PHYSIOG RA.PHY OF

WESTERN UNITED STATES

BY

NEVIN M. FE NNE MAN Professor of Geology, University of Cincinnati

FIRST EDITION

SECOND IMPRESSION

McGRAW-HILL BOOK COMPANY, INC.

NEW YORK AND LONDON

1931

COPYRIGHT, 1931, BY THE

MCGRAW-HILL BOOK COMPANY, INC.

PRINTED IN THE UNITED STATES OF AMERICA

All rights reserved. This book, or parts thereof, may not be reproduced in any form without permission of

the publishers.

THE MAPLE PRESS COMPANY, YORK, PA.

xii CONTENTS

PAGE

CHAPTER VI

THE COLUMBIA PLATEAU . . . . . . . . . . . . . . . . . . . . 225 The Province as a Whole--Snake River Plain-Payette Section­Blue Mountain Section-Walla Walla Section-Eastern Margin-The Coulee District-Yakima District-North Central Oregon­Harney Section.

CHAPTER VII

COLORADO PLATEAU PROVINCE ... ............... 274 The Province as a Whole--Grand Canyon Section-Plateaus North of the Canyon-San Francisco Plateau-Grand Canyon­High Plateaus of Utah-Rock Terraces of Southern Utah-Uinta Basin Section-Canyon Lands of Utah-Navajo Section-Datil Section-Physiographic History.

CHAPTER VIII

BASIN AND RANGE PROVINCE . . . . . . . . . . . . . . . . . . 326 The Province as a Whole--Basin Ranges-Intermont Basins-The Great Basin-Sonoran Desert-Salton Basin-Mexican Highland-Sacramento Section.

CHAPTER IX

SIERRA CASCADE PROVINCE .... 396 General Relations-Sierra Nevada Section-Southern Cascade Mountains-Northern Cascade Mountains-Middle Cascade Mountains.

CHAPTER X

PACIFIC BORDER PROVINCE . . . . . .. ... . . . ..... 442 General-Puget Trough-Olympic Section-Oregon Coast Range--Klamath Mountains-Valley of California-The Cali­fornia Coast Ranges-Angeles Section-Lower Californian Province.

INDEX ............................. 511

LIST OF MAPS FOR REFERENCE

Plate I. Map showing physical divisions of the United States . In pocket

Fig. 2. Index map; central part of the Great Plains province.

Fig. 3. Index map; northern part of the Great Plains province

Fig. 4. Index map; southern part of the Great Plains province

Fig. 27. Extent of continental glaciation on the Great Plains

Fig. 30. Index map of the southern Rocky Mountain province

Fig. 49. Index map of the Wyoming Basin and middle Rocky

Mountains .............. .

Fig. 69. Index map of the northern Rocky Mountains .

Fig. 81. Extent of glaciation west of longitude 112 degrees

PAGE

6

8

10

72

94

134

184

212

Fig. 83. Index map of Columbia Plateau and parts of adjacent

provinces . . . . . . . . . . . . . . . . 226

Fig. 101. Index map of the Colorado Plateau province . . . 275

Fig. 118. Index map of the Great Basin. . . . . . . . . 327

Fig. 132. Index map of the Sonoran Desert and adjacent sections. 368

Fig. 141. Index map of the Sierra Nevada and adjacent sections . 397

xiii

CHAPTER VII

COLORADO PLATEAU PROVINCE

THE PROVINCE AS A WHOLE

Distinguishing Features.-The name here applied to a vast province of 130,000 square miles was first given to a much smaller area in the Grand Canyon district. The larger area is often appropriately spoken of in the plural as the" Colorado Plateaus." Its several parts, some of them strongly differentiated, have certain features in common which distinguish the entire province from its neighbors.

The first distinguishing feature is approximate horizontality of its rocks. In the contiguous provinces the strata are folded. Tilted beds in this province are limited to a few great monoclines and the borders of a few local uplifts. There is no lack of steep slopes but, except on recent volcanic features, they are due to erosion guided in some cases by structure. In all the larger features the relation between structure and erosional history is obvious. There is no other province in America where such relations are more impressive.

The second distinguishing feature of the province is great elevation. Aside from canyon bottoms, no considerable portion of it is lower than 5,000 ft. Between this and 11,000 ft., there are plateaus of all altitudes, some of them being higher than the nearby mountain ranges. Except where bordered by high mountains on the north and east, this province generally over­looks its neighbors from a bold escarpment.

A feature which distinguishes the entire province is its remark­able canyons, not one but hundreds. These are favored by (1) elevation of the plateau above its base level; (2) strength of rocks and aridity of climate, both causing steep slopes to waste slowly; (3) the bordering mountains and strips of lofty plateau which provoke rainfall and thus furnish water to the through­flowing streams. Lastly (4) it must be remembered that canyons are features of youth. Considered with reference to the current

274

CHAPTER VIII

BASIN AND RANGE PROVINCE

THE PROVINCE AS A WHOLE

GENERAL DESCRIPTION

Distinctive Features.-A great region west and south of the Colorado Plateaus, embracing one-tenth of the United States and extending into Mexico, is aptly styled the Basin and Range province (Fig. 118; also Fig. 4, page 10 and Fig. 132, page 368). Topographically it is distinguished by isolated, roughly parallel mountain ranges separated by desert basins, generally almost level. Climatically it is characterized by want of sufficient run­off to reach the sea or to forward its load of detritus. In the northern half, i.e., in the Great Basin, drainage generally leads to enclosed basins. In Arizona and New Mexico such basins are by no means universal. Much of the area there has slopes on which water Inight run directly to the sea but it is too arid to supply continuous flow and considerable areas have no run-off at all.

Boundaries.-While interior drainage is highly characteristic, this affords a poor criterion for drawing boundaries. For example, the basin of internal drainage includes the eastern slope of the Sierra Nevada which belongs quite as much to the Mountain province as does the western slope. Moreover, the Pitt River, a tributary of the Sacramento, drains the northeast corner of California, a characteristic portion of the Great Basin province. In like manner a considerable portion of southern Nevada is traversed by canyons leading to the Virgin River and thus to the sea. The fact that the drainage from these marginal portions is outward does not differentiate them physiographic ally from neighboring portions whose drainage leads to salt lakes. 1

The area characterized by the "basin ranges" has a different limit. Except for their greater size, the Wasatch on the east

1 It is true that the term "Great Basin" is often used in a hydrographic sense but its more general use is physiographic. Care must be exercised to avoid confusion.

326

328 PHYSIOGRAPHY OF WESTERN UNITED STATES

istically at the foot of steep wasting slopes, covering the inter­vening troughs or basins where streams lose their velocity or disappear. It must, however, be remembered that the province as a whole is not the exact area covered by such deposits. The typical "bolson" or concave basin, coated, and in some cases deeply filled, with detritus is a very characteristic but not universal feature. The line delimiting the area thus characterized must, in parts, be arbitrary. The boundaries chosen are in part determined by the more easily defined limits of neighboring provinces, such as the edge of the Colorado Plateau and the foot of the Sierra Nevada.

Subdivisions.-The province here outlined is divided into five sections of unequal size. The Great Basin lies north of lat. 35°30'. In this the space taken by the mountains is about half of the total. Only minor marginal tracts may drain to the sea. South of this, in California and southwestern Arizona, is the Sonoran Desert section, much lower in altitude, in which mountain ranges are smaller and perhaps older, occupying perhaps one-fifth of the space. Moreover, large areas are with­out concave basins of internal drainage. The Salton Trough, whose center is several hundred feet below sea-level, deserves separate treatment. Its southward extension in Mexico embraces the Gulf of California. Between the Sonoran Desert and the Colorado Plateau, stretching east beyond the Rio Grande, is a northward continuation of the Mexican Highland not unlike the Great Basin in its major features. However, as the Plateau province is approached some of the mountains are transitional in type from that of the basin range to that of the plateau out­lier. In central Arizona the drainage from this section is to the sea. Finally, on the eastern margin of the province, mainly in New Mexico, there is a north-south strip which combines some features of this province with others of the Colorado Plateau. At the north end where its plateaus are of horizontal rocks, it has the drainage features of the Great Basin. Elsewhere, and for the greater part, its plateaus are tilted like the mountains in the northern part of the Great Basin. This is the Sacramento section.

CLIMATE

The province as a whole is the driest in the United States, being dependent for its moisture on winds from the Pacific and

BASIN AND RANGE PROVINCE 381

those of the Great Basin in their dimensions, in the rocks that compose them, in structure, and in history.l In other ranges, the Bradshaw for example, though folding is important, no significant faulting has been discovered. 2

Near the edge of the Colorado Plateau, many mountains are fault blocks without alignment, mere fragments of the plateau that have suffered displacement and erosion. There is here a kind of transitional zone between the two physiographic prov­inces. In the Clifton mining district near the New Mexico border, the entire area when seen from a high point is one of irregular ridges and uplands without apparent plan or order. It does not in the least conform to the simple conception of basin ranges, but with its complicated history of intrusion, faulting, lava flows, and various erosion cycles3 it resembles still less the horizontal plateau on the north. At some places, particularly in the mining districts, the results of faulting reach the last degree of complexity. Areas of many square miles may be broken by faults of various trend, into blocks so small that the whole district is but a huge mosaic of angular blocks. 4 To a remarkable degree the drainage of such areas has been guided by fault lines or by differences in hardness among the several blocks.

Features of the Plateau Border.-In western Arizona there is not much question as to the proper location of the province boundary. North of the Colorado River the lower and upper Carboniferous rocks and the Kaibab limestone (Permian) are almost coextensive and their combined escarpments form the Grand Wash Cliffs, the western limit of the Colorado Plateau. South of the river, the upper Carboniferous and Permian fall back many miles to the east, leaving the Lower Carboniferous (Redwall) to form the plateau surface. The height of the cliffs which limit this plateau is increased by the thickness of the underlying Cambrian (Tonto) as in the Grand Canyon (page 291). This condition persists as far east as long. 112°30', and throughout that distance the Plateau province is coextensive

1 RANSOME, F. L., Geology of the Globe Copper District, U. S. Geo!. Survey, Prof. Pap. 12, p. 16, 1903. Ransome here cites Gilbert.

2 JAGGAR, T. A., and PALACHE, CHARlJES, Bradshaw Mountains folio 126, U. S. Geo!. Survey, 1905.

3 LINDGREN, W., Clifton folio 129, U. S. Geo!. Survey, 1905. 4 See geological maps in Globe folio 111; also Bisbee special folio 112.

U. S. Geo!. Survey.