Chapter I: Front Matter

_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_

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