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diff --git a/old/63396-0.txt b/old/63396-0.txt deleted file mode 100644 index 412395b..0000000 --- a/old/63396-0.txt +++ /dev/null @@ -1,2299 +0,0 @@ -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 - - ---Retained publication information from the printed edition: this eBook - is public-domain in the country of publication. - ---In the text versions only, text in italics is delimited by - _underscores_. - - - - - - - -End of the Project Gutenberg EBook of The Geologic Story of the Great Plains, by -Donald E. 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