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+This eBook, including all associated images, markup, improvements,
+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 #63396 (https://www.gutenberg.org/ebooks/63396)
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-The Project Gutenberg EBook of The Geologic Story of the Great Plains, by 
-Donald E. Trimble
-
-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: The Geologic Story of the Great Plains
-
-Author: Donald E. Trimble
-
-Release Date: October 6, 2020 [EBook #63396]
-
-Language: English
-
-Character set encoding: UTF-8
-
-*** START OF THIS PROJECT GUTENBERG EBOOK GEOLOGIC STORY--GREAT PLAINS ***
-
-
-
-
-Produced by Stephen Hutcheson and the Online Distributed
-Proofreading Team at https://www.pgdp.net
-
-
-
-
-
-
-[Illustration: DENVER, COLORADO]
-
-  _But from these immense prairies may arise one great advantage to the
-  United States, viz., the restriction of our population to some certain
-  limits, and thereby a continuation of the union. Our citizens being so
-  prone to rambling, and extending themselves on the frontiers, will,
-  through necessity, be constrained to limit their extent on the west to
-  the borders of the Missouri and the Mississippi, while they leave the
-  prairies, incapable of cultivation, to the wandering and uncivilized
-  Aborigines of the country.
-                                                           Zebulon Pike_
-
-  Exploratory Travels Through The Western Territories of North America
-  comprising a voyage from St. Louis, on the Mississippi, to the source
-  of that river, and a journey through the interior of Louisiana and the
-  north-eastern provinces of New Spain. Performed in the years 1805,
-  1806, and 1807, by order of the Government of the United States. By
-  Zebulon Montgomery Pike. Published by Paternoster-Row, London, 1811:
-  W. H. Lawrence and Company, Denver, 1889. Quotation from pages
-  230-231, 1889 edition.
-
-
-
-
-                         The GEOLOGIC STORY of
-                            The GREAT PLAINS
-
-
-                          By DONALD E. TRIMBLE
-
-
-_A nontechnical description of the origin and evolution of the landscape
-                          of the Great Plains_
-
-
-                    GEOLOGICAL SURVEY BULLETIN 1493
-
-
-                UNITED STATES DEPARTMENT OF THE INTERIOR
-                      CECIL D. ANDRUS, _Secretary_
-
-                           GEOLOGICAL SURVEY
-                     H. William Menard, _Director_
-
-[Illustration: U. S. DEPARTMENT OF THE INTERIOR · March 3, 1849]
-
-       UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1980
-
-  Library of Congress Cataloging in Publication Data
-  Trimble, Donald E.
-  The geologic story of the Great Plains.
-  (U.S. Geological Survey Bulletin 1493)
-  Bibliography: p. 50
-  Includes index.
-  Supt. of Docs. no.: I 19.3: 1493
-  I. Geology—Great Plains. I. Title.
-  II. Series: United States Geological Survey Bulletin 1493.
-  QE75.B9 no. 1493 [QE71] 557.3s [557.8] 80-607022
-
-
- For sale by the Superintendent of Documents, U.S. Government Printing
-                                 Office
-                         Washington, D.C. 20402
-
-
-
-
-                                CONTENTS
-
-
-  Introduction                                                          1
-  What is the Great Plains?                                             5
-  The Great Plains—its parts                                            7
-  Early history                                                        10
-      Warping and stream deposition                                    11
-  Sculpturing the land                                                 18
-  Landforms of today—The surface features of the Great Plains          19
-      Black Hills                                                      20
-      Central Texas Uplift                                             22
-      Raton Section                                                    23
-      High Plains                                                      25
-      Missouri Plateau                                                 32
-          Preglacial Drainage                                          33
-          Glaciated Missouri Plateau                                   33
-          Unglaciated Missouri Plateau                                 36
-      The Colorado Piedmont                                            42
-      Pecos Valley                                                     45
-      Edwards Plateau                                                  46
-      Plains Border Section                                            48
-  Epilogue                                                             49
-  Acknowledgments                                                      49
-  Some source references                                               50
-
-
-
-
-                                FIGURES
-
-
-  FRONTISPIECE. Aerial photograph of Denver.
-  1. Index map                                                          3
-  2-3. Maps showing:
-      2. Physical divisions of the United States and maximum extent
-            of the continental ice sheets                               6
-      3. The Great Plains province and its sections                     8
-  4. Photograph of Mescalero escarpment and southern High Plains        9
-  5. Geologic time chart                                               12
-  6-8. Maps showing:
-      6. Paleogeography of U.S. in Late Cretaceous                     14
-      7. Structural setting of the Great Plains                        14
-      8. Progressive southward expansion of areas of deposition        17
-  9. Photograph of Big Horn strip mine at Acme, Wyo.                   18
-  10. Black Hills diagram                                              21
-  11-16. Photographs showing:
-      11. Weathering of granite at Sylvan Lake in the Black Hills      22
-      12. Capulin Mountain National Monument, N. Mex.                  24
-      13. Mesa de Maya, Colo.                                          25
-      14. Spanish Peaks, Colo.                                         26
-      15. “The Gangplank,” Wyo.                                        27
-      16. Scotts Bluff National Monument, Nebr.                        28
-  17. Aerial photograph of the Nebraska Sand Hills                     30
-  18. Map of the Nebraska Sand Hills                                   31
-  19-30. Photographs showing:
-      19. Loess plain in Nebraska                                      32
-      20. Ground moraine on the Coteau du Missouri in North Dakota     34
-      21. Slump blocks in North Unit of Theodore Roosevelt National
-            Memorial Park, N. Dak.                                     36
-      22. Highwood Mountains, Mont.                                    37
-      23. Devils Tower National Monument, Wyo.                         38
-      24. Glaciated valley in Crazy Mountains, Mont.                   39
-      25. Powder River Basin in vicinity of Tongue River               40
-      26. Badlands National Monument, S. Dak.                          41
-      27. Badlands of Little Missouri River in South Unit of
-            Theodore Roosevelt National Memorial Park, N. Dak.         42
-      28. Hogback ridges along the Front Range, Colo.                  43
-      29. Pawnee Buttes, Colo.                                         44
-      30. Edwards Plateau, Tex.                                        47
-
-
-
-
-                                 TABLE
-
-
-  1. Generalized chart of rocks of the Great Plains                    15
-
-
-
-
-                         The GEOLOGIC STORY of
-                            The GREAT PLAINS
-
-
-                          By Donald E. Trimble
-
-
-
-
-                              INTRODUCTION
-
-
-The Great Plains! The words alone create a sense of space and a feeling
-of destiny—a challenge. But what exactly is this special part of Western
-America that contains so much of our history? How did it come to be? Why
-is it different?
-
-Geographically, the Great Plains is an immense sweep of country; it
-reaches from Mexico far north into Canada and spreads out east of the
-Rocky Mountains like a huge welcome mat. So often maligned as a drab,
-featureless area, the Great Plains is in fact a land of marked contrasts
-and limitless variety: canyons carved into solid rock of an arid land by
-the waters of the Pecos and the Rio Grande; the seemingly endless
-grainfields of Kansas; the desolation of the Badlands; the beauty of the
-Black Hills.
-
-Before it was broken by the plow, most of the Great Plains from the
-Texas panhandle northward was treeless grassland. Trees grew only along
-the floodplains of streams and on the few mountain masses of the
-northern Great Plains. These lush prairies once were the grazing ground
-for immense herds of bison, and the land provided a bountiful life for
-those Indians who followed the herds. South of the grasslands, in Texas,
-shrubs mixed with the grasses: creosote bush along the valley of the
-Pecos River; mesquite, oak, and juniper to the east.
-
-The general lack of trees suggests that this is a land of little
-moisture, as indeed it is. Nearly all of the Great Plains receives less
-than 24 inches of rainfall a year, and most of it receives less than 16
-inches. This dryness and the strength of sunshine in this area, which
-lies mostly between 2,000 and 6,000 feet above sea level, create the
-semiarid environment that typifies the Great Plains. But it was not
-always so. When the last continental glacier stood near its maximum
-extent, some 12,000-14,000 years ago, spruce forest reached southward as
-far as Kansas, and the Great Plains farther south was covered by
-deciduous forest. The trees retreated northward as the ice front
-receded, and the Great Plains has been a treeless grassland for the last
-8,000-10,000 years.
-
-For more than half a century after Lewis and Clark crossed the country
-in 1805-6, the Great Plains was the testing ground of frontier
-America—here America grew to maturity (fig. 1). In 1805-7, explorer
-Zebulon Pike crossed the south-central Great Plains, following the
-Arkansas River from near Great Bend, Kans., to the Rocky Mountains. In
-later years, Santa Fe traders, lured by the wealth of New Mexican trade,
-followed Pike’s path as far as Bents Fort, Colo., where they turned
-southwestward away from the river route. Those pioneers who later
-crossed the plains on the Oregon Trail reached the Platte River near the
-place that would become Kearney, Nebr., by a nearly direct route from
-Independence, Mo., and followed the Platte across the central part of
-the Great Plains.
-
-Although these routes may have seemed long and tedious to those dusty
-travelers, they provided relatively easy access to the Rocky Mountains
-and had a continuous supply of fresh water, an absolute necessity in
-these plains. The minds of those frontiersmen surely were occupied with
-the dangers and demands of the moment—and with dreams—but the time
-afforded by the slow pace of travel also gave them ample opportunity for
-thought about the origins of their surroundings.
-
-Today’s traveler, who has less time for contemplation, races past a
-changing kaleidoscope of landscape. The increased awareness created by
-this rapidity of change perhaps is even more likely to stimulate
-questions about the origin of this landscape.
-
-[Illustration: _Figure 1.—Index map of the Great Plains showing route of
-Lewis and Clark and the Santa Fe and Oregon Trails._]
-
-For instance, the westbound traveler on Interstate Highway 70 traverses
-nearly a thousand miles of low, rounded hills after leaving the
-Appalachians; the rolling landscape is broken only by a few flat areas
-where glacial ice or small lakes once stood. Suddenly, near Salina,
-Kans., the observant traveler senses a difference in the landscape.
-Instead of rounded hills, widely or closely spaced, he sees on the
-skyline flat surfaces, or remnants of flat surfaces. As he climbs gently
-westward these broken horizontal lines stand etched against the sky.
-About 35 miles west of Salina he finds himself on a broad, flat plateau,
-where seemingly he can see forever. True, in places he descends into
-stream valleys, but only briefly, for he soon climbs back onto the flat
-surface.
-
-This plateau surface continues for 300 miles to the west—to within 100
-miles of the abrupt front of the Rocky Mountains. East-flowing streams,
-such as the Smoky Hill, the Saline, the Solomon, and the Republican
-Rivers and their tributary branches, have cut their valleys into this
-surface, but these valleys become increasingly shallow and disappear
-entirely near the western rim of the plateau in eastern Colorado.
-
-The distant peaks of the Rockies are seen for the first time as the
-traveler approaches the escarpment that forms the western edge of this
-great plateau. After crossing the escarpment near Limon, Colo., he
-begins the long gentle descent to Denver, on the South Platte River near
-the foot of the mountains that loom so awesomely ahead. He has crossed
-the Great Plains. The distances have been great, but the contrasts have
-been marked.
-
-Had our traveler selected a different route, either to the north or
-south, he would have found even greater contrasts, for the Great Plains
-has many parts, each with its own distinctive aspect. Why should such
-diverse landscapes be considered parts of the Great Plains? What are
-their unifying features? And what created this landscape? Has it always
-been this way? If not, when was it formed? How was it formed?
-
-We will look here at some of the answers to those questions. The history
-of events that produced the landscape of the Great Plains is interpreted
-both from the materials that compose the landforms and from the
-landforms themselves. As we will see, all landforms are the result of
-geologic processes in action. These processes determine not only the
-size and shape of the landforms, but also the materials of which they
-are made. These geologic processes, which form and shape our Earth’s
-surface, are simply the inevitable actions of the restless interior of
-the Earth and of the air, water, and carbon dioxide of the atmosphere,
-aided by gravity and solar heating (or lack of it). They all have helped
-sculpture the fascinating diversity of the part of our land we call the
-Great Plains.
-
-
-
-
-                       WHAT IS THE GREAT PLAINS?
-
-
-The United States has been subdivided into physiographic regions that,
-although they have great diversity within themselves, are distinctly
-different from each other (fig. 2).
-
-From the Rocky Mountains on the west to the Appalachians on the east,
-the interior of our country is a vast lowland (see cover) known as the
-Interior Plains. These plains are bounded on the south by a region of
-Interior Highlands, consisting of the Ozark Plateaus and the Ouachita
-province, and by the Coastal Plain. In the Great Lakes region, the
-Interior Plains laps onto the most ancient part of the continent, the
-Superior Upland. West of the Great Lakes it extends far to the north
-into Canada. Certainly the Rocky Mountains are distinctly different from
-the region to the east, which is the Great Plains. The Great Plains,
-then, is the western part of the great Interior Plains. The Rocky
-Mountains form its western margin. But what determines its eastern
-margin?
-
-During the Pleistocene Epoch or Great Ice Age, huge glaciers formed in
-Canada and advanced southward into the great, central, low-lying
-Interior Plains of the United States. (See figure 2.) These glaciers and
-their deposits modified the surface of the land they covered, mostly
-between the Missouri and the Ohio Rivers; they smoothed the contours and
-gave the land a more subdued aspect than it had before they came. This
-glacially smoothed and modified land is called the Central Lowland.
-Although the ice sheets lapped onto the northern part, the Great Plains
-is the largely unglaciated region that extends from the Gulf Coastal
-Plain in Texas northward into Canada between the Central Lowland and the
-foot of the Rocky Mountains. Its eastern margin in Texas and Oklahoma is
-marked by a prominent escarpment, the Caprock escarpment. Its southern
-margin, where it abuts the Coastal Plain in Texas, is at another abrupt
-rise or scarp along the Balcones fault zone.
-
-[Illustration: _Figure 2.—Physical divisions of the United States and
-maximum extent of the continental ice sheets during the Great Ice Age._]
-
-
-
-
-                       THE GREAT PLAINS—ITS PARTS
-
-
-Within the Great Plains are many large areas that differ greatly from
-adjoining areas (fig. 3). The Black Hills stands out distinctively from
-the surrounding lower land, and its dark, forested prominence can be
-seen for scores of miles from any direction. At the southern end of the
-Great Plains is another, less imposing, forested prominence—the Central
-Texas Uplift. Most impressive, perhaps, is the huge, nearly flat plateau
-known as the High Plains, which extends southward from the northern
-border of Nebraska through the Panhandle of Texas, and which forms the
-central part of the Great Plains. The east and west rims of the southern
-High Plains are at high, cliffed, erosional escarpments—the Caprock
-escarpment on the east and the Mescalero escarpment on the west. The
-north edge of the High Plains is defined by another escarpment, the Pine
-Ridge escarpment, which separates the High Plains from a region that has
-been greatly dissected by the Missouri River and its tributaries. There,
-several levels of rolling upland are surmounted by small mountainous
-masses and flat-topped buttes and are entrenched by streams. This region
-is the Missouri Plateau. The continental glacier lapped onto the
-northeastern part of the Missouri Plateau and altered its surface.
-
-The South Platte and Arkansas Rivers and their tributaries have
-similarly dissected an area along the mountain front that is called the
-Colorado Piedmont, and the Pecos River has excavated a broad valley
-trending southward from the Sangre de Cristo Mountains in New Mexico
-into Texas. The Mescalero escarpment separates the Pecos Valley from the
-southern High Plains (fig. 4). South and east of the Pecos Valley,
-extending to the Rio Grande and the Coastal Plain, is a broad plateau of
-bare, stripped, flat-lying limestone layers bearing little but cactus
-that is called the Edwards Plateau. Green, crop-filled valleys with
-gently sloping valley walls and rounded stream divides trend eastward
-from the High Plains of western Kansas and characterize a Plains Border
-section. And finally, between the Colorado Piedmont on the north and the
-Pecos Valley on the south, volcanic vents, cinder cones, and lava fields
-form another distinctive terrain in the part of the Great Plains called
-the Raton section.
-
-[Illustration: _Figure 3.—The Great Plains province and its sections._]
-
-[Illustration: _Figure 4.—Mescalero escarpment and the southern High
-Plains (Llano Estacado) south of Tucumcari, N. Mex., Photograph by C. D.
-Miller, U. S. Geological Survey._]
-
-Can such diverse parts of our land have a sufficiently common origin to
-justify their being considered part of one unified whole—the Great
-Plains? Probably so, but to understand why, we must examine some of the
-earlier geologic history of the Great Plains as well as subsequent
-events revealed in the present landforms. We will find that all parts of
-this region we call the Great Plains have a similar early history, and
-that the differences we see are the results of local dominance of
-certain processes in the ultimate shaping of the landscape, mostly
-during the last few million years. The distinctive character of the
-landscape in each section is determined in part by both the early events
-and the later shaping processes.
-
-
-
-
-                             EARLY HISTORY
-
-
-The Interior Plains, of which the Great Plains is the western, mostly
-unglaciated part (fig. 2), is the least complicated part of our
-continent geologically except for the Coastal Plain. For most of the
-half billion years from 570 million (fig. 5) until about 70 million
-years ago, shallow seas lay across the interior of our continent (fig. 6
-). A thick sequence of layered sediments, mostly between 5,000 and
-10,000 feet thick, but more in places, was deposited onto the subsiding
-floor of the interior ocean (table 1). These sediments, now consolidated
-into rock, rest on a floor of very old rocks that are much like the
-ancient rocks of the Superior Upland.
-
-About 70 million years ago the seas were displaced from the continental
-interior by slow uplift of the continent, and the landscape that
-appeared was simply the extensive, nearly flat floor of the former sea.
-
-
-
-
-                     WARPING AND STREAM DEPOSITION
-
-
-Most of these rocks of marine origin lie at considerable depth beneath
-the land surface, concealed by an overlying thick, layered sequence of
-rocks laid down by streams, wind, and glaciers. Nevertheless, their
-geologic character, position, and form are exceptionally well known from
-information gained from thousands of wells that have been drilled for
-oil. The initial, nearly horizontal position of the layers of rock
-beneath the Interior Plains has been little disturbed except where
-mountains like the Black Hills were uplifted about 70 million years ago.
-At those places, which are all in the northern and southern parts of the
-Great Plains, the sedimentary layers have been warped up and locally
-broken by the rise of hot molten rock from depth. Elsewhere in the
-Interior Plains, however, earth forces of about the same period caused
-only a reemphasis of gentle undulations in the Earth’s crust.
-
-These undulations affected both the older basement rocks and the
-overlying sedimentary rocks, and they take the form of gentle basins and
-arches that in some places span several States. (See sketch map, figure
-7.) A series of narrow basins lies along the mountain front on the west
-side of the Great Plains. A broad, discontinuous arch extends southwest
-from the Superior Upland to the Rocky Mountain front to form a buried
-divide that separates the large Williston basin on the north from the
-Anadarko basin to the south.
-
-While the flat-lying layers of the Interior Plains were being only
-gently warped, vastly different earth movements were taking place
-farther west, in the area of the present Rocky Mountains. Along a
-relatively narrow north-trending belt, extending from Mexico to Alaska,
-the land was being uplifted at a great rate. The layers of sedimentary
-rock deposited in the inland sea were stripped from the crest of the
-rising mountainous belt by erosion and transported to its flanks as the
-gravel, sand, and mud of streams and rivers. This transported sediment
-was deposited on the plains to form the rocks of the Cretaceous Hell
-Creek, Lance, Laramie, Vermejo, and Raton Formations. Vegetation thrived
-on this alluvial plain, and thick accumulations of woody debris were
-buried to ultimately become coal. This lush vegetation provided ample
-food for the hordes of three-horned dinosaurs (_Triceratops_) that
-roamed these plains. Their fossilized remains are found from Canada to
-New Mexico.
-
-[Illustration: _Figure 5.—Geologic time chart and the progression of
-life forms. Note Cretaceous_ Triceratops, _Oligocene_ Titanotheres, _and
-Miocene_ Moropus.]
-
-                                 GEOLOGIC TIME
-                            The Age of the Earth
-
-  The Earth is very old—4.5 billion years or more according to recent
-  estimates. Most of the evidence for an ancient Earth is contained in
-  the rocks that form the Earth’s crust. The rock layers themselves—like
-  pages in a long and complicated history—record the surface-shaping
-  events of the past, and buried within them are traces of life—the
-  plants and animals that evolved from organic structures that existed
-  perhaps 3 billion years ago.
-
-  Also contained in rocks once molten are radioactive elements whose
-  isotopes provide Earth scientists with an atomic clock. Within these
-  rocks, “parent” isotopes decay at a predictable rate to form
-  “daughter” isotopes. By determining the relative amounts of parent and
-  daughter isotopes, the age of these rocks can be calculated.
-
-  Thus, the results of studies of rock layers (stratigraphy), and of
-  fossils (paleontology), coupled with the ages of certain rocks as
-  measured by atomic clocks (geochronology), attest to a very old Earth!
-
-[Illustration: _Figure 6.—Generalized paleogeographic map of the United
-States in Late Cretaceous time (65 to 80 million years ago), when most
-of the Great Plains was beneath the sea._]
-
-[Illustration: _Figure 7.—Structural setting of the Great Plains.
-Williston basin and Anadarko basin are separated by a midcontinental
-arch._]
-
-[Illustration: Table 1.—Generalized chart of rocks of the Great Plains]
-
-   Geologic age        Missouri        High Plains—Plains         Pecos
-    Millions of       Plateau—Black      Border—Colorado      Valley—Edwards
-     years ago            Hills              Piedmont         Plateau—Central
-                                                                   Texas
-
-  Quaternary
-     Pleistocene  Glacial deposits,   Alluvium, sand       Piedmont, terrace,
-                    alluvium, and       dunes, and loess     and bolson
-                    terrace deposits                         deposits
-                2 erosional surface
-  Tertiary
-     Pliocene     EROSION
-                5 Flaxville Gravel    Ogallala formation
-                    and Ogallala
-                    Formation
-     Miocene      Arikaree Formation  Arikaree Formation
-            22-24 erosional surface
-     Oligocene    White River Group   White River Group    Mostly missing
-                                                             because of
-                                                             erosion or
-                                                             nondeposition
-            37-38 erosional surface
-     Eocene       Wasatch and Golden
-                    Valley Formations
-            53-54                     Dawson Arkose
-     Paleocene    Fort Union          Denver, Poison
-                    Formation           Canyon, and Raton
-                                        Formations
-               65
-  Cretaceous      Hell Creek and      Vermejo and Laramie
-                    Lance Formations    Formations
-                  Fox Hills Sandstone Trinidad and Fox
-                                        Hills Sandstones
-                  Shales, sandstones, and limestones
-                    deposited in Late Cretaceous sea
-                  Dakota Sandstone    Dakota Sandstone
-                    and Lakota
-                    Formation
-                                      Glen Rose and
-                                        Edwards Limestones
-              136
-  Jurassic        Sundance            Morrison Formation   Jurassic rocks not
-                    Formation, Ellis                         present
-                    Group, and
-                    Unkpapa Sandstone
-          190-195
-  Triassic        Dominantly red rocks
-              225
-  PALEOZOIC       Paleozoic rocks, undivided
-              570
-  PRECAMBRIAN     Precambrian rocks, undivided
-
-As the mountains continued to rise, the eroding streams cut into the old
-core rocks of the mountains, and that debris too was carried to the
-flanks and onto the adjoining plains. The mountainous belt continued to
-rise intermittently, and volcanoes began to appear about 50 million
-years ago. Together, the mountains and volcanoes provided huge
-quantities of sediment, which the streams transported to the plains and
-deposited. The areas nearest the mountains were covered by sediments of
-Late Cretaceous and Paleocene age (table 1)—the Poison Canyon Formation
-to the south, the Dawson and Denver Formations in the Denver area, and
-the Fort Union Formation to the north (fig. 8). Vegetation continued to
-flourish, especially in the northern part of the Great Plains, and was
-buried to form the thick lignite and subbituminous coal beds of the Fort
-Union Formation (fig. 9). The earliest mammals, most of whose remains
-come from the Paleocene Fort Union Formation, have few modern survivors.
-
-Beginning about 45 million years ago, in Eocene time, there was a long
-period of stability lasting perhaps 10 million years, when there was
-little uplift of the mountains and, therefore, little deposition on the
-plains. A widespread and strongly developed soil formed over much of the
-Great Plains during this period of stability. With renewed uplift and
-volcanism in the mountains at the end of this period, great quantities
-of sediment again were carried to the plains by streams and spread over
-the northern Great Plains and southeastward to the arch or divide
-separating the Williston and Anadarko basins (fig. 8). Those sediments
-form the White River Group, in which the South Dakota Badlands are
-carved. In addition to the _Titanotheres_, huge beasts with large, long
-horns on their snouts who lived only during the Oligocene (37 to 22
-million years ago), vast herds of camels, rhinoceroses, horses, and
-tapirs—animals now found native only on other continents—grazed those
-Oligocene semiarid grassland plains.
-
-[Illustration: _Figure 8.—Progressive southeastward expansion of areas
-covered by Paleocene, Oligocene, and Miocene-Pliocene sedimentary
-deposits._]
-
-  Powder River basin
-  Denver basin
-  Raton basin
-  PLAINS
-    Margin of Oligocene deposition
-    Margin of Miocene-Pliocene deposition
-
-[Illustration: _Figure 9.—Big Horn coal strip mine in Fort Union
-Formation at Acme, Wyo. Photograph by F. W. Osterwald, U.S. Geological
-Survey._]
-
-Sometime between 20 and 30 million years ago the streams began
-depositing sand and gravel beyond the divide, and, for another 10
-million years or more, stream sediments of the Arikaree and Ogallala
-Formations spread over the entire Great Plains from Canada to Texas,
-except where mountainous areas such as the Black Hills stood above the
-plains. Between 5 and 10 million years ago, then, the entire Great
-Plains was an eastward-sloping depositional plain surmounted only by a
-few mountain masses. Horses, camels, rhinoceroses, and a strange
-horselike creature with clawed feet (called _Moropus_) lived on this
-plain.
-
-
-
-
-                          SCULPTURING THE LAND
-
-
-Sometime between 5 and 10 million years ago, however, a great change
-took place, apparently as a result of regional uplift of the entire
-western part of the continent. While before, the streams had been
-depositing sediment on the plains for more than 60 million years,
-building up a huge thickness of sedimentary rock layers, now the streams
-were forced to cut down into and excavate the sediments they had
-formerly deposited. As uplift continued—and it may still be
-continuing—the streams cut deeper and deeper into the layered stack and
-developed tributary systems that excavated broad areas. High divides
-were left between streams in some places, and broad plateaus were formed
-and remain in other places. The great central area was essentially
-untouched by erosion and remained standing above the dissected areas
-surrounding it as the escarpment-rimmed plateau that is the High Plains.
-
-This downcutting and excavation by streams, then, which began between 5
-and 10 million years ago, roughed out the landscape of the Great Plains
-and created the sections we call the Missouri Plateau, the Colorado
-Piedmont, the Pecos Valley, the Edwards Plateau, and the Plains Border
-Section. Nearly all the individual landforms that now attract the eye
-have been created by geologic processes during the last 2 million years.
-It truly is a young landscape.
-
-
-
-
-      LANDFORMS OF TODAY—The surface features of the Great Plains
-
-
-The mountainous sections of the Great Plains were formed long before the
-remaining areas were outlined by erosion. Uplift of the Black Hills and
-the Central Texas Uplift began as the continental interior was raised
-and the last Cretaceous sea was displaced, 65 to 70 million years ago.
-They stood well above the surrounding plains long before any sediments
-from the distant Rocky Mountains began to accumulate at their bases. In
-southern Colorado and northern New Mexico, molten rock invaded the
-sedimentary layers between 22 and 26 million years ago. The Spanish
-Peaks were formed at this time from hot magma that domed up the surface
-layers but did not break through; the magma has since cooled and
-solidified and has been exposed by erosion. Elsewhere the magma reached
-the surface, forming volcanoes, fissures, and basalt flows. A great
-thickness of basalt flows accumulated at Raton Mesa and Mesa de Maya
-between 8 and 2 million years ago. Volcanism has continued
-intermittently, and the huge cinder cone of Capulin Mountain was created
-by explosive eruption only 10,000 to 4,000 years ago. Most of these
-volcanic masses were formed before major downcutting by the streams
-began. Other igneous intrusions and volcanic areas in the northern Great
-Plains similarly were formed before the streams were incised.
-
-To examine the origin of the present landscape and of the landforms
-typical of the various sections of the Great Plains, it is convenient to
-begin with the Black Hills, the Central Texas Uplift, and the Raton
-section simply because they were formed first—they existed before the
-other sections were outlined.
-
-
-                              BLACK HILLS
-
-The Black Hills is a huge, elliptically domed area in northwestern South
-Dakota and northeastern Wyoming, about 125 miles long and 65 miles wide
-(fig. 10). Rapid City, S. Dak., is on the Missouri Plateau at the east
-edge of the Black Hills. Uplift caused erosion to remove the overlying
-cover of marine sedimentary rocks and expose the granite and metamorphic
-rocks that form the core of the dome. The peaks of the central part of
-the Black Hills presently are 3,000 to 4,000 feet above the surrounding
-plains. Harney Peak, with an altitude of 7,242 feet, is the highest
-point in South Dakota. These central spires and peaks all are carved
-from granite and other igneous and metamorphic rocks that form the core
-of the uplift. The heads of four of our great Presidents are sculpted
-from this granite at Mount Rushmore National Memorial. Joints in the
-rocks have controlled weathering processes that influenced the final
-shaping of many of these landforms. Closely spaced joints have produced
-the spires of the Needles area, and widely spaced joints have produced
-the rounded forms of granite that are seen near Sylvan Lake (fig. 11).
-
-Marine sedimentary rocks surrounding the old core rocks form
-well-defined belts. Lying against the old core rocks and completely
-surrounding them are Paleozoic limestones that form the Limestone
-Plateau (fig. 10). These tilted layers have steep erosional scarps
-facing the central part of the Black Hills. Wind Cave and Jewel Cave
-were produced by ground water dissolving these limestones along joints.
-These caves are sufficiently impressive to be designated as a national
-park and a national monument, respectively. Encircling the Limestone
-Plateau is a continuous valley cut in soft Triassic shale. This valley
-has been called “the Racetrack,” because of its continuity, and the Red
-Valley, because of its color. Surrounding the Red Valley is an outer
-hogback ridge formed by the tilted layers of the Dakota Sandstone, which
-are quite hard and resistant to erosion. Streams that flow from the
-central part of the Black Hills pass through the Dakota hogback in
-narrow gaps.
-
-[Illustration: _Figure 10.—Diagram of the Black Hills uplift by A. N.
-Strahler (Strahler and Strahler, 1978). Used by permission._]
-
-  Dakota Sandstone hogback
-  Limestone plateau
-  Belle Fourche River
-  Spearfish
-  Bear Butte
-  Sundance
-  Red Valley
-  Rapid City
-  Red Valley
-  Hot Springs
-  Cheyenne River
-  Edgemont
-  Mt. Rushmore National Monument
-  Jewel Cave National Monument
-  Wind Cave National Park
-
-[Illustration: _Figure 11.—Jointed granite rounded by weathering at
-Sylvan Lake, in the central part of the Black Hills, S. Dak._]
-
-The Black Hills, then, is an uplifted area that has been carved deeply
-but differentially by streams to produce its major outlines. Those
-outlines have been modified mainly by weathering of the ancient core
-rocks and solution of the limestone of the Limestone Plateau.
-
-
-                          CENTRAL TEXAS UPLIFT
-
-The domed rocks of the Central Texas Uplift form a topography different
-from that of the Black Hills. Erosion of a broad, uplifted dome here has
-exposed a core of old granites, gneisses, and schists, as in the Black
-Hills, but in the Central Texas Uplift, erosion has produced a
-topographic basin, rather than high peaks and spires, on the old rocks
-of the central area. A low plateau surface dissected into rounded ridges
-and narrow valleys slopes gently eastward from the edge of the central
-area to an escarpment at the Balcones fault zone, which determines the
-eastern edge of the Great Plains here. Northwest of the central basin
-the Colorado River flows in a broad lowland about 100 miles long, but
-the northern edge of the uplift, forming a divide between the Brazos and
-the Colorado Rivers, is a series of mesas formed of more resistant
-sandstone and limestone.
-
-The cutting action of streams, modified or controlled in part by
-differences in hardness of the rock layers, has been responsible for the
-landforms of the Central Texas Uplift. Weathering of the old core rocks
-has softened them sufficiently to permit deeper erosion of the central
-area, and solution of limestone by ground water has formed such features
-as Longhorn Caverns, 11 miles southwest of Burnet, Tex.
-
-
-                             RATON SECTION
-
-Volcanism characterizes the Raton section. The volcanic rocks, which
-form peaks, mesas, and cones, have armored the older sedimentary rocks
-and protected them from the erosion that has cut deeply into the
-adjoining Colorado Piedmont to the north and Pecos Valley to the south.
-The south edge of the Raton section is marked by a spectacular
-south-facing escarpment cut on the nearly flat-lying Dakota Sandstone.
-This escarpment is the Canadian escarpment, north of the Canadian River.
-Northward for about 100 miles, the landscape is that of a nearly flat
-plateau cut on Cretaceous rock surmounted here and there by young
-volcanic vents, cones, and lava fields. Capulin Mountain is a cinder
-cone only 10,000 to 4,000 years old (fig. 12). Near the New
-Mexico-Colorado border, huge piles of lava were erupted 8 to 2 million
-years ago onto an older, higher surface on top of either the Ogallala
-Formation of Miocene age or the Poison Canyon Formation of Paleocene
-age. (See table 1.) These lava flows formed a resistant cap, which
-protected the underlying rock from erosion while all the surrounding
-rock washed away. The result is the high, flat-topped mesas, such as
-Raton Mesa and Mesa de Maya (fig. 13), that now form the divide between
-the Arkansas and Canadian Rivers. At Fishers Peak, on the west end of
-Raton Mesa, about 800 feet of basalt flows rest on the Poison Canyon
-Formation at about 8,800 feet in altitude. Farther east, on Mesa de
-Maya, about 400 feet of basalt flows overlie the Ogallala Formation at
-altitudes ranging from about 6,500 feet at the west end to about 5,200
-feet at the east end, some 35 miles to the east. The Ogallala here rests
-on Cretaceous Dakota Sandstone and Purgatoire Formation, for the Poison
-Canyon Formation was removed by erosion along the crest of a local
-uplift before the Ogallala was deposited.
-
-[Illustration: _Figure 12.—Capulin Mountain National Monument in
-northeastern New Mexico. This huge cinder cone, which erupted between
-4,000 and 10,000 years ago, rises more than 1,000 feet above its base.
-Photograph by R. D. Miller, U.S. Geological Survey._]
-
-East of the belt of upturned sedimentary layers that form the hogback
-ridges at the front of the Rocky Mountains, the layered rocks in the
-Raton Basin have been intruded in many places by igneous bodies, the two
-largest of which form the Spanish Peaks (fig. 14), southwest of
-Walsenburg, Colo. These two peaks are formed by igneous bodies that were
-intruded 26 to 22 million years ago and have since been exposed by
-removal of the overlying sedimentary rock layers by erosion. Radiating
-from the Spanish Peaks are hundreds of dikes, nearly vertical slabs of
-igneous rock that filled fractures radiating from the centers of
-intrusion. Erosion of the sedimentary layers has left many of these
-dikes as conspicuous vertical walls of igneous rock that project high
-above the surrounding land surface. Some of these dikes north of
-Trinidad, Colo. extend eastward for about 25 miles, almost to the
-Purgatoire River.
-
-[Illustration: _Figure 13.—Lava-capped Mesa de Maya, east of Trinidad,
-Colo. Spanish Peaks in left distance. Mesa rises about 1,000 feet above
-surrounding area. Photograph by R. B. Taylor, U.S. Geological Survey._]
-
-The northern boundary of the Raton section is placed somewhat
-indefinitely at the northern limit of the area injected by igneous
-dikes. The eastern boundary of the Raton section is at the eastern
-margin of the lavas of Mesa de Maya and adjoining mesas, where
-lava-capped outliers of Ogallala Formation are separated from the
-Ogallala of the High Plains only by the canyon of Carrizo Creek.
-
-
-                              HIGH PLAINS
-
-At the end of Ogallala deposition, some 5 million years ago, the Great
-Plains, with the exception of the uplifted and the volcanic areas, was a
-vast, gently sloping plain that extended from the mountain front
-eastward to beyond the present Missouri River in some places. Regional
-uplift of the western part of the continent forced the streams to cut
-downward; land near the mountains was stripped away by the Missouri, the
-Platte, the Arkansas, and the Pecos Rivers, and the eastern border of
-the plains was gnawed away by lesser streams. A large central area of
-the plain is preserved, however, essentially untouched and unaffected by
-the streams, as a little-modified remnant of the depositional surface of
-5 million years ago. This Ogallala-capped preserved remnant of that
-upraised surface is the High Plains. In only one place does that old
-surface still extend to the mountains—at the so-called “Gangplank” west
-of Cheyenne, Wyo. (fig. 15). In places, as at Scotts Bluff National
-Monument, Nebr. (fig. 16), small fragments of this surface have been
-isolated from the High Plains by erosion and now stand above the
-surrounding area as buttes.
-
-[Illustration: _Figure 14.—Spanish Peaks, southwest of Walsenburg, Colo.
-Igneous rocks and many radiating dikes exposed by erosion. Photograph by
-R. B. Taylor, U.S. Geological Survey._]
-
-[Illustration: _Figure 15.—Looking east toward Cheyenne at “the
-Gangplank.” Interstate Highway 80 and the Union Pacific Railroad follow
-the Gangplank from the High Plains in the distance onto the Precambrian
-rocks (older than 570 m.y.) of the Laramie Mountains in the foreground.
-Photograph by R. D. Miller, U.S. Geological Survey._]
-
-[Illustration: _Figure 16.—Aerial view of Scotts Bluff National
-Monument, Nebr. Buttes on the south side of the valley of the North
-Platte River isolated by erosion from High Plains in the background.
-Highest butte stands about 800 feet above valley floor._]
-
-The High Plains extends southward from the Pine Ridge escarpment, near
-the South Dakota-Nebraska border (fig. 3), to the Edwards Plateau in
-Texas. The Platte, the Arkansas, and the Canadian Rivers have cut
-through the High Plains. That part of the High Plains south of the
-Canadian River is called the Southern High Plains, or the Llano Estacado
-(staked plain). The origin of this name is uncertain, but it has been
-suggested that the term Llano Estacado was applied by early travelers
-because this part of the High Plains is so nearly flat and devoid of
-landmarks that it was necessary for those pioneers to set lines of
-stakes to permit them to retrace their routes.
-
-The Llano Estacado is bounded on the west by the Mescalero escarpment
-(fig. 4) and on the east by the Caprock escarpment. The southern margin
-with the Edwards Plateau is less well defined, but King Mountain, north
-of McCamey, Tex., is a scarp-bounded southern promontory of the High
-Plains. The remarkably flat surface of the Llano Estacado is abundantly
-pitted by sinks and depressions in the surface of the Ogallala
-Formation; these were formed by solution of the limestone by rainwater
-and blowing away or deflation by wind of the remaining insoluble
-particles. Many of these solution-deflation depressions are aligned like
-strings of beads, suggesting that their location is controlled by some
-kind of underlying structure, such as intersections of joints in the
-Ogallala Formation.
-
-The solution-deflation depressions are less abundant north of the
-Canadian River, but occur on the High Plains surface northward to the
-Arkansas River and along the eastern part of the High Plains north of
-the Arkansas to the South Fork of the Republican River.
-
-Covering much of the northern High Plains, however, are sand dunes and
-windblown silt deposits (loess) that mantle the Ogallala Formation and
-conceal any solution-deflation depressions that might have formed. The
-Nebraska Sand Hills (fig. 17), the largest area of sand dunes in the
-western hemisphere, is a huge area of stabilized sand dunes that extends
-from the White River in South Dakota southward beyond the Platte River
-almost to the Republican River in western Nebraska but only to the Loup
-River in the northeast part of the High Plains (fig. 18). Loess covers
-the western High Plains southward from the sand dunes almost to the
-Arkansas River, and to the South Fork of the Republican in the eastern
-part. This extensive cover of loess has created a fertile land that
-makes it an important part of America’s wheatlands (fig. 19).
-
-[Illustration: _Figure 17.—Aerial view, looking northwest, of the
-Nebraska Sand Hills west of Ashby, Nebr._]
-
-Other, smaller areas of sand dunes lie south of the Arkansas River
-valley. The only large areas of sand dunes on the Llano Estacado, or
-Southern High Plains, are along the southwestern margin near Monahans,
-southwest of Odessa, Tex.
-
-Oil and gas are present in the Paleozoic rocks that underlie the High
-Plains at depth. Gas fields are ubiquitous in much of the eastern part
-of the High Plains between the Arkansas and Canadian Rivers. Just south
-of the Canadian River, at the northeast corner of the Southern High
-Plains, a huge oil and gas field has been developed near Pampa, Tex. Oil
-and gas fields also are abundant in the southwestern part of the
-Southern High Plains, south of Littlefield, Tex.
-
-[Illustration: _Figure 18.—The Sand Hills region of Nebraska. Arrows
-show inferred direction of dune-forming winds. Map from Wright (1970),
-used by permission._]
-
-  WYOMING
-    Badlands National Monument
-    Missouri River Valley
-  JAMES RIVER LOBE
-  MINNESOTA
-  IOWA
-  SOUTH DAKOTA
-  NEBRASKA
-    Rosebud
-    Valentine
-  DES MOINES LOBE
-  NEBRASKA
-    Ashby
-  SANDHILLS
-    Platte River Valley
-  IOWA
-  MISSOURI
-  NEBRASKA
-  KANSAS
-  COLORADO
-    Muscotah
-  TOPEKA
-  EXPLANATION
-    Transverse dunes
-    Longitudinal dunes
-    Wind-blown sand
-    Loess thickness (in feet)
-
-[Illustration: _Figure 19.—Little-modified loess plain in southeastern
-Nebraska. Photograph by Judy Miller._]
-
-The surface of the High Plains, then, has been little modified by
-streams since the end of Ogallala deposition. It has been raised by
-regional uplift and pitted by solution and deflation, and large parts of
-it have been covered by wind-blown sand and silt. It has been drilled
-for oil and gas and extensively farmed, but it is still a geological
-rarity—a preserved land surface that is 5 million years old.
-
-
-                            MISSOURI PLATEAU
-
-Beginning about 5 million years ago, regional uplift of the western part
-of the continent forced streams, which for 30 million years had been
-depositing sediment nearly continuously on the Great Plains, to change
-their behavior and begin to cut into the layers of sediment they so long
-had been depositing. The predecessor of the Missouri River ate headward
-into the northern Great Plains and developed a tributary system that
-excavated deeply into the accumulated deposits near the mountain front
-and carried away huge volumes of sediment from the Great Plains to
-Hudson Bay. By 2 million years ago, the streams had cut downward to
-within a few hundred feet of their present level. This region that has
-been so thoroughly dissected by the Missouri River and its tributaries
-is called the Missouri Plateau.
-
-About 2 million years ago, after much downcutting had already taken
-place and river channels had been firmly established, great ice sheets
-advanced southward from Canada into the United States. (See figure 2.)
-These continental glaciers formed, advanced, and retreated several times
-during the last 2 million years. At the north and east margins of the
-Missouri Plateau they lapped onto a high area, leaving a mantle of
-glacial deposits covering the bedrock surface and forcing streams to
-adopt new courses along the margin of ice. The part of the Missouri
-Plateau covered by the continental glaciers now is referred to as the
-Glaciated Missouri Plateau. South of the part once covered by ice is the
-Unglaciated Missouri Plateau.
-
-    Preglacial Drainage
-
-Before the initial advance of the continental ice sheets, the Missouri
-River flowed northeastward into Canada and to Hudson Bay. Its major
-tributaries, the Yellowstone and the Little Missouri joined the Missouri
-in northwestern North Dakota. The east-flowing Knife, Heart, and
-Cannonball Rivers in North Dakota also joined a stream that flowed
-northward to Hudson Bay.
-
-    Glaciated Missouri Plateau
-
-When the continental ice sheets spread southward into northern Montana
-and the Dakotas, a few isolated areas in Montana stood above the
-surrounding plain. These are mostly areas that were uplifted by the
-intrusion of igneous bodies long before the streams began downcutting
-and carving the land. The northernmost of these isolated mountains, the
-Sweetgrass Hills, were surrounded by ice and became nunataks, or islands
-of land, in the sea of advancing ice, which pushed southward up against
-the Highwood Mountains, near Great Falls, the Bearpaws south of Havre,
-and the Little Rockies to the east.
-
-Much of the northern part of Montana is a plain of little relief that is
-the surface of a nearly continuous cover of glacial deposits, generally
-less than 50 feet thick. This plain has been incised by the east-flowing
-postglacial Teton, Marias, and Milk Rivers.
-
-In North Dakota, a high area on the east side of the Williston basin
-acted as a barrier to the advance of the ice, most of which was diverted
-southeastward. The margin of the ice sheet, however, lapped onto the
-bedrock high, where it stagnated. Earlier advances moved farthest south;
-the later advances stopped north of the present course of the Missouri
-River—their maximum position marked by ridges of unsorted, glacially
-transported rock debris (till) called terminal moraines. North of the
-terminal moraines is a distinctive landscape characterized by a rolling,
-hummocky, or hilly surface with thousands of closed depressions between
-the hills and hummocks, most of them occupied by lakes. This is the
-deposit left by the stagnant or dead ice, and it is called dead-ice
-moraine. The rolling upland in North Dakota that is covered by dead-ice
-moraine and ridges of terminal moraines from the last glacial advances
-is called the Coteau du Missouri (fig. 20). A gently sloping scarp,
-several hundred feet high and mostly covered by glacial deposits
-(referred to collectively as drift), separates the Coteau du Missouri
-from the lower, nearly flat, drift-covered plains of the Central Lowland
-to the east. This escarpment, which is called the Missouri escarpment,
-is virtually continuous across the State of North Dakota southward into
-South Dakota. The base of the Missouri escarpment is the eastern
-boundary of the Great Plains in these northern states.
-
-[Illustration: _Figure 20.—Ground moraine on the Coteau du Missouri,
-northwestern North Dakota. Photograph by R. M. Lindvall, U. S.
-Geological Survey._]
-
-The advancing ice front blocked one after another of the
-northward-flowing streams of the region, diverting them eastward along
-the ice front. Shonkin Sag, north of the Highwood Mountains near Great
-Falls, Mont., is an abandoned diversion channel of the Missouri River,
-occupied when the ice front stood close to the north slopes of the
-Highwoods. Much of the present course of the Missouri River from Great
-Falls, Mont., to Kansas City, Mo., was established as an ice-marginal
-channel, and the east-flowing part of the Little Missouri River in North
-Dakota was formed in the same way. These valleys were cut during the
-last 2 million years.
-
-The north-flowing part of the Little Missouri River and the east-flowing
-courses of the Knife, Heart, and Cannonball Rivers in North Dakota are
-for the most part older, preglacial courses. The Little Missouri was
-dammed by the ice, and its waters impounded to form a huge lake during
-the maximum stand of the ice, but the deposits of this glacial lake are
-few and make no imprint on the landscape.
-
-The valley of the east-flowing, glacially diverted part of the Little
-Missouri River, however, is markedly different from that of the
-north-flowing preglacial river. It is much narrower and has steeper
-walls than the old valley. Because it is younger, it is little modified,
-except by huge landslides that have affected both walls of the valley.
-Tremendous rotated landslide blocks in the North Unit of Theodore
-Roosevelt National Memorial Park are some of the best examples of the
-slump type of landslide to be seen anywhere (fig. 21).
-
-Melting ice at the front of the glaciers provided large volumes of
-meltwater that flowed across the till-mantled surface in front of the
-glacier as it melted back toward Canada. This meltwater took many
-courses to join the glacially diverted Missouri River, and these sinuous
-meltwater channels wind across the dead-ice moraine and the older, less
-hummocky ground moraine between the Coteau du Missouri and the Missouri
-River. Locally the sediment carried by the meltwater streams was banked
-against a wall of ice to form a small hill of stratified drift that is
-called a kame. Streams flowing in tunnels beneath the ice formed
-sinuous, ridgelike deposits called eskers, and in places the meltwater
-deposits form broad flat areas called outwash plains.
-
-[Illustration: _Figure 21.—Rotated slump blocks in huge landslide, North
-Unit of Theodore Roosevelt National Memorial Park, N. Dak. Note that
-layering of Fort Union Formation in cliffs on skyline, where landslide
-originated, is horizontal._]
-
-This rather limited variety of landforms, then, characterizes the
-landscape of the Glaciated Missouri Plateau. The landforms themselves
-are testimony to their glacial origin and to the great advances of the
-continental ice sheets. This is a stream-carved terrain that has been
-modified by continental glaciers and almost completely covered by a
-thick blanket of glacially transported and deposited rock debris,
-locally hundreds of feet thick. Subsequent stream action has not altered
-the landscape greatly.
-
-    Unglaciated Missouri Plateau
-
-Beyond the limits reached by the ice of the continental glaciers, the
-Unglaciated Missouri Plateau displays the greatest variety of landforms
-of any section of the Great Plains. In western Montana, many small
-mountain masses rise above the general level of the plateau, including
-the Highwood, Bearpaw, and Little Rocky Mountains near the margin of the
-glaciated area, and the Judith, Big Snowy, Big Belt, Little Belt,
-Castle, and Crazy Mountains farther south (fig. 22). Many of these, such
-as the Crazy, Castle, Judith, and Big Snowy Mountains, are areas
-uplifted by large, deeply rooted, intrusive igneous bodies called
-stocks, which have been exposed by subsequent erosion of the arched
-overlying sedimentary rock layers. Some, such as the Highwood and
-Bearpaw Mountains, are predominantly piles of lava flows, although in
-the Bearpaws the related intrusive bodies of igneous rock form a part of
-the mountains. The Big and Little Belt Mountains were formed by
-mushroom-shaped intrusive igneous bodies called laccoliths, which have
-spread out and domed between layers of sedimentary rocks. A number of
-igneous bodies also intrude the rocks of the Missouri Plateau around the
-periphery of the Black Hills. Devils Tower, the first feature to be
-designated a National Monument, is the best known of these igneous rock
-features (fig. 23).
-
-[Illustration: _Figure 22.—The Highwood Mountains seen from the Little
-Belt Mountains, Mont. Photograph by I. J. Witkind, U. S. Geological
-Survey._]
-
-The uplift and volcanism that formed these mountains took place before
-the streams began to cut downward and segment the Great Plains. The
-mountains had been greatly dissected before the advent of the Great Ice
-Age, when alpine glaciers formed on the Castle and the Crazy Mountains
-and flowed down some of the stream-cut valleys. Alpine glacial features
-such as cirques, in the high parts of the mountains, and glacially
-modified U-shaped valleys (fig. 24) are impressive evidence of this
-glaciation.
-
-[Illustration: _Figure 23.—Devils Tower National Monument, Wyo. An
-igneous intrusive body exposed by erosion. Photograph by F. W.
-Osterwald, U. S. Geological Survey._]
-
-The Missouri River and its tributaries—the Sun, Smith, Judith,
-Musselshell, and Yellowstone Rivers in Montana and the Little Missouri
-River in North Dakota—have cut down into the Missouri Plateau, cut broad
-upland surfaces at many levels, and established confined valleys with
-valley floors flanked by terrace remnants of older floodplains. Locally,
-high buttes that are remnants of former interstream divides rise above
-the uplands. Large lakes also were formed in most of these tributary
-valleys because of damming by the continental ice sheets.
-
-[Illustration: _Figure 24.—U-shaped, glaciated valley of Big Timber
-Creek, Crazy Mountains, Mont. Photograph by W. C. Alden, 1921, U. S.
-Geological Survey._]
-
-West of the Black Hills, in Wyoming, the Tongue River and the Powder
-River have excavated the Powder River Basin and produced similar
-features (fig. 25). The east-flowing tributaries of the Missouri
-River—the Knife, Heart, and Cannonball Rivers in North Dakota and the
-Grand, Moreau, Belle Fourche, Cheyenne, Bad, and White Rivers in South
-Dakota—similarly have shaped the landscape.
-
-Most of these rivers flow in broad, old valleys, established more than 2
-million years ago, before the first advance of the continental ice
-sheets. Some of these valleys have been widened by recession of the
-valley walls by badland development. Badlands are formed by the cutting
-action of rivulets and rills flowing down over a steeply sloping face of
-soft, fine-grained material composed mainly of clay and silt. The
-intricate carving by thousands of small streams of water produces the
-distinctive rounded and gullied terrain we call badlands. Badlands
-National Monument in South Dakota (fig. 26) has been established in the
-remarkable badlands terrain cut into the White River Group along the
-north valley wall of the White River, and the South Unit of Theodore
-Roosevelt National Memorial Park is in the colorful badlands of the
-Little Missouri River, formed on the Fort Union Formation (fig. 27).
-
-The White River also has cut a steep scarp along its southern wall that
-is called the Pine Ridge escarpment. This escarpment defines the
-boundary between the Missouri Plateau and the High Plains here.
-
-[Illustration: _Figure 25.—View northeast across the Deckers coal mine
-and the Tongue River in the Powder River Basin, southeastern Montana.
-Typical terrain of unglaciated Missouri Plateau. Small mesas with
-cliffed escarpments on capping layer of resistant sandstone, such as
-those in the foreground, are common. Coal mine is about 1 mile across.
-Photograph by R. B. Taylor, U. S. Geological Survey._]
-
-The landscape of the Unglaciated Missouri Plateau has been determined
-largely by the action of streams, but in some areas igneous intrusions
-and volcanoes have produced small mountain masses that interrupt the
-plain, and valley glaciers have modified the valleys in some of these
-mountains.
-
-[Illustration: _Figure 26.—Badlands in Badlands National Monument, S.
-Dak. Photograph by W. H. Raymond, III, U. S. Geological Survey._]
-
-[Illustration: _Figure 27.—Badlands of the Little Missouri River in
-South Unit of Theodore Roosevelt National Memorial Park, N. Dak. View
-looking northwest from Painted Canyon Overlook along Interstate Highway
-94, west of Belfield._]
-
-
-                         THE COLORADO PIEDMONT
-
-The Colorado Piedmont lies at the eastern foot of the Rockies, (fig. 1)
-largely between the South Platte River and the Arkansas River. The South
-Platte on the north and the Arkansas River on the south, after leaving
-the mountains, have excavated deeply into the Tertiary (65- to
-2-million-year-old) sedimentary rock layers of the Great Plains in
-Colorado and removed great volumes of sediment. At Denver, the South
-Platte River has cut downward 1,500 to 2,000 feet to its present level.
-Three well-formed terrace levels flank the river’s floodplain, and
-remnants of a number of well-formed higher land surfaces are preserved
-between the river and the mountains. Along the western margin of the
-Colorado Piedmont, the layers of older sedimentary rock have been
-sharply upturned by the rise of the mountains. The eroded edges of these
-upturned layers have been eroded differentially, so that the hard
-sandstone and limestone layers form conspicuous and continuous hogback
-ridges (fig. 28). North of the South Platte River, near the Wyoming
-border, a scarp that has been cut on the rocks of the High Plains marks
-the northern boundary of the Colorado Piedmont. Pawnee Buttes (fig. 29)
-are two of many butte outliers of the High Plains rocks near that scarp,
-separated from the High Plains by erosion as is Scotts Bluff, farther
-north in Nebraska. To the east, about 10 miles northwest of Limon,
-Colo., Cedar Point forms a west-jutting prow of the High Plains.
-
-The Arkansas River similarly has excavated much of the Tertiary piedmont
-deposits and cut deeply into the older Cretaceous marine rocks between
-Canon City and the Kansas border. The upturned layers along the mountain
-front, marked by hogback ridges and intervening valleys, continue nearly
-uninterrupted around the south end of the Front Range into the embayment
-in the mountains at Canon City. Skyline Drive, a scenic drive at Canon
-City, follows the crest of the Dakota hogback for a short distance and
-provides a fine panorama of the Canon City embayment.
-
-[Illustration: _Figure 28.—Hogback ridges along the Front Range west of
-Denver, Colo. South Platte River emerges from the mountains and cuts
-through hogbacks in middle distance. Photograph courtesy of Eugene
-Shearer, Intrasearch, Inc._]
-
-Extending eastward from the mountain front at Palmer Lake, a high divide
-separates the drainage of the South Platte River from that of the
-Arkansas River. The crest of the divide north of Colorado Springs is
-generally between 7,400 and 7,600 feet in altitude, but Interstate
-Highway 25 crosses it at about 7,350 feet, nearly 1,500 feet higher than
-Colorado Springs and more than 2,000 feet higher than Denver. From the
-crest of the divide to north of Castle Rock, resistant Oligocene Castle
-Rock Conglomerate (which is equivalent to part of the White River Group
-of the High Plains) is preserved in many places and forms a protective
-caprock on mesas and buttes. This picturesque part of the Colorado
-Piedmont looks quite different from the excavated valleys of the South
-Platte and Arkansas Rivers.
-
-Much of the terrain in the two river valleys has been smoothed by a
-nearly continuous mantle of windblown sand and silt. Northwesterly
-winds, which frequently blow with near-hurricane velocities, have
-whipped fine material from the floodplains of the streams and spread it
-eastward and southeastward over much of the Colorado Piedmont.
-Well-formed dunes are not common, but alined gentle ridges of sand and
-silt and abundant shallow blowout depressions inform us of the windblown
-origin of this cover.
-
-[Illustration: _Figure 29.—Pawnee Buttes in northeastern Colorado.
-Buttes isolated by erosion from High Plains in the background. Ogallala
-Formation caps top of Buttes. White River Group forms lower part. The
-top of the highest butte is about 240 feet above the saddle between the
-two buttes. Photograph by R. D. Miller, U. S. Geological Survey._]
-
-In the Colorado Piedmont, then, the erosional effects of streams are the
-most conspicuous features of the landscape, but these are enhanced by
-the steep tilting of the layered rocks along the western margin as a
-result of earth movement and modified by the nearly ubiquitous products
-of wind action, which have softened the landscape with a widespread
-cover of windblown sand and silt.
-
-
-                              PECOS VALLEY
-
-South of the land of volcanic rocks that is the Raton section, the Pecos
-River has cut a broad valley from the Sangre de Cristo Mountains, in New
-Mexico, southward to the Rio Grande, and has removed the piedmont cover
-of Ogallala Formation and cut deeply into the underlying rocks. The
-Ogallala Formation capping the High Plains to the east forms a rimrock
-at the top of the sharp Mescalero escarpment, which is the eastern
-boundary of the Pecos Valley. (See figure 4.) The western boundary of
-the Pecos Valley is the eastern base of discontinuous mountain ranges.
-
-The great thickness of Tertiary deposits that formed on the northern
-Great Plains did not accumulate here, and the Pecos River has cut its
-valley into the older marine sedimentary rocks. The rocks underlying the
-surface of much of the Pecos Valley are upper Paleozoic limestones.
-
-The soluble nature of limestone is responsible for some of the most
-spectacular features of the landscape in the Pecos Valley. For about 10
-miles north and 50 miles south of Vaughn, N. Mex., collapsed solution
-caverns in upper Paleozoic limestones have produced an unusual type of
-topography called karst. Karst topography is typified by numerous
-closely spaced sinks or closed depressions, some of which are very deep
-holes, caused by the collapse of the roof of a cave or solution cavity
-into the underground void, leaving hills, spines, or hummocks at the top
-of the intervening walls or ribs separating the depressions.
-
-Although the karst in the vicinity of Vaughn is perhaps the most
-conspicuous solution phenomenon, sinks and caves are common throughout
-the Pecos Valley. At Bottomless Lakes State Park east of Roswell, N.
-Mex., seven lakes occupy large sinkholes caused by the solution of salt
-and gypsum in underlying rocks.
-
-The most spectacular example of solution of limestone by ground water is
-Carlsbad Caverns, N. Mex., one of the most beautiful caves in the world.
-This celebrated solution cavity is preserved in a national park.
-
-The Pecos River along much of its present course flows in a
-vertical-walled canyon with limestone rims. The Canadian River, flowing
-eastward from the Sangre de Cristo Mountains, has cut a deep canyon
-along the northern part of the Pecos Valley section. The sharp rims of
-the Dakota Sandstone at the Canadian escarpment, north of the Canadian
-River, form the northern boundary of the Pecos Valley section.
-
-The sharp, northeast-trending broken flexure called the Border Hills
-that is crossed by U. S. Highway 70-380 about 20 miles west of Roswell
-is a unique landform of the Pecos Valley. This markedly linear upfolded
-(anticlinal) structure forms a ridge more than 30 miles long and about
-200 feet high.
-
-As in the Colorado Plateau, windblown sand and silt mantle the landscape
-in many places, but the greatest accumulations are along the base of the
-Mescalero escarpment at the northeast and southeast corners of the Pecos
-Valley section.
-
-East of the Pecos River, in the southeast part of the Pecos Valley, the
-underlying rocks have yielded much oil and potash. Oil fields are common
-east of Artesia and Carlsbad, and potash is mined east of Carlsbad.
-
-The Pecos and Canadian Rivers and their tributaries have created the
-general outline of the landscape of the Pecos Valley, but underground
-solution of limestone by ground water and the collapse of roofs of these
-cavities have contributed much detail to the surface that characterizes
-the Pecos Valley today.
-
-
-                            EDWARDS PLATEAU
-
-South of the Pecos Valley section, the Pecos River continues its journey
-to the Rio Grande in a steep-walled canyon cut 400 to 500 feet below the
-level of a plateau surface of Cretaceous limestone from which little has
-been stripped except a thin Tertiary cover of Ogallala Formation (fig.
-30). To the east, the plateau has been similarly incised by the Devils
-River and the West Nueces and Nueces Rivers. East of the Nueces to the
-escarpment formed by the Balcones fault zone, the southern part of the
-Edwards Plateau has been intricately dissected by the Frio, Sabinal,
-Medina, Guadalupe, and Pedernales Rivers and their tributary systems.
-San Antonio and Austin, Tex., are located on the Coastal Plain at the
-edge of the Balcones fault zone.
-
-[Illustration: _Figure 30.—Rio Grande and the flat-lying limestone
-layers of the Edwards Plateau downstream from the mouth of the Pecos
-River. Mexico on the left side of picture. Photograph by V. L. Freeman,
-U. S. Geological Survey._]
-
-The Pecos River, and to a lesser extent the Devils and Nueces Rivers,
-particularly in their lower courses, have entrenched themselves deeply
-in the plateau in remarkable meandering courses of a type that is
-usually found only in broad, low-lying floodplains. These stream courses
-reflect the stream environment prior to regional uplift.
-
-Sinkholes pit the relatively undissected limestone plateau surface in
-the northeast part of the Edwards Plateau, and some underground solution
-cavities in the limestone are well-known caves, such as the Caverns of
-Sonora, southwest of Sonora, Tex.
-
-Oil and gas fields are widely developed in the northern part of the
-Edwards Plateau, but only cattle ranches are found in the bare southern
-part.
-
-Ancient oceans deposited the limestones that now cap the Edwards
-Plateau; streams planed off the surface of the flat-lying limestone
-layers and entrenched themselves in steep-walled valleys; and ground
-water dissolved the limestone and created the solution cavities that are
-the caves and sinks of the Edwards Plateau. Water has created this
-landscape.
-
-
-                         PLAINS BORDER SECTION
-
-The Missouri Plateau, the Colorado Piedmont, the Pecos Valley, and the
-Edwards Plateau all were outlined by streams that flowed from the
-mountains. On the eastern border of the Great Plains, however, headward
-cutting by streams that have their source areas in the High Plains has
-dissected a large area, mainly in Kansas. This Plains Border Section
-comprises a number of east-trending river valleys—of the Republican,
-Solomon, Saline, Smoky Hill, Arkansas, Medicine Lodge, Cimarron, and
-North Canadian Rivers—and interstream divides, most of which are
-intricately dissected.
-
-North of the Arkansas River, the east-flowing Republican, Solomon,
-Saline, and Smoky Hill Rivers have incised themselves a few hundred feet
-below the Tertiary High Plains surface and have developed systems of
-closely spaced tributary draws. The interstream divides are narrow, and
-the tributary heads nearly meet at the divides. This intricately
-dissected part of the Plains Border section is called the Smoky Hills.
-Some isolated buttes of Cretaceous rocks left in the upper valley of the
-Smoky Hill River are called the Monument Rocks. A large area of rounded
-boulders exposed by erosion south of the Solomon River, southwest of
-Minneapolis, Kans., is called “Rock City.” These boulders originated as
-resistant nodules (concretions) within the Cretaceous rocks that
-contained them.
-
-South of the Arkansas River is a broad, nearly flat upland sometimes
-referred to as the Great Bend Plains. The Medicine Lodge River has cut
-headward into the southeastern part of the Great Bend Plains and created
-a thoroughly dissected topography in Triassic red rocks that is locally
-called the Red Hills. In a few places, badlands have formed in the Red
-Hills.
-
-Some large sinks or collapse depressions have formed because of solution
-of salt and gypsum at depth by ground water. Big and Little Basins, in
-Clark County in south-central Kansas, were formed in this way.
-
-Sand dunes have accumulated in places, especially near stream valleys.
-Dunes are common, for example, along the north side of the North
-Canadian River.
-
-Oil and gas fields are widely developed in the southeast part of the
-Plains Border section—in the Smoky Hills, the Great Bend Plains, and the
-Red Hills.
-
-The Plains Border section, like the Missouri Plateau, the Colorado
-Piedmont, and the Pecos Valley, is primarily a product of stream
-dissection. The differences in the outstanding landforms of the section
-are mainly the result of differences in the hardness of the eroded
-rocks.
-
-
-
-
-                                EPILOGUE
-
-
-The Great Plains, as we have seen, is many things. It contains thick
-layers of rock that formed in oceans, and younger layers of rocks
-deposited by streams. These rocks have been affected by earth movements
-and injected by hot molten rock, some of which reached the surface as
-volcanic rock. The rocks have been carved by streams, dissolved by
-ground water, partly covered by glaciers, and blown by winds. All of
-these agents have played important roles in determining the landscape
-and the landforms of the Great Plains. But the streams were the master
-agent. They formed the great depositional plain that was to become the
-Great Plains, and then began to destroy it—leaving only the High Plains
-to remind us of what it was. Those long miles we travel across the High
-Plains are a journey through history—geologic history.
-
-
-
-
-                            ACKNOWLEDGMENTS
-
-
-This narrative history of geologic and biologic events in the Great
-Plains had its origin in a study intended to identify potential National
-Natural Landmarks in the Great Plains, commissioned by the National Park
-Service. William A. Cobban, G. Edward Lewis, and Reuben J. Ross of the
-U. S. Geological Survey were collaborators in that study, and some of
-their contributions to the history of life on the Great Plains have been
-incorporated into this narrative, which was undertaken at the urging of
-Wallace R. Hansen.
-
-The photographic illustrations, other than those obtained from the film
-library of the U. S. Geological Survey, were provided by the interest
-and effort of my friends and colleagues of the Geological
-Survey—including C. R. Dunrud, V. L. Freeman, C. D. Miller, R. D.
-Miller, F. W. Osterwald, R. L. Parker, W. H. Raymond, III, Kenneth
-Shaver, and R. B. Taylor—and by Eugene Shearer, Intrasearch, Inc.,
-Denver, Colo. Without their help this publication would not have been
-possible.
-
-
-
-
-                         SOME SOURCE REFERENCES
-
-
-Alden, W. C., 1932, Physiography and glacial geology of eastern Montana
-    and adjacent areas: U. S. Geological Survey Professional Paper 174,
-    133 p.
-
-Bluemle, J. P., 1977, The face of North Dakota—the geologic story: North
-    Dakota Geological Survey Education Series 11, 73 p.
-
-Colton, R. B., Lemke, R. W., and Lindvall, R. M., 1961, Glacial map of
-    Montana east of the Rocky Mountains: U. S. Geological Survey
-    Miscellaneous Geologic Investigations Map I-327.
-
-Colton, R. B., Lemke, R. W., and Lindvall, R. M., 1963, Preliminary
-    glacial map of North Dakota: U. S. Geological Survey Miscellaneous
-    Geologic Investigations Map I-331.
-
-Curtis, B. F., ed., 1975, Cenozoic history of the southern Rocky
-    Mountains—Papers deriving from a symposium presented at the Rocky
-    Mountain Section meeting of the Geological Society of America,
-    Boulder, Colorado, 1973: Geological Society of America Memoir 144,
-    279 p.
-
-Darton, N. H., 1905, Preliminary report on the geology and underground
-    water resources of the central Great Plains: U. S. Geological Survey
-    Professional Paper 32, 433 p.
-
-Flint, R. F., 1955, Pleistocene geology of eastern South Dakota: U. S.
-    Geological Survey Professional Paper 262, 173 p.
-
-Frye, J. C., and Leonard, A. B., 1965, Quaternary of the southern Great
-    Plains, _in_ Wright, H. E., Jr., and Frey, D. G., eds., The
-    Quaternary of the United States—A review volume for the 7th Congress
-    of the International Association for Quaternary Research: Princeton
-    University Press, p. 203-216.
-
-Howard, A. D., 1958, Drainage evolution in northeastern Montana and
-    northwestern North Dakota: Geological Society of America Bulletin,
-    v. 69, no. 5, p. 575-588.
-
-Johnson, R. B., 1961, Patterns and origin of radial dike swarms
-    associated with West Spanish Peak and Dike Mountain, south-central
-    Colorado: Geological Society of America Bulletin, v. 72, no. 4, p.
-    579-590.
-
-Judson, S. S., Jr., 1950, Depressions of the northern portion of the
-    southern High Plains of eastern New Mexico: Geological Society of
-    America Bulletin, v. 61, no. 3, p. 253-274.
-
-Keech, C. F., and Bentall, Ray, 1971, Dunes on the plains—The Sand Hills
-    region of Nebraska: Nebraska University Conservation and Survey
-    Division Resources Report 4, 18 p.
-
-Lemke, R. W., Laird, W. M., Tipton, M. J., and Lindvall, R. M., 1965,
-    Quaternary geology of northern Great Plains, _in_ Wright, H. E.,
-    Jr., and Frey, D. G., eds., The Quaternary of the United States—A
-    review volume for the 7th Congress of the International Association
-    for Quaternary Research: Princeton University Press, p. 15-27.
-
-Mansfield, G. R., 1907, Glaciation in the Crazy Mountains of Montana:
-    Geological Society of America Bulletin, v. 19, p. 558-567.
-
-Pettyjohn, W. A., 1966, Eocene paleosol in the northern Great Plains,
-    _in_ Geological Survey research 1966: U. S. Geological Survey
-    Professional Paper 550-C, p. C61-C65.
-
-Robinson, C. S., 1956, Geology of Devils Tower National Monument,
-    Wyoming: U. S. Geological Survey Bulletin 1021-I, p. 289-302.
-
-Smith, H. T. U., 1965, Dune morphology and chronology in central and
-    western Nebraska: Journal of Geology, v. 73, no. 4, p. 557-578.
-
-Stormer, J. C., Jr., 1972, Ages and nature of volcanic activity on the
-    southern High Plains, New Mexico and Colorado: Geological Society of
-    America Bulletin, v. 83, no. 8, p. 2443-2448.
-
-Strahler, A. N., and Strahler, A. H., 1978, Modern physical geography:
-    New York, John Wiley & Sons, 502 p.
-
-Thornbury, W. D., 1965, Regional geomorphology of the United States: New
-    York, John Wiley, 609 p.
-
-Wright, H. E., Jr., 1970, Vegetational history of the Central Plains,
-    _in_ Pleistocene and recent environments of the central Great
-    Plains: Kansas University Department of Geology Special Publication
-    3, p. 157-172.
-
-
-
-
-                                 INDEX
-
-
-            [Italic page numbers indicate major references]
-
-
-                                   A
-  Page
-  Acknowledgments                                                      49
-  Agriculture                                                          30
-  Alaska                                                               11
-  Anadarko basin                                                   11, 16
-  Arikaree Formation                                                   18
-  Arkansas River                     2, 7, 23, 25, 29, 30, 42, 43, 44, 48
-  Artesia, N. Mex.                                                     46
-  Austin, Tex.                                                         47
-
-
-                                   B
-  Bad River                                                            39
-  Badland development                                                  39
-  Badlands National Monument                                           39
-  Balcones fault zone                                              23, 46
-  Basalt flows                                                     20, 24
-  Bearpaw Mountains                                                33, 36
-  Belle Fourche River                                                  39
-  Bents Fort, Colo.                                                     2
-  Big Basin, Kans.                                                     48
-  Big Belt Mountains                                                   36
-  Big Snowy Mountains                                                  36
-  Bison                                                                 1
-  Black Hills                                       7, 11, 18, 19, 20, 37
-  Border Hills                                                         46
-  Bottomless Lakes, N. Mex.                                            45
-  Brazos River                                                         23
-  Burnet, Tex.                                                         23
-
-
-                                   C
-  Camels                                                           16, 18
-  Canada                                                         1, 5, 33
-  Canadian escarpment                                              23, 46
-  Canadian River                                           23, 29, 30, 46
-  Cannonball River                                             33, 35, 39
-  Canon City, Colo.                                                    43
-  Caprock escarpment                                                7, 29
-  Capulin Mountain                                                 20, 23
-  Carlsbad, N. Mex.                                                    46
-  Carlsbad Caverns, N. Mex.                                            45
-  Carrizo Creek                                                        25
-  Castle Mountains                                                     37
-  Castle Rock, Colo.                                                   43
-  Castle Rock Conglomerate                                             43
-  Caverns of Sonora                                                    47
-  Cedar Point                                                          43
-  Central Lowland                                                   5, 34
-  Central Texas Uplift                                      7, 19, 20, 22
-  Cheyenne, Wyo.                                                       27
-  Cheyenne River                                                       39
-  Cimarron River                                                       48
-  Cirques                                                              38
-  Clark County, Kans.                                                  48
-  Climate                                                               2
-  Coal                                                                 16
-  Coastal Plain                                              5, 7, 10, 47
-  Colorado                                                             19
-  Colorado Piedmont                             7, 10, 19, 23, 42, 48, 49
-  Colorado Plateau                                                     46
-  Colorado River                                                       23
-  Colorado Springs, Colo.                                              43
-  Coteau du Missouri                                               34, 35
-  Crazy Mountains                                                      37
-  Creosote                                                              1
-  Cretaceous Period                            11, 16, 19, 24, 43, 46, 48
-
-
-                                   D
-  Dakota hogback                                                       43
-  Dakota Sandstone                                         22, 23, 24, 46
-  Dawson Formation                                                     16
-  Dead-ice moraines                                                    34
-  Definition                                                            1
-  Deformation                                                          11
-  Denver, Colo.                                                        42
-  Denver Formation                                                     16
-  Deposition                                               10, 11, 32, 44
-  Devils River                                                         46
-  Devils Tower, Wyo.                                                   37
-  Differential erosion                                         23, 25, 42
-  Dikes                                                                25
-  Dinosaurs                                                            16
-  Drift                                                                34
-
-
-                                   E
-  Edwards Plateau                                      10, 19, 29, 46, 48
-  Eocene Epoch                                                         16
-  Epilogue                                                             49
-  Erosion                                                              18
-  Escarpments                                                4, 7, 23, 34
-  Eskers                                                               35
-
-
-                                   F
-  Farming                                                              30
-  Fishers Peak                                                         23
-  Fissures                                                             20
-  Forests                                                         1, 2, 7
-  Fort Union Formation                                             16, 40
-  Fossils                                                              16
-  Frio River                                                           46
-  Front Range                                                          43
-
-
-                                   G
-  Gangplank                                                            27
-  Gas                                                          30, 47, 49
-  Glaciation                                                 2, 5, 11, 33
-  Grand River                                                          39
-  Great Bend, Kans.                                                     2
-  Great Bend Plains                                                48, 49
-  Great Falls, Mont.                                               33, 35
-  Great Ice Age                                                         5
-  Great Lakes                                                           5
-  Guadalupe River                                                      46
-  Gulf Coastal Plain                                                    7
-
-
-                                   H
-  Harney Peak                                                          20
-  Havre, Mont.                                                         33
-  Heart River                                                  33, 35, 39
-  Hell Creek Formation                                                 11
-  High Plains                                           7, 10, 25, 45, 48
-  Highwood Mountains                                           33, 35, 36
-  Horses                                                           16, 18
-  Hudson Bay                                                       32, 33
-
-
-                                   I
-  Ice Age                                                               5
-  Independence, Mo.                                                     2
-  Interior Highlands                                                    5
-  Interior Plains                                                   5, 11
-  Interstate Highway 25                                                43
-  Interstate Highway 70                                                 4
-  Introduction                                                          1
-
-
-                                   J
-  Jewel Cave                                                           21
-  Joints                                                               20
-  Judith Mountains                                                     36
-  Judith River                                                         38
-  Juniper                                                               1
-
-
-                                   K
-  Kames                                                                35
-  Kansas                                                           10, 48
-  Kansas City, Mo.                                                     35
-  Karst topography                                                     45
-  Kearney, Nebr.                                                        2
-  King Mountain                                                        29
-  Knife River                                                  33, 35, 39
-
-
-                                   L
-  Laccoliths                                                           37
-  Lake development                                                 34, 39
-  Lance Formation                                                      11
-  Laramie Formation                                                    16
-  Lava flows                                                           37
-  Lewis and Clark expedition                                            2
-  Limestone Plateau                                                21, 22
-  Limon, Colo.                                                      4, 43
-  Little Basin, Kans.                                                  48
-  Little Belt Mountains                                                36
-  Little Missouri River                                    33, 35, 38, 40
-  Little Rocky Mountains                                           33, 36
-  Littlefield, Tex.                                                    30
-  Llano Estacado                                                   29, 30
-  Loess                                                                29
-  Longhorn Caverns                                                     23
-
-
-                                   M
-  Marias River                                                         33
-  McCamey, Tex.                                                        29
-  Medicine Lodge River                                                 48
-  Medina River                                                         46
-  Mesa de Maya                                                 20, 24, 25
-  Mescalero escarpment                                      7, 29, 45, 46
-  Mesquite                                                              1
-  Mexico                                                            1, 11
-  Milk River                                                           33
-  Minneapolis, Kans.                                                   48
-  Miocene Epoch                                                        23
-  Missouri escarpment                                                  34
-  Missouri Plateau                                  7, 19, 20, 32, 48, 49
-  Missouri River                                 5, 7, 25, 32, 33, 35, 38
-  Montana                                                              33
-  Monument Rocks                                                       48
-  Moraines                                                             34
-  Moreau River                                                         39
-  _Moropus_                                                            18
-  Mount Rushmore                                                       20
-  Musselshell River                                                    38
-
-
-                                   N
-  Nebraska                                                          7, 29
-  Nebraska Sand Hills                                                  29
-  Needles area, Black Hills                                            20
-  New Mexico                                                    7, 19, 45
-  North Canadian River                                             48, 49
-  North Dakota                                                 33, 34, 35
-  Nueces River                                                         46
-  Nunataks                                                             33
-
-
-                                   O
-  Oak trees                                                             1
-  Odessa, Tex.                                                         30
-  Ogallala Formation                       18, 23, 24, 25, 27, 29, 45, 46
-  Ohio River                                                            5
-  Oil                                                      30, 46, 47, 49
-  Oklahoma                                                              7
-  Oligocene Epoch                                                  16, 43
-  Oregon Trail                                                          2
-  Ouachita province                                                     5
-  Outwash plains                                                       35
-  Ozark Plateaus                                                        5
-
-
-                                   P
-  Paleocene Epoch                                                  16, 23
-  Paleozoic Era                                                21, 30, 45
-  Palmer Lake                                                          43
-  Pampa, Tex.                                                          30
-  Pawnee Buttes                                                        42
-  Pecos River                                               7, 25, 45, 46
-  Pecos Valley                                  7, 10, 19, 23, 45, 48, 49
-  Pedernales River                                                     47
-  Pike, Zebulon                                                    iii, 2
-  Pine Ridge escarpment                                         7, 29, 40
-  Pioneers                                                              2
-  Plains Border Section                                            19, 48
-  Platte River                                                  2, 25, 29
-  Pleistocene Epoch                                                     5
-  Poison Canyon Formation                                      16, 23, 24
-  Powder River                                                         39
-  Powder River Basin                                                   39
-  Purgatoire Formation                                                 24
-  Purgatoire River                                                     25
-
-
-                                   R
-  Racetrack, The                                                       22
-  Rainfall                                                              2
-  Rapid City, S. Dak.                                                  20
-  Raton Basin                                                          24
-  Raton Formation                                                      16
-  Raton Mesa                                                       20, 23
-  Raton section                                            10, 20, 23, 45
-  Red Hills                                                        48, 49
-  Red Valley                                                           22
-  Republican River                                              4, 29, 48
-  Rhinoceroses                                                     16, 18
-  Rio Grande                                                        7, 45
-  Rocky Mountains                                                   5, 19
-  Roswell, N. Mex.                                                     45
-
-
-                                   S
-  Sabinal River                                                        46
-  Salina, Kans.                                                         4
-  Saline River                                                      4, 48
-  San Antonio, Tex.                                                    47
-  Sand dunes                                                       44, 49
-  Sand Hills, Nebr.                                                    29
-  Sangre de Cristo Mountains                                    7, 45, 46
-  Scotts Bluff National Monument                                   27, 42
-  Sedimentation                                                10, 11, 32
-  Shonkin Sag                                                          35
-  Sinkholes                                                        47, 48
-  Skyline Drive, Canon City, Colo.                                     43
-  Smith River                                                          38
-  Smoky Hill River                                                  4, 48
-  Smoky Hills                                                      48, 49
-  Soil development                                                     16
-  Solomon River                                                     4, 48
-  Solution cavities                                            45, 47, 48
-  Sonora, Tex.                                                         47
-  South Dakota                                             20, 29, 33, 34
-  South Dakota Badlands                                                16
-  South Platte River                                     4, 7, 42, 43, 44
-  Spanish Peaks                                                    19, 24
-  Spruce trees                                                          2
-  Stream deposition                                                11, 32
-  Summary                                                              49
-  Sun River                                                            38
-  Superior Upland                                                   5, 10
-  Sweetgrass Hills                                                     33
-  Sylvan Lake                                                          20
-
-
-                                   T
-  Tapirs                                                               16
-  Tertiary Period                                      42, 43, 45, 46, 48
-  Teton River                                                          33
-  Texas                                                                 7
-  Theodore Roosevelt National Memorial Park                        35, 40
-  Till                                                                 34
-  _Titanotheres_                                                       16
-  Tongue River                                                         39
-  Trails                                                                2
-  Trees                                                           1, 2, 7
-  Triassic Period                                                      21
-  Triceratops                                                          16
-  Trinidad, Colo.                                                      25
-
-
-                                   U
-  Uplift                                               11, 16, 19, 32, 37
-
-
-                                   V
-  Valley development                                                   39
-  Vaughn, N. Mex.                                                      45
-  Vegetation                                              1, 2, 7, 10, 16
-  Vermejo Formation                                                    16
-  Volcanoes                                                    16, 20, 40
-
-
-                                   W
-  Walsenburg, Colo.                                                    24
-  Warping                                                              11
-  Well-drilling                                                        11
-  West Nueces River                                                    46
-  White River                                                  29, 39, 40
-  White River Group                                            16, 40, 44
-  Williston basin                                              11, 16, 33
-  Wind Cave                                                            21
-  Wind deposition                                                      44
-  Wyoming                                                          20, 39
-
-
-                                   Y
-  Yellowstone River                                                33, 38
-
-  [Illustration: U. S. DEPARTMENT OF THE INTERIOR • March 3, 1849]
-
-
-
-
-                          Transcriber’s Notes
-
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-
-
-
-
-
-
-
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-<pre>
-
-The Project Gutenberg EBook of The Geologic Story of the Great Plains, by 
-Donald E. Trimble
-
-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: The Geologic Story of the Great Plains
-
-Author: Donald E. Trimble
-
-Release Date: October 6, 2020 [EBook #63396]
-
-Language: English
-
-Character set encoding: UTF-8
-
-*** START OF THIS PROJECT GUTENBERG EBOOK GEOLOGIC STORY--GREAT PLAINS ***
-
-
-
-
-Produced by Stephen Hutcheson and the Online Distributed
-Proofreading Team at https://www.pgdp.net
-
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-
-</pre>
-
-<div class="img">
-<img class="cover" id="coverpage" src="images/cover.jpg" alt="The Geologic Story of the Great Plains" width="500" height="787" />
-</div>
-<div class="img" id="pic_1">
-<img src="images/p01.jpg" alt="" width="800" height="689" />
-<p class="caption">DENVER, COLORADO</p>
-</div>
-<blockquote>
-<div class="pb" id="Page_iii">iii</div>
-<p><i>But from these immense prairies may arise one great
-advantage to the United States, viz., the restriction of our
-population to some certain limits, and thereby a
-continuation of the union. Our citizens being so prone to
-rambling, and extending themselves on the frontiers, will,
-through necessity, be constrained to limit their extent on
-the west to the borders of the Missouri and the
-Mississippi, while they leave the prairies, incapable of
-cultivation, to the wandering and uncivilized Aborigines of
-the country.</i>
-<span class="lr"><i>Zebulon Pike</i></span></p>
-</blockquote>
-<blockquote>
-<p>Exploratory Travels Through The Western Territories of North America comprising
-a voyage from St. Louis, on the Mississippi, to the source of that river,
-and a journey through the interior of Louisiana and the north-eastern provinces
-of New Spain. Performed in the years 1805, 1806, and 1807, by order of the
-Government of the United States. By Zebulon Montgomery Pike. Published by
-Paternoster-Row, London, 1811: W. H. Lawrence and Company, Denver, 1889.
-Quotation from pages 230-231, 1889 edition.</p>
-</blockquote>
-<div class="box">
-<h1>The GEOLOGIC STORY of
-<br /><span class="large">The GREAT PLAINS</span></h1>
-<p class="tbcenter"><span class="ss">By DONALD E. TRIMBLE</span></p>
-<p class="tbcenter"><i><span class="ss">A nontechnical description of the origin and evolution of the landscape of the Great Plains</span></i></p>
-<p class="tbcenter"><span class="ss">GEOLOGICAL SURVEY BULLETIN 1493</span></p>
-</div>
-<div class="pb" id="Page_iv">iv</div>
-<p class="tbcenter"><b>UNITED STATES DEPARTMENT OF THE INTERIOR
-<br />CECIL D. ANDRUS, <i>Secretary</i></b></p>
-<p class="center"><b>GEOLOGICAL SURVEY
-<br />H. William Menard, <i>Director</i></b></p>
-<div class="img" id="pic_2">
-<img src="images/p02.jpg" alt="U. S. DEPARTMENT OF THE INTERIOR &middot; March 3, 1849" width="300" height="297" />
-</div>
-<p class="center"><span class="ss">UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1980</span></p>
-<dl class="undent"><dt>Library of Congress Cataloging in Publication Data</dt>
-<dt>Trimble, Donald E.</dt>
-<dt>The geologic story of the Great Plains.</dt>
-<dt>(U.S. Geological Survey Bulletin 1493)</dt>
-<dt>Bibliography: p. 50</dt>
-<dt>Includes index.</dt>
-<dt>Supt. of Docs. no.: I 19.3: 1493</dt>
-<dt>I. Geology&mdash;Great Plains. I. Title.</dt>
-<dt>II. Series: United States Geological Survey Bulletin 1493.</dt>
-<dt>QE75.B9 no. 1493 [QE71] 557.3s [557.8] 80-607022</dt></dl>
-<hr class="dwide" />
-<p class="center">For sale by the Superintendent of Documents, U.S. Government Printing Office
-<br />Washington, D.C. 20402</p>
-<div class="pb" id="Page_v">v</div>
-<h2>CONTENTS</h2>
-<dl class="toc">
-<dt><a href="#c1">Introduction</a> 1</dt>
-<dt><a href="#c2">What is the Great Plains?</a> 5</dt>
-<dt><a href="#c3">The Great Plains&mdash;its parts</a> 7</dt>
-<dt><a href="#c4">Early history</a> 10</dt>
-<dd><a href="#c5">Warping and stream deposition</a> 11</dd>
-<dt><a href="#c6">Sculpturing the land</a> 18</dt>
-<dt><a href="#c7">Landforms of today&mdash;The surface features of the Great Plains</a> 19</dt>
-<dd><a href="#c8">Black Hills</a> 20</dd>
-<dd><a href="#c9">Central Texas Uplift</a> 22</dd>
-<dd><a href="#c10">Raton Section</a> 23</dd>
-<dd><a href="#c11">High Plains</a> 25</dd>
-<dd><a href="#c12">Missouri Plateau</a> 32</dd>
-<dd class="ddt2"><a href="#c13">Preglacial Drainage</a> 33</dd>
-<dd class="ddt2"><a href="#c14">Glaciated Missouri Plateau</a> 33</dd>
-<dd class="ddt2"><a href="#c15">Unglaciated Missouri Plateau</a> 36</dd>
-<dd><a href="#c16">The Colorado Piedmont</a> 42</dd>
-<dd><a href="#c17">Pecos Valley</a> 45</dd>
-<dd><a href="#c18">Edwards Plateau</a> 46</dd>
-<dd><a href="#c19">Plains Border Section</a> 48</dd>
-<dt><a href="#c20">Epilogue</a> 49</dt>
-<dt><a href="#c21">Acknowledgments</a> 49</dt>
-<dt><a href="#c22">Some source references</a> 50</dt>
-</dl>
-<div class="pb" id="Page_vi">vi</div>
-<h2><span class="h2line1">FIGURES</span></h2>
-<dl class="toc">
-<dt><a href="#pic_1">FRONTISPIECE. Aerial photograph of Denver.</a></dt>
-<dt><a href="#fig1"><span class="cn">1. </span>Index map</a> 3</dt>
-<dt><a><span class="cn">2-3. </span>Maps showing:</a></dt>
-<dd><a href="#fig2"><span class="cn">2. </span>Physical divisions of the United States and maximum extent of the continental ice sheets</a> 6</dd>
-<dd><a href="#fig3"><span class="cn">3. </span>The Great Plains province and its sections</a> 8</dd>
-<dt><a href="#fig4"><span class="cn">4. </span>Photograph of Mescalero escarpment and southern High Plains</a> 9</dt>
-<dt><a href="#fig5"><span class="cn">5. </span>Geologic time chart</a> 12</dt>
-<dt><a><span class="cn">6-8. </span>Maps showing:</a></dt>
-<dd><a href="#fig6"><span class="cn">6. </span>Paleogeography of U.S. in Late Cretaceous</a> 14</dd>
-<dd><a href="#fig7"><span class="cn">7. </span>Structural setting of the Great Plains</a> 14</dd>
-<dd><a href="#fig8"><span class="cn">8. </span>Progressive southward expansion of areas of deposition</a> 17</dd>
-<dt><a href="#fig9"><span class="cn">9. </span>Photograph of Big Horn strip mine at Acme, Wyo.</a> 18</dt>
-<dt><a href="#fig10"><span class="cn">10. </span>Black Hills diagram</a> 21</dt>
-<dt><a><span class="cn">11-16. </span>Photographs showing:</a></dt>
-<dd><a href="#fig11"><span class="cn">11. </span>Weathering of granite at Sylvan Lake in the Black Hills</a> 22</dd>
-<dd><a href="#fig12"><span class="cn">12. </span>Capulin Mountain National Monument, N. Mex.</a> 24</dd>
-<dd><a href="#fig13"><span class="cn">13. </span>Mesa de Maya, Colo.</a> 25</dd>
-<dd><a href="#fig14"><span class="cn">14. </span>Spanish Peaks, Colo.</a> 26</dd>
-<dd><a href="#fig15"><span class="cn">15. </span>&ldquo;The Gangplank,&rdquo; Wyo.</a> 27</dd>
-<dd><a href="#fig16"><span class="cn">16. </span>Scotts Bluff National Monument, Nebr.</a> 28</dd>
-<dt><a href="#fig17"><span class="cn">17. </span>Aerial photograph of the Nebraska Sand Hills</a> 30</dt>
-<dt><a href="#fig18"><span class="cn">18. </span>Map of the Nebraska Sand Hills</a> 31</dt>
-<dt><a><span class="cn">19-30. </span>Photographs showing:</a></dt>
-<dd><a href="#fig19"><span class="cn">19. </span>Loess plain in Nebraska</a> 32</dd>
-<dd><a href="#fig20"><span class="cn">20. </span>Ground moraine on the Coteau du Missouri in North Dakota</a> 34</dd>
-<dd><a href="#fig21"><span class="cn">21. </span>Slump blocks in North Unit of Theodore Roosevelt National Memorial Park, N. Dak.</a> 36</dd>
-<dd><a href="#fig22"><span class="cn">22. </span>Highwood Mountains, Mont.</a> 37</dd>
-<dd><a href="#fig23"><span class="cn">23. </span>Devils Tower National Monument, Wyo.</a> 38</dd>
-<dd><a href="#fig24"><span class="cn">24. </span>Glaciated valley in Crazy Mountains, Mont.</a> 39</dd>
-<dd><a href="#fig25"><span class="cn">25. </span>Powder River Basin in vicinity of Tongue River</a> 40</dd>
-<dd><a href="#fig26"><span class="cn">26. </span>Badlands National Monument, S. Dak.</a> 41</dd>
-<dd><a href="#fig27"><span class="cn">27. </span>Badlands of Little Missouri River in South Unit of Theodore Roosevelt National Memorial Park, N. Dak.</a> 42</dd>
-<dd><a href="#fig28"><span class="cn">28. </span>Hogback ridges along the Front Range, Colo.</a> 43</dd>
-<dd><a href="#fig29"><span class="cn">29. </span>Pawnee Buttes, Colo.</a> 44</dd>
-<dd><a href="#fig30"><span class="cn">30. </span>Edwards Plateau, Tex.</a> 47</dd>
-</dl>
-<h2><span class="h2line1">TABLE</span></h2>
-<dl class="toc">
-<dt><a href="#pic_3"><span class="cn">1. </span>Generalized chart of rocks of the Great Plains</a> 15</dt>
-</dl>
-<div class="pb" id="Page_1">1</div>
-<h1 title=""><span class="ss"><span class="smaller">The GEOLOGIC STORY of</span>
-<br />The GREAT PLAINS</span></h1>
-<p class="center"><span class="ssn">By Donald E. Trimble</span></p>
-<h2 id="c1"><span class="h2line1">INTRODUCTION</span></h2>
-<p>The Great Plains! The words alone create a sense of space
-and a feeling of destiny&mdash;a challenge. But what exactly is this
-special part of Western America that contains so much of our
-history? How did it come to be? Why is it different?</p>
-<p>Geographically, the Great Plains is an immense sweep of
-country; it reaches from Mexico far north into Canada and
-spreads out east of the Rocky Mountains like a huge welcome
-mat. So often maligned as a drab, featureless area, the
-Great Plains is in fact a land of marked contrasts and limitless
-variety: canyons carved into solid rock of an arid land
-by the waters of the Pecos and the Rio Grande; the seemingly
-endless grainfields of Kansas; the desolation of the Badlands;
-the beauty of the Black Hills.</p>
-<p>Before it was broken by the plow, most of the Great Plains
-from the Texas panhandle northward was treeless grassland.
-Trees grew only along the floodplains of streams and on the
-few mountain masses of the northern Great Plains. These
-lush prairies once were the grazing ground for immense herds
-of bison, and the land provided a bountiful life for those
-Indians who followed the herds. South of the grasslands, in
-Texas, shrubs mixed with the grasses: creosote bush along
-the valley of the Pecos River; mesquite, oak, and juniper to
-the east.</p>
-<div class="pb" id="Page_2">2</div>
-<p>The general lack of trees suggests that this is a land of little
-moisture, as indeed it is. Nearly all of the Great Plains
-receives less than 24 inches of rainfall a year, and most of it
-receives less than 16 inches. This dryness and the strength of
-sunshine in this area, which lies mostly between 2,000 and
-6,000 feet above sea level, create the semiarid environment
-that typifies the Great Plains. But it was not always so.
-When the last continental glacier stood near its maximum
-extent, some 12,000-14,000 years ago, spruce forest reached
-southward as far as Kansas, and the Great Plains farther
-south was covered by deciduous forest. The trees retreated
-northward as the ice front receded, and the Great Plains has
-been a treeless grassland for the last 8,000-10,000 years.</p>
-<p>For more than half a century after Lewis and Clark crossed
-the country in 1805-6, the Great Plains was the testing
-ground of frontier America&mdash;here America grew to maturity
-(<a href="#fig1">fig. 1</a>). In 1805-7, explorer Zebulon Pike crossed the south-central
-Great Plains, following the Arkansas River from near
-Great Bend, Kans., to the Rocky Mountains. In later years,
-Santa Fe traders, lured by the wealth of New Mexican trade,
-followed Pike&rsquo;s path as far as Bents Fort, Colo., where they
-turned southwestward away from the river route. Those pioneers
-who later crossed the plains on the Oregon Trail
-reached the Platte River near the place that would become
-Kearney, Nebr., by a nearly direct route from Independence,
-Mo., and followed the Platte across the central part of the
-Great Plains.</p>
-<p>Although these routes may have seemed long and tedious
-to those dusty travelers, they provided relatively easy access
-to the Rocky Mountains and had a continuous supply of
-fresh water, an absolute necessity in these plains. The minds
-of those frontiersmen surely were occupied with the dangers
-and demands of the moment&mdash;and with dreams&mdash;but the
-time afforded by the slow pace of travel also gave them
-ample opportunity for thought about the origins of their surroundings.</p>
-<p>Today&rsquo;s traveler, who has less time for contemplation,
-races past a changing kaleidoscope of landscape. The increased
-awareness created by this rapidity of change perhaps
-is even more likely to stimulate questions about the origin of
-this landscape.</p>
-<div class="pb" id="Page_3">3</div>
-<div class="img" id="fig1">
-<img src="images/map_lr.jpg" alt="" width="508" height="791" />
-<p class="center small"><i>Figure 1.&mdash;Index map of the Great Plains showing route of Lewis and Clark and the Santa Fe and Oregon Trails.</i></p>
-<p class="center small">[<a href="images/map_hr.jpg">This map in a higher resolution</a>]</p>
-</div>
-<div class="pb" id="Page_4">4</div>
-<p>For instance, the westbound traveler on Interstate
-Highway 70 traverses nearly a thousand miles of low,
-rounded hills after leaving the Appalachians; the rolling
-landscape is broken only by a few flat areas where glacial ice
-or small lakes once stood. Suddenly, near Salina, Kans., the
-observant traveler senses a difference in the landscape.
-Instead of rounded hills, widely or closely spaced, he sees on
-the skyline flat surfaces, or remnants of flat surfaces. As he
-climbs gently westward these broken horizontal lines stand
-etched against the sky. About 35 miles west of Salina he finds
-himself on a broad, flat plateau, where seemingly he can see
-forever. True, in places he descends into stream valleys, but
-only briefly, for he soon climbs back onto the flat surface.</p>
-<p>This plateau surface continues for 300 miles to the west&mdash;to
-within 100 miles of the abrupt front of the Rocky Mountains.
-East-flowing streams, such as the Smoky Hill, the
-Saline, the Solomon, and the Republican Rivers and their
-tributary branches, have cut their valleys into this surface,
-but these valleys become increasingly shallow and disappear
-entirely near the western rim of the plateau in eastern Colorado.</p>
-<p>The distant peaks of the Rockies are seen for the first time
-as the traveler approaches the escarpment that forms the
-western edge of this great plateau. After crossing the escarpment
-near Limon, Colo., he begins the long gentle descent to
-Denver, on the South Platte River near the foot of the mountains
-that loom so awesomely ahead. He has crossed the
-Great Plains. The distances have been great, but the contrasts
-have been marked.</p>
-<p>Had our traveler selected a different route, either to the
-north or south, he would have found even greater contrasts,
-for the Great Plains has many parts, each with its own distinctive
-aspect. Why should such diverse landscapes be
-considered parts of the Great Plains? What are their unifying
-features? And what created this landscape? Has it always
-been this way? If not, when was it formed? How was it
-formed?</p>
-<p>We will look here at some of the answers to those questions.
-The history of events that produced the landscape of
-the Great Plains is interpreted both from the materials that
-compose the landforms and from the landforms themselves.
-<span class="pb" id="Page_5">5</span>
-As we will see, all landforms are the result of geologic
-processes in action. These processes determine not only the
-size and shape of the landforms, but also the materials of
-which they are made. These geologic processes, which form
-and shape our Earth&rsquo;s surface, are simply the inevitable
-actions of the restless interior of the Earth and of the air,
-water, and carbon dioxide of the atmosphere, aided by
-gravity and solar heating (or lack of it). They all have helped
-sculpture the fascinating diversity of the part of our land we
-call the Great Plains.</p>
-<h2 id="c2"><span class="h2line1">WHAT IS THE GREAT PLAINS?</span></h2>
-<p>The United States has been subdivided into physiographic
-regions that, although they have great diversity within themselves,
-are distinctly different from each other (<a href="#fig2">fig. 2</a>).</p>
-<p>From the Rocky Mountains on the west to the Appalachians
-on the east, the interior of our country is a vast
-lowland (see <a href="#coverpage">cover</a>) known as the Interior Plains. These
-plains are bounded on the south by a region of Interior Highlands,
-consisting of the Ozark Plateaus and the Ouachita
-province, and by the Coastal Plain. In the Great Lakes
-region, the Interior Plains laps onto the most ancient part of
-the continent, the Superior Upland. West of the Great Lakes
-it extends far to the north into Canada. Certainly the Rocky
-Mountains are distinctly different from the region to the east,
-which is the Great Plains. The Great Plains, then, is the
-western part of the great Interior Plains. The Rocky Mountains
-form its western margin. But what determines its
-eastern margin?</p>
-<p>During the Pleistocene Epoch or Great Ice Age, huge glaciers
-formed in Canada and advanced southward into the
-great, central, low-lying Interior Plains of the United States.
-(See <a href="#fig2">figure 2</a>.) These glaciers and their deposits modified the
-surface of the land they covered, mostly between the Missouri
-and the Ohio Rivers; they smoothed the contours and
-gave the land a more subdued aspect than it had before they
-came. This glacially smoothed and modified land is called
-the Central Lowland. Although the ice sheets lapped onto the
-northern part, the Great Plains is the largely unglaciated
-region that extends from the Gulf Coastal Plain in Texas
-northward into Canada between the Central Lowland and
-the foot of the Rocky Mountains. Its eastern margin in Texas
-and Oklahoma is marked by a prominent escarpment, the
-Caprock escarpment. Its southern margin, where it abuts the
-Coastal Plain in Texas, is at another abrupt rise or scarp
-along the Balcones fault zone.</p>
-<div class="pb" id="Page_6">6</div>
-<div class="img" id="fig2">
-<img src="images/p04.jpg" alt="" width="800" height="495" />
-<p class="caption"><i>Figure 2.&mdash;Physical divisions of the United States and maximum extent of the continental ice
-sheets during the Great Ice Age.</i></p>
-</div>
-<div class="pb" id="Page_7">7</div>
-<h2 id="c3"><span class="h2line1">THE GREAT PLAINS&mdash;ITS PARTS</span></h2>
-<p>Within the Great Plains are many large areas that differ
-greatly from adjoining areas (<a href="#fig3">fig. 3</a>). The Black Hills stands
-out distinctively from the surrounding lower land, and its
-dark, forested prominence can be seen for scores of miles
-from any direction. At the southern end of the Great Plains is
-another, less imposing, forested prominence&mdash;the Central
-Texas Uplift. Most impressive, perhaps, is the huge, nearly
-flat plateau known as the High Plains, which extends southward
-from the northern border of Nebraska through the
-Panhandle of Texas, and which forms the central part of the
-Great Plains. The east and west rims of the southern High
-Plains are at high, cliffed, erosional escarpments&mdash;the Caprock
-escarpment on the east and the Mescalero escarpment
-on the west. The north edge of the High Plains is defined by
-another escarpment, the Pine Ridge escarpment, which separates
-the High Plains from a region that has been greatly dissected
-by the Missouri River and its tributaries. There,
-several levels of rolling upland are surmounted by small
-mountainous masses and flat-topped buttes and are entrenched
-by streams. This region is the Missouri Plateau. The
-continental glacier lapped onto the northeastern part of the
-Missouri Plateau and altered its surface.</p>
-<p>The South Platte and Arkansas Rivers and their tributaries
-have similarly dissected an area along the mountain front
-that is called the Colorado Piedmont, and the Pecos River
-has excavated a broad valley trending southward from the
-Sangre de Cristo Mountains in New Mexico into Texas. The
-Mescalero escarpment separates the Pecos Valley from the
-southern High Plains (<a href="#fig4">fig. 4</a>). South and east of the Pecos
-Valley, extending to the Rio Grande and the Coastal Plain, is
-a broad plateau of bare, stripped, flat-lying limestone layers
-bearing little but cactus that is called the Edwards Plateau.
-Green, crop-filled valleys with gently sloping valley walls
-and rounded stream divides trend eastward from the High
-Plains of western Kansas and characterize a Plains Border
-section. And finally, between the Colorado Piedmont on the
-north and the Pecos Valley on the south, volcanic vents,
-cinder cones, and lava fields form another distinctive terrain
-in the part of the Great Plains called the Raton section.</p>
-<div class="pb" id="Page_8">8</div>
-<div class="img" id="fig3">
-<img src="images/p05.jpg" alt="" width="495" height="800" />
-<p class="caption"><i>Figure 3.&mdash;The Great Plains province and its sections.</i></p>
-</div>
-<div class="pb" id="Page_9">9</div>
-<div class="img" id="fig4">
-<img src="images/p05a.jpg" alt="" width="800" height="505" />
-<p class="caption"><i>Figure 4.&mdash;Mescalero escarpment and the southern High Plains
-(Llano Estacado) south of Tucumcari, N. Mex., Photograph by
-C. D. Miller, U. S. Geological Survey.</i></p>
-</div>
-<div class="pb" id="Page_10">10</div>
-<p>Can such diverse parts of our land have a sufficiently
-common origin to justify their being considered part of one
-unified whole&mdash;the Great Plains? Probably so, but to understand
-why, we must examine some of the earlier geologic
-history of the Great Plains as well as subsequent events revealed
-in the present landforms. We will find that all parts of
-this region we call the Great Plains have a similar early
-history, and that the differences we see are the results of local
-dominance of certain processes in the ultimate shaping of the
-landscape, mostly during the last few million years. The distinctive
-character of the landscape in each section is determined
-in part by both the early events and the later shaping
-processes.</p>
-<h2 id="c4"><span class="h2line1">EARLY HISTORY</span></h2>
-<p>The Interior Plains, of which the Great Plains is the
-western, mostly unglaciated part (<a href="#fig2">fig. 2</a>), is the least complicated
-part of our continent geologically except for the
-Coastal Plain. For most of the half billion years from 570
-million (<a href="#fig5">fig. 5</a>) until about 70 million years ago, shallow seas
-lay across the interior of our continent (<a href="#fig6">fig. 6</a>). A thick
-sequence of layered sediments, mostly between 5,000 and
-10,000 feet thick, but more in places, was deposited onto the
-subsiding floor of the interior ocean (<a href="#table1">table 1</a>). These sediments,
-now consolidated into rock, rest on a floor of very
-old rocks that are much like the ancient rocks of the Superior
-Upland.</p>
-<p>About 70 million years ago the seas were displaced from
-the continental interior by slow uplift of the continent, and
-the landscape that appeared was simply the extensive, nearly
-flat floor of the former sea.</p>
-<div class="pb" id="Page_11">11</div>
-<h2 id="c5"><span class="h2line1">WARPING AND STREAM DEPOSITION</span></h2>
-<p>Most of these rocks of marine origin lie at considerable
-depth beneath the land surface, concealed by an overlying
-thick, layered sequence of rocks laid down by streams, wind,
-and glaciers. Nevertheless, their geologic character, position,
-and form are exceptionally well known from information
-gained from thousands of wells that have been drilled for oil.
-The initial, nearly horizontal position of the layers of rock
-beneath the Interior Plains has been little disturbed except
-where mountains like the Black Hills were uplifted about 70
-million years ago. At those places, which are all in the northern
-and southern parts of the Great Plains, the sedimentary
-layers have been warped up and locally broken by the rise of
-hot molten rock from depth. Elsewhere in the Interior Plains,
-however, earth forces of about the same period caused only a
-reemphasis of gentle undulations in the Earth&rsquo;s crust.</p>
-<p>These undulations affected both the older basement rocks
-and the overlying sedimentary rocks, and they take the form
-of gentle basins and arches that in some places span several
-States. (See sketch map, <a href="#fig7">figure 7</a>.) A series of narrow basins
-lies along the mountain front on the west side of the Great
-Plains. A broad, discontinuous arch extends southwest from
-the Superior Upland to the Rocky Mountain front to form a
-buried divide that separates the large Williston basin on the
-north from the Anadarko basin to the south.</p>
-<p>While the flat-lying layers of the Interior Plains were being
-only gently warped, vastly different earth movements were
-taking place farther west, in the area of the present Rocky
-Mountains. Along a relatively narrow north-trending belt,
-extending from Mexico to Alaska, the land was being
-uplifted at a great rate. The layers of sedimentary rock deposited
-in the inland sea were stripped from the crest of the
-rising mountainous belt by erosion and transported to its
-flanks as the gravel, sand, and mud of streams and rivers.
-This transported sediment was deposited on the plains to
-form the rocks of the Cretaceous Hell Creek, Lance,
-Laramie, Vermejo, and Raton Formations. Vegetation
-thrived on this alluvial plain, and thick accumulations of
-woody debris were buried to ultimately become coal. This
-lush vegetation provided ample food for the hordes of three-horned
-dinosaurs (<i>Triceratops</i>) that roamed these plains.
-Their fossilized remains are found from Canada to New
-Mexico.</p>
-<div class="pb" id="Page_12">12</div>
-<div class="img" id="fig5">
-<img src="images/time_lr.jpg" alt="" width="800" height="632" />
-<p class="center small"><i>Figure 5.&mdash;Geologic time chart and the progression of life
-forms. Note Cretaceous</i> Triceratops, <i>Oligocene</i> Titanotheres,
-<i>and Miocene</i> Moropus.</p>
-<p class="center small">[<a href="images/time_hr.jpg">This map in a higher resolution</a>]</p>
-</div>
-<blockquote>
-<h4><span class="center"><span class="ssn">GEOLOGIC TIME
-<br /><span class="small">The Age of the Earth</span></span></span></h4>
-<p><span class="ssn">The Earth is very old&mdash;4.5 billion years or more according to
-recent estimates. Most of the evidence for an ancient Earth is contained
-in the rocks that form the Earth&rsquo;s crust. The rock layers
-themselves&mdash;like pages in a long and complicated history&mdash;record
-the surface-shaping events of the past, and buried within them are
-traces of life&mdash;the plants and animals that evolved from organic
-structures that existed perhaps 3 billion years ago.</span></p>
-<p><span class="ssn">Also contained in rocks once molten are radioactive elements
-whose isotopes provide Earth scientists with an atomic clock. Within
-these rocks, &ldquo;parent&rdquo; isotopes decay at a predictable rate to form
-&ldquo;daughter&rdquo; isotopes. By determining the relative amounts of parent
-and daughter isotopes, the age of these rocks can be calculated.</span></p>
-<p><span class="ssn">Thus, the results of studies of rock layers (stratigraphy), and of
-fossils (paleontology), coupled with the ages of certain rocks as measured
-by atomic clocks (geochronology), attest to a very old Earth!</span></p>
-</blockquote>
-<div class="pb" id="Page_14">14</div>
-<div class="img" id="fig6">
-<img src="images/p07.jpg" alt="" width="800" height="564" />
-<p class="caption"><i>Figure 6.&mdash;Generalized paleogeographic map of the United States
-in Late Cretaceous time (65 to 80 million years ago), when most
-of the Great Plains was beneath the sea.</i></p>
-</div>
-<div class="img" id="fig7">
-<img src="images/p07a.jpg" alt="" width="800" height="658" />
-<p class="caption"><i>Figure 7.&mdash;Structural setting of the Great Plains. Williston basin
-and Anadarko basin are separated by a midcontinental arch.</i></p>
-</div>
-<div class="pb" id="Page_15">15</div>
-<div class="img" id="pic_3">
-<img src="images/p07b.jpg" alt="" width="800" height="527" />
-<p class="caption">Table 1.&mdash;Generalized chart of rocks of the Great Plains</p>
-</div>
-<table class="center">
-<tr class="th"><th id="table1">Geologic age<br /><span class="jr">Millions of years ago</span> </th><th>Missouri Plateau&mdash;Black Hills </th><th>High Plains&mdash;Plains Border&mdash;Colorado Piedmont </th><th>Pecos Valley&mdash;Edwards Plateau&mdash;Central Texas</th></tr>
-<tr><td class="l">Quaternary</td></tr>
-<tr><td class="l"><span class="hst">Pleistocene</span> </td><td class="l">Glacial deposits, alluvium, and terrace deposits </td><td class="l">Alluvium, sand dunes, and loess </td><td class="l">Piedmont, terrace, and bolson deposits</td></tr>
-<tr><td class="r">2 </td><td colspan="2" class="l">erosional surface</td></tr>
-<tr><td class="l">Tertiary</td></tr>
-<tr><td class="l"><span class="hst">Pliocene</span> </td><td colspan="2" class="l">EROSION</td></tr>
-<tr><td class="r">5 </td><td class="l">Flaxville Gravel and Ogallala Formation </td><td class="l">Ogallala formation</td></tr>
-<tr><td class="l"><span class="hst">Miocene</span> </td><td class="l">Arikaree Formation </td><td class="l">Arikaree Formation</td></tr>
-<tr><td class="r">22-24 </td><td colspan="2" class="l">erosional surface</td></tr>
-<tr><td class="l"><span class="hst">Oligocene</span> </td><td class="l">White River Group </td><td class="l">White River Group </td><td class="l">Mostly missing because of erosion or nondeposition</td></tr>
-<tr><td class="r">37-38 </td><td colspan="2" class="l">erosional surface</td></tr>
-<tr><td class="l"><span class="hst">Eocene</span> </td><td class="l">Wasatch and Golden Valley Formations</td></tr>
-<tr><td class="r">53-54 </td><td class="l"> </td><td class="l">Dawson Arkose</td></tr>
-<tr><td class="l"><span class="hst">Paleocene</span> </td><td class="l">Fort Union Formation </td><td class="l">Denver, Poison Canyon, and Raton Formations</td></tr>
-<tr><td class="r">65</td></tr>
-<tr><td class="l">Cretaceous </td><td class="l">Hell Creek and Lance Formations </td><td class="l">Vermejo and Laramie Formations</td></tr>
-<tr><td class="l"> </td><td class="l">Fox Hills Sandstone </td><td class="l">Trinidad and Fox Hills Sandstones</td></tr>
-<tr><td class="l"> </td><td colspan="2" class="l">Shales, sandstones, and limestones deposited in Late Cretaceous sea</td></tr>
-<tr><td class="l"> </td><td class="l">Dakota Sandstone and Lakota Formation </td><td class="l">Dakota Sandstone</td></tr>
-<tr><td class="l"> </td><td class="l"> </td><td class="l">Glen Rose and Edwards Limestones</td></tr>
-<tr><td class="r">136</td></tr>
-<tr><td class="l">Jurassic </td><td class="l">Sundance Formation, Ellis Group, and Unkpapa Sandstone </td><td class="l">Morrison Formation </td><td class="l">Jurassic rocks not present</td></tr>
-<tr><td class="r">190-195</td></tr>
-<tr><td class="l">Triassic </td><td colspan="3" class="l">Dominantly red rocks</td></tr>
-<tr><td class="r">225</td></tr>
-<tr><td class="l">PALEOZOIC </td><td colspan="3" class="l">Paleozoic rocks, undivided</td></tr>
-<tr><td class="r">570</td></tr>
-<tr><td class="l">PRECAMBRIAN </td><td colspan="3" class="l">Precambrian rocks, undivided</td></tr>
-</table>
-<div class="pb" id="Page_16">16</div>
-<p>As the mountains continued to rise, the eroding streams
-cut into the old core rocks of the mountains, and that debris
-too was carried to the flanks and onto the adjoining plains.
-The mountainous belt continued to rise intermittently, and
-volcanoes began to appear about 50 million years ago. Together,
-the mountains and volcanoes provided huge quantities
-of sediment, which the streams transported to the
-plains and deposited. The areas nearest the mountains were
-covered by sediments of Late Cretaceous and Paleocene age
-(<a href="#table1">table 1</a>)&mdash;the Poison Canyon Formation to the south, the
-Dawson and Denver Formations in the Denver area, and the
-Fort Union Formation to the north (<a href="#fig8">fig. 8</a>). Vegetation continued
-to flourish, especially in the northern part of the Great
-Plains, and was buried to form the thick lignite and subbituminous
-coal beds of the Fort Union Formation (<a href="#fig9">fig. 9</a>). The
-earliest mammals, most of whose remains come from the
-Paleocene Fort Union Formation, have few modern survivors.</p>
-<p>Beginning about 45 million years ago, in Eocene time,
-there was a long period of stability lasting perhaps 10 million
-years, when there was little uplift of the mountains and,
-therefore, little deposition on the plains. A widespread and
-strongly developed soil formed over much of the Great
-Plains during this period of stability. With renewed uplift
-and volcanism in the mountains at the end of this period,
-great quantities of sediment again were carried to the
-plains by streams and spread over the northern Great Plains
-and southeastward to the arch or divide separating the
-Williston and Anadarko basins (<a href="#fig8">fig. 8</a>). Those sediments
-form the White River Group, in which the South Dakota
-Badlands are carved. In addition to the <i>Titanotheres</i>, huge
-beasts with large, long horns on their snouts who lived only
-during the Oligocene (37 to 22 million years ago), vast herds
-of camels, rhinoceroses, horses, and tapirs&mdash;animals now
-found native only on other continents&mdash;grazed those Oligocene
-semiarid grassland plains.</p>
-<div class="pb" id="Page_17">17</div>
-<div class="img" id="fig8">
-<img src="images/p08.jpg" alt="" width="458" height="800" />
-<p class="caption"><i>Figure 8.&mdash;Progressive southeastward expansion of areas covered
-by Paleocene, Oligocene, and Miocene-Pliocene sedimentary
-deposits.</i></p>
-</div>
-<dl class="undent caption"><dt>Powder River basin</dt>
-<dt>Denver basin</dt>
-<dt>Raton basin</dt>
-<dt>PLAINS</dt>
-<dd>Margin of Oligocene deposition</dd>
-<dd>Margin of Miocene-Pliocene deposition</dd></dl>
-<div class="pb" id="Page_18">18</div>
-<div class="img" id="fig9">
-<img src="images/p09.jpg" alt="" width="800" height="550" />
-<p class="caption"><i>Figure 9.&mdash;Big Horn coal strip mine in Fort Union Formation at
-Acme, Wyo. Photograph by F. W. Osterwald, U.S. Geological
-Survey.</i></p>
-</div>
-<p>Sometime between 20 and 30 million years ago the streams
-began depositing sand and gravel beyond the divide, and, for
-another 10 million years or more, stream sediments of the
-Arikaree and Ogallala Formations spread over the entire
-Great Plains from Canada to Texas, except where mountainous
-areas such as the Black Hills stood above the plains.
-Between 5 and 10 million years ago, then, the entire Great
-Plains was an eastward-sloping depositional plain surmounted
-only by a few mountain masses. Horses, camels,
-rhinoceroses, and a strange horselike creature with clawed
-feet (called <i>Moropus</i>) lived on this plain.</p>
-<h2 id="c6"><span class="h2line1">SCULPTURING THE LAND</span></h2>
-<p>Sometime between 5 and 10 million years ago, however, a
-great change took place, apparently as a result of regional
-<span class="pb" id="Page_19">19</span>
-uplift of the entire western part of the continent. While
-before, the streams had been depositing sediment on the
-plains for more than 60 million years, building up a huge
-thickness of sedimentary rock layers, now the streams were
-forced to cut down into and excavate the sediments they had
-formerly deposited. As uplift continued&mdash;and it may still be
-continuing&mdash;the streams cut deeper and deeper into the
-layered stack and developed tributary systems that excavated
-broad areas. High divides were left between streams in
-some places, and broad plateaus were formed and remain in
-other places. The great central area was essentially untouched
-by erosion and remained standing above the dissected
-areas surrounding it as the escarpment-rimmed
-plateau that is the High Plains.</p>
-<p>This downcutting and excavation by streams, then, which
-began between 5 and 10 million years ago, roughed out the
-landscape of the Great Plains and created the sections we call
-the Missouri Plateau, the Colorado Piedmont, the Pecos
-Valley, the Edwards Plateau, and the Plains Border Section.
-Nearly all the individual landforms that now attract the eye
-have been created by geologic processes during the last 2
-million years. It truly is a young landscape.</p>
-<h2 id="c7"><span class="h2line1">LANDFORMS OF TODAY&mdash;The surface features of the Great Plains</span></h2>
-<p>The mountainous sections of the Great Plains were formed
-long before the remaining areas were outlined by erosion.
-Uplift of the Black Hills and the Central Texas Uplift began
-as the continental interior was raised and the last Cretaceous
-sea was displaced, 65 to 70 million years ago. They stood
-well above the surrounding plains long before any sediments
-from the distant Rocky Mountains began to accumulate at
-their bases. In southern Colorado and northern New Mexico,
-molten rock invaded the sedimentary layers between 22 and
-26 million years ago. The Spanish Peaks were formed at this
-time from hot magma that domed up the surface layers but
-did not break through; the magma has since cooled and
-solidified and has been exposed by erosion. Elsewhere the
-<span class="pb" id="Page_20">20</span>
-magma reached the surface, forming volcanoes, fissures, and
-basalt flows. A great thickness of basalt flows accumulated
-at Raton Mesa and Mesa de Maya between 8 and 2 million
-years ago. Volcanism has continued intermittently, and the
-huge cinder cone of Capulin Mountain was created by explosive
-eruption only 10,000 to 4,000 years ago. Most of these
-volcanic masses were formed before major downcutting by
-the streams began. Other igneous intrusions and volcanic
-areas in the northern Great Plains similarly were formed
-before the streams were incised.</p>
-<p>To examine the origin of the present landscape and of the
-landforms typical of the various sections of the Great Plains,
-it is convenient to begin with the Black Hills, the Central
-Texas Uplift, and the Raton section simply because they were
-formed first&mdash;they existed before the other sections were
-outlined.</p>
-<h3 id="c8">BLACK HILLS</h3>
-<p>The Black Hills is a huge, elliptically domed area in northwestern
-South Dakota and northeastern Wyoming, about
-125 miles long and 65 miles wide (<a href="#fig10">fig. 10</a>). Rapid City, S.
-Dak., is on the Missouri Plateau at the east edge of the Black
-Hills. Uplift caused erosion to remove the overlying cover of
-marine sedimentary rocks and expose the granite and metamorphic
-rocks that form the core of the dome. The peaks of
-the central part of the Black Hills presently are 3,000 to 4,000
-feet above the surrounding plains. Harney Peak, with an altitude
-of 7,242 feet, is the highest point in South Dakota.
-These central spires and peaks all are carved from granite
-and other igneous and metamorphic rocks that form the core
-of the uplift. The heads of four of our great Presidents are
-sculpted from this granite at Mount Rushmore National
-Memorial. Joints in the rocks have controlled weathering
-processes that influenced the final shaping of many of these
-landforms. Closely spaced joints have produced the spires of
-the Needles area, and widely spaced joints have produced the
-rounded forms of granite that are seen near Sylvan Lake (<a href="#fig11">fig. 11</a>).</p>
-<p>Marine sedimentary rocks surrounding the old core rocks
-form well-defined belts. Lying against the old core rocks and
-<span class="pb" id="Page_21">21</span>
-completely surrounding them are Paleozoic limestones that
-form the Limestone Plateau (<a href="#fig10">fig. 10</a>). These tilted layers have
-steep erosional scarps facing the central part of the Black
-Hills. Wind Cave and Jewel Cave were produced by ground
-water dissolving these limestones along joints. These caves
-are sufficiently impressive to be designated as a national park
-and a national monument, respectively. Encircling the Limestone
-Plateau is a continuous valley cut in soft Triassic shale.
-This valley has been called &ldquo;the Racetrack,&rdquo; because of its
-continuity, and the Red Valley, because of its color. Surrounding
-the Red Valley is an outer hogback ridge formed by
-the tilted layers of the Dakota Sandstone, which are quite
-hard and resistant to erosion. Streams that flow from the
-central part of the Black Hills pass through the Dakota
-hogback in narrow gaps.</p>
-<div class="img" id="fig10">
-<img src="images/p10.jpg" alt="" width="599" height="800" />
-<p class="caption"><i>Figure 10.&mdash;Diagram of the Black Hills uplift by A. N. Strahler
-(Strahler and Strahler, 1978). Used by permission.</i></p>
-</div>
-<dl class="undent caption"><dt>Dakota Sandstone hogback</dt>
-<dt>Limestone plateau</dt>
-<dt>Belle Fourche River</dt>
-<dt>Spearfish</dt>
-<dt>Bear Butte</dt>
-<dt>Sundance</dt>
-<dt>Red Valley</dt>
-<dt>Rapid City</dt>
-<dt>Red Valley</dt>
-<dt>Hot Springs</dt>
-<dt>Cheyenne River</dt>
-<dt>Edgemont</dt>
-<dt>Mt. Rushmore National Monument</dt>
-<dt>Jewel Cave National Monument</dt>
-<dt>Wind Cave National Park</dt></dl>
-<div class="pb" id="Page_22">22</div>
-<div class="img" id="fig11">
-<img src="images/p11.jpg" alt="" width="795" height="522" />
-<p class="caption"><i>Figure 11.&mdash;Jointed granite rounded by weathering at Sylvan Lake,
-in the central part of the Black Hills, S. Dak.</i></p>
-</div>
-<p>The Black Hills, then, is an uplifted area that has been
-carved deeply but differentially by streams to produce its
-major outlines. Those outlines have been modified mainly by
-weathering of the ancient core rocks and solution of the limestone
-of the Limestone Plateau.</p>
-<h3 id="c9">CENTRAL TEXAS UPLIFT</h3>
-<p>The domed rocks of the Central Texas Uplift form a topography
-different from that of the Black Hills. Erosion of a
-broad, uplifted dome here has exposed a core of old granites,
-gneisses, and schists, as in the Black Hills, but in the Central
-Texas Uplift, erosion has produced a topographic basin,
-rather than high peaks and spires, on the old rocks of the
-central area. A low plateau surface dissected into rounded
-ridges and narrow valleys slopes gently eastward from the
-<span class="pb" id="Page_23">23</span>
-edge of the central area to an escarpment at the Balcones
-fault zone, which determines the eastern edge of the Great
-Plains here. Northwest of the central basin the Colorado
-River flows in a broad lowland about 100 miles long, but the
-northern edge of the uplift, forming a divide between the
-Brazos and the Colorado Rivers, is a series of mesas formed
-of more resistant sandstone and limestone.</p>
-<p>The cutting action of streams, modified or controlled in
-part by differences in hardness of the rock layers, has been
-responsible for the landforms of the Central Texas Uplift.
-Weathering of the old core rocks has softened them sufficiently
-to permit deeper erosion of the central area, and solution
-of limestone by ground water has formed such features
-as Longhorn Caverns, 11 miles southwest of Burnet, Tex.</p>
-<h3 id="c10">RATON SECTION</h3>
-<p>Volcanism characterizes the Raton section. The volcanic
-rocks, which form peaks, mesas, and cones, have armored
-the older sedimentary rocks and protected them from the
-erosion that has cut deeply into the adjoining Colorado Piedmont
-to the north and Pecos Valley to the south. The south
-edge of the Raton section is marked by a spectacular south-facing
-escarpment cut on the nearly flat-lying Dakota Sandstone.
-This escarpment is the Canadian escarpment, north of
-the Canadian River. Northward for about 100 miles, the
-landscape is that of a nearly flat plateau cut on Cretaceous
-rock surmounted here and there by young volcanic vents,
-cones, and lava fields. Capulin Mountain is a cinder cone
-only 10,000 to 4,000 years old (<a href="#fig12">fig. 12</a>). Near the New
-Mexico-Colorado border, huge piles of lava were erupted 8
-to 2 million years ago onto an older, higher surface on top of
-either the Ogallala Formation of Miocene age or the Poison
-Canyon Formation of Paleocene age. (See <a href="#table1">table 1</a>.) These
-lava flows formed a resistant cap, which protected the underlying
-rock from erosion while all the surrounding rock
-washed away. The result is the high, flat-topped mesas, such
-as Raton Mesa and Mesa de Maya (<a href="#fig13">fig. 13</a>), that now form
-the divide between the Arkansas and Canadian Rivers. At
-Fishers Peak, on the west end of Raton Mesa, about 800 feet
-of basalt flows rest on the Poison Canyon Formation at
-<span class="pb" id="Page_24">24</span>
-about 8,800 feet in altitude. Farther east, on Mesa de Maya,
-about 400 feet of basalt flows overlie the Ogallala Formation
-at altitudes ranging from about 6,500 feet at the west end to
-about 5,200 feet at the east end, some 35 miles to the east.
-The Ogallala here rests on Cretaceous Dakota Sandstone and
-Purgatoire Formation, for the Poison Canyon Formation
-was removed by erosion along the crest of a local uplift
-before the Ogallala was deposited.</p>
-<div class="img" id="fig12">
-<img src="images/p12.jpg" alt="" width="800" height="639" />
-<p class="caption"><i>Figure 12.&mdash;Capulin Mountain National Monument in northeastern
-New Mexico. This huge cinder cone, which erupted between
-4,000 and 10,000 years ago, rises more than 1,000 feet
-above its base. Photograph by R. D. Miller, U.S. Geological
-Survey.</i></p>
-</div>
-<p>East of the belt of upturned sedimentary layers that form
-the hogback ridges at the front of the Rocky Mountains, the
-layered rocks in the Raton Basin have been intruded in many
-places by igneous bodies, the two largest of which form the
-Spanish Peaks (<a href="#fig14">fig. 14</a>), southwest of Walsenburg, Colo.
-These two peaks are formed by igneous bodies that were
-intruded 26 to 22 million years ago and have since been
-exposed by removal of the overlying sedimentary rock layers
-<span class="pb" id="Page_25">25</span>
-by erosion. Radiating from the Spanish Peaks are hundreds
-of dikes, nearly vertical slabs of igneous rock that filled fractures
-radiating from the centers of intrusion. Erosion of the
-sedimentary layers has left many of these dikes as conspicuous
-vertical walls of igneous rock that project high above
-the surrounding land surface. Some of these dikes north of
-Trinidad, Colo. extend eastward for about 25 miles, almost
-to the Purgatoire River.</p>
-<div class="img" id="fig13">
-<img src="images/p12a.jpg" alt="" width="800" height="289" />
-<p class="caption"><i>Figure 13.&mdash;Lava-capped Mesa de Maya, east of Trinidad, Colo.
-Spanish Peaks in left distance. Mesa rises about 1,000 feet above
-surrounding area. Photograph by R. B. Taylor, U.S. Geological
-Survey.</i></p>
-</div>
-<p>The northern boundary of the Raton section is placed
-somewhat indefinitely at the northern limit of the area injected
-by igneous dikes. The eastern boundary of the Raton
-section is at the eastern margin of the lavas of Mesa de Maya
-and adjoining mesas, where lava-capped outliers of Ogallala
-Formation are separated from the Ogallala of the High Plains
-only by the canyon of Carrizo Creek.</p>
-<h3 id="c11">HIGH PLAINS</h3>
-<p>At the end of Ogallala deposition, some 5 million years
-ago, the Great Plains, with the exception of the uplifted and
-the volcanic areas, was a vast, gently sloping plain that
-extended from the mountain front eastward to beyond the
-present Missouri River in some places. Regional uplift of the
-western part of the continent forced the streams to cut downward;
-land near the mountains was stripped away by the
-Missouri, the Platte, the Arkansas, and the Pecos Rivers, and
-the eastern border of the plains was gnawed away by lesser
-streams. A large central area of the plain is preserved,
-however, essentially untouched and unaffected by the
-streams, as a little-modified remnant of the depositional
-surface of 5 million years ago. This Ogallala-capped preserved
-remnant of that upraised surface is the High Plains. In
-only one place does that old surface still extend to the mountains&mdash;at
-the so-called &ldquo;Gangplank&rdquo; west of Cheyenne, Wyo.
-(<a href="#fig15">fig. 15</a>). In places, as at Scotts Bluff National Monument,
-Nebr. (<a href="#fig16">fig. 16</a>), small fragments of this surface have been isolated
-from the High Plains by erosion and now stand above
-the surrounding area as buttes.</p>
-<div class="pb" id="Page_26">26</div>
-<div class="img" id="fig14">
-<img src="images/p13.jpg" alt="" width="800" height="387" />
-<p class="caption"><i>Figure 14.&mdash;Spanish Peaks, southwest of Walsenburg, Colo. Igneous rocks and many radiating dikes exposed by
-erosion. Photograph by R. B. Taylor, U.S. Geological Survey.</i></p>
-</div>
-<div class="pb" id="Page_27">27</div>
-<div class="img" id="fig15">
-<img src="images/p13a.jpg" alt="" width="800" height="590" />
-<p class="caption"><i>Figure 15.&mdash;Looking east toward Cheyenne at &ldquo;the Gangplank.&rdquo;
-Interstate Highway 80 and the Union Pacific Railroad follow the
-Gangplank from the High Plains in the distance onto the Precambrian
-rocks (older than 570 m.y.) of the Laramie Mountains in
-the foreground. Photograph by R. D. Miller, U.S. Geological
-Survey.</i></p>
-</div>
-<div class="pb" id="Page_28">28</div>
-<div class="img" id="fig16">
-<img src="images/p14.jpg" alt="" width="800" height="390" />
-<p class="caption"><i>Figure 16.&mdash;Aerial view of Scotts Bluff National Monument, Nebr. Buttes on the south side of the valley of the North Platte
-River isolated by erosion from High Plains in the background. Highest butte stands about 800 feet above valley floor.</i></p>
-</div>
-<div class="pb" id="Page_29">29</div>
-<p>The High Plains extends southward from the Pine Ridge
-escarpment, near the South Dakota-Nebraska border (<a href="#fig3">fig. 3</a>),
-to the Edwards Plateau in Texas. The Platte, the
-Arkansas, and the Canadian Rivers have cut through the
-High Plains. That part of the High Plains south of the Canadian
-River is called the Southern High Plains, or the Llano
-Estacado (staked plain). The origin of this name is uncertain,
-but it has been suggested that the term Llano Estacado was
-applied by early travelers because this part of the High Plains
-is so nearly flat and devoid of landmarks that it was necessary
-for those pioneers to set lines of stakes to permit them to
-retrace their routes.</p>
-<p>The Llano Estacado is bounded on the west by the Mescalero
-escarpment (<a href="#fig4">fig. 4</a>) and on the east by the Caprock
-escarpment. The southern margin with the Edwards Plateau
-is less well defined, but King Mountain, north of McCamey,
-Tex., is a scarp-bounded southern promontory of the High
-Plains. The remarkably flat surface of the Llano Estacado is
-abundantly pitted by sinks and depressions in the surface of
-the Ogallala Formation; these were formed by solution of the
-limestone by rainwater and blowing away or deflation by
-wind of the remaining insoluble particles. Many of these
-solution-deflation depressions are aligned like strings of
-beads, suggesting that their location is controlled by some
-kind of underlying structure, such as intersections of joints in
-the Ogallala Formation.</p>
-<p>The solution-deflation depressions are less abundant north
-of the Canadian River, but occur on the High Plains surface
-northward to the Arkansas River and along the eastern part
-of the High Plains north of the Arkansas to the South Fork of
-the Republican River.</p>
-<p>Covering much of the northern High Plains, however, are
-sand dunes and windblown silt deposits (loess) that mantle
-the Ogallala Formation and conceal any solution-deflation
-depressions that might have formed. The Nebraska Sand
-Hills (<a href="#fig17">fig. 17</a>), the largest area of sand dunes in the western
-hemisphere, is a huge area of stabilized sand dunes that
-extends from the White River in South Dakota southward
-beyond the Platte River almost to the Republican River in
-western Nebraska but only to the Loup River in the northeast
-part of the High Plains (<a href="#fig18">fig. 18</a>). Loess covers the western
-<span class="pb" id="Page_30">30</span>
-High Plains southward from the sand dunes almost to the
-Arkansas River, and to the South Fork of the Republican in
-the eastern part. This extensive cover of loess has created a
-fertile land that makes it an important part of America&rsquo;s
-wheatlands (<a href="#fig19">fig. 19</a>).</p>
-<div class="img" id="fig17">
-<img src="images/p15.jpg" alt="" width="800" height="544" />
-<p class="caption"><i>Figure 17.&mdash;Aerial view, looking northwest, of the Nebraska Sand
-Hills west of Ashby, Nebr.</i></p>
-</div>
-<p>Other, smaller areas of sand dunes lie south of the Arkansas
-River valley. The only large areas of sand dunes on the
-Llano Estacado, or Southern High Plains, are along the
-southwestern margin near Monahans, southwest of Odessa,
-Tex.</p>
-<p>Oil and gas are present in the Paleozoic rocks that underlie
-the High Plains at depth. Gas fields are ubiquitous in much
-of the eastern part of the High Plains between the Arkansas
-and Canadian Rivers. Just south of the Canadian River, at
-the northeast corner of the Southern High Plains, a huge oil
-and gas field has been developed near Pampa, Tex. Oil and
-gas fields also are abundant in the southwestern part of the
-Southern High Plains, south of Littlefield, Tex.</p>
-<div class="pb" id="Page_31">31</div>
-<div class="img" id="fig18">
-<img src="images/p15a.jpg" alt="" width="800" height="452" />
-<p class="caption"><i>Figure 18.&mdash;The Sand Hills region of Nebraska. Arrows show inferred direction of dune-forming winds. Map from
-Wright (1970), used by permission.</i></p>
-</div>
-<dl class="undent caption"><dt>WYOMING</dt>
-<dd>Badlands National Monument</dd>
-<dd>Missouri River Valley</dd>
-<dt>JAMES RIVER LOBE</dt>
-<dt>MINNESOTA</dt>
-<dt>IOWA</dt>
-<dt>SOUTH DAKOTA</dt>
-<dt>NEBRASKA</dt>
-<dd>Rosebud</dd>
-<dd>Valentine</dd>
-<dt>DES MOINES LOBE</dt>
-<dt>NEBRASKA</dt>
-<dd>Ashby</dd>
-<dt>SANDHILLS</dt>
-<dd>Platte River Valley</dd>
-<dt>IOWA</dt>
-<dt>MISSOURI</dt>
-<dt>NEBRASKA</dt>
-<dt>KANSAS</dt>
-<dt>COLORADO</dt>
-<dd>Muscotah</dd>
-<dt>TOPEKA</dt>
-<dt>EXPLANATION</dt>
-<dd>Transverse dunes</dd>
-<dd>Longitudinal dunes</dd>
-<dd>Wind-blown sand</dd>
-<dd>Loess thickness (in feet)</dd></dl>
-<div class="pb" id="Page_32">32</div>
-<div class="img" id="fig19">
-<img src="images/p16.jpg" alt="" width="800" height="434" />
-<p class="caption"><i>Figure 19.&mdash;Little-modified loess plain in southeastern Nebraska.
-Photograph by Judy Miller.</i></p>
-</div>
-<p>The surface of the High Plains, then, has been little modified
-by streams since the end of Ogallala deposition. It has
-been raised by regional uplift and pitted by solution and
-deflation, and large parts of it have been covered by wind-blown
-sand and silt. It has been drilled for oil and gas and
-extensively farmed, but it is still a geological rarity&mdash;a preserved
-land surface that is 5 million years old.</p>
-<h3 id="c12">MISSOURI PLATEAU</h3>
-<p>Beginning about 5 million years ago, regional uplift of the
-western part of the continent forced streams, which for 30
-million years had been depositing sediment nearly continuously
-on the Great Plains, to change their behavior and
-begin to cut into the layers of sediment they so long had been
-depositing. The predecessor of the Missouri River ate headward
-into the northern Great Plains and developed a tributary
-system that excavated deeply into the accumulated
-deposits near the mountain front and carried away huge
-volumes of sediment from the Great Plains to Hudson Bay.
-By 2 million years ago, the streams had cut downward to
-within a few hundred feet of their present level. This region
-that has been so thoroughly dissected by the Missouri River
-and its tributaries is called the Missouri Plateau.</p>
-<p>About 2 million years ago, after much downcutting had already
-taken place and river channels had been firmly established,
-<span class="pb" id="Page_33">33</span>
-great ice sheets advanced southward from Canada
-into the United States. (See <a href="#fig2">figure 2</a>.) These continental
-glaciers formed, advanced, and retreated several times
-during the last 2 million years. At the north and east margins
-of the Missouri Plateau they lapped onto a high area, leaving
-a mantle of glacial deposits covering the bedrock surface and
-forcing streams to adopt new courses along the margin of ice.
-The part of the Missouri Plateau covered by the continental
-glaciers now is referred to as the Glaciated Missouri Plateau.
-South of the part once covered by ice is the Unglaciated Missouri
-Plateau.</p>
-<h4 id="c13">Preglacial Drainage</h4>
-<p>Before the initial advance of the continental ice sheets, the
-Missouri River flowed northeastward into Canada and to
-Hudson Bay. Its major tributaries, the Yellowstone and the
-Little Missouri joined the Missouri in northwestern North
-Dakota. The east-flowing Knife, Heart, and Cannonball
-Rivers in North Dakota also joined a stream that flowed
-northward to Hudson Bay.</p>
-<h4 id="c14">Glaciated Missouri Plateau</h4>
-<p>When the continental ice sheets spread southward into
-northern Montana and the Dakotas, a few isolated areas in
-Montana stood above the surrounding plain. These are
-mostly areas that were uplifted by the intrusion of igneous
-bodies long before the streams began downcutting and
-carving the land. The northernmost of these isolated mountains,
-the Sweetgrass Hills, were surrounded by ice and
-became nunataks, or islands of land, in the sea of advancing
-ice, which pushed southward up against the Highwood
-Mountains, near Great Falls, the Bearpaws south of Havre,
-and the Little Rockies to the east.</p>
-<p>Much of the northern part of Montana is a plain of little
-relief that is the surface of a nearly continuous cover of
-glacial deposits, generally less than 50 feet thick. This plain
-has been incised by the east-flowing postglacial Teton,
-Marias, and Milk Rivers.</p>
-<p>In North Dakota, a high area on the east side of the Williston
-basin acted as a barrier to the advance of the ice, most of
-<span class="pb" id="Page_34">34</span>
-which was diverted southeastward. The margin of the ice
-sheet, however, lapped onto the bedrock high, where it stagnated.
-Earlier advances moved farthest south; the later advances
-stopped north of the present course of the Missouri
-River&mdash;their maximum position marked by ridges of unsorted,
-glacially transported rock debris (till) called terminal
-moraines. North of the terminal moraines is a distinctive
-landscape characterized by a rolling, hummocky, or hilly
-surface with thousands of closed depressions between the
-hills and hummocks, most of them occupied by lakes. This is
-the deposit left by the stagnant or dead ice, and it is called
-dead-ice moraine. The rolling upland in North Dakota that is
-covered by dead-ice moraine and ridges of terminal moraines
-from the last glacial advances is called the Coteau du Missouri
-(<a href="#fig20">fig. 20</a>). A gently sloping scarp, several hundred feet
-high and mostly covered by glacial deposits (referred to collectively
-as drift), separates the Coteau du Missouri from the
-lower, nearly flat, drift-covered plains of the Central Lowland
-to the east. This escarpment, which is called the Missouri
-escarpment, is virtually continuous across the State of
-North Dakota southward into South Dakota. The base of the
-Missouri escarpment is the eastern boundary of the Great
-Plains in these northern states.</p>
-<div class="img" id="fig20">
-<img src="images/p17.jpg" alt="" width="800" height="573" />
-<p class="caption"><i>Figure 20.&mdash;Ground moraine on the Coteau du Missouri, northwestern
-North Dakota. Photograph by R. M. Lindvall, U. S.
-Geological Survey.</i></p>
-</div>
-<div class="pb" id="Page_35">35</div>
-<p>The advancing ice front blocked one after another of the
-northward-flowing streams of the region, diverting them
-eastward along the ice front. Shonkin Sag, north of the Highwood
-Mountains near Great Falls, Mont., is an abandoned
-diversion channel of the Missouri River, occupied when the
-ice front stood close to the north slopes of the Highwoods.
-Much of the present course of the Missouri River from Great
-Falls, Mont., to Kansas City, Mo., was established as an ice-marginal
-channel, and the east-flowing part of the Little Missouri
-River in North Dakota was formed in the same way.
-These valleys were cut during the last 2 million years.</p>
-<p>The north-flowing part of the Little Missouri River and the
-east-flowing courses of the Knife, Heart, and Cannonball
-Rivers in North Dakota are for the most part older, preglacial
-courses. The Little Missouri was dammed by the ice,
-and its waters impounded to form a huge lake during the
-maximum stand of the ice, but the deposits of this glacial
-lake are few and make no imprint on the landscape.</p>
-<p>The valley of the east-flowing, glacially diverted part of
-the Little Missouri River, however, is markedly different
-from that of the north-flowing preglacial river. It is much
-narrower and has steeper walls than the old valley. Because
-it is younger, it is little modified, except by huge landslides
-that have affected both walls of the valley. Tremendous
-rotated landslide blocks in the North Unit of Theodore
-Roosevelt National Memorial Park are some of the best
-examples of the slump type of landslide to be seen anywhere
-(<a href="#fig21">fig. 21</a>).</p>
-<p>Melting ice at the front of the glaciers provided large
-volumes of meltwater that flowed across the till-mantled
-surface in front of the glacier as it melted back toward
-Canada. This meltwater took many courses to join the glacially
-diverted Missouri River, and these sinuous meltwater
-channels wind across the dead-ice moraine and the older, less
-hummocky ground moraine between the Coteau du Missouri
-and the Missouri River. Locally the sediment carried by the
-meltwater streams was banked against a wall of ice to form a
-small hill of stratified drift that is called a kame. Streams
-flowing in tunnels beneath the ice formed sinuous, ridgelike
-deposits called eskers, and in places the meltwater deposits
-form broad flat areas called outwash plains.</p>
-<div class="pb" id="Page_36">36</div>
-<div class="img" id="fig21">
-<img src="images/p18.jpg" alt="" width="800" height="563" />
-<p class="caption"><i>Figure 21.&mdash;Rotated slump blocks in huge landslide, North Unit of
-Theodore Roosevelt National Memorial Park, N. Dak. Note that
-layering of Fort Union Formation in cliffs on skyline, where landslide
-originated, is horizontal.</i></p>
-</div>
-<p>This rather limited variety of landforms, then, characterizes
-the landscape of the Glaciated Missouri Plateau. The
-landforms themselves are testimony to their glacial origin
-and to the great advances of the continental ice sheets. This is
-a stream-carved terrain that has been modified by continental
-glaciers and almost completely covered by a thick
-blanket of glacially transported and deposited rock debris,
-locally hundreds of feet thick. Subsequent stream action has
-not altered the landscape greatly.</p>
-<h4 id="c15">Unglaciated Missouri Plateau</h4>
-<p>Beyond the limits reached by the ice of the continental glaciers,
-the Unglaciated Missouri Plateau displays the greatest
-variety of landforms of any section of the Great Plains. In
-western Montana, many small mountain masses rise above
-the general level of the plateau, including the Highwood,
-Bearpaw, and Little Rocky Mountains near the margin of the
-glaciated area, and the Judith, Big Snowy, Big Belt, Little
-Belt, Castle, and Crazy Mountains farther south (<a href="#fig22">fig. 22</a>).
-Many of these, such as the Crazy, Castle, Judith, and Big
-Snowy Mountains, are areas uplifted by large, deeply
-rooted, intrusive igneous bodies called stocks, which have
-been exposed by subsequent erosion of the arched overlying
-sedimentary rock layers. Some, such as the Highwood and
-Bearpaw Mountains, are predominantly piles of lava flows,
-although in the Bearpaws the related intrusive bodies of
-igneous rock form a part of the mountains. The Big and Little
-Belt Mountains were formed by mushroom-shaped intrusive
-igneous bodies called laccoliths, which have spread out and
-domed between layers of sedimentary rocks. A number of
-igneous bodies also intrude the rocks of the Missouri Plateau
-around the periphery of the Black Hills. Devils Tower, the
-first feature to be designated a National Monument, is the
-best known of these igneous rock features (<a href="#fig23">fig. 23</a>).</p>
-<div class="pb" id="Page_37">37</div>
-<div class="img" id="fig22">
-<img src="images/p18a.jpg" alt="" width="800" height="538" />
-<p class="caption"><i>Figure 22.&mdash;The Highwood Mountains seen from the Little Belt
-Mountains, Mont. Photograph by I. J. Witkind, U. S. Geological
-Survey.</i></p>
-</div>
-<p>The uplift and volcanism that formed these mountains
-took place before the streams began to cut downward and
-segment the Great Plains. The mountains had been greatly
-dissected before the advent of the Great Ice Age, when alpine
-glaciers formed on the Castle and the Crazy Mountains and
-flowed down some of the stream-cut valleys. Alpine glacial
-<span class="pb" id="Page_38">38</span>
-features such as cirques, in the high parts of the mountains,
-and glacially modified U-shaped valleys (<a href="#fig24">fig. 24</a>) are impressive
-evidence of this glaciation.</p>
-<div class="img" id="fig23">
-<img src="images/p19.jpg" alt="" width="577" height="800" />
-<p class="caption"><i>Figure 23.&mdash;Devils Tower National Monument, Wyo. An igneous
-intrusive body exposed by erosion. Photograph by F. W. Osterwald,
-U. S. Geological Survey.</i></p>
-</div>
-<p>The Missouri River and its tributaries&mdash;the Sun, Smith,
-Judith, Musselshell, and Yellowstone Rivers in Montana and
-the Little Missouri River in North Dakota&mdash;have cut down
-<span class="pb" id="Page_39">39</span>
-into the Missouri Plateau, cut broad upland surfaces at many
-levels, and established confined valleys with valley floors
-flanked by terrace remnants of older floodplains. Locally,
-high buttes that are remnants of former interstream divides
-rise above the uplands. Large lakes also were formed in most
-of these tributary valleys because of damming by the continental
-ice sheets.</p>
-<div class="img" id="fig24">
-<img src="images/p19a.jpg" alt="" width="800" height="469" />
-<p class="caption"><i>Figure 24.&mdash;U-shaped, glaciated valley of Big Timber Creek, Crazy
-Mountains, Mont. Photograph by W. C. Alden, 1921, U. S. Geological
-Survey.</i></p>
-</div>
-<p>West of the Black Hills, in Wyoming, the Tongue River
-and the Powder River have excavated the Powder River
-Basin and produced similar features (<a href="#fig25">fig. 25</a>). The east-flowing
-tributaries of the Missouri River&mdash;the Knife, Heart,
-and Cannonball Rivers in North Dakota and the Grand,
-Moreau, Belle Fourche, Cheyenne, Bad, and White Rivers in
-South Dakota&mdash;similarly have shaped the landscape.</p>
-<p>Most of these rivers flow in broad, old valleys, established
-more than 2 million years ago, before the first advance of the
-continental ice sheets. Some of these valleys have been
-widened by recession of the valley walls by badland development.
-Badlands are formed by the cutting action of rivulets
-and rills flowing down over a steeply sloping face of soft,
-fine-grained material composed mainly of clay and silt. The
-intricate carving by thousands of small streams of water produces
-the distinctive rounded and gullied terrain we call
-badlands. Badlands National Monument in South Dakota
-<span class="pb" id="Page_40">40</span>
-(<a href="#fig26">fig. 26</a>) has been established in the remarkable badlands
-terrain cut into the White River Group along the north valley
-wall of the White River, and the South Unit of Theodore
-Roosevelt National Memorial Park is in the colorful badlands
-of the Little Missouri River, formed on the Fort Union
-Formation (<a href="#fig27">fig. 27</a>).</p>
-<p>The White River also has cut a steep scarp along its southern
-wall that is called the Pine Ridge escarpment. This
-escarpment defines the boundary between the Missouri
-Plateau and the High Plains here.</p>
-<div class="img" id="fig25">
-<img src="images/p20.jpg" alt="" width="800" height="554" />
-<p class="caption"><i>Figure 25.&mdash;View northeast across the Deckers coal mine and the
-Tongue River in the Powder River Basin, southeastern Montana.
-Typical terrain of unglaciated Missouri Plateau. Small mesas
-with cliffed escarpments on capping layer of resistant sandstone,
-such as those in the foreground, are common. Coal mine is about
-1 mile across. Photograph by R. B. Taylor, U. S. Geological
-Survey.</i></p>
-</div>
-<p>The landscape of the Unglaciated Missouri Plateau
-has been determined largely by the action of streams,
-but in some areas igneous intrusions and volcanoes have produced
-small mountain masses that interrupt the plain, and
-valley glaciers have modified the valleys in some of these
-mountains.</p>
-<div class="pb" id="Page_41">41</div>
-<div class="img" id="fig26">
-<img src="images/p20a.jpg" alt="" width="800" height="466" />
-<p class="caption"><i>Figure 26.&mdash;Badlands in Badlands National Monument, S. Dak.
-Photograph by W. H. Raymond, III, U. S. Geological Survey.</i></p>
-</div>
-<div class="pb" id="Page_42">42</div>
-<div class="img" id="fig27">
-<img src="images/p21.jpg" alt="" width="800" height="414" />
-<p class="caption"><i>Figure 27.&mdash;Badlands of the Little Missouri River in South Unit of
-Theodore Roosevelt National Memorial Park, N. Dak. View
-looking northwest from Painted Canyon Overlook along Interstate
-Highway 94, west of Belfield.</i></p>
-</div>
-<h3 id="c16">THE COLORADO PIEDMONT</h3>
-<p>The Colorado Piedmont lies at the eastern foot of the
-Rockies, (<a href="#fig1">fig. 1</a>) largely between the South Platte River and
-the Arkansas River. The South Platte on the north and the
-Arkansas River on the south, after leaving the mountains,
-have excavated deeply into the Tertiary (65- to 2-million-year-old)
-sedimentary rock layers of the Great Plains in
-Colorado and removed great volumes of sediment. At
-Denver, the South Platte River has cut downward 1,500 to
-2,000 feet to its present level. Three well-formed terrace
-levels flank the river&rsquo;s floodplain, and remnants of a number
-of well-formed higher land surfaces are preserved between
-the river and the mountains. Along the western margin of the
-Colorado Piedmont, the layers of older sedimentary rock
-have been sharply upturned by the rise of the mountains.
-The eroded edges of these upturned layers have been eroded
-differentially, so that the hard sandstone and limestone
-layers form conspicuous and continuous hogback ridges (<a href="#fig28">fig. 28</a>).
-North of the South Platte River, near the Wyoming
-border, a scarp that has been cut on the rocks of the High
-Plains marks the northern boundary of the Colorado Piedmont.
-Pawnee Buttes (<a href="#fig29">fig. 29</a>) are two of many butte outliers
-of the High Plains rocks near that scarp, separated from the
-High Plains by erosion as is Scotts Bluff, farther north in
-<span class="pb" id="Page_43">43</span>
-Nebraska. To the east, about 10 miles northwest of Limon,
-Colo., Cedar Point forms a west-jutting prow of the High
-Plains.</p>
-<p>The Arkansas River similarly has excavated much of the
-Tertiary piedmont deposits and cut deeply into the older
-Cretaceous marine rocks between Canon City and the Kansas
-border. The upturned layers along the mountain front,
-marked by hogback ridges and intervening valleys, continue
-nearly uninterrupted around the south end of the Front
-Range into the embayment in the mountains at Canon City.
-Skyline Drive, a scenic drive at Canon City, follows the crest
-of the Dakota hogback for a short distance and provides a
-fine panorama of the Canon City embayment.</p>
-<div class="img" id="fig28">
-<img src="images/p21a.jpg" alt="" width="800" height="562" />
-<p class="caption"><i>Figure 28.&mdash;Hogback ridges along the Front Range west of Denver,
-Colo. South Platte River emerges from the mountains and cuts
-through hogbacks in middle distance. Photograph courtesy of
-Eugene Shearer, Intrasearch, Inc.</i></p>
-</div>
-<p>Extending eastward from the mountain front at Palmer
-Lake, a high divide separates the drainage of the South Platte
-River from that of the Arkansas River. The crest of the
-divide north of Colorado Springs is generally between 7,400
-and 7,600 feet in altitude, but Interstate Highway 25 crosses
-it at about 7,350 feet, nearly 1,500 feet higher than Colorado
-Springs and more than 2,000 feet higher than Denver. From
-the crest of the divide to north of Castle Rock, resistant
-Oligocene Castle Rock Conglomerate (which is equivalent to
-<span class="pb" id="Page_44">44</span>
-part of the White River Group of the High Plains) is preserved
-in many places and forms a protective caprock on
-mesas and buttes. This picturesque part of the Colorado
-Piedmont looks quite different from the excavated valleys of
-the South Platte and Arkansas Rivers.</p>
-<p>Much of the terrain in the two river valleys has been
-smoothed by a nearly continuous mantle of windblown sand
-and silt. Northwesterly winds, which frequently blow with
-near-hurricane velocities, have whipped fine material from
-the floodplains of the streams and spread it eastward and
-southeastward over much of the Colorado Piedmont. Well-formed
-dunes are not common, but alined gentle ridges of
-sand and silt and abundant shallow blowout depressions
-inform us of the windblown origin of this cover.</p>
-<div class="img" id="fig29">
-<img src="images/p22.jpg" alt="" width="800" height="568" />
-<p class="caption"><i>Figure 29.&mdash;Pawnee Buttes in northeastern Colorado. Buttes isolated
-by erosion from High Plains in the background. Ogallala
-Formation caps top of Buttes. White River Group forms lower
-part. The top of the highest butte is about 240 feet above the
-saddle between the two buttes. Photograph by R. D. Miller, U. S.
-Geological Survey.</i></p>
-</div>
-<p>In the Colorado Piedmont, then, the erosional effects of
-streams are the most conspicuous features of the landscape,
-but these are enhanced by the steep tilting of the layered
-rocks along the western margin as a result of earth movement
-<span class="pb" id="Page_45">45</span>
-and modified by the nearly ubiquitous products of
-wind action, which have softened the landscape with a widespread
-cover of windblown sand and silt.</p>
-<h3 id="c17">PECOS VALLEY</h3>
-<p>South of the land of volcanic rocks that is the Raton
-section, the Pecos River has cut a broad valley from the
-Sangre de Cristo Mountains, in New Mexico, southward to
-the Rio Grande, and has removed the piedmont cover of
-Ogallala Formation and cut deeply into the underlying
-rocks. The Ogallala Formation capping the High Plains to
-the east forms a rimrock at the top of the sharp Mescalero
-escarpment, which is the eastern boundary of the Pecos
-Valley. (See <a href="#fig4">figure 4</a>.) The western boundary of the Pecos
-Valley is the eastern base of discontinuous mountain ranges.</p>
-<p>The great thickness of Tertiary deposits that formed on the
-northern Great Plains did not accumulate here, and the
-Pecos River has cut its valley into the older marine sedimentary
-rocks. The rocks underlying the surface of much of
-the Pecos Valley are upper Paleozoic limestones.</p>
-<p>The soluble nature of limestone is responsible for some of
-the most spectacular features of the landscape in the Pecos
-Valley. For about 10 miles north and 50 miles south of
-Vaughn, N. Mex., collapsed solution caverns in upper Paleozoic
-limestones have produced an unusual type of topography
-called karst. Karst topography is typified by numerous
-closely spaced sinks or closed depressions, some of
-which are very deep holes, caused by the collapse of the roof
-of a cave or solution cavity into the underground void,
-leaving hills, spines, or hummocks at the top of the intervening
-walls or ribs separating the depressions.</p>
-<p>Although the karst in the vicinity of Vaughn is perhaps the
-most conspicuous solution phenomenon, sinks and caves are
-common throughout the Pecos Valley. At Bottomless Lakes
-State Park east of Roswell, N. Mex., seven lakes occupy
-large sinkholes caused by the solution of salt and gypsum in
-underlying rocks.</p>
-<p>The most spectacular example of solution of limestone by
-ground water is Carlsbad Caverns, N. Mex., one of the most
-beautiful caves in the world. This celebrated solution cavity
-is preserved in a national park.</p>
-<div class="pb" id="Page_46">46</div>
-<p>The Pecos River along much of its present course flows in
-a vertical-walled canyon with limestone rims. The Canadian
-River, flowing eastward from the Sangre de Cristo Mountains,
-has cut a deep canyon along the northern part of the
-Pecos Valley section. The sharp rims of the Dakota Sandstone
-at the Canadian escarpment, north of the Canadian
-River, form the northern boundary of the Pecos Valley
-section.</p>
-<p>The sharp, northeast-trending broken flexure called the
-Border Hills that is crossed by U. S. Highway 70-380 about
-20 miles west of Roswell is a unique landform of the Pecos
-Valley. This markedly linear upfolded (anticlinal) structure
-forms a ridge more than 30 miles long and about 200 feet
-high.</p>
-<p>As in the Colorado Plateau, windblown sand and silt
-mantle the landscape in many places, but the greatest accumulations
-are along the base of the Mescalero escarpment
-at the northeast and southeast corners of the Pecos Valley
-section.</p>
-<p>East of the Pecos River, in the southeast part of the Pecos
-Valley, the underlying rocks have yielded much oil and
-potash. Oil fields are common east of Artesia and Carlsbad,
-and potash is mined east of Carlsbad.</p>
-<p>The Pecos and Canadian Rivers and their tributaries have
-created the general outline of the landscape of the Pecos
-Valley, but underground solution of limestone by ground
-water and the collapse of roofs of these cavities have contributed
-much detail to the surface that characterizes the Pecos
-Valley today.</p>
-<h3 id="c18">EDWARDS PLATEAU</h3>
-<p>South of the Pecos Valley section, the Pecos River continues
-its journey to the Rio Grande in a steep-walled canyon
-cut 400 to 500 feet below the level of a plateau surface of Cretaceous
-limestone from which little has been stripped except
-a thin Tertiary cover of Ogallala Formation (<a href="#fig30">fig. 30</a>). To the
-east, the plateau has been similarly incised by the Devils
-River and the West Nueces and Nueces Rivers. East of the
-Nueces to the escarpment formed by the Balcones fault zone,
-the southern part of the Edwards Plateau has been intricately
-dissected by the Frio, Sabinal, Medina, Guadalupe, and
-<span class="pb" id="Page_47">47</span>
-Pedernales Rivers and their tributary systems. San Antonio
-and Austin, Tex., are located on the Coastal Plain at the edge
-of the Balcones fault zone.</p>
-<div class="img" id="fig30">
-<img src="images/p23.jpg" alt="" width="800" height="567" />
-<p class="caption"><i>Figure 30.&mdash;Rio Grande and the flat-lying limestone layers of the
-Edwards Plateau downstream from the mouth of the Pecos
-River. Mexico on the left side of picture. Photograph by
-V. L. Freeman, U. S. Geological Survey.</i></p>
-</div>
-<p>The Pecos River, and to a lesser extent the Devils and
-Nueces Rivers, particularly in their lower courses, have entrenched
-themselves deeply in the plateau in remarkable
-meandering courses of a type that is usually found only in
-broad, low-lying floodplains. These stream courses reflect
-the stream environment prior to regional uplift.</p>
-<p>Sinkholes pit the relatively undissected limestone plateau
-surface in the northeast part of the Edwards Plateau, and
-some underground solution cavities in the limestone are well-known
-caves, such as the Caverns of Sonora, southwest of
-Sonora, Tex.</p>
-<p>Oil and gas fields are widely developed in the northern
-part of the Edwards Plateau, but only cattle ranches are
-found in the bare southern part.</p>
-<p>Ancient oceans deposited the limestones that now cap the
-Edwards Plateau; streams planed off the surface of the flat-lying
-<span class="pb" id="Page_48">48</span>
-limestone layers and entrenched themselves in steep-walled
-valleys; and ground water dissolved the limestone
-and created the solution cavities that are the caves and sinks
-of the Edwards Plateau. Water has created this landscape.</p>
-<h3 id="c19">PLAINS BORDER SECTION</h3>
-<p>The Missouri Plateau, the Colorado Piedmont, the Pecos
-Valley, and the Edwards Plateau all were outlined by streams
-that flowed from the mountains. On the eastern border of the
-Great Plains, however, headward cutting by streams that
-have their source areas in the High Plains has dissected a
-large area, mainly in Kansas. This Plains Border Section
-comprises a number of east-trending river valleys&mdash;of the
-Republican, Solomon, Saline, Smoky Hill, Arkansas, Medicine
-Lodge, Cimarron, and North Canadian Rivers&mdash;and
-interstream divides, most of which are intricately dissected.</p>
-<p>North of the Arkansas River, the east-flowing Republican,
-Solomon, Saline, and Smoky Hill Rivers have incised themselves
-a few hundred feet below the Tertiary High Plains
-surface and have developed systems of closely spaced tributary
-draws. The interstream divides are narrow, and the
-tributary heads nearly meet at the divides. This intricately
-dissected part of the Plains Border section is called the
-Smoky Hills. Some isolated buttes of Cretaceous rocks left in
-the upper valley of the Smoky Hill River are called the
-Monument Rocks. A large area of rounded boulders exposed
-by erosion south of the Solomon River, southwest of
-Minneapolis, Kans., is called &ldquo;Rock City.&rdquo; These boulders
-originated as resistant nodules (concretions) within the Cretaceous
-rocks that contained them.</p>
-<p>South of the Arkansas River is a broad, nearly flat upland
-sometimes referred to as the Great Bend Plains. The Medicine
-Lodge River has cut headward into the southeastern part
-of the Great Bend Plains and created a thoroughly dissected
-topography in Triassic red rocks that is locally called the Red
-Hills. In a few places, badlands have formed in the Red Hills.</p>
-<p>Some large sinks or collapse depressions have formed
-because of solution of salt and gypsum at depth by ground
-water. Big and Little Basins, in Clark County in south-central
-Kansas, were formed in this way.</p>
-<div class="pb" id="Page_49">49</div>
-<p>Sand dunes have accumulated in places, especially near
-stream valleys. Dunes are common, for example, along the
-north side of the North Canadian River.</p>
-<p>Oil and gas fields are widely developed in the southeast
-part of the Plains Border section&mdash;in the Smoky Hills, the
-Great Bend Plains, and the Red Hills.</p>
-<p>The Plains Border section, like the Missouri Plateau, the
-Colorado Piedmont, and the Pecos Valley, is primarily a
-product of stream dissection. The differences in the outstanding
-landforms of the section are mainly the result of differences
-in the hardness of the eroded rocks.</p>
-<h2 id="c20"><span class="h2line1">EPILOGUE</span></h2>
-<p>The Great Plains, as we have seen, is many things. It contains
-thick layers of rock that formed in oceans, and younger
-layers of rocks deposited by streams. These rocks have been
-affected by earth movements and injected by hot molten
-rock, some of which reached the surface as volcanic rock.
-The rocks have been carved by streams, dissolved by ground
-water, partly covered by glaciers, and blown by winds. All
-of these agents have played important roles in determining
-the landscape and the landforms of the Great Plains. But the
-streams were the master agent. They formed the great depositional
-plain that was to become the Great Plains, and then
-began to destroy it&mdash;leaving only the High Plains to remind
-us of what it was. Those long miles we travel across the High
-Plains are a journey through history&mdash;geologic history.</p>
-<h2 id="c21"><span class="h2line1">ACKNOWLEDGMENTS</span></h2>
-<p>This narrative history of geologic and biologic events in
-the Great Plains had its origin in a study intended to identify
-potential National Natural Landmarks in the Great Plains,
-commissioned by the National Park Service. William A.
-Cobban, G. Edward Lewis, and Reuben J. Ross of the U. S.
-Geological Survey were collaborators in that study, and
-some of their contributions to the history of life on the Great
-Plains have been incorporated into this narrative, which was
-undertaken at the urging of Wallace R. Hansen.</p>
-<div class="pb" id="Page_50">50</div>
-<p>The photographic illustrations, other than those obtained
-from the film library of the U. S. Geological Survey, were
-provided by the interest and effort of my friends and colleagues
-of the Geological Survey&mdash;including C. R. Dunrud,
-V. L. Freeman, C. D. Miller, R. D. Miller, F. W. Osterwald,
-R. L. Parker, W. H. Raymond, III, Kenneth Shaver, and
-R. B. Taylor&mdash;and by Eugene Shearer, Intrasearch, Inc.,
-Denver, Colo. Without their help this publication would not
-have been possible.</p>
-<h2 id="c22"><span class="h2line1">SOME SOURCE REFERENCES</span></h2>
-<p class="revint">Alden, W. C., 1932, Physiography and glacial geology of eastern Montana
-and adjacent areas: U. S. Geological Survey Professional Paper
-174, 133 p.</p>
-<p class="revint">Bluemle, J. P., 1977, The face of North Dakota&mdash;the geologic story:
-North Dakota Geological Survey Education Series 11, 73 p.</p>
-<p class="revint">Colton, R. B., Lemke, R. W., and Lindvall, R. M., 1961, Glacial map of
-Montana east of the Rocky Mountains: U. S. Geological Survey Miscellaneous
-Geologic Investigations Map I-327.</p>
-<p class="revint">Colton, R. B., Lemke, R. W., and Lindvall, R. M., 1963, Preliminary
-glacial map of North Dakota: U. S. Geological Survey Miscellaneous
-Geologic Investigations Map I-331.</p>
-<p class="revint">Curtis, B. F., ed., 1975, Cenozoic history of the southern Rocky Mountains&mdash;Papers
-deriving from a symposium presented at the Rocky
-Mountain Section meeting of the Geological Society of America,
-Boulder, Colorado, 1973: Geological Society of America Memoir
-144, 279 p.</p>
-<p class="revint">Darton, N. H., 1905, Preliminary report on the geology and underground
-water resources of the central Great Plains: U. S. Geological Survey
-Professional Paper 32, 433 p.</p>
-<p class="revint">Flint, R. F., 1955, Pleistocene geology of eastern South Dakota: U. S. Geological
-Survey Professional Paper 262, 173 p.</p>
-<p class="revint">Frye, J. C., and Leonard, A. B., 1965, Quaternary of the southern Great
-Plains, <i>in</i> Wright, H. E., Jr., and Frey, D. G., eds., The Quaternary
-of the United States&mdash;A review volume for the 7th Congress of the
-International Association for Quaternary Research: Princeton University
-Press, p. 203-216.</p>
-<p class="revint">Howard, A. D., 1958, Drainage evolution in northeastern Montana and
-northwestern North Dakota: Geological Society of America Bulletin,
-v. 69, no. 5, p. 575-588.</p>
-<p class="revint">Johnson, R. B., 1961, Patterns and origin of radial dike swarms associated
-with West Spanish Peak and Dike Mountain, south-central Colorado:
-Geological Society of America Bulletin, v. 72, no. 4, p. 579-590.</p>
-<div class="pb" id="Page_51">51</div>
-<p class="revint">Judson, S. S., Jr., 1950, Depressions of the northern portion of the southern
-High Plains of eastern New Mexico: Geological Society of
-America Bulletin, v. 61, no. 3, p. 253-274.</p>
-<p class="revint">Keech, C. F., and Bentall, Ray, 1971, Dunes on the plains&mdash;The Sand Hills
-region of Nebraska: Nebraska University Conservation and Survey
-Division Resources Report 4, 18 p.</p>
-<p class="revint">Lemke, R. W., Laird, W. M., Tipton, M. J., and Lindvall, R. M., 1965,
-Quaternary geology of northern Great Plains, <i>in</i> Wright, H. E., Jr.,
-and Frey, D. G., eds., The Quaternary of the United States&mdash;A review
-volume for the 7th Congress of the International Association for
-Quaternary Research: Princeton University Press, p. 15-27.</p>
-<p class="revint">Mansfield, G. R., 1907, Glaciation in the Crazy Mountains of Montana:
-Geological Society of America Bulletin, v. 19, p. 558-567.</p>
-<p class="revint">Pettyjohn, W. A., 1966, Eocene paleosol in the northern Great Plains, <i>in</i>
-Geological Survey research 1966: U. S. Geological Survey Professional
-Paper 550-C, p. C61-C65.</p>
-<p class="revint">Robinson, C. S., 1956, Geology of Devils Tower National Monument,
-Wyoming: U. S. Geological Survey Bulletin 1021-I, p. 289-302.</p>
-<p class="revint">Smith, H. T. U., 1965, Dune morphology and chronology in central and
-western Nebraska: Journal of Geology, v. 73, no. 4, p. 557-578.</p>
-<p class="revint">Stormer, J. C., Jr., 1972, Ages and nature of volcanic activity on the
-southern High Plains, New Mexico and Colorado: Geological Society
-of America Bulletin, v. 83, no. 8, p. 2443-2448.</p>
-<p class="revint">Strahler, A. N., and Strahler, A. H., 1978, Modern physical geography:
-New York, John Wiley &amp; Sons, 502 p.</p>
-<p class="revint">Thornbury, W. D., 1965, Regional geomorphology of the United States:
-New York, John Wiley, 609 p.</p>
-<p class="revint">Wright, H. E., Jr., 1970, Vegetational history of the Central Plains, <i>in</i>
-Pleistocene and recent environments of the central Great Plains:
-Kansas University Department of Geology Special Publication 3, p.
-157-172.</p>
-<div class="pb" id="Page_52">52</div>
-<h2 id="c23"><span class="h2line1">INDEX</span></h2>
-<p class="center small">[Italic page numbers indicate major references]</p>
-<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> <span class="ab">Q</span> <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> <span class="ab">Z</span></b></p>
-<dl class="indexlr">
-<dt class="center" id="index_A"><b>A</b></dt>
-<dt>Page</dt>
-<dt><span class="lj">Acknowledgments</span> <a class="i" href="#Page_49">49</a></dt>
-<dt><span class="lj">Agriculture</span> <a href="#Page_30">30</a></dt>
-<dt><span class="lj">Alaska</span> <a href="#Page_11">11</a></dt>
-<dt><span class="lj">Anadarko basin</span> <a href="#Page_11">11</a>, <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Arikaree Formation</span> <a href="#Page_18">18</a></dt>
-<dt><span class="lj">Arkansas River</span> <a href="#Page_2">2</a>, <a href="#Page_7">7</a>, <a href="#Page_23">23</a>, <a href="#Page_25">25</a>, <a href="#Page_29">29</a>, <a href="#Page_30">30</a>, <a href="#Page_42">42</a>, <a href="#Page_43">43</a>, <a href="#Page_44">44</a>, <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Artesia, N. Mex.</span> <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Austin, Tex.</span> <a href="#Page_47">47</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_B"><b>B</b></dt>
-<dt><span class="lj">Bad River</span> <a href="#Page_39">39</a></dt>
-<dt><span class="lj">Badland development</span> <a href="#Page_39">39</a></dt>
-<dt><span class="lj">Badlands National Monument</span> <a href="#Page_39">39</a></dt>
-<dt><span class="lj">Balcones fault zone</span> <a href="#Page_23">23</a>, <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Basalt flows</span> <a href="#Page_20">20</a>, <a href="#Page_24">24</a></dt>
-<dt><span class="lj">Bearpaw Mountains</span> <a href="#Page_33">33</a>, <a href="#Page_36">36</a></dt>
-<dt><span class="lj">Belle Fourche River</span> <a href="#Page_39">39</a></dt>
-<dt><span class="lj">Bents Fort, Colo.</span> <a href="#Page_2">2</a></dt>
-<dt><span class="lj">Big Basin, Kans.</span> <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Big Belt Mountains</span> <a href="#Page_36">36</a></dt>
-<dt><span class="lj">Big Snowy Mountains</span> <a href="#Page_36">36</a></dt>
-<dt><span class="lj">Bison</span> <a href="#Page_1">1</a></dt>
-<dt><span class="lj">Black Hills</span> <a href="#Page_7">7</a>, <a href="#Page_11">11</a>, <a href="#Page_18">18</a>, <a href="#Page_19">19</a>, <a class="i" href="#Page_20">20</a>, <a href="#Page_37">37</a></dt>
-<dt><span class="lj">Border Hills</span> <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Bottomless Lakes, N. Mex.</span> <a href="#Page_45">45</a></dt>
-<dt><span class="lj">Brazos River</span> <a href="#Page_23">23</a></dt>
-<dt><span class="lj">Burnet, Tex.</span> <a href="#Page_23">23</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_C"><b>C</b></dt>
-<dt><span class="lj">Camels</span> <a href="#Page_16">16</a>, <a href="#Page_18">18</a></dt>
-<dt><span class="lj">Canada</span> <a href="#Page_1">1</a>, <a href="#Page_5">5</a>, <a href="#Page_33">33</a></dt>
-<dt><span class="lj">Canadian escarpment</span> <a href="#Page_23">23</a>, <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Canadian River</span> <a href="#Page_23">23</a>, <a href="#Page_29">29</a>, <a href="#Page_30">30</a>, <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Cannonball River</span> <a href="#Page_33">33</a>, <a href="#Page_35">35</a>, <a href="#Page_39">39</a></dt>
-<dt><span class="lj">Canon City, Colo.</span> <a href="#Page_43">43</a></dt>
-<dt><span class="lj">Caprock escarpment</span> <a href="#Page_7">7</a>, <a href="#Page_29">29</a></dt>
-<dt><span class="lj">Capulin Mountain</span> <a href="#Page_20">20</a>, <a href="#Page_23">23</a></dt>
-<dt><span class="lj">Carlsbad, N. Mex.</span> <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Carlsbad Caverns, N. Mex.</span> <a href="#Page_45">45</a></dt>
-<dt><span class="lj">Carrizo Creek</span> <a href="#Page_25">25</a></dt>
-<dt><span class="lj">Castle Mountains</span> <a href="#Page_37">37</a></dt>
-<dt><span class="lj">Castle Rock, Colo.</span> <a href="#Page_43">43</a></dt>
-<dt><span class="lj">Castle Rock Conglomerate</span> <a href="#Page_43">43</a></dt>
-<dt><span class="lj">Caverns of Sonora</span> <a href="#Page_47">47</a></dt>
-<dt><span class="lj">Cedar Point</span> <a href="#Page_43">43</a></dt>
-<dt><span class="lj">Central Lowland</span> <a href="#Page_5">5</a>, <a href="#Page_34">34</a></dt>
-<dt><span class="lj">Central Texas Uplift</span> <a href="#Page_7">7</a>, <a href="#Page_19">19</a>, <a href="#Page_20">20</a>, <a class="i" href="#Page_22">22</a></dt>
-<dt><span class="lj">Cheyenne, Wyo.</span> <a href="#Page_27">27</a></dt>
-<dt><span class="lj">Cheyenne River</span> <a href="#Page_39">39</a></dt>
-<dt><span class="lj">Cimarron River</span> <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Cirques</span> <a href="#Page_38">38</a></dt>
-<dt><span class="lj">Clark County, Kans.</span> <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Climate</span> <a href="#Page_2">2</a></dt>
-<dt><span class="lj">Coal</span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Coastal Plain</span> <a href="#Page_5">5</a>, <a href="#Page_7">7</a>, <a href="#Page_10">10</a>, <a href="#Page_47">47</a></dt>
-<dt><span class="lj">Colorado</span> <a href="#Page_19">19</a></dt>
-<dt><span class="lj">Colorado Piedmont</span> <a href="#Page_7">7</a>, <a href="#Page_10">10</a>, <a href="#Page_19">19</a>, <a href="#Page_23">23</a>, <a class="i" href="#Page_42">42</a>, <a href="#Page_48">48</a>, <a href="#Page_49">49</a></dt>
-<dt><span class="lj">Colorado Plateau</span> <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Colorado River</span> <a href="#Page_23">23</a></dt>
-<dt><span class="lj">Colorado Springs, Colo.</span> <a href="#Page_43">43</a></dt>
-<dt><span class="lj">Coteau du Missouri</span> <a href="#Page_34">34</a>, <a href="#Page_35">35</a></dt>
-<dt><span class="lj">Crazy Mountains</span> <a href="#Page_37">37</a></dt>
-<dt><span class="lj">Creosote</span> <a href="#Page_1">1</a></dt>
-<dt><span class="lj">Cretaceous Period</span> <a href="#Page_11">11</a>, <a href="#Page_16">16</a>, <a href="#Page_19">19</a>, <a href="#Page_24">24</a>, <a href="#Page_43">43</a>, <a href="#Page_46">46</a>, <a href="#Page_48">48</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_D"><b>D</b></dt>
-<dt><span class="lj">Dakota hogback</span> <a href="#Page_43">43</a></dt>
-<dt><span class="lj">Dakota Sandstone</span> <a href="#Page_22">22</a>, <a href="#Page_23">23</a>, <a href="#Page_24">24</a>, <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Dawson Formation</span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Dead-ice moraines</span> <a href="#Page_34">34</a></dt>
-<dt><span class="lj">Definition</span> <a href="#Page_1">1</a></dt>
-<dt><span class="lj">Deformation</span> <a href="#Page_11">11</a></dt>
-<dt><span class="lj">Denver, Colo.</span> <a href="#Page_42">42</a></dt>
-<dt><span class="lj">Denver Formation</span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Deposition</span> <a href="#Page_10">10</a>, <a href="#Page_11">11</a>, <a href="#Page_32">32</a>, <a href="#Page_44">44</a></dt>
-<dt><span class="lj">Devils River</span> <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Devils Tower, Wyo.</span> <a href="#Page_37">37</a></dt>
-<dt><span class="lj">Differential erosion</span> <a href="#Page_23">23</a>, <a href="#Page_25">25</a>, <a href="#Page_42">42</a></dt>
-<dt><span class="lj">Dikes</span> <a href="#Page_25">25</a></dt>
-<dt><span class="lj">Dinosaurs</span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Drift</span> <a href="#Page_34">34</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_E"><b>E</b></dt>
-<dt><span class="lj">Edwards Plateau</span> <a href="#Page_10">10</a>, <a href="#Page_19">19</a>, <a href="#Page_29">29</a>, <a class="i" href="#Page_46">46</a>, <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Eocene Epoch</span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Epilogue</span> <a class="i" href="#Page_49">49</a></dt>
-<dt><span class="lj">Erosion</span> <a class="i" href="#Page_18">18</a></dt>
-<dt><span class="lj">Escarpments</span> <a href="#Page_4">4</a>, <a href="#Page_7">7</a>, <a href="#Page_23">23</a>, <a href="#Page_34">34</a></dt>
-<dt><span class="lj">Eskers</span> <a href="#Page_35">35</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_F"><b>F</b></dt>
-<dt><span class="lj">Farming</span> <a href="#Page_30">30</a></dt>
-<dt><span class="lj">Fishers Peak</span> <a href="#Page_23">23</a></dt>
-<dt><span class="lj">Fissures</span> <a href="#Page_20">20</a></dt>
-<dt><span class="lj">Forests</span> <a href="#Page_1">1</a>, <a href="#Page_2">2</a>, <a href="#Page_7">7</a></dt>
-<dt><span class="lj">Fort Union Formation</span> <a href="#Page_16">16</a>, <a href="#Page_40">40</a></dt>
-<dt><span class="lj">Fossils</span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Frio River</span> <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Front Range</span> <a href="#Page_43">43</a></dt>
-</dl>
-<div class="pb" id="Page_53">53</div>
-<dl class="indexlr">
-<dt class="center" id="index_G"><b>G</b></dt>
-<dt><span class="lj">Gangplank</span> <a href="#Page_27">27</a></dt>
-<dt><span class="lj">Gas</span> <a href="#Page_30">30</a>, <a href="#Page_47">47</a>, <a href="#Page_49">49</a></dt>
-<dt><span class="lj">Glaciation</span> <a href="#Page_2">2</a>, <a href="#Page_5">5</a>, <a href="#Page_11">11</a>, <a href="#Page_33">33</a></dt>
-<dt><span class="lj">Grand River</span> <a href="#Page_39">39</a></dt>
-<dt><span class="lj">Great Bend, Kans.</span> <a href="#Page_2">2</a></dt>
-<dt><span class="lj">Great Bend Plains</span> <a href="#Page_48">48</a>, <a href="#Page_49">49</a></dt>
-<dt><span class="lj">Great Falls, Mont.</span> <a href="#Page_33">33</a>, <a href="#Page_35">35</a></dt>
-<dt><span class="lj">Great Ice Age</span> <a href="#Page_5">5</a></dt>
-<dt><span class="lj">Great Lakes</span> <a href="#Page_5">5</a></dt>
-<dt><span class="lj">Guadalupe River</span> <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Gulf Coastal Plain</span> <a href="#Page_7">7</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_H"><b>H</b></dt>
-<dt><span class="lj">Harney Peak</span> <a href="#Page_20">20</a></dt>
-<dt><span class="lj">Havre, Mont.</span> <a href="#Page_33">33</a></dt>
-<dt><span class="lj">Heart River</span> <a href="#Page_33">33</a>, <a href="#Page_35">35</a>, <a href="#Page_39">39</a></dt>
-<dt><span class="lj">Hell Creek Formation</span> <a href="#Page_11">11</a></dt>
-<dt><span class="lj">High Plains</span> <a href="#Page_7">7</a>, <a href="#Page_10">10</a>, <a class="i" href="#Page_25">25</a>, <a href="#Page_45">45</a>, <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Highwood Mountains</span> <a href="#Page_33">33</a>, <a href="#Page_35">35</a>, <a href="#Page_36">36</a></dt>
-<dt><span class="lj">Horses</span> <a href="#Page_16">16</a>, <a href="#Page_18">18</a></dt>
-<dt><span class="lj">Hudson Bay</span> <a href="#Page_32">32</a>, <a href="#Page_33">33</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_I"><b>I</b></dt>
-<dt><span class="lj">Ice Age</span> <a href="#Page_5">5</a></dt>
-<dt><span class="lj">Independence, Mo.</span> <a href="#Page_2">2</a></dt>
-<dt><span class="lj">Interior Highlands</span> <a href="#Page_5">5</a></dt>
-<dt><span class="lj">Interior Plains</span> <a href="#Page_5">5</a>, <a href="#Page_11">11</a></dt>
-<dt><span class="lj">Interstate Highway 25</span> <a href="#Page_43">43</a></dt>
-<dt><span class="lj">Interstate Highway 70</span> <a href="#Page_4">4</a></dt>
-<dt><span class="lj">Introduction</span> <a class="i" href="#Page_1">1</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_J"><b>J</b></dt>
-<dt><span class="lj">Jewel Cave</span> <a href="#Page_21">21</a></dt>
-<dt><span class="lj">Joints</span> <a href="#Page_20">20</a></dt>
-<dt><span class="lj">Judith Mountains</span> <a href="#Page_36">36</a></dt>
-<dt><span class="lj">Judith River</span> <a href="#Page_38">38</a></dt>
-<dt><span class="lj">Juniper</span> <a href="#Page_1">1</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_K"><b>K</b></dt>
-<dt><span class="lj">Kames</span> <a href="#Page_35">35</a></dt>
-<dt><span class="lj">Kansas</span> <a href="#Page_10">10</a>, <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Kansas City, Mo.</span> <a href="#Page_35">35</a></dt>
-<dt><span class="lj">Karst topography</span> <a href="#Page_45">45</a></dt>
-<dt><span class="lj">Kearney, Nebr.</span> <a href="#Page_2">2</a></dt>
-<dt><span class="lj">King Mountain</span> <a href="#Page_29">29</a></dt>
-<dt><span class="lj">Knife River</span> <a href="#Page_33">33</a>, <a href="#Page_35">35</a>, <a href="#Page_39">39</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_L"><b>L</b></dt>
-<dt><span class="lj">Laccoliths</span> <a href="#Page_37">37</a></dt>
-<dt><span class="lj">Lake development</span> <a href="#Page_34">34</a>, <a href="#Page_39">39</a></dt>
-<dt><span class="lj">Lance Formation</span> <a href="#Page_11">11</a></dt>
-<dt><span class="lj">Laramie Formation</span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Lava flows</span> <a href="#Page_37">37</a></dt>
-<dt><span class="lj">Lewis and Clark expedition</span> <a href="#Page_2">2</a></dt>
-<dt><span class="lj">Limestone Plateau</span> <a href="#Page_21">21</a>, <a href="#Page_22">22</a></dt>
-<dt><span class="lj">Limon, Colo.</span> <a href="#Page_4">4</a>, <a href="#Page_43">43</a></dt>
-<dt><span class="lj">Little Basin, Kans.</span> <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Little Belt Mountains</span> <a href="#Page_36">36</a></dt>
-<dt><span class="lj">Little Missouri River</span> <a href="#Page_33">33</a>, <a href="#Page_35">35</a>, <a href="#Page_38">38</a>, <a href="#Page_40">40</a></dt>
-<dt><span class="lj">Little Rocky Mountains</span> <a href="#Page_33">33</a>, <a href="#Page_36">36</a></dt>
-<dt><span class="lj">Littlefield, Tex.</span> <a href="#Page_30">30</a></dt>
-<dt><span class="lj">Llano Estacado</span> <a href="#Page_29">29</a>, <a href="#Page_30">30</a></dt>
-<dt><span class="lj">Loess</span> <a href="#Page_29">29</a></dt>
-<dt><span class="lj">Longhorn Caverns</span> <a href="#Page_23">23</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_M"><b>M</b></dt>
-<dt><span class="lj">Marias River</span> <a href="#Page_33">33</a></dt>
-<dt><span class="lj">McCamey, Tex.</span> <a href="#Page_29">29</a></dt>
-<dt><span class="lj">Medicine Lodge River</span> <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Medina River</span> <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Mesa de Maya</span> <a href="#Page_20">20</a>, <a href="#Page_24">24</a>, <a href="#Page_25">25</a></dt>
-<dt><span class="lj">Mescalero escarpment</span> <a href="#Page_7">7</a>, <a href="#Page_29">29</a>, <a href="#Page_45">45</a>, <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Mesquite</span> <a href="#Page_1">1</a></dt>
-<dt><span class="lj">Mexico</span> <a href="#Page_1">1</a>, <a href="#Page_11">11</a></dt>
-<dt><span class="lj">Milk River</span> <a href="#Page_33">33</a></dt>
-<dt><span class="lj">Minneapolis, Kans.</span> <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Miocene Epoch</span> <a href="#Page_23">23</a></dt>
-<dt><span class="lj">Missouri escarpment</span> <a href="#Page_34">34</a></dt>
-<dt><span class="lj">Missouri Plateau</span> <a href="#Page_7">7</a>, <a href="#Page_19">19</a>, <a href="#Page_20">20</a>, <a class="i" href="#Page_32">32</a>, <a href="#Page_48">48</a>, <a href="#Page_49">49</a></dt>
-<dt><span class="lj">Missouri River</span> <a href="#Page_5">5</a>, <a href="#Page_7">7</a>, <a href="#Page_25">25</a>, <a href="#Page_32">32</a>, <a href="#Page_33">33</a>, <a href="#Page_35">35</a>, <a href="#Page_38">38</a></dt>
-<dt><span class="lj">Montana</span> <a href="#Page_33">33</a></dt>
-<dt><span class="lj">Monument Rocks</span> <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Moraines</span> <a href="#Page_34">34</a></dt>
-<dt><span class="lj">Moreau River</span> <a href="#Page_39">39</a></dt>
-<dt><span class="lj"><i>Moropus</i></span> <a href="#Page_18">18</a></dt>
-<dt><span class="lj">Mount Rushmore</span> <a href="#Page_20">20</a></dt>
-<dt><span class="lj">Musselshell River</span> <a href="#Page_38">38</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_N"><b>N</b></dt>
-<dt><span class="lj">Nebraska</span> <a href="#Page_7">7</a>, <a href="#Page_29">29</a></dt>
-<dt><span class="lj">Nebraska Sand Hills</span> <a href="#Page_29">29</a></dt>
-<dt><span class="lj">Needles area, Black Hills</span> <a href="#Page_20">20</a></dt>
-<dt><span class="lj">New Mexico</span> <a href="#Page_7">7</a>, <a href="#Page_19">19</a>, <a href="#Page_45">45</a></dt>
-<dt><span class="lj">North Canadian River</span> <a href="#Page_48">48</a>, <a href="#Page_49">49</a></dt>
-<dt><span class="lj">North Dakota</span> <a href="#Page_33">33</a>, <a href="#Page_34">34</a>, <a href="#Page_35">35</a></dt>
-<dt><span class="lj">Nueces River</span> <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Nunataks</span> <a href="#Page_33">33</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_O"><b>O</b></dt>
-<dt><span class="lj">Oak trees</span> <a href="#Page_1">1</a></dt>
-<dt><span class="lj">Odessa, Tex.</span> <a href="#Page_30">30</a></dt>
-<dt><span class="lj">Ogallala Formation</span> <a href="#Page_18">18</a>, <a href="#Page_23">23</a>, <a href="#Page_24">24</a>, <a href="#Page_25">25</a>, <a href="#Page_27">27</a>, <a href="#Page_29">29</a>, <a href="#Page_45">45</a>, <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Ohio River</span> <a href="#Page_5">5</a></dt>
-<dt><span class="lj">Oil</span> <a href="#Page_30">30</a>, <a href="#Page_46">46</a>, <a href="#Page_47">47</a>, <a href="#Page_49">49</a></dt>
-<dt><span class="lj">Oklahoma</span> <a href="#Page_7">7</a></dt>
-<dt><span class="lj">Oligocene Epoch</span> <a href="#Page_16">16</a>, <a href="#Page_43">43</a></dt>
-<dt><span class="lj">Oregon Trail</span> <a href="#Page_2">2</a></dt>
-<dt><span class="lj">Ouachita province</span> <a href="#Page_5">5</a></dt>
-<dt><span class="lj">Outwash plains</span> <a href="#Page_35">35</a></dt>
-<dt><span class="lj">Ozark Plateaus</span> <a href="#Page_5">5</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_P"><b>P</b></dt>
-<dt><span class="lj">Paleocene Epoch</span> <a href="#Page_16">16</a>, <a href="#Page_23">23</a></dt>
-<dt><span class="lj">Paleozoic Era</span> <a href="#Page_21">21</a>, <a href="#Page_30">30</a>, <a href="#Page_45">45</a></dt>
-<dt><span class="lj">Palmer Lake</span> <a href="#Page_43">43</a></dt>
-<dt><span class="lj">Pampa, Tex.</span> <a href="#Page_30">30</a></dt>
-<dt><span class="lj">Pawnee Buttes</span> <a href="#Page_42">42</a></dt>
-<dt><span class="lj">Pecos River</span> <a href="#Page_7">7</a>, <a href="#Page_25">25</a>, <a href="#Page_45">45</a>, <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Pecos Valley</span> <a href="#Page_7">7</a>, <a href="#Page_10">10</a>, <a href="#Page_19">19</a>, <a href="#Page_23">23</a>, <a class="i" href="#Page_45">45</a>, <a href="#Page_48">48</a>, <a href="#Page_49">49</a></dt>
-<dt><span class="lj">Pedernales River</span> <a href="#Page_47">47</a></dt>
-<dt><span class="lj">Pike, Zebulon</span> <a href="#Page_iii">iii</a>, <a href="#Page_2">2</a></dt>
-<dt><span class="lj">Pine Ridge escarpment</span> <a href="#Page_7">7</a>, <a href="#Page_29">29</a>, <a href="#Page_40">40</a></dt>
-<dt><span class="lj">Pioneers</span> <a href="#Page_2">2</a></dt>
-<dt><span class="lj">Plains Border Section</span> <a href="#Page_19">19</a>, <a class="i" href="#Page_48">48</a></dt>
-<dt><span class="lj">Platte River</span> <a href="#Page_2">2</a>, <a href="#Page_25">25</a>, <a href="#Page_29">29</a></dt>
-<dt><span class="lj">Pleistocene Epoch</span> <a href="#Page_5">5</a></dt>
-<dt><span class="lj">Poison Canyon Formation</span> <a href="#Page_16">16</a>, <a href="#Page_23">23</a>, <a href="#Page_24">24</a></dt>
-<dt><span class="lj">Powder River</span> <a href="#Page_39">39</a></dt>
-<dt><span class="lj">Powder River Basin</span> <a href="#Page_39">39</a></dt>
-<dt><span class="lj">Purgatoire Formation</span> <a href="#Page_24">24</a></dt>
-<dt><span class="lj">Purgatoire River</span> <a href="#Page_25">25</a></dt>
-</dl>
-<div class="pb" id="Page_54">54</div>
-<dl class="indexlr">
-<dt class="center" id="index_R"><b>R</b></dt>
-<dt><span class="lj">Racetrack, The</span> <a href="#Page_22">22</a></dt>
-<dt><span class="lj">Rainfall</span> <a href="#Page_2">2</a></dt>
-<dt><span class="lj">Rapid City, S. Dak.</span> <a href="#Page_20">20</a></dt>
-<dt><span class="lj">Raton Basin</span> <a href="#Page_24">24</a></dt>
-<dt><span class="lj">Raton Formation</span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Raton Mesa</span> <a href="#Page_20">20</a>, <a href="#Page_23">23</a></dt>
-<dt><span class="lj">Raton section</span> <a href="#Page_10">10</a>, <a href="#Page_20">20</a>, <a class="i" href="#Page_23">23</a>, <a href="#Page_45">45</a></dt>
-<dt><span class="lj">Red Hills</span> <a href="#Page_48">48</a>, <a href="#Page_49">49</a></dt>
-<dt><span class="lj">Red Valley</span> <a href="#Page_22">22</a></dt>
-<dt><span class="lj">Republican River</span> <a href="#Page_4">4</a>, <a href="#Page_29">29</a>, <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Rhinoceroses</span> <a href="#Page_16">16</a>, <a href="#Page_18">18</a></dt>
-<dt><span class="lj">Rio Grande</span> <a href="#Page_7">7</a>, <a href="#Page_45">45</a></dt>
-<dt><span class="lj">Rocky Mountains</span> <a href="#Page_5">5</a>, <a href="#Page_19">19</a></dt>
-<dt><span class="lj">Roswell, N. Mex.</span> <a href="#Page_45">45</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_S"><b>S</b></dt>
-<dt><span class="lj">Sabinal River</span> <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Salina, Kans.</span> <a href="#Page_4">4</a></dt>
-<dt><span class="lj">Saline River</span> <a href="#Page_4">4</a>, <a href="#Page_48">48</a></dt>
-<dt><span class="lj">San Antonio, Tex.</span> <a href="#Page_47">47</a></dt>
-<dt><span class="lj">Sand dunes</span> <a href="#Page_44">44</a>, <a href="#Page_49">49</a></dt>
-<dt><span class="lj">Sand Hills, Nebr.</span> <a href="#Page_29">29</a></dt>
-<dt><span class="lj">Sangre de Cristo Mountains</span> <a href="#Page_7">7</a>, <a href="#Page_45">45</a>, <a href="#Page_46">46</a></dt>
-<dt><span class="lj">Scotts Bluff National Monument</span> <a href="#Page_27">27</a>, <a href="#Page_42">42</a></dt>
-<dt><span class="lj">Sedimentation</span> <a href="#Page_10">10</a>, <a href="#Page_11">11</a>, <a href="#Page_32">32</a></dt>
-<dt><span class="lj">Shonkin Sag</span> <a href="#Page_35">35</a></dt>
-<dt><span class="lj">Sinkholes</span> <a href="#Page_47">47</a>, <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Skyline Drive, Canon City, Colo.</span> <a href="#Page_43">43</a></dt>
-<dt><span class="lj">Smith River</span> <a href="#Page_38">38</a></dt>
-<dt><span class="lj">Smoky Hill River</span> <a href="#Page_4">4</a>, <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Smoky Hills</span> <a href="#Page_48">48</a>, <a href="#Page_49">49</a></dt>
-<dt><span class="lj">Soil development</span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Solomon River</span> <a href="#Page_4">4</a>, <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Solution cavities</span> <a href="#Page_45">45</a>, <a href="#Page_47">47</a>, <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Sonora, Tex.</span> <a href="#Page_47">47</a></dt>
-<dt><span class="lj">South Dakota</span> <a href="#Page_20">20</a>, <a href="#Page_29">29</a>, <a href="#Page_33">33</a>, <a href="#Page_34">34</a></dt>
-<dt><span class="lj">South Dakota Badlands</span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">South Platte River</span> <a href="#Page_4">4</a>, <a href="#Page_7">7</a>, <a href="#Page_42">42</a>, <a href="#Page_43">43</a>, <a href="#Page_44">44</a></dt>
-<dt><span class="lj">Spanish Peaks</span> <a href="#Page_19">19</a>, <a href="#Page_24">24</a></dt>
-<dt><span class="lj">Spruce trees</span> <a href="#Page_2">2</a></dt>
-<dt><span class="lj">Stream deposition</span> <a class="i" href="#Page_11">11</a>, <a href="#Page_32">32</a></dt>
-<dt><span class="lj">Summary</span> <a class="i" href="#Page_49">49</a></dt>
-<dt><span class="lj">Sun River</span> <a href="#Page_38">38</a></dt>
-<dt><span class="lj">Superior Upland</span> <a href="#Page_5">5</a>, <a href="#Page_10">10</a></dt>
-<dt><span class="lj">Sweetgrass Hills</span> <a href="#Page_33">33</a></dt>
-<dt><span class="lj">Sylvan Lake</span> <a href="#Page_20">20</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_T"><b>T</b></dt>
-<dt><span class="lj">Tapirs</span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Tertiary Period</span> <a href="#Page_42">42</a>, <a href="#Page_43">43</a>, <a href="#Page_45">45</a>, <a href="#Page_46">46</a>, <a href="#Page_48">48</a></dt>
-<dt><span class="lj">Teton River</span> <a href="#Page_33">33</a></dt>
-<dt><span class="lj">Texas</span> <a href="#Page_7">7</a></dt>
-<dt><span class="lj">Theodore Roosevelt National Memorial Park</span> <a href="#Page_35">35</a>, <a href="#Page_40">40</a></dt>
-<dt><span class="lj">Till</span> <a href="#Page_34">34</a></dt>
-<dt><span class="lj"><i>Titanotheres</i></span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Tongue River</span> <a href="#Page_39">39</a></dt>
-<dt><span class="lj">Trails</span> <a href="#Page_2">2</a></dt>
-<dt><span class="lj">Trees</span> <a href="#Page_1">1</a>, <a href="#Page_2">2</a>, <a href="#Page_7">7</a></dt>
-<dt><span class="lj">Triassic Period</span> <a href="#Page_21">21</a></dt>
-<dt><span class="lj">Triceratops</span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Trinidad, Colo.</span> <a href="#Page_25">25</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_U"><b>U</b></dt>
-<dt><span class="lj">Uplift</span> <a href="#Page_11">11</a>, <a href="#Page_16">16</a>, <a href="#Page_19">19</a>, <a href="#Page_32">32</a>, <a href="#Page_37">37</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_V"><b>V</b></dt>
-<dt><span class="lj">Valley development</span> <a href="#Page_39">39</a></dt>
-<dt><span class="lj">Vaughn, N. Mex.</span> <a href="#Page_45">45</a></dt>
-<dt><span class="lj">Vegetation</span> <a href="#Page_1">1</a>, <a href="#Page_2">2</a>, <a href="#Page_7">7</a>, <a href="#Page_10">10</a>, <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Vermejo Formation</span> <a href="#Page_16">16</a></dt>
-<dt><span class="lj">Volcanoes</span> <a href="#Page_16">16</a>, <a href="#Page_20">20</a>, <a href="#Page_40">40</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_W"><b>W</b></dt>
-<dt><span class="lj">Walsenburg, Colo.</span> <a href="#Page_24">24</a></dt>
-<dt><span class="lj">Warping</span> <a class="i" href="#Page_11">11</a></dt>
-<dt><span class="lj">Well-drilling</span> <a href="#Page_11">11</a></dt>
-<dt><span class="lj">West Nueces River</span> <a href="#Page_46">46</a></dt>
-<dt><span class="lj">White River</span> <a href="#Page_29">29</a>, <a href="#Page_39">39</a>, <a href="#Page_40">40</a></dt>
-<dt><span class="lj">White River Group</span> <a href="#Page_16">16</a>, <a href="#Page_40">40</a>, <a href="#Page_44">44</a></dt>
-<dt><span class="lj">Williston basin</span> <a href="#Page_11">11</a>, <a href="#Page_16">16</a>, <a href="#Page_33">33</a></dt>
-<dt><span class="lj">Wind Cave</span> <a href="#Page_21">21</a></dt>
-<dt><span class="lj">Wind deposition</span> <a href="#Page_44">44</a></dt>
-<dt><span class="lj">Wyoming</span> <a href="#Page_20">20</a>, <a href="#Page_39">39</a></dt>
-</dl>
-<dl class="indexlr">
-<dt class="center" id="index_Y"><b>Y</b></dt>
-<dt><span class="lj">Yellowstone River</span> <a href="#Page_33">33</a>, <a href="#Page_38">38</a></dt>
-</dl>
-<div class="pb" id="Page_55">55</div>
-<div class="img" id="pic_4">
-<img src="images/p24.jpg" alt="U. S. DEPARTMENT OF THE INTERIOR &#149; March 3, 1849" width="300" height="301" />
-</div>
-<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>
-</ul>
-
-
-
-
-
-
-
-<pre>
-
-
-
-
-
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