil formed on the surface and in the hollows. This
-portion of the limestone, which in some places also contains pebbles of
-chert, is named the Molas Formation. Part of the Molas may be
-Pennsylvanian in age.
-
-[Illustration: Mississippian fossils from western Colorado show that
-seas covered much of the state about 330 million years ago.]
-
-
-                          Pennsylvanian Period
-                      (270-310 million years ago)
-
-As the Pennsylvanian Period began, the Colorado area continued to rise.
-Earliest deposits of this age are fine-grained black shales and
-sands--the Glen Eyrie Formation along the southern Front Range and the
-Belden Formation in west central Colorado. Then, through millions of
-years, mountain-building took place. Some areas rose more than others,
-so that formerly flat-lying marine sediments were bent and broken, and a
-series of high mountain ridges and deep basins were formed. Geologists
-sometimes call these the Ancestral Rocky Mountains.
-
-Although the pattern of the mountains changed repeatedly, the Ancestral
-Rockies consisted principally of two large ranges. One range roughly
-paralleled the present Front Range, but lay thirty to fifty miles
-further west. The other extended from the San Luis Valley northwest
-toward Colorado National Monument, including the area around the Black
-Canyon of the Gunnison and the present Uncompahgre Plateau. Coarse
-sediments washed off both sides of both ranges, and accumulated as
-alluvial fans and valley fill along the mountain margins. These exist
-today as the Fountain Formation of the eastern Front Range, the Minturn
-Formation between the ancient uplifts, and the Hermosa Formation west of
-the western uplift.
-
-[Illustration: This paleogeographic map reflects the distribution of
-land and sea during the early part of the Pennsylvanian Period and shows
-where coarse sediments derived from the Ancestral Rockies were
-deposited.]
-
-  FOUNTAIN FORMATION
-  MINTURN FORMATION
-  HERMOSA FORMATION
-
-[Illustration: West of Denver, the main line of the Denver & Rio Grande
-Railroad tunnels beneath steeply dipping sandstones and conglomerates of
-the Fountain Formation. (Jack Rathbone photo)]
-
-[Illustration: Corals, brachiopods, and fusulinid Foraminifurida can be
-found in the Pennsylvanian Minturn Formation at many places in the
-Mountain and Plateau Provinces.]
-
-[Illustration: In western Colorado, where vegetation is sparse, rock
-structures are clearly defined. This photograph shows beds of the
-Pennsylvanian Minturn Formation sharply folded, probably as a result of
-the deformation of gypsum in underlying layers. (Jack Rathbone photo)]
-
-In the Flatirons near Boulder, Red Rocks Park near Denver, and the
-Garden of the Gods near Colorado Springs we see well exposed examples of
-the Fountain Formation. The Minturn Formation is visible along the Eagle
-River west of Wolcott, and along Gore Creek near Vail. The Hermosa
-Formation forms striking red cliffs north of Durango. In the Sangre de
-Cristo Mountains area, exceptionally great and rapid deposition took
-place, and the Minturn Formation is very thick.
-
-In west central Colorado, near the towns of Eagle and Gypsum, a large
-basin formed. In it, gypsum and other salts were deposited as arms of
-the sea were cut off from the main marine area. The unusual appearance
-of the hills along the Eagle River, especially north of U. S. Highway
-24, is caused by the presence of gypsum in the bedrock.
-
-In a similar manner, the Paradox Basin was formed in southwestern
-Colorado. Thousands of feet of gypsum, salt, and potash were deposited
-here, probably also precipitated in restricted arms of the sea. These
-minerals, the so-called evaporites, have since significantly controlled
-development of the landscape in Gypsum Valley and other parts of this
-region. (See The Plateaus in Chapter I and the section on Gypsum in
-Chapter III).
-
-Between the mountain masses and their surrounding alluvial deposits,
-shallow seas repeatedly invaded the lowland areas of the state. Marine
-fossils in some parts of the Minturn Formation bear witness to as many
-as twenty marine cycles. Strangely, the Pennsylvanian Period appears to
-have been cyclical in other parts of the United States as well, for
-marine sediments are found alternating with nonmarine sediments in
-Pennsylvania, Illinois, Kansas, Nebraska, and New Mexico. In middle
-Pennsylvanian time, general uplift occurred in Colorado, and almost the
-entire state was above sea level for the rest of the period.
-
-
-                             Permian Period
-                      (223-270 million years ago)
-
-By the end of the Pennsylvanian Period, the mountains of the Ancestral
-Rockies had been almost entirely removed by erosion, and the deep basins
-were filled with sediments. Colorado was once more a great plain,
-sloping gently to the northeast. In eastern Colorado, a shallow sea
-gradually dried up, leaving some thin limestone and gypsum beds along
-its margin. The western shore of this sea was edged with beaches and
-sand dunes, preserved as the Lyons Sandstone. The buildings of the
-University of Colorado, as well as many homes and other structures in
-the Boulder-Denver area, are faced with this beautiful salmon-colored
-sandstone.
-
-[Illustration: Balanced Rock, in the Garden of the Gods northwest of
-Colorado Springs, is an erosional remnant of iron-rich conglomerate and
-sandstone. It remains while the rest of the surrounding layers are gone
-because it is harder and more completely cemented together by silica.
-The rock is part of the Late Paleozoic Fountain Formation. (John Chronic
-photo)]
-
-In the western part of the state, Permian deposits consist mostly of
-shales and sandstones. The red color of these rocks, and the complete
-absence of fossils in them, suggest that the environment in which they
-were deposited was not marine, but was a vast, level mudflat subject to
-alternating wet and dry periods. The shales and sandstones collectively
-are called the Maroon Formation, named for Maroon Bells, near Aspen,
-where they are dramatically exposed in the mountain cliffs.
-
-[Illustration: Tracks of Permian reptiles called _Laoporus
-coloradoensis_ occur in the Lyons Sandstone near Lyons. These are about
-life size.]
-
-During part of Permian time, a shallow sea extended from Idaho, Utah,
-and Wyoming into the northwest corner of Colorado. In this sea was
-deposited the Phosphoria Formation, a highly phosphatic limestone
-containing only rare, poorly preserved molluscan fossils.
-
-As the Paleozoic Era ended, Colorado was still flat and low-lying. By
-this time land plants and animals had evolved, but if vegetation grew in
-the Colorado area, or animals roamed it, they left few fossil remains.
-Tracks of early reptiles have been found in the Lyons Sandstone. Dune
-sandstones here and in adjacent areas suggest that desert conditions may
-have prevailed, in which case Colorado would have been very similar,
-scenically and climatically, to Sahara regions today.
-
-[Illustration: Dark red Pennsylvanian and Permian conglomerates form the
-Flatirons that overlook the University of Colorado campus at Boulder.
-University buildings are faced with Permian Lyons Sandstone quarried
-along the foothills of the northern Front Range. (University of Colorado
-photo)]
-
-
-                              MESOZOIC ERA
-
-The Mesozoic Era, popularly known as the Age of Reptiles or Age of
-Dinosaurs, is divided into three periods. The climate of the entire
-earth appears to have been warmer then than it is at present, perhaps
-because of a different distribution of land and sea areas, or because
-continental areas were not as high and mountainous as they are just now.
-Colorado was a rather low land area for most of the first two Mesozoic
-periods; then a vast sea covered the entire state for the remainder of
-the era.
-
-[Illustration: The pink cliffs of Colorado National Monument are made of
-Wingate and Entrada Sandstones. Underlying them, in the valley bottom,
-Chinle shales form steep red slopes. (William C. Bradley photo)]
-
-
-                            Triassic Period
-                      (180-225 million years ago)
-
-Saharan conditions continued to prevail in western North America during
-the early part of the Mesozoic Era. In central Colorado, the lowest
-Mesozoic deposits are the Triassic Lykins Formation, a series of soft,
-bright red sandstones and shales. Where the Lykins is exposed along the
-Front Range, its bright red color identifies it. Because of its
-softness, it is often less prominent than adjacent rock layers in the
-mountain foothills. The Lykins Formation includes some evaporites,
-apparently derived from Permian evaporites washed into the Triassic
-ponds and lakes which existed occasionally in this region.
-
-Over almost the entire state, the rocks deposited at this time are very
-similar. Formation names may differ--Lykins, Moenkopi, Chinle, Ankareh,
-Wingate--but the rocks are almost universally fine-grained sandstones
-and shales with a red or pink color. They represent ancient coastal
-plain, dune, or delta deposits. Toward the western edge of the state
-they coarsen, and contain layers of conglomerates similar to the
-Triassic conglomerates of northern Arizona and Utah. These suggest that
-mountain-building was taking place west of here at that time.
-
-There are virtually no fossils known from Triassic rocks in Colorado,
-although some fossil palm fronds have been found west of the San Juan
-Mountains, in the southwestern corner of the state.
-
-
-                            Jurassic Period
-                      (135-180 million years ago)
-
-During the Jurassic Period, Colorado was still a low, flat desert area
-with intermittent streams flowing eastward over the surface of older
-sediments. The Navajo Sandstone, formed from dune sands, was deposited
-in the western part of the state. Streams flowing eastward from Utah
-brought fine sediments--silts and muds--to western Colorado, forming
-what is now the Carmel Formation. Near Canon City, coarse gravels bear
-witness to local uplift in Jurassic time. Both these gravels and the
-Carmel Formation were overlain by more dune sands, now hardened into the
-Entrada Sandstone.
-
-In Late Jurassic time the Colorado area, which had been predominantly
-desert since Permian time, appears finally to have been submerged once
-more. Fine calcareous muds of the Curtis Formation, containing
-ammonites, belemnites, and other marine shellfish, show us that a
-shallow sea transgressed from the west over the wind-blown sands. This
-sea was, geologically speaking, of short duration--only a few million
-years. Bounded on almost all sides by desert, it seems to have dried up,
-depositing the gypsum that is now present in a thin layer along the
-Front Range between Denver and Canon City in the Ralston Formation.
-
-At about this time, however, the climate underwent a major change.
-Deposits above the Ralston indicate an increasingly moist environment,
-the environment in which the Morrison Formation was deposited over most
-of Colorado and parts of the adjacent states of Kansas, Arizona, Utah,
-and Wyoming. The Morrison Formation is exposed in many places, and is
-characteristically composed of layers of fine, limy mud, brightly
-colored in streaks of red, brown, green, and blue. In most areas it is
-so soft that it becomes soil-covered; it is well exposed only in
-roadcuts or where it is protected from erosion by a "caprock" of harder
-sediments or lava. Spectacular outcrops can be seen in new roadcuts
-along U. S. Interstate highway 70 just west of Denver.
-
-[Illustration: In this roadcut along U. S. Interstate 70 west of Denver,
-Jurassic and Cretaceous rocks are unusually well exposed in the Dakota
-hogback. Green and purple shales represent the dinosaur-bearing Morrison
-Formation. The Cretaceous Dakota Group forms the eastern, higher half of
-the cut. Black layers are carbon-rich clays of the South Platte
-Formation, frequently quarried locally for ceramic uses. (John Chronic
-photo)]
-
-Fossil dinosaur bones occur in great numbers in the Morrison Formation
-near the towns of Morrison and Canon City and at several other places in
-Colorado. Those at Canon City have been quarried extensively, and are
-now mounted in a number of museums in the United States. At Dinosaur
-National Monument, in eastern Utah and northwestern Colorado, many
-excellent remains have been found; those in Utah can be seen in place in
-the rock in a striking exhibit at the National Monument.
-
-[Illustration: In an old painting, a paleontologist contemplates fossil
-bones found near Morrison. The date is 1877. The bones are those of the
-70-foot dinosaur _Apatosaurus_, more commonly known as _Brontosaurus_,
-shown below in reconstruction.]
-
-[Illustration: Apatosaurus]
-
-Some of the dinosaurs known from the Morrison Formation reached 80 feet
-in length. Both plant-eating and meat-eating types are known. In
-addition to the bones themselves, gastroliths or gizzard stones can
-frequently be found; these highly polished stones were as essential to
-dinosaur digestion as gravel is to a chicken or a caged canary.
-
-Along with the dinosaur fossils are found abundant remains of water
-plants called charophytes. These plants formed tiny spiralled balls of
-calcite as part of their reproductive activities; both the little balls
-and the stalks of the plants themselves occur in many parts of the
-state. In western Colorado, near Grand Junction, silicified shells of
-freshwater snails can also be found in the Morrison.
-
-Early in the 1900s vanadium, radium, and uranium were discovered in
-Jurassic sandstones and mudstones of western Colorado. Extensive mining
-in this area has revealed that these elements often become concentrated
-by groundwater in organic material such as fossil plant stems or
-dinosaur bones. The search for radioactive minerals has thus brought to
-light many ancient fossil accumulations.
-
-
-                           Cretaceous Period
-                       (70-135 million years ago)
-
-Early in Cretaceous time, marine conditions once more prevailed in
-Colorado. This is indicated by a marked change in rock types from beach
-and near-shore deposits to true marine sediments.
-
-[Illustration: Between the Front Range and the Plains the Cretaceous
-Dakota Formation forms a hogback ridge which can be traced for 200 miles
-or more. The well-cemented sandstone resists erosion, and so remains as
-a ridge when softer layers are stripped away. (Jack Rathbone photo)]
-
-The sandstones derived from beach sands sometimes include coarse pebbles
-of chert which can be traced to sources in Permian rocks of Utah and
-Nevada. Occasionally the beach and near-shore deposits include marine
-shells like oysters, indicating that there were brackish and salt water
-lagoons and marshes along the shore. The Dakota Formation represents the
-beach of the transgressive or advancing sea. This formation contains oil
-in eastern Colorado, Nebraska, and Wyoming; the oil itself may have been
-derived from decay of organic materials in swamps behind the beaches and
-bars.
-
-As the sea deepened in eastern Colorado, finer sediments were deposited.
-These included the black muds of the Benton Shale, and the Niobrara
-Limestone, a shallow-water deposit containing abundant shells of clams
-(_Inoceramus_ and _Ostrea_) and ammonites and tiny one-celled animals
-called Foraminiferida. Above the Benton and Niobrara Formations lie the
-fine gray muds of the Pierre Shale. Several thousand feet thick, the
-Pierre contains occasional beautifully preserved ammonite shells as well
-as bones from fossil fish and swimming reptiles.
-
-[Illustration: Cretaceous rocks in Colorado are rich in fossil
-pelecypods. Each of the fossils illustrated above may grow to a much
-larger size than shown.]
-
-[Illustration: Shales of the Laramie Formation contain many recognizable
-plant fossils.]
-
-The rocks deposited in western Colorado at this time are markedly
-different from those deposited in eastern Colorado. In the east,
-deposits are fine and very limy, containing abundant shells and little
-in the way of coarse debris. In the west, sandstones of the Mesa Verde
-Formation dominate, and coal beds suggest marshy or swampy conditions
-inshore from the ancient ocean. This is just the pattern we would expect
-from a low-lying region bordering a shallow sea, a region similar
-perhaps to the southeastern Atlantic and Gulf coasts of the United
-States today.
-
-Toward the end of the Cretaceous Period, the sea receded from Colorado.
-Beaches and bars of the retreating sea left a sandstone layer which now
-outcrops prominently east of the Front Range as the Fox Hills Sandstone.
-Above lie interbedded sands and coals, the Laramie Formation. The
-presence of coal above beach sands shows that the coal swamps moved
-eastward as the sea retreated.
-
-The exact age of the shoreline deposits and coal beds varies from place
-to place in such a way as to indicate that the sea withdrew slowly and
-irregularly. In general the shore moved eastward, but there are
-localities such as North Park where deposition lasted much longer than
-elsewhere. In some places no real beach was formed at the ancient strand
-line.
-
-In western Colorado, the end of Cretaceous time is marked by coarser
-beds, indicating an increased rate of uplift in Utah. Conglomerates were
-deposited in the beds of the McDermott Formation, now visible along the
-Animas River south of Durango.
-
-
-                              CENOZOIC ERA
-
-It is characteristic of earth history that the younger the rocks are,
-the more we know about them. This is because younger rocks lie near the
-surface, have not been disturbed as much by mountain building processes
-as have older rocks, and have not been affected as strongly by repeated
-erosion. Many of the events of the Cenozoic Era are documented in detail
-in the geology of Colorado, and these events have intimately influenced
-the scenery as we see it today.
-
-The Cenozoic is the Age of Mammals. How it happened that mammals
-triumphed over reptiles is one of the mysteries of geology. Some
-scientists think that climatic changes--dropping temperatures and
-increases in rainfall--swung the balance in favor of the warm-blooded
-mammals. Others believe that cosmic ray bombardment during some unusual
-astronomical event may have destroyed many surface-living dinosaurs,
-while small burrowing mammals (as well as many small reptiles) were able
-to survive. Still others maintain that the superior intelligence and
-regulated body temperatures of mammals enabled them to win out in the
-battle for survival without the aid of climatic or cosmic change.
-
-The names Tertiary and Quaternary, used for the two Cenozoic Periods,
-are holdovers from early studies in geology in which rocks were divided
-into Primary (very hard, crystalline rocks such as igneous and
-metamorphic rocks), Secondary (well consolidated layered rocks),
-Tertiary (layered rocks which are not fully cemented but which are
-nevertheless fairly well consolidated), and Quaternary (sediments in
-which the grains have not become cemented together).
-
-
-                            Tertiary Period
-                        (3-70 million years ago)
-
-During the first part of the Tertiary Period, uplift began in earnest in
-Colorado and adjacent states. This uplift was part of the great Laramide
-Orogeny that built the Rocky Mountain chain from Alaska to New Mexico.
-The entire area rose above the level of the sea, and mountains were
-thrust up in a great series of north-south ranges that extended unbroken
-almost the length of the continent. Between the ranges, thick layers of
-gravel and sand, derived from the surrounding highlands, were deposited
-in intermontane basins. Occasional freshwater limestones and shales
-indicate the presence of lakes.
-
-In Colorado, many details of the formation of the Rockies stand out in
-bold relief. The Front Range moved upward sharply, mostly as a linear
-block broken or faulted along both edges. Paleozoic and Mesozoic
-sediments along the margins of the block were steeply tipped and in some
-places even overturned, while in some localities Precambrian rocks were
-thrust out over the younger sediments.
-
-Just east of the Front Range, especially in the area around Denver, the
-land remained lower and was the site of thick deposits of gravel and
-sand eroded from the range. The Denver Formation, the Arapahoe
-Conglomerate, and the Dawson Arkose are more than 2,000 feet thick in
-this area. These are delta and river sediments, all varying a great deal
-from place to place. Individual layers of sand or gravel are not
-continuous over extensive areas, but some, such as the Castle Rock
-Conglomerate, are very prominent locally.
-
-[Illustration: On Wolford Mountain, just north of Kremmling, Precambrian
-granite lies on top of Cretaceous shale. The older rocks were thrust up
-and over younger rocks during the Laramide Orogeny. The position of the
-fault shows clearly because trees prefer the granite soil above the
-fault to the shale below. (Jack Rathbone photo)]
-
-Along the eastern margin of the Front Range west of Castle Rock and
-Sedalia, rocks deposited at this time are now folded steeply, indicating
-that the mountains continued to rise even as basin sediments were being
-deposited.
-
-In southern Colorado, the Sangre de Cristo and Wet Mountains were also
-formed as upthrust blocks. Between them, the Huerfano Basin and
-adjoining Raton Basin received particularly rapid alluvial deposition.
-In the Raton Basin, quantities of vegetation were deposited in swamps
-and marshes, forming the thick coal beds which can now be seen in road
-cuts west of Trinidad and along the Raton Pass highway. Huerfano Basin
-deposits contain some of the earliest known horse remains, skeletons of
-a tiny four-toed horse called _Hyracotherium_ (formerly known as
-_Eohippus_).
-
-[Illustration: Bones of _Hyracotherium_, the "dawn horse," have been
-found northwest of Walsenburg in Early Tertiary sediments of the
-Huerfano Basin. (C. R. Knight painting, courtesy American Museum of
-Natural History)]
-
-Other rising ranges provided material for alluvial deposition in North
-Park, Middle Park, South Park, and the San Luis Valley. Layers of basalt
-and volcanic peaks show that as the mountains rose, the crust cracked
-and allowed lava to rise to the surface in great quantities. Tertiary
-basalts are very much part of the Colorado landscape: some can be seen
-west of Granby, others in Table Mountains east of Golden. Near Boulder,
-Valmont Dike was intruded, though lava may not have reached the surface
-in that area. Spanish Peaks in southern Colorado, Mesa de Maya, the
-Rabbit Ears Range, Grand and Battlement Mesas, and many other volcanic
-features were formed at this time.
-
-[Illustration: The town of Golden nestles between the Front Range and
-South Table Mountain. Tertiary basalt capping South Table Mountain
-covers beds of the Denver Formation. It thins to the right, or south,
-indicating that its source was probably to the north or northwest.
-Buildings in the right foreground are the Colorado School of Mines.
-(Jack Rathbone photo)]
-
-[Illustration: A series of almost vertical dikes radiate from West
-Spanish Peak. Surrounding sediments are Tertiary. Weathering and erosion
-along sets of joints in the largest dike have shaped it into the
-"Devil's Staircase." (Jack Rathbone photo)]
-
-Most of the rich mineral deposits of Colorado are thought also to have
-been formed during the early part of the Tertiary Period. Solutions rich
-in gold, silver, zinc, lead, copper, and sulfides of iron seeped into
-joints and faults in the crust as the mountains were pushed upward. Ore
-minerals crystallized out, sometimes in veins in the ancient Precambrian
-igneous and metamorphic rocks, sometimes in Paleozoic sediments. These
-are further discussed in Chapter III.
-
-[Illustration: The Eocene Green River Formation includes great
-thicknesses of oil shale, an untapped petroleum reserve containing
-perhaps three trillion barrels of oil. The richest part of the oil shale
-is a dark brown layer called Mahogany Ledge, visible here on cliffs just
-west of Rifle. If placed in a campfire, fragments of this shale release
-enough oil to burn with a yellow, smoky flame. (Jack Rathbone photo)]
-
-Further to the north and west, the Uinta Mountains rose. They are a
-fault-block range, but they lie at right angles to the general
-north-south trend of the Rocky Mountains. South of them the Uinta Basin,
-one of the largest of the intermontane basins, received shaly deposits
-in a great lake which existed here for probably several million years.
-The lake extended over some 100,000 square miles, and during its
-existence great quantities of tiny organisms lived in its waters. Oily
-material from these organisms was deposited in the mud of the lake
-sediments, particularly in the eastern end of the basin, there to remain
-trapped in a great oil-shale deposit. Fossil fish, crayfish, algae, and
-many forms of insect and plant life have been found as fossils in these
-lake shales.
-
-West of Pikes Peak, another lake formed, dammed by a lava flow from a
-nearby volcanic field. Fine volcanic ash falling into this lake
-preserved the trunks and leaves of many plants as well as abundant
-insects, fish, and occasional mammal bones. These are now protected and
-exhibited in Florissant Fossil Beds National Monument. The fossil
-plants, among them redwoods, poplar, hackberry, and pine, suggest a
-climate warmer than the present one, and have been taken to indicate
-that regional uplift to the present altitude had not yet occurred.
-
-Another rich deposit of fossil insects and plants occurs near Creede.
-Other lake deposits in South Park contain ash layers with fossil algae
-and snails.
-
-[Illustration: Large petrified trunks of redwoods and other trees can be
-seen at Florissant Fossil Beds National Monument, west of Colorado
-Springs. (John Chronic photo)]
-
-In southwestern Colorado, extensive Tertiary lava flows, ash falls, and
-river deposits form the eastern part of the San Juan Mountains, the
-largest volcanic area in the state. Mineral collectors are attracted to
-this region by the many excellent localities for agate and other
-siliceous stones.
-
-Still another center of Tertiary volcanism was located in what is now
-Rocky Mountain National Park. Specimen Mountain, northwest of Trail
-Ridge, was an active volcano about 30 million years ago, shedding ash
-and lava over much of northern Colorado. The rhyolite which now caps the
-hill west of Iceberg Lake, on Trail Ridge Road, was derived from this
-volcano, but is now separated from it by the deep glaciated valley of
-the Cache la Poudre River and Milner Pass.
-
-Volcanic ash at times drifted far eastward and blanketed the surface of
-the plains, burying specimens of many animals and plants. The White
-River Formation, extending from northeast Colorado northward into South
-Dakota, is formed of such drifting ash. Many now-extinct mammals have
-been excavated from this formation.
-
-Sometime after the mid-Tertiary episode of violent volcanic activity,
-Colorado was uplifted to its present altitude. This was a general
-uplift, raising the plains and plateau areas as well as the mountains.
-The uplift was not an abrupt process, but continued for perhaps ten
-million years. It raised the entire state 3,000 to 5,000 feet above its
-previous level.
-
-[Illustration: Pawnee Buttes, about 40 miles north of Fort Morgan, rise
-like castles from the eastern Prairie Province. Remnants of Oligocene
-and Miocene sedimentary rock that once covered much of northeastern
-Colorado and adjacent states, they contain jaws, teeth, and other bones
-of primitive mammals. (Department of Highways photo)]
-
-During the remainder of the Tertiary Period, Colorado was the site of
-erosion rather than deposition. However, some stream material was
-deposited in the mountain valleys, and on the prairies wind-blown and
-stream-borne sands were spread thinly, interlayered with impure
-limestones deposited in ponds and lakes. In the San Luis Valley,
-deposition was probably more continuous than elsewhere, as the exit from
-the valley was blocked by volcanic flows. The deposits in this valley,
-sands and clays of the Santa Fe and Alamosa Formations, form a great
-artesian basin. The rich agricultural development of the valley is made
-possible by water wells tapping these formations.
-
-[Illustration: Remains of many now-extinct mammals have been found in
-Tertiary sedimentary rocks of northeastern Colorado, in the general area
-of Pawnee Buttes. Those illustrated are _Oreodon_ from Oligocene strata
-and a "giraffe-camel" (_Oxydactylus_) from Miocene rocks.]
-
-
-                           Quaternary Period
-                    (3 million years ago to present)
-
-The most significant feature of the Quaternary Period in Colorado, as
-elsewhere in the northern hemisphere, is the evidence of glaciation.
-During the first part of the Quaternary Period, known as the Pleistocene
-Epoch, great continental glaciers covered most of Canada and much of
-northern United States. The ice sheets did not extend southward as far
-as Colorado, but large valley glaciers developed in many of the mountain
-ranges of the state and left their traces in many mountain valleys.
-
-[Illustration: Mills and Jewel Lakes, in Rocky Mountain National Park,
-occupy small glacier-gouged basins in Glacier Gorge. The flat-topped
-peak at the upper left is Longs Peak, elevation 14,256 feet; Pagoda
-Mountain is in the center of the skyline. Bedrock in this area is
-Precambrian granite, gneiss, and schist at the Front Range "core." (Jack
-Rathbone photo)]
-
-The conditions leading to Pleistocene glaciation are not fully
-understood. Climatic changes may have been initiated by a decrease in
-solar radiation, changing patterns of ocean currents, reduction of solar
-heating by volcanic dust, or an increase in general elevation of the
-land. As the climate became cooler and moister, snowfall increased in
-the north and at high altitudes. In areas where winter snowfall exceeded
-summer melting, glaciers developed.
-
-In Colorado, glaciers formed along the crests of the Front Range, the
-Sawatch Range, the Elk Mountains and West Elk Mountains, the Sangre de
-Cristo and Mosquito Ranges, the San Juan Mountains, and the Park and
-Gore Ranges. Glaciation in Colorado was selective: in many places
-elevation was sufficient for glaciation, but snowfall apparently was not
-great enough. Where they did occur, the glaciers extended down to
-elevations of about 8,000 feet. There, temperatures became mild enough
-to melt the ice.
-
-The mountain glaciers have left many tell-tale signs of their presence.
-Valleys above 8,000 feet are U-shaped, their upper ends bounded by
-horseshoe-shaped, steep-walled cirques. In the lower portions of the
-valleys, at elevations just above 8,000 feet, lie long lines of glacial
-debris known as moraines: terminal moraines forming crescents across the
-valleys to show where melting glaciers dropped their rocky loads;
-lateral moraines along the sides of valleys; medial moraines where
-glaciers from two valleys met. Terminal moraines, often forming
-effective barriers across the present streams, may act as dams, creating
-lakes such as Grand Lake in Rocky Mountain National Park.
-
-There were at least three distinct glacial episodes in Colorado. This is
-known because careful studies of glacial debris in moraines reveal three
-different degrees of rock weathering. All three stages can be seen in or
-near Rocky Mountain National Park. The oldest is represented by a
-moraine about three miles west of Estes Park, where the Big Thompson
-River traverses a wide U-shaped valley before entering its narrow,
-unglaciated canyon. The next oldest is represented in terminal moraines
-further up the valley, at Aspenglen campground. The youngest is shown in
-a prominent terminal moraine about one mile west of the park entrance in
-Horseshoe Park.
-
-A large lateral moraine separates Hidden Valley from the south side of
-Horseshoe Park, and an almost equally large lateral moraine is present
-on the north side of this valley. At Moraine Park, both sides of the
-valley are edged with lateral moraines also.
-
-Studies in Rocky Mountain National Park have revealed many other details
-of glaciation in this area. These are described in Park Service
-brochures and guidebooks, in the museum at Park headquarters, and in
-informative roadside signs.
-
-[Illustration: A line of hikers approaches Arapaho Glacier, west of
-Boulder. Movement of the glacier is evidenced by the crevasses apparent
-just below the snowfield in the dirty gray glacial ice. (H. H. Heuston
-photo)]
-
-Several small glaciers are still present in the Colorado mountains, all
-in sheltered cirques above 11,000 feet. These may be remnants of the
-former larger glaciers, or new glaciers formed after a long warming
-episode. A hike to one of these glaciers is a rewarding experience for
-anyone interested in geology. Some of the more accessible are St. Mary's
-Glacier west of Denver, Arapaho Glacier west of Boulder (the Boulder
-Chamber of Commerce sponsors a festive hike to Arapaho Glacier every
-August), and Tyndall Glacier in Rocky Mountain National Park.
-
-The Ice Age brought drastic changes also to the landscape below 8,000
-feet elevation. Heavily loaded with glacial debris, mountain streams
-disgorged coarse sands and gravels along the mountain front and in the
-intermontane basins. As the glaciers melted after each period of
-expansion, the swollen streams cut deeply into their former deposits and
-into much older rocks as well. Royal Gorge, the Black Canyon of the
-Gunnison, and many of the deep, colorful canyons of the Plateau Province
-were cut or at least deepened by these waters. The canyons along the
-east face of the mountains--Big Thompson, Boulder, Clear Creek, and
-others--were also deepened and sharpened by the rushing ice-fed
-torrents.
-
-On the prairies, rivers dumping their loads of sand covered the older
-rocks. Sand dunes developed along the river channels. Bones and huge
-tusks of hairy mammoths were sometimes buried in these soft deposits;
-now they are occasionally revealed as the dune and river sands are
-washed or blown away by continuing erosion.
-
-About 20,000 years ago, man arrived in Colorado. Soon after this, the
-water supply of the valleys diminished greatly, and erosion slowed down
-correspondingly. The climate gradually became semiarid to arid. Many
-features of the natural scene were much as they must have been a century
-ago, without the highways, dams, and television aerials of today.
-Buffalo and many smaller types of game roamed the plains and foothills;
-deer, elk, and bighorn sheep were plentiful in the mountains. Nomadic
-tribes camped and hunted in both mountain and prairie. In the western
-part of the state, homes could be built in the shelter of great caves,
-as at Mesa Verde, and game could be supplemented with corn and squash
-planted on plateau surfaces.
-
-Several features of Colorado scenery changed with increasing aridity.
-The glaciers of course were gone or nearly gone. Streams were no longer
-the violent torrents they had been. Many mountain lakes, filled with
-sediment and vegetation, became instead mountain meadows. And the once
-fertile intermontane valleys became deserts.
-
-[Illustration: During the last Ice Age, elephant-like mastodons roamed
-Colorado. As present-day erosion removes sediments, bones, teeth, and
-tusks are frequently exposed, especially in the Prairie Province. (C. R.
-Knight painting, courtesy American Museum of Natural History)]
-
-[Illustration: Mastodon]
-
-On the eastern side of the San Luis Valley, the Great Sand Dunes
-developed at this time. These dunes nestle against the Sangre de Cristo
-Range, where strong southwesterly winds blowing across the wide valley
-tend to funnel toward Mosca and Music Passes. These winds lift loads of
-sand from the lightly vegetated valley floor, and drop it as they rise
-over the mountains. Where the sand is dropped, the dunes have formed.
-They rise to about 700 feet above the valley floor, and cover about
-forty square miles. The low rainfall of the area, seven to eight inches
-per year, keeps vegetation from creeping over the dunes and makes them a
-most distinctive feature of Colorado, a lesson in geology in the making.
-
-                            * * * * * * * *
-
-Geologic processes in Colorado now seem to be much reduced from what
-they were a few thousand years ago. Reduction in rainfall has led to
-reduced erosion. Mountain-building, having reached a climax in Tertiary
-time, has declined markedly. However, we find evidence that volcanism
-has occurred within the last few thousand years and faulting within the
-last few hundred, and Colorado streams rise after sudden mountain storms
-to approximate the violent torrents of glacial times. Colorado's
-scenery, fashioned during some three billion years of earth history, is
-ever changing.
-
-[Illustration: The Great Sand Dunes of Colorado were formed during
-Pleistocene and Recent time by deposition of quartz sand lifted from
-unconsolidated alluvial deposits in the San Luis Valley. The highest of
-the dunes rises 700 feet above the adjacent valley floor. (John Chronic
-photo)]
-
-
-
-
-                                  III
-                      Geology and Man in Colorado
-
-
-Colorado's first permanent settlers arrived in 1858, when gold was
-discovered in river sands near what is now the city of Denver. The
-ensuing gold rush, coming ten years after the rush to California,
-rivalled it in fury and brought sudden wealth to lucky miners and the
-adventurous merchants who grubstaked them. Several hundred mining towns
-or "camps" sprang into existence almost overnight, their sites
-determined by the geology of the mountain areas. The cities of Denver,
-Boulder, and Golden were established as milling and shipping centers for
-the products of the mines. In 1876 the now-wealthy area, previously part
-of Kansas Territory, became the State of Colorado.
-
-For more than a hundred years Colorado's minerals--products of her long
-and diverse geologic history--have influenced her development in many
-ways. The state's early wealth, stemming from bonanzas in gold and
-silver, is evidenced by palatial homes, hotels, and public buildings
-constructed during the first few decades of mining activity. Some of
-these are still standing--the opera houses at Central City and Aspen,
-Central City's famous Teller House, and the Grand Imperial Hotel at
-Silverton are examples.
-
-Many of the stories and legends of Colorado's gold camps are recounted
-in _Stampede to Timberline_, by Muriel Sibell Wolle, delightfully
-illustrated with sketches of old mining towns as they appear today.
-_Mining in Colorado_, published by the U. S. Geological Survey, also
-makes fascinating reading, as it contains many historical anecdotes and
-eyewitness accounts of gold-rush days.
-
-Development of the metal-mining areas in Colorado followed a definite
-sequence. Placer gold was usually discovered first. Recovery of placer
-gold was followed by mining of gold from veins or "lodes." Although at
-first only native gold was mined, gold-bearing compounds such as
-telluride were soon recognized as an additional source, especially at
-Gold Hill, Cripple Creek, and of course the camp that came to be known
-as Telluride. As gold sources were depleted, silver, first produced as a
-byproduct, became of prime interest. Lead and zinc were in turn
-byproducts of silver mining. Other metals, notably copper, vanadium,
-tungsten, and iron, were produced later. Molybdenum is the
-Johnny-come-lately of the state's mining industry, but is now the chief
-metal produced. A uranium boom in the 1950s brought a short rush to
-western Colorado and new vigor to the economy.
-
-Oil was discovered near Canon City in 1862. The nearby Florence field
-and a small, shallow field near Boulder preceded much greater
-discoveries in the Denver Basin, the Uinta Basin, and southwest
-Colorado. Oil reservoirs, confined to areas of sedimentary rock, are
-found primarily in the Prairie and Plateau Provinces of the state, and
-recovery of the oil has done much to distribute population to these
-areas.
-
-Coal is also restricted to sedimentary rock areas. Coal production in
-Colorado has waxed and waned with the years, but has provided fuel for
-export, for the railroads, for the manufacture of electric power, and
-for many of the state's industries.
-
-A good picture of present mineral production in Colorado can be obtained
-from the following summary for 1971, prepared by the Colorado Bureau of
-Mines:
-
-                        Product                Value
-
-               Molybdenum                    $105,389,456
-               Petroleum                       90,494,459
-               Sand and gravel                 32,842,503
-               Coal                            30,251,443
-               Natural gas                     18,695,225
-               Uranium                         18,048,692
-               Vanadium                        15,863,554
-               Cement                          13,377,520
-               Zinc                            13,310,787
-               Lead                             6,582,025
-               Tungsten                         6,360,020
-               Limestone and dolomite           5,397,570
-               Silver                           4,198,054
-               Fluorspar                        3,887,210
-               Copper                           3,875,976
-               Stone                            1,961,279
-               Gold                             1,832,791
-               Clay                               962,986
-               Iron                               880,047
-               Pumice                             309,370
-               Tin                                278,862
-               Gypsum                             253,856
-               Pyrites                            142,640
-               All others                       1,091,927
-                  Total                    ($376,288,252)
-
-Colorado is now the nation's leading producer of molybdenum, tin, and
-vanadium, and second in output of tungsten. In oil production it ranked
-twelfth among the states in 1968, but ninth in reserves, with
-420,000,000 barrels of proven reserves on 1 January 1969. An as yet
-untapped source of oil lies in the oil shales of western Colorado.
-
-As part of the natural environment, water plays a major role in man's
-activities. Water problems in Colorado revolve mainly around the best
-use of runoff in a state whose major catchment basins are across the
-continental divide from her largest population centers and most fertile
-farm land. Groundwater, closely related to surface water distribution
-and movement, is a geological problem, and in Colorado as in other
-states many government and private geologists serve farm and industrial
-communities in the search for usable supplies.
-
-
-
-
-CAUTION: Old mines are dangerous! They may contain water or deadly
-gases, or be on the verge of collapse. Keep away from abandoned prospect
-pits and mine shafts. WARN AND WATCH YOUR CHILDREN.
-
-
-                     GOLD, SILVER, AND OTHER METALS
-
-Colorado's placer and lode sources of gold, which gave first impetus to
-the series of mining booms in the state, were fantastically rich. Summit
-and Lake Counties, for instance, each produced more than $5,000,000 in
-placer gold between 1859 and 1867. During the same nine-year period,
-more than $9,000,000 in lode gold was produced from Gregory Gulch, a
-tiny canyon between Central City and Black Hawk. Other districts
-rivalled or surpassed these figures.
-
-Early in the game it was recognized that almost all the deposits
-occurred along what came to be known as the "mineral belt," a
-fifty-mile-wide zone extending southwest from the Boulder region. Most
-of the metals mined in the state come from this belt, but there are
-three notable exceptions: Cripple Creek, Silver Cliff, and western
-Colorado vanadium and uranium districts. In the first few years of the
-Colorado rush, gold ores and placer gold were discovered only in the
-northeastern part of the mineral belt. Gradually the belt was found to
-extend further and further southwest: Tincup was discovered in 1861,
-Silverton in 1870, Lake City in 1871, and Telluride in 1875. Aspen, on
-the western edge of the belt, was not discovered until 1879, perhaps
-because the area was difficult of access and lacked the easily
-recognizable native gold.
-
-In the northeast part of the mineral belt, gold and other minerals occur
-in veins in Precambrian granite and gneiss. In the Leadville and Aspen
-areas, ores are associated with altered Paleozoic limestones. At the
-southwest end of the mineral belt, in the San Juan Mountains, ore veins
-are found near or in Tertiary volcanic rocks. Native gold, gold-bearing
-compounds, and other metallic ores in these veins originated where
-mineral-rich solutions from deep within the earth penetrated fissures
-and joints in the surrounding rock. Regardless of the age of the host
-rock, almost all the ores of Colorado were deposited in the early or
-middle Tertiary Period, about 35 to 70 million years ago.
-
-Gold and silver are no longer mined extensively in Colorado, although
-any summer Sunday will see weekend operators panning near mountain
-streams or trundling rock from one-man mines. The recent rise in the
-price of silver has encouraged many miners to reopen old shafts. The
-most active mines in the state today are those producing molybdenum,
-lead, zinc, and vanadium. (Vanadium, although a metal, usually occurs in
-Colorado with radioactive minerals, and so is discussed with them rather
-than with the metals.)
-
-[Illustration: The Colorado mineral belt extends from Boulder County on
-the northeast to San Juan County on the southwest. Almost all of the
-prominent mining districts in Colorado lie along this belt. Cripple
-Creek and Silver Cliff, however, lie far to the east of the general
-trend.]
-
-    Telluride
-    Denver
-    Colorado Springs
-    Alamosa
-  BOULDER
-    Ward
-    Gold Hill
-    Boulder
-    Nederland
-  GILPIN
-    Central City
-    Black Hawk
-  JEFFERSON
-    Golden
-  CLEAR CREEK
-    Empire
-    Georgetown
-    Silver Plume
-    Idaho Springs
-  SUMMIT
-    Breckenridge
-  EAGLE
-  PITKIN
-    Aspen
-  GUNNISON
-    Tincup
-  CHAFFEE
-  PARK
-    Climax
-    Alma
-    Como
-    Fairplay
-  TELLER
-    Cripple Creek
-  FREMONT
-  OURAY
-    Ouray
-    Camp Bird
-    Ironton
-  SAN JUAN
-    Silverton
-  HINSDALE
-    Lake City
-  LA PLATA
-    Durango
-  MINERAL
-    Creede
-  CUSTER
-    Silver Cliff
-
-All told, some 430 metal mining districts have been established as legal
-entities in the state of Colorado. Each of these districts had the right
-to draw up its own regulations concerning prospecting, claims, and
-mining rights, within a framework established by the Federal government.
-Only a few of the districts ever became really significant producers.
-The geology and history of several of the leading areas are presented in
-the pages that follow.
-
-
-                             Boulder County
-
-Gold Run, near Gold Hill, was the scene of one of the earliest strikes
-in Colorado. Gold was found here in December 1858, and was sluiced from
-stream sands and mined from veins early in 1859. Active placer mining
-lasted only about a year, however, and lode mining dropped off rapidly
-as near-surface oxidized ores were worked out. When a smelter was
-erected at Black Hawk in 1868, and sulfide ores could be treated, there
-was a revival of activity. In 1869 the Caribou and Poorman mines near
-Nederland were discovered; they quickly became the most active mines in
-the county. The Ward district opened soon after.
-
-In 1872, a gold-silver telluride called petzite was found in veins at
-Gold Hill. Renewed prospecting in this area resulted in location of
-mines near Sunshine, Salina, and Magnolia. During the years that
-followed, new mines appeared almost as fast as old ones were depleted.
-In 1892, the peak year, more than $1,000,000 in gold and silver was
-produced; total production has been about $25,000,000.
-
-In 1900, a black mineral common in the Nederland area was recognized as
-ferberite, an ore of tungsten, and a new rush to the area started.
-During the next eighteen years Boulder County was the main tungsten
-producer in the United States; about 24,000 tons of tungsten trioxide,
-worth $23,000,000, were produced here. The ore was found in nearly
-vertical veins six inches to three feet thick, in a lenticular area
-about nine miles long extending from Nederland northeast to Arkansas
-Mountain, four miles west of Boulder.
-
-Boulder County is characterized by an abundance of small mines. Old
-shafts, pits, and mine buildings can be found throughout the central
-part of the county. Little mining is done here today; many of the towns
-that once peppered these hills have fallen into decay or disappeared
-entirely.
-
-
-                     Central City and Idaho Springs
-
-The Central City-Idaho Springs area was the principal metal mining
-region in the state until the late 1880s. In 1858, rich placer deposits
-were discovered in gravels and river terraces along both forks of Clear
-Creek. Exploration upstream led to discoveries of rich oxidized quartz
-veins at Central City, Black Hawk, and Idaho Springs. These veins, which
-generally trend northeast-southwest, extend through the mountains in a
-zone about six miles long and three miles wide between the two forks of
-Clear Creek.
-
-The ores filled a multitude of cracks and fissures in the Precambrian
-bedrock. The veins are usually less than five feet thick, and are almost
-vertical and often clustered in zones up to thirty feet wide. The
-position of one of the vein systems may be seen clearly between Black
-Hawk and Central City--the ore-bearing rock has been mined out, but a
-series of collapsed tunnels marks the line where the veins crossed the
-valley. A monument here commemorates the discovery of Gregory Gulch, one
-of the richest localities in the state.
-
-Several rich veins were mined in both directions--southwest from Central
-City and northeast from Idaho Springs--until the mines met. The Argo
-tunnel, marked by dilapidated buildings and extensive dumps on the north
-side of Idaho Springs, connected the two districts; it was completed in
-1904.
-
-The "Patch," a deep crater-like hole on Quartz Hill, about one mile
-southwest of Central City, is an intriguing feature in this area. It was
-produced by glory-holing, a mining technique in which a deep tunnel is
-deliberately caved by blasting, so that ores above the tunnel can be
-removed. This glory hole was dynamited below an irregular mass of highly
-broken rock where many ore-rich veins converged. After the caving, ores
-were taken out through the remaining part of the tunnel.
-
-The principal ore minerals of Central City and Idaho Springs are native
-gold, pyrite, sphalerite, galena, chalcopyrite, and tennantite.
-Prospecting for uranium was carried out during the 1950s but no uranium
-was ever mined here.
-
-The area has produced almost $200,000,000 worth of gold, silver, lead,
-zinc, and copper. A few mines still operate seasonally or on a small
-scale, but tourists, many of them riding Jeeps across the mountainous
-terrain to visit mines and ghost towns, are often more visibly active
-than the mines.
-
-
-                  Georgetown, Empire, and Silver Plume
-
-A few miles southwest of Idaho Springs, another mining area had a
-similar, though less productive, history. In 1859, placer and lode gold
-were discovered near what is now Georgetown. Placer mining dominated
-here between 1859 and 1863. Gravel and crushed rock from decomposed
-quartz and sulfide veins were washed through sluiceboxes in the same way
-as placer gravel, gold being caught in riffles or gunny sacking on the
-bottoms of the troughs. The veins were found to be decomposed to depths
-of about 40 feet; below this the gold occurred closely associated with
-sulfides such as pyrite, sphalerite, galena, and chalcopyrite, from
-which it could not easily be separated. However, smelters were developed
-in 1866 for treatment of these sulfides, and gold, silver, lead, and
-copper were recovered. Gradually, as the gold was worked out, silver and
-lead became the important products of the mines.
-
-[Illustration: Sluicebox mining was a common sight near the early gold
-camps, where primary recovery was from placer deposits or decomposed
-quartz and sulfide veins. (State Historical Society of Colorado photo)]
-
-
-                               Leadville
-
-Placer gold was discovered in 1859 in California Gulch, about seven
-miles north of the present town of Leadville. The rush that followed was
-short but sweet; the camp was called Oro--gold! About $5,000,000 was
-produced from the placer mines within two years, though by 1861 the area
-was all but deserted, for the easily won placer gold was gone.
-
-[Illustration: Early-day Leadville sprawled among its mine dumps at an
-elevation of 10,200 feet. The Sawatch Range, in the background,
-contained many smaller mining communities, now deserted. Mt. Massive,
-the state's second highest peak, forms the crest of the continental
-divide here. (State Historical Society of Colorado photo)]
-
-In 1875 a smelter was erected a few miles downstream from Oro to process
-cerussite--silver-rich lead carbonate--that occurred in the placer
-sands. For years this mineral had been considered a nuisance because,
-being much heavier than sand, it tended to separate out with the gold.
-The new town of Leadville sprang up near the smelter and shortly
-afterward more lode deposits were discovered south of the placer
-workings. From $63,000 in 1875, production climbed to $2,500,000 in 1878
-and more than $15,000,000 in the peak year of 1882.
-
-Geologically, the ores of this district occur as Tertiary replacements
-and veins in Ordovician, Devonian, and Mississippian limestones. The
-"Blue" or Leadville Limestone, of Mississippian age, contains the
-richest ore. Ore deposits were formed after the limestones had been
-faulted and cracked extensively by mountain-building movements; the ores
-themselves probably crystallized from molten or gaseous materials
-involved in related igneous intrusions. River gravels and glacial debris
-mask the true nature of the lode deposits, but studies in the mines show
-that the fault systems along which ores are deposited trend north or
-north-northeast.
-
-The Leadville district is now experiencing its third mining boom as a
-newly recognized lead-zinc orebody is being developed. Production is
-expected to reach 700 tons of ore per day by 1971. Total production of
-gold, silver, lead, zinc, and copper in the district has reached
-$500,000,000.
-
-
-                              Breckenridge
-
-Breckenridge was also discovered in 1859, with placer gold the first
-attraction. The placers gave out in 1862 after about $3,000,000 in gold
-had been recovered. Earliest attempts to mine the rich silver and lead
-veins of the district were in 1869.
-
-As at Leadville, the sedimentary rocks of the area were intruded by
-granitic masses in Tertiary time, but here the sedimentary rocks are
-mostly Pennsylvanian sandstones and shales. These rocks were badly
-faulted and broken during the intrusion, and the ores were deposited as
-the granitic material cooled. The lode deposits occur mostly in small
-veins well hidden by surface sands and gravels. Some of the veins
-yielded exceptionally beautiful crystallized wire and flake gold,
-specimens of which are on display at the Colorado School of Mines
-library in Golden and in the Denver Museum of Natural History.
-
-Dredging for alluvial gold was attempted in 1898 in the Breckenridge
-district, but this method of extracting gold was not successful until
-1905. A number of dredges operated between 1910 and 1925. These floating
-behemoths shovel up gold-bearing gravels from the bottom and one side of
-the pond on which they float, sort out the gold in giant sluiceboxes,
-and spew out the leftover gravels in great arc-shaped heaps that can be
-seen near Breckenridge and Fairplay and in a number of other valleys in
-Colorado. They depend for their operation on a plentiful supply of water
-and a shallow water table, but they can sift through quantities of
-gravel at relatively low cost. All told, about $7,000,000 in gold has
-been dredged from this district.
-
-
-                                Fairplay
-
-[Illustration: This gold dredge, still floating in its pond just south
-of Fairplay, operated from 1941 to 1952. With chains of buckets like
-those in the foreground, it dug gravel 70 feet below water level,
-carving a 35-foot bank above water level; in effect it mined to a depth
-of 105 feet. This dredge extracted nearly 115,000 ounces of gold from
-about 33 million cubic yards of gravel (John Chronic photo)]
-
-Another gold field discovered in 1859 was in the northwest corner of
-South Park, along the headwaters of the South Platte River. Several
-mining camps were established here. After early production of rich
-placer deposits, claims were consolidated and large flumes constructed
-so that gold could be recovered by hydraulic mining. In this type of
-mining, streams of water from high-pressure hoses are directed at gravel
-surfaces. The gravels are washed into long sluiceboxes, where gold is
-caught in riffles. Hydraulic mining continued upstream from Fairplay
-until about 1900.
-
-In 1922 a dredge was constructed near Fairplay to process gravel along
-the South Platte and in the valley floor. An even larger dredge,
-constructed in 1941, operated until 1952, when rising labor costs
-overrode the narrow margin on which it operated. At the time operations
-ceased, the dredge was recovering about six cents in gold for each cubic
-yard of gravel processed.
-
-Placer gold has always been the principal mineral product of the
-Fairplay area, but native gold also occurs in the surrounding mountains
-in quartz veins, and many small mines were developed to extract it.
-Sulfide ores were also mined; they contained silver, lead, and zinc as
-well as gold. In the Mosquito Pass and Horseshoe Amphitheater areas,
-there is renewed activity now because of the recent rise in the price of
-silver.
-
-
-                               Silverton
-
-Gold was discovered in the San Juan Mountains of southwest Colorado in
-1870. The earliest mine, near what is now Silverton, was located by a
-group of prospectors sent out by Governor Pile of New Mexico Territory.
-Since the site was on Ute Indian land, real mining did not begin until a
-treaty allowing it was ratified in 1874.
-
-Production in the Silverton district has been from veins in Tertiary
-volcanic rocks within an elliptical area known as the Silverton
-cauldron. Here the volcanic rocks, part of the several thousand feet of
-lava flows and ash falls of the San Juan volcanic field, were cracked
-and faulted by a second period of igneous activity. Ores formed in the
-cracks and fissures.
-
-In the 1870s the Silverton district was very remote, and difficulties
-with transportation retarded activity there. In 1882, however, a
-narrow-gauge railroad was built connecting Silverton with Durango, and
-the problem of transporting ore out of the isolated mountain valley was
-simplified. The railway still exists; a train makes daily passenger runs
-during the summer--the only remaining operating narrow-gauge line in the
-United States. The track follows the Animas River canyon, whose cliffs
-and crags are dotted with long-abandoned mines, prospect holes, and mine
-buildings, monuments to the tenacity and determination of the men who
-mined here.
-
-Production in this district was more than $22,000,000 in gold and
-$20,000,000 in silver between 1874 and 1923. New activity is evident
-here, as in other silver-rich areas of Colorado, because of recent
-demand for silver, lead, and zinc.
-
-[Illustration: Silverton lies in a remote mountain valley in the San
-Juan Mountains. Silver, gold, lead, and zinc have been mined here since
-1874. Storm Peak, composed of Tertiary volcanic rocks, forms the
-backdrop; the narrow-gauge railroad track is visible in the foreground.
-(Jack Rathbone photo)]
-
-
-                                 Ouray
-
-Ouray was settled in 1875, when gold and silver deposits were found near
-Mount Sneffels. Since 1877, mines in Ouray County have produced over
-$35,000,000 in gold and $32,000,000 in silver. The district is still
-quite active: in 1965, mines in this area produced more than $9,000,000
-in gold, silver, copper, lead, and zinc, about a third of total Colorado
-production of these metals for that year.
-
-[Illustration: A few miles south of Ouray, along Uncompahgre Gorge, an
-old mine clings to the slope below the Million Dollar Highway (U. S.
-550). Abrams Mountain rises in the background. The Precambrian
-Uncompahgre Quartzite outcrops up to about the road level; Miocene
-Sunshine Peak Rhyolite caps the peak. (Jack Rathbone photo)]
-
-A mile north of Ouray a prominent intrusive stock marks the center of
-mining activity closest to Ouray. The richest deposits of the Ouray
-area, however, lie about five miles southwest, near Mount Sneffels and
-Red Mountain Creek. There, several large mines, including the famous
-Camp Bird mine, have operated for many years, extracting ore from
-hundreds of veins that underly the surface. Some of these veins are two
-to four miles long. They are in Tertiary volcanic rocks of the San Juan
-Formation. Quartz and calcite are the common gangue (non-economic)
-minerals, and pyrite, sphalerite, galena, and chalcopyrite are the most
-abundant ores. Most of the silver is in the galena; gold occurs in
-streaks and nodules associated with quartz.
-
-About ten miles south of Ouray, along the "Million Dollar Highway" (U.
-S. 550), the Red Mountain district lies on the northwest edge of the
-Silverton volcanic cauldron. It contains a number of small pipelike
-bodies very rich in silver-copper and silver-lead ores. Following the
-mid-Tertiary volcanism and ore intrusion, surface rocks in this area
-were intensely oxidized: resulting iron oxides now form the gaudy reds
-and yellows of Red Mountain and the slopes near Ironton. This
-alteration, as well as the fact that much of the area is covered with
-fallen rock, stream gravels, or glacial deposits, compounds difficulties
-of locating the small though high-grade ore deposits.
-
-The Idarado Mine, on the east side of U. S. highway 550 near Red
-Mountain, used to produce ores from nearby volcanic pipes; now it
-produces from veins some distance to the northwest. The area is
-honeycombed with tunnels and shafts.
-
-
-                                 Aspen
-
-Silver was found at Castle Creek and on Aspen Mountain in 1879. A group
-of prospectors from Leadville, apparently after examining maps of the
-Geological and Geographical Atlas of Colorado published in 1877,
-explored along the line of Paleozoic limestones encircling the Sawatch
-Range. As they had hoped, they found ores similar to those at Leadville
-in rocks of the same age.
-
-Mining began at Aspen in 1880. Here, as at Leadville, intrusion of
-granite porphyry into or near the Leadville Limestone had broken and
-deformed the layers, and ores were deposited in fissures and as
-replacements during cooling of the intrusions. The intricacy of faulting
-which controls the ore pockets in the limestone is well shown on the map
-of Aspen Mountain in Chapter II.
-
-Glaciation occurred in this area, and glacial deposits cover most of the
-ore bodies and outcrops so that little bedrock is exposed. Mapping was
-accomplished by extrapolating to the surface the bedrock patterns shown
-in mine pits, shafts, and tunnels.
-
-Aspen produced some of the richest silver ores in the world, and thrived
-as a boom town for most of two decades. In 1888 the value of ores
-produced reached over $7,000,000; the next year it topped $10,000,000.
-After the silver crash of 1893 production declined rapidly; the last
-mines were closed in the 1920s. Total production of silver, lead, zinc,
-and copper reached about $100,000,000. There was virtually no gold in
-the ores at Aspen.
-
-
-                                 Creede
-
-[Illustration: Creede and its mines are located in an area of Tertiary
-rhyolite and dacite, light-colored volcanic rocks.]
-
-  Happy Thought Mine
-  Amethyst Mine
-  West Willow Creek
-  AMETHYST FAULT
-  Last Chance Mine
-  Del Monte Mine
-  Commodore Mine
-  Jackpot Mine
-  Coppervein Mine
-  Bachelor Mine
-  BULLDOG MOUNTAIN FAULT
-  Kansas City Star Mine
-  Commodore Tunnel
-  Mustang Tunnel
-  Nelson Tunnel
-  Exchequer Mine
-  SOLOMON FAULT
-  CAMPBELL MOUNTAIN
-  Holy Moses #2
-  Holy Moses Mine
-  Ridge Mine
-  Solomon Mine
-  Monte Carlo Mine
-  Mollie S. Mine
-  East Willow Creek
-  Ramey Tunnel
-  Dora Belle Mine
-  Mammoth Tunnel
-  Homestake Mine
-  Mammoth Mine
-  MAMMOTH MOUNTAIN
-  Nancy Hanks Mine
-  Pipe Dream Mine
-  THE NARROWS
-  Windy Gulch
-  CREEDE
-  Willow Creek
-
-The Creede district ranks as one of the most productive silver areas in
-the United States. It came into being largely as a result of a discovery
-by N.H. Creede in 1889. When exploring in this area, he was reported to
-have exclaimed "Holy Moses!" on examining a rich piece of ore, thus
-giving the name to the mine which initiated the rapid development of the
-district. By the end of 1892 the Holy Moses and nearby mines had
-produced ore valued at more than $4,000,000. The area was so rich that
-it managed to survive 1893's great decline in the price of silver; by
-1920 almost $42,000,000 in gold, silver, lead, and zinc had been mined
-there.
-
-The ores, silver-bearing galena, sphalerite, native gold, pyrite, and
-chalcopyrite, are in quartz or amethyst veins in faulted and shattered
-Tertiary volcanic rocks. Nearly all the ore deposits lie along a complex
-system of vertical faults, the Amethyst fault zone, which runs more or
-less northwest-southeast through this region. Both the faulting and the
-enrichment of the fault fissures are believed to have taken place in
-mid-Tertiary time, shortly after deposition of the volcanic host rocks.
-
-
-                             Cripple Creek
-
-[Illustration: Cripple Creek, on the flanks of the Pikes Peak massif,
-has produced more than $400,000,000 worth of gold. The Sangre de Cristo
-Mountains are visible in the distance beyond the Arkansas River valley.
-(Jack Rathbone photo)]
-
-In 1890, two sheepherders stumbled on some richly mineralized rocks near
-Cripple Creek. A boom developed immediately, for the rocks contained
-both gold and silver. Since then, the area has produced more than
-2,000,000 ounces of silver and nearly 19,000,000 ounces of gold.
-
-Cripple Creek has produced almost half of all the state's gold and
-silver. The ores are located in or at the edge of a large mass of middle
-Tertiary volcanic rocks which form an elliptical basin or _caldera_
-several miles across. The caldera, surrounded by Precambrian gneiss and
-granite of the Pikes Peak massif, was probably formed by collapse of a
-volcanic center that had erupted through the older rock. The collapse
-shattered the rocks around the basin margin, and subsequent volcanic
-activity introduced mineral-rich solutions into the many faults and
-fissures produced by the collapse. Tellurides of gold, silver, and
-copper, as well as pyrite, sphalerite, galena, tetrahedrite, and other
-minerals, are characteristic.
-
-
-                                 Climax
-
-[Illustration: At Climax, the ore occurs scattered through the intrusive
-Climax Granite Porphyry and the intruded Idaho Springs Formation.
-Visitors can tour the surface workings during the summer months.]
-
-    Tertiary dikes
-    Shell of Climax stock
-    Core of Climax stock
-    Ore zone
-    Precambrian granite
-    Fault
-    Dykes
-
-Molybdenum now ranks as the number one metal mined in Colorado. Over
-$105,000,000 of "moly" was mined here during 1969, almost all of it from
-the Climax Mine, the world's largest single source of this metal. The
-Climax deposit is located high on the west slope of Ten Mile Range in
-central Colorado, about 100 miles southwest of Denver. It is in the
-central part of the Colorado mineral belt, near the Mosquito Fault, a
-prominent structural feature which extends about sixty miles along the
-north-south trend of the mountains. Rocks on both sides of this fault
-are intruded by Tertiary granite dikes, sills, and stocks. The Climax
-Mine is in a stock just east of the fault, near the axis of a broad
-anticline in Precambrian metamorphic rocks.
-
-Ore minerals at Climax are molybdenite, huebnerite, and cassiterite;
-pyrite is recovered also for the manufacture of sulfuric acid. The ore
-is very low in metal content, containing only one-third of a percent of
-molybdenum, 0.005% tungsten trioxide, and 0.0001% tin. The great size of
-the ore body and efficient recovery by modern methods make Climax a
-profitable mine, however. Production has risen each year since the mine
-began operation.
-
-Urad Mine near Berthoud Pass is a newly developed near-surface
-molybdenum mine similar to Climax. Nearby at the Henderson Mine the ore
-body is more than half a mile below the surface of the ground.
-
-
-                     RADIUM, URANIUM, AND VANADIUM
-
-Over a large area of the Plateau Province in western Colorado, Mesozoic
-sedimentary rocks are locally stained bright yellow, orange, or green.
-Such staining suggests mineralization, and radioactive compounds were
-recognized here before 1900. At that time, however, there was little or
-no market for them or for the vanadium frequently associated with them.
-When Marie Curie required radium for experiments with her newly
-discovered element, the raw materials were sent from western Colorado;
-by and large, though, production of radium from these ores was
-prohibitively expensive.
-
-In 1905, vanadium was found to be effective in toughening steel. The
-Vanadium Corporation of America was formed to mine the Colorado ore.
-This company mines a rich zone in the Jurassic Entrada Sandstone, where
-vanadinite occurs with carnotite and other uranium ores. In the early
-days of vanadium mining, the uranium ores were discarded with other
-gangue materials; now, of course, uranium is produced from them.
-
-Since 1945, uranium production has been an important Colorado industry;
-in 1969 about $17,500,000 worth was produced. Uranium occurs in the
-state in two very different situations. In the Plateau Province, where
-it was first discovered, it occurs in sedimentary rocks as patches of
-pitchblende, carnotite, and a greenish yellow mineral called
-schroekingerite. It is most abundant in the Triassic Chinle Formation
-and the Jurassic Entrada and Morrison Formations, where it was probably
-deposited by downward movement of rainwater from overlying uranium-rich
-Tertiary volcanic rocks. Concentrations of uranium often occur in or
-near organic matter such as coal, fossil bone, or petrified wood, so
-mines tend to be located along rock layers carrying abundant organic
-material.
-
-Another type of uranium ore is found in the Mountain Province. Veins in
-Precambrian rocks of the Front Range and several other ranges contain
-pitchblende which seems to have been deposited by hot groundwater rising
-through broken and fissured Precambrian rocks. Often exceedingly rich,
-such ore is mined in the manner of most of Colorado's metals. The
-Schwartzwalder Mine, a few miles northwest of Golden, has produced more
-ore of this type than any other mine in Colorado.
-
-
-                    OIL, NATURAL GAS, AND OIL SHALE
-
-Petroleum and natural gas have been found in large quantities in the
-Prairie and Plateau Provinces in Colorado, as well as in smaller
-quantities in North Park in the Mountain Province. They generally occur
-in porous sandstone and limestone layers, where they have been trapped
-by overlying finer-grained, less permeable layers in or near folds and
-faults.
-
-Several oil and gas seeps were found along the mountain front shortly
-after the arrival of the earliest settlers. Near Canon City, on Oil
-Creek, a plaque commemorates the first production:
-
-  Oil Creek--site of the first oil well in the west--second place in the
-  United States to produce petroleum from wells. In 1862 ... A. M.
-  Cassedy drilled an oil well 50 feet deep. By February, 1863,
-  production was one barrel a day. Later, several thousand gallons of
-  petroleum were produced by primitive methods, and kerosene and
-  lubricating oil were shipped by ox team as far as Denver and Santa Fe.
-
-About twenty miles to the southeast, near Florence, the Cretaceous
-Pierre shales were drilled in 1876. Oil was found in a system of
-intersecting fractures and joints. Some of the early wells in the
-Florence field are still producing, making this Colorado's oldest and
-longest producing field. It has yielded more than 10,000,000 barrels of
-oil.
-
-Small quantities of oil have been produced near Boulder since about
-1900, also from Pierre sandstones and shales. In this area, wells were
-located by "dowsing" or "witching," as was fashionable at the time.
-Several old rigs can be seen near Boulder Reservoir. As at Florence, oil
-has been trapped in fractures of otherwise dense and impervious shale.
-Some gas is produced and is used by local farms.
-
-More recently, oil was found far beneath the surface in the northern
-part of the Prairie Province. Here, in the Denver Basin, oil is produced
-from several levels in the Dakota Sandstone. The oil has accumulated in
-lenses of beach sand deposited along the shoreline of the Cretaceous
-sea. The general trend of the shoreline, and of the oil fields, is
-northeast-southwest. The shore appears to have been similar to Georgia's
-present coastline: a swampy tidal zone separated from open sea by
-lagoons, sandy bars, and clean sand beaches.
-
-Individual oil pools in the Denver Basin are small, but there are many
-of them; they lie nearly a mile below the surface, under much of Morgan
-and Logan Counties and adjacent parts of Nebraska. Exploratory and
-development drilling keeps total oil production at about 50,000 barrels
-a day. Oil and gas produced here is piped to Denver and other Colorado
-cities.
-
-In southeastern Colorado, oil and gas occur in late Paleozoic limestones
-and sandstones similar to those which outcrop at the edge of the Wet
-Mountains. Prospecting by geophysical methods and by drilling has
-revealed several small, rich accumulations, one of which is thought to
-contain about 30,000,000 barrels of oil.
-
-The Rangely field, in northwestern Colorado, is the most productive
-field in the state. Located in the northeastern part of the Uinta Basin,
-it is an outstanding example of an anticlinal field, where oil is
-trapped in a large, gentle dome. The shape of the dome shows up well on
-the surface; rock layers can be seen dipping outward in all directions
-from the town of Rangely. Oil was found by drilling on the crest of the
-dome. At first, oil was produced from fractures in the Cretaceous Mancos
-Shale at less than 1,000 feet depth. Later, deeper drilling showed that
-oil had also accumulated in the Permian Weber Sandstone, at 5,000 to
-7,000 feet. At present this field is producing about 28,000 barrels of
-oil a day, but the figure is dropping each year as the field is
-depleted.
-
-Oil and gas are produced in southwestern Colorado from the eastern edge
-of the Paradox Basin and the northern edge of the San Juan Basin. In the
-Paradox Basin, oil comes from Pennsylvanian limestone mounds or reefs.
-Production in the Colorado part of the basin has been at most a few
-thousand barrels per day; more is produced in adjacent Utah. In the San
-Juan Basin, gas and oil are trapped in thin porous layers of Cretaceous
-and Pennsylvanian sandstone, between impervious layers of shale. Most of
-the production is in New Mexico, although some oil comes from the
-Colorado part of the basin.
-
-The greatest known potential oil resource in the world lies in the oil
-shales of western Colorado. The richest of these shales cover an area of
-1,600 square miles north of the Colorado River, south of the White
-River, and just east of the Colorado-Utah line. The oil shales are part
-of the Tertiary Green River Formation, which extends over much of
-northwest Colorado, northeast Utah, and southern Wyoming. Oily material
-called _kerogen_ is locked in these rocks, too solid to flow out of the
-fine pore spaces of the shale. To free it the shale must be mined,
-finely crushed, and heated until the kerogen converts to liquid oil.
-This is an expensive process, and as yet production of petroleum from
-the oil shale has not been possible at a cost which will compete with
-production of oil and gas from wells. The United States Bureau of Mines,
-as well as a number of oil companies, have sought for more than fifty
-years to discover a less expensive method for extracting oil from the
-shale. No doubt at some time in the future a competitive technique will
-be developed, or a growing shortage of other oil will bring world prices
-to a level with which present production techniques can compete.
-
-Oil and gas production in Colorado is decreasing at present, even though
-great efforts are being made to find new oil pools. Petroleum
-prospecting and wildcat drilling are carried out in as yet unproductive
-basins in the Plateau Province, in intermontane basins such as the San
-Luis Valley, and on the Plains. Known reserves will continue to provide
-the state with significant income for many years to come, and if oil
-shale recovery becomes profitable. Colorado's hydrocarbons will become
-the most prominent of her commodities.
-
-
-                                  COAL
-
-Coal resources of Colorado amount to about 60 billion tons. Only one per
-cent of this has been mined. Thousands of tons are now being produced
-daily from large mines in central, southern, and northwestern parts of
-the state.
-
-Colorado's coal deposits were formed during late Cretaceous and early
-Tertiary time, when seas were receding from this region and the land was
-rising. They represent accumulations of leaves and other plant material
-in swamps and flood plains similar to those now found in the delta of
-the Mississippi River and in the swamps of southeastern United States.
-Almost all Colorado coal is bituminous or soft coal.
-
-Coal was recognized early in Colorado history by settlers along the
-mountain front, and was mined west and north of Denver in the 1860s.
-Several large underground mines still operate in this district,
-supplying local power plants, but production does not compare with that
-of the Walsenburg-Trinidad area in southern Colorado or the Hayden area
-in northwest Colorado.
-
-The Walsenburg-Trinidad region, part of the Raton coal field, has
-produced coal since the building of the Santa Fe Railroad in the early
-1870s. For many years coal from these mines moved the Santa Fe trains
-and many of the numerous smaller railroads that served Colorado's cities
-and mining camps. The location of the mines helped to determine the
-location of the Colorado Fuel and Iron Company smelter in Pueblo. Now,
-most southern Colorado coal is used to produce electric power. Many
-small mines, miles away from the power plant west of Trinidad, are
-deserted.
-
-A large coal-burning power plant has recently been built between Hayden
-and Steamboat Springs, just west of the Yampa River. Here, some of the
-extensive coal deposits can be seen in road cuts along U. S. highway 40.
-Until conversion to diesel fuel became almost universal in North
-American railroads, mines of this district produced coal for
-locomotives.
-
-In the heyday of the gold and silver mines, coal was also mined near
-Coalmont, in North Park, and Como, in South Park. Coal from these areas
-was used for fuel in nearby mining towns and ranches, and for the
-narrow-gauge railroads that penetrated the mountains here.
-
-At Anthracite, near Crested Butte, high-grade anthracite coal was mined
-for a time. Identical in origin with other Colorado coal, the anthracite
-of this region was hardened by heat and pressures from Tertiary igneous
-intrusions forcing their way into local sedimentary rocks during
-post-Cretaceous mountain building.
-
-A multitude of other coal camps are scattered about Colorado: Cokedale,
-Delcarbon, Coaldale, Roncarbo, Carbondale, and Cardiff stand out because
-of their suggestive names. These early small camps are, like their
-metal-mine cousins, largely deserted today.
-
-
-                         CONSTRUCTION MATERIALS
-
-
-                         Sand, Gravel, and Clay
-
-Sand, gravel, and crushed rock rate high among geologic products in
-Colorado; more than $27,000,000 worth of these materials were produced
-in the state in 1969. Highway and construction activities have brought
-recent expansion in the number and size of quarries and gravel pits.
-Increasingly, Coloradoans are insisting that quarries and pits be
-excavated only where they will not mar the natural beauty of the
-landscape, and many old pits are now being filled in. Unfortunately, the
-scars left by some quarries--such as that on the Rampart Range near
-Colorado Springs--are difficult to erase.
-
-Clay of good quality occurs in Cretaceous deposits in many parts of
-Colorado, most frequently in the Dakota or Laramie Formations. In the
-area around Golden, the Coors Porcelain Company for many years mined
-clay for use in pottery and low temperature ceramic ware. Scars from
-this mining can be seen along the mountain front north and south of
-Golden, and deep clefts within the town, just west of Colorado School of
-Mines, testify to the amounts of clay that have been removed. Colorado
-clay is not pure enough to be used in high temperature ceramics, and the
-present use for it is in the manufacture of common tiles and bricks.
-
-A recent development in Colorado is the use of Cretaceous Pierre shales
-in manufacturing lightweight aggregate for building. The shale is mined
-between Golden and Boulder, near Colorado highway 93. In the nearby
-plant, it is pulverized and then heated in a large rotating cylinder
-until the surface of each particle fuses. Then the particles are quickly
-cooled. The resulting product is much like cinder, light in weight and
-yet strong. It can be mixed with cement for use in construction work
-requiring a great strength-to-weight ratio, or made into concrete
-blocks.
-
-[Illustration: Quarrying of Paleozoic limestones and dolomites along the
-east flank of the Rampart Range northwest of Colorado Springs has badly
-defaced a prominent mountain backdrop. Recent seeding efforts by quarry
-operators are returning the exhausted part of the quarry to its original
-lightly vegetated condition, and hopefully, as the quarry is depleted,
-the scar will disappear. (John Chronic photo)]
-
-
-                                 Stone
-
-In Colorado, as in most parts of the world, building stone for local use
-is quarried locally. Two of the state's stones, however--Yule Marble
-from the Crystal River Canyon, and Lyons Sandstone of the Front
-Range--have been more widely used.
-
-The Yule Marble, or Yule Colorado Marble, was produced by metamorphism
-of Leadville Limestone in an area intruded by the Treasure Mountain
-Granite, thirty-five miles south of Glenwood Springs. This exquisite
-marble, which has graced many famous monuments and buildings (among them
-the Lincoln Memorial and the Tomb of the Unknown Soldier), is known for
-its almost uniform snowy whiteness and regular, fine crystallization.
-Although its beauty, massive character, and uniformity made it a
-sought-after ornamental stone, quarrying was economically marginal
-because of the remoteness of the site. In spite of this, nearly
-$7,000,000 worth of the marble was produced before the quarry closed in
-1940.
-
-[Illustration: Pure white marble was quarried for many years at the Yule
-Colorado Marble Quarry, about three miles southeast of the village of
-Marble. (U. S. Geological Survey photo)]
-
-The Lyons area, north of Boulder, provides pink, hard, even-grained
-sandstone which splits readily into slabs or flagstones. These are used
-in the Denver-Boulder area for sidewalks and patios as well as for
-facing buildings. Quarries owned by the University of Colorado provide a
-constant supply of handsome facing material and flagstone for new
-university buildings, although in recent years the high cost of stone
-construction has limited its use on the campus.
-
-[Illustration: Lyons Sandstone is quarried near Lyons, Colorado. The
-salmon-colored sandstone splits along surfaces defined by slight
-differences in size and arrangement of the sand grains. (John Chronic
-photo)]
-
-[Illustration: Most of the buildings of the University of Colorado are
-faced with Permian Lyons Sandstone, which is widely used for buildings
-and flagstones throughout the Boulder-Denver area. The University
-Museum, shown here, was established in 1902, and contains over a million
-scientific specimens, including many Colorado fossils and minerals.
-Exhibits in the Hall of Earth portray Colorado's geologic history.
-(Tichnor Bros. photo)]
-
-The Lyons Sandstone was deposited as beach and bar sand along the edge
-of a sea which lay east of the Front Range in Permian time. After
-deposition, the sand was deeply buried and compacted. Now tilted up
-along the Front Range uplift, it comes to the surface along the east
-side of the range. Only between Fort Collins and Boulder does the stone
-have the desirable combination of hardness, thin-beddedness, and color
-which makes it desirable for ornamental use. The pink color of the Lyons
-Sandstone is derived from iron oxides, mostly hematite, disseminated
-between the sand grains. Dendrites (often erroneously called fossil
-ferns or plants) ornament some slabs; they were formed by
-crystallization of manganese dioxide from groundwater as it slowly
-percolated through the rock.
-
-
-                            Lime and Gypsum
-
-Outcrops of the Cretaceous Greenhorn and Niobrara Limestones provide
-most of the cement materials in Colorado. A number of plants along the
-mountain front, including a completely automated and dust-free one near
-Lyons, provide the major population centers with millions of tons of
-cement each year.
-
-Colorado is richly endowed with gypsum, useful in cement and plaster
-manufacture and for ornamental stone and sculpture. Along the eastern
-front of the mountains, gypsum occurs in the Triassic Lykins Formation;
-in the Mountain Province, it is abundant in Pennsylvanian sedimentary
-rocks. Particularly high-quality Pennsylvanian gypsum is quarried at the
-town of Gypsum, west of Eagle.
-
-The Colorado portion of the Paradox Basin, in the Plateau Province,
-contains immense deposits of Pennsylvanian gypsum. Here, rocks near the
-surface have been pushed up into sharp northwest-trending faulted
-anticlines by upward movements of gypsum and salt from depths of several
-thousands of feet. The soluble salt and gypsum cores of these structures
-have been washed away more rapidly than the surrounding layers of
-sandstone and shale, leaving depressions such as Gypsum Valley, Paradox
-Valley, and Sinbad Valley, on the crests of the anticlines. Red and
-yellow Triassic sandstones and shales, especially the Chinle Formation
-and the Wingate Sandstone, dip away from these valleys. Exploratory
-wells indicate that vast masses of salt and gypsum are present beneath
-the surface, and may extend to depths greater than 10,000 feet.
-
-
-                       GEMS AND ORNAMENTAL STONES
-
-More than thirty different gems and ornamental stones are known to occur
-in Colorado. Amazonstone, amethyst, garnet, tourmaline, aquamarine,
-topaz, lapis lazuli, quartz crystal, smoky and rose quartz, sapphire,
-several varieties of agate, zircon, and other attractive stones are
-gathered within the state, mainly in the Mountain Province. Turquoise is
-known at several places in the volcanic area of southern Colorado.
-Alabaster is mined along the northeastern mountain front near Fort
-Collins and Loveland. Localities of interest to gem hunters are
-described in _Colorado Gem Trails and Mineral Guide_, by Richard M.
-Pearl.
-
-Gem Village, in southwestern Colorado on U. S. highway 160 between
-Durango and Pagosa Springs, is a favorite stopping place for tourists
-wishing to see or buy colorful and attractive Colorado stones such as
-petrified wood, agatized dinosaur bones, chalcedony, and jasper.
-
-
-                                 WATER
-
-Although not all aspects of water and water supply are geologic, water
-is an important geologic agent, determining the shape of the surface,
-the distribution of minerals, and the location of caves. Water used in
-Colorado comes entirely from precipitation within the state, as all of
-Colorado's rivers flow from Colorado outward toward the surrounding
-lower-elevation states.
-
-
-                             Surface Water
-
-[Illustration: A cross section through the Front Range northwest of
-Denver shows the redistribution and use of western slope water in
-eastern Colorado through the Colorado-Big Thompson Project. This project
-has cost about $160,000,000, but it is repaying the investment many
-times over by providing electric power and increasing farm production.]
-
-Moisture carried by prevailing westerly or northwesterly winds falls
-primarily on Colorado's western slope, although at some times of year
-precipitation may come from the northeast or southeast. West of the
-continental divide, where population is sparse, there is a surplus of
-water. East of the divide, where more than 90 per cent of the population
-lives, water is in desperately short supply. The high and largely
-unpopulated Mountain Province receives by far the greatest proportion of
-precipitation, while agricultural areas of the Prairie and Plateau
-Provinces receive much less. Needless to say, the major problem
-involving water in Colorado is how to move it from areas where it is
-abundant to areas where it is needed.
-
-In many parts of the state, complex water laws and complicated
-irrigation canals and water systems were developed soon after the area
-became settled. Gradually but inevitably, water resources have been
-transferred from the western slope to the eastern. However, such
-transfer must be undertaken with due regard for the rights of downstream
-users, notably California, Arizona, and New Mexico.
-
-One of the largest water movement schemes in the state is the
-Colorado-Big Thompson Project. Water that otherwise would flow into the
-Colorado River is piped from Grand Lake through the Alva B. Adams tunnel
-under the high mountains of Rocky Mountain National Park, and into the
-Big Thompson drainage near Estes Park. It then travels through a series
-of reservoirs and tunnels into the South Platte River basin, where it is
-used for irrigation and household water. The water is pumped up the
-western gradient of this system by electric power produced as it flows
-down the eastern slope. Surplus electric power serves the
-Colorado-Wyoming area.
-
-Another large project is the Denver Water Board's Dillon Reservoir
-Project, in which western slope water collected at Dillon is pumped
-twenty-three miles under the continental divide through the Harold D.
-Roberts tunnel to the North Fork of the South Platte River for use by
-the city of Denver. The exit point of this tunnel can be seen a few
-miles west of Grant along U. S. highway 285. This project is
-continuously growing as Denver's water needs mount.
-
-In each of these projects, engineering geologists played a prominent
-part in locating dams and tunnels that would not leak or fail, and that
-could collect and transport a maximum amount of water during the
-high-runoff spring season for distribution through the rest of the year.
-Fortunately for geologists, the tunnels and bores necessary to the
-projects allowed them to learn a great deal about the structure of the
-interior of the high mountains, and helped to improve their
-interpretation of earth history in this most interesting region.
-
-The necessity for storing irrigation water along the eastern mountain
-front has led to the creation of hundreds of new lakes in the region.
-Although water levels vary with the season, many of the lakes provide
-opportunities for water sports and recreation for the burgeoning inland
-population.
-
-Two large dams have recently been built in western Colorado for another
-purpose: to control the flow of water in the Colorado River drainage
-basin. Electric power for western Colorado also comes from these dams.
-One of the dams is on the Gunnison River at Curecanti, upstream from the
-Black Canyon of the Gunnison National Monument, and the other is on the
-Frying Pan River near Ruedi. The latter was completed over the
-objections of geologists, who believed that the extensive gypsum
-deposits underlying the damsite would cause its failure. Cement pumped
-deep into the rocks in the vicinity has so far prevented serious
-rupture.
-
-There is strong resistance by conservation groups to the construction of
-more dams on Colorado River drainage, primarily because the Colorado and
-its tributaries pass through many irreplaceable canyons, some of them
-parts of National Parks and Monuments, that are very much a part of our
-western heritage.
-
-
-                              Groundwater
-
-[Illustration: In the San Luis Valley, runoff from the San Juan and
-Sangre de Cristo Mountains sinks into layers of sand in the Alamosa
-Formation. Flowing along the sand layers toward the center of the
-valley, it provides artesian water for irrigation of valley farmlands.]
-
-  SAN JUAN MOUNTAINS
-  LIMIT OF FLOWING WELLS
-  HUBBARD'S WELL
-  OTTOWAY'S WELL
-  ALAMOSA WELL
-  GEORGE NEWSOM'S WELL
-  CALKIN'S WELL
-  LIMIT OF FLOWING WELLS
-  Moraine
-  Alluvial Slope
-  SANGRE DE CRISTO MOUNTAINS
-  Sands, lava beds, gravels, conglomerates, etc.
-  Alamosa formation
-  Granites
-  WEST
-  SANTE FE FORMATION
-  SANTE FE FORMATION
-  EAST
-
-Groundwater is extremely important to Colorado, especially in the
-Prairie Province and the San Luis Valley. Below these two areas lie a
-number of distinct and productive groundwater aquifers, several of them
-artesian. In Otero County, for example, there are five major aquifers:
-three separate Quaternary gravel deposits, the Cretaceous Dakota
-Sandstone, and the Cheyenne Sandstone Member of the Purgatoire
-Formation, also Cretaceous. All these aquifers are characterized by
-their high porosity and permeability, which allow water to flow rapidly
-through them. Wells in the younger, shallower aquifers produce as much
-as 2,000 gallons per minute; those in the older, deeper aquifers produce
-about eighty gallons per minute, some of it with an artesian "head."
-
-The San Luis Valley supports intensive agriculture, made possible by a
-great artesian water supply. A thick series of soft interlayered clays
-and sands, the Alamosa Formation, slopes down toward the center of the
-basin from the surrounding mountains. Water entering the sandstone beds
-at the mountain edges flows through the sand layers held there by the
-impermeable clay beds. By the time it reaches the center of the valley,
-it has developed considerable hydrostatic head, and the water rises in
-wells without pumping. Unfortunately, both the irrigation water and the
-soils in the San Luis Valley are highly alkaline. Constant evaporation
-from the irrigated fields has concentrated the alkali near and on the
-surface, rendering some of the land less usable than it was originally.
-
-
-                                 Caves
-
-Colorado has many caves, most of them carved by underground water in
-Paleozoic limestone. The Cave of the Winds at Manitou is the only one in
-the state which has been developed as a tourist attraction. It is in
-highly faulted Ordovician and Mississippian limestone near the mountain
-front, where the faulting, coupled with the high relief, has accelerated
-solution of the rock by allowing groundwater to percolate downward
-rapidly. The cavern was probably carved during the Pleistocene Ice Age,
-when surface water and groundwater were much more abundant than at
-present. Deposition of stalactites and stalagmites has occurred within
-the last few thousand years, as supplies and movement of water have
-decreased.
-
-Spanish Cave, above timberline on Marble Mountain in the Sangre de
-Cristo Range, is probably the nation's highest limestone cave. It is in
-thick folded and faulted Pennsylvanian reef limestone, at an elevation
-of over 12,000 feet. The cave has many intricate passageways branching
-from its main vertical tubes and channels.
-
-Fulford Cave, south of Eagle, is in the Mississippian Leadville
-Limestone of the northern part of the Sawatch Range. Many other caves
-are situated south of Fulford, near Woods Lake, where the limestone is
-widely exposed and highly dissected.
-
-Fairy Cave, northeast of Glenwood Springs, is the best known of the many
-caverns in the Paleozoic limestones that form the southern flanks of the
-White River Plateau.
-
-[Illustration: In Cave of the Winds near Manitou, Paleozoic limestones,
-cracked and tilted by uplift of the Front Range, have been honeycombed
-by ground water. Calcite stalactites hang from the ceiling, while
-stalagmites grow up from the floor. (Cave of the Winds Company photo)]
-
-In the Plateau Province another type of cave is formed not so much by
-groundwater as by weathering of the flat-lying alternating beds of
-massive resistant sandstone and less resistant, thinly bedded mudstone
-and shale. Where the resistant layers are undermined, great arching
-caves develop. These are best observed at Mesa Verde National Park,
-where many of them once sheltered Indian communities. They can also be
-seen in Colorado National Monument and along the Colorado River and
-several of its major tributaries.
-
-[Illustration: Along the edge at Mesa Verde, caves in Cretaceous Mesa
-Verde sandstone were used for shelter by Indians. Springs near the bases
-of the caves, which provided the Indian communities with water, probably
-contributed to the undermining of the sandstone cliffs. (Colorado
-Department of Highways photo)]
-
-
-                                Springs
-
-The multitudes of mineral and hot springs in Colorado are a fascinating
-and interesting facet of the Mountain Province. Some are located along
-major faults, where the rocks are so broken and shattered that
-groundwater can move freely toward the surface. Colorado Springs,
-Manitou Springs, and Eldorado Springs are on the fault complex that
-forms the east edge of the Front Range. Glenwood, Juniper, Steamboat,
-and Poncha Springs are on well defined faults also.
-
-[Illustration: Glenwood Hot Springs flow from Pennsylvanian shales of
-the Belden Formation, where sedimentary layers are faulted by the sharp
-upward tilting against the south side of the White River Plateau. Behind
-the hotel and on the right can be seen the Mississippian Leadville
-Limestone, cut by the Colorado River. (From a painting by William H.
-Jackson, courtesy of Colorado State Archives and Public Record)]
-
-Many other springs do not seem to be controlled so strongly by faulting,
-but owe their presence to sources of volcanic or magmatic heat which
-exist near to the surface of the ground. Some springs of this type issue
-from Precambrian granite, or Cenozoic volcanic rock, while others flow
-from sedimentary rock layers. Waunita Hot Springs and Pagosa Springs,
-although near volcanic rocks, reach the surface through porous
-sandstones and shales of Cretaceous age. Mt. Princeton Hot Springs comes
-from alluvium but its heat source is the intrusive igneous rock which
-makes up part of the adjacent mountain.
-
-Springs of another general type are also present in Colorado where
-aquifers, generally sandstones, are dissected by erosion. These springs,
-usually not highly mineralized or warm, are most often found in the
-Plateau Province. Such springs are frequent at the bases of the great
-sandstone cliffs of Mesa Verde and Colorado National Monument.
-
-Manitou's carbonated springs, which attract many tourists, have their
-origin in the arrangement and nature of the rocks through which the
-water flows. Water from the Pikes Peak region, slightly acid from its
-contact with the granitic rock, flows into the Manitou limestone all
-along Ute Pass fault, which extends from Cheyenne Mountain northwest to
-Woodland Park. Descending through channels along the fault, the water
-becomes pressurized. Because of its pressure and its acid content, it
-partly dissolves the calcium carbonate of the limestone, and from then
-on carries carbon dioxide in solution. As the water comes to the surface
-at the low point of the fault exposure, near the west edge of Manitou,
-the pressure is released and the carbon dioxide effervesces, just as a
-bottle of soda water effervesces when the cap is removed.
-
-
-                         ENVIRONMENTAL GEOLOGY
-
-The preceding part of this chapter mentions many ways in which man's
-destiny in Colorado has been shaped by geologic factors. Early
-Coloradoans settled near gold and silver placers, later ones near mines
-that produced ores of other metals, or in the towns that sprang up
-around the mills and smelters that processed these ores. Our present
-distribution of population is partly a heritage from these first
-settlements, partly a result of later discoveries of oil, gas, and
-radioactive minerals, and partly a response to the state's extreme
-topographic variation, which controls and delineates agricultural areas
-and transportation routes.
-
-In recent years, man has begun to appreciate the fact that he may
-benefit in other ways from knowledge about geology. A new geology has
-developed--_environmental geology_--which may be defined as the total of
-all geological conditions and influences affecting the life and
-development of man.
-
-Environmental geology is a broad science, concerned not only with the
-location of cities and towns, but with the uses people make of the land
-and its economic products, and with the relationship between the
-geological character of the land and the present and future location of
-roads, dams, bridges, factories, homes, recreation facilities, sanitary
-land fills, and even sewage plants.
-
-Two aspects of environmental geology which are particularly pertinent to
-Colorado's residents are discussed below.
-
-
-_Landslides_ and slumping rock or earth are a frequent menace to
-Colorado's development in the Mountain Province. Often activated by
-heavy rains or deep manmade cuts, they can cause--and _have_
-caused--much damage to roads, buildings, and other works of man.
-
-The flanks of North and South Table Mountains, near Golden, are mantled
-by thick landslide debris; intermittent movement of the individual
-slides has repeatedly affected the railroad, irrigation ditches, and
-roads. As many as six different slides have moved within a single year.
-In one slide area, asphalt road material is estimated to be thirteen
-feet thick; successive layers of pavement have been laid one on top of
-another to keep the street up to grade.
-
-Landslides and landslide-prone areas may not be obvious to the untrained
-eye. Each year buildings and roads are constructed on unsuitable rock
-and soil foundations, in places where some degree of land slip is almost
-inevitable. Building in such areas is risky, but sometimes worth the
-risk; if condition are less than ideal, risks can be reduced by
-specialized types of construction.
-
-
-_Floods_ are a perennial threat to much of the state, because of the
-high relief of the drainage basins and the torrential nature of the
-spring and summer rainfall. Their damaging effects were realized early
-in Colorado's history, when canyons were used as highways and railroad
-routes.
-
-Colorado's most expensive flood was probably the flood in the South
-Platte River basin south of Denver in 1965, which caused $508,000,000
-worth of damage and drowned six people. The losses can be attributed to
-man's failure to realize the significance of the South Platte drainage
-routes and flood plains. Homes, shopping centers, and many other
-buildings occupied--and still occupy, as of 1971--land that has been
-intermittently flooded for many years. The following description of this
-flood, by H. F. Matthai of the U. S. Geological Survey, may help to
-convey some warning to residents or potential residents of the South
-Platte valley and other river valleys in Colorado:
-
-"The morning of June 16 was most pleasant, but conditions changed
-rapidly shortly before noon. A tornado touched ground 15 miles south
-southeast of Denver about 1 p.m. Within the next hour, another unroofed
-30 homes in the little town of Palmer Lake, 40 miles south of Denver.
-About 2 p.m., a dense mass of clouds descended and concealed the top of
-Dawson Butte, 7 miles southwest of Castle Rock; and the little light
-remaining faded until it was dark black and frightening, according to
-some people. A nearby rancher's wife described the intense quiet as
-awesome, but the calm did not last very long.
-
-"The deluge began, not only near Dawson Butte, but also at Raspberry
-Mountain, 6 miles to the south, near Larkspur. The rain came down harder
-than any rain the local residents had ever seen, and the temperature
-dropped rapidly until it was cold. The quiet was shattered by the
-terrible roar of wind, rain, and rushing water. Then the thudding of
-huge boulders, the snapping and tearing of trees, and the grinding of
-cobbles and gravel increased the tumult. The small natural channels on
-the steep slopes could not carry the runoff; so water took shortcuts,
-following the line of least resistance. Creeks overflowed, roads became
-rivers, and fields became lakes--all in a matter of minutes.
-
-"The flow from glutted ravines and from fields and hillsides soon
-reached East and West Plum Creeks. The combined flow in these creeks
-have been described as awesome, fantastic, and unbelievable; yet none of
-these superlatives seem adequate to describe what actually occurred.
-Large waves, high velocities, crosscurrents, and eddies swept away
-trees, houses, bridges, automobiles, heavy construction equipment, and
-livestock. All sorts of debris and large volumes of sand and gravel were
-torn from the banks and beds of the streams and were dumped, caught,
-plastered, or buried along the channel and flood plains downstream. A
-local resident stated, 'The banks of the creek disappeared as if the
-land was made of sugar.'
-
-"The flood reached the South Platte River and the urban areas of
-Littleton, Englewood, and Denver about 8 p.m. Here the rampaging waters
-picked up house trailers, large butane storage tanks, lumber, and other
-flotsam and smashed them against bridges and structures near the river.
-Many of the partly plugged bridges could not withstand the added
-pressure and washed out. Other bridges held, but they forced water over
-approach fills, causing extensive erosion. The flood plains carried and
-stored much of the flood water, which inundated many homes, businesses,
-industries, railroad yards, highways, and streets.
-
-"The flood peak passed through Denver during the night, and the
-immediate crisis was over by morning; but those in the inundated areas
-were faced with a Herculean task. The light of day revealed the nature
-of the destruction--mud in every nook and cranny, soggy merchandise,
-warped bowling alleys, drowned animals, the loss of irreplaceable
-possessions, to name a few types. The colossal cleanup job, which would
-take months, began."
-
-Hydrogeological studies by the U. S. Geological Survey and Corps of
-Engineers give knowledgeable estimates of flood danger for different
-populated areas of the state, and recommend that homes, roads, and other
-structures be placed above likely flood levels.
-
-
-
-
-                                GLOSSARY
-
-
-Alluvial fan. A cone-shaped mass of sediment built by rivers or streams
-    as they issue from mountains onto more level ground.
-
-Alluvium. Stream deposits formed in recent geologic time, composed of
-    sand, gravel, and stones.
-
-Ammonite. One of a large group of extinct mollusks related to the living
-    chambered _Nautilus_. Ammonite shells, usually cone-shaped or
-    coiled, are divided into many chambers by crenellated septa.
-
-Angular unconformity. A surface separating tilted or folded layers of
-    rock from overlying less disturbed layers.
-
-Anticline. An upward fold or elongated arch in rock layers.
-
-Aquifer. A rock layer that is water-bearing.
-
-Artesian water. Groundwater that is under sufficient pressure to rise
-    above the level at which it is encountered in a well. It does not
-    necessarily rise completely to the surface.
-
-Basalt. An extrusive igneous rock, fine-grained and dark colored,
-    composed mainly of calcium-rich feldspar and the black mineral
-    pyroxene.
-
-Basement. A name commonly applied to metamorphic or igneous rocks
-    underlying the sedimentary rock layers.
-
-Batholith. A large body of intrusive igneous rock, 40 square miles or
-    more in outcrop area, which extends downward to an unknown depth.
-
-Bedrock. The solid rock which underlies soil, sand, clay, or other loose
-    surface material.
-
-Belemnite. The cigar-shaped internal shell of an extinct marine mollusk
-    similar to a squid.
-
-Brachiopod. One of a large group of marine shelled animals having two
-    unequal, bilaterally symmetrical shells.
-
-Bryozoa. A large group of tiny colonial marine animals that secrete
-    calcareous or horny coverings in a great variety of shapes.
-
-Caldera. A large basin-shaped depression caused by explosion or collapse
-    around a volcanic center.
-
-Cassiterite. A heavy, brown to brownish black mineral composed of tin
-    and oxygen (SnO_2) that is an ore of tin.
-
-Cephalopod. A marine mollusk with a head surrounded by tentacles. Squids
-    and octupuses belong to this group, as do fossil forms having
-    straight or coiled shells divided into numerous interior chambers.
-
-Chalcopyrite. A reddish-gold colored ore of copper (CuFeS_2).
-
-Cirque. A deep, steep-walled recess in a mountain, caused by glacial
-    erosion at the head of a valley.
-
-Concretion. A nodular or irregular concentration of minerals such as
-    calcite or limonite, formed by precipitation of the mineral from
-    groundwater around a nucleus.
-
-Conglomerate. A rock containing coarse fragments of an older rock,
-    usually as rounded water-worn stones or pebbles.
-
-Conodont. One of a group of tiny dark brown tooth-like fossils thought
-    to be dermal or dental parts of some extinct group of fish.
-
-Diatreme. A volcanic vent or pipe drilled through rocks by the explosive
-    energy of gas-charged molten rock, now containing igneous rock and
-    often altered or unaltered fragments of the surrounding rock.
-
-Dike. A vertical or nearly vertical sheet of igneous rock which cuts
-    across the structure of adjacent rocks.
-
-Diorite. An intrusive igneous rock composed of sodium-rich feldspar and
-    dark minerals, with only small amounts of quartz.
-
-Dip. The angle at which a layer of rock is inclined below the
-    horizontal.
-
-Dome. A roughly circular upfold in which the rock layers dip outward in
-    all directions from the center.
-
-Dowsing. Searching for underground water or ore with a divining rod,
-    usually a forked stick supposed to locate spots where the desired
-    substance may be found under the surface.
-
-Echinoderm. One of a large group of marine invertebrate animals, most of
-    which have pentagonal symmetry and a skeleton of many calcite
-    plates. Many forms are spiny. The group includes starfish and sea
-    urchins.
-
-Evaporite. Chemical sediments precipitated when water (usually sea
-    water) evaporates.
-
-Extrusive rocks. Igneous rocks formed when molten rock material is
-    ejected onto the surface. Synonymous with volcanic rocks.
-
-Fault. A break in the rocks in which there has been displacement of the
-    two sides relative to each other.
-
-Fault block range. A mountain range bounded on two or more sides by
-    faults.
-
-Feldspar. A group of light-colored aluminum silicate minerals that are
-    major constituents of igneous rocks. They contain potassium, sodium,
-    and calcium in differing proportions.
-
-Fold. A bend in rock layers.
-
-Foraminiferida. One-celled marine animals with microscopic, perforated,
-    many-chambered calcium carbonate shells, often called forams.
-
-Fossil. The remains or traces of an animal or plant which has been
-    preserved in the rock.
-
-Fusulinid. One-celled marine animals (forams) with shells which look
-    like a grain of wheat in shape and size, frequently abundant in
-    Colorado Pennsylvanian rocks.
-
-Galena. A heavy gray metallic mineral (PbS), often cubic in form, that
-    is the most important ore of lead.
-
-Gangue. Nonvaluable minerals occurring in veins with ore minerals.
-
-Glaciation. Alteration of the earth's surface by erosion and deposition
-    by glacier ice.
-
-Glacier. A body of ice originating on land by recrystallization of snow,
-    and showing evidence of movement by flowing.
-
-Gneiss. A coarse-grained metamorphic rock usually banded with streaks of
-    darker, finer-grained rock.
-
-Granite. An intrusive igneous rock consisting essentially of sodium or
-    potassium feldspar and quartz, often speckled with dark-colored
-    minerals.
-
-Graptolite. Extinct marine organisms without known close living
-    relatives, with small black sawblade-like chitinous hard parts
-    preserved as fossils.
-
-Hematite. A steel gray or metallic grayish black or reddish gray mineral
-    (Fe_2O_3) that is an important ore of iron.
-
-Hogback. A sharp-crested ridge formed by a resistant layer of steeply
-    dipping rock.
-
-Huebnerite. A heavy reddish brown mineral (MnWO_4) that is a major ore
-    of tungsten.
-
-Igneous rocks. Rocks formed by solidification from a molten state,
-    either at the surface (extrusive) or below the surface (intrusive).
-
-Intrusive rocks. Igneous rocks formed when molten rock material
-    solidifies without reaching the surface.
-
-Joint. A fracture in the rock, along which no discernible movement has
-    taken place.
-
-Kerogen. Solid bituminous material in oil shales.
-
-Laccolith. A lens-shaped mass of igneous rock intruded into layered
-    rocks.
-
-Lava. Fluid or molten rock such as that which issues from a volcano.
-
-Lode. A rock mass, often a vein, containing valuable minerals.
-
-Massif. A mountainous mass that has relatively uniform geologic
-    characteristics and which may embrace a number of peaks.
-
-Mesa. A flat-topped mountain bounded on at least one side by a steep
-    cliff.
-
-Metamorphic rock. Rock formed by alteration of pre-existing rock,
-    especially by great temperatures and pressures.
-
-Mollusk. Any one of the large group of invertebrate animals which
-    includes the snails, clams, octopuses, squids, and their extinct
-    relatives.
-
-Molybdenite. A soft bluish gray, metallic mineral (MoS_2) that is a
-    major ore of molybdenum.
-
-Monocline. A steplike fold in otherwise horizontal or gently dipping
-    rock layers.
-
-Moraine. An accumulation of unsorted rock material built up by the
-    action of glacier ice.
-
-Native gold. Gold occurring in nature uncombined with other elements.
-
-Peneplain. A land surface worn down by erosion to a nearly flat or
-    broadly undulating plain.
-
-Petzite. A heavy black or steel gray metallic telluride ore of gold and
-    silver (Ag_3AuTe_2).
-
-Placer. A sand or gravel deposit containing particles or nuggets of gold
-    or other heavy valuable minerals.
-
-Plateau. An elevated, comparatively flat surface of land, usually larger
-    than a mesa, sometimes composed of many mesas, and often dissected
-    by deep stream valleys.
-
-Porphyry. An igneous rock, usually intrusive, which contains conspicuous
-    large crystals in a fine-grained matrix.
-
-Pyrite. A brass-yellow metallic mineral (FeS_2) that is an important
-    source of sulfur. It is commonly known as fool's gold.
-
-Reef. A moundlike limestone structure built in the sea by sedentary
-    organisms such as corals.
-
-Rhyolite. A light-colored volcanic rock with quartz and feldspar as the
-    principal constituents.
-
-Schist. A metamorphic rock characterized by parallel orientation of
-    flat-grained minerals like mica.
-
-Sedimentary rocks. Rocks formed of fragments of other rock transported
-    by wind or water, or formed by precipitation from solution.
-
-Sphalerite. An amber-yellow to black mineral (ZnS) that is an important
-    ore of zinc.
-
-Stalactite. A cylindrical or conical deposit of calcite hanging from the
-    roof of a cavern, formed by evaporation of water droplets containing
-    calcium carbonate.
-
-Stalagmite. Columns or ridges of calcite rising from the floor of a
-    cavern, formed by water containing calcium carbonate dripping from a
-    stalactite.
-
-Stock. A mass of igneous intrusive rock that covers less than 40 square
-    miles, has steep sides, and extends to an unknown depth.
-
-Tennantite. A metallic gray mineral that contains copper, iron, and
-    arsenic, and is an ore of copper.
-
-Tetrahedrite. A brittle, dark gray to black, metallic mineral containing
-    copper, iron, zinc, and silver.
-
-Trilobite. One of a primitive group of extinct marine crustaceans,
-    related to crabs and lobsters, having segmented bodies divided by
-    longitudinal grooves into three lobes.
-
-Unconformity. A surface separating layers of rock, formed by a period of
-    nondeposition or erosion.
-
-Vein. A crack or fissure filled with mineral material, often with
-    valuable ore minerals.
-
-
-
-
-                           SUGGESTED READING
-
-
-There are thousands of scientific articles and books on Colorado
-geology, and many new ones appear each year. Following is a selection of
-books and booklets which we believe will be most useful and interesting
-in extending your knowledge of the state's geology.
-
-Donnell, John R., editor, 1960, GEOLOGICAL ROAD LOGS OF COLORADO. Rocky
-    Mountain Association of Geologists, Denver. Itineraries for a number
-    of geological trips along Colorado highways and byways.
-
-Eckel, Edwin B., 1961, MINERALS OF COLORADO, A 100-YEAR RECORD. U. S.
-    Geological Survey Bulletin 1114.
-
-Emmons, S. F., Cross, Whitman, and Eldridge, G. H., 1896, GEOLOGY OF THE
-    DENVER BASIN IN COLORADO. U. S. Geological Survey Monograph 27. The
-    classic early treatment of the surface geology around Denver, with
-    many historic illustrations.
-
-Hansen, Wallace R., 1965, THE BLACK CANYON OF THE GUNNISON TODAY AND
-    YESTERDAY. U. S. Geological Survey Bulletin 1191. A readable account
-    of this unusual national monument near Montrose.
-
-Hansen, Wallace R., 1969, THE GEOLOGIC STORY OF THE UINTA MOUNTAINS. U.
-    S. Geological Survey Bulletin 1291. The eastern part of this range
-    is in Colorado.
-
-Henderson, C. W., 1926, MINING IN COLORADO, A HISTORY OF DISCOVERY,
-    DEVELOPMENT AND PRODUCTION. U. S. Geological Survey Professional
-    Paper 138.
-
-Lee, W. T., 1917, THE GEOLOGIC STORY OF THE ROCKY MOUNTAIN NATIONAL
-    PARK, COLORADO. U. S. National Park Service Publication. An old
-    report, not adequately superseded.
-
-Lovering, T. S., and Goddard, E. N., 1950, GEOLOGY AND ORE DEPOSITS OF
-    THE FRONT RANGE, COLORADO. U. S. Geological Survey Professional
-    Paper 223. A comprehensive study of mineral-bearing areas in the
-    Front Range.
-
-Lohman, S. W., 1965, THE GEOLOGIC STORY OF COLORADO NATIONAL MONUMENT.
-    Colorado and Black Canyon Natural History Association, Grand
-    Junction.
-
-Pearl, Richard M., 1956, NATURE AS SCULPTOR: A GEOLOGIC INTERPRETATION
-    OF COLORADO SCENERY. Denver Museum of Natural History Popular Series
-    No. 6, Revised Edition.
-
-Pearl, Richard M., 1969, EXPLORING ROCKS, MINERALS, FOSSILS IN COLORADO.
-    Swallow Press, Revised Edition.
-
-Pearl, Richard M., 1971, COLORADO GEM TRAILS AND MINERAL GUIDE. Swallow
-    Press, 3rd Edition.
-
-Powell, John Wesley, 1876, REPORT ON THE GEOLOGY OF THE EASTERN PORTION
-    OF THE UINTA MOUNTAINS AND A REGION OF COUNTRY ADJACENT THERETO. U.
-    S. Geological and Geographical Survey of the Territories. One of the
-    earliest accounts of geology in Colorado, written by the explorer of
-    the Colorado River and the father of the U. S. Geological Survey.
-
-Rabbit, Mary C., and others, 1969, THE COLORADO RIVER AND JOHN WESLEY
-    POWELL. U. S. Geological Survey Professional Paper 669. A resum� of
-    part of Powell's work and a good discussion of the geologic history
-    of the entire Colorado River, which begins near Grand Lake.
-
-Richmond, Gerald M., 1965, GLACIATION OF THE ROCKY MOUNTAINS. A part of
-    THE QUATERNARY OF THE UNITED STATES, Princeton University Press. A
-    summary of current knowledge of glaciation in Colorado and
-    surrounding areas.
-
-Rodeck, Hugo G., editor, 1964, NATURAL HISTORY OF THE BOULDER AREA.
-    University of Colorado Museum Leaflet No. 13. Contains articles on
-    geology and biology.
-
-Untermann, G. E., and Untermann, B. R., 1954, GEOLOGY OF DINOSAUR
-    NATIONAL MONUMENT AND VICINITY, UTAH--COLORADO. Utah Geological and
-    Mineralogical Survey Bulletin 42. A detailed study of the eastern
-    Uinta Mountains.
-
-Weimer, Robert J., and Haun, John D., editors, 1960, GUIDE TO THE
-    GEOLOGY OF COLORADO. Geological Society of America, Rocky Mountain
-    Association of Geologists, and Colorado Scientific Society, Denver.
-    A concise summary of many aspects of Colorado geology, this guide
-    includes several geological itineraries and many reference listings.
-
-Wolle, Muriel Sibell, 1949, STAMPEDE TO TIMBERLINE, Sage Books. An
-    excellent account of early mining activity in the state, with many
-    fine drawings of the early settlements.
-
-
-
-
-                                 INDEX
-
-
-                                   A
-  Abrams Mountain, 87
-  Alamosa, 35
-  Alamosa Formation, 67, 105, 106
-  Alma, 78
-  Ancestral Rocky Mountains, 44, 45
-  Animas River, 58, 86
-  Ankareh Formation, 52
-  Antero Junction, 21
-  Anthracite, 97
-  Arapahoe Conglomerate, 60
-  Arapaho Glacier, 70, 71
-  Arkansas Hills, 21
-  Arkansas Mountain, 79
-  Arkansas River, 3, 22, 35, 90
-  Arkansas Valley, 21
-  Aspen, _Front._, 1, 22, 35, 50, 74, 77, 78, 88-89
-  Aspen Mountain, 23, 88
-  Avon, 22
-
-
-                                   B
-  Battlement Mesa, 62
-  Belden Formation, 44, 109
-  Benton Shale, 57
-  Berthoud Pass, 12, 92
-  Big Thompson Canyon, 12, 71
-  Big Thompson River, 69, 103, 104
-  Black Canyon of the Gunnison, 36, 37, 44, 71, 105
-  Black Hawk, 14, 77, 78, 79, 80
-  Blue River, 103
-  Book Cliffs, 29
-  Boulder, 8, 14, 33, 45, 47, 48, 50, 71, 74, 75, 94, 98, 99, 100,
-          101
-  Boulder County, 78, 79
-  Boulder Creek, 1, 15, 71, 103
-  Boulder Creek Granite, 14, 33, 35
-  Boulder Reservoir, 103
-  Breckenridge, 1, 78, 83-84
-  Bross, Mt., 21
-  Buena Vista, 22
-  Buffalo Peaks, 21
-  Building stone, 24, 48, 50, 99-101
-
-
-                                   C
-  Cache la Poudre River, 66, 103
-  Cambrian, 7, 34, 39
-  Camp Bird, 78, 88
-  Canon City, 3, 11, 16, 52, 53, 75, 94
-  Canon City Embayment, 16
-  Carbondale, 97
-  Carboniferous, see Mississippian, Pennsylvanian
-  Cardiff, 97
-  Carmel Formation, 52
-  Carter Lake, 103
-  Castle Creek, 88
-  Castle Rock, 8, 61, 112
-  Castle Rock Conglomerate, 60
-  Cave of the Winds, 106, 107
-  Caves, 31, 106-108
-  Cenozoic (see also Tertiary, Quaternary), 7, 16, 18, 26, 28, 29,
-          59-73, 109
-  Central City, 1, 14, 74, 77, 78, 80
-  Chaffee Formation, 42
-  Cherry Creek, 1
-  Cheyenne Mountain, 14, 15, 110
-  Cheyenne Sandstone, 105
-  Chinle Formation, 51, 52, 93, 101
-  Clay, 75, 97-99
-  Clear Creek, 1, 71, 80
-  Climax, 21, 78, 91-92
-  Climax Granite Porphyry, 91, 92
-  Coal, 23, 75, 96-97
-  Coal Creek, 14, 15
-  Coal Creek Quartzite, 33
-  Coaldale, 97
-  Coalmont, 97
-  Cokedale, 97
-  Collegiate Range, 22
-  Colorado National Monument, 29, 31, 44, 51, 108
-  Colorado River, 3, 20, 21, 28, 29, 35, 39, 103, 104, 105, 108, 109
-  Colorado Springs, 14, 15, 35, 37, 48, 97, 98, 109
-  Columbia, Mt., 22
-  Como, 78, 97
-  Construction materials, 97-102
-  Copper, 74, 75, 80, 81, 83, 89, 91
-  Creede, 65, 78, 89-90
-  Crested Butte, 24, 97
-  Cretaceous, 7, 12, 20, 23, 29, 30, 53, 56-58, 94, 95, 97, 98, 101,
-          105, 108, 110
-  Cripple Creek, 1, 74, 77, 78, 90-91
-  Cross Mountain, 26, 29
-  Crystal River, 24, 99
-  Culebra Range, 17
-  Curecanti, 105
-  Curtis Formation, 52
-
-
-                                   D
-  Dakota Formation, 12, 51, 53, 56, 94, 97, 105
-  Dawson Arkose, 60
-  Dawson Butte, 112
-  Delcarbon, 97
-  Democrat, Mt., 21
-  Denver, 3, 8, 14, 33, 35, 37, 45, 47, 48, 52, 53, 60, 74, 83, 94,
-          96, 99, 100, 104, 112, 113
-  Denver Basin, 8, 75, 94, 95
-  Denver Formation, 60, 62
-  Devonian, 7, 42-43, 83
-  Dillon, 104
-  Dinosaur National Monument, 27, 53, 55
-  Durango, 25, 28, 35, 47, 58, 78, 85, 102
-  Dyer Dolomite, 42
-
-
-                                   E
-  Eagle, 47, 101, 106
-  Eagle River, 22, 47
-  Edwards, 22
-  Elbert, Mt., 22
-  Eldorado Springs, 109
-  Elk Mountains, 24, 69
-  Empire, 1, 78, 81
-  Englewood, 113
-  Entrada Sandstone, 51, 93
-  Environmental geology, 111-113
-  Eocene, 64
-  Estes Lake, 103
-  Estes Park, 69, 104
-  Evans, Mt., 3, 12
-
-
-                                   F
-  Fairplay, 78, 84-85
-  Fairy Cave, 107
-  Flattop Mountain, 19
-  Floods, 112-113
-  Florence, 74, 94
-  Florissant Fossil Beds National Monument, 65
-  Fort Carson, 15
-  Fort Collins, 35, 101, 102
-  Fountain Formation, 12, 14, 45, 47, 48
-  Fox Hills Sandstone, 58
-  Fremont Limestone, 40, 41
-  Frisco, 21
-  Front Range, 11-16, 33, 35, 44, 50, 51, 52, 56, 60, 61, 68, 69,
-          70, 71, 93, 99, 101, 103, 107, 109
-  Frying Pan River, 105
-  Fulford, 107
-  Fulford Cave, 106
-
-
-                                   G
-  Garden of the Gods, 4, 14, 15, 47, 48
-  Garfield, Mt., 30
-  Gas, natural, 1, 28, 75, 94-96
-  Gems, 75, 102
-  Gem Village, 102
-  Georgetown, 78, 81
-  Gilman, 21
-  Gilpin County, 78
-  Glen Eyrie Formation, 44
-  Glenwood Canyon, 37, 39
-  Glenwood Springs, 24, 29, 35, 99, 107, 109
-  Gold, 1, 22, 29, 74, 75, 77-91
-  Golden, 8, 14, 62, 74, 78, 83, 93, 98, 111
-  Gold Hill, 1, 74, 78, 79
-  Gore Creek, 47
-  Gore Pass, 19, 20
-  Gore Range, 20-21, 35, 69
-  Gore Range-Eagle's Nest Wilderness Area, 20, 21
-  Granby, 20, 62
-  Granby Lake, 103
-  Grand Hogback, 28, 29
-  Grand Junction, 29, 30, 35, 55
-  Grand Lake, 12, 69, 103, 104
-  Grand Mesa, 35, 62
-  Grand Valley, 25
-  Gravel, 75, 97-99
-  Great Sand Dunes National Monument, 17, 18, 73
-  Green River, 27, 103
-  Green River Basin, 4
-  Green River Canyon, 31
-  Green River Formation, 64, 95-96
-  Greenhorn Formation, 101
-  Greenhorn Peak, 16
-  Groundwater, 76, 105-106
-  Gunnison, 35
-  Gunnison, Black Canyon of the, 36, 37, 44, 71, 105
-  Gunnison River, 35, 36, 37, 105
-  Gypsum (mineral), 22, 30, 75, 101-102
-  Gypsum (town), 47, 101
-  Gypsum Valley, 30, 47, 101
-
-
-                                   H
-  Hahn's Peak, 19
-  Harding Sandstone, 40, 41
-  Harvard, Mt., 22
-  Hayden, 96, 97
-  Hayden Pass, 17
-  Hermosa Formation, 45, 47
-  Hidden Valley, 69
-  Horseshoe Amphitheater, 85
-  Horseshoe Park, 69
-  Horsetooth Reservoir, 103
-  Huerfano Basin, 35, 61
-
-
-                                   I
-  Ice Age, see Pleistocene
-  Iceberg Lake, 66
-  Idaho Springs, 14, 78, 80
-  Idaho Springs Formation, 33, 92
-  Independence Pass, 22
-  Iron, 1, 17, 74
-  Ironton, 78, 88
-
-
-                                   J
-  Jewel Lake, 68
-  Juniper Mountain, 26, 29
-  Juniper Springs, 109
-  Jurassic, 7, 9, 23, 36, 52-55, 93
-
-
-                                   K
-  Kremmling, 19, 20, 60
-
-
-                                   L
-  La Junta, 8, 35
-  Lake City, 77, 78
-  Lake County, 77
-  Lamar, 8
-  Landslides, 111-112
-  La Plata Mountains, 26
-  Laramide Orogeny, 59, 60
-  Laramie Formation, 57, 58, 97
-  Larkspur, 112
-  La Veta Pass, 17, 18, 37
-  Lead, 74, 75, 80, 81, 82, 83, 85, 86, 89
-  Leadville, 1, 22, 77, 78, 82-83
-  Leadville Limestone, 43, 44, 83, 88, 99, 106, 109
-  Lime, 75, 101
-  Lincoln, Mt., 21
-  Lincoln Porphyry, 21
-  Lipalian Interval, 7, 36, 39
-  Littleton, 113
-  Logan County, 95
-  Longs Peak, 3, 11, 12, 68
-  Loveland, 14, 102
-  Loveland Pass, 12
-  Lykins Formation, 12, 51, 52, 101
-  Lyons, 14, 49, 99, 100, 101
-  Lyons Sandstone, 12, 48, 49, 50, 99, 100, 101
-
-
-                                   M
-  Magnolia, 79
-  Mancos Shale, 30, 95
-  Manitou, 39, 106, 107, 110
-  Manitou Formation, 40, 41, 110
-  Manitou Springs, 109
-  Marble, 24, 99
-  Marble Mountain, 106
-  Maroon Bells, Front., 24, 50
-  Maroon Creek, 24
-  Maroon Formation, 50
-  Mary's Lake, 103
-  Massive, Mt., 82
-  McDermott Formation, 58
-  Mesa de Maya, 8, 35, 62
-  Mesa Verde, 28, 29, 35
-  Mesa Verde Formation, 30, 58, 108
-  Mesa Verde National Park, 31, 71, 108
-  Mesozoic (see also Triassic etc.), 7, 10, 11, 12, 14, 15, 26, 28,
-          51-58, 60, 93
-  Mestas, Mt., 17
-  Middle Park, 4, 16, 35, 61
-  Million Dollar Highway, 87, 88
-  Mills Lake, 68
-  Milner Pass, 66
-  Minturn, 39
-  Minturn Formation, 45, 46, 47
-  Miocene, 66, 67, 87
-  Mississippian, 6, 7, 43-44, 83, 106, 109
-  Moenkopi Formation, 52
-  Molas Formation, 44
-  Molas Lake, 25
-  Molybdenum, 1, 74, 75, 76, 77, 91-92
-  Monarch Pass, 23
-  Morgan County, 95
-  Morrison, 53, 54, 55
-  Morrison Formation, 12, 36, 51, 53, 55, 93
-  Mosca Pass, 17, 73
-  Mosquito Pass, 85
-  Mosquito Range, 21, 22, 35, 39, 69
-  Mountain Province, 3, 4, 10-27, 35, 46, 93, 94, 101, 102, 103,
-          109, 111
-  Mt. Bross, 21
-  Mt. Columbia, 22
-  Mt. Democrat, 21
-  Mt. Elbert, 22
-  Mt. Evans, 3, 12
-  Mt. Garfield, 30
-  Mt. Harvard, 22
-  Mt. Lincoln, 21
-  Mt. Massive, 82
-  Mt. Mestas, 17
-  Mt. Princeton, 22
-  Mt. Princeton Hot Springs, 22, 110
-  Mt. Sneffels, 87, 88
-  Mt. Sopris, 24
-  Mt. Yale, 22
-  Mt. Zirkel, 19
-  Music Pass, 17, 73
-
-
-                                   N
-  Navajo Sandstone, 52
-  Nederland, 78, 79
-  Needle Mountains, 26
-  Niobrara Formation, 57, 101
-  North Park, 4, 16, 35, 58, 61, 94, 97
-
-
-                                   O
-  Oil, 1, 29, 30, 75, 76, 94-96
-  Oil Creek, 94
-  Oil shale, 95-96
-  Oligocene, 66, 67
-  Ordovician, 7, 40-41, 83, 106
-  Orient, 17
-  Oro, 82
-  Otero County, 105
-  Ouray, 4, 25, 26, 34, 42, 78, 87-88
-  Ouray Formation, 42
-
-
-                                   P
-  Pagoda Mountain, 68
-  Pagosa Springs, 102, 109
-  Paleozoic (see also Cambrian etc.), 7, 10, 11, 12, 14, 15, 17, 21,
-          22, 24, 26, 27, 28, 30, 34, 37, 38-50, 60, 64, 77, 95, 98,
-          106, 107
-  Paradox Basin, 4, 47, 95, 101
-  Paradox Valley, 30, 101
-  Park Range, 19-20, 35, 69
-  Parting Sandstone, 42
-  Pawnee Buttes, 9, 66, 67
-  Peak Province, see Mountain Province
-  Peat, 75
-  Pennsylvanian, _Front._, 6, 7, 14, 23, 44-47, 48, 50, 83, 95, 101,
-          106, 109
-  Permian, _Front._, 7, 23, 48-50, 95, 99, 100, 101
-  Petroleum, 1, 29, 30, 75, 76, 94-96
-  Phosphoria Formation, 50
-  Piceance Basin, 29
-  Pierre Formation, 57, 94, 98
-  Pikes Peak, 3, 4, 11, 12, 15, 65, 90, 91, 110
-  Pikes Peak Granite, 4, 14, 33, 36
-  Plains Province, see Prairie Province
-  Plateau Province, 3, 4, 9, 28-31, 35, 46, 71, 75, 93, 94, 96, 101,
-          103, 107, 110
-  Platte River, 3
-  Pleistocene, 7, 8, 25, 59, 68-73, 105, 106
-  Plum Creek, 112
-  Poncha Springs, 109
-  Prairie Province, 3, 8-10, 12, 35, 66, 72, 75, 94, 96, 103, 105
-  Precambrian, 7, 10, 11, 14, 15, 16, 17, 19, 20, 21, 26, 33-37, 40,
-          60, 64, 68, 77, 87, 91, 92, 93, 109
-  Princeton, Mt., 22
-  Pueblo, 23, 97
-  Pumice, 75
-  Purgatoire Formation, 105
-  Pyrites, 75
-
-
-                                   Q
-  Quandary Peak, 21
-  Quaternary, 7, 8, 25, 59, 68-73, 105, 106
-
-
-                                   R
-  Rabbit Ears Pass, 19
-  Rabbit Ears Range, 20, 35, 62
-  Radium, 93
-  Rampart Range, 15, 97, 98
-  Rangely, 29, 95
-  Raspberry Mountain, 112
-  Rattlesnake Reservoir, 103
-  Raton Basin, 61
-  Raton Pass, 61
-  Red Cliff, 39
-  Red Mountain, 88
-  Red Mountain Creek, 88
-  Red Rocks Park, 14, 37, 47
-  Redstone, 24
-  Rico, 26
-  Rico Range, 26
-  Rifle, 64
-  Rio Grande, 35
-  Roan Plateau, 28, 29, 35
-  Rocky Mountain National Park, 11, 12, 66, 68, 71, 104
-  Roncarbo, 97
-  Royal Gorge, 37, 71
-  Ruedi, 105
-
-
-                                   S
-  St. Mary's Glacier, 71
-  Salida, 17, 21, 35
-  Salina, 79
-  Sand, 75, 97-99
-  Sangre de Cristo Range, 10, 17-18, 35, 47, 61, 69, 73, 90, 105,
-          106
-  San Juan Basin, 95
-  San Juan County, 78
-  San Juan Formation, 88
-  San Juan Mountains, 4, 25-26, 35, 52, 65, 69, 77, 85, 86, 87, 88,
-          105
-  San Luis Valley, 4, 35, 44, 61, 67, 73, 96, 106
-  San Miguel Range, 26
-  Santa Fe Formation, 67, 105
-  Sawatch Range, 22-23, 35, 39, 69, 82, 106
-  Sawatch Sandstone, 34, 39, 40
-  Sedalia, 61
-  Shadow Mountain Reservoir, 103
-  Sierra Blanca, 17, 18
-  Silurian, 7, 42
-  Silver, 22, 74, 77-91
-  Silver Cliff, 16, 77, 78
-  Silver Plume, 78, 81
-  Silver Plume Granite, 33, 35
-  Silverton, 4, 26, 74, 77, 78, 85-86, 88
-  Sinbad Valley, 101
-  Sneffels, Mt., 87, 88
-  Sopris, Mt., 24
-  South Park, 4, 16, 21, 35, 61, 65, 84, 97
-  South Platte River, 1, 3, 35, 85, 103, 104, 112, 113
-  Spanish Cave, 106
-  Spanish Peaks, 10, 18, 62
-  Specimen Mountain, 66
-  Springs, 17, 22, 109-110
-  Steamboat Springs, 97, 109
-  Summit County, 77
-  Sunshine, 79
-  Sunshine Peak Rhyolite, 87
-  Swandyke Gneiss, 33
-
-
-                                   T
-  Table Mountain, 8, 62, 111
-  Telluride, 26, 74, 77, 78
-  Tenmile Gorge, 21
-  Tenmile Range, 21, 91
-  Tertiary, 7, 15, 20, 21, 25, 26, 29, 59-67, 73, 77, 83, 87, 88,
-          89, 90, 91, 92, 93, 95, 96, 97
-  Tin, 75
-  Tincup, 22, 77, 78
-  Trail Ridge Road, 12, 66
-  Treasure Mountain Granite, 99
-  Triassic, 7, 23, 51-52, 93, 101
-  Trinidad, 8, 61, 96, 97
-  Trout Creek Pass, 21, 22
-  Tungsten, 1, 74, 75, 79
-  Tyndall Glacier, 71
-
-
-                                   U
-  Uinta Basin, 4, 29, 64, 75, 95
-  Uinta Mountain Formation, 26
-  Uinta Mountains, 4, 10, 26-27, 29, 35, 37, 64
-  Uncompahgre Gorge, 87
-  Uncompahgre Plateau, 29, 35, 44
-  Uncompahgre Quartzite, 87
-  Urad Mine, 92
-  Uranium, 1, 29, 80, 93
-
-
-                                   V
-  Vail, 21, 47
-  Vail Pass, 21
-  Valmont, 62
-  Vanadium, 74, 75, 93
-  Villa Grove, 17
-
-
-                                   W
-  Walden, 20
-  Walsenburg, 35, 61, 96
-  Ward, 78
-  Water, 76, 103-110
-  Waunita Hot Springs, 109
-  Weber Sandstone, 95
-  West Elk Mountains, 24, 35, 69
-  Wet Mountains, 16, 35, 61, 95
-  Wet Mountain Valley, 35
-  Whiskey Creek Pass, 17
-  White River, 35, 95
-  White River Formation, 66
-  White River Plateau, 28, 29, 35, 43, 107, 109
-  Williams Canyon, 37, 39
-  Willow Creek Pass, 20
-  Willow Creek Reservoir, 103
-  Wingate Formation, 51, 52, 101
-  Wolcott, 22, 47
-  Wolford Mountain, 60
-  Woodland Park, 110
-  Woods Lake, 107
-
-
-                                   Y
-  Yale, Mt., 22
-  Yampa River, 3, 27, 31, 35, 97
-  Yule Marble, 24, 99
-
-
-                                   Z
-  Zinc, 74, 75, 80, 82, 83, 85, 86, 89
-  Zirkel, Mt., 19
-
-
-
-
-                          Transcriber's Notes
-
-
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-
-
-
-
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-<pre>
-
-The Project Gutenberg EBook of Prairie Peak and Plateau, by 
-John Chronic and Halka Chronic
-
-This eBook is for the use of anyone anywhere in the United States and most
-other parts of the world at no cost and with almost no restrictions
-whatsoever.  You may copy it, give it away or re-use it under the terms of
-the Project Gutenberg License included with this eBook or online at
-www.gutenberg.org.  If you are not located in the United States, you'll have
-to check the laws of the country where you are located before using this ebook.
-
-Title: Prairie Peak and Plateau
-       A Guide to the Geology of Colorado
-
-Author: John Chronic
-        Halka Chronic
-
-Release Date: August 21, 2019 [EBook #60143]
-
-Language: English
-
-Character set encoding: UTF-8
-
-*** START OF THIS PROJECT GUTENBERG EBOOK PRAIRIE PEAK AND PLATEAU ***
-
-
-
-
-Produced by Stephen Hutcheson and the Online Distributed
-Proofreading Team at http://www.pgdp.net
-
-
-
-
-
-
-</pre>
-
-<div class="img">
-<img class="cover" id="coverpage" src="images/cover.jpg" alt="Prairie Peak and Plateau: A Guide to the Geology of Colorado" width="500" height="784" />
-</div>
-<div class="verse">
-<p class="t0">STATE OF COLORADO</p>
-<p class="t0">John A. Love, <i>Governor</i></p>
-</div>
-<div class="verse">
-<p class="t0">DEPARTMENT OF NATURAL RESOURCES</p>
-<p class="t0">T. W. Ten Eyck, <i>Executive Director</i></p>
-</div>
-<div class="verse">
-<p class="t0">COLORADO GEOLOGICAL SURVEY</p>
-<p class="t0">John W. Rold, <i>State Geologist and Director</i></p>
-<p class="t0">A. L. Hornbaker, <i>Mineral Deposits Geologist</i></p>
-<p class="t0">Richard H. Pearl, <i>Ground Water Geologist</i></p>
-<p class="t0">William P. Rogers, <i>Engineering Geologist</i></p>
-<p class="t0">Antoinette M. Ray, <i>Secretary</i></p>
-</div>
-<p>MISSION OF THE COLORADO GEOLOGICAL SURVEY</p>
-<p>The Colorado Geological Survey was legislatively re-established
-in February 1969 to meet the geologic needs of the citizens,
-governmental agencies, and mineral industries of Colorado. This
-modern legislation was aimed at applying geologic knowledge
-toward the solution of today&rsquo;s and tomorrow&rsquo;s problems of an
-expanding population, mounting environmental concern, and the
-growing demand for mineral resources.</p>
-<p>SPECIFIC LEGISLATIVE CHARGES:</p>
-<dl class="undent"><dt>&ldquo;Assist, consult with, and advise state and local governmental agencies on geologic problems.&rdquo;</dt>
-<dt>&ldquo;Promote economic development of mineral resources.&rdquo;</dt>
-<dt>&ldquo;Evaluate the physical features of Colorado with reference to present and potential human and animal use.&rdquo;</dt>
-<dt>&ldquo;Conduct studies to develop geologic information.&rdquo;</dt>
-<dt>&ldquo;Inventory the state&rsquo;s mineral resources.&rdquo;</dt>
-<dt>&ldquo;Collect, preserve and distribute geologic information.&rdquo;</dt>
-<dt>&ldquo;Determine areas of geologic hazard that could affect the safety of or economic loss to the citizens of Colorado.&rdquo;</dt>
-<dt>&ldquo;Prepare, publish, and distribute geologic reports, maps, and bulletins.&rdquo;</dt></dl>
-<h1>PRAIRIE
-<br />PEAK and
-<br />PLATEAU</h1>
-<p class="center"><span class="ss">A GUIDE TO THE GEOLOGY OF COLORADO</span></p>
-<p class="center"><span class="large"><i>by John and Halka Chronic</i></span></p>
-<div class="img" id="pic_1">
-<img src="images/p02.jpg" alt="Relief image of Colorado" width="600" height="440" />
-</div>
-<p class="center"><span class="ss">COLORADO GEOLOGICAL SURVEY BULLETIN 32
-<br />1972</span></p>
-<p class="center">Available from Colorado Geological Survey
-<br />1845 Sherman Street
-<br />Denver, Colorado 80203
-<br />Price&mdash;$2.00</p>
-<div class="pb" id="Page_i">i</div>
-<h3>ACKNOWLEDGMENTS</h3>
-<p>This guidebook was written at the request of the Colorado
-Geological Survey to fulfill a long-felt need for a popular
-account of the state&rsquo;s geology and its relationship to Man.</p>
-<p>The authors wish to thank those of their colleagues who have
-assisted at various times in the preparation of this book. John
-Rold, Colorado State Geologist, and William Weber, of the University
-of Colorado Museum staff, made many helpful suggestions
-concerning the manuscript. John Schooland, vice president of the
-Colorado Historical Society, generously provided several pictures
-of early mining activities in Colorado. Permission to reproduce
-drawings and paintings of fossils and reconstructions of past
-environments was granted by the American Museum of Natural
-History and the University of Colorado Museum. Drawings, maps,
-and diagrams are largely the work of Robert Maurer, who also
-designed the cover and title page.</p>
-<div class="pb" id="Page_ii">ii</div>
-<div class="img" id="pic_2">
-<img src="images/p03.jpg" alt="" width="800" height="561" />
-<p class="caption">Tilted dark red sedimentary rocks of the Pennsylvanian-Permian
-Maroon Formation are well exposed in the cliffs of Maroon Bells,
-southwest of Aspen. (Photo courtesy Hydraulic Unlimited Mfg. Co.)</p>
-</div>
-<div class="pb" id="Page_iii">iii</div>
-<h3>CONTENTS</h3>
-<dl class="toc">
-<dt><i>Page</i></dt>
-<dt><a href="#c1">Introduction</a> 1</dt>
-<dt><a href="#c2"><span class="cn">I </span>Colorado&rsquo;s Three Provinces</a> 3</dt>
-<dd><a href="#c3">The Prairies</a> 8</dd>
-<dd><a href="#c4">The Peaks</a> 10</dd>
-<dd class="ddt"><a href="#c5">Front Range</a> 11</dd>
-<dd class="ddt"><a href="#c6">Wet Mountains</a> 16</dd>
-<dd class="ddt"><a href="#c7">Sangre de Cristo Range and Spanish Peaks</a> 17</dd>
-<dd class="ddt"><a href="#c8">Park Range and Rabbit Ears Range</a> 19</dd>
-<dd class="ddt"><a href="#c9">Gore Range</a> 20</dd>
-<dd class="ddt"><a href="#c10">Tenmile and Mosquito Ranges</a> 21</dd>
-<dd class="ddt"><a href="#c11">Sawatch Range</a> 22</dd>
-<dd class="ddt"><a href="#c12">Elk Mountains and West Elk Mountains</a> 24</dd>
-<dd class="ddt"><a href="#c13">San Juan Mountains</a> 25</dd>
-<dd class="ddt"><a href="#c14">Uinta Mountains</a> 26</dd>
-<dd><a href="#c15">The Plateaus</a> 28</dd>
-<dt><a href="#c16"><span class="cn">II </span>Geologic History of Colorado</a> 32</dt>
-<dd><a href="#c17">Precambrian Era</a> 33</dd>
-<dd><a href="#c18">Paleozoic Era</a> 38</dd>
-<dd class="ddt"><a href="#c19">Cambrian Period</a> 39</dd>
-<dd class="ddt"><a href="#c20">Ordovician Period</a> 40</dd>
-<dd class="ddt"><a href="#c21">Silurian Period</a> 42</dd>
-<dd class="ddt"><a href="#c22">Devonian Period</a> 42</dd>
-<dd class="ddt"><a href="#c23">Mississippian Period</a> 43</dd>
-<dd class="ddt"><a href="#c24">Pennsylvanian Period</a> 44</dd>
-<dd class="ddt"><a href="#c25">Permian Period</a> 48</dd>
-<dd><a href="#c26">Mesozoic Era</a> 51</dd>
-<dd class="ddt"><a href="#c27">Triassic Period</a> 51</dd>
-<dd class="ddt"><a href="#c28">Jurassic Period</a> 52</dd>
-<dd class="ddt"><a href="#c29">Cretaceous Period</a> 56</dd>
-<dd><a href="#c30">Cenozoic Era</a> 59</dd>
-<dd class="ddt"><a href="#c31">Tertiary Period</a> 59</dd>
-<dd class="ddt"><a href="#c32">Quaternary Period</a> 68</dd>
-<dt><a href="#c33"><span class="cn">III </span>Geology and Man in Colorado</a> 74</dt>
-<dd><a href="#c34">Gold, Silver, and Other Metals</a> 77</dd>
-<dd class="ddt"><a href="#c35">Boulder County</a> 79</dd>
-<dd class="ddt"><a href="#c36">Central City and Idaho Springs</a> 80</dd>
-<dd class="ddt"><a href="#c37">Georgetown, Empire, and Silver Plume</a> 81</dd>
-<dd class="ddt"><a href="#c38">Leadville</a> 82</dd>
-<dd class="ddt"><a href="#c39">Breckenridge</a> 83</dd>
-<dd class="ddt"><a href="#c40">Fairplay</a> 84</dd>
-<dd class="ddt"><a href="#c41">Silverton</a> 85</dd>
-<dd class="ddt"><a href="#c42">Ouray</a> 87</dd>
-<dd class="ddt"><a href="#c43">Aspen</a> 88</dd>
-<dd class="ddt"><a href="#c44">Creede</a> 89</dd>
-<dd class="ddt"><a href="#c45">Cripple Creek</a> 90</dd>
-<dd class="ddt"><a href="#c46">Climax</a> 91</dd>
-<dd><a href="#c47">Radium, Uranium, and Vanadium</a> 93</dd>
-<dd><a href="#c48">Oil, Natural Gas, and Oil Shale</a> 94</dd>
-<dd><a href="#c49">Coal</a> 96</dd>
-<dd><a href="#c50">Construction Materials</a> 97</dd>
-<dd class="ddt"><a href="#c51">Sand, Gravel, and Clay</a> 97</dd>
-<dd class="ddt"><a href="#c52">Stone</a> 99</dd>
-<dd class="ddt"><a href="#c53">Lime and Gypsum</a> 101</dd>
-<dd><a href="#c54">Gems</a> 102</dd>
-<dd><a href="#c55">Water</a> 103</dd>
-<dd class="ddt"><a href="#c56">Surface Water</a> 103</dd>
-<dd class="ddt"><a href="#c57">Groundwater</a> 105</dd>
-<dd class="ddt"><a href="#c58">Caves</a> 106</dd>
-<dd class="ddt"><a href="#c59">Springs</a> 109</dd>
-<dd><a href="#c60">Environmental Geology</a> 111</dd>
-<dt><a href="#c61">Glossary</a> 114</dt>
-<dt><a href="#c62">Suggested Reading</a> 119</dt>
-<dt><a href="#c63">Index</a> 121</dt>
-</dl>
-<div class="pb" id="Page_v">v</div>
-<h3>ILLUSTRATIONS</h3>
-<dl class="toc">
-<dt><i>Page</i></dt>
-<dt><a href="#fig1">Colorado&rsquo;s three geologic provinces</a> 2</dt>
-<dt><a href="#fig2">Pikes Peak, seen from the Garden of the Gods</a> 4</dt>
-<dt><a href="#fig3">Rock classification (chart)</a> 5</dt>
-<dt><a href="#fig4">Stratigraphic column (chart)</a> 7</dt>
-<dt><a href="#fig5">Jurassic rocks in Colorado (map)</a> 9</dt>
-<dt><a href="#fig6">East face of Longs Peak</a> 11</dt>
-<dt><a href="#fig7">Rocky Mountain National Park (east-west profile)</a> 12</dt>
-<dt><a href="#fig8">Big Thompson Canyon, west of Loveland</a> 13</dt>
-<dt><a href="#fig9">Red Rocks Amphitheater, west of Denver</a> 14</dt>
-<dt><a href="#fig10">Colorado Springs area (map and cross section)</a> 15</dt>
-<dt><a href="#fig11">Joint systems in Precambrian rocks, Boulder Canyon</a> 15</dt>
-<dt><a href="#fig12">Spanish Peaks, southwest of Walsenburg</a> 18</dt>
-<dt><a href="#fig13">Hahn&rsquo;s Peak, north of Steamboat Springs</a> 19</dt>
-<dt><a href="#fig14">Gore Range from the east</a> 20</dt>
-<dt><a href="#fig15">Aspen Mountain geology (map)</a> 23</dt>
-<dt><a href="#fig16">Mt. Sopris, south of Glenwood Springs</a> 24</dt>
-<dt><a href="#fig17">Ouray, in the San Juan Mountains</a> 25</dt>
-<dt><a href="#fig18">Steamboat Rock, Dinosaur National Monument</a> 27</dt>
-<dt><a href="#fig19">Grand Hogback, near Rifle (block diagram)</a> 28</dt>
-<dt><a href="#fig20">Mt. Garfield, near Grand Junction</a> 30</dt>
-<dt><a href="#fig21">Precambrian-Cambrian unconformity south of Ouray</a> 34</dt>
-<dt><a href="#fig22">Geologic map of Colorado</a> 35</dt>
-<dt><a href="#fig23">Black Canyon of the Gunnison National Monument</a> 36</dt>
-<dt><a href="#fig24">Precambrian-Cambrian unconformity, Glenwood Canyon</a> 38</dt>
-<dt><a href="#fig25">Cambrian fossils</a> 39</dt>
-<dt><a href="#fig26">Ordovician fossils</a> 41</dt>
-<dt><a href="#fig27">Devonian fossils</a> 43</dt>
-<dt><a href="#fig28">Mississippian fossils</a> 44</dt>
-<dt><a href="#fig29">Pennsylvanian paleogeography (map)</a> 45</dt>
-<dt><a href="#fig30">Fountain Formation northwest of Denver</a> 45</dt>
-<dt><a href="#fig31">Pennsylvanian fossils</a> 46</dt>
-<dt><a href="#fig32">Contorted Pennsylvanian rocks near Gypsum</a> 46</dt>
-<dt><a href="#fig33">Balanced Rock, Garden of the Gods</a> 48</dt>
-<dt><a href="#fig34">Permian reptile tracks</a> 49</dt>
-<dt><a href="#fig35">The Flatirons, near Boulder</a> 50</dt>
-<dt><a href="#fig36">Colorado National Monument</a> 51</dt>
-<dt><a href="#fig37">Morrison Formation, west of Denver</a> 53</dt>
-<dt><a href="#fig38">Dinosaur bones, found near Morrison</a> 54</dt>
-<dt><a href="#fig39">Dakota Sandstone hogback</a> 56</dt>
-<dt><a href="#fig40">Cretaceous fossils</a> 57</dt>
-<dt><a href="#fig41">Wolford Mountain, north of Kremmling</a> 60</dt>
-<dt><a href="#fig42">Eohippus, the &ldquo;Dawn Horse&rdquo;</a> 61</dt>
-<dt><a href="#fig43">Golden and South Table Mountain</a> 62</dt>
-<dt><a href="#fig44">Devil&rsquo;s Staircase, near Spanish Peaks</a> 63</dt>
-<dt><a href="#fig45">Green River oil shale, west of Rifle</a> 64</dt>
-<dt><a href="#fig46">Florissant Fossil Beds National Monument</a> 65</dt>
-<dt><a href="#fig47">Pawnee Buttes, north of Fort Morgan</a> 66</dt>
-<dt><a href="#fig48">Fossil mammals, northeastern Colorado</a> 67</dt>
-<dt><a href="#fig49">Glacial lakes in Rocky Mountain National Park</a> 68</dt>
-<dt><a href="#fig50">Arapaho Glacier, west of Boulder</a> 70</dt>
-<dt><a href="#fig51">Pleistocene mastodons</a> 72</dt>
-<dt><a href="#fig52">Great Sand Dunes National Monument</a> 73</dt>
-<dt><a href="#fig53">Colorado Mineral Belt (map)</a> 78</dt>
-<dt><a href="#fig54">Sluicebox mining in early Colorado</a> 81</dt>
-<dt><a href="#fig55">Early-day Leadville</a> 82</dt>
-<dt><a href="#fig56">Gold dredge, Fairplay</a> 84</dt>
-<dt><a href="#fig57">Silverton, in the San Juan Mountains</a> 86</dt>
-<dt><a href="#fig58">Abrams Mountain, south of Ouray</a> 87</dt>
-<dt><a href="#fig59">Creede and its mines (map)</a> 89</dt>
-<dt><a href="#fig60">Cripple Creek, near Pikes Peak</a> 90</dt>
-<dt><a href="#fig61">Climax molybdenum mine (cross section)</a> 91</dt>
-<dt><a href="#fig62">Rampart Range quarry, near Colorado Springs</a> 98</dt>
-<dt><a href="#fig63">Yule Marble quarry, near the town of Marble</a> 99</dt>
-<dt><a href="#fig64">Lyons Sandstone quarry</a> 100</dt>
-<dt><a href="#fig65">University of Colorado Museum</a> 100</dt>
-<dt><a href="#fig66">Colorado-Big Thompson Project (cross section)</a> 103</dt>
-<dt><a href="#fig67">San Luis Valley (cross section)</a> 105</dt>
-<dt><a href="#fig68">Cave of the Winds, near Manitou</a> 107</dt>
-<dt><a href="#fig69">Mesa Verde cave and Indian dwellings</a> 108</dt>
-<dt><a href="#fig70">Glenwood Hot Springs</a> 109</dt>
-</dl>
-<div class="pb" id="Page_1">1</div>
-<h1 title="">PRAIRIE PEAK and PLATEAU</h1>
-<h2 id="c1"><span class="h2line1">Introduction</span></h2>
-<p>Gold was discovered in the bed of the South Platte River in
-1858. Prospectors flocked to Colorado as they had flocked
-only a few years before to California. They worked the sands and
-gravels of Cherry Creek, Clear Creek, Boulder Creek, and California
-Gulch. Exhausting the <a class="gloss" href="#g_Placer">placer</a> sands of the stream bottoms,
-they moved higher to mine gold-bearing <a class="gloss" href="#g_Vein">veins</a> at Central City and
-Blackhawk. Mining camps sprang into existence overnight, each
-heralding some new &ldquo;strike,&rdquo; each populated by a new rush of
-fortune seekers. As lower areas were mined out, prospectors
-moved yet higher&mdash;to Breckenridge, Gold Hill, and Empire,
-Aspen, Leadville, and Cripple Creek. Silver was found as well as
-gold, then iron, and later tungsten and molybdenum. The metallic
-ring of mining tools echoed from Colorado&rsquo;s peaks. Fortunes
-were made here. Legends were born.</p>
-<p>Prospectors and miners were not, however, the first people
-interested in the rocks of Colorado. Earlier, bands of nomadic
-Cheyenne and Arapaho Indians had searched Colorado&rsquo;s hills
-for flint for arrowheads and brightly colored clays for warpaint.
-Cliff-dwelling Pueblo Indians in southwestern Colorado sought
-clay for their pottery and <a class="gloss" href="#g_Fossil">fossil</a> seashells for the magic of their
-medicine men. And from farther to the southwest, Navajo tribesmen
-came to Colorado for turquoise.</p>
-<p>From clay to gold, much of Colorado&rsquo;s wealth has come from
-her mountains. But after the rush to the mines, as <a class="gloss" href="#g_Vein">veins</a> were
-mined out and placers worked over, as values and prices changed,
-her population sought the riches of the prairies: fertile lands for
-agriculture, and in the rock layers below, black gold&mdash;vast
-accumulations of oil and natural gas. The tablelands and <a class="gloss" href="#g_Plateau">plateaus</a>
-west of the mountains yield their wealth, too. Here are valley
-farms, fed often by irrigation water, and ranch country. Here is
-more oil, and in some areas precious metals and uranium.</p>
-<div class="pb" id="Page_2">2</div>
-<p>In recent years Colorado&rsquo;s prairies, peaks, and <a class="gloss" href="#g_Plateau">plateaus</a> have
-brought new meaning to all America: the state now provides an
-attractive playground for state residents and their visitors. Campgrounds,
-streams, lakes, and high trails beckon in summer; barren
-slopes deep in winter snow attract the skier. More and more, those
-who live in Colorado and those who visit her seek to understand
-these mountains and hills and prairies, to learn of her geologic
-origins and her far distant past. For tourist and resident, casual
-visitor, ski enthusiast, Sunday picnicker, for all those who have
-met Colorado and enjoyed her, this book is written.</p>
-<div class="img" id="fig1">
-<img src="images/p04.jpg" alt="" width="700" height="532" />
-<p class="caption">Topographically, scenically, and geologically, Colorado can be divided
-into the three provinces shown here.</p>
-</div>
-<dl class="undent caption"><dt><a class="gloss" href="#g_Plateau">PLATEAUS</a></dt>
-<dd>UINTA MTS.</dd>
-<dd>GREEN RIVER BASIN</dd>
-<dd>Yampa River</dd>
-<dd>Steamboat Springs</dd>
-<dd>UINTA BASIN</dd>
-<dd>White River</dd>
-<dd>WHITE RIVER PLATEAU</dd>
-<dd>ROAN PLATEAU</dd>
-<dd>Glenwood Springs</dd>
-<dd>Colorado River</dd>
-<dd>Grand Junction</dd>
-<dd>GRAND <a class="gloss" href="#g_Mesa">MESA</a></dd>
-<dd>Gunnison River</dd>
-<dd>UNCOMPAHGRE PLATEAU</dd>
-<dd>Dolores River</dd>
-<dd>PARADOX BASIN</dd>
-<dd>MESA VERDE</dd>
-<dt>MOUNTAINS</dt>
-<dd>NORTH PARK</dd>
-<dd>RABIT EARS RANGE</dd>
-<dd>PARK RANGE</dd>
-<dd>MIDDLE PARK</dd>
-<dd>GORE RANGE</dd>
-<dd>FRONT RANGE</dd>
-<dd>ELK MTS.</dd>
-<dd>Aspen</dd>
-<dd>SAWATCH RANGE</dd>
-<dd>Leadville</dd>
-<dd>MOSQUITO RANGE</dd>
-<dd>Fairplay</dd>
-<dd>SOUTH PARK</dd>
-<dd>WEST ELK MTS.</dd>
-<dd>Gunnison</dd>
-<dd>Salida</dd>
-<dd>WET MTS.</dd>
-<dd>SANGRE DE CRISTO RANGE</dd>
-<dd>SAN LUIS VALLEY</dd>
-<dd>Rio Grande</dd>
-<dd>Alamosa</dd>
-<dd>SAN JUAN MTS.</dd>
-<dd>Ouray</dd>
-<dd>Silverton</dd>
-<dd>Durango</dd>
-<dd>MESA DE MAYA</dd>
-<dt>PLAINS</dt>
-<dd>Fort Collins</dd>
-<dd>South Platte River</dd>
-<dd>Denver</dd>
-<dd>GREAT PLAINS</dd>
-<dd>Colorado Springs</dd>
-<dd>Arkansas River</dd>
-<dd>WET MT. VALLEY</dd>
-<dd>HUERFANO PARK</dd>
-<dd>La Junta</dd>
-<dd>Walsenburg</dd></dl>
-<div class="pb" id="Page_3">3</div>
-<h2 id="c2"><span class="h2line1">I</span>
-<br /><span class="h2line2">Colorado&rsquo;s Three Provinces</span></h2>
-<p>Scenically, Colorado is divided into three provinces:
-the Plains or Prairies on the east, the Rocky Mountains
-bisecting the state from north to south, and the Colorado <a class="gloss" href="#g_Plateau">Plateaus</a>
-on the west. There are a number of local variations of course, but
-by and large the provinces are clearly defined. These three
-divisions will form the basis for our discussion of the geology of
-Colorado, for the scenic differences are almost exactly paralleled,
-and usually controlled, by differences in geologic structure.</p>
-<p>The Plains rise gently from an elevation of about 3350 feet
-at the eastern border of the state to 5000 feet where they meet
-the mountains 150 miles further west.</p>
-<p>Two major rivers cross the Colorado Plains: the South Platte
-River, flowing northeastward from the Denver region, and the
-Arkansas River, which leaves the mountains at Canon City south
-of Colorado Springs and travels eastward across the southern
-portion of the state. Tributaries of these two main river systems
-have etched the prairie surface, so that much of eastern Colorado
-has a gently rolling, hilly appearance.</p>
-<p>The Mountains rise abruptly along a north-south line at about
-105&deg; west longitude. They reach elevations of over 14,000 feet
-at Pikes Peak, Mount Evans, Longs Peak (all visible from far
-out on the plains), and fifty other peaks further west. The ranges
-of the Colorado Rockies form rank upon rank of ridges and peaks,
-roughly north-south in trend, about 100 miles across from east
-to west, extending from the northern to the southern border of
-the state. Here, in mountain springs and lakes, are born the rivers
-of Colorado: the Platte, the Arkansas, the Yampa, the Colorado.
-Crags and cliffs tower above tree-covered slopes, the rocks always
-a dominant part of the landscape. The continental divide runs
-through the state along the summit ridges. West of the divide,
-all streams flow to the Colorado River and the Pacific; east of it,
-streams flow into the Mississippi or the Rio Grande, and thence
-to the Gulf of Mexico.</p>
-<p>West of the highest ranges, the country flattens out once more
-into the <a class="gloss" href="#g_Plateau">Plateaus</a>, which extend across western Colorado, southern
-Utah, and northern Arizona. Here, the predominant land forms
-are flat-topped <a class="gloss" href="#g_Mesa">mesas</a> and deep canyons. Redrock walls shimmer
-in the brilliance of the western sun, offset by deep purple shadows
-<span class="pb" id="Page_4">4</span>
-sometimes hiding ancient cliff dwellings. Fragrance of pine and
-juniper mingles with the pungency of sage. Narrow tracks lure
-the explorer. Despite the canyons, water is scarce except along
-major river systems, for this is the beginning of the desert west.</p>
-<p>The scenic and geologic division of the state into three north-south
-strips is not everywhere clearly defined. In southwestern
-Colorado, the San Juan Mountains and the complicated uplifts
-surrounding Ouray and Silverton are out of key with either
-mountain or <a class="gloss" href="#g_Plateau">plateau</a>. They are best considered part of the Mountain
-Province, however, although they extend it far to the west.
-Other exceptions to these divisions occur also. The Mountain
-Province is interrupted by four broad high-altitude valleys: North
-Park, Middle Park, South Park, and the San Luis Valley. The
-Uinta Mountains jut into the northwest corner of Colorado from
-adjacent Utah. And the Paradox, Uinta, and Green River Basins
-protrude into the Plateau Province, modifying its topographic
-character.</p>
-<div class="img" id="fig2">
-<img src="images/p05.jpg" alt="" width="796" height="514" />
-<p class="caption">Pikes Peak rises to an elevation at 14,110 feet. Composed of Pikes
-Peak <a class="gloss" href="#g_Granite">Granite</a>, the mountain is almost surrounded by younger <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a>, including those of the Garden of the Gods, in the
-foreground. (Floyd Walters photo)</p>
-</div>
-<div class="pb" id="Page_5">5</div>
-<p>Before discussing the geologic nature of the three provinces,
-let us review briefly two sets of geologic terms. The first set has
-to do with the rocks themselves&mdash;What kind of rock is that?&mdash;but
-serves also to tell something about the origin of the rocks.
-The second set is concerned with time&mdash;When was that rock
-formed? Is it older or younger than adjacent rock? How does it
-relate, time-wise, to geologic events in other parts of the world?</p>
-<p>These two sets of terms are presented in the charts that follow.
-If you are unfamiliar with geologic terminology, refer to these
-charts as often as you need to while you read this book, as well as
-to the glossary on pages <a href="#Page_114">114</a>-118.</p>
-<blockquote>
-<p>Geologists divide rocks into three main groups, depending on their
-modes of origin.</p>
-<p><i><a class="gloss" href="#g_IgneousRocks">Igneous rocks</a></i> originate from molten material, cooling deep below
-the surface of the earth (intrusive igneous rocks) or flowing out and
-hardening at the surface (extrusive igneous rocks).</p>
-<p><i><a class="gloss" href="#g_SedimentaryRocks">Sedimentary rocks</a></i> are formed from broken or dissolved bits of other
-rock, washed by wind and water and deposited as layers of fragments
-or as chemical precipitates. They often contain <a class="gloss" href="#g_Fossil">fossil</a> plants or animals.</p>
-<p><i>Metamorphic rocks</i> are pre-existing rocks (igneous or sedimentary)
-changed by heat, pressure, or chemical action.</p>
-<p>Examples of these three classes of rocks are given in the accompanying
-figure. Many varieties of all three classes occur in Colorado.</p>
-</blockquote>
-<table class="center">
-<tr class="th"><th id="fig3"><b>Class</b> </th><th><b>Example</b> </th><th><b>Occurrence in Colorado</b></th></tr>
-<tr><td class="l">Sedimentary </td><td class="l">Sandstone </td><td class="l">Plains, <a class="gloss" href="#g_Plateau">plateaus</a>, flanks of mountain areas</td></tr>
-<tr><td class="l"> </td><td class="l">Shale</td></tr>
-<tr><td class="l"> </td><td class="l"><a class="gloss" href="#g_Conglomerate">Conglomerate</a></td></tr>
-<tr><td class="l"> </td><td class="l">Limestone</td></tr>
-<tr><td class="l">Igneous </td><td class="l">Extrusive:<br /><span class="hst"><a class="gloss" href="#g_Basalt">Basalt</a></span> </td><td class="l">Volcanic areas such as San Juan Mountains, Spanish Peaks</td></tr>
-<tr><td class="l"> </td><td class="l">Intrusive:<br /><span class="hst"><a class="gloss" href="#g_Granite">Granite</a></span><br /><span class="hst"><a class="gloss" href="#g_Diorite">Diorite</a></span> </td><td class="l">Pikes Peak, Longs Peak, and most central mountain areas</td></tr>
-<tr><td class="l">Metamorphic </td><td class="l">Marble (from limestone) </td><td class="l">Mountain areas</td></tr>
-<tr><td class="l"> </td><td class="l">Quartzite (from sandstone)</td></tr>
-<tr><td class="l"> </td><td class="l"><a class="gloss" href="#g_Gneiss">Gneiss</a> (from granite or sandstone)</td></tr>
-<tr><td class="l"> </td><td class="l"><a class="gloss" href="#g_Schist">Schist</a> (from shale or basalt)</td></tr>
-</table>
-<blockquote>
-<div class="pb" id="Page_6">6</div>
-<p>Geologists arrange rocks in their chronologic sequence by studying
-the <a class="gloss" href="#g_Fossil">fossils</a> and minerals which they contain. The age of some rocks
-can be determined with reasonable precision from ratios of radioactive
-minerals and their fission products. The relative age of others
-can be determined from their position, the fossils enclosed in them,
-and many minor details of their structure.</p>
-<p>The <i>stratigraphic column</i> shown <a href="#fig4">opposite</a> may be thought of as a
-calendar by which geologic events in Colorado can be arranged in
-their proper order and related to events in the rest of the world.
-Mississippian and Pennsylvanian Periods are American divisions;
-elsewhere this time interval is known as the Carboniferous Period.
-Other time terms are in worldwide use.</p>
-<p>In the generalized geologic map of Colorado which accompanies
-<a href="#c33">Chapter II</a>, rocks are identified by the era in which they were formed.
-A more detailed geologic map can be obtained from the U.S. Geologic
-Survey map distribution center in the Federal Building, Denver.</p>
-</blockquote>
-<div class="pb" id="Page_7">7</div>
-<div class="img" id="fig4">
-<img src="images/p06.jpg" alt="" width="600" height="933" />
-<p class="caption">Stratigraphic Column</p>
-</div>
-<table class="center">
-<tr class="th"><th>ERA Period </th><th>Millions of years ago </th><th>Distinctive <a class="gloss" href="#g_Fossil">fossils</a> </th><th>Events in Colorado</th></tr>
-<tr><td colspan="4" class="l">CENOZOIC</td></tr>
-<tr><td colspan="4" class="l">(Age of Mammals)</td></tr>
-<tr><td class="l"><span class="hst">Quaternary</span> </td><td class="r"> </td><td class="l">Modern types of animals and plants </td><td class="l">Development of present topography; <a class="gloss" href="#g_Glaciation">glaciation</a> in mountains</td></tr>
-<tr><td colspan="2" class="r">3</td></tr>
-<tr><td class="l"><span class="hst">Tertiary</span> </td><td class="r"> </td><td class="l">Mammals, flowering plants </td><td class="l">Uplift and mountain building</td></tr>
-<tr><td colspan="2" class="r">70</td></tr>
-<tr><td colspan="2" class="l">MESOZOIC<br />(Age of Reptiles) </td><td class="l">Dinosaurs and other reptiles</td></tr>
-<tr><td class="l"><span class="hst">Cretaceous</span> </td><td class="r"> </td><td class="l"> </td><td class="l">Submergence, then uplift</td></tr>
-<tr><td colspan="2" class="r">135</td></tr>
-<tr><td class="l"><span class="hst">Jurassic</span> </td><td class="r"> </td><td class="l"> </td><td class="l">Desert, then submergence</td></tr>
-<tr><td colspan="2" class="r">180</td></tr>
-<tr><td class="l"><span class="hst">Triassic</span> </td><td class="r"> </td><td class="l"> </td><td class="l">Widespread floodplains and deserts</td></tr>
-<tr><td colspan="2" class="r">225</td></tr>
-<tr><td colspan="4" class="l">PALEOZOIC</td></tr>
-<tr><td colspan="4" class="l">(Age of Fishes)</td></tr>
-<tr><td class="l"><span class="hst">Permian</span> </td><td class="r"> </td><td class="l">First reptiles </td><td class="l">Widespread floodplains and deserts</td></tr>
-<tr><td colspan="2" class="r">270</td></tr>
-<tr><td class="l"><span class="hst">Pennsylvanian</span> </td><td class="r"> </td><td class="l">Swamp and forest plants </td><td class="l">&ldquo;Ancestral Rocky Mountains&rdquo;</td></tr>
-<tr><td colspan="2" class="r">310</td></tr>
-<tr><td class="l"><span class="hst">Mississippian</span> </td><td class="r"> </td><td class="l"><a class="gloss" href="#g_Reef">Reef</a> corals, sharks </td><td class="l">Partial submergence</td></tr>
-<tr><td colspan="2" class="r">350</td></tr>
-<tr><td class="l"><span class="hst">Devonian</span> </td><td class="r"> </td><td class="l">Armored fish, first insects </td><td class="l">Probable submergence</td></tr>
-<tr><td colspan="2" class="r">400</td></tr>
-<tr><td class="l"><span class="hst">Silurian</span> </td><td class="r"> </td><td class="l">Corals and shellfish </td><td class="l">Probable submergence</td></tr>
-<tr><td colspan="2" class="r">440</td></tr>
-<tr><td class="l"><span class="hst">Ordovician</span> </td><td class="r"> </td><td class="l">First fish </td><td class="l">Submergence</td></tr>
-<tr><td colspan="2" class="r">500</td></tr>
-<tr><td class="l"><span class="hst">Cambrian</span> </td><td class="r"> </td><td class="l">First hard-shelled animals </td><td class="l">Gradual encroachment of sea from west</td></tr>
-<tr><td colspan="2" class="r">570</td></tr>
-<tr><td class="l">PRECAMBRIAN </td><td colspan="2" class="c">&ldquo;Lipalian Interval&rdquo; </td><td class="l">Erosion to almost flat surface or <a class="gloss" href="#g_Peneplain">peneplain</a></td></tr>
-<tr><td class="l"> </td><td class="r"> </td><td class="l">Primitive soft-bodied marine organisms </td><td class="l">Alternate episodes of mountain building and erosion</td></tr>
-<tr><td colspan="2" class="r">3,600 plus</td></tr>
-</table>
-<div class="pb" id="Page_8">8</div>
-<h3 id="c3">THE PRAIRIES</h3>
-<p>Beneath the flat prairies of eastern Colorado, <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> form a series of layers. Those near the surface are among
-the youngest rocks in Colorado. We know this from the <a class="gloss" href="#g_Fossil">fossils</a>
-they bear, fossils of large mammals such as the hairy mammoth,
-which lived in early Quaternary time, the bison, and many smaller
-mammals living today.</p>
-<p>The layers below&mdash;sandstones, shales, and limestones&mdash;become
-progressively older as one goes deeper. Most of them
-were formed originally on the bottoms of shallow seas that covered
-this part of North America several times during the history of the
-continent. In most places the layers are horizontal or nearly so,
-but westward, as they approach the mountains, they bend upward,
-gently at first and then more steeply. At the very edge of the
-mountains, where they were dragged upward when the mountains
-rose, their eroded edges appear at the surface.</p>
-<p>The entire sequence of flat-lying rocks can be studied where
-they are exposed along the mountain front or where streams and
-rivers have dissected them. They are also known from cuttings
-and cores of oil and water wells. Some parts of Colorado&rsquo;s eastern
-plains have been drilled so intensively in the search for oil and
-gas that we know a great deal about the subsurface sedimentary rock and can even make maps showing the distribution and
-character of the individual rock layers. From such maps, the
-history of the region can be deduced. We know, for example,
-that the area around Denver has subsided more in the past than
-has the area near La Junta or Lamar; it is called the Denver
-Basin because of its past history and not because it is a basin at
-present.</p>
-<p>Although the plains of Colorado appear flat, they really slope
-gently eastward. The rock layers near the surface slope eastward
-also, but the deeper rock layers may not.</p>
-<p>Near the western edge of the Plains Province, hills and valleys
-are formed by differential erosion of hard and soft rock layers.
-Some hills, such as Castle Rock, are topped with resistant sandstone;
-others, like <a class="gloss" href="#g_Mesa">Mesa</a> de Maya south of Trinidad and Table
-Mountain near Golden, are capped with layers of <a class="gloss" href="#g_Basalt">basalt</a>. Close to
-the mountains flat-topped foothills result from partial dissection
-of former erosion surfaces as the mountains, stabilized for a time,
-rose again, or as climatic cycles changed. Examples of these
-dissected erosion surfaces can be seen north and south of Boulder.</p>
-<p>Far east of the mountain front, near the northern border of
-<span class="pb" id="Page_9">9</span>
-Colorado, remnants of another, higher prairie surface stand as
-Pawnee Buttes. Torrential erosion&mdash;spring floods and summer
-thunderstorms&mdash;has deeply furrowed the prairie surface here and
-left these buttes as lonely sentinels.</p>
-<div class="img" id="fig5">
-<img src="images/p07.jpg" alt="" width="800" height="772" />
-<p class="caption">This map shows the distribution, character, and thickness of certain
-Jurassic rocks in Colorado. These rocks are deeply buried beneath
-the plains and are known there only from well samples. They have
-been eroded from most mountain areas. They come to the surface
-along the edges of the mountains and in the deeply incised canyons
-of the <a class="gloss" href="#g_Plateau">Plateau</a> Province.</p>
-</div>
-<dl class="undent caption"><dt>PRECAMBRIAN ROCKS</dt>
-<dt>PALEOZOIC ROCKS</dt>
-<dt>JURASSIC ROCKS</dt>
-<dd>SANDSTONE</dd>
-<dd>SHALY SANDSTONE</dd>
-<dd>SANDY SHALE</dd>
-<dd>SHALE</dd>
-<dt>JURASSIC ROCKS COVERED WITH VOLCANICS OR NEVER DEPOSITED.</dt></dl>
-<p>What lies below the sedimentary layers of the plains? The
-<a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> are 5,000 to 10,000 feet thick. They lie on an
-<span class="pb" id="Page_10">10</span>
-almost horizontal surface of much, much older rock, the Precambrian
-or &ldquo;<a class="gloss" href="#g_Basement">basement</a>&rdquo; rock. This is igneous and metamorphic rock,
-much crumpled and folded, the roots of long gone mountains
-which were beveled and leveled to an almost flat surface or
-<i><a class="gloss" href="#g_Peneplain">peneplain</a></i> perhaps a billion years ago.</p>
-<p>We know little of the ancient <a class="gloss" href="#g_Basement">basement</a> rocks below the
-sedimentary layers of the plains, for few wells penetrate this deep.
-What we do know indicates that they are similar to rocks of the
-mountain masses to the west, and are composed of <a class="gloss" href="#g_Granite">granite</a>, <a class="gloss" href="#g_Schist">schist</a>,
-and <a class="gloss" href="#g_Gneiss">gneiss</a>. They probably are not rich in valuable minerals,
-however, for the mineral-rich <a class="gloss" href="#g_Vein">veins</a> of the mountains came about
-as a result of uplift of the mountain areas.</p>
-<h3 id="c4">THE PEAKS</h3>
-<p>Most of the individual ranges making up the Rocky Mountains
-in Colorado are the result of highly localized movements of the
-crust as the entire region was thrust upward from below. These
-movements broke the deep, massive igneous and metamorphic rocks of the Precambrian <a class="gloss" href="#g_Basement">basement</a>, and bent the more flexible
-Paleozoic and Mesozoic layered rocks above them until they
-arched upward in a series of corrugations. The mountains thus
-formed are known to geologists as <i>faulted <a class="gloss" href="#g_Anticline">anticlines</a></i>.</p>
-<p>As the mountains rose, they were of course attacked by the
-forces of erosion. The sedimentary layers were completely stripped
-from the crests of many of the uplifts, so that Precambrian rocks
-were exposed. It is these rocks which form the summits of the
-highest peaks of Colorado. As with all rules, there are exceptions:
-the Spanish Peaks are volcanic, and the crest of the Sangre de
-Cristo Range is composed of <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a>.</p>
-<p>The trend of most of the ranges in Colorado is north-south,
-swinging to northwest-southeast near the southern end. Surprisingly,
-in the northwestern corner of the state there is an east-west
-trending range, the Uinta Mountains.</p>
-<p>Fifty or more mountain ridges in Colorado have been named
-as separate ranges. Of these, the most prominent, frequently visited
-ones will be discussed here.</p>
-<div class="pb" id="Page_11">11</div>
-<h3 id="c5">Front Range</h3>
-<p>The easternmost range of the Rocky Mountains is the longest
-continuous uplift in the state. It is a relatively simple faulted
-<a class="gloss" href="#g_Anticline">anticline</a> extending from Canon City northward to the Wyoming
-border, where it splits into two ridges, the Medicine Bow Mountains
-and the Laramie Range.</p>
-<div class="img" id="fig6">
-<img src="images/p08.jpg" alt="" width="630" height="800" />
-<p class="caption">Longs Peak challenges technical climbers with its 2000-foot vertical
-east face, the Diamond. This magnificent cliff is the result of glacial
-action and freezing and thawing in homogeneous but fractured
-<a class="gloss" href="#g_Granite">granite</a>. The small remnant of ice and snow at the lower left is all
-that remains of the <a class="gloss" href="#g_Glacier">glacier</a>. The flat summit may be part of an ancient
-erosion surface formed toward the end of Precambrian time. (Jack
-Rathbone photo)</p>
-</div>
-<p>Along the highest portion of the range, from Pikes Peak to
-Rocky Mountain National Park, the Paleozoic and Mesozoic
-<span class="pb" id="Page_12">12</span>
-sediments formerly draped over the top of the range have long
-since been washed away, leaving only the <a class="gloss" href="#g_Gneiss">gneiss</a>, <a class="gloss" href="#g_Granite">granite</a>, and
-<a class="gloss" href="#g_Schist">schist</a> of the mountain core. The almost flat tops of Longs Peak,
-Mt. Evans, and Pikes Peak, and the rolling upland traversed by
-Trail Ridge Road in Rocky Mountain National Park are thought
-to be remnants of the 600-million-year-old erosion surface that
-once existed at the top of the Precambrian rocks, and that still
-exists below the <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> of the Plains Province. This
-surface, formed near sea level, has been raised 12,000 to 14,000
-feet within the Mountain Province.</p>
-<p>Throughout most of its length, the Front Range displays
-some of the most striking high-altitude scenery in the world.
-Particularly accessible areas, well worthy of visits, are Rocky
-Mountain National Park, Berthoud and Loveland Passes, Mt.
-Evans, and Pikes Peak. In these areas the Precambrian rocks can
-be seen and studied, and the effects of <a class="gloss" href="#g_Glaciation">glaciation</a> observed.</p>
-<p>The <a class="gloss" href="#g_Granite">granite</a>, <a class="gloss" href="#g_Gneiss">gneiss</a>, and <a class="gloss" href="#g_Schist">schist</a> of the mountain core are shattered
-and broken into blocks of various sizes. The breaks between
-the blocks are called <i><a class="gloss" href="#g_Joint">joints</a></i> if there is no apparent displacement
-between adjacent blocks, and <i><a class="gloss" href="#g_Fault">faults</a></i> where there is obvious
-displacement. The joints frequently appear in parallel arrays or
-sets; there may be two or more intersecting sets, giving a cross-hatched
-appearance to large exposures.</p>
-<div class="img" id="fig7">
-<img src="images/p08a.jpg" alt="" width="800" height="160" />
-<p class="caption">East-west profile across Rocky Mountain National Park, through Grand
-Lake and Longs Peak, showing the inferred position of the original
-surface of the anticlinal uplift of the Front Range. This diagram is
-generalized, and <a class="gloss" href="#g_Fault">faults</a> are not shown. (USGS Bull. 730a)</p>
-</div>
-<dl class="undent caption"><dt>Restoration of surface which emerged from Cretaceous sea</dt>
-<dt>Restoration of Dakota sandstone</dt>
-<dt>MIDDLE PARK</dt>
-<dt><i>Grand Lake</i></dt>
-<dt>Longs Peak</dt>
-<dt>Foothills</dt>
-<dt>GREAT PLAINS</dt>
-<dt><a class="gloss" href="#g_SedimentaryRocks">Sedimentary rocks</a></dt>
-<dt><a class="gloss" href="#g_Granite">Granite</a> and <a class="gloss" href="#g_Schist">schist</a></dt>
-<dt>Sedimentary rock of plains</dt>
-<dt><i>South Platte R.</i></dt></dl>
-<div class="pb" id="Page_13">13</div>
-<div class="img" id="fig8">
-<img src="images/p09.jpg" alt="" width="628" height="1000" />
-<p class="caption">Big Thompson Canyon, west of Loveland on U.S. highway 34, is
-carved in almost vertical layers of Precambrian metamorphic rocks.
-Gently dipping Late Paleozoic and Mesozoic <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> of the
-Fountain, Lyons, Lykins, and Morrison Formations can be seen in the
-distance, capped by the Cretaceous Dakota Sandstone. (Floyd Walters
-photo)</p>
-</div>
-<div class="pb" id="Page_14">14</div>
-<p>The Precambrian rocks vary from place to place. Several
-irregular masses of <a class="gloss" href="#g_Granite">granite</a>, called <i><a class="gloss" href="#g_Batholith">batholiths</a></i>, make up portions
-of the range. Batholiths are large intrusions of molten rock that
-cooled slowly at great depth. The minerals in them form distinct
-crystals, often quite large. The Pikes Peak Granite and the Boulder
-Creek Granite are examples. Highly contorted and banded <a class="gloss" href="#g_Gneiss">gneiss</a>
-and <a class="gloss" href="#g_Schist">schist</a> are well exposed elsewhere, particularly in the Idaho
-Springs-Central City-Black Hawk region.</p>
-<p>Along the flanks of the Front Range, the eroded edges of
-the <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> which once covered the range are exposed.
-These rocks are usually tilted sharply against the mountains, as
-at Garden of the Gods, Denver&rsquo;s Red Rocks Park, and the
-Flatirons near Boulder. The Rocky Mountain Association of
-Geologists has erected a plaque explaining the geology of the
-Red Rocks area; look for it about half a mile northeast of the
-Red Rocks Amphitheater. Tilted layers of Paleozoic and Mesozoic
-sandstones form <a class="gloss" href="#g_Hogback">hogback</a> ridges along the mountain front, and
-stand out clearly on aerial photographs.</p>
-<p>In some areas, particularly near Boulder, Coal Creek, and
-Golden, the tilting of the sedimentary layers has been so extreme
-that the layers are upside down. <a class="gloss" href="#g_Basement">Basement</a> rocks may even be
-thrust out above them.</p>
-<div class="img" id="fig9">
-<img src="images/p10.jpg" alt="" width="800" height="412" />
-<p class="caption">Sandstones and <a class="gloss" href="#g_Conglomerate">conglomerates</a> of the Pennsylvanian Fountain Formation
-<a class="gloss" href="#g_Dip">dip</a> steeply toward the plains along the eastern edge of the
-Rockies. Near Denver, erosion has carved these rocks into a natural
-amphitheater, now the site of Red Rocks Amphitheater. Precambrian
-<a class="gloss" href="#g_Granite">granite</a> forms the hill in the background. (Jack Rathbone photo)</p>
-</div>
-<p>Further north, near Loveland and Lyons, as well as further
-south at Colorado Springs, irregularities in the uplift have caused
-abrupt breaks in the generally smooth eastern edge of the range.
-<a class="gloss" href="#g_Fold">Folds</a> and <a class="gloss" href="#g_Fault">faults</a> in these areas trend northwest, cutting across and
-offsetting the mountain front.</p>
-<div class="pb" id="Page_15">15</div>
-<div class="img" id="fig10">
-<img src="images/p10a.jpg" alt="" width="600" height="683" />
-<p class="caption">South of Colorado Springs, between Fort Carson and the NORAD
-installation in Cheyenne Mountain, Mesozoic rocks are faulted against
-the mountain front. Paleozoic rocks are deeply covered by as much
-as 3000 feet of Mesozoic sediments. They come to the surface about
-10 miles further south.</p>
-</div>
-<dl class="undent caption"><dt>RAMPART RANGE</dt>
-<dd>Garden of the Gods</dd>
-<dd>Ute Pass <a class="gloss" href="#g_Fault">Fault</a></dd>
-<dt>MANITOU SPRINGS</dt>
-<dt>PIKES PEAK <a class="gloss" href="#g_Massif">MASSIF</a></dt>
-<dt>CHEYENNE MOUNTAIN</dt>
-<dd>COLORADO SPRINGS</dd>
-<dt>CROSS SECTION</dt>
-<dd>Ute Pass Fault</dd>
-<dd>Rampart Fault</dd>
-<dd class="t">Tertiary</dd>
-<dd class="t">Mesozoic</dd>
-<dd class="t">Paleozoic</dd>
-<dd class="t">Precambrian</dd></dl>
-<div class="img" id="fig11">
-<img src="images/p10e.jpg" alt="" width="800" height="457" />
-<p class="caption">West of Boulder, several intersecting sets of <a class="gloss" href="#g_Joint">joints</a> pattern the Precambrian
-rocks above Boulder Creek. (John Chronic photo)</p>
-</div>
-<div class="pb" id="Page_16">16</div>
-<p>The west margin of the Front Range is not as sharply defined
-as the eastern margin. Prominent <a class="gloss" href="#g_Fault">faults</a> edge North, Middle, and
-South Parks, however. The northern end of the range merges with
-the Medicine Bow Mountains, where <a class="gloss" href="#g_Dip">dips</a> of sedimentary rocks
-seldom exceed 30 to 40 degrees. At its southern end, the Front
-Range plunges into the plains, although a southwest-trending
-ridge connects it with the Wet Mountains.</p>
-<p>Within the Precambrian core of the Front Range, many
-economic mineral deposits have been found. These are discussed
-in <a href="#c33">Chapter III</a>. Glacial features of the Front Range are discussed
-in Chapter II in the section on the <a href="#c32">Quaternary Period</a>.</p>
-<h3 id="c6">Wet Mountains</h3>
-<p>The Wet Mountains are the easternmost range of the Rockies
-south of Canon City. Their crest has a distinct northwest-southeast
-trend, with the north end offset about 25 miles westward
-from the south end of the Front Range. The Canon City
-Embayment lies at the junction between the ranges.</p>
-<p>Though smaller and lower than the Front Range, the Wet
-Mountains include many pleasant and easily accessible recreation
-areas and a number of attractive streams and reservoirs. Greenhorn
-Peak, the summit of the range, is 12,334 feet high. It is formed
-of Precambrian <a class="gloss" href="#g_Granite">granite</a>, as is most of the crest of the range.</p>
-<p>The structure of the eastern side of the Wet Mountains is
-similar to that of the Front Range, except that there are more
-<a class="gloss" href="#g_Fault">faults</a> in the sedimentary layers. The southern end plunges southeastward
-into the plains. On the western side, westward-dipping
-sediments are completely submerged in Cenozoic <a class="gloss" href="#g_Lava">lava</a> flows and
-debris from the mountains. Ore minerals very like those of the
-Front Range occur near Silver Cliff, but they have so far proved
-to be of little economic importance.</p>
-<div class="pb" id="Page_17">17</div>
-<h3 id="c7">Sangre de Cristo Range and Spanish Peaks</h3>
-<p>The Sangre de Cristo Mountains are visible from many parts
-of southeastern Colorado as a jagged, sawtoothed, snow-crested
-ridge on the western skyline. They extend about 150 miles from
-the Arkansas River near Salida southward into New Mexico.</p>
-<p>Few mountain ranges form so impassable a barrier as the
-Sangre de Cristos. Only at La Veta Pass does a highway cross the
-range. However, old wagon roads, passable now by jeep or on foot,
-once existed across Hayden, Music, Mosca, and Whiskey Creek
-Passes.</p>
-<p>Often no more than twenty miles wide, the central portion of
-the range is composed largely of red Late Paleozoic sediments
-like those exposed in the Garden of the Gods and Red Rocks
-Park. These rocks are intricately folded and faulted, but not
-metamorphosed. They include sandstones, shale, <a class="gloss" href="#g_Conglomerate">conglomerates</a>,
-and fossil-bearing limestones. The northern end of the range is
-formed of Precambrian igneous and metamorphic rocks.</p>
-<p>Just west of La Veta Pass, Sierra Blanca stands as an outpost
-of the range where its continuity is interrupted and its structure
-changed. Huge blocks of Precambrian <a class="gloss" href="#g_Granite">granite</a> were here pushed
-upward and thrust westward to form a cluster of peaks, several
-of which are over 14,000 feet in elevation.</p>
-<p>Many prominent rock <a class="gloss" href="#g_Glacier">glaciers</a> are present in the Sangre de
-Cristo Mountains. They are composed of fragments of rock,
-lubricated by snow and ice, creeping almost imperceptibly down
-the steep flanks of the high peaks. One of these rock glaciers can
-be seen on the slope of Mt. Mestas east of La Veta Pass; others
-are visible from Great Sand Dunes National Monument.</p>
-<p>South of La Veta Pass, an igneous intrusion along the axis
-of the range changes the character of the Sangre de Cristos. This
-intrusion is harder and has weathered more slowly than the rest
-of the range, and forms a group of prominent peaks known as the
-Culebra Range.</p>
-<p>On the west flank of the Sangre de Cristo Range, east of Villa
-Grove, a prominent iron-mineralized area can be seen. Here the
-ghost mine of Orient marks the site where iron ores were mined
-in the early days of the Colorado Fuel and Iron Company.
-Nearby, an abrupt terrace along the edge of the valley marks the
-position of a <a class="gloss" href="#g_Fault">fault</a>. Recent gravels are involved in this fault, indicating
-that movement has taken place here within the last few
-hundred years. A number of hot springs occur along the base of
-the mountains nearby.</p>
-<div class="pb" id="Page_18">18</div>
-<p>The Spanish Peaks, not structurally related to the Sangre de
-Cristos, are visible from La Veta Pass highway. These two peaks
-represent a pair of Cenozoic volcanoes, now deeply eroded and
-much reduced from their former height. Numerous <a class="gloss" href="#g_Dike">dikes</a> radiating
-from the bases of these peaks represent fissures which were filled
-with <a class="gloss" href="#g_Lava">lava</a> as the peaks formed.</p>
-<p>The Great Sand Dunes, close to the Sangre de Cristo Mountains
-north of Sierra Blanca, are discussed in Chapter II in the
-section on the <a href="#c32">Quaternary Period</a>.</p>
-<div class="img" id="fig12">
-<img src="images/p11.jpg" alt="" width="800" height="572" />
-<p class="caption">Spanish Peaks, south of Colorado Springs and southwest of Walsenburg,
-are twin mountains of volcanic and intrusive rock, the roots
-of Tertiary volcanoes greatly worn down and reshaped by erosion.
-This view looks southeast from near La Veta Pass, on U.S. Highway
-160. (Jack Rathbone photo)</p>
-</div>
-<div class="pb" id="Page_19">19</div>
-<h3 id="c8">Park Range and Rabbit Ears Range</h3>
-<p>Bordering the western side of North, Middle, and South Parks,
-another long north-south trending ridge extends from the Wyoming
-border toward the center of Colorado. The northern part of this
-ridge, forming the western boundary of the main mountain mass
-in the state, is called the Park Range.</p>
-<p>The structure of the Park Range is similar to that of the
-Front Range: a huge linear corrugation in the earth&rsquo;s crust,
-bounded by <a class="gloss" href="#g_Fault">faults</a>. Because this area has fewer resistant sedimentary rock layers above the Precambrian <a class="gloss" href="#g_Basement">basement</a> rocks, it is not
-prominently edged with upturned sedimentary layers.</p>
-<div class="img" id="fig13">
-<img src="images/p11a.jpg" alt="" width="780" height="104" />
-<p class="caption">Hahn&rsquo;s Peak, a highly eroded <a class="gloss" href="#g_Laccolith">laccolith</a> of <a class="gloss" href="#g_Rhyolite">rhyolite</a> <a class="gloss" href="#g_Porphyry">porphyry</a>, lies on
-the west side of the Park Range, along the eastern margin of the
-<a class="gloss" href="#g_Plateau">Plateau</a> Province. <a class="gloss" href="#g_Placer">Placer</a> gold was discovered here in 1865, but the
-<a class="gloss" href="#g_Bedrock">bedrock</a> source of the gold was never found. (Jack Rathbone photo)
-A geologic section shows the structure of the area.</p>
-</div>
-<dl class="undent caption"><dt>TERTIARY</dt>
-<dt>RED BEDS</dt>
-<dt>JURASSIC</dt>
-<dt>DAKOTA</dt>
-<dt>MANCOS</dt>
-<dt>DAKOTA</dt>
-<dd>Hahn&rsquo;s Peak</dd>
-<dt><a class="gloss" href="#g_Porphyry">PORPHYRY</a></dt>
-<dt>MANCOS</dt>
-<dt>DAKOTA</dt>
-<dt>PORPHYRY</dt>
-<dt>JURASSIC</dt>
-<dt>RED BEDS</dt>
-<dt>RE-CAMBRIAN</dt></dl>
-<div class="img" id="pic_3">
-<img src="images/p11c.jpg" alt="Hahn&rsquo;s Peak" width="800" height="555" />
-</div>
-<p>The range is crossed by Rabbit Ears Pass in the north; Gore
-Pass near Kremmling marks its southern end. Mt. Zirkel (12,180
-feet) and Flattop Mountain (12,118 feet) are the two high points
-<span class="pb" id="Page_20">20</span>
-of the range; these and a number of unnamed peaks over 11,000
-feet high are upward-faulted blocks of Precambrian <a class="gloss" href="#g_Granite">granite</a>.</p>
-<p>A rough ridge of volcanic country joins the Park Range with
-the Front Range and effectively separates North Park and Middle
-Park. This is the Rabbit Ears Range, named for a double-eared
-knob of Precambrian <a class="gloss" href="#g_Granite">granite</a> near Rabbit Ears Pass on U. S.
-highway 40. Many Tertiary volcanic features, including <a class="gloss" href="#g_Dike">dikes</a>
-and <a class="gloss" href="#g_Lava">lava</a> flows, can be seen along this ridge, which is also traversed
-by Colorado state highway 125 between Granby and Walden via
-Willow Creek Pass.</p>
-<h3 id="c9">Gore Range</h3>
-<p>The Gore Range lies south of Gore Pass, along the Park
-Range trend. The ridge of this range is low for about 15 miles
-south of Kremmling, but the southern part of the range forms a
-spectacular high cluster of peaks with many relatively inaccessible
-and rugged summits. Many of the peaks in this remote country
-are as yet unnamed; the area has been set aside as the Gore
-Range-Eagle&rsquo;s Nest Wilderness Area. The Colorado River cuts
-directly across the northern part of the Gore Range just west of
-Kremmling, in a steep-walled canyon that is one of the wild scenic
-spots of Colorado.</p>
-<div class="img" id="fig14">
-<img src="images/p12.jpg" alt="" width="800" height="286" />
-<p class="caption">The southern part of the Gore Range, viewed from the east, shows
-Precambrian <a class="gloss" href="#g_Granite">granite</a> and metamorphic rocks rising above Cretaceous
-shale hills. The nearly horizontal crest of the range probably represents
-the Precambrian erosion surface. (Jack Rathbone photo)</p>
-</div>
-<p>The Gore Range is, like the Front Range, a faulted <a class="gloss" href="#g_Anticline">anticline</a>
-with Precambrian rocks at its core. The red <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a>
-on the west flank of the range, visible at Vail Pass and Vail ski
-area, are of the same age as those in Red Rocks Park near Denver
-and the Garden of the Gods near Colorado Springs. Paleozoic
-rocks are absent on the east flank of the range, having been eroded
-<span class="pb" id="Page_21">21</span>
-from that area before Mesozoic deposition. South of the Colorado
-River and north of the Wilderness Area, Mesozoic rocks extend
-over the crest of the range.</p>
-<p>The south end of the Gore Range is marked by Tenmile Gorge
-(U. S. highway 6 between Frisco and Vail Pass). This gorge is a
-glacial valley, carved during the Ice Age by a <a class="gloss" href="#g_Glacier">glacier</a> more than
-1,000 feet thick, along a weak faulted zone in the range. A <a class="gloss" href="#g_Fault">fault</a>
-surface can be seen on the east side of the valley.</p>
-<p>From Vail Pass, or from the top of the Vail ski lift, other
-evidences of <a class="gloss" href="#g_Glaciation">glaciation</a> can be seen&mdash;<a class="gloss" href="#g_Cirque">cirques</a> and U-shaped
-valleys&mdash;testifying to the former presence here of many large
-valley <a class="gloss" href="#g_Glacier">glaciers</a>.</p>
-<h3 id="c10">Tenmile and Mosquito Ranges</h3>
-<p>With scarcely a break, the Park Range-Gore Range structure
-continues southward into the Tenmile and Mosquito Ranges.
-These high ridges separate South Park from the upper Arkansas
-Valley, and include a cluster of very high peaks, Quandary, Mt.
-Lincoln, Mt. Democrat, and Mt. Bross, all over 14,000 feet in
-elevation.</p>
-<p>Structurally, both the Tenmile Range and the Mosquito Range
-are highly asymmetrical <a class="gloss" href="#g_Anticline">anticlines</a>, gentle on the east and steeply
-faulted on the west. Paleozoic sedimentary rock layers containing
-many <a class="gloss" href="#g_Fossil">fossils</a> cover large portions of the higher parts of these
-ranges, but two of the highest peaks, Mt. Bross and Mt. Lincoln,
-are capped by the Lincoln <a class="gloss" href="#g_Porphyry">Porphyry</a>, a Tertiary intrusive, while
-Quandary Peak is Precambrian <a class="gloss" href="#g_Granite">granite</a>.</p>
-<p>These mountains are highly mineralized, and have been
-extensively explored and mined. The Climax Molybdenum
-Corporation operates an especially large mine at Climax, and
-the New Jersey Zinc Company has a large underground mine and
-mill at Gilman, on the western slopes of Tenmile Range.</p>
-<p>Buffalo Peaks, two highly eroded volcanic mountains near the
-south end of Mosquito Range, are extrusions of <a class="gloss" href="#g_Lava">lava</a> and ash
-which have buried the axis of the Mosquito uplift. They are major
-volcanoes related to a group of small volcanic cones near Antero
-Junction, in South Park.</p>
-<p>South of Buffalo Peaks, near Trout Creek Pass, the Mosquito
-Range loses altitude rapidly and merges with the rough country
-called the Arkansas Hills. Cinder cones, <a class="gloss" href="#g_Dike">dikes</a>, and other evidences
-of Tertiary volcanic activity can be seen between Trout Creek
-Pass and Salida.</p>
-<div class="pb" id="Page_22">22</div>
-<h3 id="c11">Sawatch Range</h3>
-<p>Bordering the Arkansas River valley on the west, the Sawatch
-Range includes Colorado&rsquo;s highest mountain, Mt. Elbert (14,417
-feet). With several other 14,000-foot summits, this range is the
-highest in the state. One group of peaks, known as the Collegiate
-Range (Mts. Harvard, Yale, Columbia, and Princeton) forms
-a particularly imposing vista from U. S. highway 24 between
-Trout Creek Pass and Buena Vista. The Independence Pass
-highway (Colorado 82) between Leadville and Aspen penetrates
-the heart of the Sawatch high country.</p>
-<p>The Sawatch Range as a whole is about 100 miles long (north
-to south) and 40 miles wide. It is a great faulted <a class="gloss" href="#g_Anticline">anticline</a> intruded
-by <a class="gloss" href="#g_IgneousRocks">igneous rocks</a>. The high area north of Leadville shows that the
-Sawatch and Mosquito Ranges are in reality one huge <a class="gloss" href="#g_Dome">dome</a> with
-a slight sag in the middle. The ranges, though, are sharply separated
-topographically by the deep valley of the Arkansas River.
-Precambrian rocks are near the surface between the ranges, hidden
-only by a thin cover of stream gravels. Near Leadville, some
-complexly faulted Paleozoic limestones lie in the sag between the
-ranges.</p>
-<p>At Mt. Princeton Hot Springs there is evidence of repeated
-faulting and igneous activity. The rocks are strongly altered by
-hot water coming to the surface through fissures and cracks.</p>
-<p>On the west side of the Sawatch range, the old mining towns
-of Tincup and Aspen grew up where limestone and sandstone
-layers, broken and crumpled as the Sawatch Range rose, were
-mineralized by solutions rich in gold and silver. The Aspen
-Mining District was studied extensively by geologists of the U.S.
-Geological Survey, and their maps show almost unbelievable
-complexity in the faulting of the rock layers which exist there.</p>
-<p>The north end of the Sawatch Range plunges under shales
-and sandstones along the Eagle River east of Wolcott. Gypsum
-in the sediments here has acted like putty: the layers of rock in
-which it was deposited have become peculiarly crumpled, making
-the area along the Eagle River (visible from U. S. Interstate 70)
-between Avon and Edwards hummocky and irregular. Vegetation
-is unusually sparse here because of gypsum in the soil.</p>
-<p>About midway between Edwards and Wolcott, the Eagle
-River suddenly changes direction and flows northward for about
-a mile before resuming its former westward course. This sudden
-change is caused by a sharp north-south <a class="gloss" href="#g_Fold">fold</a> in the <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> on the northwestern flank of the Sawatch Range. A magnificent
-series of roadcut and hillside exposures along the highway
-<span class="pb" id="Page_23">23</span>
-here illustrates the close relation between rock layers and river
-course. Within about a mile, the highway cuts through rocks of
-Pennsylanian, Permian, Triassic, Jurassic, and Cretaceous age,
-spanning a geologic time interval of more than 200 million years.</p>
-<p>The south end of the Sawatch Range, at Monarch Pass,
-contains steeply dipping Late Paleozoic limestones and coal beds.
-The coal has been mined on a small scale; the limestone is now
-quarried for use as a flux in iron smelters at Pueblo.</p>
-<div class="img" id="fig15">
-<img src="images/m_lr.jpg" alt="" width="603" height="800" />
-<p class="center small">The area below the Aspen Mountain ski lift is highly complex geologically. It is particularly well known because of extensive prospecting and mining activity in the region.</p>
-<p class="center small">[<a href="images/m_hr.jpg">This map in a higher resolution</a>]</p>
-</div>
-<div class="pb" id="Page_24">24</div>
-<h3 id="c12">Elk Mountains and West Elk Mountains</h3>
-<p>The Elk Mountains and West Elk Mountains appear to be
-westward continuations of the Sawatch Range. Structurally, however,
-they are not faulted <a class="gloss" href="#g_Anticline">anticlines</a> like most of the other ranges
-in Colorado, but are composed of a series of layers of Paleozoic
-sediments thrust westward over one another. These rocks, often
-crumpled and highly metamorphosed, are cut by numerous sills,
-<a class="gloss" href="#g_Dike">dikes</a>, and other intrusions, many of which have caused mineral
-enrichment locally.</p>
-<p>At Maroon Bells, in the canyon of Maroon Creek, and at
-Redstone on the Crystal River, these metamorphosed sediments
-are well exposed. Here, red sandstones and shales have been
-altered to quartzites and slate. At Marble, metamorphism of a
-thick limestone bed has produced white marble of great beauty,
-known as Yule Marble. This decorative stone was quarried extensively
-until about 1940. It was used in the Lincoln Memorial and
-several other monumental structures; in the town of Marble it
-has been used for the doorsteps of log cabins! The largest block
-quarried, for the Tomb of the Unknown Soldier in Arlington
-National Cemetery, measured 14 by 7.4 by 6 feet in the rough,
-and weighed 56 tons.</p>
-<div class="img" id="fig16">
-<img src="images/p14.jpg" alt="" width="800" height="486" />
-<p class="caption">Mt. Sopris, south of Glenwood Springs, is an igneous intrusion. (Jack
-Rathbone photo)</p>
-</div>
-<p>Crested Butte, at the south end of the Elk Mountains, is a
-small intrusive igneous mass called a <i><a class="gloss" href="#g_Laccolith">laccolith</a></i>. Hard and resistant
-to erosion, it stands over 2,000 feet above the adjacent valley floor.</p>
-<div class="pb" id="Page_25">25</div>
-<h3 id="c13">San Juan Mountains</h3>
-<p>The San Juan Mountains are the most extensive range in
-Colorado, and also the most heterogeneous. Covering more than
-10,000 square miles of the southwestern part of the state, these
-mountains are formed mostly of Tertiary volcanic rocks, the result
-of repeated outpourings of <a class="gloss" href="#g_Lava">lava</a> and ash from a cluster of volcanoes.
-Water-laid gravels composed of volcanic sand and pebbles are
-interlayered with <a class="gloss" href="#g_Basalt">basalts</a> and ash beds; the total thickness of these
-beds reaches many thousands of feet.</p>
-<div class="img" id="fig17">
-<img src="images/p14a.jpg" alt="" width="800" height="612" />
-<p class="caption">The mining town of Ouray, now also a tourist haven and summer
-resort, nestles below Pennsylvanian <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> of Ouray
-Canyon. At the north end at town can be seen the Ouray Hot Springs
-swimming pool. Gold, silver, lead, and zinc are still mined in this
-area. (Jack Rathbone photo)</p>
-</div>
-<p>The widespread volcanic activity which formed most of the
-range began in mid-Tertiary time and continued for several million
-years. A few Quaternary volcanic flows are known in the region,
-but there is no active volcanism there at present.</p>
-<p>The western side of the main range, including some of the
-highest peaks, consists primarily of uplifted and faulted Paleozoic
-sedimentary layers. These layers, highly dissected by erosion, can
-be seen near Ouray, at Molas Lake, and at Durango. Large
-<span class="pb" id="Page_26">26</span>
-patches of Precambrian <a class="gloss" href="#g_Granite">granite</a> and metamorphic rocks protrude
-through the sediments, as in the Needle Mountains; they indicate
-that this part of the range is a faulted <a class="gloss" href="#g_Anticline">anticline</a> like many other
-Colorado ranges.</p>
-<p>Early Cenozoic glacial deposits occur in some parts of the
-San Juans. These are unusual features, as <a class="gloss" href="#g_Glaciation">glaciation</a> of this age is
-unknown elsewhere in Colorado.</p>
-<p>Three small ranges rise just west of the San Juans: the San
-Miguel, Rico, and La Plata Mountains. Each consists of several
-small masses of Tertiary igneous rock intruded into Paleozoic
-<a class="gloss" href="#g_Conglomerate">conglomerates</a>, shales, and limestones.</p>
-<p>Mineralization has been intense in the San Juans; most of it
-took place during the Late Tertiary volcanic period. Rich <a class="gloss" href="#g_Vein">veins</a>
-penetrate Precambrian <a class="gloss" href="#g_Gneiss">gneiss</a> and <a class="gloss" href="#g_Granite">granite</a>, and Paleozoic limestones
-are often enriched also. Several mines are still active near
-Ouray, Silverton, Telluride, and Rico.</p>
-<h3 id="c14">Uinta Mountains</h3>
-<p>The eastern end of Utah&rsquo;s Uinta Mountains extends into
-Colorado. Unlike other ranges in Colorado, these mountains trend
-east-west. Structurally, the range is a faulted <a class="gloss" href="#g_Anticline">anticline</a>. It is quite
-asymmetrical, however, and is tilted and folded upward on the
-south, and overturned or thrust-faulted on the north. Steeply
-dipping Mesozoic and Paleozoic sediments on the south side of
-the range, sparsely vegetated and often thrown into spectacular
-<a class="gloss" href="#g_Fold">folds</a>, are a prominent feature of northwest Colorado scenery.</p>
-<p>In Colorado the crest of the Uintas reaches an elevation of
-about 8,500 feet. It consists of Precambrian rocks, but these are
-not the igneous and metamorphic rocks that characterize the
-Precambrian core of other Colorado mountains. They are easily
-recognized as sediments&mdash;dark red <a class="gloss" href="#g_Conglomerate">conglomerates</a>, sandstones,
-and mudstones&mdash;virtually unmetamorphosed though they were
-deposited nearly a billion years ago. Called the Uinta Mountain
-Formation, these rocks are found only in this part of Colorado
-and adjacent areas of Utah. They are probably related to similar
-Precambrian rocks found in Montana and Canada.</p>
-<p>At the east end of the Uintas two isolated uplifts, Cross
-Mountain and Juniper Mountain, are faulted blocks of Paleozoic
-rocks standing like islands in a sea of Cenozoic valley fill. They
-<span class="pb" id="Page_27">27</span>
-are the last outposts of the Uinta anticlinal pattern as it wanes
-toward the southeast.</p>
-<p>Dinosaur National Monument, a Uinta Mountain tourist attraction,
-encompasses a vast area of wilderness on both sides of the
-Yampa River in Colorado. Here many of the features of the east
-end of the Uinta Mountain structure can be seen. A unique display
-of the world&rsquo;s largest <a class="gloss" href="#g_Fossil">fossils</a> can be visited in the Utah portion of
-the Monument.</p>
-<div class="img" id="fig18">
-<img src="images/p15.jpg" alt="" width="800" height="666" />
-<p class="caption">At their confluence in Dinosaur National Monument, the Yampa and
-Green Rivers have carved Late Paleozoic sandstone into the precipitous
-cliffs of Steamboat Rock. (William C. Bradley photo)</p>
-</div>
-<div class="pb" id="Page_28">28</div>
-<h3 id="c15">THE <a class="gloss" href="#g_Plateau">PLATEAUS</a></h3>
-<p>The western quarter of Colorado is a region of flat-lying
-Paleozoic, Mesozoic, and Cenozoic <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> which have
-not been bent up into mountains except in a few isolated instances.
-This area lies more than a mile above sea level, however, and
-because of the gradient such an elevation affords, it is deeply
-sculptured. The Colorado River and its tributaries have sliced into
-the <a class="gloss" href="#g_Plateau">plateau</a> surface, separating it into many isolated tablelands
-or <a class="gloss" href="#g_Mesa">mesas</a>. Some are capped with sedimentary rock, others with
-Tertiary <a class="gloss" href="#g_Basalt">basalt</a>.</p>
-<div class="img" id="fig19">
-<img src="images/p16.jpg" alt="" width="700" height="623" />
-<p class="caption">The Grand <a class="gloss" href="#g_Hogback">Hogback</a> is a good example of the type of geologic
-structure known as a <i><a class="gloss" href="#g_Monocline">monocline</a></i>. The hogback ridge is formed by
-differential erosion, where soft layers wear away more easily than
-hard layers.</p>
-</div>
-<p>Simple <a class="gloss" href="#g_Fold">folds</a> and <a class="gloss" href="#g_Fault">faults</a> have given the <a class="gloss" href="#g_Mesa">mesas</a> different elevations.
-Thus the average elevation of the White River <a class="gloss" href="#g_Plateau">Plateau</a> is
-11,000 feet, that of the Roan Plateau 9,500 feet, and that of
-Mesa Verde only 7,000 feet. West of Durango the plateaus <a class="gloss" href="#g_Dip">dip</a>
-gently southward, as can be seen at Mesa Verde. Igneous intrusions
-and extrusions have altered plateau topography in some
-<span class="pb" id="Page_29">29</span>
-areas. West of Mesa Verde, for instance, an intrusive <a class="gloss" href="#g_Stock">stock</a> forms
-a prominent <a class="gloss" href="#g_Dome">dome</a> in the Southern Ute Indian Reservation.</p>
-<p>West of the northern Colorado mountains, and north and
-west of the White River <a class="gloss" href="#g_Plateau">Plateau</a>, a rolling upland extends from
-Colorado into Utah and Wyoming. It is interrupted by the Uinta
-Mountains and a number of smaller related uplifts such as Juniper
-Mountain and Cross Mountain. South of the Uinta axis the area
-is known as the Uinta Basin.</p>
-<p>The northern part of this area is structurally the south edge
-of the Green River or Washakie Basin in Wyoming. The Rangely
-<a class="gloss" href="#g_Anticline">anticline</a>, in the northeastern corner of the Uinta Basin, is one
-of Colorado&rsquo;s richest oil fields; it is discussed in <a href="#c33">Chapter III</a>.</p>
-<p>Although surfaced with much younger sediments than the
-rest of the <a class="gloss" href="#g_Plateau">Plateau</a> Province, this area is structurally similar.
-On the whole, sedimentary layers are relatively flat-lying, and
-where they are uplifted they are deeply sculptured by streams and
-rivers. The <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> in this region contain uranium and
-<a class="gloss" href="#g_Placer">placer</a> gold in addition to great oil and gas deposits. The southeastern
-part of the Uinta Basin, usually called the Piceance Basin,
-is the site of a great deposit of oil shale (see <a href="#c33">Chapter III</a>). The
-term &ldquo;basin&rdquo; may here seem unusual to the casual observer, for
-the oil shales occur on the Roan Plateau at places well over
-10,000 feet in elevation. However, the entire region was basin-like&mdash;lower
-than the surrounding ranges&mdash;for many millions
-of years, and during Tertiary time thousands of feet of valley and
-lake deposits were laid down in it.</p>
-<p>The White River <a class="gloss" href="#g_Plateau">Plateau</a>, north of Glenwood Springs, is
-composed of almost horizontal Paleozoic <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> that
-<a class="gloss" href="#g_Fold">fold</a> downward sharply along its south and west edges. The fold
-is 135 miles long and is clearly marked by the Grand <a class="gloss" href="#g_Hogback">Hogback</a>,
-the eroded edge of hard Cretaceous and early Cenozoic rock
-layers. Shale and coaly layers involved in the same fold have
-eroded more readily, leaving the resistant sandstone as a prominent
-ridge.</p>
-<p>The Uncompahgre <a class="gloss" href="#g_Plateau">Plateau</a>, southwest of Grand Junction, is
-structurally very like the White River Plateau. Its features can be
-well observed in Colorado National Monument. It has been elevated
-several thousand feet more than the Book Cliffs and Grand
-Valley areas to the north. Sharp folding and faulting near the
-Colorado River at the north boundary of the National Monument
-show that differential movement between the two regions was
-sharp and localized.</p>
-<p>A series of northwest-trending <a class="gloss" href="#g_Anticline">anticlines</a> along the Utah border
-<span class="pb" id="Page_30">30</span>
-in southwestern Colorado are of special geologic interest. They
-represent peculiar structures in which salt and gypsum have
-played a major part. These minerals were deposited in thick
-layers late in Paleozoic time; subsequently they were covered by
-thousands of feet of sand, shale, and limestone. Because of their
-low density and high plasticity they have since crept upward
-along weak spots in the overlying sediments, often contorting
-these rocks as they moved. Breaking through to the surface, the
-salt and some of the gypsum washed away more rapidly than
-the surrounding rock, leaving long faulted troughs such as Gypsum
-Valley and Paradox Valley. In most of these structures the
-gypsum can still be seen, although the more soluble salt has
-eroded away. Oil wells in this part of Colorado and in adjacent
-parts of southeast Utah have penetrated thousands of feet of
-<a class="gloss" href="#g_Evaporite">evaporites</a>, including pure salt, gypsum, and potassium salts.</p>
-<div class="img" id="fig20">
-<img src="images/p17.jpg" alt="" width="800" height="637" />
-<p class="caption">In the arid climate of the Colorado <a class="gloss" href="#g_Plateau">Plateaus</a>, ledges of well-cemented
-sandstone stand out sharply from slopes of shale or mudstone. The
-<a class="gloss" href="#g_Mesa">Mesa</a> Verde and Mancos Formations, Cretaceous in age, form the
-slopes and top of Mt. Garfield near Grand Junction (Jack Rathbone
-photo)</p>
-</div>
-<div class="pb" id="Page_31">31</div>
-<p>The peculiar weathering characteristics of flat-lying <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> in an arid climate are well demonstrated in Colorado
-National Monument, <a class="gloss" href="#g_Mesa">Mesa</a> Verde National Park, and elsewhere
-in the <a class="gloss" href="#g_Plateau">Plateau</a> Province. Those fortunate enough to make a river
-trip through the Yampa or Green River Canyons in northwestern
-Colorado or on the rivers of eastern Utah and northern Arizona
-will have an unusually fine opportunity to observe close at hand
-the weathering and erosion in this area. Resistant sandstone and
-limestone layers break into sheer cliffs, often many hundreds of
-feet high, while the softer layers of mudstone and shale form gentle
-slopes and terraces. Vast arching caves often develop where resistant
-layers are undermined&mdash;caves sometimes containing ancient
-Indian dwellings.</p>
-<div class="pb" id="Page_32">32</div>
-<h2 id="c16"><span class="h2line1">II</span>
-<br /><span class="h2line2">Geologic History of Colorado</span></h2>
-<p>Astronomical and geologic evidence indicates that the
-earth was probably formed as an immense blob of molten
-rock, held together and shaped into spherical form by its own
-gravity. It may even have been gaseous at first, cooling gradually
-to a molten state. After hundreds of millions of years it became
-cool enough to begin to harden.</p>
-<p>As the surface cooled, a crust formed, and lay like a blanket
-over the liquid mass beneath. Convection currents&mdash;large-scale
-boiling movements&mdash;stirred the molten interior, thrust portions
-of the crust upward, and sucked other portions downward to be
-remelted. Some of the lighter components, such as compounds
-of silicon and oxygen and hydrogen, accumulated on the surface
-like froth on a kettle: the continents were born. With further
-cooling the atmosphere and oceans came into being.</p>
-<p>Something can be told of the age of the continents. Measurements
-of radioactivity in the most ancient rocks exposed at the
-surface today indicate that the oldest known continental rock is
-between three and four billion years old. Since the continents
-were formed, they have been bent and shifted and broken by the
-pressures exerted against them by convection in the interior.
-Parts of the continents at times have been submerged below the
-level of the sea, even as they are today. Other portions, lifted
-above sea level, were immediately attacked by the wearing-down
-processes of erosion. The battle between mountain-building forces
-and erosion has been a continuous one ever since the crust was
-formed. Even now earthquakes give testimony to continued crustal
-movement, storms still sweep across the continents and wash mud
-and frost-loosened rocks into churning torrents, rivers still deposit
-great floodplains and deltas, sediments accumulate slowly but
-persistently upon the bottoms of the seas.</p>
-<div class="pb" id="Page_33">33</div>
-<h3 id="c17">PRECAMBRIAN ERA</h3>
-<p>Only part of the earth&rsquo;s very early history is represented in
-Colorado, where the oldest known rocks are the <a class="gloss" href="#g_Gneiss">gneisses</a> and
-schists of the Idaho Springs Formation, at least 1,800,000,000
-years old. These rocks appear to be the remains of ancient sediments,
-folded and metamorphosed into vast mountain areas long
-before recognizable life inhabited the earth.</p>
-<p>Precambrian rocks in Colorado are on the whole very poorly
-known. They have, however, been studied in detail in the Front
-Range west of Denver and Boulder, where they have been intensively
-explored for valuable minerals. The lack of <a class="gloss" href="#g_Fossil">fossils</a> in the
-oldest rocks makes their close correlation difficult, but from
-studies of radioactive minerals contained in these rocks, and of the
-relationships of the rock units themselves, we can list them in
-order of their relative ages.</p>
-<p>Note that the rock sequence given below reads chronologically
-from bottom to top&mdash;a logical pattern in geology since younger
-rocks, especially those of sedimentary origin, normally lie above
-older ones. Recent studies indicate that the sequence may be
-much more complex than shown here.</p>
-<table class="center">
-<tr><td class="r">(youngest) Silver Plume <a class="gloss" href="#g_Granite">Granite</a>: </td><td class="l">light pinkish gray, fine-grained granite.</td></tr>
-<tr><td class="r">Pikes Peak Granite: </td><td class="l">pink, coarse-grained granite.</td></tr>
-<tr><td class="r">Boulder Creek Granite: </td><td class="l">dark gray, faintly banded granodiorite.</td></tr>
-<tr><td class="r">Coal Creek Quartzite: </td><td class="l">light gray quartzite with grains ranging in size from fine sand to boulders, with some interbedded <a class="gloss" href="#g_Schist">schist</a>.</td></tr>
-<tr><td class="r">Swandyke Hornblende <a class="gloss" href="#g_Gneiss">Gneiss</a>: </td><td class="l">dark gray to black, strongly banded gneiss.</td></tr>
-<tr><td class="r">(oldest) Idaho Springs Formation: </td><td class="l">gray to black schist and gneiss.</td></tr>
-</table>
-<p>From a sequence such as this, it is possible to reconstruct
-some features of Colorado&rsquo;s early history. The first chapter of
-which we have a record is the deposition of the Idaho Springs
-Formation, probably as an accumulation of mud, sand, and limy
-mud in an ancient sea. Swandyke deposition followed&mdash;the
-sediments were iron-rich, perhaps derived from ancient volcanic
-materials. The original Coal Creek sediments were sands and
-<span class="pb" id="Page_34">34</span>
-gravels, some of them quite coarse and therefore indicative of
-near-shore deposition. The <a class="gloss" href="#g_Schist">schist</a> layers suggest that muds must
-have been deposited also.</p>
-<div class="img" id="fig21">
-<img src="images/p18.jpg" alt="" width="605" height="800" />
-<p class="caption">South of Ouray, Cambrian sandstones of the Sawatch Formation lie
-almost horizontally across the vertical Precambrian metamorphic rocks.
-(Jack Rathbone photo)</p>
-</div>
-<p>Together these three formations represent some 40,000 feet
-of sedimentary layers. Deposition of such a great thickness of mud,
-sand, and lime must have taken a very long period of time.
-Details of the geography of the continent during that period have
-<span class="pb" id="Page_35">35</span>
-of course been obscured by later events, when these rocks were
-subjected to repeated uplift, crumpling, folding, various degrees
-of remelting and recrystallization, and erosion. But the ancient
-sediments must have been derived from even more ancient highlands,
-either folded and faulted mountains or volcanoes, and
-probably were deposited under water in broad expanses of sea
-that covered portions of the continent.</p>
-<div class="img" id="fig22">
-<img src="images/p18a.jpg" alt="" width="800" height="637" />
-<p class="caption">Geologic map of Colorado. Geologic maps show the age of rocks
-appearing at the surface, disregarding soil cover. A more detailed
-geologic map of Colorado may be obtained from the U.S. Geological
-Survey at the Federal Center in Denver.</p>
-</div>
-<dl class="undent caption"><dt>PRECAMBRIAN</dt>
-<dt>PALEOZOIC</dt>
-<dt>MESOZOIC</dt>
-<dt>CENOZOIC SEDIMENTS</dt>
-<dt>CENOZOIC VOLCANICS</dt>
-<dd>Yampa River</dd>
-<dd>White River</dd>
-<dd>Fort Collins</dd>
-<dd>South Platte River</dd>
-<dd>Glenwood Springs</dd>
-<dd>Denver</dd>
-<dd>Colorado River</dd>
-<dd>Grand Junction</dd>
-<dd>Aspen</dd>
-<dd>Gunnison River</dd>
-<dd>Colorado Springs</dd>
-<dd>Gunnison</dd>
-<dd>Salida</dd>
-<dd>Dolores River</dd>
-<dd>Rio Grande</dd>
-<dd>Arkansas River</dd>
-<dd>La Junta</dd>
-<dd>Walsenburg</dd>
-<dd>Alamosa</dd>
-<dd>Durango</dd></dl>
-<p>The Boulder Creek, Pikes Peak, and Silver Plume <a class="gloss" href="#g_Granite">Granites</a>
-cut through the metamorphic rocks, and are therefore younger.
-They represent pulses of molten rock forced upward from deep
-within the crust, probably during three separate episodes of mountain
-building. As each set of mountains was formed, it was worn
-down, perhaps to low rolling hills, perhaps to flat plains almost
-<span class="pb" id="Page_36">36</span>
-at sea level, and partially or entirely covered with thick layers of
-sediment. Each time, another mountain building episode followed,
-with new intrusions of granite and new metamorphism of the
-pre-existing rocks.</p>
-<p>Each succeeding period of metamorphism and mountain
-building further changed the nature of the rocks involved, complicating
-the patterns of folding and faulting, adding recrystallization
-to recrystallization, until the oldest of the rocks bore little trace
-of their original sedimentary nature. In general, the rocks that
-are oldest were most altered by the repeated metamorphism, while
-the younger rocks were less altered.</p>
-<div class="img" id="fig23">
-<img src="images/p19.jpg" alt="" width="800" height="561" />
-<p class="caption">The Black Canyon of the Gunnison River is one of the state&rsquo;s deep
-and spectacular chasms. Canyon walls are of Precambrian <a class="gloss" href="#g_Gneiss">gneiss</a>
-intruded by many <a class="gloss" href="#g_Dike">dikes</a> and highly fractured by later uplifts. The flat
-upper surface of the Precambrian rocks represents an ancient plain on
-which, during Jurassic time, the dinosaur-bearing Morrison Formation
-was deposited. (John Chronic photo)</p>
-</div>
-<p>The Precambrian Era ended with a long period of erosion, a
-period known to geologists as the Lipalian Interval. During this
-time, over almost the entire world there was no mountain building.
-The land lay sleeping, subject only to the forces of erosion. The
-last mountains were flattened nearly to sea level. Slow, sluggish
-streams and rivers carried sand and mud toward the oceans&mdash;oceans
-<span class="pb" id="Page_37">37</span>
-in which perhaps primitive, soft-bodied organisms, with
-no hard parts to be preserved as <a class="gloss" href="#g_Fossil">fossils</a>, were beginning to evolve.</p>
-<p>On the continents, the time of intense metamorphism was
-over; most rocks of later eras are preserved today in pretty much
-their original state. The boundary between the Precambrian and
-later rocks is normally well defined. It is visible at many places in
-Colorado: in Williams Canyon near Colorado Springs, in Glenwood
-Canyon, near Red Rocks west of Denver, just west of
-La Veta Pass, at the top of Royal Gorge and the Black Canyon
-of the Gunnison. At most of these localities it is a smoothly
-beveled surface, with highly contorted Precambrian rocks below
-it and flat-lying Paleozoic sediments above it. Near Red Rocks
-and La Veta Pass, the same relationship prevails, but the entire
-contact, and the rocks above and below it, have been steeply
-tilted by the uplift of the present mountains.</p>
-<p>In portions of western North America, deposition late in
-Precambrian time has left a series of flat-lying rocks between the
-contorted Precambrian and later Paleozoic sediments. These rocks
-can be seen in northwestern Colorado, where they form the dark
-red sedimentary core of the Uinta Mountains.</p>
-<div class="pb" id="Page_38">38</div>
-<h3 id="c18">PALEOZOIC ERA</h3>
-<p>Geologists have divided the second great era of geologic time
-into units called Periods. The rocks deposited during a Period are
-called Systems, but more often than not it is convenient to discuss
-them in terms of easily recognized units of rock, called Formations.
-Formations are named after areas in which they are well
-exposed.</p>
-<p>The <a href="#fig4">stratigraphic column</a> given in Chapter I shows the Periods
-and Systems in their correct order, and gives the age in years for
-each, as determined by radioactivity methods. As you read, refer
-as often as necessary to this column.</p>
-<p>The geologic map on <a href="#Page_35">page 35</a> will help you locate areas where
-the rocks discussed in the text are exposed, and will greatly facilitate
-your understanding of the geology of the state.</p>
-<div class="img" id="fig24">
-<img src="images/p20.jpg" alt="" width="638" height="800" />
-<p class="caption">The Cambrian Sawatch Sandstone lies almost horizontally on Precambrian
-<a class="gloss" href="#g_Granite">granite</a> in Glenwood Canyon. In the foreground is the
-Colorado River. (Jack Rathbone photo)</p>
-</div>
-<div class="pb" id="Page_39">39</div>
-<h3 id="c19">Cambrian Period
-<br /><span class="small">(500-570 million years ago)</span></h3>
-<p>The first fossiliferous rocks in Colorado were deposited during
-the Cambrian Period, at a time when over much of the world
-the seas were creeping in across wide, level plains formed during
-the Lipalian Interval. Colorado was not covered by these seas
-until quite late in the Cambrian Period. Beach deposits progressively
-younger in age suggest that the sea invaded from the west,
-and spread slowly eastward, inundating most of the central part
-of the state but not the extreme north or south.</p>
-<p>The beach deposits, now called the Sawatch Sandstone because
-they are well exposed in the Sawatch Range, are composed mostly
-of fine quartz sand. They are colored with glauconite, a green
-mineral, and <a class="gloss" href="#g_Hematite">hematite</a>, a dark red mineral, so that the rock has
-a variegated appearance. The post office at Manitou is built of this
-red and green rock, and good exposures of it exist in Williams
-Canyon near Manitou, along U. S. Highway 24 northwest of
-Manitou, near Red Cliff and Minturn, and in Glenwood Canyon.</p>
-<p>The sea which crept over Colorado at this time contained
-small conical-shelled <a class="gloss" href="#g_Mollusk">mollusks</a>, <a class="gloss" href="#g_Brachiopod">brachiopods</a>, and <a class="gloss" href="#g_Trilobite">trilobites</a>. Their
-shells can occasionally be found in Cambrian rocks in Williams
-Canyon and in the Sawatch and Mosquito Ranges. At two localities
-unusual <a class="gloss" href="#g_Fossil">fossils</a> called <a class="gloss" href="#g_Graptolite">graptolites</a> have been found in thin
-Upper Cambrian shales overlying the Sawatch Sandstone.</p>
-<div class="img" id="fig25">
-<img src="images/p20a.jpg" alt="" width="700" height="275" />
-<p class="caption">These <a class="gloss" href="#g_Fossil">fossils</a> can occasionally be found in Cambrian rocks in central
-Colorado.</p>
-</div>
-<div class="pb" id="Page_40">40</div>
-<h3 id="c20">Ordovician Period
-<br /><span class="small">(440-500 million years ago)</span></h3>
-<p>The sea deepened and widened as the Ordovician Period
-began, and a series of limestones and dolomites was deposited,
-either on top of the Sawatch Sandstone or, where the Sawatch
-had not been deposited, directly on the Precambrian. These rocks
-are now called the Manitou Formation.</p>
-<p>The <a class="gloss" href="#g_Fossil">fossils</a> in these rocks are much more varied than those
-in the Sawatch Sandstone: snails, <a class="gloss" href="#g_Echinoderm">echinoderms</a>, sponges, <a class="gloss" href="#g_Cephalopod">cephalopods</a>,
-<a class="gloss" href="#g_Brachiopod">brachiopods</a>, and <a class="gloss" href="#g_Trilobite">trilobites</a> are common. The Ordovician
-sea must have teemed with life, as many rocks deposited at this
-time are more than half composed of animal remains. In addition
-to hard-shelled animals which formed fossils, there were probably
-abundant soft-bodied animals such as jellyfish and worms, which
-left no record of their presence.</p>
-<p>After deposition of the Manitou Formation, the seas receded
-slightly. A new series of sands was deposited above the Manitou
-in central Colorado. These now form the Harding Sandstone,
-a formation of unusual interest because it contains remains of the
-earth&rsquo;s earliest known vertebrates, primitive jawless fish called
-Agnathids. In places in the Harding Sandstone there are dense
-accumulations of the tiny polygonal armor plates from these fish.
-Although no whole fish have been found, we can reconstruct
-their appearance by comparing individual plates or groups of
-plates with later, better known relatives.</p>
-<p>Also present in great quantities in the Harding Sandstone are
-<a class="gloss" href="#g_Conodont">conodonts</a>, peculiar tiny brown tooth-like <a class="gloss" href="#g_Fossil">fossils</a>. Relationships
-of the conodonts are unknown; they may be parts of the Agnathids,
-or perhaps they represent some entirely different group of animals,
-with no living relatives.</p>
-<p>After deposition of the sands of the Harding Sandstone, the
-sea deepened locally and the Fremont Limestone, a massive gray
-crystalline limestone containing many marine <a class="gloss" href="#g_Fossil">fossils</a>, was deposited.
-<a class="gloss" href="#g_Mollusk">Mollusks</a> (some quite large), <a class="gloss" href="#g_Brachiopod">brachiopods</a>, and corals contributed
-their shells to the Fremont Limestone. The chain coral <i>Catenipora</i>
-and the horn coral <i>Streptelasma</i> may often be used to identify the
-formation.</p>
-<p>The Fremont Limestone was deposited very late in the Ordovician
-Period. Probably the seas were much more extensive then
-than present deposits indicate; subsequent erosion has at several
-times erased the evidence in uplifted areas.</p>
-<div class="pb" id="Page_41">41</div>
-<div class="img" id="fig26">
-<img src="images/p21.jpg" alt="" width="605" height="331" />
-<p class="caption">These Ordovician <a class="gloss" href="#g_Fossil">fossils</a> can be found in the Manitou Formation in
-the Colorado Springs area.</p>
-</div>
-<div class="img" id="pic_4">
-<img src="images/p21a.jpg" alt="" width="497" height="139" />
-<p class="caption">The earliest known fish remains come from the Ordovician Harding
-Sandstone of central Colorado. These fragments of the protective
-plates have been magnified about five times.</p>
-</div>
-<div class="img" id="pic_5">
-<img src="images/p21c.jpg" alt="" width="700" height="500" />
-<p class="caption">Corals and coral-like organisms occur in the Ordovician Fremont
-Limestone.</p>
-</div>
-<div class="pb" id="Page_42">42</div>
-<h3 id="c21">Silurian Period
-<br /><span class="small">(400-440 million years ago)</span></h3>
-<p>Until very recently, no Silurian rocks or <a class="gloss" href="#g_Fossil">fossils</a> were known
-in Colorado, and it was thought that seas did not extend into the
-state during this period. However, a few years ago good Silurian
-corals and <a class="gloss" href="#g_Brachiopod">brachiopods</a> were discovered near the northern edge
-of the state. They occur in broken blocks and patches of Silurian
-limestone, mingled with blocks of other <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> and,
-oddly enough, with volcanic material.</p>
-<p>What seems to have happened here is that sedimentary layers
-of Silurian age <i>were</i> present over northern Colorado at one time.
-During some subsequent period of volcanism, volcanic lavas
-penetrated these sediments from below. Near the volcanic tubes,
-broken, angular fragments of the surrounding sedimentary rocks
-were sometimes carried upward or downward by the motion of
-the <a class="gloss" href="#g_Lava">lava</a>.</p>
-<p>Much later, both the volcanic outpourings (if the lavas ever
-reached the surface) and the sediments were stripped away by
-erosion, probably at a time when mountains were rising in the
-area. Only the deep portions of the tubes that fed the volcanoes
-were preserved. These tubes are called <a class="gloss" href="#g_Diatreme">diatremes</a>, and thanks to
-the blocks of sedimentary rock in them we know that there were
-indeed seas in Colorado during Silurian time, seas containing the
-abundant life of a shallow marine environment very much like that
-existing at the same time in Illinois, Iowa, and Indiana.</p>
-<h3 id="c22">Devonian Period
-<br /><span class="small">(350-400 million years ago)</span></h3>
-<p>As far as we know now, Colorado was just a little above sea
-level during most of Devonian time. Early and Middle Devonian
-deposits are lacking. Late in the period, however, Colorado was
-widely inundated once more. Embayments of a western sea covered
-most of the central part of the state and an area in southwestern
-Colorado around Ouray.</p>
-<p>Deposits formed in these embayments have been given several
-names. Chaffee Formation is the name most commonly used in
-central Colorado; Ouray Formation identifies rocks of the same
-age in southwest Colorado. The Chaffee Formation has been
-subdivided into two well defined units, the Parting Sandstone or
-Quartzite, and the Dyer Dolomite or Limestone. Many ore deposits
-<span class="pb" id="Page_43">43</span>
-are associated with these rock units&mdash;notably deposits of lead
-and zinc. The Parting Sandstone is frequently so well cemented
-with silica that it is actually a quartzite; thin shale beds or
-&ldquo;partings&rdquo; make it easy to recognize. It frequently contains
-remains of <a class="gloss" href="#g_Fossil">fossil</a> fish and distinctive beds of algae.</p>
-<p>The Dyer Dolomite contains <a class="gloss" href="#g_Brachiopod">brachiopods</a> and <a class="gloss" href="#g_Bryozoa">bryozoans</a>,
-<a class="gloss" href="#g_Mollusk">mollusks</a> and corals. Some of the best <a class="gloss" href="#g_Fossil">fossil</a> hunting in Colorado
-is in Dyer beds around the White River <a class="gloss" href="#g_Plateau">Plateau</a>, where the fossils
-frequently weather out of the rock as almost perfect specimens.</p>
-<div class="img" id="fig27">
-<img src="images/p22.jpg" alt="" width="700" height="464" />
-<p class="caption">These Devonian <a class="gloss" href="#g_Brachiopod">brachiopods</a> come from the White River <a class="gloss" href="#g_Plateau">Plateau</a> in
-western Colorado.</p>
-</div>
-<h3 id="c23">Mississippian Period
-<br /><span class="small">(310-350 million years ago)</span></h3>
-<p>The sea continued to cover most of Colorado after the end of
-the Devonian Period, well into Mississippian time. Mississippian
-rocks are characteristically thick, massive gray limestones collectively
-called the Leadville Limestone. This unit is well known
-as the host rock for many Colorado ore deposits, notably those
-around the town of Leadville.</p>
-<p>During Mississippian time the western sea, warm and rich
-in organisms, covered much of North America. <a class="gloss" href="#g_Brachiopod">Brachiopods</a> and
-corals flourished, as did many other forms of life. The seas during
-part of this time extended completely across Colorado to merge
-with seas that covered the midwestern part of the United States.</p>
-<p>Over all this vast area, as well as southwest into Arizona, the
-gray, massive, fossiliferous Mississippian limestone is remarkably
-<span class="pb" id="Page_44">44</span>
-uniform and easily recognized, although it is called by different
-names in different areas.</p>
-<p>Late in Mississippian time, the Colorado area rose slightly
-and the sea in which the Leadville Limestone was deposited
-receded. An interval of erosion followed. The surface of the limestone
-was dissolved and pitted, tunnels and caves formed where
-running water etched deep into the rock, and a reddish soil formed
-on the surface and in the hollows. This portion of the limestone,
-which in some places also contains pebbles of chert, is named the
-Molas Formation. Part of the Molas may be Pennsylvanian in age.</p>
-<div class="img" id="fig28">
-<img src="images/p23.jpg" alt="" width="700" height="224" />
-<p class="caption">Mississippian <a class="gloss" href="#g_Fossil">fossils</a> from western Colorado show that seas covered
-much of the state about 330 million years ago.</p>
-</div>
-<h3 id="c24">Pennsylvanian Period
-<br /><span class="small">(270-310 million years ago)</span></h3>
-<p>As the Pennsylvanian Period began, the Colorado area continued
-to rise. Earliest deposits of this age are fine-grained black
-shales and sands&mdash;the Glen Eyrie Formation along the southern
-Front Range and the Belden Formation in west central Colorado.
-Then, through millions of years, mountain-building took place.
-Some areas rose more than others, so that formerly flat-lying
-marine sediments were bent and broken, and a series of high
-mountain ridges and deep basins were formed. Geologists sometimes
-call these the Ancestral Rocky Mountains.</p>
-<p>Although the pattern of the mountains changed repeatedly,
-the Ancestral Rockies consisted principally of two large ranges.
-One range roughly paralleled the present Front Range, but lay
-thirty to fifty miles further west. The other extended from the
-San Luis Valley northwest toward Colorado National Monument,
-including the area around the Black Canyon of the Gunnison and
-the present Uncompahgre <a class="gloss" href="#g_Plateau">Plateau</a>. Coarse sediments washed off
-both sides of both ranges, and accumulated as <a class="gloss" href="#g_AlluvialFan">alluvial fans</a> and
-valley fill along the mountain margins. These exist today as the
-Fountain Formation of the eastern Front Range, the Minturn
-Formation between the ancient uplifts, and the Hermosa Formation
-west of the western uplift.</p>
-<div class="pb" id="Page_45">45</div>
-<div class="img" id="fig29">
-<img src="images/p23a.jpg" alt="" width="800" height="719" />
-<p class="caption">This paleogeographic map reflects the distribution of land and sea
-during the early part of the Pennsylvanian Period and shows where
-coarse sediments derived from the Ancestral Rockies were deposited.</p>
-</div>
-<dl class="undent caption"><dt>FOUNTAIN FORMATION</dt>
-<dt>MINTURN FORMATION</dt>
-<dt>HERMOSA FORMATION</dt></dl>
-<div class="img" id="fig30">
-<img src="images/p23c.jpg" alt="" width="800" height="499" />
-<p class="caption">West of Denver, the main line of the Denver &amp; Rio Grande Railroad
-tunnels beneath steeply dipping sandstones and <a class="gloss" href="#g_Conglomerate">conglomerates</a> of the
-Fountain Formation. (Jack Rathbone photo)</p>
-</div>
-<div class="pb" id="Page_46">46</div>
-<div class="img" id="fig31">
-<img src="images/p24.jpg" alt="" width="700" height="463" />
-<p class="caption">Corals, <a class="gloss" href="#g_Brachiopod">brachiopods</a>, and <a class="gloss" href="#g_Fusulinid">fusulinid</a> Foraminifurida can be found in the
-Pennsylvanian Minturn Formation at many places in the Mountain
-and <a class="gloss" href="#g_Plateau">Plateau</a> Provinces.</p>
-</div>
-<div class="img" id="fig32">
-<img src="images/p24a.jpg" alt="" width="800" height="646" />
-<p class="caption">In western Colorado, where vegetation is sparse, rock structures are
-clearly defined. This photograph shows beds of the Pennsylvanian
-Minturn Formation sharply folded, probably as a result of the deformation
-of gypsum in underlying layers. (Jack Rathbone photo)</p>
-</div>
-<div class="pb" id="Page_47">47</div>
-<p>In the Flatirons near Boulder, Red Rocks Park near Denver,
-and the Garden of the Gods near Colorado Springs we see well
-exposed examples of the Fountain Formation. The Minturn
-Formation is visible along the Eagle River west of Wolcott, and
-along Gore Creek near Vail. The Hermosa Formation forms
-striking red cliffs north of Durango. In the Sangre de Cristo
-Mountains area, exceptionally great and rapid deposition took
-place, and the Minturn Formation is very thick.</p>
-<p>In west central Colorado, near the towns of Eagle and
-Gypsum, a large basin formed. In it, gypsum and other salts were
-deposited as arms of the sea were cut off from the main marine
-area. The unusual appearance of the hills along the Eagle River,
-especially north of U. S. Highway 24, is caused by the presence
-of gypsum in the <a class="gloss" href="#g_Bedrock">bedrock</a>.</p>
-<p>In a similar manner, the Paradox Basin was formed in southwestern
-Colorado. Thousands of feet of gypsum, salt, and potash
-were deposited here, probably also precipitated in restricted arms
-of the sea. These minerals, the so-called <a class="gloss" href="#g_Evaporite">evaporites</a>, have since
-significantly controlled development of the landscape in Gypsum
-Valley and other parts of this region. (See <a href="#c15">The Plateaus</a> in Chapter
-I and the section on <a href="#c53">Gypsum</a> in Chapter III).</p>
-<p>Between the mountain masses and their surrounding alluvial deposits, shallow seas repeatedly invaded the lowland areas of
-the state. Marine <a class="gloss" href="#g_Fossil">fossils</a> in some parts of the Minturn Formation
-bear witness to as many as twenty marine cycles. Strangely, the
-Pennsylvanian Period appears to have been cyclical in other parts
-of the United States as well, for marine sediments are found
-alternating with nonmarine sediments in Pennsylvania, Illinois,
-Kansas, Nebraska, and New Mexico. In middle Pennsylvanian
-time, general uplift occurred in Colorado, and almost the entire
-state was above sea level for the rest of the period.</p>
-<div class="pb" id="Page_48">48</div>
-<h3 id="c25">Permian Period
-<br /><span class="small">(223-270 million years ago)</span></h3>
-<p>By the end of the Pennsylvanian Period, the mountains of the
-Ancestral Rockies had been almost entirely removed by erosion,
-and the deep basins were filled with sediments. Colorado was
-once more a great plain, sloping gently to the northeast. In eastern
-Colorado, a shallow sea gradually dried up, leaving some thin
-limestone and gypsum beds along its margin. The western shore
-of this sea was edged with beaches and sand dunes, preserved as
-the Lyons Sandstone. The buildings of the University of Colorado,
-as well as many homes and other structures in the Boulder-Denver
-area, are faced with this beautiful salmon-colored sandstone.</p>
-<div class="img" id="fig33">
-<img src="images/p25.jpg" alt="" width="800" height="541" />
-<p class="caption">Balanced Rock, in the Garden of the Gods northwest of Colorado
-Springs, is an erosional remnant of iron-rich <a class="gloss" href="#g_Conglomerate">conglomerate</a> and sandstone.
-It remains while the rest of the surrounding layers are gone
-because it is harder and more completely cemented together by silica.
-The rock is part of the Late Paleozoic Fountain Formation. (John
-Chronic photo)</p>
-</div>
-<p>In the western part of the state, Permian deposits consist
-mostly of shales and sandstones. The red color of these rocks, and
-the complete absence of <a class="gloss" href="#g_Fossil">fossils</a> in them, suggest that the environment
-in which they were deposited was not marine, but was a vast,
-level mudflat subject to alternating wet and dry periods. The
-shales and sandstones collectively are called the Maroon Formation,
-named for Maroon Bells, near Aspen, where they are
-dramatically exposed in the mountain cliffs.</p>
-<div class="pb" id="Page_49">49</div>
-<div class="img" id="fig34">
-<img src="images/p25a.jpg" alt="" width="487" height="801" />
-<p class="caption">Tracks of Permian reptiles called <i>Laoporus coloradoensis</i> occur in the
-Lyons Sandstone near Lyons. These are about life size.</p>
-</div>
-<div class="pb" id="Page_50">50</div>
-<p>During part of Permian time, a shallow sea extended from
-Idaho, Utah, and Wyoming into the northwest corner of Colorado.
-In this sea was deposited the Phosphoria Formation, a highly
-phosphatic limestone containing only rare, poorly preserved
-molluscan <a class="gloss" href="#g_Fossil">fossils</a>.</p>
-<p>As the Paleozoic Era ended, Colorado was still flat and low-lying.
-By this time land plants and animals had evolved, but if
-vegetation grew in the Colorado area, or animals roamed it, they
-left few <a class="gloss" href="#g_Fossil">fossil</a> remains. Tracks of early reptiles have been found
-in the Lyons Sandstone. Dune sandstones here and in adjacent
-areas suggest that desert conditions may have prevailed, in which
-case Colorado would have been very similar, scenically and
-climatically, to Sahara regions today.</p>
-<div class="img" id="fig35">
-<img src="images/p26.jpg" alt="" width="800" height="631" />
-<p class="caption">Dark red Pennsylvanian and Permian <a class="gloss" href="#g_Conglomerate">conglomerates</a> form the Flatirons
-that overlook the University of Colorado campus at Boulder. University
-buildings are faced with Permian Lyons Sandstone quarried along the
-foothills of the northern Front Range. (University of Colorado photo)</p>
-</div>
-<div class="pb" id="Page_51">51</div>
-<h3 id="c26">MESOZOIC ERA</h3>
-<p>The Mesozoic Era, popularly known as the Age of Reptiles
-or Age of Dinosaurs, is divided into three periods. The climate
-of the entire earth appears to have been warmer then than it is
-at present, perhaps because of a different distribution of land
-and sea areas, or because continental areas were not as high and
-mountainous as they are just now. Colorado was a rather low
-land area for most of the first two Mesozoic periods; then a vast
-sea covered the entire state for the remainder of the era.</p>
-<div class="img" id="fig36">
-<img src="images/p26a.jpg" alt="" width="800" height="554" />
-<p class="caption">The pink cliffs of Colorado National Monument are made of Wingate
-and Entrada Sandstones. Underlying them, in the valley bottom, Chinle
-shales form steep red slopes. (William C. Bradley photo)</p>
-</div>
-<h3 id="c27">Triassic Period
-<br /><span class="small">(180-225 million years ago)</span></h3>
-<p>Saharan conditions continued to prevail in western North
-America during the early part of the Mesozoic Era. In central
-Colorado, the lowest Mesozoic deposits are the Triassic Lykins
-Formation, a series of soft, bright red sandstones and shales.
-Where the Lykins is exposed along the Front Range, its bright
-<span class="pb" id="Page_52">52</span>
-red color identifies it. Because of its softness, it is often less
-prominent than adjacent rock layers in the mountain foothills.
-The Lykins Formation includes some <a class="gloss" href="#g_Evaporite">evaporites</a>, apparently
-derived from Permian evaporites washed into the Triassic ponds
-and lakes which existed occasionally in this region.</p>
-<p>Over almost the entire state, the rocks deposited at this time
-are very similar. Formation names may differ&mdash;Lykins, Moenkopi,
-Chinle, Ankareh, Wingate&mdash;but the rocks are almost
-universally fine-grained sandstones and shales with a red or pink
-color. They represent ancient coastal plain, dune, or delta deposits.
-Toward the western edge of the state they coarsen, and contain
-layers of <a class="gloss" href="#g_Conglomerate">conglomerates</a> similar to the Triassic conglomerates of
-northern Arizona and Utah. These suggest that mountain-building
-was taking place west of here at that time.</p>
-<p>There are virtually no <a class="gloss" href="#g_Fossil">fossils</a> known from Triassic rocks in
-Colorado, although some fossil palm fronds have been found west
-of the San Juan Mountains, in the southwestern corner of the state.</p>
-<h3 id="c28">Jurassic Period
-<br /><span class="small">(135-180 million years ago)</span></h3>
-<p>During the Jurassic Period, Colorado was still a low, flat desert
-area with intermittent streams flowing eastward over the surface
-of older sediments. The Navajo Sandstone, formed from dune
-sands, was deposited in the western part of the state. Streams flowing
-eastward from Utah brought fine sediments&mdash;silts and muds&mdash;to
-western Colorado, forming what is now the Carmel Formation.
-Near Canon City, coarse gravels bear witness to local uplift
-in Jurassic time. Both these gravels and the Carmel Formation
-were overlain by more dune sands, now hardened into the Entrada
-Sandstone.</p>
-<p>In Late Jurassic time the Colorado area, which had been
-predominantly desert since Permian time, appears finally to have
-been submerged once more. Fine calcareous muds of the Curtis
-Formation, containing <a class="gloss" href="#g_Ammonite">ammonites</a>, <a class="gloss" href="#g_Belemnite">belemnites</a>, and other marine
-shellfish, show us that a shallow sea transgressed from the west
-over the wind-blown sands. This sea was, geologically speaking,
-of short duration&mdash;only a few million years. Bounded on almost
-all sides by desert, it seems to have dried up, depositing the gypsum
-that is now present in a thin layer along the Front Range between
-Denver and Canon City in the Ralston Formation.</p>
-<div class="pb" id="Page_53">53</div>
-<p>At about this time, however, the climate underwent a major
-change. Deposits above the Ralston indicate an increasingly moist
-environment, the environment in which the Morrison Formation
-was deposited over most of Colorado and parts of the adjacent
-states of Kansas, Arizona, Utah, and Wyoming. The Morrison
-Formation is exposed in many places, and is characteristically
-composed of layers of fine, limy mud, brightly colored in streaks
-of red, brown, green, and blue. In most areas it is so soft that it
-becomes soil-covered; it is well exposed only in roadcuts or where
-it is protected from erosion by a &ldquo;caprock&rdquo; of harder sediments
-or <a class="gloss" href="#g_Lava">lava</a>. Spectacular outcrops can be seen in new roadcuts along
-U. S. Interstate highway 70 just west of Denver.</p>
-<div class="img" id="fig37">
-<img src="images/p27.jpg" alt="" width="800" height="553" />
-<p class="caption">In this roadcut along U. S. Interstate 70 west of Denver, Jurassic and
-Cretaceous rocks are unusually well exposed in the Dakota <a class="gloss" href="#g_Hogback">hogback</a>.
-Green and purple shales represent the dinosaur-bearing Morrison
-Formation. The Cretaceous Dakota Group forms the eastern, higher
-half of the cut. Black layers are carbon-rich clays of the South Platte
-Formation, frequently quarried locally for ceramic uses. (John Chronic
-photo)</p>
-</div>
-<p><a class="gloss" href="#g_Fossil">Fossil</a> dinosaur bones occur in great numbers in the Morrison
-Formation near the towns of Morrison and Canon City and at
-several other places in Colorado. Those at Canon City have been
-quarried extensively, and are now mounted in a number of
-museums in the United States. At Dinosaur National Monument, in
-eastern Utah and northwestern Colorado, many excellent remains
-have been found; those in Utah can be seen in place in the rock
-in a striking exhibit at the National Monument.</p>
-<div class="pb" id="Page_54">54</div>
-<div class="img" id="fig38">
-<img src="images/p28.jpg" alt="" width="800" height="629" />
-<p class="caption">In an old painting, a paleontologist contemplates <a class="gloss" href="#g_Fossil">fossil</a> bones found
-near Morrison. The date is 1877. The bones are those of the 70-foot
-dinosaur <i>Apatosaurus</i>, more commonly known as <i>Brontosaurus</i>, shown
-below in reconstruction.</p>
-</div>
-<div class="img" id="pic_6">
-<img src="images/p28a.jpg" alt="Apatosaurus" width="700" height="390" />
-</div>
-<div class="pb" id="Page_55">55</div>
-<p>Some of the dinosaurs known from the Morrison Formation
-reached 80 feet in length. Both plant-eating and meat-eating types
-are known. In addition to the bones themselves, gastroliths or
-gizzard stones can frequently be found; these highly polished
-stones were as essential to dinosaur digestion as gravel is to a
-chicken or a caged canary.</p>
-<p>Along with the dinosaur <a class="gloss" href="#g_Fossil">fossils</a> are found abundant remains
-of water plants called charophytes. These plants formed tiny
-spiralled balls of calcite as part of their reproductive activities;
-both the little balls and the stalks of the plants themselves occur
-in many parts of the state. In western Colorado, near Grand
-Junction, silicified shells of freshwater snails can also be found
-in the Morrison.</p>
-<p>Early in the 1900s vanadium, radium, and uranium were
-discovered in Jurassic sandstones and mudstones of western Colorado.
-Extensive mining in this area has revealed that these
-elements often become concentrated by groundwater in organic
-material such as <a class="gloss" href="#g_Fossil">fossil</a> plant stems or dinosaur bones. The search
-for radioactive minerals has thus brought to light many ancient
-fossil accumulations.</p>
-<div class="pb" id="Page_56">56</div>
-<h3 id="c29">Cretaceous Period
-<br /><span class="small">(70-135 million years ago)</span></h3>
-<p>Early in Cretaceous time, marine conditions once more
-prevailed in Colorado. This is indicated by a marked change in
-rock types from beach and near-shore deposits to true marine
-sediments.</p>
-<div class="img" id="fig39">
-<img src="images/p29.jpg" alt="" width="700" height="593" />
-<p class="caption">Between the Front Range and the Plains the Cretaceous Dakota Formation
-forms a <a class="gloss" href="#g_Hogback">hogback</a> ridge which can be traced for 200 miles or
-more. The well-cemented sandstone resists erosion, and so remains as
-a ridge when softer layers are stripped away. (Jack Rathbone photo)</p>
-</div>
-<p>The sandstones derived from beach sands sometimes include
-coarse pebbles of chert which can be traced to sources in Permian
-rocks of Utah and Nevada. Occasionally the beach and near-shore
-deposits include marine shells like oysters, indicating that
-there were brackish and salt water lagoons and marshes along the
-shore. The Dakota Formation represents the beach of the transgressive
-or advancing sea. This formation contains oil in eastern
-Colorado, Nebraska, and Wyoming; the oil itself may have been
-<span class="pb" id="Page_57">57</span>
-derived from decay of organic materials in swamps behind the
-beaches and bars.</p>
-<p>As the sea deepened in eastern Colorado, finer sediments were
-deposited. These included the black muds of the Benton Shale,
-and the Niobrara Limestone, a shallow-water deposit containing
-abundant shells of clams (<i>Inoceramus</i> and <i>Ostrea</i>) and <a class="gloss" href="#g_Ammonite">ammonites</a>
-and tiny one-celled animals called <a class="gloss" href="#g_Foraminiferida">Foraminiferida</a>. Above the
-Benton and Niobrara Formations lie the fine gray muds of the
-Pierre Shale. Several thousand feet thick, the Pierre contains
-occasional beautifully preserved ammonite shells as well as bones
-from <a class="gloss" href="#g_Fossil">fossil</a> fish and swimming reptiles.</p>
-<div class="img" id="fig40">
-<img src="images/p29a.jpg" alt="" width="673" height="462" />
-<p class="caption">Cretaceous rocks in Colorado are rich in <a class="gloss" href="#g_Fossil">fossil</a> pelecypods. Each of the
-fossils illustrated above may grow to a much larger size than shown.</p>
-</div>
-<div class="img" id="pic_7">
-<img src="images/p29c.jpg" alt="" width="689" height="261" />
-<p class="caption">Shales of the Laramie Formation contain many recognizable plant
-<a class="gloss" href="#g_Fossil">fossils</a>.</p>
-</div>
-<div class="pb" id="Page_58">58</div>
-<p>The rocks deposited in western Colorado at this time are
-markedly different from those deposited in eastern Colorado. In
-the east, deposits are fine and very limy, containing abundant
-shells and little in the way of coarse debris. In the west, sandstones
-of the <a class="gloss" href="#g_Mesa">Mesa</a> Verde Formation dominate, and coal beds suggest
-marshy or swampy conditions inshore from the ancient ocean.
-This is just the pattern we would expect from a low-lying region
-bordering a shallow sea, a region similar perhaps to the southeastern
-Atlantic and Gulf coasts of the United States today.</p>
-<p>Toward the end of the Cretaceous Period, the sea receded
-from Colorado. Beaches and bars of the retreating sea left a
-sandstone layer which now outcrops prominently east of the Front
-Range as the Fox Hills Sandstone. Above lie interbedded sands
-and coals, the Laramie Formation. The presence of coal above
-beach sands shows that the coal swamps moved eastward as the
-sea retreated.</p>
-<p>The exact age of the shoreline deposits and coal beds varies
-from place to place in such a way as to indicate that the sea
-withdrew slowly and irregularly. In general the shore moved
-eastward, but there are localities such as North Park where deposition
-lasted much longer than elsewhere. In some places no real
-beach was formed at the ancient strand line.</p>
-<p>In western Colorado, the end of Cretaceous time is marked by
-coarser beds, indicating an increased rate of uplift in Utah. <a class="gloss" href="#g_Conglomerate">Conglomerates</a>
-were deposited in the beds of the McDermott
-Formation, now visible along the Animas River south of Durango.</p>
-<div class="pb" id="Page_59">59</div>
-<h3 id="c30">CENOZOIC ERA</h3>
-<p>It is characteristic of earth history that the younger the rocks
-are, the more we know about them. This is because younger rocks
-lie near the surface, have not been disturbed as much by mountain
-building processes as have older rocks, and have not been affected
-as strongly by repeated erosion. Many of the events of the Cenozoic
-Era are documented in detail in the geology of Colorado, and these
-events have intimately influenced the scenery as we see it today.</p>
-<p>The Cenozoic is the Age of Mammals. How it happened that
-mammals triumphed over reptiles is one of the mysteries of
-geology. Some scientists think that climatic changes&mdash;dropping
-temperatures and increases in rainfall&mdash;swung the balance in
-favor of the warm-blooded mammals. Others believe that cosmic
-ray bombardment during some unusual astronomical event may
-have destroyed many surface-living dinosaurs, while small burrowing
-mammals (as well as many small reptiles) were able to survive.
-Still others maintain that the superior intelligence and regulated
-body temperatures of mammals enabled them to win out in the
-battle for survival without the aid of climatic or cosmic change.</p>
-<p>The names Tertiary and Quaternary, used for the two Cenozoic
-Periods, are holdovers from early studies in geology in which
-rocks were divided into Primary (very hard, crystalline rocks such
-as igneous and metamorphic rocks), Secondary (well consolidated
-layered rocks), Tertiary (layered rocks which are not fully
-cemented but which are nevertheless fairly well consolidated),
-and Quaternary (sediments in which the grains have not become
-cemented together).</p>
-<h3 id="c31">Tertiary Period
-<br /><span class="small">(3-70 million years ago)</span></h3>
-<p>During the first part of the Tertiary Period, uplift began in
-earnest in Colorado and adjacent states. This uplift was part of
-the great Laramide Orogeny that built the Rocky Mountain chain
-from Alaska to New Mexico. The entire area rose above the level
-of the sea, and mountains were thrust up in a great series of north-south
-ranges that extended unbroken almost the length of the
-continent. Between the ranges, thick layers of gravel and sand,
-<span class="pb" id="Page_60">60</span>
-derived from the surrounding highlands, were deposited in intermontane
-basins. Occasional freshwater limestones and shales
-indicate the presence of lakes.</p>
-<p>In Colorado, many details of the formation of the Rockies
-stand out in bold relief. The Front Range moved upward sharply,
-mostly as a linear block broken or faulted along both edges.
-Paleozoic and Mesozoic sediments along the margins of the block
-were steeply tipped and in some places even overturned, while
-in some localities Precambrian rocks were thrust out over the
-younger sediments.</p>
-<p>Just east of the Front Range, especially in the area around
-Denver, the land remained lower and was the site of thick deposits
-of gravel and sand eroded from the range. The Denver Formation,
-the Arapahoe <a class="gloss" href="#g_Conglomerate">Conglomerate</a>, and the Dawson Arkose are more
-than 2,000 feet thick in this area. These are delta and river
-sediments, all varying a great deal from place to place. Individual
-layers of sand or gravel are not continuous over extensive areas,
-but some, such as the Castle Rock Conglomerate, are very prominent
-locally.</p>
-<div class="img" id="fig41">
-<img src="images/p30.jpg" alt="" width="800" height="569" />
-<p class="caption">On Wolford Mountain, just north of Kremmling, Precambrian <a class="gloss" href="#g_Granite">granite</a>
-lies on top of Cretaceous shale. The older rocks were thrust up and
-over younger rocks during the Laramide Orogeny. The position of the
-<a class="gloss" href="#g_Fault">fault</a> shows clearly because trees prefer the granite soil above the
-fault to the shale below. (Jack Rathbone photo)</p>
-</div>
-<div class="pb" id="Page_61">61</div>
-<p>Along the eastern margin of the Front Range west of Castle
-Rock and Sedalia, rocks deposited at this time are now folded
-steeply, indicating that the mountains continued to rise even as
-basin sediments were being deposited.</p>
-<p>In southern Colorado, the Sangre de Cristo and Wet Mountains
-were also formed as upthrust blocks. Between them, the Huerfano
-Basin and adjoining Raton Basin received particularly rapid
-alluvial deposition. In the Raton Basin, quantities of vegetation
-were deposited in swamps and marshes, forming the thick coal
-beds which can now be seen in road cuts west of Trinidad and
-along the Raton Pass highway. Huerfano Basin deposits contain
-some of the earliest known horse remains, skeletons of a tiny
-four-toed horse called <i>Hyracotherium</i> (formerly known as
-<i>Eohippus</i>).</p>
-<div class="img" id="fig42">
-<img src="images/p30a.jpg" alt="" width="800" height="635" />
-<p class="caption">Bones of <i>Hyracotherium</i>, the &ldquo;dawn horse,&rdquo; have been found northwest
-of Walsenburg in Early Tertiary sediments of the Huerfano Basin.
-(C. R. Knight painting, courtesy American Museum of Natural History)</p>
-</div>
-<p>Other rising ranges provided material for alluvial deposition
-in North Park, Middle Park, South Park, and the San Luis Valley.
-<span class="pb" id="Page_62">62</span>
-Layers of <a class="gloss" href="#g_Basalt">basalt</a> and volcanic peaks show that as the mountains
-rose, the crust cracked and allowed <a class="gloss" href="#g_Lava">lava</a> to rise to the surface
-in great quantities. Tertiary basalts are very much part of the
-Colorado landscape: some can be seen west of Granby, others
-in Table Mountains east of Golden. Near Boulder, Valmont <a class="gloss" href="#g_Dike">Dike</a>
-was intruded, though lava may not have reached the surface in
-that area. Spanish Peaks in southern Colorado, <a class="gloss" href="#g_Mesa">Mesa</a> de Maya,
-the Rabbit Ears Range, Grand and Battlement Mesas, and many
-other volcanic features were formed at this time.</p>
-<div class="img" id="fig43">
-<img src="images/p31.jpg" alt="" width="800" height="569" />
-<p class="caption">The town of Golden nestles between the Front Range and South Table
-Mountain. Tertiary <a class="gloss" href="#g_Basalt">basalt</a> capping South Table Mountain covers beds
-of the Denver Formation. It thins to the right, or south, indicating that
-its source was probably to the north or northwest. Buildings in the
-right foreground are the Colorado School of Mines. (Jack Rathbone
-photo)</p>
-</div>
-<div class="pb" id="Page_63">63</div>
-<div class="img" id="fig44">
-<img src="images/p31a.jpg" alt="" width="620" height="1000" />
-<p class="caption">A series of almost vertical <a class="gloss" href="#g_Dike">dikes</a> radiate from West Spanish Peak.
-Surrounding sediments are Tertiary. Weathering and erosion along
-sets of <a class="gloss" href="#g_Joint">joints</a> in the largest dike have shaped it into the &ldquo;Devil&rsquo;s
-Staircase.&rdquo; (Jack Rathbone photo)</p>
-</div>
-<div class="pb" id="Page_64">64</div>
-<p>Most of the rich mineral deposits of Colorado are thought
-also to have been formed during the early part of the Tertiary
-Period. Solutions rich in gold, silver, zinc, lead, copper, and
-sulfides of iron seeped into <a class="gloss" href="#g_Joint">joints</a> and <a class="gloss" href="#g_Fault">faults</a> in the crust as the
-mountains were pushed upward. Ore minerals crystallized out,
-sometimes in <a class="gloss" href="#g_Vein">veins</a> in the ancient Precambrian igneous and metamorphic rocks, sometimes in Paleozoic sediments. These are
-further discussed in <a href="#c33">Chapter III</a>.</p>
-<div class="img" id="fig45">
-<img src="images/p32.jpg" alt="" width="800" height="656" />
-<p class="caption">The Eocene Green River Formation includes great thicknesses of oil
-shale, an untapped petroleum reserve containing perhaps three trillion
-barrels of oil. The richest part of the oil shale is a dark brown layer
-called Mahogany Ledge, visible here on cliffs just west of Rifle. If
-placed in a campfire, fragments of this shale release enough oil to
-burn with a yellow, smoky flame. (Jack Rathbone photo)</p>
-</div>
-<p>Further to the north and west, the Uinta Mountains rose.
-They are a fault-block range, but they lie at right angles to the
-general north-south trend of the Rocky Mountains. South of them
-the Uinta Basin, one of the largest of the intermontane basins,
-received shaly deposits in a great lake which existed here for
-probably several million years. The lake extended over some
-100,000 square miles, and during its existence great quantities
-of tiny organisms lived in its waters. Oily material from these
-<span class="pb" id="Page_65">65</span>
-organisms was deposited in the mud of the lake sediments, particularly
-in the eastern end of the basin, there to remain trapped in
-a great oil-shale deposit. <a class="gloss" href="#g_Fossil">Fossil</a> fish, crayfish, algae, and many
-forms of insect and plant life have been found as fossils in these
-lake shales.</p>
-<p>West of Pikes Peak, another lake formed, dammed by a <a class="gloss" href="#g_Lava">lava</a>
-flow from a nearby volcanic field. Fine volcanic ash falling into
-this lake preserved the trunks and leaves of many plants as well
-as abundant insects, fish, and occasional mammal bones. These
-are now protected and exhibited in Florissant <a class="gloss" href="#g_Fossil">Fossil</a> Beds National
-Monument. The fossil plants, among them redwoods, poplar,
-hackberry, and pine, suggest a climate warmer than the present
-one, and have been taken to indicate that regional uplift to the
-present altitude had not yet occurred.</p>
-<p>Another rich deposit of <a class="gloss" href="#g_Fossil">fossil</a> insects and plants occurs near
-Creede. Other lake deposits in South Park contain ash layers
-with fossil algae and snails.</p>
-<div class="img" id="fig46">
-<img src="images/p32a.jpg" alt="" width="800" height="584" />
-<p class="caption">Large petrified trunks of redwoods and other trees can be seen at
-Florissant <a class="gloss" href="#g_Fossil">Fossil</a> Beds National Monument, west of Colorado Springs.
-(John Chronic photo)</p>
-</div>
-<p>In southwestern Colorado, extensive Tertiary <a class="gloss" href="#g_Lava">lava</a> flows, ash
-falls, and river deposits form the eastern part of the San Juan
-Mountains, the largest volcanic area in the state. Mineral collectors
-<span class="pb" id="Page_66">66</span>
-are attracted to this region by the many excellent localities for
-agate and other siliceous stones.</p>
-<p>Still another center of Tertiary volcanism was located in what
-is now Rocky Mountain National Park. Specimen Mountain,
-northwest of Trail Ridge, was an active volcano about 30 million
-years ago, shedding ash and <a class="gloss" href="#g_Lava">lava</a> over much of northern Colorado.
-The <a class="gloss" href="#g_Rhyolite">rhyolite</a> which now caps the hill west of Iceberg Lake, on
-Trail Ridge Road, was derived from this volcano, but is now
-separated from it by the deep glaciated valley of the Cache la
-Poudre River and Milner Pass.</p>
-<p>Volcanic ash at times drifted far eastward and blanketed the
-surface of the plains, burying specimens of many animals and
-plants. The White River Formation, extending from northeast
-Colorado northward into South Dakota, is formed of such drifting
-ash. Many now-extinct mammals have been excavated from this
-formation.</p>
-<p>Sometime after the mid-Tertiary episode of violent volcanic
-activity, Colorado was uplifted to its present altitude. This was a
-general uplift, raising the plains and <a class="gloss" href="#g_Plateau">plateau</a> areas as well as the
-mountains. The uplift was not an abrupt process, but continued
-for perhaps ten million years. It raised the entire state 3,000 to
-5,000 feet above its previous level.</p>
-<div class="img" id="fig47">
-<img src="images/p33.jpg" alt="" width="800" height="433" />
-<p class="caption">Pawnee Buttes, about 40 miles north of Fort Morgan, rise like castles
-from the eastern Prairie Province. Remnants of Oligocene and Miocene
-sedimentary rock that once covered much of northeastern Colorado
-and adjacent states, they contain jaws, teeth, and other bones of
-primitive mammals. (Department of Highways photo)</p>
-</div>
-<p>During the remainder of the Tertiary Period, Colorado was
-<span class="pb" id="Page_67">67</span>
-the site of erosion rather than deposition. However, some stream
-material was deposited in the mountain valleys, and on the
-prairies wind-blown and stream-borne sands were spread thinly,
-interlayered with impure limestones deposited in ponds and lakes.
-In the San Luis Valley, deposition was probably more continuous
-than elsewhere, as the exit from the valley was blocked by volcanic
-flows. The deposits in this valley, sands and clays of the Santa Fe
-and Alamosa Formations, form a great artesian basin. The rich
-agricultural development of the valley is made possible by water
-wells tapping these formations.</p>
-<div class="img" id="fig48">
-<img src="images/p33a.jpg" alt="" width="700" height="628" />
-<p class="caption">Remains of many now-extinct mammals have been found in Tertiary
-<a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> of northeastern Colorado, in the general area of
-Pawnee Buttes. Those illustrated are <i>Oreodon</i> from Oligocene strata
-and a &ldquo;giraffe-camel&rdquo; (<i>Oxydactylus</i>) from Miocene rocks.</p>
-</div>
-<div class="pb" id="Page_68">68</div>
-<h3 id="c32">Quaternary Period
-<br /><span class="small">(3 million years ago to present)</span></h3>
-<p>The most significant feature of the Quaternary Period in
-Colorado, as elsewhere in the northern hemisphere, is the evidence
-of <a class="gloss" href="#g_Glaciation">glaciation</a>. During the first part of the Quaternary Period,
-known as the Pleistocene Epoch, great continental <a class="gloss" href="#g_Glacier">glaciers</a> covered
-most of Canada and much of northern United States. The ice
-sheets did not extend southward as far as Colorado, but large
-valley glaciers developed in many of the mountain ranges of the
-state and left their traces in many mountain valleys.</p>
-<div class="img" id="fig49">
-<img src="images/p34.jpg" alt="" width="800" height="666" />
-<p class="caption">Mills and Jewel Lakes, in Rocky Mountain National Park, occupy small
-glacier-gouged basins in <a class="gloss" href="#g_Glacier">Glacier</a> Gorge. The flat-topped peak at the
-upper left is Longs Peak, elevation 14,256 feet; Pagoda Mountain is
-in the center of the skyline. <a class="gloss" href="#g_Bedrock">Bedrock</a> in this area is Precambrian <a class="gloss" href="#g_Granite">granite</a>,
-<a class="gloss" href="#g_Gneiss">gneiss</a>, and <a class="gloss" href="#g_Schist">schist</a> at the Front Range &ldquo;core.&rdquo; (Jack Rathbone photo)</p>
-</div>
-<p>The conditions leading to Pleistocene <a class="gloss" href="#g_Glaciation">glaciation</a> are not fully
-understood. Climatic changes may have been initiated by a
-decrease in solar radiation, changing patterns of ocean currents,
-<span class="pb" id="Page_69">69</span>
-reduction of solar heating by volcanic dust, or an increase in
-general elevation of the land. As the climate became cooler and
-moister, snowfall increased in the north and at high altitudes.
-In areas where winter snowfall exceeded summer melting, <a class="gloss" href="#g_Glacier">glaciers</a>
-developed.</p>
-<p>In Colorado, <a class="gloss" href="#g_Glacier">glaciers</a> formed along the crests of the Front
-Range, the Sawatch Range, the Elk Mountains and West Elk
-Mountains, the Sangre de Cristo and Mosquito Ranges, the San
-Juan Mountains, and the Park and Gore Ranges. <a class="gloss" href="#g_Glaciation">Glaciation</a> in
-Colorado was selective: in many places elevation was sufficient
-for glaciation, but snowfall apparently was not great enough.
-Where they did occur, the glaciers extended down to elevations
-of about 8,000 feet. There, temperatures became mild enough to
-melt the ice.</p>
-<p>The mountain <a class="gloss" href="#g_Glacier">glaciers</a> have left many tell-tale signs of their
-presence. Valleys above 8,000 feet are U-shaped, their upper ends
-bounded by horseshoe-shaped, steep-walled <a class="gloss" href="#g_Cirque">cirques</a>. In the lower
-portions of the valleys, at elevations just above 8,000 feet, lie long
-lines of glacial debris known as <a class="gloss" href="#g_Moraine">moraines</a>: terminal moraines
-forming crescents across the valleys to show where melting glaciers
-dropped their rocky loads; lateral moraines along the sides of
-valleys; medial moraines where glaciers from two valleys met.
-Terminal moraines, often forming effective barriers across the
-present streams, may act as dams, creating lakes such as Grand
-Lake in Rocky Mountain National Park.</p>
-<p>There were at least three distinct glacial episodes in Colorado.
-This is known because careful studies of glacial debris in <a class="gloss" href="#g_Moraine">moraines</a>
-reveal three different degrees of rock weathering. All three stages
-can be seen in or near Rocky Mountain National Park. The oldest
-is represented by a moraine about three miles west of Estes Park,
-where the Big Thompson River traverses a wide U-shaped valley
-before entering its narrow, unglaciated canyon. The next oldest
-is represented in terminal moraines further up the valley, at Aspenglen
-campground. The youngest is shown in a prominent terminal
-moraine about one mile west of the park entrance in Horseshoe
-Park.</p>
-<p>A large lateral <a class="gloss" href="#g_Moraine">moraine</a> separates Hidden Valley from the south
-side of Horseshoe Park, and an almost equally large lateral moraine
-is present on the north side of this valley. At Moraine Park, both
-sides of the valley are edged with lateral moraines also.</p>
-<p>Studies in Rocky Mountain National Park have revealed many
-other details of <a class="gloss" href="#g_Glaciation">glaciation</a> in this area. These are described in Park
-Service brochures and guidebooks, in the museum at Park headquarters,
-and in informative roadside signs.</p>
-<div class="pb" id="Page_70">70</div>
-<div class="img" id="fig50">
-<img src="images/p35.jpg" alt="" width="695" height="1000" />
-<p class="caption">A line of hikers approaches Arapaho <a class="gloss" href="#g_Glacier">Glacier</a>, west of Boulder. Movement
-of the glacier is evidenced by the crevasses apparent just below
-the snowfield in the dirty gray glacial ice. (H. H. Heuston photo)</p>
-</div>
-<div class="pb" id="Page_71">71</div>
-<p>Several small <a class="gloss" href="#g_Glacier">glaciers</a> are still present in the Colorado mountains,
-all in sheltered <a class="gloss" href="#g_Cirque">cirques</a> above 11,000 feet. These may be
-remnants of the former larger glaciers, or new glaciers formed
-after a long warming episode. A hike to one of these glaciers is
-a rewarding experience for anyone interested in geology. Some of
-the more accessible are St. Mary&rsquo;s Glacier west of Denver,
-Arapaho Glacier west of Boulder (the Boulder Chamber of
-Commerce sponsors a festive hike to Arapaho Glacier every
-August), and Tyndall Glacier in Rocky Mountain National Park.</p>
-<p>The Ice Age brought drastic changes also to the landscape
-below 8,000 feet elevation. Heavily loaded with glacial debris,
-mountain streams disgorged coarse sands and gravels along the
-mountain front and in the intermontane basins. As the <a class="gloss" href="#g_Glacier">glaciers</a>
-melted after each period of expansion, the swollen streams cut
-deeply into their former deposits and into much older rocks as
-well. Royal Gorge, the Black Canyon of the Gunnison, and many
-of the deep, colorful canyons of the <a class="gloss" href="#g_Plateau">Plateau</a> Province were cut or
-at least deepened by these waters. The canyons along the east
-face of the mountains&mdash;Big Thompson, Boulder, Clear Creek, and
-others&mdash;were also deepened and sharpened by the rushing ice-fed
-torrents.</p>
-<p>On the prairies, rivers dumping their loads of sand covered
-the older rocks. Sand dunes developed along the river channels.
-Bones and huge tusks of hairy mammoths were sometimes buried
-in these soft deposits; now they are occasionally revealed as the
-dune and river sands are washed or blown away by continuing
-erosion.</p>
-<p>About 20,000 years ago, man arrived in Colorado. Soon after
-this, the water supply of the valleys diminished greatly, and erosion
-slowed down correspondingly. The climate gradually became
-semiarid to arid. Many features of the natural scene were much
-as they must have been a century ago, without the highways, dams,
-and television aerials of today. Buffalo and many smaller types
-of game roamed the plains and foothills; deer, elk, and bighorn
-sheep were plentiful in the mountains. Nomadic tribes camped
-and hunted in both mountain and prairie. In the western part of
-the state, homes could be built in the shelter of great caves, as at
-<a class="gloss" href="#g_Mesa">Mesa</a> Verde, and game could be supplemented with corn and
-squash planted on <a class="gloss" href="#g_Plateau">plateau</a> surfaces.</p>
-<p>Several features of Colorado scenery changed with increasing
-aridity. The <a class="gloss" href="#g_Glacier">glaciers</a> of course were gone or nearly gone. Streams
-were no longer the violent torrents they had been. Many mountain
-lakes, filled with sediment and vegetation, became instead mountain
-meadows. And the once fertile intermontane valleys became
-deserts.</p>
-<div class="pb" id="Page_72">72</div>
-<div class="img" id="fig51">
-<img src="images/p36.jpg" alt="" width="700" height="391" />
-<p class="caption">During the last Ice Age, elephant-like mastodons roamed Colorado.
-As present-day erosion removes sediments, bones, teeth, and tusks
-are frequently exposed, especially in the Prairie Province. (C. R. Knight
-painting, courtesy American Museum of Natural History)</p>
-</div>
-<div class="img" id="pic_8">
-<img src="images/p36a.jpg" alt="Mastodon" width="700" height="657" />
-</div>
-<div class="pb" id="Page_73">73</div>
-<p>On the eastern side of the San Luis Valley, the Great Sand
-Dunes developed at this time. These dunes nestle against the
-Sangre de Cristo Range, where strong southwesterly winds blowing
-across the wide valley tend to funnel toward Mosca and Music
-Passes. These winds lift loads of sand from the lightly vegetated
-valley floor, and drop it as they rise over the mountains. Where
-the sand is dropped, the dunes have formed. They rise to about
-700 feet above the valley floor, and cover about forty square miles.
-The low rainfall of the area, seven to eight inches per year, keeps
-vegetation from creeping over the dunes and makes them a most
-distinctive feature of Colorado, a lesson in geology in the making.</p>
-<p class="center"><span class="gs">* * * * * * * *</span></p>
-<p>Geologic processes in Colorado now seem to be much
-reduced from what they were a few thousand years ago. Reduction
-in rainfall has led to reduced erosion. Mountain-building, having
-reached a climax in Tertiary time, has declined markedly. However,
-we find evidence that volcanism has occurred within the last
-few thousand years and faulting within the last few hundred, and
-Colorado streams rise after sudden mountain storms to approximate
-the violent torrents of glacial times. Colorado&rsquo;s scenery,
-fashioned during some three billion years of earth history, is ever
-changing.</p>
-<div class="img" id="fig52">
-<img src="images/p36c.jpg" alt="" width="800" height="427" />
-<p class="caption">The Great Sand Dunes of Colorado were formed during Pleistocene
-and Recent time by deposition of quartz sand lifted from unconsolidated
-alluvial deposits in the San Luis Valley. The highest of the
-dunes rises 700 feet above the adjacent valley floor. (John Chronic
-photo)</p>
-</div>
-<div class="pb" id="Page_74">74</div>
-<h2 id="c33"><span class="h2line1">III</span>
-<br /><span class="h2line2">Geology and Man in Colorado</span></h2>
-<p>Colorado&rsquo;s first permanent settlers arrived in 1858, when
-gold was discovered in river sands near what is now the
-city of Denver. The ensuing gold rush, coming ten years after
-the rush to California, rivalled it in fury and brought sudden
-wealth to lucky miners and the adventurous merchants who grubstaked
-them. Several hundred mining towns or &ldquo;camps&rdquo; sprang
-into existence almost overnight, their sites determined by the
-geology of the mountain areas. The cities of Denver, Boulder, and
-Golden were established as milling and shipping centers for the
-products of the mines. In 1876 the now-wealthy area, previously
-part of Kansas Territory, became the State of Colorado.</p>
-<p>For more than a hundred years Colorado&rsquo;s minerals&mdash;products
-of her long and diverse geologic history&mdash;have influenced
-her development in many ways. The state&rsquo;s early wealth,
-stemming from bonanzas in gold and silver, is evidenced by
-palatial homes, hotels, and public buildings constructed during
-the first few decades of mining activity. Some of these are still
-standing&mdash;the opera houses at Central City and Aspen, Central
-City&rsquo;s famous Teller House, and the Grand Imperial Hotel at
-Silverton are examples.</p>
-<p>Many of the stories and legends of Colorado&rsquo;s gold camps are
-recounted in <i>Stampede to Timberline</i>, by Muriel Sibell Wolle,
-delightfully illustrated with sketches of old mining towns as they
-appear today. <i>Mining in Colorado</i>, published by the U. S. Geological
-Survey, also makes fascinating reading, as it contains many
-historical anecdotes and eyewitness accounts of gold-rush days.</p>
-<p>Development of the metal-mining areas in Colorado followed
-a definite sequence. <a class="gloss" href="#g_Placer">Placer</a> gold was usually discovered first.
-Recovery of placer gold was followed by mining of gold from
-<a class="gloss" href="#g_Vein">veins</a> or &ldquo;<a class="gloss" href="#g_Lode">lodes</a>.&rdquo; Although at first only <a class="gloss" href="#g_NativeGold">native gold</a> was mined,
-gold-bearing compounds such as telluride were soon recognized
-as an additional source, especially at Gold Hill, Cripple Creek,
-and of course the camp that came to be known as Telluride.
-As gold sources were depleted, silver, first produced as a byproduct,
-became of prime interest. Lead and zinc were in turn
-byproducts of silver mining. Other metals, notably copper,
-vanadium, tungsten, and iron, were produced later. Molybdenum
-is the Johnny-come-lately of the state&rsquo;s mining industry, but is
-<span class="pb" id="Page_75">75</span>
-now the chief metal produced. A uranium boom in the 1950s
-brought a short rush to western Colorado and new vigor to the
-economy.</p>
-<p>Oil was discovered near Canon City in 1862. The nearby
-Florence field and a small, shallow field near Boulder preceded
-much greater discoveries in the Denver Basin, the Uinta Basin,
-and southwest Colorado. Oil reservoirs, confined to areas of
-sedimentary rock, are found primarily in the Prairie and <a class="gloss" href="#g_Plateau">Plateau</a>
-Provinces of the state, and recovery of the oil has done much to
-distribute population to these areas.</p>
-<p>Coal is also restricted to sedimentary rock areas. Coal production
-in Colorado has waxed and waned with the years, but has
-provided fuel for export, for the railroads, for the manufacture
-of electric power, and for many of the state&rsquo;s industries.</p>
-<p>A good picture of present mineral production in Colorado
-can be obtained from the following summary for 1971, prepared
-by the Colorado Bureau of Mines:</p>
-<table class="center">
-<tr class="th"><th><span class="u">Product</span> </th><th><span class="u">Value</span></th></tr>
-<tr><td class="l">Molybdenum </td><td class="r">$105,389,456</td></tr>
-<tr><td class="l">Petroleum </td><td class="r">90,494,459</td></tr>
-<tr><td class="l">Sand and gravel </td><td class="r">32,842,503</td></tr>
-<tr><td class="l">Coal </td><td class="r">30,251,443</td></tr>
-<tr><td class="l">Natural gas </td><td class="r">18,695,225</td></tr>
-<tr><td class="l">Uranium </td><td class="r">18,048,692</td></tr>
-<tr><td class="l">Vanadium </td><td class="r">15,863,554</td></tr>
-<tr><td class="l">Cement </td><td class="r">13,377,520</td></tr>
-<tr><td class="l">Zinc </td><td class="r">13,310,787</td></tr>
-<tr><td class="l">Lead </td><td class="r">6,582,025</td></tr>
-<tr><td class="l">Tungsten </td><td class="r">6,360,020</td></tr>
-<tr><td class="l">Limestone and dolomite </td><td class="r">5,397,570</td></tr>
-<tr><td class="l">Silver </td><td class="r">4,198,054</td></tr>
-<tr><td class="l">Fluorspar </td><td class="r">3,887,210</td></tr>
-<tr><td class="l">Copper </td><td class="r">3,875,976</td></tr>
-<tr><td class="l">Stone </td><td class="r">1,961,279</td></tr>
-<tr><td class="l">Gold </td><td class="r">1,832,791</td></tr>
-<tr><td class="l">Clay </td><td class="r">962,986</td></tr>
-<tr><td class="l">Iron </td><td class="r">880,047</td></tr>
-<tr><td class="l">Pumice </td><td class="r">309,370</td></tr>
-<tr><td class="l">Tin </td><td class="r">278,862</td></tr>
-<tr><td class="l">Gypsum </td><td class="r">253,856</td></tr>
-<tr><td class="l"><a class="gloss" href="#g_Pyrite">Pyrites</a> </td><td class="r">142,640</td></tr>
-<tr><td class="l">All others </td><td class="r">1,091,927</td></tr>
-<tr><td class="l"><span class="hst">Total</span> </td><td class="r"><span class="over">$376,288,252</span></td></tr>
-</table>
-<div class="pb" id="Page_76">76</div>
-<p>Colorado is now the nation&rsquo;s leading producer of molybdenum,
-tin, and vanadium, and second in output of tungsten. In oil
-production it ranked twelfth among the states in 1968, but ninth
-in reserves, with 420,000,000 barrels of proven reserves on
-1 January 1969. An as yet untapped source of oil lies in the oil
-shales of western Colorado.</p>
-<p>As part of the natural environment, water plays a major role
-in man&rsquo;s activities. Water problems in Colorado revolve mainly
-around the best use of runoff in a state whose major catchment
-basins are across the continental divide from her largest population
-centers and most fertile farm land. Groundwater, closely
-related to surface water distribution and movement, is a geological
-problem, and in Colorado as in other states many government
-and private geologists serve farm and industrial communities in
-the search for usable supplies.</p>
-<div class="box">
-<p>CAUTION: Old mines are dangerous! They may contain
-water or deadly gases, or be on the verge of collapse.
-Keep away from abandoned prospect pits and mine shafts.
-WARN AND WATCH YOUR CHILDREN.</p>
-</div>
-<div class="pb" id="Page_77">77</div>
-<h3 id="c34">GOLD, SILVER, AND OTHER METALS</h3>
-<p>Colorado&rsquo;s <a class="gloss" href="#g_Placer">placer</a> and <a class="gloss" href="#g_Lode">lode</a> sources of gold, which gave first
-impetus to the series of mining booms in the state, were fantastically
-rich. Summit and Lake Counties, for instance, each
-produced more than $5,000,000 in placer gold between 1859 and
-1867. During the same nine-year period, more than $9,000,000
-in lode gold was produced from Gregory Gulch, a tiny canyon
-between Central City and Black Hawk. Other districts rivalled
-or surpassed these figures.</p>
-<p>Early in the game it was recognized that almost all the deposits
-occurred along what came to be known as the &ldquo;mineral belt,&rdquo; a
-fifty-mile-wide zone extending southwest from the Boulder region.
-Most of the metals mined in the state come from this belt, but
-there are three notable exceptions: Cripple Creek, Silver Cliff, and
-western Colorado vanadium and uranium districts. In the first
-few years of the Colorado rush, gold ores and <a class="gloss" href="#g_Placer">placer</a> gold were
-discovered only in the northeastern part of the mineral belt.
-Gradually the belt was found to extend further and further southwest:
-Tincup was discovered in 1861, Silverton in 1870, Lake
-City in 1871, and Telluride in 1875. Aspen, on the western edge
-of the belt, was not discovered until 1879, perhaps because the
-area was difficult of access and lacked the easily recognizable
-<a class="gloss" href="#g_NativeGold">native gold</a>.</p>
-<p>In the northeast part of the mineral belt, gold and other
-minerals occur in <a class="gloss" href="#g_Vein">veins</a> in Precambrian <a class="gloss" href="#g_Granite">granite</a> and <a class="gloss" href="#g_Gneiss">gneiss</a>. In the
-Leadville and Aspen areas, ores are associated with altered
-Paleozoic limestones. At the southwest end of the mineral belt,
-in the San Juan Mountains, ore veins are found near or in Tertiary
-volcanic rocks. <a class="gloss" href="#g_NativeGold">Native gold</a>, gold-bearing compounds, and other
-metallic ores in these veins originated where mineral-rich solutions
-from deep within the earth penetrated fissures and <a class="gloss" href="#g_Joint">joints</a> in the
-surrounding rock. Regardless of the age of the host rock, almost
-all the ores of Colorado were deposited in the early or middle
-Tertiary Period, about 35 to 70 million years ago.</p>
-<p>Gold and silver are no longer mined extensively in Colorado,
-although any summer Sunday will see weekend operators panning
-near mountain streams or trundling rock from one-man mines.
-The recent rise in the price of silver has encouraged many miners
-to reopen old shafts. The most active mines in the state today
-are those producing molybdenum, lead, zinc, and vanadium.
-(Vanadium, although a metal, usually occurs in Colorado with
-<span class="pb" id="Page_78">78</span>
-radioactive minerals, and so is discussed with them rather than
-with the metals.)</p>
-<div class="img" id="fig53">
-<img src="images/p38.jpg" alt="" width="664" height="786" />
-<p class="caption">The Colorado mineral belt extends from Boulder County on the northeast
-to San Juan County on the southwest. Almost all of the prominent
-mining districts in Colorado lie along this belt. Cripple Creek
-and Silver Cliff, however, lie far to the east of the general trend.</p>
-</div>
-<dl class="undent caption"><dd>Telluride</dd>
-<dd>Denver</dd>
-<dd>Colorado Springs</dd>
-<dd>Alamosa</dd>
-<dt>BOULDER</dt>
-<dd>Ward</dd>
-<dd>Gold Hill</dd>
-<dd>Boulder</dd>
-<dd>Nederland</dd>
-<dt>GILPIN</dt>
-<dd>Central City</dd>
-<dd>Black Hawk</dd>
-<dt>JEFFERSON</dt>
-<dd>Golden</dd>
-<dt>CLEAR CREEK</dt>
-<dd>Empire</dd>
-<dd>Georgetown</dd>
-<dd>Silver Plume</dd>
-<dd>Idaho Springs</dd>
-<dt>SUMMIT</dt>
-<dd>Breckenridge</dd>
-<dt>EAGLE</dt>
-<dt>PITKIN</dt>
-<dd>Aspen</dd>
-<dt>GUNNISON</dt>
-<dd>Tincup</dd>
-<dt>CHAFFEE</dt>
-<dt>PARK</dt>
-<dd>Climax</dd>
-<dd>Alma</dd>
-<dd>Como</dd>
-<dd>Fairplay</dd>
-<dt>TELLER</dt>
-<dd>Cripple Creek</dd>
-<dt>FREMONT</dt>
-<dt>OURAY</dt>
-<dd>Ouray</dd>
-<dd>Camp Bird</dd>
-<dd>Ironton</dd>
-<dt>SAN JUAN</dt>
-<dd>Silverton</dd>
-<dt>HINSDALE</dt>
-<dd>Lake City</dd>
-<dt>LA PLATA</dt>
-<dd>Durango</dd>
-<dt>MINERAL</dt>
-<dd>Creede</dd>
-<dt>CUSTER</dt>
-<dd>Silver Cliff</dd></dl>
-<p>All told, some 430 metal mining districts have been established
-as legal entities in the state of Colorado. Each of these districts
-had the right to draw up its own regulations concerning prospecting,
-claims, and mining rights, within a framework established by
-the Federal government. Only a few of the districts ever became
-really significant producers. The geology and history of several
-of the leading areas are presented in the pages that follow.</p>
-<div class="pb" id="Page_79">79</div>
-<h3 id="c35">Boulder County</h3>
-<p>Gold Run, near Gold Hill, was the scene of one of the earliest
-strikes in Colorado. Gold was found here in December 1858, and
-was sluiced from stream sands and mined from <a class="gloss" href="#g_Vein">veins</a> early in 1859.
-Active <a class="gloss" href="#g_Placer">placer</a> mining lasted only about a year, however, and <a class="gloss" href="#g_Lode">lode</a>
-mining dropped off rapidly as near-surface oxidized ores were
-worked out. When a smelter was erected at Black Hawk in 1868,
-and sulfide ores could be treated, there was a revival of activity.
-In 1869 the Caribou and Poorman mines near Nederland were
-discovered; they quickly became the most active mines in the
-county. The Ward district opened soon after.</p>
-<p>In 1872, a gold-silver telluride called <a class="gloss" href="#g_Petzite">petzite</a> was found in
-<a class="gloss" href="#g_Vein">veins</a> at Gold Hill. Renewed prospecting in this area resulted in
-location of mines near Sunshine, Salina, and Magnolia. During
-the years that followed, new mines appeared almost as fast as old
-ones were depleted. In 1892, the peak year, more than $1,000,000
-in gold and silver was produced; total production has been about
-$25,000,000.</p>
-<p>In 1900, a black mineral common in the Nederland area was
-recognized as ferberite, an ore of tungsten, and a new rush to the
-area started. During the next eighteen years Boulder County was
-the main tungsten producer in the United States; about 24,000
-tons of tungsten trioxide, worth $23,000,000, were produced
-here. The ore was found in nearly vertical <a class="gloss" href="#g_Vein">veins</a> six inches to
-three feet thick, in a lenticular area about nine miles long extending
-from Nederland northeast to Arkansas Mountain, four miles
-west of Boulder.</p>
-<p>Boulder County is characterized by an abundance of small
-mines. Old shafts, pits, and mine buildings can be found throughout
-the central part of the county. Little mining is done here
-today; many of the towns that once peppered these hills have
-fallen into decay or disappeared entirely.</p>
-<div class="pb" id="Page_80">80</div>
-<h3 id="c36">Central City and Idaho Springs</h3>
-<p>The Central City-Idaho Springs area was the principal metal
-mining region in the state until the late 1880s. In 1858, rich
-<a class="gloss" href="#g_Placer">placer</a> deposits were discovered in gravels and river terraces along
-both forks of Clear Creek. Exploration upstream led to discoveries
-of rich oxidized quartz <a class="gloss" href="#g_Vein">veins</a> at Central City, Black Hawk, and
-Idaho Springs. These veins, which generally trend northeast-southwest,
-extend through the mountains in a zone about six
-miles long and three miles wide between the two forks of Clear
-Creek.</p>
-<p>The ores filled a multitude of cracks and fissures in the
-Precambrian <a class="gloss" href="#g_Bedrock">bedrock</a>. The <a class="gloss" href="#g_Vein">veins</a> are usually less than five feet
-thick, and are almost vertical and often clustered in zones up to
-thirty feet wide. The position of one of the vein systems may be
-seen clearly between Black Hawk and Central City&mdash;the ore-bearing
-rock has been mined out, but a series of collapsed tunnels
-marks the line where the veins crossed the valley. A monument
-here commemorates the discovery of Gregory Gulch, one of the
-richest localities in the state.</p>
-<p>Several rich <a class="gloss" href="#g_Vein">veins</a> were mined in both directions&mdash;southwest
-from Central City and northeast from Idaho Springs&mdash;until the
-mines met. The Argo tunnel, marked by dilapidated buildings and
-extensive dumps on the north side of Idaho Springs, connected
-the two districts; it was completed in 1904.</p>
-<p>The &ldquo;Patch,&rdquo; a deep crater-like hole on Quartz Hill, about
-one mile southwest of Central City, is an intriguing feature in this
-area. It was produced by glory-holing, a mining technique in which
-a deep tunnel is deliberately caved by blasting, so that ores above
-the tunnel can be removed. This glory hole was dynamited below
-an irregular mass of highly broken rock where many ore-rich <a class="gloss" href="#g_Vein">veins</a>
-converged. After the caving, ores were taken out through the
-remaining part of the tunnel.</p>
-<p>The principal ore minerals of Central City and Idaho Springs
-are <a class="gloss" href="#g_NativeGold">native gold</a>, <a class="gloss" href="#g_Pyrite">pyrite</a>, <a class="gloss" href="#g_Sphalerite">sphalerite</a>, <a class="gloss" href="#g_Galena">galena</a>, <a class="gloss" href="#g_Chalcopyrite">chalcopyrite</a>, and
-<a class="gloss" href="#g_Tennantite">tennantite</a>. Prospecting for uranium was carried out during the
-1950s but no uranium was ever mined here.</p>
-<p>The area has produced almost $200,000,000 worth of gold,
-silver, lead, zinc, and copper. A few mines still operate seasonally
-or on a small scale, but tourists, many of them riding Jeeps across
-the mountainous terrain to visit mines and ghost towns, are often
-more visibly active than the mines.</p>
-<div class="pb" id="Page_81">81</div>
-<h3 id="c37">Georgetown, Empire, and Silver Plume</h3>
-<p>A few miles southwest of Idaho Springs, another mining area
-had a similar, though less productive, history. In 1859, <a class="gloss" href="#g_Placer">placer</a> and
-<a class="gloss" href="#g_Lode">lode</a> gold were discovered near what is now Georgetown. Placer
-mining dominated here between 1859 and 1863. Gravel and
-crushed rock from decomposed quartz and sulfide <a class="gloss" href="#g_Vein">veins</a> were
-washed through sluiceboxes in the same way as placer gravel,
-gold being caught in riffles or gunny sacking on the bottoms of
-the troughs. The veins were found to be decomposed to depths
-of about 40 feet; below this the gold occurred closely associated
-with sulfides such as <a class="gloss" href="#g_Pyrite">pyrite</a>, <a class="gloss" href="#g_Sphalerite">sphalerite</a>, <a class="gloss" href="#g_Galena">galena</a>, and <a class="gloss" href="#g_Chalcopyrite">chalcopyrite</a>,
-from which it could not easily be separated. However, smelters
-were developed in 1866 for treatment of these sulfides, and gold,
-silver, lead, and copper were recovered. Gradually, as the gold
-was worked out, silver and lead became the important products
-of the mines.</p>
-<div class="img" id="fig54">
-<img src="images/p39.jpg" alt="" width="658" height="800" />
-<p class="caption">Sluicebox mining was a common sight near the early gold camps,
-where primary recovery was from <a class="gloss" href="#g_Placer">placer</a> deposits or decomposed
-quartz and sulfide <a class="gloss" href="#g_Vein">veins</a>. (State Historical Society of Colorado photo)</p>
-</div>
-<div class="pb" id="Page_82">82</div>
-<h3 id="c38">Leadville</h3>
-<p><a class="gloss" href="#g_Placer">Placer</a> gold was discovered in 1859 in California Gulch, about
-seven miles north of the present town of Leadville. The rush that
-followed was short but sweet; the camp was called Oro&mdash;gold!
-About $5,000,000 was produced from the placer mines within
-two years, though by 1861 the area was all but deserted, for the
-easily won placer gold was gone.</p>
-<div class="img" id="fig55">
-<img src="images/p40.jpg" alt="" width="800" height="648" />
-<p class="caption">Early-day Leadville sprawled among its mine dumps at an elevation
-of 10,200 feet. The Sawatch Range, in the background, contained
-many smaller mining communities, now deserted. Mt. Massive, the
-state&rsquo;s second highest peak, forms the crest of the continental divide
-here. (State Historical Society of Colorado photo)</p>
-</div>
-<p>In 1875 a smelter was erected a few miles downstream from
-Oro to process cerussite&mdash;silver-rich lead carbonate&mdash;that
-occurred in the <a class="gloss" href="#g_Placer">placer</a> sands. For years this mineral had been
-considered a nuisance because, being much heavier than sand, it
-tended to separate out with the gold. The new town of Leadville
-sprang up near the smelter and shortly afterward more <a class="gloss" href="#g_Lode">lode</a> deposits
-were discovered south of the placer workings. From $63,000 in
-<span class="pb" id="Page_83">83</span>
-1875, production climbed to $2,500,000 in 1878 and more than
-$15,000,000 in the peak year of 1882.</p>
-<p>Geologically, the ores of this district occur as Tertiary replacements
-and <a class="gloss" href="#g_Vein">veins</a> in Ordovician, Devonian, and Mississippian
-limestones. The &ldquo;Blue&rdquo; or Leadville Limestone, of Mississippian
-age, contains the richest ore. Ore deposits were formed after the
-limestones had been faulted and cracked extensively by mountain-building
-movements; the ores themselves probably crystallized
-from molten or gaseous materials involved in related igneous intrusions. River gravels and glacial debris mask the true nature
-of the <a class="gloss" href="#g_Lode">lode</a> deposits, but studies in the mines show that the <a class="gloss" href="#g_Fault">fault</a>
-systems along which ores are deposited trend north or north-northeast.</p>
-<p>The Leadville district is now experiencing its third mining
-boom as a newly recognized lead-zinc orebody is being developed.
-Production is expected to reach 700 tons of ore per day by 1971.
-Total production of gold, silver, lead, zinc, and copper in the
-district has reached $500,000,000.</p>
-<h3 id="c39">Breckenridge</h3>
-<p>Breckenridge was also discovered in 1859, with <a class="gloss" href="#g_Placer">placer</a> gold
-the first attraction. The placers gave out in 1862 after about
-$3,000,000 in gold had been recovered. Earliest attempts to mine
-the rich silver and lead <a class="gloss" href="#g_Vein">veins</a> of the district were in 1869.</p>
-<p>As at Leadville, the <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> of the area were
-intruded by granitic masses in Tertiary time, but here the sedimentary rocks are mostly Pennsylvanian sandstones and shales.
-These rocks were badly faulted and broken during the intrusion,
-and the ores were deposited as the granitic material cooled. The
-<a class="gloss" href="#g_Lode">lode</a> deposits occur mostly in small <a class="gloss" href="#g_Vein">veins</a> well hidden by surface
-sands and gravels. Some of the veins yielded exceptionally beautiful
-crystallized wire and flake gold, specimens of which are on display
-at the Colorado School of Mines library in Golden and in the
-Denver Museum of Natural History.</p>
-<p>Dredging for alluvial gold was attempted in 1898 in the
-Breckenridge district, but this method of extracting gold was not
-successful until 1905. A number of dredges operated between
-1910 and 1925. These floating behemoths shovel up gold-bearing
-gravels from the bottom and one side of the pond on which they
-<span class="pb" id="Page_84">84</span>
-float, sort out the gold in giant sluiceboxes, and spew out the
-leftover gravels in great arc-shaped heaps that can be seen near
-Breckenridge and Fairplay and in a number of other valleys in
-Colorado. They depend for their operation on a plentiful supply
-of water and a shallow water table, but they can sift through
-quantities of gravel at relatively low cost. All told, about
-$7,000,000 in gold has been dredged from this district.</p>
-<h3 id="c40">Fairplay</h3>
-<div class="img" id="fig56">
-<img src="images/p41.jpg" alt="" width="800" height="569" />
-<p class="caption">This gold dredge, still floating in its pond just south of Fairplay,
-operated from 1941 to 1952. With chains of buckets like those in
-the foreground, it dug gravel 70 feet below water level, carving a
-35-foot bank above water level; in effect it mined to a depth of 105
-feet. This dredge extracted nearly 115,000 ounces of gold from about
-33 million cubic yards of gravel (John Chronic photo)</p>
-</div>
-<p>Another gold field discovered in 1859 was in the northwest
-corner of South Park, along the headwaters of the South Platte
-River. Several mining camps were established here. After early
-production of rich <a class="gloss" href="#g_Placer">placer</a> deposits, claims were consolidated and
-large flumes constructed so that gold could be recovered by
-<span class="pb" id="Page_85">85</span>
-hydraulic mining. In this type of mining, streams of water from
-high-pressure hoses are directed at gravel surfaces. The gravels
-are washed into long sluiceboxes, where gold is caught in riffles.
-Hydraulic mining continued upstream from Fairplay until about
-1900.</p>
-<p>In 1922 a dredge was constructed near Fairplay to process
-gravel along the South Platte and in the valley floor. An even
-larger dredge, constructed in 1941, operated until 1952, when
-rising labor costs overrode the narrow margin on which it operated.
-At the time operations ceased, the dredge was recovering about
-six cents in gold for each cubic yard of gravel processed.</p>
-<p><a class="gloss" href="#g_Placer">Placer</a> gold has always been the principal mineral product of
-the Fairplay area, but <a class="gloss" href="#g_NativeGold">native gold</a> also occurs in the surrounding
-mountains in quartz <a class="gloss" href="#g_Vein">veins</a>, and many small mines were developed
-to extract it. Sulfide ores were also mined; they contained silver,
-lead, and zinc as well as gold. In the Mosquito Pass and Horseshoe
-Amphitheater areas, there is renewed activity now because
-of the recent rise in the price of silver.</p>
-<h3 id="c41">Silverton</h3>
-<p>Gold was discovered in the San Juan Mountains of southwest
-Colorado in 1870. The earliest mine, near what is now Silverton,
-was located by a group of prospectors sent out by Governor Pile
-of New Mexico Territory. Since the site was on Ute Indian land,
-real mining did not begin until a treaty allowing it was ratified in
-1874.</p>
-<p>Production in the Silverton district has been from <a class="gloss" href="#g_Vein">veins</a> in
-Tertiary volcanic rocks within an elliptical area known as the
-Silverton cauldron. Here the volcanic rocks, part of the several
-thousand feet of <a class="gloss" href="#g_Lava">lava</a> flows and ash falls of the San Juan volcanic
-field, were cracked and faulted by a second period of igneous activity. Ores formed in the cracks and fissures.</p>
-<p>In the 1870s the Silverton district was very remote, and difficulties
-with transportation retarded activity there. In 1882,
-however, a narrow-gauge railroad was built connecting Silverton
-with Durango, and the problem of transporting ore out of the
-isolated mountain valley was simplified. The railway still exists;
-a train makes daily passenger runs during the summer&mdash;the only
-remaining operating narrow-gauge line in the United States. The
-<span class="pb" id="Page_86">86</span>
-track follows the Animas River canyon, whose cliffs and crags
-are dotted with long-abandoned mines, prospect holes, and mine
-buildings, monuments to the tenacity and determination of the
-men who mined here.</p>
-<p>Production in this district was more than $22,000,000 in gold
-and $20,000,000 in silver between 1874 and 1923. New activity
-is evident here, as in other silver-rich areas of Colorado, because
-of recent demand for silver, lead, and zinc.</p>
-<div class="img" id="fig57">
-<img src="images/p42.jpg" alt="" width="800" height="611" />
-<p class="caption">Silverton lies in a remote mountain valley in the San Juan Mountains.
-Silver, gold, lead, and zinc have been mined here since 1874. Storm
-Peak, composed of Tertiary volcanic rocks, forms the backdrop; the
-narrow-gauge railroad track is visible in the foreground. (Jack
-Rathbone photo)</p>
-</div>
-<div class="pb" id="Page_87">87</div>
-<h3 id="c42">Ouray</h3>
-<p>Ouray was settled in 1875, when gold and silver deposits were
-found near Mount Sneffels. Since 1877, mines in Ouray County
-have produced over $35,000,000 in gold and $32,000,000 in
-silver. The district is still quite active: in 1965, mines in this area
-produced more than $9,000,000 in gold, silver, copper, lead, and
-zinc, about a third of total Colorado production of these metals
-for that year.</p>
-<div class="img" id="fig58">
-<img src="images/p42a.jpg" alt="" width="646" height="794" />
-<p class="caption">A few miles south of Ouray, along Uncompahgre Gorge, an old mine
-clings to the slope below the Million Dollar Highway (U. S. 550).
-Abrams Mountain rises in the background. The Precambrian Uncompahgre
-Quartzite outcrops up to about the road level; Miocene
-Sunshine Peak <a class="gloss" href="#g_Rhyolite">Rhyolite</a> caps the peak. (Jack Rathbone photo)</p>
-</div>
-<p>A mile north of Ouray a prominent intrusive <a class="gloss" href="#g_Stock">stock</a> marks the
-center of mining activity closest to Ouray. The richest deposits
-of the Ouray area, however, lie about five miles southwest, near
-<span class="pb" id="Page_88">88</span>
-Mount Sneffels and Red Mountain Creek. There, several large
-mines, including the famous Camp Bird mine, have operated for
-many years, extracting ore from hundreds of <a class="gloss" href="#g_Vein">veins</a> that underly
-the surface. Some of these veins are two to four miles long. They
-are in Tertiary volcanic rocks of the San Juan Formation. Quartz
-and calcite are the common <a class="gloss" href="#g_Gangue">gangue</a> (non-economic) minerals,
-and <a class="gloss" href="#g_Pyrite">pyrite</a>, <a class="gloss" href="#g_Sphalerite">sphalerite</a>, <a class="gloss" href="#g_Galena">galena</a>, and <a class="gloss" href="#g_Chalcopyrite">chalcopyrite</a> are the most abundant
-ores. Most of the silver is in the galena; gold occurs in
-streaks and nodules associated with quartz.</p>
-<p>About ten miles south of Ouray, along the &ldquo;Million Dollar
-Highway&rdquo; (U. S. 550), the Red Mountain district lies on the
-northwest edge of the Silverton volcanic cauldron. It contains a
-number of small pipelike bodies very rich in silver-copper and
-silver-lead ores. Following the mid-Tertiary volcanism and ore
-intrusion, surface rocks in this area were intensely oxidized:
-resulting iron oxides now form the gaudy reds and yellows of
-Red Mountain and the slopes near Ironton. This alteration, as
-well as the fact that much of the area is covered with fallen rock,
-stream gravels, or glacial deposits, compounds difficulties of
-locating the small though high-grade ore deposits.</p>
-<p>The Idarado Mine, on the east side of U. S. highway 550
-near Red Mountain, used to produce ores from nearby volcanic
-pipes; now it produces from <a class="gloss" href="#g_Vein">veins</a> some distance to the northwest.
-The area is honeycombed with tunnels and shafts.</p>
-<h3 id="c43">Aspen</h3>
-<p>Silver was found at Castle Creek and on Aspen Mountain in
-1879. A group of prospectors from Leadville, apparently after
-examining maps of the Geological and Geographical Atlas of
-Colorado published in 1877, explored along the line of Paleozoic
-limestones encircling the Sawatch Range. As they had hoped, they
-found ores similar to those at Leadville in rocks of the same age.</p>
-<p>Mining began at Aspen in 1880. Here, as at Leadville, intrusion
-of <a class="gloss" href="#g_Granite">granite</a> <a class="gloss" href="#g_Porphyry">porphyry</a> into or near the Leadville Limestone had
-broken and deformed the layers, and ores were deposited in
-fissures and as replacements during cooling of the intrusions.
-The intricacy of faulting which controls the ore pockets in the
-limestone is well shown on the map of <a href="#fig15">Aspen Mountain</a> in
-Chapter II.</p>
-<p><a class="gloss" href="#g_Glaciation">Glaciation</a> occurred in this area, and glacial deposits cover
-most of the ore bodies and outcrops so that little <a class="gloss" href="#g_Bedrock">bedrock</a> is
-<span class="pb" id="Page_89">89</span>
-exposed. Mapping was accomplished by extrapolating to the
-surface the bedrock patterns shown in mine pits, shafts, and
-tunnels.</p>
-<p>Aspen produced some of the richest silver ores in the world,
-and thrived as a boom town for most of two decades. In 1888
-the value of ores produced reached over $7,000,000; the next
-year it topped $10,000,000. After the silver crash of 1893 production
-declined rapidly; the last mines were closed in the 1920s.
-Total production of silver, lead, zinc, and copper reached about
-$100,000,000. There was virtually no gold in the ores at Aspen.</p>
-<h3 id="c44">Creede</h3>
-<div class="img" id="fig59">
-<img src="images/p43.jpg" alt="" width="568" height="800" />
-<p class="caption">Creede and its mines are located in an area of Tertiary <a class="gloss" href="#g_Rhyolite">rhyolite</a> and
-dacite, light-colored volcanic rocks.</p>
-</div>
-<dl class="undent caption"><dt>Happy Thought Mine</dt>
-<dt>Amethyst Mine</dt>
-<dt>West Willow Creek</dt>
-<dt>AMETHYST <a class="gloss" href="#g_Fault">FAULT</a></dt>
-<dt>Last Chance Mine</dt>
-<dt>Del Monte Mine</dt>
-<dt>Commodore Mine</dt>
-<dt>Jackpot Mine</dt>
-<dt>Coppervein Mine</dt>
-<dt>Bachelor Mine</dt>
-<dt>BULLDOG MOUNTAIN FAULT</dt>
-<dt>Kansas City Star Mine</dt>
-<dt>Commodore Tunnel</dt>
-<dt>Mustang Tunnel</dt>
-<dt>Nelson Tunnel</dt>
-<dt>Exchequer Mine</dt>
-<dt>SOLOMON FAULT</dt>
-<dt>CAMPBELL MOUNTAIN</dt>
-<dt>Holy Moses #2</dt>
-<dt>Holy Moses Mine</dt>
-<dt>Ridge Mine</dt>
-<dt>Solomon Mine</dt>
-<dt>Monte Carlo Mine</dt>
-<dt>Mollie S. Mine</dt>
-<dt>East Willow Creek</dt>
-<dt>Ramey Tunnel</dt>
-<dt>Dora Belle Mine</dt>
-<dt>Mammoth Tunnel</dt>
-<dt>Homestake Mine</dt>
-<dt>Mammoth Mine</dt>
-<dt>MAMMOTH MOUNTAIN</dt>
-<dt>Nancy Hanks Mine</dt>
-<dt>Pipe Dream Mine</dt>
-<dt>THE NARROWS</dt>
-<dt>Windy Gulch</dt>
-<dt>CREEDE</dt>
-<dt>Willow Creek</dt></dl>
-<p>The Creede district ranks as one of the most productive silver
-areas in the United States. It came into being largely as a result
-of a discovery by N.H. Creede in 1889. When exploring in this
-<span class="pb" id="Page_90">90</span>
-area, he was reported to have exclaimed &ldquo;Holy Moses!&rdquo; on examining
-a rich piece of ore, thus giving the name to the mine which
-initiated the rapid development of the district. By the end of 1892
-the Holy Moses and nearby mines had produced ore valued at
-more than $4,000,000. The area was so rich that it managed to
-survive 1893&rsquo;s great decline in the price of silver; by 1920 almost
-$42,000,000 in gold, silver, lead, and zinc had been mined there.</p>
-<p>The ores, silver-bearing <a class="gloss" href="#g_Galena">galena</a>, <a class="gloss" href="#g_Sphalerite">sphalerite</a>, <a class="gloss" href="#g_NativeGold">native gold</a>, <a class="gloss" href="#g_Pyrite">pyrite</a>,
-and <a class="gloss" href="#g_Chalcopyrite">chalcopyrite</a>, are in quartz or amethyst <a class="gloss" href="#g_Vein">veins</a> in faulted and
-shattered Tertiary volcanic rocks. Nearly all the ore deposits lie
-along a complex system of vertical <a class="gloss" href="#g_Fault">faults</a>, the Amethyst fault
-zone, which runs more or less northwest-southeast through this
-region. Both the faulting and the enrichment of the fault fissures
-are believed to have taken place in mid-Tertiary time, shortly
-after deposition of the volcanic host rocks.</p>
-<h3 id="c45">Cripple Creek</h3>
-<div class="img" id="fig60">
-<img src="images/p44.jpg" alt="" width="794" height="501" />
-<p class="caption">Cripple Creek, on the flanks of the Pikes Peak <a class="gloss" href="#g_Massif">massif</a>, has produced
-more than $400,000,000 worth of gold. The Sangre de Cristo Mountains
-are visible in the distance beyond the Arkansas River valley.
-(Jack Rathbone photo)</p>
-</div>
-<p>In 1890, two sheepherders stumbled on some richly mineralized
-rocks near Cripple Creek. A boom developed immediately,
-for the rocks contained both gold and silver. Since then, the area
-<span class="pb" id="Page_91">91</span>
-has produced more than 2,000,000 ounces of silver and nearly
-19,000,000 ounces of gold.</p>
-<p>Cripple Creek has produced almost half of all the state&rsquo;s gold
-and silver. The ores are located in or at the edge of a large mass
-of middle Tertiary volcanic rocks which form an elliptical basin
-or <i><a class="gloss" href="#g_Caldera">caldera</a></i> several miles across. The caldera, surrounded by
-Precambrian <a class="gloss" href="#g_Gneiss">gneiss</a> and <a class="gloss" href="#g_Granite">granite</a> of the Pikes Peak <a class="gloss" href="#g_Massif">massif</a>, was
-probably formed by collapse of a volcanic center that had erupted
-through the older rock. The collapse shattered the rocks around
-the basin margin, and subsequent volcanic activity introduced
-mineral-rich solutions into the many <a class="gloss" href="#g_Fault">faults</a> and fissures produced
-by the collapse. Tellurides of gold, silver, and copper, as well as
-<a class="gloss" href="#g_Pyrite">pyrite</a>, <a class="gloss" href="#g_Sphalerite">sphalerite</a>, <a class="gloss" href="#g_Galena">galena</a>, <a class="gloss" href="#g_Tetrahedrite">tetrahedrite</a>, and other minerals, are
-characteristic.</p>
-<h3 id="c46">Climax</h3>
-<div class="img" id="fig61">
-<img src="images/p44a.jpg" alt="" width="800" height="659" />
-<p class="caption">At Climax, the ore occurs scattered through the intrusive Climax
-<a class="gloss" href="#g_Granite">Granite</a> <a class="gloss" href="#g_Porphyry">Porphyry</a> and the intruded Idaho Springs Formation. Visitors
-can tour the surface workings during the summer months.</p>
-</div>
-<dl class="undent caption"><dd>Tertiary <a class="gloss" href="#g_Dike">dikes</a></dd>
-<dd>Shell of Climax <a class="gloss" href="#g_Stock">stock</a></dd>
-<dd>Core of Climax stock</dd>
-<dd>Ore zone</dd>
-<dd>Precambrian <a class="gloss" href="#g_Granite">granite</a></dd>
-<dd><a class="gloss" href="#g_Fault">Fault</a></dd>
-<dd>Dykes</dd></dl>
-<p>Molybdenum now ranks as the number one metal mined in
-Colorado. Over $105,000,000 of &ldquo;moly&rdquo; was mined here during
-1969, almost all of it from the Climax Mine, the world&rsquo;s largest
-single source of this metal. The Climax deposit is located high
-on the west slope of Ten Mile Range in central Colorado, about
-<span class="pb" id="Page_92">92</span>
-100 miles southwest of Denver. It is in the central part of the
-Colorado mineral belt, near the Mosquito <a class="gloss" href="#g_Fault">Fault</a>, a prominent
-structural feature which extends about sixty miles along the north-south
-trend of the mountains. Rocks on both sides of this fault
-are intruded by Tertiary <a class="gloss" href="#g_Granite">granite</a> <a class="gloss" href="#g_Dike">dikes</a>, sills, and stocks. The
-Climax Mine is in a <a class="gloss" href="#g_Stock">stock</a> just east of the fault, near the axis of
-a broad <a class="gloss" href="#g_Anticline">anticline</a> in Precambrian metamorphic rocks.</p>
-<p>Ore minerals at Climax are <a class="gloss" href="#g_Molybdenite">molybdenite</a>, <a class="gloss" href="#g_Huebnerite">huebnerite</a>, and
-<a class="gloss" href="#g_Cassiterite">cassiterite</a>; <a class="gloss" href="#g_Pyrite">pyrite</a> is recovered also for the manufacture of sulfuric
-acid. The ore is very low in metal content, containing only one-third
-of a percent of molybdenum, 0.005% tungsten trioxide, and
-0.0001% tin. The great size of the ore body and efficient recovery
-by modern methods make Climax a profitable mine, however.
-Production has risen each year since the mine began operation.</p>
-<p>Urad Mine near Berthoud Pass is a newly developed near-surface
-molybdenum mine similar to Climax. Nearby at the
-Henderson Mine the ore body is more than half a mile below
-the surface of the ground.</p>
-<div class="pb" id="Page_93">93</div>
-<h3 id="c47">RADIUM, URANIUM, AND VANADIUM</h3>
-<p>Over a large area of the <a class="gloss" href="#g_Plateau">Plateau</a> Province in western Colorado,
-Mesozoic <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> are locally stained bright yellow,
-orange, or green. Such staining suggests mineralization, and radioactive
-compounds were recognized here before 1900. At that time,
-however, there was little or no market for them or for the vanadium
-frequently associated with them. When Marie Curie required
-radium for experiments with her newly discovered element, the
-raw materials were sent from western Colorado; by and large,
-though, production of radium from these ores was prohibitively
-expensive.</p>
-<p>In 1905, vanadium was found to be effective in toughening
-steel. The Vanadium Corporation of America was formed to mine
-the Colorado ore. This company mines a rich zone in the Jurassic
-Entrada Sandstone, where vanadinite occurs with carnotite and
-other uranium ores. In the early days of vanadium mining, the
-uranium ores were discarded with other <a class="gloss" href="#g_Gangue">gangue</a> materials; now,
-of course, uranium is produced from them.</p>
-<p>Since 1945, uranium production has been an important Colorado
-industry; in 1969 about $17,500,000 worth was produced.
-Uranium occurs in the state in two very different situations. In the
-<a class="gloss" href="#g_Plateau">Plateau</a> Province, where it was first discovered, it occurs in <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> as patches of pitchblende, carnotite, and a greenish
-yellow mineral called schroekingerite. It is most abundant in the
-Triassic Chinle Formation and the Jurassic Entrada and Morrison
-Formations, where it was probably deposited by downward movement
-of rainwater from overlying uranium-rich Tertiary volcanic
-rocks. Concentrations of uranium often occur in or near organic
-matter such as coal, <a class="gloss" href="#g_Fossil">fossil</a> bone, or petrified wood, so mines tend
-to be located along rock layers carrying abundant organic material.</p>
-<p>Another type of uranium ore is found in the Mountain
-Province. <a class="gloss" href="#g_Vein">Veins</a> in Precambrian rocks of the Front Range and
-several other ranges contain pitchblende which seems to have
-been deposited by hot groundwater rising through broken and
-fissured Precambrian rocks. Often exceedingly rich, such ore is
-mined in the manner of most of Colorado&rsquo;s metals. The Schwartzwalder
-Mine, a few miles northwest of Golden, has produced more
-ore of this type than any other mine in Colorado.</p>
-<div class="pb" id="Page_94">94</div>
-<h3 id="c48">OIL, NATURAL GAS, AND OIL SHALE</h3>
-<p>Petroleum and natural gas have been found in large quantities
-in the Prairie and <a class="gloss" href="#g_Plateau">Plateau</a> Provinces in Colorado, as well as in
-smaller quantities in North Park in the Mountain Province. They
-generally occur in porous sandstone and limestone layers, where
-they have been trapped by overlying finer-grained, less permeable
-layers in or near <a class="gloss" href="#g_Fold">folds</a> and <a class="gloss" href="#g_Fault">faults</a>.</p>
-<p>Several oil and gas seeps were found along the mountain front
-shortly after the arrival of the earliest settlers. Near Canon City,
-on Oil Creek, a plaque commemorates the first production:</p>
-<blockquote>
-<p>Oil Creek&mdash;site of the first oil well in the west&mdash;second
-place in the United States to produce petroleum from wells.
-In 1862 ... A. M. Cassedy drilled an oil well 50 feet deep.
-By February, 1863, production was one barrel a day.
-Later, several thousand gallons of petroleum were produced
-by primitive methods, and kerosene and lubricating
-oil were shipped by ox team as far as Denver and Santa Fe.</p>
-</blockquote>
-<p>About twenty miles to the southeast, near Florence, the
-Cretaceous Pierre shales were drilled in 1876. Oil was found in a
-system of intersecting fractures and <a class="gloss" href="#g_Joint">joints</a>. Some of the early wells
-in the Florence field are still producing, making this Colorado&rsquo;s
-oldest and longest producing field. It has yielded more than
-10,000,000 barrels of oil.</p>
-<p>Small quantities of oil have been produced near Boulder since
-about 1900, also from Pierre sandstones and shales. In this area,
-wells were located by &ldquo;<a class="gloss" href="#g_Dowsing">dowsing</a>&rdquo; or &ldquo;witching,&rdquo; as was fashionable
-at the time. Several old rigs can be seen near Boulder Reservoir.
-As at Florence, oil has been trapped in fractures of otherwise
-dense and impervious shale. Some gas is produced and is used
-by local farms.</p>
-<p>More recently, oil was found far beneath the surface in the
-northern part of the Prairie Province. Here, in the Denver Basin,
-oil is produced from several levels in the Dakota Sandstone.
-The oil has accumulated in lenses of beach sand deposited along
-the shoreline of the Cretaceous sea. The general trend of the
-shoreline, and of the oil fields, is northeast-southwest. The shore
-appears to have been similar to Georgia&rsquo;s present coastline: a
-swampy tidal zone separated from open sea by lagoons, sandy
-bars, and clean sand beaches.</p>
-<div class="pb" id="Page_95">95</div>
-<p>Individual oil pools in the Denver Basin are small, but there
-are many of them; they lie nearly a mile below the surface, under
-much of Morgan and Logan Counties and adjacent parts of
-Nebraska. Exploratory and development drilling keeps total oil
-production at about 50,000 barrels a day. Oil and gas produced
-here is piped to Denver and other Colorado cities.</p>
-<p>In southeastern Colorado, oil and gas occur in late Paleozoic
-limestones and sandstones similar to those which outcrop at the
-edge of the Wet Mountains. Prospecting by geophysical methods
-and by drilling has revealed several small, rich accumulations, one
-of which is thought to contain about 30,000,000 barrels of oil.</p>
-<p>The Rangely field, in northwestern Colorado, is the most
-productive field in the state. Located in the northeastern part of
-the Uinta Basin, it is an outstanding example of an anticlinal field,
-where oil is trapped in a large, gentle <a class="gloss" href="#g_Dome">dome</a>. The shape of the
-dome shows up well on the surface; rock layers can be seen
-dipping outward in all directions from the town of Rangely. Oil
-was found by drilling on the crest of the dome. At first, oil was
-produced from fractures in the Cretaceous Mancos Shale at less
-than 1,000 feet depth. Later, deeper drilling showed that oil had
-also accumulated in the Permian Weber Sandstone, at 5,000 to
-7,000 feet. At present this field is producing about 28,000 barrels
-of oil a day, but the figure is dropping each year as the field is
-depleted.</p>
-<p>Oil and gas are produced in southwestern Colorado from the
-eastern edge of the Paradox Basin and the northern edge of the San
-Juan Basin. In the Paradox Basin, oil comes from Pennsylvanian
-limestone mounds or <a class="gloss" href="#g_Reef">reefs</a>. Production in the Colorado part of the
-basin has been at most a few thousand barrels per day; more is
-produced in adjacent Utah. In the San Juan Basin, gas and oil are
-trapped in thin porous layers of Cretaceous and Pennsylvanian
-sandstone, between impervious layers of shale. Most of the production
-is in New Mexico, although some oil comes from the Colorado
-part of the basin.</p>
-<p>The greatest known potential oil resource in the world lies in
-the oil shales of western Colorado. The richest of these shales
-cover an area of 1,600 square miles north of the Colorado River,
-south of the White River, and just east of the Colorado-Utah line.
-The oil shales are part of the Tertiary Green River Formation,
-which extends over much of northwest Colorado, northeast Utah,
-and southern Wyoming. Oily material called <i><a class="gloss" href="#g_Kerogen">kerogen</a></i> is locked in
-these rocks, too solid to flow out of the fine pore spaces of the shale.
-To free it the shale must be mined, finely crushed, and heated
-until the kerogen converts to liquid oil. This is an expensive
-<span class="pb" id="Page_96">96</span>
-process, and as yet production of petroleum from the oil shale has
-not been possible at a cost which will compete with production
-of oil and gas from wells. The United States Bureau of Mines,
-as well as a number of oil companies, have sought for more than
-fifty years to discover a less expensive method for extracting oil
-from the shale. No doubt at some time in the future a competitive
-technique will be developed, or a growing shortage of other oil
-will bring world prices to a level with which present production
-techniques can compete.</p>
-<p>Oil and gas production in Colorado is decreasing at present,
-even though great efforts are being made to find new oil pools.
-Petroleum prospecting and wildcat drilling are carried out in as
-yet unproductive basins in the <a class="gloss" href="#g_Plateau">Plateau</a> Province, in intermontane
-basins such as the San Luis Valley, and on the Plains. Known
-reserves will continue to provide the state with significant income
-for many years to come, and if oil shale recovery becomes profitable.
-Colorado&rsquo;s hydrocarbons will become the most prominent
-of her commodities.</p>
-<h3 id="c49">COAL</h3>
-<p>Coal resources of Colorado amount to about 60 billion tons.
-Only one per cent of this has been mined. Thousands of tons are
-now being produced daily from large mines in central, southern,
-and northwestern parts of the state.</p>
-<p>Colorado&rsquo;s coal deposits were formed during late Cretaceous
-and early Tertiary time, when seas were receding from this region
-and the land was rising. They represent accumulations of leaves
-and other plant material in swamps and flood plains similar to
-those now found in the delta of the Mississippi River and in the
-swamps of southeastern United States. Almost all Colorado coal is
-bituminous or soft coal.</p>
-<p>Coal was recognized early in Colorado history by settlers along
-the mountain front, and was mined west and north of Denver in the
-1860s. Several large underground mines still operate in this district,
-supplying local power plants, but production does not compare
-with that of the Walsenburg-Trinidad area in southern Colorado
-or the Hayden area in northwest Colorado.</p>
-<p>The Walsenburg-Trinidad region, part of the Raton coal field,
-has produced coal since the building of the Santa Fe Railroad in
-the early 1870s. For many years coal from these mines moved
-the Santa Fe trains and many of the numerous smaller railroads
-<span class="pb" id="Page_97">97</span>
-that served Colorado&rsquo;s cities and mining camps. The location of
-the mines helped to determine the location of the Colorado Fuel
-and Iron Company smelter in Pueblo. Now, most southern Colorado
-coal is used to produce electric power. Many small mines,
-miles away from the power plant west of Trinidad, are deserted.</p>
-<p>A large coal-burning power plant has recently been built
-between Hayden and Steamboat Springs, just west of the Yampa
-River. Here, some of the extensive coal deposits can be seen in
-road cuts along U. S. highway 40. Until conversion to diesel fuel
-became almost universal in North American railroads, mines of
-this district produced coal for locomotives.</p>
-<p>In the heyday of the gold and silver mines, coal was also mined
-near Coalmont, in North Park, and Como, in South Park. Coal
-from these areas was used for fuel in nearby mining towns and
-ranches, and for the narrow-gauge railroads that penetrated the
-mountains here.</p>
-<p>At Anthracite, near Crested Butte, high-grade anthracite coal
-was mined for a time. Identical in origin with other Colorado coal,
-the anthracite of this region was hardened by heat and pressures
-from Tertiary igneous intrusions forcing their way into local
-<a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a> during post-Cretaceous mountain building.</p>
-<p>A multitude of other coal camps are scattered about Colorado:
-Cokedale, Delcarbon, Coaldale, Roncarbo, Carbondale, and
-Cardiff stand out because of their suggestive names. These early
-small camps are, like their metal-mine cousins, largely deserted
-today.</p>
-<h3 id="c50">CONSTRUCTION MATERIALS</h3>
-<h3 id="c51">Sand, Gravel, and Clay</h3>
-<p>Sand, gravel, and crushed rock rate high among geologic
-products in Colorado; more than $27,000,000 worth of these
-materials were produced in the state in 1969. Highway and
-construction activities have brought recent expansion in the number
-and size of quarries and gravel pits. Increasingly, Coloradoans
-are insisting that quarries and pits be excavated only where they
-will not mar the natural beauty of the landscape, and many old
-pits are now being filled in. Unfortunately, the scars left by some
-quarries&mdash;such as that on the Rampart Range near Colorado
-Springs&mdash;are difficult to erase.</p>
-<p>Clay of good quality occurs in Cretaceous deposits in many
-parts of Colorado, most frequently in the Dakota or Laramie
-<span class="pb" id="Page_98">98</span>
-Formations. In the area around Golden, the Coors Porcelain
-Company for many years mined clay for use in pottery and low
-temperature ceramic ware. Scars from this mining can be seen
-along the mountain front north and south of Golden, and deep
-clefts within the town, just west of Colorado School of Mines,
-testify to the amounts of clay that have been removed. Colorado
-clay is not pure enough to be used in high temperature ceramics,
-and the present use for it is in the manufacture of common tiles
-and bricks.</p>
-<p>A recent development in Colorado is the use of Cretaceous
-Pierre shales in manufacturing lightweight aggregate for building.
-The shale is mined between Golden and Boulder, near Colorado
-highway 93. In the nearby plant, it is pulverized and then heated
-in a large rotating cylinder until the surface of each particle fuses.
-Then the particles are quickly cooled. The resulting product is
-much like cinder, light in weight and yet strong. It can be mixed
-with cement for use in construction work requiring a great
-strength-to-weight ratio, or made into concrete blocks.</p>
-<div class="img" id="fig62">
-<img src="images/p45.jpg" alt="" width="800" height="574" />
-<p class="caption">Quarrying of Paleozoic limestones and dolomites along the east flank
-of the Rampart Range northwest of Colorado Springs has badly
-defaced a prominent mountain backdrop. Recent seeding efforts by
-quarry operators are returning the exhausted part of the quarry to
-its original lightly vegetated condition, and hopefully, as the quarry
-is depleted, the scar will disappear. (John Chronic photo)</p>
-</div>
-<div class="pb" id="Page_99">99</div>
-<h3 id="c52">Stone</h3>
-<p>In Colorado, as in most parts of the world, building stone for
-local use is quarried locally. Two of the state&rsquo;s stones, however&mdash;Yule
-Marble from the Crystal River Canyon, and Lyons Sandstone
-of the Front Range&mdash;have been more widely used.</p>
-<p>The Yule Marble, or Yule Colorado Marble, was produced by
-metamorphism of Leadville Limestone in an area intruded by the
-Treasure Mountain <a class="gloss" href="#g_Granite">Granite</a>, thirty-five miles south of Glenwood
-Springs. This exquisite marble, which has graced many famous
-monuments and buildings (among them the Lincoln Memorial
-and the Tomb of the Unknown Soldier), is known for its almost
-uniform snowy whiteness and regular, fine crystallization. Although
-its beauty, massive character, and uniformity made it a sought-after
-ornamental stone, quarrying was economically marginal
-because of the remoteness of the site. In spite of this, nearly
-$7,000,000 worth of the marble was produced before the quarry
-closed in 1940.</p>
-<div class="img" id="fig63">
-<img src="images/p45a.jpg" alt="" width="800" height="523" />
-<p class="caption">Pure white marble was quarried for many years at the Yule Colorado
-Marble Quarry, about three miles southeast of the village of Marble.
-(U. S. Geological Survey photo)</p>
-</div>
-<p>The Lyons area, north of Boulder, provides pink, hard, even-grained
-sandstone which splits readily into slabs or flagstones.
-These are used in the Denver-Boulder area for sidewalks and
-patios as well as for facing buildings. Quarries owned by the
-University of Colorado provide a constant supply of handsome
-facing material and flagstone for new university buildings, although
-in recent years the high cost of stone construction has limited its
-use on the campus.</p>
-<div class="pb" id="Page_100">100</div>
-<div class="img" id="fig64">
-<img src="images/p46.jpg" alt="" width="800" height="468" />
-<p class="caption">Lyons Sandstone is quarried near Lyons, Colorado. The salmon-colored
-sandstone splits along surfaces defined by slight differences in size
-and arrangement of the sand grains. (John Chronic photo)</p>
-</div>
-<div class="img" id="fig65">
-<img src="images/p46a.jpg" alt="" width="800" height="516" />
-<p class="caption">Most of the buildings of the University of Colorado are faced with
-Permian Lyons Sandstone, which is widely used for buildings and
-flagstones throughout the Boulder-Denver area. The University Museum,
-shown here, was established in 1902, and contains over a million
-scientific specimens, including many Colorado <a class="gloss" href="#g_Fossil">fossils</a> and minerals.
-Exhibits in the Hall of Earth portray Colorado&rsquo;s geologic history.
-(Tichnor Bros. photo)</p>
-</div>
-<div class="pb" id="Page_101">101</div>
-<p>The Lyons Sandstone was deposited as beach and bar sand
-along the edge of a sea which lay east of the Front Range in
-Permian time. After deposition, the sand was deeply buried and
-compacted. Now tilted up along the Front Range uplift, it comes
-to the surface along the east side of the range. Only between
-Fort Collins and Boulder does the stone have the desirable combination
-of hardness, thin-beddedness, and color which makes it
-desirable for ornamental use. The pink color of the Lyons Sandstone
-is derived from iron oxides, mostly <a class="gloss" href="#g_Hematite">hematite</a>, disseminated
-between the sand grains. Dendrites (often erroneously called
-<a class="gloss" href="#g_Fossil">fossil</a> ferns or plants) ornament some slabs; they were formed by
-crystallization of manganese dioxide from groundwater as it slowly
-percolated through the rock.</p>
-<h3 id="c53">Lime and Gypsum</h3>
-<p>Outcrops of the Cretaceous Greenhorn and Niobrara Limestones
-provide most of the cement materials in Colorado. A number
-of plants along the mountain front, including a completely automated
-and dust-free one near Lyons, provide the major population
-centers with millions of tons of cement each year.</p>
-<p>Colorado is richly endowed with gypsum, useful in cement and
-plaster manufacture and for ornamental stone and sculpture.
-Along the eastern front of the mountains, gypsum occurs in the
-Triassic Lykins Formation; in the Mountain Province, it is abundant
-in Pennsylvanian <a class="gloss" href="#g_SedimentaryRocks">sedimentary rocks</a>. Particularly high-quality
-Pennsylvanian gypsum is quarried at the town of Gypsum, west
-of Eagle.</p>
-<p>The Colorado portion of the Paradox Basin, in the <a class="gloss" href="#g_Plateau">Plateau</a>
-Province, contains immense deposits of Pennsylvanian gypsum.
-Here, rocks near the surface have been pushed up into sharp
-northwest-trending faulted <a class="gloss" href="#g_Anticline">anticlines</a> by upward movements of
-gypsum and salt from depths of several thousands of feet. The
-soluble salt and gypsum cores of these structures have been
-washed away more rapidly than the surrounding layers of sandstone
-and shale, leaving depressions such as Gypsum Valley,
-Paradox Valley, and Sinbad Valley, on the crests of the anticlines.
-Red and yellow Triassic sandstones and shales, especially the
-Chinle Formation and the Wingate Sandstone, <a class="gloss" href="#g_Dip">dip</a> away from these
-<span class="pb" id="Page_102">102</span>
-valleys. Exploratory wells indicate that vast masses of salt and
-gypsum are present beneath the surface, and may extend to depths
-greater than 10,000 feet.</p>
-<h3 id="c54">GEMS AND ORNAMENTAL STONES</h3>
-<p>More than thirty different gems and ornamental stones are
-known to occur in Colorado. Amazonstone, amethyst, garnet,
-tourmaline, aquamarine, topaz, lapis lazuli, quartz crystal, smoky
-and rose quartz, sapphire, several varieties of agate, zircon, and
-other attractive stones are gathered within the state, mainly in the
-Mountain Province. Turquoise is known at several places in
-the volcanic area of southern Colorado. Alabaster is mined
-along the northeastern mountain front near Fort Collins and
-Loveland. Localities of interest to gem hunters are described in
-<i>Colorado Gem Trails and Mineral Guide</i>, by Richard M. Pearl.</p>
-<p>Gem Village, in southwestern Colorado on U. S. highway 160
-between Durango and Pagosa Springs, is a favorite stopping place
-for tourists wishing to see or buy colorful and attractive Colorado
-stones such as petrified wood, agatized dinosaur bones, chalcedony,
-and jasper.</p>
-<div class="pb" id="Page_103">103</div>
-<h3 id="c55">WATER</h3>
-<p>Although not all aspects of water and water supply are
-geologic, water is an important geologic agent, determining the
-shape of the surface, the distribution of minerals, and the location
-of caves. Water used in Colorado comes entirely from precipitation
-within the state, as all of Colorado&rsquo;s rivers flow from
-Colorado outward toward the surrounding lower-elevation states.</p>
-<h3 id="c56">Surface Water</h3>
-<div class="img" id="fig66">
-<img src="images/p47.jpg" alt="" width="800" height="495" />
-<p class="caption">A cross section through the Front Range northwest of Denver shows
-the redistribution and use of western slope water in eastern Colorado
-through the Colorado-Big Thompson Project. This project has cost
-about $160,000,000, but it is repaying the investment many times
-over by providing electric power and increasing farm production.</p>
-</div>
-<p>Moisture carried by prevailing westerly or northwesterly winds
-falls primarily on Colorado&rsquo;s western slope, although at some
-times of year precipitation may come from the northeast or
-southeast. West of the continental divide, where population is
-sparse, there is a surplus of water. East of the divide, where more
-than 90 per cent of the population lives, water is in desperately
-short supply. The high and largely unpopulated Mountain Province
-receives by far the greatest proportion of precipitation, while
-agricultural areas of the Prairie and <a class="gloss" href="#g_Plateau">Plateau</a> Provinces receive
-<span class="pb" id="Page_104">104</span>
-much less. Needless to say, the major problem involving water
-in Colorado is how to move it from areas where it is abundant
-to areas where it is needed.</p>
-<p>In many parts of the state, complex water laws and complicated
-irrigation canals and water systems were developed soon
-after the area became settled. Gradually but inevitably, water
-resources have been transferred from the western slope to the
-eastern. However, such transfer must be undertaken with due
-regard for the rights of downstream users, notably California,
-Arizona, and New Mexico.</p>
-<p>One of the largest water movement schemes in the state is the
-Colorado-Big Thompson Project. Water that otherwise would flow
-into the Colorado River is piped from Grand Lake through the
-Alva B. Adams tunnel under the high mountains of Rocky
-Mountain National Park, and into the Big Thompson drainage
-near Estes Park. It then travels through a series of reservoirs and
-tunnels into the South Platte River basin, where it is used for
-irrigation and household water. The water is pumped up the
-western gradient of this system by electric power produced as it
-flows down the eastern slope. Surplus electric power serves the
-Colorado-Wyoming area.</p>
-<p>Another large project is the Denver Water Board&rsquo;s Dillon
-Reservoir Project, in which western slope water collected at
-Dillon is pumped twenty-three miles under the continental divide
-through the Harold D. Roberts tunnel to the North Fork of the
-South Platte River for use by the city of Denver. The exit point
-of this tunnel can be seen a few miles west of Grant along U. S.
-highway 285. This project is continuously growing as Denver&rsquo;s
-water needs mount.</p>
-<p>In each of these projects, engineering geologists played a
-prominent part in locating dams and tunnels that would not leak
-or fail, and that could collect and transport a maximum amount
-of water during the high-runoff spring season for distribution
-through the rest of the year. Fortunately for geologists, the tunnels
-and bores necessary to the projects allowed them to learn a great
-deal about the structure of the interior of the high mountains, and
-helped to improve their interpretation of earth history in this most
-interesting region.</p>
-<p>The necessity for storing irrigation water along the eastern
-mountain front has led to the creation of hundreds of new lakes
-in the region. Although water levels vary with the season, many
-of the lakes provide opportunities for water sports and recreation
-for the burgeoning inland population.</p>
-<div class="pb" id="Page_105">105</div>
-<p>Two large dams have recently been built in western Colorado
-for another purpose: to control the flow of water in the Colorado
-River drainage basin. Electric power for western Colorado also
-comes from these dams. One of the dams is on the Gunnison
-River at Curecanti, upstream from the Black Canyon of the
-Gunnison National Monument, and the other is on the Frying Pan
-River near Ruedi. The latter was completed over the objections
-of geologists, who believed that the extensive gypsum deposits
-underlying the damsite would cause its failure. Cement pumped
-deep into the rocks in the vicinity has so far prevented serious
-rupture.</p>
-<p>There is strong resistance by conservation groups to the construction
-of more dams on Colorado River drainage, primarily
-because the Colorado and its tributaries pass through many
-irreplaceable canyons, some of them parts of National Parks and
-Monuments, that are very much a part of our western heritage.</p>
-<h3 id="c57">Groundwater</h3>
-<div class="img" id="fig67">
-<img src="images/p48.jpg" alt="" width="800" height="192" />
-<p class="caption">In the San Luis Valley, runoff from the San Juan and Sangre de Cristo
-Mountains sinks into layers of sand in the Alamosa Formation. Flowing
-along the sand layers toward the center of the valley, it provides
-<a class="gloss" href="#g_ArtesianWater">artesian water</a> for irrigation of valley farmlands.</p>
-</div>
-<dl class="undent caption"><dt>SAN JUAN MOUNTAINS</dt>
-<dt>LIMIT OF FLOWING WELLS</dt>
-<dt>HUBBARD&rsquo;S WELL</dt>
-<dt>OTTOWAY&rsquo;S WELL</dt>
-<dt>ALAMOSA WELL</dt>
-<dt>GEORGE NEWSOM&rsquo;S WELL</dt>
-<dt>CALKIN&rsquo;S WELL</dt>
-<dt>LIMIT OF FLOWING WELLS</dt>
-<dt><a class="gloss" href="#g_Moraine">Moraine</a></dt>
-<dt>Alluvial Slope</dt>
-<dt>SANGRE DE CRISTO MOUNTAINS</dt>
-<dt>Sands, <a class="gloss" href="#g_Lava">lava</a> beds, gravels, <a class="gloss" href="#g_Conglomerate">conglomerates</a>, etc.</dt>
-<dt>Alamosa formation</dt>
-<dt><a class="gloss" href="#g_Granite">Granites</a></dt>
-<dt>WEST</dt>
-<dt>SANTE FE FORMATION</dt>
-<dt>SANTE FE FORMATION</dt>
-<dt>EAST</dt></dl>
-<p>Groundwater is extremely important to Colorado, especially
-in the Prairie Province and the San Luis Valley. Below these two
-areas lie a number of distinct and productive groundwater <a class="gloss" href="#g_Aquifer">aquifers</a>,
-several of them artesian. In Otero County, for example, there are
-five major aquifers: three separate Quaternary gravel deposits,
-the Cretaceous Dakota Sandstone, and the Cheyenne Sandstone
-Member of the Purgatoire Formation, also Cretaceous. All these
-aquifers are characterized by their high porosity and permeability,
-<span class="pb" id="Page_106">106</span>
-which allow water to flow rapidly through them. Wells in the
-younger, shallower aquifers produce as much as 2,000 gallons
-per minute; those in the older, deeper aquifers produce about
-eighty gallons per minute, some of it with an artesian &ldquo;head.&rdquo;</p>
-<p>The San Luis Valley supports intensive agriculture, made
-possible by a great <a class="gloss" href="#g_ArtesianWater">artesian water</a> supply. A thick series of soft
-interlayered clays and sands, the Alamosa Formation, slopes down
-toward the center of the basin from the surrounding mountains.
-Water entering the sandstone beds at the mountain edges flows
-through the sand layers held there by the impermeable clay beds.
-By the time it reaches the center of the valley, it has developed
-considerable hydrostatic head, and the water rises in wells without
-pumping. Unfortunately, both the irrigation water and the soils
-in the San Luis Valley are highly alkaline. Constant evaporation
-from the irrigated fields has concentrated the alkali near and on
-the surface, rendering some of the land less usable than it was
-originally.</p>
-<h3 id="c58">Caves</h3>
-<p>Colorado has many caves, most of them carved by underground
-water in Paleozoic limestone. The Cave of the Winds at
-Manitou is the only one in the state which has been developed as
-a tourist attraction. It is in highly faulted Ordovician and Mississippian
-limestone near the mountain front, where the faulting,
-coupled with the high relief, has accelerated solution of the rock
-by allowing groundwater to percolate downward rapidly. The
-cavern was probably carved during the Pleistocene Ice Age, when
-surface water and groundwater were much more abundant than
-at present. Deposition of <a class="gloss" href="#g_Stalactite">stalactites</a> and <a class="gloss" href="#g_Stalagmite">stalagmites</a> has occurred
-within the last few thousand years, as supplies and movement of
-water have decreased.</p>
-<p>Spanish Cave, above timberline on Marble Mountain in the
-Sangre de Cristo Range, is probably the nation&rsquo;s highest limestone
-cave. It is in thick folded and faulted Pennsylvanian <a class="gloss" href="#g_Reef">reef</a> limestone,
-at an elevation of over 12,000 feet. The cave has many
-intricate passageways branching from its main vertical tubes and
-channels.</p>
-<p>Fulford Cave, south of Eagle, is in the Mississippian Leadville
-Limestone of the northern part of the Sawatch Range. Many other
-<span class="pb" id="Page_107">107</span>
-caves are situated south of Fulford, near Woods Lake, where the
-limestone is widely exposed and highly dissected.</p>
-<p>Fairy Cave, northeast of Glenwood Springs, is the best known
-of the many caverns in the Paleozoic limestones that form the
-southern flanks of the White River <a class="gloss" href="#g_Plateau">Plateau</a>.</p>
-<div class="img" id="fig68">
-<img src="images/p49.jpg" alt="" width="717" height="700" />
-<p class="caption">In Cave of the Winds near Manitou, Paleozoic limestones, cracked
-and tilted by uplift of the Front Range, have been honeycombed by
-ground water. Calcite <a class="gloss" href="#g_Stalactite">stalactites</a> hang from the ceiling, while <a class="gloss" href="#g_Stalagmite">stalagmites</a>
-grow up from the floor. (Cave of the Winds Company photo)</p>
-</div>
-<p>In the <a class="gloss" href="#g_Plateau">Plateau</a> Province another type of cave is formed not
-so much by groundwater as by weathering of the flat-lying alternating
-beds of massive resistant sandstone and less resistant, thinly
-<span class="pb" id="Page_108">108</span>
-bedded mudstone and shale. Where the resistant layers are undermined,
-great arching caves develop. These are best observed at
-<a class="gloss" href="#g_Mesa">Mesa</a> Verde National Park, where many of them once sheltered
-Indian communities. They can also be seen in Colorado National
-Monument and along the Colorado River and several of its major
-tributaries.</p>
-<div class="img" id="fig69">
-<img src="images/p50.jpg" alt="" width="752" height="800" />
-<p class="caption">Along the edge at <a class="gloss" href="#g_Mesa">Mesa</a> Verde, caves in Cretaceous Mesa Verde
-sandstone were used for shelter by Indians. Springs near the bases
-of the caves, which provided the Indian communities with water,
-probably contributed to the undermining of the sandstone cliffs.
-(Colorado Department of Highways photo)</p>
-</div>
-<div class="pb" id="Page_109">109</div>
-<h3 id="c59">Springs</h3>
-<p>The multitudes of mineral and hot springs in Colorado are a
-fascinating and interesting facet of the Mountain Province. Some
-are located along major <a class="gloss" href="#g_Fault">faults</a>, where the rocks are so broken and
-shattered that groundwater can move freely toward the surface.
-Colorado Springs, Manitou Springs, and Eldorado Springs are on
-the fault complex that forms the east edge of the Front Range.
-Glenwood, Juniper, Steamboat, and Poncha Springs are on well
-defined faults also.</p>
-<div class="img" id="fig70">
-<img src="images/p50a.jpg" alt="" width="800" height="576" />
-<p class="caption">Glenwood Hot Springs flow from Pennsylvanian shales of the Belden
-Formation, where sedimentary layers are faulted by the sharp upward
-tilting against the south side of the White River <a class="gloss" href="#g_Plateau">Plateau</a>. Behind the
-hotel and on the right can be seen the Mississippian Leadville Limestone,
-cut by the Colorado River. (From a painting by William H.
-Jackson, courtesy of Colorado State Archives and Public Record)</p>
-</div>
-<p>Many other springs do not seem to be controlled so strongly
-by faulting, but owe their presence to sources of volcanic or magmatic
-heat which exist near to the surface of the ground. Some
-springs of this type issue from Precambrian <a class="gloss" href="#g_Granite">granite</a>, or Cenozoic
-volcanic rock, while others flow from sedimentary rock layers.
-Waunita Hot Springs and Pagosa Springs, although near volcanic
-rocks, reach the surface through porous sandstones and shales of
-<span class="pb" id="Page_110">110</span>
-Cretaceous age. Mt. Princeton Hot Springs comes from <a class="gloss" href="#g_Alluvium">alluvium</a>
-but its heat source is the intrusive igneous rock which makes up
-part of the adjacent mountain.</p>
-<p>Springs of another general type are also present in Colorado
-where <a class="gloss" href="#g_Aquifer">aquifers</a>, generally sandstones, are dissected by erosion.
-These springs, usually not highly mineralized or warm, are most
-often found in the <a class="gloss" href="#g_Plateau">Plateau</a> Province. Such springs are frequent at
-the bases of the great sandstone cliffs of <a class="gloss" href="#g_Mesa">Mesa</a> Verde and Colorado
-National Monument.</p>
-<p>Manitou&rsquo;s carbonated springs, which attract many tourists,
-have their origin in the arrangement and nature of the rocks
-through which the water flows. Water from the Pikes Peak region,
-slightly acid from its contact with the granitic rock, flows into the
-Manitou limestone all along Ute Pass <a class="gloss" href="#g_Fault">fault</a>, which extends from
-Cheyenne Mountain northwest to Woodland Park. Descending
-through channels along the fault, the water becomes pressurized.
-Because of its pressure and its acid content, it partly dissolves
-the calcium carbonate of the limestone, and from then on carries
-carbon dioxide in solution. As the water comes to the surface at
-the low point of the fault exposure, near the west edge of Manitou,
-the pressure is released and the carbon dioxide effervesces, just
-as a bottle of soda water effervesces when the cap is removed.</p>
-<div class="pb" id="Page_111">111</div>
-<h3 id="c60">ENVIRONMENTAL GEOLOGY</h3>
-<p>The preceding part of this chapter mentions many ways
-in which man&rsquo;s destiny in Colorado has been shaped by
-geologic factors. Early Coloradoans settled near gold and silver
-placers, later ones near mines that produced ores of other
-metals, or in the towns that sprang up around the mills and
-smelters that processed these ores. Our present distribution of
-population is partly a heritage from these first settlements, partly
-a result of later discoveries of oil, gas, and radioactive minerals,
-and partly a response to the state&rsquo;s extreme topographic variation,
-which controls and delineates agricultural areas and transportation
-routes.</p>
-<p>In recent years, man has begun to appreciate the fact that he
-may benefit in other ways from knowledge about geology. A new
-geology has developed&mdash;<i>environmental geology</i>&mdash;which may be
-defined as the total of all geological conditions and influences
-affecting the life and development of man.</p>
-<p>Environmental geology is a broad science, concerned not only
-with the location of cities and towns, but with the uses people
-make of the land and its economic products, and with the relationship
-between the geological character of the land and the present
-and future location of roads, dams, bridges, factories, homes,
-recreation facilities, sanitary land fills, and even sewage plants.</p>
-<p>Two aspects of environmental geology which are particularly
-pertinent to Colorado&rsquo;s residents are discussed below.</p>
-<p class="tb"><i>Landslides</i> and slumping rock or earth are a frequent menace
-to Colorado&rsquo;s development in the Mountain Province. Often
-activated by heavy rains or deep manmade cuts, they can cause&mdash;and
-<i>have</i> caused&mdash;much damage to roads, buildings, and other
-works of man.</p>
-<p>The flanks of North and South Table Mountains, near Golden,
-are mantled by thick landslide debris; intermittent movement of
-the individual slides has repeatedly affected the railroad, irrigation
-ditches, and roads. As many as six different slides have moved
-within a single year. In one slide area, asphalt road material is
-estimated to be thirteen feet thick; successive layers of pavement
-have been laid one on top of another to keep the street up to grade.</p>
-<p>Landslides and landslide-prone areas may not be obvious to
-the untrained eye. Each year buildings and roads are constructed
-on unsuitable rock and soil foundations, in places where some
-degree of land slip is almost inevitable. Building in such areas
-<span class="pb" id="Page_112">112</span>
-is risky, but sometimes worth the risk; if condition are less than
-ideal, risks can be reduced by specialized types of construction.</p>
-<p class="tb"><i>Floods</i> are a perennial threat to much of the state, because
-of the high relief of the drainage basins and the torrential nature
-of the spring and summer rainfall. Their damaging effects were
-realized early in Colorado&rsquo;s history, when canyons were used as
-highways and railroad routes.</p>
-<p>Colorado&rsquo;s most expensive flood was probably the flood in
-the South Platte River basin south of Denver in 1965, which
-caused $508,000,000 worth of damage and drowned six people.
-The losses can be attributed to man&rsquo;s failure to realize the significance
-of the South Platte drainage routes and flood plains. Homes,
-shopping centers, and many other buildings occupied&mdash;and still
-occupy, as of 1971&mdash;land that has been intermittently flooded
-for many years. The following description of this flood, by H. F.
-Matthai of the U. S. Geological Survey, may help to convey some
-warning to residents or potential residents of the South Platte
-valley and other river valleys in Colorado:</p>
-<p>&ldquo;The morning of June 16 was most pleasant, but conditions
-changed rapidly shortly before noon. A tornado touched ground
-15 miles south southeast of Denver about 1 p.m. Within the next
-hour, another unroofed 30 homes in the little town of Palmer
-Lake, 40 miles south of Denver. About 2 p.m., a dense mass of
-clouds descended and concealed the top of Dawson Butte, 7 miles
-southwest of Castle Rock; and the little light remaining faded
-until it was dark black and frightening, according to some people.
-A nearby rancher&rsquo;s wife described the intense quiet as awesome,
-but the calm did not last very long.</p>
-<p>&ldquo;The deluge began, not only near Dawson Butte, but also at
-Raspberry Mountain, 6 miles to the south, near Larkspur. The
-rain came down harder than any rain the local residents had ever
-seen, and the temperature dropped rapidly until it was cold.
-The quiet was shattered by the terrible roar of wind, rain, and
-rushing water. Then the thudding of huge boulders, the snapping
-and tearing of trees, and the grinding of cobbles and gravel
-increased the tumult. The small natural channels on the steep
-slopes could not carry the runoff; so water took shortcuts, following
-the line of least resistance. Creeks overflowed, roads became
-rivers, and fields became lakes&mdash;all in a matter of minutes.</p>
-<p>&ldquo;The flow from glutted ravines and from fields and hillsides
-soon reached East and West Plum Creeks. The combined flow
-in these creeks have been described as awesome, fantastic, and
-unbelievable; yet none of these superlatives seem adequate to
-<span class="pb" id="Page_113">113</span>
-describe what actually occurred. Large waves, high velocities,
-crosscurrents, and eddies swept away trees, houses, bridges, automobiles,
-heavy construction equipment, and livestock. All sorts
-of debris and large volumes of sand and gravel were torn from the
-banks and beds of the streams and were dumped, caught, plastered,
-or buried along the channel and flood plains downstream. A local
-resident stated, &lsquo;The banks of the creek disappeared as if the land
-was made of sugar.&rsquo;</p>
-<p>&ldquo;The flood reached the South Platte River and the urban areas
-of Littleton, Englewood, and Denver about 8 p.m. Here the rampaging
-waters picked up house trailers, large butane storage tanks,
-lumber, and other flotsam and smashed them against bridges and
-structures near the river. Many of the partly plugged bridges could
-not withstand the added pressure and washed out. Other bridges
-held, but they forced water over approach fills, causing extensive
-erosion. The flood plains carried and stored much of the flood
-water, which inundated many homes, businesses, industries, railroad
-yards, highways, and streets.</p>
-<p>&ldquo;The flood peak passed through Denver during the night, and
-the immediate crisis was over by morning; but those in the inundated
-areas were faced with a Herculean task. The light of day
-revealed the nature of the destruction&mdash;mud in every nook and
-cranny, soggy merchandise, warped bowling alleys, drowned
-animals, the loss of irreplaceable possessions, to name a few types.
-The colossal cleanup job, which would take months, began.&rdquo;</p>
-<p>Hydrogeological studies by the U. S. Geological Survey and
-Corps of Engineers give knowledgeable estimates of flood danger
-for different populated areas of the state, and recommend that
-homes, roads, and other structures be placed above likely flood
-levels.</p>
-<div class="pb" id="Page_114">114</div>
-<h2 id="c61"><span class="h2line1">GLOSSARY</span></h2>
-<p class="revint"><b id="g_AlluvialFan">Alluvial fan</b>. A cone-shaped mass of sediment built by rivers or
-streams as they issue from mountains onto more level ground.</p>
-<p class="revint"><b id="g_Alluvium">Alluvium</b>. Stream deposits formed in recent geologic time, composed
-of sand, gravel, and stones.</p>
-<p class="revint"><b id="g_Ammonite">Ammonite</b>. One of a large group of extinct <a class="gloss" href="#g_Mollusk">mollusks</a> related to the
-living chambered <i>Nautilus</i>. <a class="gloss" href="#g_Ammonite">Ammonite</a> shells, usually cone-shaped
-or coiled, are divided into many chambers by crenellated
-septa.</p>
-<p class="revint"><b id="g_AngularUnconformity">Angular unconformity</b>. A surface separating tilted or folded layers
-of rock from overlying less disturbed layers.</p>
-<p class="revint"><b id="g_Anticline">Anticline</b>. An upward <a class="gloss" href="#g_Fold">fold</a> or elongated arch in rock layers.</p>
-<p class="revint"><b id="g_Aquifer">Aquifer</b>. A rock layer that is water-bearing.</p>
-<p class="revint"><b id="g_ArtesianWater">Artesian water</b>. Groundwater that is under sufficient pressure to
-rise above the level at which it is encountered in a well. It
-does not necessarily rise completely to the surface.</p>
-<p class="revint"><b id="g_Basalt">Basalt</b>. An extrusive igneous rock, fine-grained and dark colored,
-composed mainly of calcium-rich <a class="gloss" href="#g_Feldspar">feldspar</a> and the black mineral
-pyroxene.</p>
-<p class="revint"><b id="g_Basement">Basement</b>. A name commonly applied to metamorphic or <a class="gloss" href="#g_IgneousRocks">igneous rocks</a> underlying the sedimentary rock layers.</p>
-<p class="revint"><b id="g_Batholith">Batholith</b>. A large body of intrusive igneous rock, 40 square miles
-or more in outcrop area, which extends downward to an
-unknown depth.</p>
-<p class="revint"><b id="g_Bedrock">Bedrock</b>. The solid rock which underlies soil, sand, clay, or other
-loose surface material.</p>
-<p class="revint"><b id="g_Belemnite">Belemnite</b>. The cigar-shaped internal shell of an extinct marine
-<a class="gloss" href="#g_Mollusk">mollusk</a> similar to a squid.</p>
-<p class="revint"><b id="g_Brachiopod">Brachiopod</b>. One of a large group of marine shelled animals having
-two unequal, bilaterally symmetrical shells.</p>
-<p class="revint"><b id="g_Bryozoa">Bryozoa</b>. A large group of tiny colonial marine animals that secrete
-calcareous or horny coverings in a great variety of shapes.</p>
-<p class="revint"><b id="g_Caldera">Caldera</b>. A large basin-shaped depression caused by explosion or
-collapse around a volcanic center.</p>
-<p class="revint"><b id="g_Cassiterite">Cassiterite</b>. A heavy, brown to brownish black mineral composed
-of tin and oxygen (SnO&#8322;) that is an ore of tin.</p>
-<p class="revint"><b id="g_Cephalopod">Cephalopod</b>. A marine <a class="gloss" href="#g_Mollusk">mollusk</a> with a head surrounded by tentacles.
-Squids and octupuses belong to this group, as do <a class="gloss" href="#g_Fossil">fossil</a>
-forms having straight or coiled shells divided into numerous
-interior chambers.</p>
-<p class="revint"><b id="g_Chalcopyrite">Chalcopyrite</b>. A reddish-gold colored ore of copper (CuFeS&#8322;).</p>
-<div class="pb" id="Page_115">115</div>
-<p class="revint"><b id="g_Cirque">Cirque</b>. A deep, steep-walled recess in a mountain, caused by
-glacial erosion at the head of a valley.</p>
-<p class="revint"><b id="g_Concretion">Concretion</b>. A nodular or irregular concentration of minerals such
-as calcite or limonite, formed by precipitation of the mineral
-from groundwater around a nucleus.</p>
-<p class="revint"><b id="g_Conglomerate">Conglomerate</b>. A rock containing coarse fragments of an older
-rock, usually as rounded water-worn stones or pebbles.</p>
-<p class="revint"><b id="g_Conodont">Conodont</b>. One of a group of tiny dark brown tooth-like <a class="gloss" href="#g_Fossil">fossils</a>
-thought to be dermal or dental parts of some extinct group of
-fish.</p>
-<p class="revint"><b id="g_Diatreme">Diatreme</b>. A volcanic vent or pipe drilled through rocks by the
-explosive energy of gas-charged molten rock, now containing
-igneous rock and often altered or unaltered fragments of the
-surrounding rock.</p>
-<p class="revint"><b id="g_Dike">Dike</b>. A vertical or nearly vertical sheet of igneous rock which cuts
-across the structure of adjacent rocks.</p>
-<p class="revint"><b id="g_Diorite">Diorite</b>. An intrusive igneous rock composed of sodium-rich <a class="gloss" href="#g_Feldspar">feldspar</a>
-and dark minerals, with only small amounts of quartz.</p>
-<p class="revint"><b id="g_Dip">Dip</b>. The angle at which a layer of rock is inclined below the horizontal.</p>
-<p class="revint"><b id="g_Dome">Dome</b>. A roughly circular upfold in which the rock layers <a class="gloss" href="#g_Dip">dip</a>
-outward in all directions from the center.</p>
-<p class="revint"><b id="g_Dowsing">Dowsing</b>. Searching for underground water or ore with a divining
-rod, usually a forked stick supposed to locate spots where the
-desired substance may be found under the surface.</p>
-<p class="revint"><b id="g_Echinoderm">Echinoderm</b>. One of a large group of marine invertebrate animals,
-most of which have pentagonal symmetry and a skeleton of
-many calcite plates. Many forms are spiny. The group includes
-starfish and sea urchins.</p>
-<p class="revint"><b id="g_Evaporite">Evaporite</b>. Chemical sediments precipitated when water (usually
-sea water) evaporates.</p>
-<p class="revint"><b id="g_ExtrusiveRocks">Extrusive rocks</b>. <a class="gloss" href="#g_IgneousRocks">Igneous rocks</a> formed when molten rock material
-is ejected onto the surface. Synonymous with volcanic rocks.</p>
-<p class="revint"><b id="g_Fault">Fault</b>. A break in the rocks in which there has been displacement
-of the two sides relative to each other.</p>
-<p class="revint"><b id="g_FaultBlockRange">Fault block range</b>. A mountain range bounded on two or more
-sides by <a class="gloss" href="#g_Fault">faults</a>.</p>
-<p class="revint"><b id="g_Feldspar">Feldspar</b>. A group of light-colored aluminum silicate minerals that
-are major constituents of <a class="gloss" href="#g_IgneousRocks">igneous rocks</a>. They contain potassium,
-sodium, and calcium in differing proportions.</p>
-<p class="revint"><b id="g_Fold">Fold</b>. A bend in rock layers.</p>
-<p class="revint"><b id="g_Foraminiferida">Foraminiferida</b>. One-celled marine animals with microscopic,
-perforated, many-chambered calcium carbonate shells, often
-called forams.</p>
-<div class="pb" id="Page_116">116</div>
-<p class="revint"><b id="g_Fossil">Fossil</b>. The remains or traces of an animal or plant which has been
-preserved in the rock.</p>
-<p class="revint"><b id="g_Fusulinid">Fusulinid</b>. One-celled marine animals (forams) with shells which
-look like a grain of wheat in shape and size, frequently abundant
-in Colorado Pennsylvanian rocks.</p>
-<p class="revint"><b id="g_Galena">Galena</b>. A heavy gray metallic mineral (PbS), often cubic in form,
-that is the most important ore of lead.</p>
-<p class="revint"><b id="g_Gangue">Gangue</b>. Nonvaluable minerals occurring in <a class="gloss" href="#g_Vein">veins</a> with ore minerals.</p>
-<p class="revint"><b id="g_Glaciation">Glaciation</b>. Alteration of the earth&rsquo;s surface by erosion and deposition
-by <a class="gloss" href="#g_Glacier">glacier</a> ice.</p>
-<p class="revint"><b id="g_Glacier">Glacier</b>. A body of ice originating on land by recrystallization of
-snow, and showing evidence of movement by flowing.</p>
-<p class="revint"><b id="g_Gneiss">Gneiss</b>. A coarse-grained <a class="gloss" href="#g_MetamorphicRock">metamorphic rock</a> usually banded with
-streaks of darker, finer-grained rock.</p>
-<p class="revint"><b id="g_Granite">Granite</b>. An intrusive igneous rock consisting essentially of sodium
-or potassium <a class="gloss" href="#g_Feldspar">feldspar</a> and quartz, often speckled with dark-colored
-minerals.</p>
-<p class="revint"><b id="g_Graptolite">Graptolite</b>. Extinct marine organisms without known close living
-relatives, with small black sawblade-like chitinous hard parts
-preserved as <a class="gloss" href="#g_Fossil">fossils</a>.</p>
-<p class="revint"><b id="g_Hematite">Hematite</b>. A steel gray or metallic grayish black or reddish gray
-mineral (Fe&#8322;O&#8323;) that is an important ore of iron.</p>
-<p class="revint"><b id="g_Hogback">Hogback</b>. A sharp-crested ridge formed by a resistant layer of
-steeply dipping rock.</p>
-<p class="revint"><b id="g_Huebnerite">Huebnerite</b>. A heavy reddish brown mineral (MnWO&#8324;) that is a
-major ore of tungsten.</p>
-<p class="revint"><b id="g_IgneousRocks">Igneous rocks</b>. Rocks formed by solidification from a molten state,
-either at the surface (extrusive) or below the surface (intrusive).</p>
-<p class="revint"><b id="g_IntrusiveRocks">Intrusive rocks</b>. <a class="gloss" href="#g_IgneousRocks">Igneous rocks</a> formed when molten rock material
-solidifies without reaching the surface.</p>
-<p class="revint"><b id="g_Joint">Joint</b>. A fracture in the rock, along which no discernible movement
-has taken place.</p>
-<p class="revint"><b id="g_Kerogen">Kerogen</b>. Solid bituminous material in oil shales.</p>
-<p class="revint"><b id="g_Laccolith">Laccolith</b>. A lens-shaped mass of igneous rock intruded into layered
-rocks.</p>
-<p class="revint"><b id="g_Lava">Lava</b>. Fluid or molten rock such as that which issues from a volcano.</p>
-<p class="revint"><b id="g_Lode">Lode</b>. A rock mass, often a <a class="gloss" href="#g_Vein">vein</a>, containing valuable minerals.</p>
-<p class="revint"><b id="g_Massif">Massif</b>. A mountainous mass that has relatively uniform geologic
-characteristics and which may embrace a number of peaks.</p>
-<p class="revint"><b id="g_Mesa">Mesa</b>. A flat-topped mountain bounded on at least one side by a
-steep cliff.</p>
-<p class="revint"><b id="g_MetamorphicRock">Metamorphic rock</b>. Rock formed by alteration of pre-existing
-rock, especially by great temperatures and pressures.</p>
-<div class="pb" id="Page_117">117</div>
-<p class="revint"><b id="g_Mollusk">Mollusk</b>. Any one of the large group of invertebrate animals which
-includes the snails, clams, octopuses, squids, and their extinct
-relatives.</p>
-<p class="revint"><b id="g_Molybdenite">Molybdenite</b>. A soft bluish gray, metallic mineral (MoS&#8322;) that is
-a major ore of molybdenum.</p>
-<p class="revint"><b id="g_Monocline">Monocline</b>. A steplike <a class="gloss" href="#g_Fold">fold</a> in otherwise horizontal or gently dipping
-rock layers.</p>
-<p class="revint"><b id="g_Moraine">Moraine</b>. An accumulation of unsorted rock material built up by
-the action of <a class="gloss" href="#g_Glacier">glacier</a> ice.</p>
-<p class="revint"><b id="g_NativeGold">Native gold</b>. Gold occurring in nature uncombined with other
-elements.</p>
-<p class="revint"><b id="g_Peneplain">Peneplain</b>. A land surface worn down by erosion to a nearly flat
-or broadly undulating plain.</p>
-<p class="revint"><b id="g_Petzite">Petzite</b>. A heavy black or steel gray metallic telluride ore of gold
-and silver (Ag&#8323;AuTe&#8322;).</p>
-<p class="revint"><b id="g_Placer">Placer</b>. A sand or gravel deposit containing particles or nuggets of
-gold or other heavy valuable minerals.</p>
-<p class="revint"><b id="g_Plateau">Plateau</b>. An elevated, comparatively flat surface of land, usually
-larger than a <a class="gloss" href="#g_Mesa">mesa</a>, sometimes composed of many mesas, and
-often dissected by deep stream valleys.</p>
-<p class="revint"><b id="g_Porphyry">Porphyry</b>. An igneous rock, usually intrusive, which contains conspicuous
-large crystals in a fine-grained matrix.</p>
-<p class="revint"><b id="g_Pyrite">Pyrite</b>. A brass-yellow metallic mineral (FeS&#8322;) that is an important
-source of sulfur. It is commonly known as fool&rsquo;s gold.</p>
-<p class="revint"><b id="g_Reef">Reef</b>. A moundlike limestone structure built in the sea by sedentary
-organisms such as corals.</p>
-<p class="revint"><b id="g_Rhyolite">Rhyolite</b>. A light-colored volcanic rock with quartz and <a class="gloss" href="#g_Feldspar">feldspar</a>
-as the principal constituents.</p>
-<p class="revint"><b id="g_Schist">Schist</b>. A <a class="gloss" href="#g_MetamorphicRock">metamorphic rock</a> characterized by parallel orientation
-of flat-grained minerals like mica.</p>
-<p class="revint"><b id="g_SedimentaryRocks">Sedimentary rocks</b>. Rocks formed of fragments of other rock
-transported by wind or water, or formed by precipitation from
-solution.</p>
-<p class="revint"><b id="g_Sphalerite">Sphalerite</b>. An amber-yellow to black mineral (ZnS) that is an
-important ore of zinc.</p>
-<p class="revint"><b id="g_Stalactite">Stalactite</b>. A cylindrical or conical deposit of calcite hanging from
-the roof of a cavern, formed by evaporation of water droplets
-containing calcium carbonate.</p>
-<p class="revint"><b id="g_Stalagmite">Stalagmite</b>. Columns or ridges of calcite rising from the floor of a
-cavern, formed by water containing calcium carbonate dripping
-from a <a class="gloss" href="#g_Stalactite">stalactite</a>.</p>
-<p class="revint"><b id="g_Stock">Stock</b>. A mass of igneous intrusive rock that covers less than 40
-square miles, has steep sides, and extends to an unknown depth.</p>
-<div class="pb" id="Page_118">118</div>
-<p class="revint"><b id="g_Tennantite">Tennantite</b>. A metallic gray mineral that contains copper, iron,
-and arsenic, and is an ore of copper.</p>
-<p class="revint"><b id="g_Tetrahedrite">Tetrahedrite</b>. A brittle, dark gray to black, metallic mineral containing
-copper, iron, zinc, and silver.</p>
-<p class="revint"><b id="g_Trilobite">Trilobite</b>. One of a primitive group of extinct marine crustaceans,
-related to crabs and lobsters, having segmented bodies divided
-by longitudinal grooves into three lobes.</p>
-<p class="revint"><b id="g_Unconformity">Unconformity</b>. A surface separating layers of rock, formed by a
-period of nondeposition or erosion.</p>
-<p class="revint"><b id="g_Vein">Vein</b>. A crack or fissure filled with mineral material, often with
-valuable ore minerals.</p>
-<div class="pb" id="Page_119">119</div>
-<h2 id="c62"><span class="h2line1">SUGGESTED READING</span></h2>
-<p>There are thousands of scientific articles and books on Colorado
-geology, and many new ones appear each year. Following is a
-selection of books and booklets which we believe will be most
-useful and interesting in extending your knowledge of the state&rsquo;s
-geology.</p>
-<p class="revint">Donnell, John R., editor, 1960, GEOLOGICAL ROAD LOGS
-OF COLORADO. Rocky Mountain Association of Geologists,
-Denver. Itineraries for a number of geological trips along
-Colorado highways and byways.</p>
-<p class="revint">Eckel, Edwin B., 1961, MINERALS OF COLORADO, A 100-YEAR
-RECORD. U. S. Geological Survey Bulletin 1114.</p>
-<p class="revint">Emmons, S. F., Cross, Whitman, and Eldridge, G. H., 1896,
-GEOLOGY OF THE DENVER BASIN IN COLORADO.
-U. S. Geological Survey Monograph 27. The classic early
-treatment of the surface geology around Denver, with many
-historic illustrations.</p>
-<p class="revint">Hansen, Wallace R., 1965, THE BLACK CANYON OF THE
-GUNNISON TODAY AND YESTERDAY. U. S. Geological
-Survey Bulletin 1191. A readable account of this unusual
-national monument near Montrose.</p>
-<p class="revint">Hansen, Wallace R., 1969, THE GEOLOGIC STORY OF THE
-UINTA MOUNTAINS. U. S. Geological Survey Bulletin
-1291. The eastern part of this range is in Colorado.</p>
-<p class="revint">Henderson, C. W., 1926, MINING IN COLORADO, A HISTORY
-OF DISCOVERY, DEVELOPMENT AND PRODUCTION.
-U. S. Geological Survey Professional Paper 138.</p>
-<p class="revint">Lee, W. T., 1917, THE GEOLOGIC STORY OF THE ROCKY
-MOUNTAIN NATIONAL PARK, COLORADO. U. S.
-National Park Service Publication. An old report, not adequately
-superseded.</p>
-<p class="revint">Lovering, T. S., and Goddard, E. N., 1950, GEOLOGY AND
-ORE DEPOSITS OF THE FRONT RANGE, COLORADO.
-U. S. Geological Survey Professional Paper 223. A comprehensive
-study of mineral-bearing areas in the Front Range.</p>
-<p class="revint">Lohman, S. W., 1965, THE GEOLOGIC STORY OF COLORADO
-NATIONAL MONUMENT. Colorado and Black
-Canyon Natural History Association, Grand Junction.</p>
-<p class="revint">Pearl, Richard M., 1956, NATURE AS SCULPTOR: A GEOLOGIC
-INTERPRETATION OF COLORADO SCENERY.
-<span class="pb" id="Page_120">120</span>
-Denver Museum of Natural History Popular Series No. 6,
-Revised Edition.</p>
-<p class="revint">Pearl, Richard M., 1969, EXPLORING ROCKS, MINERALS,
-<a class="gloss" href="#g_Fossil">FOSSILS</a> IN COLORADO. Swallow Press, Revised Edition.</p>
-<p class="revint">Pearl, Richard M., 1971, COLORADO GEM TRAILS AND
-MINERAL GUIDE. Swallow Press, 3rd Edition.</p>
-<p class="revint">Powell, John Wesley, 1876, REPORT ON THE GEOLOGY OF
-THE EASTERN PORTION OF THE UINTA MOUNTAINS
-AND A REGION OF COUNTRY ADJACENT
-THERETO. U. S. Geological and Geographical Survey of the
-Territories. One of the earliest accounts of geology in Colorado,
-written by the explorer of the Colorado River and the father
-of the U. S. Geological Survey.</p>
-<p class="revint">Rabbit, Mary C., and others, 1969, THE COLORADO RIVER
-AND JOHN WESLEY POWELL. U. S. Geological Survey
-Professional Paper 669. A resum&eacute; of part of Powell&rsquo;s work
-and a good discussion of the geologic history of the entire
-Colorado River, which begins near Grand Lake.</p>
-<p class="revint">Richmond, Gerald M., 1965, <a class="gloss" href="#g_Glaciation">GLACIATION</a> OF THE ROCKY
-MOUNTAINS. A part of THE QUATERNARY OF THE
-UNITED STATES, Princeton University Press. A summary
-of current knowledge of glaciation in Colorado and surrounding
-areas.</p>
-<p class="revint">Rodeck, Hugo G., editor, 1964, NATURAL HISTORY OF THE
-BOULDER AREA. University of Colorado Museum Leaflet
-No. 13. Contains articles on geology and biology.</p>
-<p class="revint">Untermann, G. E., and Untermann, B. R., 1954, GEOLOGY
-OF DINOSAUR NATIONAL MONUMENT AND VICINITY,
-UTAH&mdash;COLORADO. Utah Geological and Mineralogical
-Survey Bulletin 42. A detailed study of the eastern
-Uinta Mountains.</p>
-<p class="revint">Weimer, Robert J., and Haun, John D., editors, 1960, GUIDE
-TO THE GEOLOGY OF COLORADO. Geological Society
-of America, Rocky Mountain Association of Geologists, and
-Colorado Scientific Society, Denver. A concise summary of
-many aspects of Colorado geology, this guide includes several
-geological itineraries and many reference listings.</p>
-<p class="revint">Wolle, Muriel Sibell, 1949, STAMPEDE TO TIMBERLINE,
-Sage Books. An excellent account of early mining activity in
-the state, with many fine drawings of the early settlements.</p>
-<div class="pb" id="Page_121">121</div>
-<h2 id="c63"><span class="h2line1">INDEX</span></h2>
-<p class="center"><b><a class="ab" href="#index_A">A</a> <a class="ab" href="#index_B">B</a> <a class="ab" href="#index_C">C</a> <a class="ab" href="#index_D">D</a> <a class="ab" href="#index_E">E</a> <a class="ab" href="#index_F">F</a> <a class="ab" href="#index_G">G</a> <a class="ab" href="#index_H">H</a> <a class="ab" href="#index_I">I</a> <a class="ab" href="#index_J">J</a> <a class="ab" href="#index_K">K</a> <a class="ab" href="#index_L">L</a> <a class="ab" href="#index_M">M</a> <a class="ab" href="#index_N">N</a> <a class="ab" href="#index_O">O</a> <a class="ab" href="#index_P">P</a> <a class="ab" href="#index_Q">Q</a> <a class="ab" href="#index_R">R</a> <a class="ab" href="#index_S">S</a> <a class="ab" href="#index_T">T</a> <a class="ab" href="#index_U">U</a> <a class="ab" href="#index_V">V</a> <a class="ab" href="#index_W">W</a> <span class="ab">X</span> <a class="ab" href="#index_Y">Y</a> <a class="ab" href="#index_Z">Z</a></b></p>
-<dl class="index">
-<dt class="center" id="index_A"><b>A</b></dt>
-<dt>Abrams Mountain, <a href="#Page_87">87</a></dt>
-<dt>Alamosa, <a href="#Page_35">35</a></dt>
-<dt>Alamosa Formation, <a href="#Page_67">67</a>, <a href="#Page_105">105</a>, <a href="#Page_106">106</a></dt>
-<dt>Alma, <a href="#Page_78">78</a></dt>
-<dt>Ancestral Rocky Mountains, <a href="#Page_44">44</a>, <a href="#Page_45">45</a></dt>
-<dt>Animas River, <a href="#Page_58">58</a>, <a href="#Page_86">86</a></dt>
-<dt>Ankareh Formation, <a href="#Page_52">52</a></dt>
-<dt>Antero Junction, <a href="#Page_21">21</a></dt>
-<dt>Anthracite, <a href="#Page_97">97</a></dt>
-<dt>Arapahoe <a class="gloss" href="#g_Conglomerate">Conglomerate</a>, <a href="#Page_60">60</a></dt>
-<dt>Arapaho <a class="gloss" href="#g_Glacier">Glacier</a>, <a href="#Page_70">70</a>, <a href="#Page_71">71</a></dt>
-<dt>Arkansas Hills, <a href="#Page_21">21</a></dt>
-<dt>Arkansas Mountain, <a href="#Page_79">79</a></dt>
-<dt>Arkansas River, <a href="#Page_3">3</a>, <a href="#Page_22">22</a>, <a href="#Page_35">35</a>, <a href="#Page_90">90</a></dt>
-<dt>Arkansas Valley, <a href="#Page_21">21</a></dt>
-<dt>Aspen, <i><a href="#pic_2">Front.</a></i>, <a href="#Page_1">1</a>, <a href="#Page_22">22</a>, <a href="#Page_35">35</a>, <a href="#Page_50">50</a>, <a href="#Page_74">74</a>, <a href="#Page_77">77</a>, <a href="#Page_78">78</a>, <a href="#Page_88">88</a>-89</dt>
-<dt>Aspen Mountain, <a href="#Page_23">23</a>, <a href="#Page_88">88</a></dt>
-<dt>Avon, <a href="#Page_22">22</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_B"><b>B</b></dt>
-<dt>Battlement <a class="gloss" href="#g_Mesa">Mesa</a>, <a href="#Page_62">62</a></dt>
-<dt>Belden Formation, <a href="#Page_44">44</a>, <a href="#Page_109">109</a></dt>
-<dt>Benton Shale, <a href="#Page_57">57</a></dt>
-<dt>Berthoud Pass, <a href="#Page_12">12</a>, <a href="#Page_92">92</a></dt>
-<dt>Big Thompson Canyon, <a href="#Page_12">12</a>, <a href="#Page_71">71</a></dt>
-<dt>Big Thompson River, <a href="#Page_69">69</a>, <a href="#Page_103">103</a>, <a href="#Page_104">104</a></dt>
-<dt>Black Canyon of the Gunnison, <a href="#Page_36">36</a>, <a href="#Page_37">37</a>, <a href="#Page_44">44</a>, <a href="#Page_71">71</a>, <a href="#Page_105">105</a></dt>
-<dt>Black Hawk, <a href="#Page_14">14</a>, <a href="#Page_77">77</a>, <a href="#Page_78">78</a>, <a href="#Page_79">79</a>, <a href="#Page_80">80</a></dt>
-<dt>Blue River, <a href="#Page_103">103</a></dt>
-<dt>Book Cliffs, <a href="#Page_29">29</a></dt>
-<dt>Boulder, <a href="#Page_8">8</a>, <a href="#Page_14">14</a>, <a href="#Page_33">33</a>, <a href="#Page_45">45</a>, <a href="#Page_47">47</a>, <a href="#Page_48">48</a>, <a href="#Page_50">50</a>, <a href="#Page_71">71</a>, <a href="#Page_74">74</a>, <a href="#Page_75">75</a>, <a href="#Page_94">94</a>, <a href="#Page_98">98</a>, <a href="#Page_99">99</a>, <a href="#Page_100">100</a>, <a href="#Page_101">101</a></dt>
-<dt>Boulder County, <a href="#Page_78">78</a>, <a href="#Page_79">79</a></dt>
-<dt>Boulder Creek, <a href="#Page_1">1</a>, <a href="#Page_15">15</a>, <a href="#Page_71">71</a>, <a href="#Page_103">103</a></dt>
-<dt>Boulder Creek <a class="gloss" href="#g_Granite">Granite</a>, <a href="#Page_14">14</a>, <a href="#Page_33">33</a>, <a href="#Page_35">35</a></dt>
-<dt>Boulder Reservoir, <a href="#Page_103">103</a></dt>
-<dt>Breckenridge, <a href="#Page_1">1</a>, <a href="#Page_78">78</a>, <a href="#Page_83">83</a>-84</dt>
-<dt>Bross, Mt., <a href="#Page_21">21</a></dt>
-<dt>Buena Vista, <a href="#Page_22">22</a></dt>
-<dt>Buffalo Peaks, <a href="#Page_21">21</a></dt>
-<dt>Building stone, <a href="#Page_24">24</a>, <a href="#Page_48">48</a>, <a href="#Page_50">50</a>, <a href="#Page_99">99</a>-101</dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_C"><b>C</b></dt>
-<dt>Cache la Poudre River, <a href="#Page_66">66</a>, <a href="#Page_103">103</a></dt>
-<dt>Cambrian, <a href="#Page_7">7</a>, <a href="#Page_34">34</a>, <a href="#Page_39">39</a></dt>
-<dt>Camp Bird, <a href="#Page_78">78</a>, <a href="#Page_88">88</a></dt>
-<dt>Canon City, <a href="#Page_3">3</a>, <a href="#Page_11">11</a>, <a href="#Page_16">16</a>, <a href="#Page_52">52</a>, <a href="#Page_53">53</a>, <a href="#Page_75">75</a>, <a href="#Page_94">94</a></dt>
-<dt>Canon City Embayment, <a href="#Page_16">16</a></dt>
-<dt>Carbondale, <a href="#Page_97">97</a></dt>
-<dt>Carboniferous, see Mississippian, Pennsylvanian</dt>
-<dt>Cardiff, <a href="#Page_97">97</a></dt>
-<dt>Carmel Formation, <a href="#Page_52">52</a></dt>
-<dt>Carter Lake, <a href="#Page_103">103</a></dt>
-<dt>Castle Creek, <a href="#Page_88">88</a></dt>
-<dt>Castle Rock, <a href="#Page_8">8</a>, <a href="#Page_61">61</a>, <a href="#Page_112">112</a></dt>
-<dt>Castle Rock <a class="gloss" href="#g_Conglomerate">Conglomerate</a>, <a href="#Page_60">60</a></dt>
-<dt>Cave of the Winds, <a href="#Page_106">106</a>, <a href="#Page_107">107</a></dt>
-<dt>Caves, <a href="#Page_31">31</a>, <a href="#Page_106">106</a>-108</dt>
-<dt>Cenozoic (see also Tertiary, Quaternary), <a href="#Page_7">7</a>, <a href="#Page_16">16</a>, <a href="#Page_18">18</a>, <a href="#Page_26">26</a>, <a href="#Page_28">28</a>, <a href="#Page_29">29</a>, <a href="#Page_59">59</a>-73, <a href="#Page_109">109</a></dt>
-<dt>Central City, <a href="#Page_1">1</a>, <a href="#Page_14">14</a>, <a href="#Page_74">74</a>, <a href="#Page_77">77</a>, <a href="#Page_78">78</a>, <a href="#Page_80">80</a></dt>
-<dt>Chaffee Formation, <a href="#Page_42">42</a></dt>
-<dt>Cherry Creek, <a href="#Page_1">1</a></dt>
-<dt>Cheyenne Mountain, <a href="#Page_14">14</a>, <a href="#Page_15">15</a>, <a href="#Page_110">110</a></dt>
-<dt>Cheyenne Sandstone, <a href="#Page_105">105</a></dt>
-<dt>Chinle Formation, <a href="#Page_51">51</a>, <a href="#Page_52">52</a>, <a href="#Page_93">93</a>, <a href="#Page_101">101</a></dt>
-<dt>Clay, <a href="#Page_75">75</a>, <a href="#Page_97">97</a>-99</dt>
-<dt>Clear Creek, <a href="#Page_1">1</a>, <a href="#Page_71">71</a>, <a href="#Page_80">80</a></dt>
-<dt>Climax, <a href="#Page_21">21</a>, <a href="#Page_78">78</a>, <a href="#Page_91">91</a>-92</dt>
-<dt>Climax <a class="gloss" href="#g_Granite">Granite</a> <a class="gloss" href="#g_Porphyry">Porphyry</a>, <a href="#Page_91">91</a>, <a href="#Page_92">92</a></dt>
-<dt>Coal, <a href="#Page_23">23</a>, <a href="#Page_75">75</a>, <a href="#Page_96">96</a>-97</dt>
-<dt>Coal Creek, <a href="#Page_14">14</a>, <a href="#Page_15">15</a></dt>
-<dt>Coal Creek Quartzite, <a href="#Page_33">33</a></dt>
-<dt>Coaldale, <a href="#Page_97">97</a></dt>
-<dt>Coalmont, <a href="#Page_97">97</a></dt>
-<dt>Cokedale, <a href="#Page_97">97</a></dt>
-<dt>Collegiate Range, <a href="#Page_22">22</a></dt>
-<dt>Colorado National Monument, <a href="#Page_29">29</a>, <a href="#Page_31">31</a>, <a href="#Page_44">44</a>, <a href="#Page_51">51</a>, <a href="#Page_108">108</a></dt>
-<dt>Colorado River, <a href="#Page_3">3</a>, <a href="#Page_20">20</a>, <a href="#Page_21">21</a>, <a href="#Page_28">28</a>, <a href="#Page_29">29</a>, <a href="#Page_35">35</a>, <a href="#Page_39">39</a>, <a href="#Page_103">103</a>, <a href="#Page_104">104</a>, <a href="#Page_105">105</a>, <a href="#Page_108">108</a>, <a href="#Page_109">109</a></dt>
-<dt>Colorado Springs, <a href="#Page_14">14</a>, <a href="#Page_15">15</a>, <a href="#Page_35">35</a>, <a href="#Page_37">37</a>, <a href="#Page_48">48</a>, <a href="#Page_97">97</a>, <a href="#Page_98">98</a>, <a href="#Page_109">109</a></dt>
-<dt>Columbia, Mt., <a href="#Page_22">22</a></dt>
-<dt>Como, <a href="#Page_78">78</a>, <a href="#Page_97">97</a></dt>
-<dt>Construction materials, <a href="#Page_97">97</a>-102</dt>
-<dt class="pb" id="Page_122">122</dt>
-<dt>Copper, <a href="#Page_74">74</a>, <a href="#Page_75">75</a>, <a href="#Page_80">80</a>, <a href="#Page_81">81</a>, <a href="#Page_83">83</a>, <a href="#Page_89">89</a>, <a href="#Page_91">91</a></dt>
-<dt>Creede, <a href="#Page_65">65</a>, <a href="#Page_78">78</a>, <a href="#Page_89">89</a>-90</dt>
-<dt>Crested Butte, <a href="#Page_24">24</a>, <a href="#Page_97">97</a></dt>
-<dt>Cretaceous, <a href="#Page_7">7</a>, <a href="#Page_12">12</a>, <a href="#Page_20">20</a>, <a href="#Page_23">23</a>, <a href="#Page_29">29</a>, <a href="#Page_30">30</a>, <a href="#Page_53">53</a>, <a href="#Page_56">56</a>-58, <a href="#Page_94">94</a>, <a href="#Page_95">95</a>, <a href="#Page_97">97</a>, <a href="#Page_98">98</a>, <a href="#Page_101">101</a>, <a href="#Page_105">105</a>, <a href="#Page_108">108</a>, <a href="#Page_110">110</a></dt>
-<dt>Cripple Creek, <a href="#Page_1">1</a>, <a href="#Page_74">74</a>, <a href="#Page_77">77</a>, <a href="#Page_78">78</a>, <a href="#Page_90">90</a>-91</dt>
-<dt>Cross Mountain, <a href="#Page_26">26</a>, <a href="#Page_29">29</a></dt>
-<dt>Crystal River, <a href="#Page_24">24</a>, <a href="#Page_99">99</a></dt>
-<dt>Culebra Range, <a href="#Page_17">17</a></dt>
-<dt>Curecanti, <a href="#Page_105">105</a></dt>
-<dt>Curtis Formation, <a href="#Page_52">52</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_D"><b>D</b></dt>
-<dt>Dakota Formation, <a href="#Page_12">12</a>, <a href="#Page_51">51</a>, <a href="#Page_53">53</a>, <a href="#Page_56">56</a>, <a href="#Page_94">94</a>, <a href="#Page_97">97</a>, <a href="#Page_105">105</a></dt>
-<dt>Dawson Arkose, <a href="#Page_60">60</a></dt>
-<dt>Dawson Butte, <a href="#Page_112">112</a></dt>
-<dt>Delcarbon, <a href="#Page_97">97</a></dt>
-<dt>Democrat, Mt., <a href="#Page_21">21</a></dt>
-<dt>Denver, <a href="#Page_3">3</a>, <a href="#Page_8">8</a>, <a href="#Page_14">14</a>, <a href="#Page_33">33</a>, <a href="#Page_35">35</a>, <a href="#Page_37">37</a>, <a href="#Page_45">45</a>, <a href="#Page_47">47</a>, <a href="#Page_48">48</a>, <a href="#Page_52">52</a>, <a href="#Page_53">53</a>, <a href="#Page_60">60</a>, <a href="#Page_74">74</a>, <a href="#Page_83">83</a>, <a href="#Page_94">94</a>, <a href="#Page_96">96</a>, <a href="#Page_99">99</a>, <a href="#Page_100">100</a>, <a href="#Page_104">104</a>, <a href="#Page_112">112</a>, <a href="#Page_113">113</a></dt>
-<dt>Denver Basin, <a href="#Page_8">8</a>, <a href="#Page_75">75</a>, <a href="#Page_94">94</a>, <a href="#Page_95">95</a></dt>
-<dt>Denver Formation, <a href="#Page_60">60</a>, <a href="#Page_62">62</a></dt>
-<dt>Devonian, <a href="#Page_7">7</a>, <a href="#Page_42">42</a>-43, <a href="#Page_83">83</a></dt>
-<dt>Dillon, <a href="#Page_104">104</a></dt>
-<dt>Dinosaur National Monument, <a href="#Page_27">27</a>, <a href="#Page_53">53</a>, <a href="#Page_55">55</a></dt>
-<dt>Durango, <a href="#Page_25">25</a>, <a href="#Page_28">28</a>, <a href="#Page_35">35</a>, <a href="#Page_47">47</a>, <a href="#Page_58">58</a>, <a href="#Page_78">78</a>, <a href="#Page_85">85</a>, <a href="#Page_102">102</a></dt>
-<dt>Dyer Dolomite, <a href="#Page_42">42</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_E"><b>E</b></dt>
-<dt>Eagle, <a href="#Page_47">47</a>, <a href="#Page_101">101</a>, <a href="#Page_106">106</a></dt>
-<dt>Eagle River, <a href="#Page_22">22</a>, <a href="#Page_47">47</a></dt>
-<dt>Edwards, <a href="#Page_22">22</a></dt>
-<dt>Elbert, Mt., <a href="#Page_22">22</a></dt>
-<dt>Eldorado Springs, <a href="#Page_109">109</a></dt>
-<dt>Elk Mountains, <a href="#Page_24">24</a>, <a href="#Page_69">69</a></dt>
-<dt>Empire, <a href="#Page_1">1</a>, <a href="#Page_78">78</a>, <a href="#Page_81">81</a></dt>
-<dt>Englewood, <a href="#Page_113">113</a></dt>
-<dt>Entrada Sandstone, <a href="#Page_51">51</a>, <a href="#Page_93">93</a></dt>
-<dt>Environmental geology, <a href="#Page_111">111</a>-113</dt>
-<dt>Eocene, <a href="#Page_64">64</a></dt>
-<dt>Estes Lake, <a href="#Page_103">103</a></dt>
-<dt>Estes Park, <a href="#Page_69">69</a>, <a href="#Page_104">104</a></dt>
-<dt>Evans, Mt., <a href="#Page_3">3</a>, <a href="#Page_12">12</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_F"><b>F</b></dt>
-<dt>Fairplay, <a href="#Page_78">78</a>, <a href="#Page_84">84</a>-85</dt>
-<dt>Fairy Cave, <a href="#Page_107">107</a></dt>
-<dt>Flattop Mountain, <a href="#Page_19">19</a></dt>
-<dt>Floods, <a href="#Page_112">112</a>-113</dt>
-<dt>Florence, <a href="#Page_74">74</a>, <a href="#Page_94">94</a></dt>
-<dt>Florissant <a class="gloss" href="#g_Fossil">Fossil</a> Beds National Monument, <a href="#Page_65">65</a></dt>
-<dt>Fort Carson, <a href="#Page_15">15</a></dt>
-<dt>Fort Collins, <a href="#Page_35">35</a>, <a href="#Page_101">101</a>, <a href="#Page_102">102</a></dt>
-<dt>Fountain Formation, <a href="#Page_12">12</a>, <a href="#Page_14">14</a>, <a href="#Page_45">45</a>, <a href="#Page_47">47</a>, <a href="#Page_48">48</a></dt>
-<dt>Fox Hills Sandstone, <a href="#Page_58">58</a></dt>
-<dt>Fremont Limestone, <a href="#Page_40">40</a>, <a href="#Page_41">41</a></dt>
-<dt>Frisco, <a href="#Page_21">21</a></dt>
-<dt>Front Range, <a href="#Page_11">11</a>-16, <a href="#Page_33">33</a>, <a href="#Page_35">35</a>, <a href="#Page_44">44</a>, <a href="#Page_50">50</a>, <a href="#Page_51">51</a>, <a href="#Page_52">52</a>, <a href="#Page_56">56</a>, <a href="#Page_60">60</a>, <a href="#Page_61">61</a>, <a href="#Page_68">68</a>, <a href="#Page_69">69</a>, <a href="#Page_70">70</a>, <a href="#Page_71">71</a>, <a href="#Page_93">93</a>, <a href="#Page_99">99</a>, <a href="#Page_101">101</a>, <a href="#Page_103">103</a>, <a href="#Page_107">107</a>, <a href="#Page_109">109</a></dt>
-<dt>Frying Pan River, <a href="#Page_105">105</a></dt>
-<dt>Fulford, <a href="#Page_107">107</a></dt>
-<dt>Fulford Cave, <a href="#Page_106">106</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_G"><b>G</b></dt>
-<dt>Garden of the Gods, <a href="#Page_4">4</a>, <a href="#Page_14">14</a>, <a href="#Page_15">15</a>, <a href="#Page_47">47</a>, <a href="#Page_48">48</a></dt>
-<dt>Garfield, Mt., <a href="#Page_30">30</a></dt>
-<dt>Gas, natural, <a href="#Page_1">1</a>, <a href="#Page_28">28</a>, <a href="#Page_75">75</a>, <a href="#Page_94">94</a>-96</dt>
-<dt>Gems, <a href="#Page_75">75</a>, <a href="#Page_102">102</a></dt>
-<dt>Gem Village, <a href="#Page_102">102</a></dt>
-<dt>Georgetown, <a href="#Page_78">78</a>, <a href="#Page_81">81</a></dt>
-<dt>Gilman, <a href="#Page_21">21</a></dt>
-<dt>Gilpin County, <a href="#Page_78">78</a></dt>
-<dt>Glen Eyrie Formation, <a href="#Page_44">44</a></dt>
-<dt>Glenwood Canyon, <a href="#Page_37">37</a>, <a href="#Page_39">39</a></dt>
-<dt>Glenwood Springs, <a href="#Page_24">24</a>, <a href="#Page_29">29</a>, <a href="#Page_35">35</a>, <a href="#Page_99">99</a>, <a href="#Page_107">107</a>, <a href="#Page_109">109</a></dt>
-<dt>Gold, <a href="#Page_1">1</a>, <a href="#Page_22">22</a>, <a href="#Page_29">29</a>, <a href="#Page_74">74</a>, <a href="#Page_75">75</a>, <a href="#Page_77">77</a>-91</dt>
-<dt>Golden, <a href="#Page_8">8</a>, <a href="#Page_14">14</a>, <a href="#Page_62">62</a>, <a href="#Page_74">74</a>, <a href="#Page_78">78</a>, <a href="#Page_83">83</a>, <a href="#Page_93">93</a>, <a href="#Page_98">98</a>, <a href="#Page_111">111</a></dt>
-<dt>Gold Hill, <a href="#Page_1">1</a>, <a href="#Page_74">74</a>, <a href="#Page_78">78</a>, <a href="#Page_79">79</a></dt>
-<dt>Gore Creek, <a href="#Page_47">47</a></dt>
-<dt>Gore Pass, <a href="#Page_19">19</a>, <a href="#Page_20">20</a></dt>
-<dt>Gore Range, <a href="#Page_20">20</a>-21, <a href="#Page_35">35</a>, <a href="#Page_69">69</a></dt>
-<dt>Gore Range-Eagle&rsquo;s Nest Wilderness Area, <a href="#Page_20">20</a>, <a href="#Page_21">21</a></dt>
-<dt>Granby, <a href="#Page_20">20</a>, <a href="#Page_62">62</a></dt>
-<dt>Granby Lake, <a href="#Page_103">103</a></dt>
-<dt>Grand <a class="gloss" href="#g_Hogback">Hogback</a>, <a href="#Page_28">28</a>, <a href="#Page_29">29</a></dt>
-<dt>Grand Junction, <a href="#Page_29">29</a>, <a href="#Page_30">30</a>, <a href="#Page_35">35</a>, <a href="#Page_55">55</a></dt>
-<dt>Grand Lake, <a href="#Page_12">12</a>, <a href="#Page_69">69</a>, <a href="#Page_103">103</a>, <a href="#Page_104">104</a></dt>
-<dt>Grand <a class="gloss" href="#g_Mesa">Mesa</a>, <a href="#Page_35">35</a>, <a href="#Page_62">62</a></dt>
-<dt>Grand Valley, <a href="#Page_25">25</a></dt>
-<dt>Gravel, <a href="#Page_75">75</a>, <a href="#Page_97">97</a>-99</dt>
-<dt>Great Sand Dunes National Monument, <a href="#Page_17">17</a>, <a href="#Page_18">18</a>, <a href="#Page_73">73</a></dt>
-<dt class="pb" id="Page_123">123</dt>
-<dt>Green River, <a href="#Page_27">27</a>, <a href="#Page_103">103</a></dt>
-<dt>Green River Basin, <a href="#Page_4">4</a></dt>
-<dt>Green River Canyon, <a href="#Page_31">31</a></dt>
-<dt>Green River Formation, <a href="#Page_64">64</a>, <a href="#Page_95">95</a>-96</dt>
-<dt>Greenhorn Formation, <a href="#Page_101">101</a></dt>
-<dt>Greenhorn Peak, <a href="#Page_16">16</a></dt>
-<dt>Groundwater, <a href="#Page_76">76</a>, <a href="#Page_105">105</a>-106</dt>
-<dt>Gunnison, <a href="#Page_35">35</a></dt>
-<dt>Gunnison, Black Canyon of the, <a href="#Page_36">36</a>, <a href="#Page_37">37</a>, <a href="#Page_44">44</a>, <a href="#Page_71">71</a>, <a href="#Page_105">105</a></dt>
-<dt>Gunnison River, <a href="#Page_35">35</a>, <a href="#Page_36">36</a>, <a href="#Page_37">37</a>, <a href="#Page_105">105</a></dt>
-<dt>Gypsum (mineral), <a href="#Page_22">22</a>, <a href="#Page_30">30</a>, <a href="#Page_75">75</a>, <a href="#Page_101">101</a>-102</dt>
-<dt>Gypsum (town), <a href="#Page_47">47</a>, <a href="#Page_101">101</a></dt>
-<dt>Gypsum Valley, <a href="#Page_30">30</a>, <a href="#Page_47">47</a>, <a href="#Page_101">101</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_H"><b>H</b></dt>
-<dt>Hahn&rsquo;s Peak, <a href="#Page_19">19</a></dt>
-<dt>Harding Sandstone, <a href="#Page_40">40</a>, <a href="#Page_41">41</a></dt>
-<dt>Harvard, Mt., <a href="#Page_22">22</a></dt>
-<dt>Hayden, <a href="#Page_96">96</a>, <a href="#Page_97">97</a></dt>
-<dt>Hayden Pass, <a href="#Page_17">17</a></dt>
-<dt>Hermosa Formation, <a href="#Page_45">45</a>, <a href="#Page_47">47</a></dt>
-<dt>Hidden Valley, <a href="#Page_69">69</a></dt>
-<dt>Horseshoe Amphitheater, <a href="#Page_85">85</a></dt>
-<dt>Horseshoe Park, <a href="#Page_69">69</a></dt>
-<dt>Horsetooth Reservoir, <a href="#Page_103">103</a></dt>
-<dt>Huerfano Basin, <a href="#Page_35">35</a>, <a href="#Page_61">61</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_I"><b>I</b></dt>
-<dt>Ice Age, see Pleistocene</dt>
-<dt>Iceberg Lake, <a href="#Page_66">66</a></dt>
-<dt>Idaho Springs, <a href="#Page_14">14</a>, <a href="#Page_78">78</a>, <a href="#Page_80">80</a></dt>
-<dt>Idaho Springs Formation, <a href="#Page_33">33</a>, <a href="#Page_92">92</a></dt>
-<dt>Independence Pass, <a href="#Page_22">22</a></dt>
-<dt>Iron, <a href="#Page_1">1</a>, <a href="#Page_17">17</a>, <a href="#Page_74">74</a></dt>
-<dt>Ironton, <a href="#Page_78">78</a>, <a href="#Page_88">88</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_J"><b>J</b></dt>
-<dt>Jewel Lake, <a href="#Page_68">68</a></dt>
-<dt>Juniper Mountain, <a href="#Page_26">26</a>, <a href="#Page_29">29</a></dt>
-<dt>Juniper Springs, <a href="#Page_109">109</a></dt>
-<dt>Jurassic, <a href="#Page_7">7</a>, <a href="#Page_9">9</a>, <a href="#Page_23">23</a>, <a href="#Page_36">36</a>, <a href="#Page_52">52</a>-55, <a href="#Page_93">93</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_K"><b>K</b></dt>
-<dt>Kremmling, <a href="#Page_19">19</a>, <a href="#Page_20">20</a>, <a href="#Page_60">60</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_L"><b>L</b></dt>
-<dt>La Junta, <a href="#Page_8">8</a>, <a href="#Page_35">35</a></dt>
-<dt>Lake City, <a href="#Page_77">77</a>, <a href="#Page_78">78</a></dt>
-<dt>Lake County, <a href="#Page_77">77</a></dt>
-<dt>Lamar, <a href="#Page_8">8</a></dt>
-<dt>Landslides, <a href="#Page_111">111</a>-112</dt>
-<dt>La Plata Mountains, <a href="#Page_26">26</a></dt>
-<dt>Laramide Orogeny, <a href="#Page_59">59</a>, <a href="#Page_60">60</a></dt>
-<dt>Laramie Formation, <a href="#Page_57">57</a>, <a href="#Page_58">58</a>, <a href="#Page_97">97</a></dt>
-<dt>Larkspur, <a href="#Page_112">112</a></dt>
-<dt>La Veta Pass, <a href="#Page_17">17</a>, <a href="#Page_18">18</a>, <a href="#Page_37">37</a></dt>
-<dt>Lead, <a href="#Page_74">74</a>, <a href="#Page_75">75</a>, <a href="#Page_80">80</a>, <a href="#Page_81">81</a>, <a href="#Page_82">82</a>, <a href="#Page_83">83</a>, <a href="#Page_85">85</a>, <a href="#Page_86">86</a>, <a href="#Page_89">89</a></dt>
-<dt>Leadville, <a href="#Page_1">1</a>, <a href="#Page_22">22</a>, <a href="#Page_77">77</a>, <a href="#Page_78">78</a>, <a href="#Page_82">82</a>-83</dt>
-<dt>Leadville Limestone, <a href="#Page_43">43</a>, <a href="#Page_44">44</a>, <a href="#Page_83">83</a>, <a href="#Page_88">88</a>, <a href="#Page_99">99</a>, <a href="#Page_106">106</a>, <a href="#Page_109">109</a></dt>
-<dt>Lime, <a href="#Page_75">75</a>, <a href="#Page_101">101</a></dt>
-<dt>Lincoln, Mt., <a href="#Page_21">21</a></dt>
-<dt>Lincoln <a class="gloss" href="#g_Porphyry">Porphyry</a>, <a href="#Page_21">21</a></dt>
-<dt>Lipalian Interval, <a href="#Page_7">7</a>, <a href="#Page_36">36</a>, <a href="#Page_39">39</a></dt>
-<dt>Littleton, <a href="#Page_113">113</a></dt>
-<dt>Logan County, <a href="#Page_95">95</a></dt>
-<dt>Longs Peak, <a href="#Page_3">3</a>, <a href="#Page_11">11</a>, <a href="#Page_12">12</a>, <a href="#Page_68">68</a></dt>
-<dt>Loveland, <a href="#Page_14">14</a>, <a href="#Page_102">102</a></dt>
-<dt>Loveland Pass, <a href="#Page_12">12</a></dt>
-<dt>Lykins Formation, <a href="#Page_12">12</a>, <a href="#Page_51">51</a>, <a href="#Page_52">52</a>, <a href="#Page_101">101</a></dt>
-<dt>Lyons, <a href="#Page_14">14</a>, <a href="#Page_49">49</a>, <a href="#Page_99">99</a>, <a href="#Page_100">100</a>, <a href="#Page_101">101</a></dt>
-<dt>Lyons Sandstone, <a href="#Page_12">12</a>, <a href="#Page_48">48</a>, <a href="#Page_49">49</a>, <a href="#Page_50">50</a>, <a href="#Page_99">99</a>, <a href="#Page_100">100</a>, <a href="#Page_101">101</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_M"><b>M</b></dt>
-<dt>Magnolia, <a href="#Page_79">79</a></dt>
-<dt>Mancos Shale, <a href="#Page_30">30</a>, <a href="#Page_95">95</a></dt>
-<dt>Manitou, <a href="#Page_39">39</a>, <a href="#Page_106">106</a>, <a href="#Page_107">107</a>, <a href="#Page_110">110</a></dt>
-<dt>Manitou Formation, <a href="#Page_40">40</a>, <a href="#Page_41">41</a>, <a href="#Page_110">110</a></dt>
-<dt>Manitou Springs, <a href="#Page_109">109</a></dt>
-<dt>Marble, <a href="#Page_24">24</a>, <a href="#Page_99">99</a></dt>
-<dt>Marble Mountain, <a href="#Page_106">106</a></dt>
-<dt>Maroon Bells, <a href="#pic_2">Front.</a>, <a href="#Page_24">24</a>, <a href="#Page_50">50</a></dt>
-<dt>Maroon Creek, <a href="#Page_24">24</a></dt>
-<dt>Maroon Formation, <a href="#Page_50">50</a></dt>
-<dt>Mary&rsquo;s Lake, <a href="#Page_103">103</a></dt>
-<dt>Massive, Mt., <a href="#Page_82">82</a></dt>
-<dt>McDermott Formation, <a href="#Page_58">58</a></dt>
-<dt><a class="gloss" href="#g_Mesa">Mesa</a> de Maya, <a href="#Page_8">8</a>, <a href="#Page_35">35</a>, <a href="#Page_62">62</a></dt>
-<dt>Mesa Verde, <a href="#Page_28">28</a>, <a href="#Page_29">29</a>, <a href="#Page_35">35</a></dt>
-<dt>Mesa Verde Formation, <a href="#Page_30">30</a>, <a href="#Page_58">58</a>, <a href="#Page_108">108</a></dt>
-<dt>Mesa Verde National Park, <a href="#Page_31">31</a>, <a href="#Page_71">71</a>, <a href="#Page_108">108</a></dt>
-<dt>Mesozoic (see also Triassic etc.), <a href="#Page_7">7</a>, <a href="#Page_10">10</a>, <a href="#Page_11">11</a>, <a href="#Page_12">12</a>, <a href="#Page_14">14</a>, <a href="#Page_15">15</a>, <a href="#Page_26">26</a>, <a href="#Page_28">28</a>, <a href="#Page_51">51</a>-58, <a href="#Page_60">60</a>, <a href="#Page_93">93</a></dt>
-<dt>Mestas, Mt., <a href="#Page_17">17</a></dt>
-<dt>Middle Park, <a href="#Page_4">4</a>, <a href="#Page_16">16</a>, <a href="#Page_35">35</a>, <a href="#Page_61">61</a></dt>
-<dt>Million Dollar Highway, <a href="#Page_87">87</a>, <a href="#Page_88">88</a></dt>
-<dt>Mills Lake, <a href="#Page_68">68</a></dt>
-<dt>Milner Pass, <a href="#Page_66">66</a></dt>
-<dt>Minturn, <a href="#Page_39">39</a></dt>
-<dt>Minturn Formation, <a href="#Page_45">45</a>, <a href="#Page_46">46</a>, <a href="#Page_47">47</a></dt>
-<dt>Miocene, <a href="#Page_66">66</a>, <a href="#Page_67">67</a>, <a href="#Page_87">87</a></dt>
-<dt class="pb" id="Page_124">124</dt>
-<dt>Mississippian, <a href="#Page_6">6</a>, <a href="#Page_7">7</a>, <a href="#Page_43">43</a>-44, <a href="#Page_83">83</a>, <a href="#Page_106">106</a>, <a href="#Page_109">109</a></dt>
-<dt>Moenkopi Formation, <a href="#Page_52">52</a></dt>
-<dt>Molas Formation, <a href="#Page_44">44</a></dt>
-<dt>Molas Lake, <a href="#Page_25">25</a></dt>
-<dt>Molybdenum, <a href="#Page_1">1</a>, <a href="#Page_74">74</a>, <a href="#Page_75">75</a>, <a href="#Page_76">76</a>, <a href="#Page_77">77</a>, <a href="#Page_91">91</a>-92</dt>
-<dt>Monarch Pass, <a href="#Page_23">23</a></dt>
-<dt>Morgan County, <a href="#Page_95">95</a></dt>
-<dt>Morrison, <a href="#Page_53">53</a>, <a href="#Page_54">54</a>, <a href="#Page_55">55</a></dt>
-<dt>Morrison Formation, <a href="#Page_12">12</a>, <a href="#Page_36">36</a>, <a href="#Page_51">51</a>, <a href="#Page_53">53</a>, <a href="#Page_55">55</a>, <a href="#Page_93">93</a></dt>
-<dt>Mosca Pass, <a href="#Page_17">17</a>, <a href="#Page_73">73</a></dt>
-<dt>Mosquito Pass, <a href="#Page_85">85</a></dt>
-<dt>Mosquito Range, <a href="#Page_21">21</a>, <a href="#Page_22">22</a>, <a href="#Page_35">35</a>, <a href="#Page_39">39</a>, <a href="#Page_69">69</a></dt>
-<dt>Mountain Province, <a href="#Page_3">3</a>, <a href="#Page_4">4</a>, <a href="#Page_10">10</a>-27, <a href="#Page_35">35</a>, <a href="#Page_46">46</a>, <a href="#Page_93">93</a>, <a href="#Page_94">94</a>, <a href="#Page_101">101</a>, <a href="#Page_102">102</a>, <a href="#Page_103">103</a>, <a href="#Page_109">109</a>, <a href="#Page_111">111</a></dt>
-<dt>Mt. Bross, <a href="#Page_21">21</a></dt>
-<dt>Mt. Columbia, <a href="#Page_22">22</a></dt>
-<dt>Mt. Democrat, <a href="#Page_21">21</a></dt>
-<dt>Mt. Elbert, <a href="#Page_22">22</a></dt>
-<dt>Mt. Evans, <a href="#Page_3">3</a>, <a href="#Page_12">12</a></dt>
-<dt>Mt. Garfield, <a href="#Page_30">30</a></dt>
-<dt>Mt. Harvard, <a href="#Page_22">22</a></dt>
-<dt>Mt. Lincoln, <a href="#Page_21">21</a></dt>
-<dt>Mt. Massive, <a href="#Page_82">82</a></dt>
-<dt>Mt. Mestas, <a href="#Page_17">17</a></dt>
-<dt>Mt. Princeton, <a href="#Page_22">22</a></dt>
-<dt>Mt. Princeton Hot Springs, <a href="#Page_22">22</a>, <a href="#Page_110">110</a></dt>
-<dt>Mt. Sneffels, <a href="#Page_87">87</a>, <a href="#Page_88">88</a></dt>
-<dt>Mt. Sopris, <a href="#Page_24">24</a></dt>
-<dt>Mt. Yale, <a href="#Page_22">22</a></dt>
-<dt>Mt. Zirkel, <a href="#Page_19">19</a></dt>
-<dt>Music Pass, <a href="#Page_17">17</a>, <a href="#Page_73">73</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_N"><b>N</b></dt>
-<dt>Navajo Sandstone, <a href="#Page_52">52</a></dt>
-<dt>Nederland, <a href="#Page_78">78</a>, <a href="#Page_79">79</a></dt>
-<dt>Needle Mountains, <a href="#Page_26">26</a></dt>
-<dt>Niobrara Formation, <a href="#Page_57">57</a>, <a href="#Page_101">101</a></dt>
-<dt>North Park, <a href="#Page_4">4</a>, <a href="#Page_16">16</a>, <a href="#Page_35">35</a>, <a href="#Page_58">58</a>, <a href="#Page_61">61</a>, <a href="#Page_94">94</a>, <a href="#Page_97">97</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_O"><b>O</b></dt>
-<dt>Oil, <a href="#Page_1">1</a>, <a href="#Page_29">29</a>, <a href="#Page_30">30</a>, <a href="#Page_75">75</a>, <a href="#Page_76">76</a>, <a href="#Page_94">94</a>-96</dt>
-<dt>Oil Creek, <a href="#Page_94">94</a></dt>
-<dt>Oil shale, <a href="#Page_95">95</a>-96</dt>
-<dt>Oligocene, <a href="#Page_66">66</a>, <a href="#Page_67">67</a></dt>
-<dt>Ordovician, <a href="#Page_7">7</a>, <a href="#Page_40">40</a>-41, <a href="#Page_83">83</a>, <a href="#Page_106">106</a></dt>
-<dt>Orient, <a href="#Page_17">17</a></dt>
-<dt>Oro, <a href="#Page_82">82</a></dt>
-<dt>Otero County, <a href="#Page_105">105</a></dt>
-<dt>Ouray, <a href="#Page_4">4</a>, <a href="#Page_25">25</a>, <a href="#Page_26">26</a>, <a href="#Page_34">34</a>, <a href="#Page_42">42</a>, <a href="#Page_78">78</a>, <a href="#Page_87">87</a>-88</dt>
-<dt>Ouray Formation, <a href="#Page_42">42</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_P"><b>P</b></dt>
-<dt>Pagoda Mountain, <a href="#Page_68">68</a></dt>
-<dt>Pagosa Springs, <a href="#Page_102">102</a>, <a href="#Page_109">109</a></dt>
-<dt>Paleozoic (see also Cambrian etc.), <a href="#Page_7">7</a>, <a href="#Page_10">10</a>, <a href="#Page_11">11</a>, <a href="#Page_12">12</a>, <a href="#Page_14">14</a>, <a href="#Page_15">15</a>, <a href="#Page_17">17</a>, <a href="#Page_21">21</a>, <a href="#Page_22">22</a>, <a href="#Page_24">24</a>, <a href="#Page_26">26</a>, <a href="#Page_27">27</a>, <a href="#Page_28">28</a>, <a href="#Page_30">30</a>, <a href="#Page_34">34</a>, <a href="#Page_37">37</a>, <a href="#Page_38">38</a>-50, <a href="#Page_60">60</a>, <a href="#Page_64">64</a>, <a href="#Page_77">77</a>, <a href="#Page_95">95</a>, <a href="#Page_98">98</a>, <a href="#Page_106">106</a>, <a href="#Page_107">107</a></dt>
-<dt>Paradox Basin, <a href="#Page_4">4</a>, <a href="#Page_47">47</a>, <a href="#Page_95">95</a>, <a href="#Page_101">101</a></dt>
-<dt>Paradox Valley, <a href="#Page_30">30</a>, <a href="#Page_101">101</a></dt>
-<dt>Park Range, <a href="#Page_19">19</a>-20, <a href="#Page_35">35</a>, <a href="#Page_69">69</a></dt>
-<dt>Parting Sandstone, <a href="#Page_42">42</a></dt>
-<dt>Pawnee Buttes, <a href="#Page_9">9</a>, <a href="#Page_66">66</a>, <a href="#Page_67">67</a></dt>
-<dt>Peak Province, see Mountain Province</dt>
-<dt>Peat, <a href="#Page_75">75</a></dt>
-<dt>Pennsylvanian, <i><a href="#pic_2">Front.</a></i>, <a href="#Page_6">6</a>, <a href="#Page_7">7</a>, <a href="#Page_14">14</a>, <a href="#Page_23">23</a>, <a href="#Page_44">44</a>-47, <a href="#Page_48">48</a>, <a href="#Page_50">50</a>, <a href="#Page_83">83</a>, <a href="#Page_95">95</a>, <a href="#Page_101">101</a>, <a href="#Page_106">106</a>, <a href="#Page_109">109</a></dt>
-<dt>Permian, <i><a href="#pic_2">Front.</a></i>, <a href="#Page_7">7</a>, <a href="#Page_23">23</a>, <a href="#Page_48">48</a>-50, <a href="#Page_95">95</a>, <a href="#Page_99">99</a>, <a href="#Page_100">100</a>, <a href="#Page_101">101</a></dt>
-<dt>Petroleum, <a href="#Page_1">1</a>, <a href="#Page_29">29</a>, <a href="#Page_30">30</a>, <a href="#Page_75">75</a>, <a href="#Page_76">76</a>, <a href="#Page_94">94</a>-96</dt>
-<dt>Phosphoria Formation, <a href="#Page_50">50</a></dt>
-<dt>Piceance Basin, <a href="#Page_29">29</a></dt>
-<dt>Pierre Formation, <a href="#Page_57">57</a>, <a href="#Page_94">94</a>, <a href="#Page_98">98</a></dt>
-<dt>Pikes Peak, <a href="#Page_3">3</a>, <a href="#Page_4">4</a>, <a href="#Page_11">11</a>, <a href="#Page_12">12</a>, <a href="#Page_15">15</a>, <a href="#Page_65">65</a>, <a href="#Page_90">90</a>, <a href="#Page_91">91</a>, <a href="#Page_110">110</a></dt>
-<dt>Pikes Peak <a class="gloss" href="#g_Granite">Granite</a>, <a href="#Page_4">4</a>, <a href="#Page_14">14</a>, <a href="#Page_33">33</a>, <a href="#Page_36">36</a></dt>
-<dt>Plains Province, see Prairie Province</dt>
-<dt><a class="gloss" href="#g_Plateau">Plateau</a> Province, <a href="#Page_3">3</a>, <a href="#Page_4">4</a>, <a href="#Page_9">9</a>, <a href="#Page_28">28</a>-31, <a href="#Page_35">35</a>, <a href="#Page_46">46</a>, <a href="#Page_71">71</a>, <a href="#Page_75">75</a>, <a href="#Page_93">93</a>, <a href="#Page_94">94</a>, <a href="#Page_96">96</a>, <a href="#Page_101">101</a>, <a href="#Page_103">103</a>, <a href="#Page_107">107</a>, <a href="#Page_110">110</a></dt>
-<dt>Platte River, <a href="#Page_3">3</a></dt>
-<dt>Pleistocene, <a href="#Page_7">7</a>, <a href="#Page_8">8</a>, <a href="#Page_25">25</a>, <a href="#Page_59">59</a>, <a href="#Page_68">68</a>-73, <a href="#Page_105">105</a>, <a href="#Page_106">106</a></dt>
-<dt>Plum Creek, <a href="#Page_112">112</a></dt>
-<dt>Poncha Springs, <a href="#Page_109">109</a></dt>
-<dt>Prairie Province, <a href="#Page_3">3</a>, <a href="#Page_8">8</a>-10, <a href="#Page_12">12</a>, <a href="#Page_35">35</a>, <a href="#Page_66">66</a>, <a href="#Page_72">72</a>, <a href="#Page_75">75</a>, <a href="#Page_94">94</a>, <a href="#Page_96">96</a>, <a href="#Page_103">103</a>, <a href="#Page_105">105</a></dt>
-<dt>Precambrian, <a href="#Page_7">7</a>, <a href="#Page_10">10</a>, <a href="#Page_11">11</a>, <a href="#Page_14">14</a>, <a href="#Page_15">15</a>, <a href="#Page_16">16</a>, <a href="#Page_17">17</a>, <a href="#Page_19">19</a>, <a href="#Page_20">20</a>, <a href="#Page_21">21</a>, <a href="#Page_26">26</a>, <a href="#Page_33">33</a>-37, <a href="#Page_40">40</a>, <a href="#Page_60">60</a>, <a href="#Page_64">64</a>, <a href="#Page_68">68</a>, <a href="#Page_77">77</a>, <a href="#Page_87">87</a>, <a href="#Page_91">91</a>, <a href="#Page_92">92</a>, <a href="#Page_93">93</a>, <a href="#Page_109">109</a></dt>
-<dt>Princeton, Mt., <a href="#Page_22">22</a></dt>
-<dt>Pueblo, <a href="#Page_23">23</a>, <a href="#Page_97">97</a></dt>
-<dt>Pumice, <a href="#Page_75">75</a></dt>
-<dt class="pb" id="Page_125">125</dt>
-<dt>Purgatoire Formation, <a href="#Page_105">105</a></dt>
-<dt><a class="gloss" href="#g_Pyrite">Pyrites</a>, <a href="#Page_75">75</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_Q"><b>Q</b></dt>
-<dt>Quandary Peak, <a href="#Page_21">21</a></dt>
-<dt>Quaternary, <a href="#Page_7">7</a>, <a href="#Page_8">8</a>, <a href="#Page_25">25</a>, <a href="#Page_59">59</a>, <a href="#Page_68">68</a>-73, <a href="#Page_105">105</a>, <a href="#Page_106">106</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_R"><b>R</b></dt>
-<dt>Rabbit Ears Pass, <a href="#Page_19">19</a></dt>
-<dt>Rabbit Ears Range, <a href="#Page_20">20</a>, <a href="#Page_35">35</a>, <a href="#Page_62">62</a></dt>
-<dt>Radium, <a href="#Page_93">93</a></dt>
-<dt>Rampart Range, <a href="#Page_15">15</a>, <a href="#Page_97">97</a>, <a href="#Page_98">98</a></dt>
-<dt>Rangely, <a href="#Page_29">29</a>, <a href="#Page_95">95</a></dt>
-<dt>Raspberry Mountain, <a href="#Page_112">112</a></dt>
-<dt>Rattlesnake Reservoir, <a href="#Page_103">103</a></dt>
-<dt>Raton Basin, <a href="#Page_61">61</a></dt>
-<dt>Raton Pass, <a href="#Page_61">61</a></dt>
-<dt>Red Cliff, <a href="#Page_39">39</a></dt>
-<dt>Red Mountain, <a href="#Page_88">88</a></dt>
-<dt>Red Mountain Creek, <a href="#Page_88">88</a></dt>
-<dt>Red Rocks Park, <a href="#Page_14">14</a>, <a href="#Page_37">37</a>, <a href="#Page_47">47</a></dt>
-<dt>Redstone, <a href="#Page_24">24</a></dt>
-<dt>Rico, <a href="#Page_26">26</a></dt>
-<dt>Rico Range, <a href="#Page_26">26</a></dt>
-<dt>Rifle, <a href="#Page_64">64</a></dt>
-<dt>Rio Grande, <a href="#Page_35">35</a></dt>
-<dt>Roan <a class="gloss" href="#g_Plateau">Plateau</a>, <a href="#Page_28">28</a>, <a href="#Page_29">29</a>, <a href="#Page_35">35</a></dt>
-<dt>Rocky Mountain National Park, <a href="#Page_11">11</a>, <a href="#Page_12">12</a>, <a href="#Page_66">66</a>, <a href="#Page_68">68</a>, <a href="#Page_71">71</a>, <a href="#Page_104">104</a></dt>
-<dt>Roncarbo, <a href="#Page_97">97</a></dt>
-<dt>Royal Gorge, <a href="#Page_37">37</a>, <a href="#Page_71">71</a></dt>
-<dt>Ruedi, <a href="#Page_105">105</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_S"><b>S</b></dt>
-<dt>St. Mary&rsquo;s <a class="gloss" href="#g_Glacier">Glacier</a>, <a href="#Page_71">71</a></dt>
-<dt>Salida, <a href="#Page_17">17</a>, <a href="#Page_21">21</a>, <a href="#Page_35">35</a></dt>
-<dt>Salina, <a href="#Page_79">79</a></dt>
-<dt>Sand, <a href="#Page_75">75</a>, <a href="#Page_97">97</a>-99</dt>
-<dt>Sangre de Cristo Range, <a href="#Page_10">10</a>, <a href="#Page_17">17</a>-18, <a href="#Page_35">35</a>, <a href="#Page_47">47</a>, <a href="#Page_61">61</a>, <a href="#Page_69">69</a>, <a href="#Page_73">73</a>, <a href="#Page_90">90</a>, <a href="#Page_105">105</a>, <a href="#Page_106">106</a></dt>
-<dt>San Juan Basin, <a href="#Page_95">95</a></dt>
-<dt>San Juan County, <a href="#Page_78">78</a></dt>
-<dt>San Juan Formation, <a href="#Page_88">88</a></dt>
-<dt>San Juan Mountains, <a href="#Page_4">4</a>, <a href="#Page_25">25</a>-26, <a href="#Page_35">35</a>, <a href="#Page_52">52</a>, <a href="#Page_65">65</a>, <a href="#Page_69">69</a>, <a href="#Page_77">77</a>, <a href="#Page_85">85</a>, <a href="#Page_86">86</a>, <a href="#Page_87">87</a>, <a href="#Page_88">88</a>, <a href="#Page_105">105</a></dt>
-<dt>San Luis Valley, <a href="#Page_4">4</a>, <a href="#Page_35">35</a>, <a href="#Page_44">44</a>, <a href="#Page_61">61</a>, <a href="#Page_67">67</a>, <a href="#Page_73">73</a>, <a href="#Page_96">96</a>, <a href="#Page_106">106</a></dt>
-<dt>San Miguel Range, <a href="#Page_26">26</a></dt>
-<dt>Santa Fe Formation, <a href="#Page_67">67</a>, <a href="#Page_105">105</a></dt>
-<dt>Sawatch Range, <a href="#Page_22">22</a>-23, <a href="#Page_35">35</a>, <a href="#Page_39">39</a>, <a href="#Page_69">69</a>, <a href="#Page_82">82</a>, <a href="#Page_106">106</a></dt>
-<dt>Sawatch Sandstone, <a href="#Page_34">34</a>, <a href="#Page_39">39</a>, <a href="#Page_40">40</a></dt>
-<dt>Sedalia, <a href="#Page_61">61</a></dt>
-<dt>Shadow Mountain Reservoir, <a href="#Page_103">103</a></dt>
-<dt>Sierra Blanca, <a href="#Page_17">17</a>, <a href="#Page_18">18</a></dt>
-<dt>Silurian, <a href="#Page_7">7</a>, <a href="#Page_42">42</a></dt>
-<dt>Silver, <a href="#Page_22">22</a>, <a href="#Page_74">74</a>, <a href="#Page_77">77</a>-91</dt>
-<dt>Silver Cliff, <a href="#Page_16">16</a>, <a href="#Page_77">77</a>, <a href="#Page_78">78</a></dt>
-<dt>Silver Plume, <a href="#Page_78">78</a>, <a href="#Page_81">81</a></dt>
-<dt>Silver Plume <a class="gloss" href="#g_Granite">Granite</a>, <a href="#Page_33">33</a>, <a href="#Page_35">35</a></dt>
-<dt>Silverton, <a href="#Page_4">4</a>, <a href="#Page_26">26</a>, <a href="#Page_74">74</a>, <a href="#Page_77">77</a>, <a href="#Page_78">78</a>, <a href="#Page_85">85</a>-86, <a href="#Page_88">88</a></dt>
-<dt>Sinbad Valley, <a href="#Page_101">101</a></dt>
-<dt>Sneffels, Mt., <a href="#Page_87">87</a>, <a href="#Page_88">88</a></dt>
-<dt>Sopris, Mt., <a href="#Page_24">24</a></dt>
-<dt>South Park, <a href="#Page_4">4</a>, <a href="#Page_16">16</a>, <a href="#Page_21">21</a>, <a href="#Page_35">35</a>, <a href="#Page_61">61</a>, <a href="#Page_65">65</a>, <a href="#Page_84">84</a>, <a href="#Page_97">97</a></dt>
-<dt>South Platte River, <a href="#Page_1">1</a>, <a href="#Page_3">3</a>, <a href="#Page_35">35</a>, <a href="#Page_85">85</a>, <a href="#Page_103">103</a>, <a href="#Page_104">104</a>, <a href="#Page_112">112</a>, <a href="#Page_113">113</a></dt>
-<dt>Spanish Cave, <a href="#Page_106">106</a></dt>
-<dt>Spanish Peaks, <a href="#Page_10">10</a>, <a href="#Page_18">18</a>, <a href="#Page_62">62</a></dt>
-<dt>Specimen Mountain, <a href="#Page_66">66</a></dt>
-<dt>Springs, <a href="#Page_17">17</a>, <a href="#Page_22">22</a>, <a href="#Page_109">109</a>-110</dt>
-<dt>Steamboat Springs, <a href="#Page_97">97</a>, <a href="#Page_109">109</a></dt>
-<dt>Summit County, <a href="#Page_77">77</a></dt>
-<dt>Sunshine, <a href="#Page_79">79</a></dt>
-<dt>Sunshine Peak <a class="gloss" href="#g_Rhyolite">Rhyolite</a>, <a href="#Page_87">87</a></dt>
-<dt>Swandyke <a class="gloss" href="#g_Gneiss">Gneiss</a>, <a href="#Page_33">33</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_T"><b>T</b></dt>
-<dt>Table Mountain, <a href="#Page_8">8</a>, <a href="#Page_62">62</a>, <a href="#Page_111">111</a></dt>
-<dt>Telluride, <a href="#Page_26">26</a>, <a href="#Page_74">74</a>, <a href="#Page_77">77</a>, <a href="#Page_78">78</a></dt>
-<dt>Tenmile Gorge, <a href="#Page_21">21</a></dt>
-<dt>Tenmile Range, <a href="#Page_21">21</a>, <a href="#Page_91">91</a></dt>
-<dt>Tertiary, <a href="#Page_7">7</a>, <a href="#Page_15">15</a>, <a href="#Page_20">20</a>, <a href="#Page_21">21</a>, <a href="#Page_25">25</a>, <a href="#Page_26">26</a>, <a href="#Page_29">29</a>, <a href="#Page_59">59</a>-67, <a href="#Page_73">73</a>, <a href="#Page_77">77</a>, <a href="#Page_83">83</a>, <a href="#Page_87">87</a>, <a href="#Page_88">88</a>, <a href="#Page_89">89</a>, <a href="#Page_90">90</a>, <a href="#Page_91">91</a>, <a href="#Page_92">92</a>, <a href="#Page_93">93</a>, <a href="#Page_95">95</a>, <a href="#Page_96">96</a>, <a href="#Page_97">97</a></dt>
-<dt>Tin, <a href="#Page_75">75</a></dt>
-<dt>Tincup, <a href="#Page_22">22</a>, <a href="#Page_77">77</a>, <a href="#Page_78">78</a></dt>
-<dt>Trail Ridge Road, <a href="#Page_12">12</a>, <a href="#Page_66">66</a></dt>
-<dt>Treasure Mountain <a class="gloss" href="#g_Granite">Granite</a>, <a href="#Page_99">99</a></dt>
-<dt>Triassic, <a href="#Page_7">7</a>, <a href="#Page_23">23</a>, <a href="#Page_51">51</a>-52, <a href="#Page_93">93</a>, <a href="#Page_101">101</a></dt>
-<dt>Trinidad, <a href="#Page_8">8</a>, <a href="#Page_61">61</a>, <a href="#Page_96">96</a>, <a href="#Page_97">97</a></dt>
-<dt>Trout Creek Pass, <a href="#Page_21">21</a>, <a href="#Page_22">22</a></dt>
-<dt>Tungsten, <a href="#Page_1">1</a>, <a href="#Page_74">74</a>, <a href="#Page_75">75</a>, <a href="#Page_79">79</a></dt>
-<dt>Tyndall <a class="gloss" href="#g_Glacier">Glacier</a>, <a href="#Page_71">71</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_U"><b>U</b></dt>
-<dt>Uinta Basin, <a href="#Page_4">4</a>, <a href="#Page_29">29</a>, <a href="#Page_64">64</a>, <a href="#Page_75">75</a>, <a href="#Page_95">95</a></dt>
-<dt>Uinta Mountain Formation, <a href="#Page_26">26</a></dt>
-<dt>Uinta Mountains, <a href="#Page_4">4</a>, <a href="#Page_10">10</a>, <a href="#Page_26">26</a>-27, <a href="#Page_29">29</a>, <a href="#Page_35">35</a>, <a href="#Page_37">37</a>, <a href="#Page_64">64</a></dt>
-<dt>Uncompahgre Gorge, <a href="#Page_87">87</a></dt>
-<dt class="pb" id="Page_126">126</dt>
-<dt>Uncompahgre <a class="gloss" href="#g_Plateau">Plateau</a>, <a href="#Page_29">29</a>, <a href="#Page_35">35</a>, <a href="#Page_44">44</a></dt>
-<dt>Uncompahgre Quartzite, <a href="#Page_87">87</a></dt>
-<dt>Urad Mine, <a href="#Page_92">92</a></dt>
-<dt>Uranium, <a href="#Page_1">1</a>, <a href="#Page_29">29</a>, <a href="#Page_80">80</a>, <a href="#Page_93">93</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_V"><b>V</b></dt>
-<dt>Vail, <a href="#Page_21">21</a>, <a href="#Page_47">47</a></dt>
-<dt>Vail Pass, <a href="#Page_21">21</a></dt>
-<dt>Valmont, <a href="#Page_62">62</a></dt>
-<dt>Vanadium, <a href="#Page_74">74</a>, <a href="#Page_75">75</a>, <a href="#Page_93">93</a></dt>
-<dt>Villa Grove, <a href="#Page_17">17</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_W"><b>W</b></dt>
-<dt>Walden, <a href="#Page_20">20</a></dt>
-<dt>Walsenburg, <a href="#Page_35">35</a>, <a href="#Page_61">61</a>, <a href="#Page_96">96</a></dt>
-<dt>Ward, <a href="#Page_78">78</a></dt>
-<dt>Water, <a href="#Page_76">76</a>, <a href="#Page_103">103</a>-110</dt>
-<dt>Waunita Hot Springs, <a href="#Page_109">109</a></dt>
-<dt>Weber Sandstone, <a href="#Page_95">95</a></dt>
-<dt>West Elk Mountains, <a href="#Page_24">24</a>, <a href="#Page_35">35</a>, <a href="#Page_69">69</a></dt>
-<dt>Wet Mountains, <a href="#Page_16">16</a>, <a href="#Page_35">35</a>, <a href="#Page_61">61</a>, <a href="#Page_95">95</a></dt>
-<dt>Wet Mountain Valley, <a href="#Page_35">35</a></dt>
-<dt>Whiskey Creek Pass, <a href="#Page_17">17</a></dt>
-<dt>White River, <a href="#Page_35">35</a>, <a href="#Page_95">95</a></dt>
-<dt>White River Formation, <a href="#Page_66">66</a></dt>
-<dt>White River <a class="gloss" href="#g_Plateau">Plateau</a>, <a href="#Page_28">28</a>, <a href="#Page_29">29</a>, <a href="#Page_35">35</a>, <a href="#Page_43">43</a>, <a href="#Page_107">107</a>, <a href="#Page_109">109</a></dt>
-<dt>Williams Canyon, <a href="#Page_37">37</a>, <a href="#Page_39">39</a></dt>
-<dt>Willow Creek Pass, <a href="#Page_20">20</a></dt>
-<dt>Willow Creek Reservoir, <a href="#Page_103">103</a></dt>
-<dt>Wingate Formation, <a href="#Page_51">51</a>, <a href="#Page_52">52</a>, <a href="#Page_101">101</a></dt>
-<dt>Wolcott, <a href="#Page_22">22</a>, <a href="#Page_47">47</a></dt>
-<dt>Wolford Mountain, <a href="#Page_60">60</a></dt>
-<dt>Woodland Park, <a href="#Page_110">110</a></dt>
-<dt>Woods Lake, <a href="#Page_107">107</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_Y"><b>Y</b></dt>
-<dt>Yale, Mt., <a href="#Page_22">22</a></dt>
-<dt>Yampa River, <a href="#Page_3">3</a>, <a href="#Page_27">27</a>, <a href="#Page_31">31</a>, <a href="#Page_35">35</a>, <a href="#Page_97">97</a></dt>
-<dt>Yule Marble, <a href="#Page_24">24</a>, <a href="#Page_99">99</a></dt>
-</dl>
-<dl class="index">
-<dt class="center" id="index_Z"><b>Z</b></dt>
-<dt>Zinc, <a href="#Page_74">74</a>, <a href="#Page_75">75</a>, <a href="#Page_80">80</a>, <a href="#Page_82">82</a>, <a href="#Page_83">83</a>, <a href="#Page_85">85</a>, <a href="#Page_86">86</a>, <a href="#Page_89">89</a></dt>
-<dt>Zirkel, Mt., <a href="#Page_19">19</a></dt>
-</dl>
-<h2>Transcriber&rsquo;s Notes</h2>
-<ul>
-<li>Retained publication information from the printed edition: this eBook is public-domain in the country of publication.</li>
-<li>In the text versions only, text in italics is delimited by _underscores_.</li>
-<li>In the ASCII version only, subscripted numbers are preceded by underscore and delimited by brackets.</li>
-</ul>
-
-
-
-
-
-
-
-<pre>
-
-
-
-
-
-End of the Project Gutenberg EBook of Prairie Peak and Plateau, by 
-John Chronic and Halka Chronic
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