DEPARTMENT OF THE INTERIOR 

UNITED STATES GEOLOGICAL SURVEY

, ' ' ' *< ! !-"

GEORGE OTIS SMITH, DIRECTOB

BULLETIN 549

THE SHINUMO QUADRANGLE

GRAND CANYON DISTRICT 

ARIZONA

BY

L. F. NOBLE

WASHINGTON

GOVERNMENT PRINTING OFFICE 

1914

CONTENTS.

Preface, by F. L. Kansome.................................................

Introduction..............................................................

Location and geography................................................

Field work............................................................

Literature............................................................

Acknowledgments.........................................."............

Physiography of the Grand Canyon district................................. 15

Topography of the Shinumo quadrangle...................................... 2l

Climate. .........=...................................................... 25

Vegetation............................................................... 27

Indian ruins.............................................................. 28

Geology.................................................................. 29

Age and character of the rocks.......................................... 29

. Series of rocks discriminated........................................... 31

Proterozoic rocks..................................................... I 32

Archean system.................................................... 32

Vishnu schist.................................................. 32

Name.................................................... 32

Distribution in the Grand Canyon........................... 32

Occurrence and distribution in the Shinumo quadrangle..... 32

Types of the schist......................................... 33

Lithology of the types..................................... 33

Origin of the schist............................:............ 34

Age and correlation....................................... 35

Intrusive quartz diorite and dikes of pegmatite associated with the

Vishnu schist............................................ 35

Quartz diorite............................................. 35

Pegmatite................................................ 36

Algonkian system.................................................. 37

Grand Canyon series........................................... 37

Name.................................................... 37

Distribution in the Grand Canyon........................... 37

Structure and distribution in Shinumo quadrangle.......... 39

Unkargroup............................................... . 40

Character and subdivisions............................. 40

Hotauta conglomerate................................... 42

Bass limestone........................................ 43

Hakatai shale.......................................... 48

Shinumo quartzite.................................... 51

Dox sandstone......................................... 53

Comparison with type section in Unkar Valley........... 53

Age and correlation of the Grand Canyon series......... 54
4 CONTENTS.

Geology Continued. . ' page. 

Proterozoic rocks Continued. ' 

Algonkian system Continued.

Grand Canyon series Continued.

Intrusive diabase associated with the Unkar group.......... 55

Occurrence............................................ 55

Petrography.......................................... 56

Variations in character................................ 56

Contact metamorphism................................. 57

Asbestos.............................................. 58

Age of diabase........................................ 60

Paleozoic rocks........................................................ 60

Results of previous work in the region............................... 60

General succession of the Paleozoic rocks........................... 61

Cambrian system................................................... 61

Tonto group................................................... 61

Tapeats sandstone........................................ 61

Bright Angel shale........................................ 62

Muav limestone....... i.................................... 64

Correlation of Tonto group. ................................. 65

Unconformity.................................................... 65

Carboniferous system.............................................. 66

Redwall limestone............................................. 66

Aubrey group................................................. 68

Supaiformation........................................... 68

Coconino sandstone........................................ 69

Kaibab limestone......................................... 70

Variations in thickness of the Paleozoic strata........................ 71

Effect of the variation in thickness of the Paleozoic strata upon topography of the canyon wall......................................... ' 73

Structural geology........................................................ 75

West Kaibab fault..................................................... 75

Faults of the Unkar wedge. .................................... ^....... 77

Displacements of the Paleozoic strata.................. i ............... 78

Geologic history.......................................................... 80

The sedimentary and erosional record................................... 80

The plateau problem................................................... 88

Scenic interest of the Shinumo quadrangle................................. 91

Copper deposits of the Shinumo quadrangle.................................. 93

Index.................................................................... 97
ILLUSTRATIONS.

Pago.

PLATE I. Geologic map of Shinumo quadrangle, Ariz., with structure sections. .................................................... In pocket.

II. A, Traveling on trail in Grand Canyon with pack train; 5, At

Bedrock tank, Bass Canyon.................................... 12

III. A and B, Views up Colorado River near Cable Crossing............ 16

IV. A, Panoramic view of Po.well Plateau across Muav Saddle from the 

Kaibab Plateau; B, Panoramic view of Unkar wedge from Tonto 

platform................................................... 18

V. Tonto platform: View eastward up Kaibab division of Grand Canyon

from level of the Esplanade directly under Havasupai Point..... 20

VI. The Esplanade: View northwestward from Havasupai Point........ 21

VII. A, View northward from Bass Camp; B, View eastward from the

summit of Mount Huethawali.................................. 22

VIII. A, East wall of canyon of Shinumo Creek near Shinumo garden; B, 

View eastward up Colorado River from a point near the mouth of 

Bass Canyon..................... ; ............................ 28.

I.. Generalized columnar section of the rocks of Shinumo quadrangle.., 30 

X. A, Bass limestone, in Hotauta Canyon; B, Strata of Unkar group near

mouth of Bright Angel Creek.................................. 38

XL View northward across the Grand Canyon from the end of Grand

Scenic Divide................................................. 39

XII. Shinumo quartzite: A, North of Cable Crossing; B, In canyon of

Shinumo Creek, showing garden................................ 52

XIII. A, View near Cable Crossing, looking down Colorado River; B, Dox

sandstone in canyon of Shinumo Creek.......................... 54

XIV. Lower contact of diabase sill: A, On Shinumo Creek; B, At Bedrock

tank, Bass Canyon ............................................ 55

XV. A, Muav limestone in Muav Canyon; B, Faults in Unkar wedge in

canyon of Shinumo Creek...................................... 64

XVI. A, Pinnacles of erosion (hoodoos) in Kaibab limestone along rim of

Kaibab Plateau; B, Wheeler fold in Bass Canyon............... 78

XVII. A, Wheeler fold from bed of Bass Canyon; B, Faulting in strata of

the Unkar wedge in Burro Canyon.............................. 79

XVIII. Geologic history of the Shinumo quadrangle as revealed in the

canyon wall................................................... 86

FIGURE 1. Index map showing location of Shinumo quadrangle............... 12

6

PREFACE.

By F. L. RANSOME.

Ever since Powell's daring boat trip down the Colorado in 1869 

geologists have known that the walls of the Grand Canyon display 

one of the most remarkable and instructive geologic sections in the 

world. At first glance the impressive feature of that section is the 

great thickness of nearly horizontal strata through which the river 

has sunk its bed strata ranging in age from Carboniferous (Pennsylvanian) at the top, on the brink of the chasm, to Cambrian at the 

base. Powell found, however, that unconformably below the Cambrian in certain portions of the canyon there are extensive remnants 

of an older and much thicker series of sediments in beds which had 

been upturned into mountains and truncated by prolonged erosion 

before the sands of the Cambrian sea covered them. These beds he 

called the Grand Canyon group and described as resting with profound unconformity on the vastly more ancient crystalline rocks into 

which the river has also cut deeply in the so-called Granite Gorge.

In 1882 appeared Button's well-known "Tertiary history of the 

Grand Canyon district," which dealt mainly with the erosional 

development of the canyon and barely touched upon the earlier 

chapters of the geologic history recorded in its walls.

Between 1883 and 1895 Dr. Charles D. Walcott, in a number of 

papers, described in greater detail the Grand Canyon group of PoweU, 

dividing it into an upper or Chuar terrane, 5,120 feet thick, and a 

lower or Unkar terrane, 6,830 feet thick. He assigned both to the 

Algonkian system, showed that the conformably overlying sandstone is. Cambrian, not Carboniferous, as had been supposed by 

Powell and by Button, and applied the name Vishnu .terrane to the 

fundamental crystalline rocks. These he described as micaceous 

schists and quartzites cut by granite.

During the next 10 or 12 years not much advance was made in our 

knowledge of the character and stratigraphy of the older rocks in 

the Grand Canyon, although the period was by no means barren of 

geologic literature on other problems connected with the growthr of 

that vast abyss. Yet there were awaiting solution a number of 

problems fully as interesting to students of stratigraphy and pre-
& SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARlZ.

Cambrian geology as are the processes and results of earth sculpture 

to investigators who are chiefly concerned with the origin of those 

forms whose collective aspect constitutes what we term scenery. 

For example: Much remained to be learned about the lithologic 

character and divisions of the great masses of strata which Walcott 

had named the Unkar and Chuar terranes. Doubt existed and still 

exists as to the true character of the fundamental crystalline complex, 

some observers failing to find in it material recognizable as metiamorphosed sediments and seeing at the localities visited by them only 

such intrusive and highly metamorphosed rocks as are suggestive of 

igneous origin and Archean age. Within the Paleozoic series the 

part of the stratigraphic column most obviously in need of study is 

that between the Cambrian and the Carboniferous, where the Devonian appears to be represented at some localities and absent at others.

Detailed geologic work demands an accurate topographic base 

map, and no good map of the Grand Canyon existed until the publication, between 1906 and 1908, of the Vishnu, Bright Angel, and 

Shinumo topographic sheets, on the scale of 1:48,000, very nearly If 

inches to the mile. The topography of these maps, by Francois E. 

Matthes and Richard T. Evans, fully meets the requirements of the 

geologists, and one sheet, the Shinumo, was immediately utilized by 

the author of the present bulletin in a study devoted particularly to 

the lithology and stratigraphy of the Unkar group. Begun as a 

university thesis, the work was completed under arrangement with 

the Geological Survey.

In his careful measurement, description, and subdivision of the 

Unkar group Dr. Noble has not only thrown light on the pre-Cambrian 

history of the Colorado Plateau region, but has supplied geologists 

who are working in the southwestern part of the country with a standard of comparison for Algonkian strata exposed elsewhere in that 

region. In addition to pursuing what may be considered the main 

purpose of the investigation, Dr. Noble has added much to our 

knowledge of the general geology and erosional history of the Shinumo 

quadrangle that is, of the western part of the Kaibab division of the 

Grand Canyon and the map which accompanies this bulletin represents the first geologic mapping done in the canyon that attains the 

standard of accuracy and detail set for the Geologic Atlas of the 

United States. By describing examples additional to those previously known he has shown the prevalence and structural importance 

of pre-Cambrian faults and the recurrence of movement in postPaleozoic time along these ancient fractures. He has also called 

attention to the influence of minor joints and of fractures not associated with noticeable displacement in guiding the forces of erosion 

and in determining topographic form.
PREFACE. . ' 9

Although the bulletin contains considerable lithologic and stratigraphic material that will scarcely interest those who are not geologists, Dr. Noble has very properly remembered that the people as a 

whole have unusual claims to consideration in any publication dealing 

with the Grand Canyon, and has skillfully supplied as a setting to his 

more strictly scientific work much vivid description and lucid explanation which will help all those who take more than a transient and 

superficial interest in what they see to understand one of the most 

impressive and significant of the inanimate works of nature.

THE SHINDIG QUADEANGLE, GKAND CANYOI 

DISTRICT, ARIZONA.

By L. F. NOBLE.

INTRODUCTION.

LOCATION AND GEOGRAPHY.

The Shinumo quadrangle, in Coconino County, northern Arizona,

j is the westernmost of three quadrangles covered by the United States

Geological Survey's maps of a part of the Grand Canyon of the Colo-

\ rado the Vishnu, Bright Angel, and Shinumo sheets which show

_» the Kaibab division of the Grand Canyon. The quadrangle is

, . bounded on the north and south by parallels 36° 20' and 36° 5'.

Its eastern and western boundaries are irregular and it lies for the

most part between meridians 112° 15' and 112° 30', but extends

northward somewhat beyond these limits. Its total area is about

~* 270 square miles.

The only permanent habitation in the quadrangle is Bass Camp, 

which is at the rim of the Grand Canyon on the Coconino Plateau, 

^ about a mile west of Havasupai Point. The camp was established by 

Mr. W. W. Bass some 25 years ago to accommodate tourists. From 

Bass Camp a trail that has been constructed across the Grand Canyon descends its southern wall through Bass Canyon to Colorado 

River and ascends its northern wall through Shinumo and Muav 

canyons. The river is crossed by means of a car that travels on wire 

* cables suspended 50 feet above the surface of the stream, so that men 

and animals may be transported at all seasons of the year regardless 

of high water (PI. XIII, A, p. 54). The length of the trail from the 

southern rim of the canyon to the river is 6£ miles; from the river to 

-the summit of the northern wall it is 10 miles. Mr. Bass has recently 

\ discovered in the depths of the canyon deposits of copper and asbesv tos, to which he has constructed additional trails. The trails afford 

access with pack animals (PL II) to all points of geologic interest in 

the interior of the canyon and to points on Powell and Kaibab 

) plateaus, as well as to settlements in southern Utah. A permanent 

; camp (PI. VIII, A, p. 28) has been established in the depths of the 

canyon about a mile up Shinumo Creek from the Colorado, where
12 SHINUMO QUADEANGLE, GEAND CANYON DISTEICT, AEIZ.

an irrigated garden (PI. XII, B, p. 52) is now cultivated on the 

site of one made by the prehistoric inhabitants of the region. Bass 

Camp is most easily reached from Grand Canyon station on the 

Grand Canyon Railway, a branch of the Santa Fe System, by a 

wagon road 25 miles in length. Another road leads southwestward

.FIGURE 1. Index map showing location of Shinumo quadrangle.

from Bass Camp to the rim of Cataract Canyon, about 20 miles 

away, whence a trail descends to the Havasupai Indian village in 

Cataract Canyon. Roads also lead to the towns of Williams and 

A^h Fork, about 60 miles respectively south and southwest of Bass 

Camp. The north rim of the Grand Canyon is reached by a wagon 

road across the Kaibab Plateau from the town of Kanab, in southern 

Utah.
U. S. GEOLOGICAL SURVEY BULLETIN 549 PLATE II

A. TRAVELING ON TRAIL IN THE GRAND CANYON WITH PACK TRAIN.

B. AT BEDROCK TANK, BASS CANYON.
INTRODUCTION. 13 

FIELD WORK.

The greater part of the' geologic field work on which this report is 

based was done between August 23 and December 12, 1908, in preparation for a thesis which was presented to the faculty of Yale University in 1909 in partial fulfillment of the requirements for the 

degree of doctor of philosophy. A part of the thesis, dealing with 

the Archean and Algonkian rocks of the Shinumo quadrangle has 

already been published.1

In February, 1910, the writer returned to the Grand Canyon to 

complete, on an enlarged base and in greater detail, the geologic map 

made to accompany the thesis. This work, begun February 24 and 

ended March 16, 1910, was done under the direction of the United 

States Geological Survey. The area covered by this map (PI. I, in 

pocket) is somewhat over 200 square miles, or about three-fourths of 

the Shinumo quadrangle, and includes all exposures of Algonkian 

rocks in the quadrangle and all features of exceptional geologic 

interest.

LITERATURE.

Maj. Dutton, in his monograph entitled "Tertiary history of the 

Grand Canyon district,"2 describes most fully and charmingly the 

geology of the north rim in this section of the Grand Canyon. Chap- 

'ter VII describes the surface features and scenery of the Kaibab 

Plateau in the vicinity of Point Sublime. Chapter VIII is devoted 

to the panorama disclosed from Point Sublime, and Chapter IX 

describes in detail the walls of the amphitheaters of the north side. 

The Muav Saddle and Powell Plateau are described on pages 162-167 

and the Shinumo Amphitheater on pages 167-174. Dutton's work, 

however, did not extend into the depths of the canyon.

J. S. Diller, of the United States Geological Survey, in reports 

on the production of asbestos, describes deposits of asbestos occurring 

in the Algonkian rocks of this area near Bass Ferry. Diller's first 

report 3 contains the earliest mention of Algonkian strata in this 

part of the Grand Canyon.

- BIBLIOGRAPHY.

BARRELL, JOSEPH, Kelative geological importance of continental littoral and marine 

sedimentation: Jour. Geology, vol. 14, pp. 316, 356, 430-457, 524-568, 1906.

CROSS, WHITMAN, U. S; Geol. Survey Geol. Atlas, Needle Mountains folio (No. 131), 

1905.

> Noble, L. F., Contributions to the geology of the Grand Canyon, Arizona. The geology of the Shinumo 

area: Am. Jour Sci., 4th ser., vol. 29, pp. 369-386, May, 1910; pp. 497-528, June, 1910.

»Dutton, C. E., Tertiary history of the Grand Canyon district, with atlas: U. S. Geol. Survey Mon. 2, 

1882.

«Diller, J. S., The production of asbestos in 1907; U. S. Geol. Survey Mineral Resources, 1907, pt. 2, 

pp. 720-721,1908; also The production of asbestos in 1908: U. S. Geol. Survey Mineral Resources, 1908, pt. 

2, p. 705,1909. _
14 SHINUMO QUADRANGLE, GRAND CANYON" DISTRICT, ARIZ.

DAKTON, N. H., Reconnaissance of parts of northern New Mexico and northern Arizona: U. S. Geol. Survey Bull. 435, 1910.

DA vis, W. M., An excursion to the Grand Canyon of the Colorado: Harvard Univ. 

Mus. Comp. Zool. Bull. 38, geol. ser., vol. 5, No. 4, 1901.

 An excursion to the Plateau province of Utah and Arizona: Harvard Univ. 

Mus. Comp. Zool. Bull. 42, geol. ser., vol. 6, No. 1, 1904.

DILLBR, J. S., The production of asbestos in 1907: U. S. Geol. Survey Mineral Resources, 1907, pt. 2, pp. 720-721, 1908. /

 The production of asbestos in 1908: U. S. Geol. Survey Mineral Resources,

1908, pt. 2, p. 705, 1909. 

BUTTON, C. E,, Tertiary history of the Grand Canyon district, with Atlas: U. S.

Geol. Survey Mon. 2,1882. 

FRECH, F., Section in Congress Canyon opposite Point Sublime: Internat. Geol.

Gong., fifth session, Compte rendu, pp. 476-481, 1894. (The supposition that

Congress Canyon is opposite Point Sublime is erroneous. Point Sublime is 25

miles west of "a'point opposite Congress Canyon.) 

GILBERT, G. K., Report on the geology of portions of Nevada, Utah, California, and

Arizona examined in the years 1871 and 1872: U. S. Geog. Surveys W. 100th

Mer., vol. 3, pt. 1, pp. 17-187, 1875. 

HUNTINGTON, EiLswoRTH, and GOLDTHWAIT, J. W., The Hurricane fault in the

Toquerville district, Utah: Harvard Univ. Mus. Comp. Zool. Bull. 42 geol. ser.,

vol. 6, No. 5, 1904. 

IVES, J. C., Report upon the Colorado River of the West: Senate Ex. Doc., 36th Cong.,

1st sess., pt. 1, general rept., pp. 13-131, 1861, 

JOHNSON, D. W., A geological excursion in the Grand Canyon district: Boston Soc.

Nat. Hist. Proc., vol. 34, pp. 135-161, 1909. 

LEE, W. T., Geologic reconnaissance of a part of western Arizona: U. S. Geol. Survey.

Bull. 352, 1908. 

NEWBERRY, J. S., Report upon the Colorado River of the West: Senate Ex. Doc.,

36th Cong., 1st sess., pt. 3, geol. rept., pp. 1-154, 1861. 

POWELL, J. W., Exploration of the Colorado River of the West and its tributaries.

Explored in 1869, 1870, 1871, and 1872 under the direction of the Secretary of

the Smithsonian Institution, 1875.

 Geology of the eastern portion of the Uinta Mountains, U. S. Geol. and

Geog. Survey Terr., 1876. 

RANSOME, F. L., Geology of the Globe Copper district, Arizona: U. S. Geol. Survey

Prof. Paper 12, 1903. . .

 The geology and ore deposits of the Bisbee quadrangle, Arizona: U. S. 

Geol. Survey Prof. Paper 21,1904.

A comparison of some Paleozoic and pre-Cambrian sections in Arizona:

Science, new eer., vol. 27, pp. 68-69, 1908.

Pre-Cambrian sediments and faults in the Grand Canyon of the Colorado:

Science, new ser., vol. 27, No. 695, pp. 667-669,1908.

ROBINSON, H. H., The Tertiary peneplain of the Plateau district and adjacent country 

in Arizona and New Mexico: Am. Jour. Sci., 4th ser., vol. 24, pp. 109-129, Aug., 

1907.

 A new erosion cycle in the Grand Canyon district, Arizona. Jour. Geology, vol. 18, No. 8 (Nov.-Dec., 1910), pp. 742-763, 1910.

The single cycle development of the Grand Canyon of the Colorado:

Science, new ser., vol. 34, No. 864, 1911. 

WALCOTT, C. D., The Permian and other Paleozoic groups of the Kanab Valley, Arizona:

Am. Jour. Sci., 3d ser., vol. 20, pp. 221-225,1880. 

 Pre-Carboniferous strata in the Grand Canyon of the Colorado, Arizona:

Am. Jour. Sci., 3d ser., vol. 26, pp. 437^42, 484, 1883.
PHYSIOGRAPHY OF THE DISTRICT. 15

D, Ei Li,. Study of a line of displacement in the Grand Canyon of the Colorado in northern Arizona: Geol. Soc. America Bull., vol. 1, pp. 49, 1890.

Pre-Cambrian igneous rocks of the Unkar terrane, Grand Canyon of the

Colorado, Arizona, with notes on the petrographic character of the lavas, by 

Joseph P. Iddings: IT. S. Geol. Survey Fourteenth Ann. Kept, for 1892-93, 

pt. 2, pp. 497-519 (Walcott) and 520-524 (Iddings), 1894.

Algonkian rocks of the Grand Canyon of the Colorado: Jour. Geology,

yol. 3, No. 3, pp. 312-330, 1895.

ACKNOWLEDGMENTS.

In 1901 Mr. Charles D. Walcott and Mr. G. K. Gilbert spent several 

days at Bass Camp and on Shinumo Creek and worked out the 

structure of the pre-Cambrian sediments, which Mr. Walcott correlated with the section described by him in Unkar Valley. His 

notes, however, are unpublished, and it is due to his kindness and 

courtesy that the writer is enabled to present the first description 

of the area. To Mr. Walcott the writer is also indebted for the

identification of Cambrian fossils, for a list of the Cambrian fossils 

found in the region, and for assistance in interpreting the stratigraphy. 

To Prof. Joseph Barrell, to Prof. Charles Schuchert, and to Prof. 

Louis V. Pirsson, all of Yale University, the most sincere thanks are 

due for continued interest and advice during all stages of the work.

PHYSIOGKAPHY OF THE GRAND CANYON DISTRICT.

The great physiographic province of which the Shinumo quadrangle 

is a part is known as the Colorado Plateau. It is a region of nearly 

horizontal strata, and most of its surface lies a mile or more above 

sea level. The strata are beds of sandstone, shale, and limestone, 

which show by their character and the marine fossils they contain 

that they accumulated as sediments beneath the sea. It is therefore 

clear that after the beds were deposited and consolidated into rock 

they were lifted high above sea level to form the present plateau, 

and that the uplift was equal and general over the whole region, 

for the beds retain very nearly the horizontal attitude that they 

originally had on the sea bottom. As the strata are prevailingly 

horizontal, the region is preeminently a land of mesa scenery of 

broad, level or slightly tilted platforms which stretch evenly away 

for miles, rising to younger or dropping to older formations of rock 

by lines of cliff; a land of encanyoned valleys whose walls descend 

by steps and ledges; of long, even sky line, the sweep of which is 

broken here and there by one or more isolated mountain masses of 

volcanic rock or by fantastic buttes and mesas that suggest ruined 

masonry. The higher portions 'of the region are comparatively 

moist and are heavily wooded with forests of spruce and pine; the 

middle altitudes are semiarid arid are covered with a scattered 

growth of juniper and pinyon; the lower levels are deserts, the sur-
16

faces of which either take the color of the underlying rock, or are 

gray with the desert brush. The scenery is, above all, orderly and 

symmetrical, for through every land form except the volcanoes 

run continuous parallel layers of level strata, and each cliff shows 

in all its parts similar vertical profiles.

In few other regions are the topography and scenery so closely 

related to the character and structure of the underlying rocks. 

Every platform is the summit of a resistant stratum; each cliff is 

its edge. The gentler slopes are on the edges of weaker strata.

Nowhere else are geologic relations revealed on so vast a scale 

and yet so clearly, for any departure from the horizontal structure 

appears with startling distinctness. A great fault traversing the 

plateau may be expressed by a line of cliffs many miles in length; 

the slightest break in the beds in the walls of a canyon at once 

catches the eye; and the sweep of a great fold or monocline may 

dominate an entire landscape. The walls of the deep canyons cut 

by the larger streams display great natural geologic vertical and 

cross sections; the mountains are masses of volcanic rock which 

either have been poured out upon the surface of the plateau or 

have cut into and domed the strata. The arid climate tends to 

keep rock surfaces bare of soil and cliff profiles sharp and fresh, 

and the clear air extends the range of vision over vast distances. 

The prevailing aridity of the region and the impassability of the 

steep-walled canyons that traverse it have kept large areas untouched 

by civilization to the present day. In the past its lonely canyons 

were the home of the cliff dwellers. To-day it is the refuge of tribes 

of Indians who still retain their primitive customs. The natural 

conditions thus described make the Colorado Plateau the most 

fascinating region in the world for geologic study.

The southwestern part of the Plateau province, marked off by

certain structural and topographic features, is the Grand Canyon 

district. This district has long been known through the writings 

of Newberry, Ives, Gilbert, Powell, and Dutton; and the work of 

these geologic explorers, combined with the later studies of Walcott, 

Davis, Robinson, Huntington, and Johnson, has given rise to a 

voluminous literature and has made it a classic region for geologists. 

The Grand Canyon district lies in northwestern Arizona and coincides with a local uplif t, or structural swell, in the Colorado Plateau. 

Its area is about 16,000 square miles and over practically all of this 

nearly level expanse one geologic formation, the Kaibab limestone, 

is the surface rock. This great platform is abruptly elevated above 

the Basin region that lies west of it by a sharp break (or fault) in the 

earth's crust, on the east side of which the strata stand at an elevation several thousand feet higher than the same strata on the ^west 

side- Along the eastern border of the district a sharp downward
BULLETIN 549 PLATE 111

'." ," : . A. GRANITE GORGE NEAR CABLE CROSSING. rV-~

Showing open gorge due to the presence of weak and easily eroded strata of the Unkar group. Cable crossing 

is at the narrowest point on the river, in the center of the view.

B. GRANITE GORGE ABOVE CABLE CROSSING.

Showing somber, V-shaped profile of the gorge where the massive, resistant Vishnu schist forms its walls and no

weak stratified rock is present.

VIEWS UP COLORADO RIVER NEAR CABLE CROSSING.
PHYSIOGRAPHY OF THE DISTRICT. 17

bend, known as a monocline, carries the beds to a lower level, where 

they resume their nearly horizontal attitude and continue eastward 

beneath the higher strata of the Colorado Plateau. The upturned 

edges of these higher strata face the district as Echo Cliffs. On the 

north the district is walled in by another line of cliffs and terraces, 

running east and west along the southern border of Utah. These 

have been carved by erosion out of the higher strata of the Colorado 

Plateau and rise in huge steps northward to elevations of 11,000 feet 

or more. The southern border of the district is marked by an abrupt 

descent to loVer country along a series of cliffs carved from the 

plateau strata.

The northern portion of the Grand Canyon district is divided into 

five minor platforms or plateau blocks by great lines of fracture or 

flexure, which trend north and south and are roughly parallel. The 

fractures are represented in the topography by cliffs and the flexures 

by steep slopes, so that the blocked plateaus are sharply separated 

from one another. The westernmost plateau, the Shivwits, is the 

lowest; its surface lies about 6,000 feet above the sea. Next in order 

toward the east are the Uinkaret, Kanab, and Kaibab plateaus, each 

elevated about 1,000 feet above its western neighbor by a fault. 

Most of the Kaibab Plateau lies above an altitude of 8,500 feet. East 

of the Kaibab is the fifth plateau, the Marble platform, which has 

been dropped 2,500 feet below the Kaibab by an eastward-dipping 

flexure.

Colorado River crosses the plateau province from northeast to 

southwest. It has carved a series of canyons whose total length 

exceeds 500 miles. All these canyons are clear-cut deep gashes in 

nearly level platforms, and their steplike walls descend abruptly by 

alternations of bold cliffs and narrow ledges. The river at the bottom (PI. Ill) carries the drainage from the whole western front of 

the Rocky Mountains in Colorado and southwestern Wyoming. It 

is swift and turbulent and in many places flows between sheer walls. 

Because of the general impassabiHty and the inhospitable character 

of the bordering deserts, these canyons form a barrier to human 

travel more effective than the Rocky Mountains. The Colorado is 

unbridged for 700 miles, a distance about equal to that directly 

between New York and Chicago.

In the high blocked plateaus of the Grand Canyon district the canyons reach their culmination in size and grandeur. The pathway of 

the river across these plateaus is the most remarkable valley in the 

world. The section that traverses the Marble platform is known as 

the Marble Canyon; it is 60 miles in length. The part cut through 

the Kaibab, Kanab, Uinkaret, and Shivwits plateaus is the Grand 

Canyon. The Grand Canyon is about 220 miles long and averages 

a mile in depth and about 10 miles in width, from rim to rim. The

29745° Bull. 549 14 2
18 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

Kaibab division is 50 miles in length, the Kanab 50 miles, the 

Uinkaret 25 miles, and the Shivwits 75 miles.

The lines of displacement that bound the plateau blocks die out 

in the area south of the Grand Canyon in the part of the Grand 

Canyon- district that is known as the San Francisco Plateau. The 

high part of the San Francisco Plateau lying just south of the* Grand 

Canyon,is called the Coconino Plateau.

The south end of the Kaibab Plateau stands 2,000 feet above the 

Kanab Plateau, which lies southwest of it, and the San Francisco 

Plateau, which lies south of it, but it has attained this higher elevation by a gentle tilting of the earth's crust instead of by a fault 

or monocline. The strata around the south end of Kaibab Plateau 

descend very gently toward the south and southwest until they 

reach the level of the Kanab and San Francisco plateaus.

The Kaibab division of the Grand Canyon is cut through the 

highest land and is the deepest part of the canyon. Here the walls 

are intricately carved by erosion, and here the visitor finds that 

wealth of fantastic architectural detail for which the canyon is noted. 

This division is a relatively wide valley, which presents to the observer not a deep and gloomy gorge, but a vast, bright, open expanse. 

In the depths of the canyon near the base of the series of horizontal 

Paleozoic rocks there is a wide, shelf, known as the Tonto platform, 

or "lower plateau" (PL V). A trail known as the Tonto trail runs 

along the Tonto platform throughout the Kaibab division. The 

river has cut through this platform below the base of the Paleozoic 

rocks into the Archean rocks, on which it flows in a V-shaped gorge 

whose walls descend by a steep, unbroken slope that contrasts strikingly with the steplike profile of the walls in the Paleozoic rocks 

above. This gorge in the bottom of the canyon is known as the 

Granite Gorge. (See Pis. Ill, V, and VIII, B, p. 28.)

The Kaibab division does not lie in the highest part of the Kaibab 

Plateau; it crosses, rather, the higher part of the inclined plane that 

bounds the Kaibab uplift on the south, in a direction nearly at right 

angles to the dip of the strata. Consequently the position of the 

canyon with respect to the bordering lands in this division is a peculiar one for a river valley. The Kaibab Plateau, which lies north of 

the canyon, slopes gradually toward the rim, and the Coconino 

Plateau, which lies south of the canyon, slopes gradually away from 

the rim, so that the canyon is a huge trench dug along a hillside.

The three divisions of the canyon west of the Kaibab are cut 

through lower plateaus and are not so deep as the Kaibab division. 

The scenery is no less imposing but is very different. In the upper 

part of the wall there is a platform, several miles wide, named by 

Dutton the Esplanade (PL VI), in which the main canyon is cut in a 

sharp gorge that has nearly vertical walls. This inner gorge is far
U. S. GEOLOGICAL SURVEY BULLETIN 549 PLATE IV

..-. ,." . ' A. PANORAMIC VIEW OF POWELL PLATEAU ACROSS MUAV SADDLE FROM THE KA1BAB. ' _ ,.

Z>, Dutton Point; NW, Northwest corner of Powell Plateau; M, Muav Canyon; MS, Muav Saddle; T, Tapeats Amphitheater. The effect of the West Kaibab fault maybe seen in Muav Canyon in the flexed beds of 

sandstone of the Supai formation and at the Muav Saddle, where the beds of Kaibab limestone that form the surface of Powell Plateau plunge downward into the saddle directly toward the observer.

Ji. PANORAMIC VIEW OF UNKAR WEDGE FROM TONTO PLATFORM, ON SOUTH SIDE OF COLORADO RIVER.

C, Colorado River.
PHYSIOGRAPHY OF THE DISTRICT- 19

'narrower in proportion to its depth than any part of the Kaibab 

division and corresponds more nearly to the popular idea of a canyon. 

Its walls are not greatly carved by erosion, and its scenic effect is 

somber and grand rather than bright and fantastic. The Kanab 

division shows best this somber type of scenery. In the Uinkaret 

division floods of lava have been poured over the walls from a great 

volcanic center on the Uinkaret Plateau and have reached the river. 

The Shivwits is the only division west of the Kaibab in which the 

river has cut beneath the base of the Paleozoic rocks.

The surface of the southern or Coconino Plateau slopes to the southwest, away from the canyon rim, at the rate of about 100 feet to the 

mile. The drainage of the plateau surface is carried in a series of 

shallow, open-floored valleys which have gently sloping sides, and 

contain no living streams. These valleys trend southwestward from 

the canyon rim as a consequence of the general slope of the plateau 

surface in that direction and drain into the broad, shallow synclinal 

basin occupied by Cataract Canyon. By the slow wearing back of 

its steep southern wall the Grand Canyon has encroached on the 

heads of many of these stream ways, so that their truncated valleys 

appear along the rim as shallow notches. So general is this phenomenon that the stranger who loses his way on the Coconino Plateau 

has only to keep in mind the fact that if he will follow any main valley 

far enough headward he will come out upon the rim of the Grand 

Canyon.

The surface of the northern or Kaibab Plateau likewise slopes 

gently to the southwest and is covered with a similar system of south-- 

westward-trending valleys. The drainage system of the Kaibab, 

however, runs directly into the Grand Canyon instead of away from 

it. Neither plateau bears a living stream.

Powell Plateau (PI. IV, A) may be regarded as a disjoined part of 

the Kaibab Plateau. It formed on beds that lie at the same horizon 

in the Kaibab limestone as the Kaibab Plateau but slopes more 

steeply to the southwest than the Kaibab or the Coconino, its grade 

being about 200 feet to the mile. Towell Plateau is really a great 

butte, surrounded on three sides by mile-deep canyons and isolated 

from the Kaibab Plateau by erosion in the line of the West Kaibab 

fault. A narrow isthmus, notched 800 feet below the surface of the 

plateaus in. the line of the fault, connects Powell Plateau with the 

Kaibab. This isthmus or gap, which is known as the Muav Saddle, 

forms a sharp divide that separates Muav Canyon from a lateral 

gorge of Tapeats Amphitheater on the north. The trail up the 

northern wall of the Grand Canyon divides in Muav Saddle, one 

branch leading to the Powell Plateau and another to the Kaibab 

Plateau.
20 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

In many places along the north wall of the Grand Canyon the deep 

side gorges of the great amphitheaters have encroached upon the valley system of the Kaibab Plateau in the same, way in which the south 

wall of the Grand Canyon has beheaded the stream ways of the 

Coconino Plateau. Along the eastern edge of Powell Plateau several 

of these shallow valleys are truncated headward by the southern wall 

of Muav Canyon and the same phenomenon may be noted at other 

places, as along the eastern edge of the Rainbow Plateau, a promontory of the Kaibab Plateau. These beheaded valleys of the Rainbow 

Plateau illustrate a phenomenon which is described by Dutton 1 as 

characteristic of other parts of the Kaibab wall east of the Shinumo 

quadrangle: "We of ten. find an old ravine suddenly cut off on the 

brink of the abyss, and the continuation of the same ravine upon the 

other side of the amphitheater." In some places where the capture of a ravine is imminent, but not yet accomplished, the ravine 

will run along for a considerable distance parallel to the rim of the 

Grand Canyon and so near to it that one may stand in the bottom of 

the ravine and hurl a stone over the narrow divide that separates it 

from the great gorge. Examples are Dutton Canyon, on Powell 

Plateau; Saffron Valley, on the Kaibab; and the long ravine that lies 

east of Crescent Ridge and runs for 3 miles parallel to the rim of 

Shinumo Amphitheater.

The Shinumo quadrangle is on the southwest border of the Kaibab 

uplift and shows the transition from the Kaibab to the Kanab division of the Grand Canyon. . In all the region north of the quadrangle 

the western boundary of the Kaibab Plateau is the West Kaibab 

fault, which throws the strata downward to the west and forms an 

abrupt topographic break. This great displacement runs into the 

Shinumo quadrangle, but it has here become so changed in character 

that it affects the strata only locally; in the greater part of its course 

across the quadrangle its usual westward throw is reversed, the strata 

being dropped on its east side. West of the Kaibab Plateau the drop 

is accomplished, not by a fault but by a warping of the strata. 

Throughout the quadrangle the Paleozoic strata dip southwestward 

away from the highest part of the Kaibab uplift, at a rate varying 

from 100 to 200 feet to the mile. This dip is well shown by the corresponding southwestward slope of the plateau surfaces, all of which 

accord with the rock structure. A zone of maximum warping, about 

5 miles in width, runs diagonally across the quadrangle from northwest to southeast, carrying the strata downward to the southwest at 

the rate.of 200 feet to the mile. Elsewhere in the quadrangle the 

dip is about 100 feet to the mile. This zone of maximum warping is 

shown by the. surf ace of Powell Plateau,, which drops 1,000 feet from 

Dutton Point at its eastern end to Ives Point at its western end.

i Dutton, C. E., op. cit, p. 170.
U. S. GEOLOGICAL SURVEY 

TONTO PLATFORM: VIEW EASTWARD UP KAIBAB DIVISION OF GRAND CANYON FROM LEVEL 

PS, End of Point Sublime; MA, Monadnock Amphitheater; V, Vishnu schist; U, Unkar group; T. Tapeats sands

5ff, sandstone of Supai formation; Ssh, shale of Supai formation; C, Coconino sa
U. S. GEOLOGICAL SURVEY

THE ESPLANADE; VIEW NORTHWESTWARD THROUGH THE GRAND C

Powell Plateau: JO, Inner Gorge of Colorado River; Ss, sandstone of Supai formation; Ss!l, shale of Supai formation; (,'
TOPOGBAPHY OF SHINUMO QUADEANGLE. 21

Colorado River begins to flow across the zone of maximum warping 

at the mouth of Shinumo Creek. This point therefore marks the west 

end of the Kaibab division of the canyon.

TOPOGRAPHY OF THE SHINUMO QUADRANGLE.

In the Shinumo quadrangle the surfaces of the plateaus through 

which the Grand Canyon is trenched are developed on the highest 

Paleozoic formation occurring in the canyon wall the Kaibab limestone the Mesozoic and Tertiary formations having been eroded back 

to the terraces'of southern Utah.

Within the Shinumo quadrangle the profile of the wall of the Grand 

Canyon changes from that which is characteristic of the Kaibab division to that which is characteristic of the Kanab. The most accessible outlook from which to view this scenic change is the end of 

Havasupai Point (PL VII, B), the longest promontory that runs out

from the southern wall of the Grand Canyon. To the east is a vista 

of 40 miles through the characteristic scenery of the Kaibab division 

(See PL V.) The walls are greatly dissected, particularly on the 

northern side; great amphitheaters, filled with fantastic buttes and 

temples and trenched with innumerable side gorges run far back into 

the walls. The profile of the wall is especially distinctive; the edges 

of the Paleozoic strata descend abruptly through a series of cliffs, 

steep slopes, and narrow ledges to the Tonto platform, 3,000 feet 

below the rim of the canyon, and within the Tonto platform is the 

Granite Gorge.

On turning westward the spectator beholds a striking change. 

(See PI. VI.) Directly below him, about 1,000 feet beneath the 

rim, a great flat-topped spur of red sandstone of the Supai formation 

runs far out into the canyon. Farther west more and more of these 

spurs appear, each capped with a similar platform, which everywhere 

lies upon the same layers of red sandstone. Gradually the platform 

widens and becomes a broad expanse of red rock, which is covered 

with patches of scanty soil and dotted with scrubby trees juniper 

and pin6n. The buttes and temples disappear; the walls are much 

less dissected by side gorges and extend along the canyon's sides in 

solemn palisades. The profile of the canyon wall is simpler, consisting of a wide outer valley whose floor is the great red platform, or 

Esplanade, and a deep inner canyon. The wall of the inner canyon 

is stupendous, the edges of the Tonto, Redwall, and Supai strata 

appearing almost as a single cliff 3,000 feet in height. The long red 

spurs of the Esplanade platform (PI. VII, A) form a strange and 

impressive feature of the landscape and attract the attention as 

strongly as do the buttes and temples of the Kaibab division. Many 

of them have been named: Drummond Plateau, Grand Scenic 

Divide, Huxley Terrace, and Spencer Terrace, on the south side of
22

the river; Masonic Temple, Marcos, De Vaca, Tobar, Alarcon, and 

Garces terraces, on the north side.

The profile of the canyon wall in the central part of the Shinumo 

quadrangle is a combination of two types of topography, for both the 

Esplanade and Tonto platforms are present, separated vertically by 

over 2,000 feet. This feature is well seen in the wall of Shinumo 

Amphitheater, directly opposite Havasupai Point.

The canyon wall is more deeply dissected in the Kaibab division 

than in the Kanab division, the transition taking place in the Shinumo 

quadrangle. The dissection not only diminishes from east to west 

but also differs strikingly in amount in the opposite walls of the 

canyon in the two divisions. In the Kanab division, beyond the 

western border of the Shinumo quadrangle, the river flows in the very 

center x>f the canyon and the northern wall is no more dissected than 

the southern wall, but in the Kaibab division the north rim lies 

three times as far back from the river as the south rim; the great 

amphitheaters and their limiting promontories, which extend far into 

the canyon, the buttes and temples, and the deep lateral gorges all 

belong to the north side of the canyon. The south wall presents a 

simpler aspect; few of the side gorges extend back into the rim of the 

canyon, there are few buttes and outliers, and the great amphitheaters are wholly lacking. When compared with that of the fantastic topography of the north side, the scenic effect of the precipitous 

south wall is somber.

The variations in the amount of dissection of the canyon wall 

depend upon climatic and structural conditions, whereas the change 

from east to west in the profile of the wall is explained by certain 

variations in the thickness and character of the Paleozoic strata. 

The origin of these topographic features will be discussed elsewhere

in this report after the conditions Upon which they depend have been 

described.

The Colorado maintains its general northwesterly course through 

the Kaibab division into the Shinumo quadrangle as far as the mouth 

of Shinumo Creek, where it bends westward and flows across the 

zone of warping that marks the boundary of the Kaibab uplift. 

Swinging in two great loops, first to the south and then to the west, 

it doubles back again and flows northeastward around Powell Plateau, 

passing thence beyond the northern boundary of the quadrangle. 

Several miles beyond the northern boundary of the quadrangle 

Tapeats Creek enters the river from the east, draining a great amphitheater of the same name which lies north of Powell Plateau. At the 

mouth of Tapeats Creek the river bends to the southwest and maintains a southwestward course for 40 miles through the Kanab Plateau, 

nearly the entire length of the Kanab division.
U. S. GEOLOGICAL SURVEY BULLETIN 549 PLATE VII

A. VIEW NORTHWARD FROM BASS CAMP, SHOWING MOUNT HUETHAWALI, A BUTTE ON THE 

ESPLANADE (AT THE LEFT) AND HUXLEY TERRACE, A DISSECTED SPUR OF THE ESPLANADE.

B. VIEW EASTWARD FROM THE SUMMIT OF MOUNT HUETHAWALI, SHOWING FOSSIL MOUNTAIN 

AND HAVASUPAI POINT.

The cirque in the foreground is the head of Bass Canyon, down which Bass trail descends to Colorado River. 

The peaklike promontory in the center of the view is Fossil Mountain, which is gradually being isolated from 

the Coconino Plateau by erosion and will in time become a butte or outlier like Mount Huethawali. The same 

fate, though it is more remote, awaits Havasupai Point, the high promontory at the left of Fossil Mountain.
TOPOGKAPHY OF SHINUMO QUADRANGLE. 23

The general course of the great gorge itself is not affected by the 

smaller bends of the river and may be considered simply as northwesterly through the Kaibab division and.beyond, to the mouth of 

Tapeats Creek, and thence southwesterly through the Kanab division.

The Granite Gorge, which forms the interior of the canyon through 

the Kaibab division, is not continuous in the Shinumo quadrangle 

west of the mouth of Garnet Canyon, because of changes in the course 

of Colorado River with reference to the rock structure. Thus the 

bend westward and southward at the mouth of the Shinumo causes 

the river to flow in the direction of the dip of the Paleozoic strata, and 

as the dip is greater than the grade of the stream the river bed is 

gradually carried out of the Archean rocks into the basal sandstone 

of the Tonto group, which terminates the Granite Gorge a short distance below the mouth of Garnet Canyon. Through Stephen Aisle 

and Conquistador Aisle the bed of the river is in the Paleozoic strata. 

Beyond the end of Alarcon Terrace the river bends and again flows 

northeastward, taking .a course that soon carries the bed back into 

the Archean rocks, so that the Granite Gorge reappears in this part 

of the canyon, continuing until the river finally turns southwestward, 

at the mouth of Tapeats Creek. This section is called the Lower 

Granite Gorge. In all the Kanab division west of the mouth of 

Tapeats Creek the river flows in Paleozoic strata.

The actual length of the course of the Colorado across the quadrangle, measured along the surface of the stream, is 31£ miles. The 

mean elevation of the surface of the river where it enters the quadrangle on the east is 2,285 feet; where it leaves the quadrangle on the 

north, 2,035 feet. The total descent of the river within the quadrangle is therefore 250 feet, and the average declivity is 7.9 feet to the 

mile. The declivity, however, is not uniform. East of the mouth 

. of Garnet Canyon it is 10 feet to the mile; west of this point it is 6.2 

feet to the mile. The difference is explained by the fact that above 

Garnet Canyon the river flows upon resistant Archean rocks, whereas 

below Garnet Canyon it flows chiefly upon less resistant sedimentary 

rocks. At the Cable Crossing the width of the river is 300 feet, its 

depth is 50 feet, and its average rise at times of high water is 40 feet.

The only living tributary of the Colorado in the quadrangle is 

Shinumo Creek (PI. XIV, A, p. 55), the master stream that drains 

Shinumo Amphitheater, of the north wall. It is of the same size 

and kind as Bright Angel Creek, 20 miles to the east, and its clear 

water presents a striking contrast to the muddy torrent of the Colorado. The length of Shinumo Creek from its source at Big Spring, 

on the rim of- the Kaibab, to its confluence with the Colorado is 12 

miles, and in this distance it falls 5,400 feet, its average declivity 

being 450 feet to the mile.
24 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

The topography of Shinumo Amphitheater, besides presenting an 

equal development of both the Esplanade and Tonto platforms, is 

remarkable in another way. In the other great amphitheaters of 

the Kaibab division the. master gorges trend southwestward, the 

tributary gorges trend in the same general direction, and lateral 

gorges perpendicular to the main axes of the amphitheaters are of 

minor development. In Shinumo Amphitheater the lateral gorges 

have become dominant features, so that the main axis of the amphitheater trends northwestward, lying at. right angles to the course of 

the master stream and parallel to the course of the Colorado. The 

greatest lateral gorge extends entirely across Shinumo Amphitheater 

from Point Sublime on the southeast to the Muav Saddle on the northwest. Only a mile of this lateral gorge is occupied by the master 

stream of Shinumo Amphitheater; the remainder is occupied by two 

small intermittent streams. The western part of the gorge, which 

extends from the Muav Saddle'to Shinumo Creek, is drained by Muav 

Creek and White Creek and is called Muav Canyon; the eastern part, 

extending from Shinumo Creek to Point Sublime, is drained by Flint 

Creek and has no local name. The entire lateral gorge will be referred to as the "Muav-Flint Canyon." This remarkable rectilinear 

depression is situated upon the line of the West Kaibab fault. Two 

smaller lateral gorges cross the heart of the amphitheater parallel 

to .the Muav-Flint Canyon; these are situated upon minor lilies of 

fracture.

The course of Shinumo Creek through the canyons of Shinumo 

Amphitheater everywhere lies in one of two main lines which are 

perpendicular to each other. The course in the northeast-southwest 

line, which carries the stream onward toward its junction with the 

Colorado, is consequent upon the dip of the Paleozoic rocks; the 

course in the northwest-southeast line, which holds the stream in 

the lateral gorges, is controlled by the West Kaibab faults and by 

fracture lines. (See pp. 75-80.)

The highest point in the Shinumo quadrangle is the surface of the 

Kaibab Plateau in the northeast corner of the quadrangle, where the 

elevation is 8,450 feet; the lowest point is the bed of the Colorado 

River, at the place where it flows beyond the northern boundary of 

the quadrangle, where the elevation is about 2,000 feet. As the 

surfaces of the plateaus and of the platforms within the canyon are 

everywhere accordant with the rock structure, the altitudes of these 

surfaces diminish progressively toward the southwest in all parts of 

the quadrangle in conformity with the dip of the Paleozoic rocks.

For example, the elevation of the Kaibab Plateau at the head of 

Shinumo Amphitheater is 8,000 feet; but at Point Sublime, 5 miles 

south, it is only 7,500 feet. Farther southwest, on the opposite side 

of the Grand Canyon, at Havasupai Point, the Coconino Plateau
CLIMATE. 25

stands at 6,750 feet; 10 miles farther southwest it stands at 5,900 

feet. At the head of.Shinumo Amphitheater the elevation of the 

Esplanade, a platform within the canyon, is 6,750 feet; at Holy 

Grail Temple, in the center of the amphitheater, it is 6,100 feet; 

farther southwest, across the river, at Darwin Plateau, it is 5,400 

feet, and in Aztec Amphitheater it is 5,000 feet. The Tonto platform 

stands at.3,750 feet under Dox Castle; directly opposite, on the south 

side of the river under Tyndall Dome, its altitude is 3,300 feet.

The wall of the Grand Canyon drops most abruptly at Dutton 

Point (PI. XVIII, p. 86), where it descends 5,355 feet from Powell 

Plateau to the river in 3 miles; and at Havasupai Point, where it 

descends 4,500 feet in a mile and a half, presenting.the most precipitous descent in the Grand Canyon.

The greatest width of the Grand Canyon in the quadrangle is in 

the stretch from the head of Aztec Amphitheater to the head of 

Shinumo Amphitheater, a distance of 16 miles. The narrowest point 

is between Apache Point and Ives Point, 4f miles. Even at this 

narrowest point the width is over five times the depth.

CLIMATE.

The climatic differences within the Shinumo quadrangle are remarkable. The range in climate between the Kaibab Plateau and the 

bottom of the canyon is as great as that between the mountains of 

Colorado and the Mojave Desert. The winters on the Kaibab 

Plateau are extremely severe; from November to April the snow lies 

deep in the woods, in places accumulating to a depth of 10 feet. 

Even in midsummer the nights are chilly and the days are delightfully cool. Within the canyon, however, snow rarely falls below the 

'level of the Esplanade, and on the Tonto platform a fall of snow is 

practically unknown. In the depths of the canyon the winters are 

mild and freezing temperatures are rare. From April.to October, 

whenever the days are cloudless, the entire interior of the canyon 

concentrates the solar heat and becomes a veritable oven. All day 

the bare rocks absorb the heat of the sun, becoming so hot as to burn 

the hand; by afternoon the wind is like a furnace blast, and the 

rocks continue to radiate their heat long after dark. The summer 

heat is tempered greatly on the cloudy days during the period of 

rains. The climate of the southern or Coconino Plateau at Bass 

Camp is characterized by more open winters as well as by warmer 

summers than the Kaibab. Snow rarely accumulates on the surface 

to a great depth and as a rule vanishes entirely within three days 

after a storm; and in summer many days are unpleasantly hot.

The climate of the Kaibab Plateau is decidedly moist, the precipitation being probably twice as great as that received upon the 

Coconino Plateau, across the canyon. This difference is due chiefly 

to the greater altitude of the Kaibab Plateau. In winter the precipi-
26 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT,. ARIZ.

tation on the Kaibab takes the form of snow; in summer it comes in 

thundershowers which occur during the afternoon and evening. 

Looking across the canyon from Bass Camp on the south rim on 

almost any summer evening one may see storm after storm sweeping 

over the surface of the Kaibab Plateau, most of them accompanied 

by violent electrical display, while the sky overhead and to the west 

over the Kanab Desert remains as clear as crystal. Another factor 

that contributes to the greater rainfall of the Kaibab seems to be 

the presence of the Grand Canyon itself. Every general winter storm 

that visits both sides of the canyon alike is followed on the south rim 

by a day of clearing; but the clouds that rise out of the canyon after 

the storm sweep back over the north wall and reprecipitate on the 

surface of the Kaibab. Few of these secondary storms return over 

the south run. The climate of the Coconino Plateau in the quadrangle 

is semiarid; in spring and early summer no rain may fall for a 

month. The precipitation is greatest in winter and in the months of 

July, August, and September. Much of the rain that falls within the 

canyon evaporates before it reaches its lower part, which is therefore 

more arid than the Coconino Plateau.

Powell Plateau (PI. IV, A, p. 18), whose higher eastern portion 

stands at the same altitude as the Kaibab rim and whose lower western 

portion stands at the altitude of the Coconino, has a climate that is 

intermediate between those of these two divisions. Its situation in 

the canyon, where it forms an island, serves to moderate the cold 

in winter, for the warm ah- which rises out of the deep canyons that 

surround it acts as a radiator; snow does not accumulate so deep on 

its eastern end as on the Kaibab, and on its western end does not 

accumulate at all. It is a resort in whiter for game and cattle that 

are driven out of the Kaibab by snow. Its higher eastern end 

receives abundant rainfall, whereas its lower western end is semiarid. Owing to its exposed position it is at all times of the year 

subject to violent gales of wind.

The variation in the amount of rainfall with difference in altitude is 

the chief cause of the variations in the degree of dissection of the canyon walls. The .plateaus on both sides of the canyon in the Kaibab 

division are much higher than those in the Kanab division, where the 

rainfall is therefore much greater and the forces of erosion more active, 

and the walls are consequently far more dissected in the Kaibab than 

in the Kanab division. The much greater dissection of the northern 

than of the southern wall of the canyon in the Kaibab division may 

be similarly explained, the higher altitude of the northern wall giving 

it much greater rainfall than the southern wall.

In this dissection the rock structure is also important. Since the 

surface of the Kaibab Plateau slopes toward the rim of the canyon, all 

the surface water within a radius of many miles finds its way into the 

canyon over the northern wall. Even the water that sinks under-
VEGETATION. 27

ground which far exceeds the surface water in quantity because of 

the system of caves, sink holes, and underground drainage channels 

with which the Kaibab Mmestone is honeycombed eventually finds 

its way southwestward .along the dip of the strata and reappears as 

springs in the northern wall of the Grand Canyon, feeding the tributary streams of the Colorado and increasing the activity of the forces 

of erosion on that side of. the river.

The waters of the semiarid Coconino Plateau, on the contrary, both 

surface and underground, are carried directly away from the Grand 

Canyon by the slope of the surface and by the southwesterly dip of 

the strata; consequently the forces of erosion are less active in the 

southern wall of the canyon.

VEGETATION.

The variation in the flora in the Shinumo quadrangle is as great as 

that in the climate. The surface of the Kaibab Plateau is covered 

with a magnificent open forest of yellow pine; the trees grow large 

and far apart and the ground is free from undergrowth, so that the 

plateau has the aspect of a great park. Englemann spruce grows on 

the north slopes of the washes, and cottonwood, aspen, and scrub oak 

in their bottoms. A minor flora of flowering plants exceedingly rich 

in species covers the floor of the forest. The flora of the Coconino 

Plateau in the quadrangle differs completely from that of the Kaibab. 

The surface is covered with a dwarf forest of gnarled juniper, pifi6n, 

and "mountain mahogany" (Cercocarpus ledifolius); the little trees 

grow wide apart and the open stretches are covered with sagebrush 

and "Mormon tea," with occasional cactus, "mescal," and other 

plants of the century family.

This difference between the floras of the two plateaus is due to differences in precipitation and temperature, which vary directly with the 

altitude, and for this reason the floras of the plateaus furnish an almost 

unfailing index of their elevation, a fact that is strikingly shown on the 

southwestward-sloping surface of Powell Plateau. The whole eastern 

half of this plateau lies at an elevation of 7,000 to 7,500 feet and is covered with the open pine forest characteristic of the Kaibab, but at an 

elevation of about 7,000 feet the flora changes, passing into the dwarf 

forest of juniper and pin6n that characterizes .the southern plateau 

across the canyon.

In the region farther east, beyond the border of the Shinumo 

quadrangle, the Coconuio Plateau attains a much greater altitude 

and the flora there becomes more like that of the Kaibab Plateau.

Within the canyon itself the variation in the flora is just as great, 

and is again an index of the elevation.

The flora of the Esplanade platform, a thousand feet below the 

south run, consists of stunted juniper and pin6n with Coleogyne 

ramosissima (locally known as "greasewood") as the predominant
28 SHINUMO QUADRANGLE; GRAND CANYON" DISTRICT, ARIZ.

bush in place of the sagebrush of the Coconino Plateau. Cacti and 

plants of the century family are more abundant than on the plateau, 

but less abundant and smaller than in the bottom of the canyon, a condition due to the fact that the Esplanade level is within reach of the 

winter snows and frosts. On the north side of the canyon, where 

the elevation of the Esplanade is much greater than on the south 

side, mountain mahogany, manzanita, live oak, and other dwarf 

trees appear in the flora, making a thick chaparral that cloaks all 

the slopes with a dense mantle of green.

The flora of the Tonto platform, 3,000 feet below the south rim, 

and of all the interior of the canyon below the^Red Wall is the flora 

of a hot and arid desert. The dominant plants are Coleogyne ramosissima, "Mormon tea," and other small gray perennial shrubs of 

various species, each plant standing apart by itself in the formal 

manner characteristic of desert vegetation. Cacti, aloes or agaves, 

and yuccas here attain their densest growth and greatest size, the. 

cacti being particularly rich in species. Every plant in the flora is 

either prickly or aromatic, leaf surfaces are reduced to a minhnum, 

devices for storing water attain the greatest perfection, and the 

dominant color is a dull gray. The somber colors and the reduction 

of leaf surfaces are likely to deceive the observer both in regard to 

the richness of the flora in species and the abundance of plant life, 

which is far greater than one would suspect. Small trees of Acacia 

greggi, or " cat claw," and here and there a few of Cercis occidentalis, or 

"red bud," grow in the beds of washes that contain living or intermittent streams.

The vegetation in the bottoms of the canyons of the north side of 

Shinumo Amphitheater that contain living streams is beautiful 

beyond description and affords a refreshing contrast to the desert 

flora of the Tonto platform. Tall cottonwoods grow in the lower 

canyons, maiden-hair ferns hang on the walls in shady places, thickets 

of willow border the streams, and grass grows on the banks where 

there is soil. Higher up in the canyons, oaks, maples, and other 

deciduous trees grow, and in some places there are beds of tall 

rushes. The most characteristic bush of these upper north-side 

canyons is the manzanita, which apparently does not grow on the 

south side of the: Grand Canyon in the quadrangle.

INDIAN RUINS.

Evidences of former human occupation are found everywhere in 

the Grand Canyon region and the observant traveler will see them in 

many places in the Shinumo quadrangle, but as few of these ruins 

are well preserved he must not expect to see anything so spectacular 

as the wonderful ruins of the Mesa Verde in southwestern Colorado 

or the Canyon De Chelly in northeastern Arizona. Ruins are most 

numerous hi the canyons of Shinumo Amphitheater and consist of
U. S. GEOLOGICAL SURVEY

EAST WALL OF CANYON OF SH1NUMO CREEK 

NEAR SHINUMO GARDEN.

li. VIEW EAbTWARD UP COLORADO 
GEOLOGY. 29

the fallen and crumbled walls of rude stone houses! Some of these 

ruins are perched high under, overhanging ledges which still show 

the blackening of smoke; others lie among huge blocks of debris 

that have fallen from the cliffs; still others stand in the open, away 

from any natural shelter. The only well-preserved structures are 

tiny storehouses, built high up along the crevices in the canyon 

walls. Numerous relics have been found by digging in or around 

the ruins, among them mealing stones, mortars, pestles, corncobs, 

ropes of yucca fiber, arrowheads, and various stone implements. 

Fragments of pottery are littered about and remains of irrigation 

ditches are still visible in Shinumo Canyon, where gardens were 

cultivated. The walls of the ruins on the plateaus have crumbled 

to almost shapeless heaps of stone, and in some of those on Powell 

Plateau tall pine trees are growing. The only ruin that is at all 

well preserved is at the head of Bass trail, on the Coconino Plateau. 

It is supposed that most of these ruins are the work of the cliff 

dwellers, the ancestors of the present Pueblo Indians of the Southwest. 

The trails into the Grand Canyon on both sides of the river follow 

old Indian trails. All the way down Bass trail and all the way up 

the trails through Shinumo and Muav canyons the traveler will see 

at intervals the blackened ruins of circular pits where the Indians 

have roasted the "mescal," a species of agave that grows everywhere 

in the canyon. These mescal pits are found in every canyon on the 

south side of the river. The Havasupai Indians, who dwell inCataract 

Canyon, 25 miles southwest of Bass Camp, still make occasional 

use of a trail that descends to the Esplanade at Apache Point.

GEOLOGY.

AGE AND CHARACTER OF THE ROCKS,

Four great systems of rock are exposed in the walls of the Grand 

Canyon in the Shinumo quadrangle. (See PI. IX.) These systems 

represent three of the earliest eons of geologic time, the Archean and 

Algonkian periods and the Paleozoic era, the last being represented 

by the Cambrian and Carboniferous systems.

The foundation rocks of the region are crystalline schists, gneisses, 

and granitic rocks of Archean age. The schists and gneisses are 

metamorphic rocks, whose original character has been changed by 

pressure, so that they are gnarled and crumpled. These metamorphic 

rocks are known as the Vishnu schist. The granitic rocks are igneous. 

They invaded the metamorphic rocks in a molten state and are massive in aspect. The Archean rocks form the walls of the Granite 

Gorge (Pis. Ill, p. 16, and VIII, B) in the bottom of the canyon. All 

types of these Archean rocks are about equally resistant to erosion, 

and consequently they form a continuous ragged slope, which gives 

the walls of the Granite Gorge a V-shaped profile. In color they are 

.dark and somber. By these features and by their lack of stratifica-
30 SHIFUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

'. ' . \

tion they may be readily distinguished from the Algonkian and v' 

Paleozoic rocks.

The Archean rocks are separated by a profound unconformity (Pis. 

VIII, B, and XVIII, p. 86) from a series of overlying sedimentary ^ 

rocks, which is inset in the Archean rocks by block faulting and is of 

Algonkian age. The sedimentary rocks (Pis. IV, B, p. 18, and XI, p. 39) 

are as little altered as the still higher Paleozoic rocks. Unlike the 

Paleozoic rocks, however, they do not lie in their original horizontal 

position but are inclined at various angles. They comprise limestones, shales, sandstones, and intrusive masses of diabase, and are 

found only within the greater depths .of the Grand Canyon.

The Archean and Algonkian rocks are alike separated by another 

profound unconformity (PL XVIII) from the Paleozoic rocks, consisting 

of limestone, shale, and sandstone. The Paleozoic rocks (PL XVIII) 

lie in a nearly horizontal position, practically as they were laid down. 

They form the floors of all the plateaus and the greater part of the 

walls of the Grand Canyon and have determined the whole character 

and spirit of the scenery. The huge scale and the infinite multiplication of the characteristic architectural rock forms make the scenery 

of the Grand Canyon seem strange and unreal, yet it is but the supreme 

expression of all that is most characteristic in the land sculpture of 

the Plateau province. The processes of earth sculpture are going on 

here, as in other regions, under the attacks of rain, running water, 

frost, and wind. The erosion is spasmodic, because of the aridity 

of the climate, yet it is none the less effective. Slopes are kept partly 

bare because the desert plants grow'far apart, so that the concentrated 

energy of a single torrential shower wreaks more havoc here than a 

season's rainfall on the densely covered slopes of a humid region. 

But these forces are'working on rocks which, as we have seen, lie in 

nearly level beds that are continuous over great areas. Therefore 

they produce everywhere forms that are nearly identical in the vertical element, or profile, though varied and irregular in plan, as might 

be seen on looking down on.them from a balloon or examining their 

outlines on the map. As the beds, from top to bottom, show infinite 

variations in their resistance to erosion, every part of the canyon 

wall, every pinnacle and butte, is characterized by its own steplike 

alternation of cliff and terrace or slope, in delicate response to the 

varying character of the strata. In the canyon wall the cliffs are 

determined by the edges of the harder strata. Upon the plateaus 

the soft rocks have been washed away over miles of the country, 

leaving platforms whose floors are a hard' stratum. As erosion goes 

on, parts of the plateau become separated by growing canyons or 

ravines and stand as solitary outliers, capped by remnants of the 

harder rock; these are the buttes. Finally, all these land forms, 

which in a moister region would soon be dulled or obscured, are kept 

sharp and fresh by the prevailing aridity, the effect of which is to
U. 8. GEOLOGICAL SURVEY BULLETIN 549 PLATE IX

LITHOLOGIC CHARACTER FORMATION.

Dense crystalline limestone containing chert at the top. 

Fossils are present in great abundance

Buff limestone and calcareous sandstone

Kaibab.limestone, 400-600 feet

Massive buff sandstone of very fine and even grain, 

characterized by cross-bedding on a huge scale_____ Coconino sandstone, 250-360 feet

Soft red shaly sandstone and red shale,

Supai formation, 1,250-1,400 feet

 Hard fine-grained cross-bedded sandstone, with interbedded layers of red shale

*u3

Alternating layers of calcareous sandstone, thin-bedded 

Fossils are present but not well preserved

Redwall limestone, 600-700 feet

Impure thin-bedded bluish-gray .limestone which has 

acharacteristicmottled appearance imparted by numerous 

thin bands or lenses of miff or greenish shaly material

-UnconformityMuav limestone, 450-475 feet

Soft greenish micaceous sandy shale' with two thin 

layers of brown crystalline limestone locally present in the 

middle of the formation. Contains fairly abundant fossils Bright Angel shale, 25-375 feet

Brown slabby cross-bedded'.sandstone. Basal portion 

contains lenses of conglomerate, the pebbles of which are 

rounded. Rests on a moderately even surface produced 

by erosion

Tapeats sandstone, 0-285 feet 

 .Great unconformity 

Micaceous shaly sandstone; greenish gray in lower 

portion, red-brown and vermilion above. Characterized 

by ripple marks and cross-bedding. Cut by thin sills of 

intrusive diabase

Dox sandstone, 2,297 feet 

plus unknown thickness removed by pre-Cambrian erosion

Hard, compact cross-bedded sandstone and quartzite, 

usually of fine and even grain

Shinumo quartzite, 1564 feet

Argillaceous red shale, grading upward into arenaceous red shale and sandstone. Nearly all beds contain 

sun cracks and ripple marks. Cut by a thick sill of intrusive diabase, which has converted the shale into slate and 

jasper'near the contact

Hakatai shale, 580 feet

White crystalline limestone alternating with beds of 

argillaceous and calcareous red shale containing sun 

cracks. Cut by a thick sill of intrusive diabase_____

Bass limestone, 335 feet

Arkose conglomerate characterized by lack of sorting 

and transportation. Rests on an extremely even surface 

produced by erosion ____________

Hotauta conglomerate, 0-6 feet 

 Great unconformity 

Quartz, mica, and hornblende schists. Cut by'quartz 

diorite and granitic pegmatite intrusjves ' Vishnu schist

1,000 1,000 2,000 3,000 Feet

GENERALIZED COLUMNAR SECTION OF THE ROCKS OF SHINUMO QUADRANGLE.
GEOLOGY. 31

maintain clean-cut cliff profiles and to retard the formation of soil 

and the growth of dense vegetation to mantle the slopes.

The strata are as easily distinguished by their colors as by the 

shapes they have taken under erosion. In the color scheme of the 

Grand Canyon these Paleozoic rocks play the dominant part. They 

are of the familiar shades of red, brown, buff, and gray shown by 

sedimentary rocks throughout the Rocky Mountain and Plateau 

regions of the western United States, and although the colors are 

neither so brilliant nor so varied as the visitor at the Grand Canyon 

is commonly led to expect, their general effect is very striking. They 

appeal to the eye and to the imagination through the stupendous 

panorama extending over many miles; through the extreme contrast between the vast, bright expanse of bare rock of the unforested 

interior of the canyon and the verdant wooded plateaus on the rim, 

and through the rigorously architectural effect imparted by the wide 

extent of the horizontal strata. Much of the charm of the varied 

tints, like that of most western desert coloring, lies in their dullness 

and oddity. They are mostly old, subdued shades, which vary just 

a little from conventional hues. The most beautiful effects, however, 

are wrought not so much by the colors of the rocks as by the purple 

haze that late in the afternoon, particularly in midsummer, often 

hangs over the canyon.

SERIES OP ROCKS DISCRIMINATED.

The lithologic representatives of the Permian, Mesozoic, and Tertiary, which, as shown by Dutton, once covered the region, have been 

removed by erosion. The following table shows the systems, series, 

groups, and formations discriminated in the quadrangle:

Generalized section of the rocks of the Shinumo quadrangle.

System.

Carboniferous.

Unconformity of erosion w 

Cambrian. 

Great angular unconformit

Algonkian.

Greatest angular unconfo 

Archean.

Series.

Pennsylvanian.

Misslssippian. 

thout unconformity ol

rGrand Canyon.

Group.

Aubrey.

dip. 

Tonto.

Unkar (Intruded by sills of 

diabase).

-

Formation.

Kaibab limestone. 

Coconino sandstone. 

Supai formation.

Redwall limestone.

Muav limestone. 

Bright Angel shale. 

Tapeats sandstone.

Dox sandstone. 

Shinumo quartzite. ' 

Hakatai shale. 

Bass limestone. ' 

Hotauta conglomerate.

Vishnu schist (intruded 

by masses of quartz 

diorite and by dikes of 

pegmatite).
32 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

The names employed in this report for the Paleozoic formations 

have been recently authorized by the United States Geological Survey to supplant older descriptive and duplicated names and to bring 

them into conformity with present usage. The following table gives 

equivalents of the older in the newer nomenclature.

Present nomenclature. Former nomenclature (reports of Button, Gilbert, 

and Walcott).

Kaibab limestone... 

Coconino sandstone. 

Supai formation.... 

Redwall limestone.. 

Muav limestone..... 

Bright Angel shale.. 

Tapeats sandstone..

Cherty limestone. 

Cross-bedded sandstone. 

Lower Aubrey sandstone. 

Redwall limestone. 

Marbled (or mottled) limestone. 

Tonto shale. 

Tonto sandstone.

PROTEROZOIC ROCKS. 

ABCHEAN SYSTEM. 

VISHNU SCHIST. 

NAME.

The name Vishnu terrane has been given by Walcott 1 to the 

fundamental crystalline complex of the Grand Canyon region .that 

underlies the unaltered sedimentary rocks of Algonkian age and is 

separated from them, as well as from the overlying Cambrian, by 

a profound unconformity. The type locality is on Colorado River, 

30 miles east of the mouth of Shinumo Creek, at the base of one 

of the great buttes called "Vishnu's Temple," from which Walcott 

derived the name.

DISTRIBUTION IN THE GRAND CANYON.

In the Kaibab division the Vishnu schist is exposed continuously 

for more than 40 miles in the walls of the Granite Gorge (PI. VIII, B). 

In the eastern part of the Kanab division it is exposed in Lower 

Granite Gorge and is probably exposed in other places in the Kanab 

division between the end of Lower Granite Gorge and the mouth of 

Kanab Creek, for Powell,2 in his account of this portion of his journey down the river, mentions " passing for a short distance through 

patches of granite, like hills thrust up into the limestone," The 

Vishnu is exposed through the greater part of the Shivwits division 

and around the southwestern border of the Grand Canyon district.

OCCURRENCE AND DISTRIBUTION IN THE SHINUMO QUADRANGLE.

The length of the exposure of the Vishnu schist in the Granite 

Gorge along the course of the river is about 17 miles; in Lower 

Granite Gorge it is 4 miles. A small but interesting exposure in

1 Walcott, C. D., Pre-Cambrian igneous rocks of the Unkar terrane, Grand Canyon of the Colorado, 

Arizona, with notes on the petrographic character of the lavas, byJ. P. Iddings: U. S. Geol.Survey Four-, 

teenth Ann. Rept., pt. 2, pp. 497-519, 520-524,1894.

2 Powell, J. W., Exploration of the Colorado River of the West and its tributaries; explored In 1869, 

1870,1871, and 1872, under the direction of the Secretary of the Smithsonian Institution, p. 92,1875.
PROTEROZOIC ROCKS. 33

the depths of the Muav-Flint Canyon lies on the northeast side of 

the West Kaibab fault and extends for 3 miles southeastward in 

the canyons of White, Shinumo, and Flint creeks, and for 1 mile 

northeastward up the canyon of Shinumo Creek.

No detailed study of the Vishnu schist was made in the Shinumo 

quadrangle beyond that required to locate and determine the 

various types represented in the area shown on the geologic map, 

and owing to the small extent of these exposures it was not possible 

to determine the general Archean structure from a study of this 

area alone. The rocks here are a metamorphic complex of quartz, 

mica, and hornblende schists and are invaded by a batholithic mass 

of quartz diorite and injected by veins of pegmatite and apUte. 

East of the Shinumo quadrangle and west of the mouth of Walthenberg Canyon in the Shinumo quadrangle the prevailing rocks are 

gneisses.

TYPES OF THE SCHIST.

Three main types of rock are found in the formation within the 

area studied:

The first type is a quartz schist that grades into mica schist. 

It comprises the greater part of the Vishnu schist that is exposed 

in the gorge of the Colorado River west of the Cable Crossing and 

is also exposed in the canyon of White Creek and in the canyon of 

Flint Creek just above its junction with Shinumo Creek.

The-second type is a quar.tz schist that grades into quartz-hornblende schist. It is exposed chiefly in that part of the Muav-Flint 

Canyon that is occupied by Shinumo Creek, grading both eastward 

and westward into the quartz-mica schist.

The third type is a hornblende schist. It occurs in one small 

outcrop, about 200 feet wide, on the east side of a dry wash that joins 

the valley of Shinumo Creek just below the mouth of White Creek, 

and is sharply bounded on both sides by the quartz-mica schist.

The rocks are typically schistose. The planes of schistosity generally stand almost vertical and trend northeastward, though- their 

direction varies from place to place. The schists are locally much 

twisted and contorted.

LITHOLOGY OF THE TYPES.

The less micaceous phase of the quartz-mica schist is dark greenish 

gray and its fresh surfaces have a satiny luster. Its cleavage is 

imperfect, its texture is fine grained, and it contains no visible mineral 

constituent except quartz. The microscope shows that it is composed 

almost entirely of fine interlocking grains of quartz, and some small 

flakes of white mica, arranged in parallel lines. The extreme quartzose phase of the schist contains very little mica just enough to 

impart a satiny luster to the rock. 

29745° Bull. 549 14 3
34 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

Freshly fractured surfaces of the micaceous phase of the schist are 

grayish, with either a pinkish or greenish tinge, but the weathered 

rock is ~ red. This phase shows a rather distinct cleavage and a 

texture ranging from fine to coarse. The unaided eye can distinguish 

both quartz and mica in the rock, and the microscope shows that it is 

composed of interlocking grains of quartz and an almost equal amount 

of mica, the flakes of mica being arranged in parallel lines. The mica 

is chiefly muscovite, but includes some flakes of brown biotite.

Locally the schist is garnetiferous, and in one place tourmaline was 

observed. All gradations between the quartzose and the micaceous 

phases occur, but in no specimen does the mica exceed the quartz in 

quantity.

The quartz-hornblende schist is a dark-green, dense, hard rock, 

with imperfect cleavage and fine-grained and uniform texture. Its 

mineral constituents can not usually be distinguished in the hand 

specimen without the aid of the lens, but the microscope shows that 

it consists of about equal proportions of quartz and green hornblende. 

The quartz occurs in interlocking grains and the hornblende tends to 

form automorphic crystals whose longer axes are roughly parallel. 

No other minerals were observed in the slides examined. Some 

phases of the rock contain more quartz than hornblende.

The hornblende schist is a dark-green, soft, coarse-grained rock, 

considerably disintegrated, and crumbles under the hammer. Megascopically it consists almost entirely of dark-green hornblende and 

exhibits no schistosity. The microscope shows that it consists 

almost wholly of large crystals of green hornblende in all stages of 

alteration, with a small amount of interstitial quartz, the quartz 

granules being strung out in roughly parallel lines. The rock is much 

altered and a thin section of it is unsatisfactory.

ORIGIN OF THE SCHIST.

The rocks in the Shinumo area afford no clear evidence of the 

original character of the Vishnu schist no evidence of banding that 

can be clearly referred to original sedimentary bedding and no evidence of original clastic texture but the mineralogic composition 

of the quartz schists of the mica and hornblende type suggests their 

sedimentary origin. Either type might have resulted from the 

regional metamorphism of an arkose sandstone or shale.

Such rocks would become either quartz-mica or quartz-hornblende 

schist, the type assumed being determined by the proportion of iron 

in the original sediments. Certainly the great preponderance of 

quartz in these rocks creates a presumption against their igneous 

origin. The present aspect of the schists is doubtless due to processes connected with regional metamorphism, namely, subsidence 

and deep burial, subsequent folding and mashing, and slow recrystallization.
PROTEBOZOIC BOOKS. 35

The original character of the hornblende schist described as occur-, 

ring in a narrow outcrop between the other schists can not easily be 

determined. The fact that the rock consists of little else than hornblende suggests that it was originally an igneous rock of a basic type. 

The fact that the microscope discloses in it a schistose structure shows 

that it is at least earlier than the period of regional metamorphism in 

which the schists wherein it, is inclosed assumed their present structural and mineralogic character.

AGE AND CORRELATION.

The Vishnu schist consists of rocks which, in the light of present 

knowledge, can be conceived to have acquired then' character only 

at great depths beneath the earth's surface, in what is technically 

known as the "zone of flowage." It is therefore evident that the 

unconformity which separates them from the overlying Algonkian 

sediments of -the Grand Canyon series represents a vast amount of 

erosion and a long period of time a period much greater in events 

even than that represented by the profound unconformity which 

separates the succeeding Grand Canyon series from the overlying 

Paleozoic. The Vishnu schist is therefore assigned to the Archean 

system. It seems likely, as stated by Kansome,1 that it may. be 

correlated with the Final schist of the Globe and Bisbee regions, and 

that it presents "somewhat different aspects of the fundamental 

crystalline complex of Arizona."

These rocks have not yet been studied in detail in the Grand Canyon 

region,, and their internal structural relations are unknown. A 

careful study of their exposures in the Kaibab division, in the Shivwits division, and along the southwestern border of the Plateau 

province may reveal the general Archean structure and the relation 

of these rocks to the fundamental complex of the southern part of 

Arizona.

INTRUSIVE QUARTZ DIORITE AND DIKES OF PEGMATITE ASSOCIATED 

WITH THE VISHNU SCHIST.

The Vishnu schist is intruded by masses of quartz diorite and by 

dikes of pegmatite. .

QUARTZ DIORITE.

So far as observed, quartz diorite constitutes all the Archean 

system in the Shinumo quadrangle that is exposed in the Granite 

Gorge of Colorado River for half a mile east of Cable Crossing. Its 

western contact is well defined, but its eastern limit was not located.

The quartz diorite in the river gorge east of Cable' Crossing is a 

coarse-grained, dense, resistant rock of typical granitic texture,

i Kansome, F. L., The geology and ore deposits of the Bisbee quadrangle, Arizona: U. S. Geol.Survey 

Prof. Paper 21, p. 21,1904.
36 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

which tends to weather into roughly angular blocks and thus to 

assume forms that distinguish it in the mass from the Vishnu schist. 

It is dark gray, looks remarkably fresh, and contains visible particles 

of white striated feldspar, dark hornblende, and glistening black 

biotite. The rock is uniform in texture throughout the exposures 

observed, is apparently without contact modifications, and shows no 

gneissoid banding.

Under the microscope it is seen to be a coarse-granular rock of 

granitic texture. . Its dominant mineral constituents are plagioclase 

and common hornblende, the plagioclase ranging from oligoclase to 

labradorite. Microcline, orthoclase, and quartz are present in about 

equal proportions, but their total amount does not equal that of the 

plagioclase. Brown biotite appears in somewhat less quantity than 

the hornblende, and titanite and magnetite are accessories. Occa-r 

sionally the quartz is poikilitic in the orthoclase. The feldspathic 

and ferromagnesian minerals occur in about equal proportions. If 

it were not for the preponderance of plagioclase the rock might be 

classed as a quartz monzonite or granodiorite, but it is probably best 

classed as a quartz diorite with a monzonitic aspect. The microscope 

reveals no cataclastic structure nor other evidence of dynamic action, 

and the minerals are fresh and unaltered.

The origin of the quartz diorite is reasonably clear. As it is a 

coarse-grained igneous rock of plutonic aspect occurring over a large 

area, sharply cutting the Vishnu schist, and showing no textural modifications at the contact, it doubtless represents a deep-seated igneous 

invasion of a large mass, of the type known as-a batholith. As the 

rock is unaltered and shows no gneissoid or cataclastic structure the 

batholithic invasion probably occurred after the period of regional 

metamorphism that produced recrystallization and schistosity in the 

inclosing schists. The invasion of the batholith may in itself have 

aided in producing this recrystallization and schistosity, but the 

field evidence seems to be adverse to such a conclusion, for the schist 

shows no change either in texture or in mineral composition with increase of distance from the contact.

PEGMATITE.

A granitic pegmatite occurs in dikes that cut all types of the Vishnu 

schist and that may readily be divided into two generations. The 

older generation is folded with the schists; the younger generation 

is a great network or mesh of dikes that cuts both the quartz diorite 

intrusive and-the Vishnu schist. A vertical section covering a thousand feet exposes .a huge mesh of these dikes in the wall of the Granite 

Gorge east of the mouth of Hotauta Canyon. (See PI. VIII, B, p. 28.)

The pegmatites are pink, very coarse-grained rocks, composed 

chiefly of quartz and pink orthoclase, ,and in places contain large 

crystals of silvery-white mica. Most of the dikes exhibit typical
PEOTEEOZOIC EOCKS. 37

comb structure inward from their walls and a graphic arrangement 

of the quartz and feldspar. Along the walls of some of the dikes the 

texture becomes aplitic.

The older pegmatite dikes are folded intimately with the Vishnu 

schist. Their injection may have either preceded or accompanied 

the regional metamorphism. The younger pegmatite dikes cut both 

the Vishnu schist and the intrusive quartz diorite. Where they cut 

the schists they break clean across the schistosity. The injection of 

these dikes is the latest recorded event in the igneous activity of 

Archean time within the area.

ALGONKIAN SYSTEM.

GEAND CANYON SEEIES. 

NAME.

The unaltered pre-Cambrian sedimentary rocks of the Grand 

Canyon region were first recognized by Powell l and were afterward 

more carefully studied by Walcott 2 at the eastern end of the Kaibab 

division of the canyon. They are described by Walcott as a series 

of sedimentary rocks 12,000 feet in thickness, comprising limestones, 

shales, sandstones, and interbedded flows of lava, separated both 

from the underlying Vishnu schist and from the overlying Cambrian 

sediments by profound unconformities, and exposed over a considerable area in the greater depths of the Grand Canyon and in the intercanyon valleys of the north side. To this series of sedimentary rocks 

Powell 3 gave the name Grand Canyon group, which was modified by 

Walcott to Grand Canyon series.

A slight unconformity of erosion was found in the middle of the 

series. The stata lying below this minor unconformity were called 

by Walcott the Unkar terrane, the name being derived from Unkar 

Valley, in which the strata are typically exposed. The rocks above 

the minor unconformity were called by him the Chuar terrane from 

typical exposures in Chuar Valley. These two valleys are parallel 

intercanyon valleys of the north side of the Colorado in the area described by Walcott. According to the Survey classification the Unkar 

and Chuar are designated as groups.

DISTRIBUTION IN THE GRAND CANYON.

At six localities in the Grand Canyon between the mouth of the 

Little Colorado, in the eastern end of the Kaibab division, and the 

mouth of Tapeats Creek, some 80 miles below, in the eastern part of

i Powell, J. W., Exploration of the Colorado River of the West, p. 212 and fig. 79, Washington, 1875.

8 Walcott, C. D., Pre-Cambrian igneous rocks of the Unkar terrane, Grand Canyon of the Colorado, 

Arizona, with notes on the petrographic character Of the lavas Dy J. P. Iddings: U. S. Geol. Survey Fourteenth Ann. Kept., pt. 2, pp. 497-519, 520-524,1894.

8 Powell, J. W., Geology of the eastern portion of the Uinta Mountains: U.S. Geol. and Geog. Survey 

Terr., p. 70,1876.
38 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

the Kanab division, the strata of the Grand Canyon series are exposed 

between the crystalline schists of the Archean and the basal sandstone 

of the Cambrian. Five of the localities are within the Kaibab division; the sixth is within the Kanab.

The first of these localities is the classic area below the mouth of the 

Little Colorado, described by Walcott. This is the largest areal exposure of these rocks in the Grand Canyon, and includes both the 

Unkar and Chuar groups. It extends northwestward across the 

canyon of Vishnu Creek and into the canyon next west of it.

The second locality lies 5 miles west of the first, at the head of 

the inner gorge of Clear Creek, on the north side of Colorado River, 

within the. depths of Ottoman Amphitheater. The exposure is 

limited to less than a square mile. It comprises a small portion of 

the basal part of the Unkar group and is structurally a unit with the 

first locality.

The third locality lies along the north side of Colorado River at 

the mouth of Bright Angel Creek (PI. X, B), opposite the railroad 

terminus and hotels of the Grand Canyon Railway, Sante Fe System. 

About 1,000 feet of the basal portion of the Unkar group is there 

represented and the areal extent of the exposure is about 3 square 

miles. This locality has already been described chiefly by Ransome.1 

It lies about 10 miles west of the type locality and extends southeastward across Colorado River into the canyon of Cremation Creek, 

along the line of a flexure in the Paleozoic strata.

The fourth locality comprises a small exposure of basal Unkar 

strata in the depths of Hindu Amphitheater, on the north side of 

the Colorado about 3 miles up Crystal Creek from its mouth, some 

20 miles west of the type locality. The exposure covers about 1 

square mile and has not yet been described.

The fifth locality, to be described in the present report, lies near 

the mouth of Shinumo Creek, about 30 miles west of the type locality. 

The exposures cover between 10 and 12 square miles and include 

rocks representing nearly the entire Unkar group.

The sixth locality is in Lower Granite Gorge just above the mouth 

of Tapeats Creek, in the Kanab division of the canyon. It lies 42 

miles northwest of the type locality and 12 miles directly northwest 

of the Shinumo area. It extends about 3 miles along the river and 

includes about half of the total thickness of the Unkar group. This 

locality has not yet been described.

Dutton 2 figures "rocks of Lower Silurian and Archean unconformable" in the bed of the river beneath the "basal Carboniferous," 

in the western part of the Kanab division, in a section across the 

Grand Canyon at the foot of Toroweap Valley. As Dutton means by

IRansome, F. L., Pre-Cambrian sediments and faults in the Grand Canyon of the Colorado: Science, vol. 

27, No. 695,1908. 

* Dutton, C. E., Tertiary history of the Grand Canyon district: U. S. Geol. Survey Mon. 2, p. 88,1882.
I U. S. GEOLOGICAL SURVEY

A. BASS LIMESTONE IN HOTAUTA CANYON.

53E l?f.;t®*~>

B. STRATA OF UNKAR GROUP NEAR MOUTH OF BRIGHT ANGEL CREEK, BRIGHT ANGEL

QUADRANGLE.

V, Vishnu schist; //, Hakatai shale; Sh, Shinumo quartzite; T, Tapeats sandstone; _B, Bright Angel shale; 

R, Redwall limestone; Ssr sandstone of Supai formation; 6', Coconino sandstone. Photograph bv 

N. W. Carkhuff. '
U. S. GEOLOGICAL SURVEY

VIEW NORTHWARD ACROSS THE GRAND CANYON FROM THE E

SC, Shinumo Creek; V, Vishnu schist; B, Bass limestone; II, Hakatai shale; Sh, Shinumo quartzrte; D, Dox san

M, Muav limestone; ]t , Redwall limestone: Ss, sandstone of Supai formation; Ssh, shale of Supai formatio

Photograph by N. W. Carkhuff.
PEOTER0201C BOCKS. 30

"basal Carboniferous" what is now known as the basal sandstone 

of the Tonto group, of Cambrian age, it is possible that the "Lower 

Silurian" rocks in that locality are the Grand Canyon series. In 

the Shivwits division, according to Powell, 1 these rocks occur at least 

in one place.

STRUCTURE AND DISTRIBUTION IN THE SHINUMO-QUADRANGLE.

Practically all the exposures in the quadrangle belong to the mass 

about the mouth of Shinumo Creek. (See Pis. IV, B, p. 18, and 

XI.) The rocks of the Grand Canyon series here lie in a wedgeshaped body, the apex of which is the intersection of the unconformities by erosion that separate them from the Archean below and from 

the Paleozoic above. The apex of the wedge lies near Colorado 

River, parallel to its northwestward course. The mass as a whole 

constitutes a great tilted block, which in turn consists of a great 

number of smaller faulted and tilted blocks pitching at successively 

greater angles to the northeast, away from the apex of the wedge. 

In the Muav-Flint Canyon, about 3 miles northeast of the apex of 

the wedge, the whole mass is dropped by a profound fault, which 

brings up the underlying Archean rocks from a great depth on the 

northeast side of the fault plane and produces a structure that 

strikingly resembles that of areas of similarly faulted Triassic blocks 

in the Connecticut Valley. The strike of the strata of the wedge is 

N. 40° W.; the dip varies from place to place. The strata of the 

fault blocks near the apex of the wedge generally dip 10°-15° NE.; 

those near the center of the wedge dip on an average about 25° 

NW.; but those near the great limiting fault on the northwest are 

completely overturned by the "drag" along the fault plane. This 

pre-Cambrian structure is truncated by the unconformity at the base 

of the Tonto group. (For structure, see PI. I, sections, in pocket.)

The great pre-Cambrian fault that limits the wedge on the northeast is the West Kaibab fault, which displays in a most spectacular 

manner a phenomenon analogous to that on the line of the East 

Kaibab monocline, described by Walcott.2 On the line of this ancient fault in the Shinumo quadrangle two later displacements took 

place after the deposition of the Paleozoic strata of the canyon wall 

and probably later strata. The first of these is a monoclinal flexure 

which reverses the throw of the pre-Cambrian fault; the second is 

a still more recent fault superposed upon the line of the monocHnal 

flexure. (PL I, sections, in pocket.)

On the north side of the Colorado the strata of the Grand Canyon 

series are exposed continuously along their strike for about 7 miles in 

the wall of Granite Gorge (PI. XI), the exposures running back several

1 Powell, J. W., op. cit., p. 62.

' s Walcott, C. D., Studyof alineof displacement in the Grand Canyonof the Colorado in northern Arizona: 

Geol. Soc. America Bull., vol. 1, p. 49,1890.
40 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

miles from the river in the larger side canyons, which are cut beneath 

the base of the Paleozoic. These side canyons, named from east to 

west, are Hotauta, Shinumo, Burro, and Hakatai canyons. They are 

trenched directly across the strike of the strata and reveal them in 

cross section. The higher formations of the wedge are exposed for 

about 3 miles along the strike in that part of the interior gorge of the 

Muav-Flint canyon which lies southwest of the West Kaibab fault.

On the south side of the Colorado the exposures are confined to the 

basal formations and are small, for the wedge thins out in that direction. The rocks are exposed along the strike in the wall of Granite 

Gorge between the small canyon east of Serpentine Canyon and the 

mouth of Copper Canyon, a distance of 3 miles. The only long exposure across the strike is in Bass Canyon (PL XVI, B, p. 78).

The gorge of the Colorado has everywhere been trenched deep 

enough to expose the Archean rocks along the river beneath the Grand 

Canyon series (PL I'll, A and B, p. 16), for the stream flows close to 

the apex of the wedge.

The hard quartzite strata of the wedge resisted the erosion that 

preceded the deposition of the Cambrian sandstone and stood as a 

long, narrow residual- hill or "monadnock" in the pre-Tonto plain 

(PL XVIII, p. 86)' When the Tonto sea came in over the plain the 

monadnock formed a_long rocky inland extending for an unknown 

distance from northwest to southeast parallel to the strike of the 

Algonkian strata. In many places the rocks of this island-monadnock project well above the basal sandstone of the Tonto group and 

are exposed in narrow outcrops above the Tonto platform, forming 

isolated outliers of the main mass of Algonkian strata. The largest 

of these outliers is in Monadnock Amphitheater, 2 miles southeast of 

Hotauta Canyon.

The strata of the Grand Canyon series that are exposed in. Lower 

Granite Gorge are structurally a part of the Shinumo wedge. They 

represent strata of the wedge that are prolonged northwestward along 

the strike and reappear beyond Powell Plateau. These exposures lie 

just beyond the northern boundary of the Shinumo quadrangle, beginning about 2 miles down Colorado River from the north of Specter 

Chasm. They include about 4,000 feet of the Unkar group, which 

strike northwest-southeast and dip about 15° NE.

UNKAR GROUP.

CHARACTER AND SUBDIVISIONS.

The greater part of the Unkar group of the Grand Canyon series, 

of Algonkian. age, is represented in the Shinumo quadrangle. The 

upper or Chuar group is not represented. Although these preCambrian sediments show no more evidence of alteration or metamorphism, apart from local igneous contact phenomena, than the
PBOTEROZOIC ROCKS. 41

overlying Paleozoic beds, they are destitute of fossils or of other 

evidence of life. In .the absence of fossils the rocks of the group may 

be divided into formations by their lithology, according to which the 

portion of the Unkar group in the Shinumo quadrangle is divisible 

into five formations, which appear in conformable stratigraphic 

succession. The importance of this division should not be greatly 

emphasized, its,chief value lying in the fact that it furnishes a means 

of comparing the lithologic succession of the Unkar group in this area 

with that in the type locality described by Walcott, 30 miles to the 

east, as well as a means of distinguishing in a broad way the main 

changes in the physical conditions under which these sediments were 

laid down.

At the base, resting upon the profoundly eroded and base-leveled 

surface of the metamorphic rocks of the Vishnu schist, is a thin 

conglomerate. Upon the conglomerate lies a series of limestones 

and calcareous shales. These grade upward into argillaceous and 

arenaceous shales which are locally intruded by a thick sill of diabase 

and are overlain in turn by great thicknesses of sandstone and 

quartzite. The uppermost exposed formation of the group in the 

quadrangle is a thick series of micaceous shaly sandstones.

The following section shows the geologic plan of the group and the 

formations into which it has been subdivided:

Section showing relations and subdivisions of Unkar group. 

Tonto group. 

Unconformity.

Unkar group: 1

Feet. 

Dox sandstone (micaceous shaly sandstone)............................. 2,297

Shinumo quartzite (sandstone and quartzite)............................ 1,564

Hakatai shale (argillaceous and arenaceous shale)........................ 580

Bass limestone (calcareous shale and limestone).......................... 335

Hotauta conglomerate (basal conglomerate).............................. 6

4,782

Unconformity. 

Vishnu schist.

These strata lie in a wedge-shaped mass that is inset in the Vishnu 

schist (see PI. I, sections) a wedge composed of a great number of 

small tilted fault blocks, the relations showing that nowhere in the 

Shinumo area can the thickness of these rocks be measured in one 

unbroken section. As the lithologic characters of the strata are 

constant and the beds easily recognized, however, and as the throw 

of the faults that bound the tilted blocks seldom exceeds 100 feet, a 

section showing the unbroken sequence can be easily obtained.

Detailed sections were, made from the base of the Unkar upward 

through each fault block until its limit was reached, and the highest

i The diabase that was Included by Walcott in his Unkar "terrane" but that is now known to be 

intrusive is, in accordance with modern practice, excluded from the Unkar group.
42 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

bed measured was then located in the next block to the northeast and the measurement resumed at that point. All sections 

except those in the highest formation of the group'were measured 

with a tape along the nearly vertical walls of the canyons of the 

Shinumo and other washes that cut across the strike of the strata. 

The strong drag of the great fault on the northeast has flexed and 

contorted the shaly strata of the Dox sandstone in such a manner that 

accurate measurement with the tape alone was impossible. Their 

thickness was computed .trigonometrically, by using the combined 

data afforded by the tape, the topographic map, and the observed 

strikes and dips.

The section here given was made in two places. The greater part 

of it was measured in a traverse up Shinumo Canyon. This part of 

the section includes all the strata above the diabase sill, which is 

intruded midway in the Hakatai shale in that locality. A complete 

section of the group could have been made in a traverse of the course 

of Shinumo Creek from the basal unconformity at the mouth of the 

creek'to the great fault 3 miles above, although four faults cross the 

creek between its mouth and the place where the diabase sill dips 

beneath the bed of the stream, but a place was found in Hotauta 

Canyon where all the strata between the basal unconformity and the 

diabase sill lie in a continuous unfaulted section, in a fault block that 

is tilted about 10° NE., so the section of the basal members of the 

group was measured in this locality.

HOTAUTA CONGLOMERATE.

Base of the formation. The surface of erosion represented by the 

unconformity upon which the Hotauta conglomerate rests is an 

almost perfect plane, for nowhere in the 7 linear miles exposed in the 

Shinumo quadrangle is there a difference in relief exceeding 20 feet. 

The depth of weathering below this surface appears to be slight, in 

spite of the enormous amount of rock that has been removed, and the 

weathering appears to be the result of physical disintegration rather 

than of chemical decomposition.

Name and character. The .name of the formation is that of the 

canyon in which the lower part of the geologic section was measured.

The Hotauta conglomerate is an arkose conglomerate which varies 

in thickness from 1 to 6 feet in the Shinumo quadrangle. It is composed of angular or subangular fragments of the rocks of the underlying Vishnu schist, cemented by a matrix of red arkose mud, which 

generally contains small fragments of pink feldspar and sporadically 

small rounded grains of quartz.

This conglomerate varies greatly in hardness, from place to place, 

ranging from a hard, dense, siliceous rock, which fractures across
PBOTEROZOIC BOCKS. 43

matrix and inclosed rock fragments alike, to an easily disintegrated 

rock in which the matrix crumbles away from the inclosed fragments. 

The degree of hardness, however, does not depend on original cementation, but on local metamorphic effects produced by the diabase sill 

that is intruded in the overlying rocks, the degree of induration 

depending on the depth of the conglomerate below the contact of 

the sill. ^

The matrix everywhere is generally of the same composition, but 

the character of the inclosed fragments depends on the character of 

the underlying Vishnu schist. The rock that underlies the conglomerate in Hotauta Canyon is the quartz diorite of the batholith 

already described. The diorite for 3 feet below the conglomerate is 

divided into roughly angular blocks by joints, which are filled with 

the red arkose material of the matrix. Above the diorite lies a layer 

of the conglomerate a foot thick, composed of weathered fragments 

of diorite cemented with the red arkose. Above this lies a layer, 

6 inches thick, of small rounded quartz pebbles and fragments of 

chert like that in the overlying limestones. The whole is cemented 

with the red mud. Although the contact of the diorite with the 

mica' schists in the underlying Vishnu formation is not 200 yards 

distant, no fragments of the mica schist were observed in the 

conglomerate.

In Hakatai Canyon, 4 miles west of Hotauta Canyon, the underlying rocks are mica schists and veins of quartz and pegmatite. 

Here the Vishnu schist is scarcely weathered at all below the unconformity. The overlying conglomerate is 6 feet thick and consists of angular fragments of the underlying mica schists, fragments 

of pegmatitic feldspar and vein quartz, and the arkose cement 

described above. The rock here is very hard, and when fractured 

breaks across the grains like a dense quartzite. This hardness is an 

effect of the intrusion of the diabase sill, the lower contact of which 

in Hakatai Canyon, lies only 150 feet above the basal conglomerate, 

whereas in Hotauta Canyon it lies 550 feet above.

Summary. The Hotauta conglomerate is characterized by two 

important features an arkose nature and a lack of sorting and 

transportation of its component fragments.

BASS LIMESTONE.

Name and subdivisions. The name of the Bass limestone is derived 

from Bass Canyon, where the strata are typically exposed. (See PI. 

X, A.) The following section was measured on the west side of 

Hotauta Canyon. The typographic arrangement shows the natural 

order of the beds, A representing the top bed of the section and 1 the 

top member of each bed.
44 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

Section of Bass limestone in Hotauta Canyon.'

 Ft. in. 

A. Blue slate and white limestone............................. 108 2

B. White limestone.................................:......... 105 2

C. Argillaceous and calcareous red shale and limestone.......... 85 5

D. Basal white limestone..................................... 6 0

304 9 

Order, character, and thickness of subdivisions of the Bass limestone.

A. Blue slate and white limestone: Ft. in.

1. Layers of dense white crystalline limestone separated.

by bands of pale-green talcose material................ 2 0

2. Dense red and black banded jasper, weathering green between the layers and forming a cliff. The .layers contain shrinkage cracks and ripple marks................. 11 4

3. Layers of dense white crystalline limestone separated

by thin bands of pale-green talcose material......... 10 0

4. Pinkish-green fissile siliceous slate of a jaspery appearance, forming a cliff.................................. 5 0

5. Dense, lumpy white crystalline limestone.............. 2 0

6. Fissile blue slate...................................... 7 0

7. Thin-bedded platy white limestone..................... 4 6

8. Calcareous blue slate, forming a cliff.................... 3 0

9. Very thin lamellar fissile blue slate.................... 3 0

10. Thin-bedded platy white limestone..................... 2 6

11. Dense blue crystalline limestone, forming small cliff.... 23

12. Gnarly layers of fine lamellar blue calcareous slate with 

a very coarse concretionary structure and irregular 

nodules of chert in the middle part of the bed ...... 33 0

13. Thin-lamellar spotted blue slate........................ 6 6

14. Same as 16, forming a small cliff........................ 8

15. Sameasl7............................................ 2 2

16. Dense purple crystalline limestone, forming a small cliff 7

17. Thin-bedded purple crystalline limestone............... 1 2

18. Fissile blue slates with fine partings.................... 7 0

19. Hard blue slate, forming small cliff.................... 1 0

20. Soft purple shale..................................... 3 6

108 2

B. White limestone: >

1. Very hard, dense layer of flint, forming small cliff...... 5

2. Gnarled and nodular white cherty limestone............ 7 0

3. Thin-bedded crystalline white limestone............... 5 6

4. Thick-bedded crystalline white limestone of the same

character as 8, forming a strong cliff................. 3 6

5. Red shale below and purple shale above, separated by a '

thin layer of chert................................... 5 0

. , 6. Undulatory-banded cherty limestone, becoming crystalline above.......................................... 10 0

7. Same in thinner beds................................. 6 6

8. Thick-bedded layers of pure, homogeneous white marble, forming the strongest cliff in the second formation 

of the Unkar group................................. 6 8
PBOTEEOZOIC BOCKS. 45

B. White limestone Continued. Ft. in.

9. Layers of undulatory-banded nodular chert in a matrix

of earthy white limestone........................... 3 10

10. Purpleshale.......................................... 3 3

11. Dense crystalline blue limestone....................... 4

12. Homogeneous thin-bedded white limestone, crumbling 

to a white powder and weathering into plates like a 

shale............................................... 15 0

13. Dense blue crystalline limestone, forming a small cliff... 3 0

14. Soft purple shale..................................... 1 10

15. Thin-bedded crystalline white limestone............... 3 10

16. Soft purple shale...................................... 1 0

17. Thin-bedded white limestone crumbling to white powder

or weathering into thin plates like a shale............. 2 0

18. Layer of gnarled and twisted chert nodules in a matrix of 

white talc whose surface is covered with dendritic 

markings........................................... 2 0

19. Soft purple shale...................................... 5

20. Layers of undulatory-banded bluish chert.............. 1 10

21. Purpleshale..............................'............ (?)

22. Lumpy and gnarly white limestone carrying chert in

large, irregular nodules. Crumbles to a white powder.. 2 6

23. White limestone carrying a large amount of chert in

undulatory and gnarled bands...................... 2 .4

24. Homogeneous thin-bedded white crystalline limestone 

containing occasional thin bands of chert and nodules 

resembling Cryptozoon............................. 8 6

25. Dense homogeneous white crystalline limestone, forming a cliff. Upper part is thin bedded.............. 3 8

26. Nodular white cherty limestone. The chert occurs in 

irregular-shaped nodules. The upper part of the stratum has a paper-thin bedding, giving it the aspect of a 

calcareous shale. The limestone weathers to a white 

powder. Bears dendritic markings.................. 2 0

27. Thin-bedded white cherty limestone, carrying the chert 

in parallel bands and containing three paper-thin layers of purple shale. Weathers to a white powder. 

Bears dendritic markings............................ 2 0

105 2

C. Argillaceous and calcareous red shale and limestone:

1. Blue' calcareous shale with an onion-like concretionary

structure on a large scale........................... 5 0

2. Dense purple calcareous shale, carrying bands of pink 

calcite and forming a cliff. Contains occasional thin 

bands of chert...............'....................... 9 6

3. Alternating layers of buff and red shale................. 13 6

4. Compact red shale, forming a cliff..................... 8 0

5. Cherty white limestone............................... 4"

6. Red shale-.......................................... 4 4

7. Pink limestone...................................... 1 0

8. Blue limestone............................:.......... 2

9. Red shale............................................ 1 0

10. Blue limestone................ ...................... 3
46 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, AEIZ.

. C. Argillaceous and calcareous red shale and limestone Con. Ft. in.

11. Bedshale......,.............!....................... 11 0

12. Red crystalline limestone.............................. 1 0

13. Red shale............................................ 1 0

14. Red crystalline limestone.............................. 1 0

15. Calcareous red shale with three thin bands of purple

limestone........................................... 9 10

16. Purple limestone...................................... 6

17. Redshale............................................. 3 10

18. Blue limestone............................... '........ 4

19. Redshale............................................ 1 5

20. Blue limestone, white for 1 inch at the base and showing

dendritic markings.................................. 5

21. Alternating layers of buff and chocolate-red shale with a 

splintery habit of weathering and a roughly concretionary structure. Like all.the succeeding shales and 

sandstones of the Unkar group, they are mottled with 

light spots, generally circular or elliptical in form and 

of all sizes......................................... 5 6

22. Purple crystalline limestone. ......................... 1 0

23. Purple shale with occasional bands of purple calcite.... 4 0

24. Purple cherty limestone.............................. 1 0

25. Soft purple shale..................................... 6

85 5

D. Basal white limestone:

1. White cherty limestone carrying the chert in thin parallel 

bands, which are etched out by the weather on the 

cross sections. The surface of each chert layer shows 

polygonal cracks suggestive of eun cracks in shale. 

This structure belongs to each separate chert layer and 

is not a columnar structure. The weathered surfaces 

of these chert layers are dotted with small cubic depressions which were apparently formed by the leaching out 

of some mineral of cubic form....................... 4 6

2. White nodular cherty limestone. The chert occurs in 

nodules having a roughly concentric structure somewhat suggestive of the structure of Cryptozoon........ 1 6

6 0

Specimens of these limestones when examined in the laboratory 

proved to be more or less magnesian, and all, those of division B were 

found to be dolomites.

TJpin sections were cut from specimens taken from 20 separate 

beds in division B. Eighteen of these slides were cut from the limestone strata and two from the red shales. The sections of the limestones were cut both from the chert bands and nodules and from 

the limestone itself, for the purpose of ascertaining the exact mineralogical character of these rocks and in the hope that they might 

reveal traces of a structure that could be referred to something organic. 

The microscope revealed no minerals other than calcite and quartz 

in any of the slides. The silica of the chert bands and nodules
PROTEROZOIC ROCKS. 47

appeared in the form of interlocking grains of quartz. None of these 

grains were rounded and there was no evidence that the quartz 

grains represented an inwashed sand. No trace of organic structure 

was revealed either in the chert or in the limestone. The purer 

limestones were found to consist of calcite (or dolomite) alone, the 

crystalline forms having the typical structure of marble. The 

impure varieties were seen to consist of mixtures of quartz and calcite 

in all proportions, the greater part of the limestone being of this 

impure character. The shales were found to consist of a fine, impalpable ferruginous or calcareous mud, containing here and there a 

minute grain of quartz.

Summary. The section of the Bass limestone shows several interesting features. Ripple marks and sun cracks appear for the first 

time in the shales in stratum 2 of division A, just below the limestone 

stratum at the summit, of the formation. An increase in the intensity of local metamorphism in the section from the base upward was 

also noted, the rocks becoming harder and changing in color with 

increasing proximity to the lower contact of the diabase sill, which 

is intruded in the overlying Hakatai shale. Nearly all the shales of 

division C are red, but from the summit of this division upward they 

are purple and blue. The shales below division A are soft and 

crumbly; those in this division, however, have become dark-blue 

slates, and those in the upper part of the section have become extremely 

hard, siliceous jaspers.

The section is broadly characterized by oft-repeated alternations 

of limestone and shale, and according to the dominance of one or the 

other type of rock the four divisions A, B, C, and D, are separated: 

D is entirely limestone; C is -alternating limestone and shale; B is 

predominantly shale; A is largely slate and jasper. Thus there are 

four major cycles of oscillation of sediments upon which the minor 

cycles are superimposed.

A comparison of the above section in Hotauta Canyon with a 

section measured in Hakatai Canyon, 4 miles to the west, is of interest. 

In Hakatai Canyon the "basal white limestone" (D) has a thickness 

of 30 feet, contrasted with a thickness of 6 feet in Hotauta Canyon. 

The thickness of lower stratum of "white, nodular, cherty limestone" 

in Hakatai Canyon is 7 feet 9 inches, whereas in Hotauta Canyon it 

is only 1 foot 6 inches. The upper stratum of this section, a parallelbanded, cherty, white limestone, which is 4 feet 6 inches thick in 

Hotauta Canyon, is 22 feet 3 inches thick in Hakatai Canyon, and 

contains in the middle an intercalated layer of purple shale and near 

the top a thin layer of rather fine arkose conglomerate. In Hakatai 

Canyon the "argillaceous and calcareous red shales and limestones" 

of division C are 88 feet thick, but in Hotauta Canyon they are 85 

feet 5 inches thick and have not the red color that characterizes
them in Hakatai Canyon, being purple and blue and much indurated. 

This change of color and difference in hardness are due to their closer 

proximity to the diabase sill in Hakatai Canyon.

The correspondence in the lithologic character and vertical succession of the beds of these two sections, 4 miles apart, is so close 

that the individual strata of the sections can be matched bed for bed.

The only marked contrast in thickness occurs in the basal white 

limestone (D).

HAKATAI SHALE.

The name of the Hakatai shale is taken from Hakatai Canyon, 

where the formation is typically exposed.

Section of Hakatai shale.

Ft. In.

A. Alternating vermilion arenaceous shale and sandstone....... 78 1

B. Alternating vermilion argillaceous shale and sandstone..... 109 4

C. Red argillaceous shale..................................... 81 0

D. Blue slate....................... 1....................... 100 0

E. Blue slate and quartzite................................... 20 0

F. (Intrusive diabase.)

G. Ejed and blue jasper...................................... 31 0

H. Sandy quartzitic jasper.................................. 52 0

I. Cliff-forming jasper........................................ 17 6

J. Blue slate with calcareous band...................:........ 18 0

K. Cliff-forming jasper....................................... 73 0

579 11 

Order, character, and thickness of subdivisions of the Hakatai shale.

Ft. in. 

A. Alternating vermilion arenaceous shale and sandstone.... : ... 78 1

B. Alternating vermilion argillaceous shale and sandstone..;... 109 4 

C. Red argillaceous shale, sun cracked throughout. The rock is 

very soft and forms a slope together with the underlying 

blue slate............................................. 81 0

D. Blue slate, forming a slope ............................^,.. 100 0

E. Blue slate and quartzite, forming a cliff................... 20 0

F. At this horizon is intruded a sill of diabase whose thickness 

varies from 650 feet on Shinumo Canyon to 950 feet or more 

in Hakatai Canyon. . ' / 

The section from A.to F was measured in a traverse up'the 

Shinumo, starting with the upper contact of the diabase 

sill. 

G. Red and blue jasper:

1. Red and black banded jasper.......................... 9 0

2. Banded blue jasper with curious spots, sun cracked

throughout......................................... 22 0

31 0

H. Sandy quartzitic jasper:

1. Fine-grained pink sandy jasper, sun cracked.......... 11 0

2. Fine-grained pink quartzite.........................;. 4 0

3. Pink quartzitic jasper................................. 5 0
PEOTEEOZOIC ROCKS; 49

H. Sandy quartzitic jasper Continued. Ft. in.

4. Fine-grained pink quartzite, ripple marked............ 1 0

5. Slaty-blue spotted jasper with sun cracks. ........... C 0

6. Fine-grained pink quartzite.......................... 40

7. Slaty-blue spotted jasper............................. 12 0

8. Fine-grained pink quartzite, ripple marked ............ 5 0

9. Slaty-blue spotted jasper............................. 4 0

	52 0

I. Cliff-forming jasper:

1. Dense, hard layer of blue-black jasper mottled with red 

spots, having a soft, slaty layer at the base and forming 

with the bed below a strong overhanging cliff........ 3 6

2. Same as 1, without soft layer.......................... 14 0

17

J. Calcareous blue slate:

1. Slaty-blue jasper with small red spots................. 4 6

2. Pink crystalline limestone............................ 1 6

3. Slaty black jasper, sun cracked throughout............ 12 0

18 0

K. Cliff-forming jasper:

1. Dense, hard layer of blue-black jasper, showing banded

structure, with a soft layer at the base............... 12 0

2. Sameasl............................................. 14 0

3. Same general character as 2. The lower 2 feet are slaty

and weather out, giving the cliff an overhang......... 19 0

4. Dense, hard layer of blue-black jasper, mottled with red 

spots and showing no banding in the mass, forming with 

the three layers above a strong perpendicular cliff. 

This is the most resista,nt rock in the Unkar group. 

Where the under surface shows beneath the overhang 

of the cliff, it is sun cracked on a large scale and in 

several generations................................. 28 0

73 0

The sandstone in series A is white, compact, and fine grained. It 

is cross-bedded and ripple marked throughout. The under surface 

of each sandstone layer is sun cracked where it rests upon the arenaceous shale. The shale is vermilion in color, soft, and very sandy. 

Sun cracks occur throughout.

The succession is as follows:

Ft. in.

1. Sandstone:................................................. 1 0

2. Arenaceous shale.......................................... 24 0

3. Sandstone.................................................. 2 0

. 4. Arenaceous shale.......................................... 11 8

5. Sandstone.................................................. 9 0

6. Arenaceous shale.......................................... 21 1

7. Sandstone.................'................................. 9 4

78 1 

29745° Bull. 549 14 4
50 SHINUMO QUADRANGLE, GRAND- CANYON DISTRICT, ARIZ.

The alternations in series B are remarkably regular. The sandstone is white, compact, and fine grained and is cross-bedded and 

ripple marked throughout. The shales of the alternating beds are 

very soft and weather out, leaving etched-out bands between the 

sandstones, which are very conspicuous in the .cliff faces. On the 

under surface of each sandstone layer are well-preserved sun cracks. 

The shales are fine grained, fissile, and argillaceous.

The succession in this alternating series is as follows:

'Order and thickness of beds of sandstone and shale in series B of Hakatai formation, with 

thickness of groups of beds representing each sandstone-shale cycle.

1. Shale. ..........

2. Sandstone ........

3. Shale.. .........

4. Sandstone....... -

5. Shale. .......... 

6. Sandstone........

7. Shale...........

8'. Sandstone........

9. Shale........... 

10. Sandstone........

11. Shale. .......... 

12. Sandstone........

13. Shale. ..........

14. Sandstone ........

15. Shale...........

16. Sandstone........

17. Shale...........

18. Sandstone....... -

19. Shale... ........

20. Sandstone........

21. Shale...........

22. Sandstone........

23. Shale...........

24. Sandstone........

25. Shale...........

26. Sandstone. .......

27. Shale. ..........

28. Sandstone........

Total........

Ft.

....... 4

....... 3

....... 6

....... 2

....... 2 

....... 3

....... 1

....... 2

....... 0 

....... 3

....... 4 

....... 7

....... 3

....... 6

....... 3

....... 6

....... 2

....... 6

....... 3

....... 5

....... 10

....... 7

....... 2

....... 1

....... 3

....... 2

....... 3

........ 4

....... 109

In.

0| of- ------"- - -

...............

lof-- 1 

} ...............

61 6f- - "; '

°l 6f...............

...............

61

 oj- -- - - --- 

...............

...............

6)

................

...............

101

4 Average .

Ft.

......... 7

......... 8

......... 6

......... 3

......... 4

......... 11

......... 9

......... 9

......... 8

......... 8

......... 17

......... 3

......... 5

......... 8

......... 7

In.

0

6

4

0

0

6

6

6

6

0

6

0

0

0

10

Thin sections were cut from several specimens of the jaspers, but 

they were unsatisfactory, because of the exceedingly fine grain of the 

rock. The highest power of the microscope revealed nothing more 

than an impalpable silicified mud. A slide of the " quartzitic jasper" 

showed that the rock was a somewhat arkose sandstone indurated to 

a siliceous quartzite, composed chiefly of small rounded quartz grains 

about which secondary silica had been deposited, lying in a fine 

arkose matrix made up of small fragments of pink feldspar. A thin
PEOTEROZOIC ROCKS. 51

section was also made from a specimen of sandstone taken from one 

of the layers in the "alternating argillaceous shale and sandstone" 

of division B. The rock proved to consist of small, well-rounded 

grains of quartz, cemented by silica in the form of secondary quartz. 

It is a pure, fine-grained sandstone.

The metamorphic effects produced by the diabase sill intruded at 

the horizon F are seen in the section marked " I." This metamorphic 

action produces induration by silicification, forming jaspers; induration by baking, forming slates; decoloration, red changing to blue 

and black.

In the summary of the features of the Bass limestone it was noted 

that the shales became successively slates and jaspers above, while 

their color changed from red to blue. In division I of the Hakatai 

formation the shales are represented entirely by jaspers and quartzites. (See PI. XIV, B, p. 64.) Just below the contact, at the top 

of division G, the induration is very great, and the jaspers are tough 

and vitreous; their prevailing color is blue or black. Above the contact the overlying rocks are hard blue slates for 20 feet, succeeded by 

100 feet of less indurated slate, grading up into the original red shale.

The metamorphic effects above and below the contact differ in 

intensity as well as in kind; above the contact the induration and 

decoloration characterize only about 100 feet of strata; below the 

contact they extend through 300 feet. Above the contact the strata 

have been baked and decolored only, the red shale changing to a blue 

slate; below the contact considerable silica has been added, transforming the red shales to blue and black jaspers; added to this are the 

effects of baking and decoloration.

The Hakatai formation is characterized by argillaceous shales in 

its lower portion, which grade upward into arenaceous shales and 

sandstones through the interesting series of alternations described in 

division B. Nearly every stratum in the formation bears marks of 

shallow-water origin sun cracks, ripple marks, or cross bedding.

SHINUMO QUARTZITE.

The following section, of the Shinumo quartzite was made in the 

canyon of Shinumo Creek (see Pis. VIII, A, p. 28, and XII, B), 

whence the name of the formation is derived:

Section of Shinumo quartzite in Shinumo Canyon.

A. Irregularly bedded sandstone: Feet.

1. Cross-bedded green sandstone............................ 21

2. Banded purple sandstones............................... 20

3. "Curiously twisted and gnarled layers" of fine-grained 

white sandstone containing large red spots of circular 

and elliptical form. The upper part of the bed is 

more, massive. The twisted and gnarled structure 

seems to have been a phenomenon of the original
52 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

Feet, 

deposition and suggests that the original sand was

moist and plastic and once flowed by rolling over and

over in the form of a quicksand. ..................... 105

(A bed of this character is described by Walcott in his 

section in Unkar Valley. (Walcott, Fourteenth Ann. 

 Kept. U. S. Geol. Survey, p. 511.) It occurs at the 

same horizon as the bed described above and contains 

the same red spots.) 

B. Banded white quartzite................................... 20

C. Compact cliff-forming white quartzite of the same character

as G below, though not so massive in structure........... 250

D. Fine-grained purple sandstone with a white band in the 

middle. The white band is constant and is a conspicuous feature by which this sandstone can be distinguished 

at a distance of several miles. The rock is cross bedded 

and in some places displays a " twisted and gnarled" 

structure................................................ 150

E. Banded white quartzite, stained magenta on the exposures

and forming a cliff....................................... 120

F. Purple-brown fine-grained sandstone containing lenses of

conglomerate and thin beds of shale....................... 353

G. Compact white quartzite of fine and uniform grain, displaying a faint cross-bedded structure. This quartzite is the 

most resistant rock in the formation. It is exposed everywhere in one massive perpendicular cliff face, which does 

not display the slightest break except where it is cut 

by faults. Wherever its base rests upon a shaly lens its 

under surface displays well-preserved mud cracks. The 

face of the cliff is stained magenta by the ferruginous 

cement that washes down from the shale lenses in the overlying sandstones......................................... 119

H. Purple-brown sandstone of fine grain containing in some 

places an occasional lens of fine conglomerate 'and a thin 

local bed of red or purple shale. Cross bedded throughout.. 406

1,564

An examination of slides cut from several specimens of the sandstones and quartzites showed that they consist of small rounded 

quartz grains, few of which exceed 0.7 millimeter in diameter. This 

extreme fineness and roundness of the grains, as well as the cleanness 

of the sorting, is remarkable. The cement is generally siliceous, in 

places slightly ferruginous. A slide made from a specimen taken 

from one of the small conglomerate lenses in division H showed that 

the rock consisted of small rounded quartz pebbles lying in a fine 

arkose matrix, and disclosed also occasional large angular fragments 

of orthoclase and microcline.

The Shinumo quartzite (PI. XII, A) is the most resistant rock in 

the Grand Canyon series, its beds forming the Algonkian monadnocks, 

which appear in all parts of the Grand Canyon. In the canyons that 

are cut across the strike of the strata, such as the deep canyons of the
U. S. GEOLOGICAL SURVEY

^1. SHINUMO QUARTZITE NORTH OF CABLE CROSSING, 

Sti, Shinumo quartzite; //, Hakatai shale; (/, Diabase intrusive.

^?, QUARTZITE IN CANYON OF SHINUMO CREEK. 

Shinumo Garden, irrigated from Shfnumo Creek, is shown in lower right corner of view.
PEOTEEOZOIC BOOKS. 53

Shinumo, these beds stand in great plunging cliffs (Pis. VIII, A, 

p. 28, and XII, B).

The Shinumo quartzite includes great thicknesses of pure, fine-, 

grained, uniform sandstone. All its beds are very resistant and form 

cliffs, and many of them show ripple marks and cross bedding.

DOX SANDSTONE.

The name Dox sandstone is derived from Dox Castle, underneath 

which a typical section is found beneath the formations of the Tonto 

group, which make the castle. The following section Was measured 

on the west side of the canyon of Shinumo Creek (PI. XIII, J9):

Section of Dox sandstone in Shinumo Canyon.

Feet.

A. Red and vermilion micaceous shaly sandstones, cross bedded 

and ripple marked, with arenaceous and argillaceous shaly 

partings, which display well-preserved mud cracks. The 

shaly partings are either green or red..................... 1,197

B. Gray-green, pinkish-green, and brown micaceous shaly sandstones, cross bedded and ripple marked, varying in character only through gradations in color. Many arenaceous 

and argillaceous shaly partings occur, causing the rock to 

weather like a soft sandy shale. Most of the shale partings are green. Some of the sandy layers near the base 

show a " gnarled and twisted structure"............... 1,100

2,297

The beds above the top of this section have been removed by erosion, the top of the highest bed of division A marking the plane of 

the pre-Tonto unconformity. The highest beds of this division lie at 

the upper end of the dry wash that joins the canyon of Shinumo Creek 

from the north just below the mouth of White Creek. The beds are 

dragged up against the Vishnu schist by the great pre-Cambrian 

fault, and the whole series is overlain by the basal (Tapeats) sandstone of the Tonto group. (See PL I, sections, in pocket.)

The Dox sandstone may be summarized as a series of micaceous 

shaly sandstones of uniform character, varying only in color and bearing marks of shallow-water origin throughout.

COMPARISON WITH TYPE SECTION IN UNKAR VALLEY.

A comparison of the above section of the Unkar group with that 

described by Walcott * in the type locality, 30 miles to the east, 

reveals the fact that the two sections correspond closely in thickness 

and in lithologic succession; only in their lower parts do they differ 

materially. The type section in Unkar Valley is characterized by a 

greater thickness of the basal conglomerate and by only a third as

i Walcott, C. D., Pre-Cambrian igneous rocks of the Unkar terrane, Grand Canyon of the Colorado, 

Arizona: U. S. Geol. Survey Fourteenth Ann. Kept., pt. 2,497-519,1894.
5.4 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT. ARIZ.

much limestone in the members that correspond to the Bass limestone; the deficiency in limestone is made up by a greater thickness 

of arenaceous and argillaceous shales. The beds farther up in the 

section, in that division of Walcott's section which corresponds to 

the Hakatai shale, contain a greater proportion of sand. The succeeding members correspond closely in character and thickness even 

to the minor divisions, an example being the "gnarled and twisted 

layers" previously cited.

The writer had the privilege of examining Mr. Walcott's field specimens in the National Museum at Washington and was particularly 

impressed by their absolute lithologic identity with the series collected by himself from corresponding horizons on Shinumo Creek. 

The two series of specimens, those of rocks altered by local metamorphic phenomena, might have come from the same locality.

AGE AND CORRELATION OF THE GRAND CANYON SERIES.

By the usage of the United States Geological Survey the Grand 

Canyon series is referred to the Algonkian system. It has been tentatively correlated with the Keweenawan series of the Lake Superior 

region by Walcott, 1 and according to Darton 2 it may also be correlated with a series of Algonkian rocks that occur in the Fort Apache 

region in Arizona.

During the summer of 1909 the writer had the opportunity of 

studying the rocks of the San Juan Mountains in southwestern Colorado, under the direction of Mr. Whitman Cross, and was particularly impressed with the similarity of the Needle Mountains group 

(Algonkian) to the Grand Canyon series, both in stratigraphic position 

and general lithology.3 Like the Grand Canyon series, the Needle 

Mountains group (consisting of the Vallecito conglomerate below and 

the Uncompahgre formation, composed of quartzites and slates, 

above) rests unconformably upon a very old metamorphic complex 

and is likewise separated from an overlying Cambrian sandstone by 

a great angular unconformity which represents a base-leveled surface 

of erosion and truncates the pre-Cambrian structure as completely as 

does the pre-Tonto unconformity in the Grand Canyon region. The 

basal Cambrian sandstone of the San Juan region is similar in every 

respect to the basal (Tapeats) sandstone of the Tonto group and 

should doubtless be correlated with that formation. Lithologically 

the Needle Mountains group resembles the Grand Canyon series in 

the great amount of cross-bedded quartzitic sandstone it includes, 

but it differs from the Grand Canyon series in containing a great 

thickness of coarse conglomerate in its basal part and in exhibiting

1 Walcott, C. D., Pre-Cambrian igneous rocks of the Unkar terrane, Grand Canyon of the Colorado: U. S. 

Geol. Survey Fourteenth Ann. Kept., pt. 2, p. 518,1894.

2 Darton, N. H., A reconnaissance of parts of northwestern New Mexico and northern Arizona: U. S. 

Geol. Survey Bull. 435,1910. 

»Cross, Whitman, U. S. Geol. Survey Geol. Atlas, Needle Mountains folio (No. 131), 1905.
U. 8. GEOLOGICAL SURVEY

A. VIEW NEAR CABLE CROSSING, LOOKING DOWN COLORADO RIVER. 

V, Vishnu schist; B, Bass limeslone; //, Hakatai shale (jasper); d, Diabase intrusive.

. DOX SANDSTONE IN CANYON OF SHINUMO CREEK, OVERLAIN UNCONFORMABLY BY TAPEATS 

SANDSTONE OF THE TONTO GROUP,

D, Dox sandstone; T, Tapeats sandstone; M, Muav limestone; R, Redwall limestone. Photograph by N. W.

Carkhuff.
U. S. GEOLOGICAL SURVEY 

A. SHINUMO CREEK.

LOWER CONTACT OF DIABAS

//, Hakatai shale, here converted to jasper; d, Diabase; T
PROTEROZOIC ROCKS. 55

metamorphism by pressure, whereas the Grand Canyon series is 

unaltered. In the opinion of the writer there is little doubt that the 

Needle Mountains group is the correlative of the Grand Canyon series.

INTRUSIVE DIABASE ASSOCIATED WITH THE UNKAR GROUP.

OCCURRENCE.

The diabase in the Shinumo quadrangle occurs in the form of 

intrusive sheets, or sills, which lie between the beds of the Unkar 

group.

In the uppermost part of division A of the Dox sandstone are four 

thin sills of diabase, the largest less than 25 feet thick, which are 

extremely rotten, weathering green and crumbling to small fragments. They occur between vermilion beds of sandstone and shale, 

and their intrusive character is shown by the fact that the vermilion 

beds are baked and decolorized for a few inches above and below the 

diabase, the vermilion color having been changed to purple. The 

diabase of these sills is too much weathered to permit an exact petrographic determination of its character in a thin section.

The greater part of the diabase forms a single mass, which occurs 

at three or more stratigraphic horizons in the sediments of the Unkar 

group in different parts of the quadrangle. (See Pis. XIII, A, XIV, A 

and B, and XVIII, p. 86.) In Hakatai Canyon, 3 miles west of Shinumo Creek, it lies within the Bass limestone. On the east side of Hakatai Canyon it rises out of the Bass limestone and enters the Hakatai 

shale, breaking clean across the edges of the intervening strata. 

Most of the lower and part of the upper contact of the eruptive rock 

are clearly displayed in the walls of this canyon. Between the 

exposures in Hakatai Canyon and the main exposures of the Unkar 

group about the mouth of Shinumo Creek the pre-Cambrian structure 

is hidden beneath the basal (Tapeats) sandstone of the Tonto platform. In all the region about the mouth of Shinumo Creek the 

diabase lies within the Hakatai shale at a horizon 400 feet above that 

at which it occurs in the Bass limestone in Hakatai Canyon. (See 

Pis. XIII, A, and XIV, A and 5.) East of Hotauta Canyon, on 

the Colorado, the Unkar structure is again hidden beneath the Tonto 

platform, but about 3 miles up the river from Hotauta Canyon 

small outcrops of the basal formations of the Unkar group are again 

exposed in the intercanyon valleys on both sides of the river, where 

the lower contact of the diabase lies just at the summit of division 

B of the Bass limestone.

So much of the exposed portion of the sill is traversed by faults 

that lie parallel to the strike of the strata that it is impossible to 

measure it exactly. Its thickness reaches a maximum of about 

1,000 feet on the west side of the Hakatai Canyon and decreases 

gradually eastward.
56 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

PETROGRAPHY.

Megascopic features. Fresh specimens typical of the greater part 

of the mass show that the diabase is a tough, heavy, holocrystalline 

rock of medium to coarse grain and of gray color. The minerals 

visible to the unaided eye are plagioclase, olivine, augite, and an 

occasional grain of magnetite. Although the olivine exceeds the 

augite in amount, it is less conspicuous to the eye. Aside from a 

somewhat waxy luster of the feldspars the rock is remarkably fresh. 

The weathered surface has a characteristic warty appearance, 

imparted by the presence of lumps or balls which are more resistant 

than the mass of the rock and of coarser grain and different texture. 

These lumps and balls consist of coarse ophitic intergrowths oi; augite 

and plagioclase. The diabase weathers by mechanical disintegration 

to a greenish-olive sand, in which lie innumerable lumpy kernels of 

all sizes derived from the ophitic masses described above. The rock 

has no typical columnar structure, but generally displays a rough 

vertical jointing, such as is characteristic of granite.

Microscopic features. The slides examined show that the typical 

rock consists primarily of plagioclase feldspar (near labradorite) and 

olivine in about equal amounts, a subordinate quantity of augite and 

brown biotite, and very little magnetite. The feldspar is somewhat 

altered, but all the other minerals are fresh. The olivine occurs 

characteristically in rather large rounded crystals of automorphic 

habit. The augite is confined chiefly to the globular masses, which 

weather out as lumps and kernels, and does not characterize the rock 

as a whole. Slides cut from these kernels show that they are composed entirely of augite and feldspar. The augite is inclosed within 

the feldspar, displaying fine examples of ophitic texture. Several of 

the magnetite crystals have rims of brown biotite. The small amount 

of magnetite is rather remarkable, and it seems likely on this account 

that the olivine is rich in magnesia. Because of the predominance 

of olivine and plagioclase in the greater part of the rock, the diabase 

is classified as an olivine diabase with a troctolitic aspect.

VARIATIONS IN CHARACTER.

All parts of the mass are subject to variations in texture and composition toward a coarser grain. These variations are of two types. 

The first type occurs in the ophitic intergrowths of augite and plagioclase of the lumps and balls described above, and is a segregation 

phenomenon characterizing the mass as a whole. In some places 

this texture becomes very coarse, the separate crystals of augite or 

plagioclase being an inch in length. The second type occurs in 

typical pegmatite dikes, which cut the diabase in many places and 

vary in width from a few inches to several feet. The minerals are
PBOTEROZOIC BOCKS. 57

plagioclase and augite and the texture is usually, but not invariably, 

ophitic. In some, of these dikes crystals of plagioclase exceeding 3 

inches in length were observed.

The contact f.acies of the diabase are in places fine grained or 

glassy, but for only a few inches from the contact. The slides typical 

of this zone- reveal a hyalopilitic arrangement of glass, with skeleton 

crystals of magnetite between much altered crystals of feldspar.

For about half a mile east and half a, mile west of the canyon of 

Shinumo Creek a pink holocrystalline rock of medium grain occurs 

in the upper part of the diabase sill along the upper contact. Its 

contact with the overlying blue slates is sharp and well defined, and 

it appears to grade downward into the normal diabase, no definite 

line of contact having been anywhere observed.

A slide cut from a specimen taken from the middle of a pink mass 

of the sill showed that it is a granular rock of medium texture, consisting of rather fresh crystals of orthoclase, with subordinate quartz 

and a somewhat altered ferromagnesian mineral, which appeared to 

have been originally a hornblende. Some of the quartz displayed a 

micrographic arrangement within the feldspar. The rock is a typical hornblende syenite and is apparently an interesting example of 

differentiation in place within the diabase sill.

In Hakatai Canyon both the lower and upper eruptive contacts of 

the diabase are ragged and considerably injected. Many small dikes 

penetrate the country rock from the main mass. They are glassy in 

texture and greatly altered.

Ransome 1 describes a diabase of post-Carboniferous age occurring 

in thick sills in the pre-Carboniferous sedimentary rocks in the Globe 

Copper district in Arizona. This diabase closely resembles the Algonkian diabase described above both in mineralogic character and in 

the presence of the ophitic balls of plagioclase and augite. The 

analogy is made the more striking by the fact that several small 

masses of pink hornblende syenite are described as occurring within 

the diabase sills of the Globe district, possibly as segregations within 

the diabasic magma.

CONTACT METAMORPHISM.

As the diabase sill occupies different horizons in the Unkar group 

in the canyon of Shinumo Creek and in Hakatai Canyon, and as the 

strata between which the sill is intruded in Shinumo Canyon lie in 

undisturbed sedimentary contact in Hakatai Canyon, and vice versa, 

the effects of the intrusion on the invaded strata can be easily noted.

The contact effect upon the shales that lie above and below the 

diabase along Shinumo Creek has already been described in the

» Ransome, F. L., Geology of the Globe Copper district, Arizona: U. S. Geol. Survey Prof. Paper 12. 

p. 80 et seq., 1903.
58 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ,ARIZ.

detailed section of the Unkar group, where the shales were shown to 

be altered to jaspers by baking and silicification (PI. XIV, B). The 

intensity of metamorphic action was much greater below the sill 

than above, extending through 300 feet of strata below the lower 

contact and through only 100 feet above the upper contact. In 

Hakatai Canyon these rocks lie in undisturbed sedimentary contact 

and are there unaltered red shales.

The contact effect on the limestones can be studied in Hakatai 

Canyon, .where the diabase sill lies intruded within them. Immediately below the lower contact of the diabase, which is sharp and 

well defined, is a thin layer of green serpentine. Below he layers of 

pure crystalline limestone (dolomite) alternating with similar layers 

containing bands and nodules of serpentine. Within one of the 

layers containing the bands and nodules of serpentine are cross-fiber 

veins of golden-yellow chrysotile asbestos, which are parallel in general trend to the bedding of the limestone. These limestones are 

the layers at the base of division B of the Bass limestone. They 

overlie the red shales of division C, which are here baked to blue 

slates.

The following section, including a part of the Bass limestone 

beneath the lower contact of the diabase - near the tunnel of the 

Asbestos mine in Hakatai Canyon, shows effect of local metamorphism in the strata. The numbers of the beds correspond (so far as 

the beds can be identified) to the numbers used in the detailed section of the Unkar group (pp. 40-53). The printed section represents 

the natural order, B,'24, 25, being at the top.

Section of part of the Bass limestone beneath diabase sill at the Asbestos mine in HaJcatai

Canyon.

-Ft. in.

Diabase sill............................................... 1,000±

B, 24, 25. Layer of green serpentine........ .^.............. 2

Pure white crystalline limestone................ 1 6

White crystalline limestone, with bands and 

nodules of serpentine......................... 2

Serpentinous nodular and .banded layer carrying 

veins of asbestos.............................. 1

Banded crystalline limestone, with bands and 

nodules of serpentine......................... 10

B, 26, 27. Nodular cherty limestone....................... 4

C, 1. Soft blue slate................................. 3

0,2. Dense purple calcareous slate.................... 9

ASBESTOS.

Occurrence. The limestones above the upper contact of the diabase contain several alternating layers of green serpentine and 

narrow veins of asbestos, which occur at several horizons near the 

contact.
PROTEROZOIC ROCKS. 59

The geologic occurrence of the asbestos is fully described by 

Diller.1 A microscopic study was made of 25 thin sections cut 

from the limestones, the bands and nodules of serpentine, and the 

veins of asbestos. Aside from the serpentine and asbestos no other 

minerals were revealed in the limestones than the dolomitic calcite 

and interlocking grains of quartz in the slides cut from the limestones of the same horizon in the section in Hotauta Canyon, where 

the same strata he in undisturbed sedimentary contact. The 

limestones have the texture of marble. The serpentine of the bands 

and nodules shows no trace of alteration in structure due to deriva-. 

tion from pyroxene, hornblende, or olivine. The slides cut across 

the veins of asbestos showed that they are later than the serpentine 

in which they are generally inclosed. A great number of microscopic veins of asbestos were revealed in some of the slides where 

their presence was unsuspected. Some of these veins cut across 

both the sepentine and the limestone in the same slide.

The asbestos in the larger veins is of high grade and is said by 

Diller to be the best yet found in the United States.2 Locally its 

cross fiber is 4 inches in length and is of great tensile strength. The 

larger veins, so far as known, are confined to the limestones that lie 

beneath the diabase sill, the veins above the sill, though more widely 

distributed through the limestones, being generally smaller. The 

veins below the sill are not absolutely constant in stratigraphic 

position; they may lie anywhere from 3 to 15 feet below the contact. 

The width of these veins varies greatly from place to place, so that 

a vein that is 3 inches wide in one locality may be represented by a 

zone of innumerable small veins in another, but the actual continuity 

of the zone that carries the asbestos is rarely broken.

Origin. The limestones contain serpentine and asbestos only 

where the strata are invaded by the diabase sill; the shales that are 

invaded by the diabase do not contain these minerals, which in no 

place in the area occur within the diabase itself. They are therefore 

a product of the contact metamorphism.of the limestones by the 

diabase, and, as Diller suggests,3 the serpentine that incloses the 

veins of asbestos is probably derived from some mineral in the 

limestones and not from the diabase. The limestones themselves 

are magnesian and contain bands and nodules of chert. In another 

part of the area the shales in contact with the diabase were converted 

to jaspers, the change indicating that the fumarolic action accompanying the injection of the diabasic magma was characterized by 

aqueous and probably siliceous emanations and was fairly intense.

i Diller, J. S., U. S. Geol. Survey Mineral Resources, 1907, pt. 2, pp. 720-721,1908; idem, 1908, pt. 2, p. 705, 

1909.

« Diller, J. S., U. S. Geol. Survey Mineral Resources, 1908, pt. 2, p. 705,1909. 

n Diller, J. S., loc. cit.
60 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

The fumarolic action on the magnesian limestones may have converted their more siliceous portions into serpentine. The occurrence of the asbestos in veins that cut across both the nodules of 

serpentine and the limestones shows that the cross-fiber asbestos 

was formed somewhat later in the sequence of events attending the 

fumarolic action.

AGE OF THE DIABASE.

The sills of diabase are displaced by the faults of the wedge in the 

same manner as the inclosing strata, the invasions having evidently 

occurred before the faulting. (See PI. I, sections, in pocket.) The diabase of the Shinumo quadrangle is closely related in chemical and mineral composition to the basalt of the lava flows described, by Iddings,1 

which are interbedded with the sediments of the upper part of the 

Unkar group in the type section in Unkar Valley. As the diabase 

lies at a much lower horizon than the lava flows, it is probably an 

intrusive rock of the same cycle of igneous activity, the sills and 

flows being probably contemporaneous.

PALEOZOIC ROCKS. 

RESULTS OF PREVIOUS WORK IN THE REGION.

In a large and general way the distribution and broader character 

of the Paleozoic rocks of the Grand Canyon are familiar to every 

geologist through the writings of Newberry, Ives, Powell, Gilbert, 

Button, and Walcott. 2 A thorough analysis of their topographic 

and scenic expression in the canyon has been made by Davis.1

The details of the stratigraphy, however, are not yet known. Sections have been made at several widely separated places in the canyon wall in the eastern part of the Kaibab division, by Walcott and 

by Frech; at Kanab Canyon, in the Kanab division, by Walcott; 

and at Diamond Creek and at the Grand Wash, in the Shivwits division, by Gilbert. 2 A recent report by Darton 2 gives a compilation 

of these sections and some additional data collected by himself at 

many points in the region. In all these sections and in this report 

certain groups of strata, particularly the Tonto, are given in detail, 

but no single section includes all the beds of all the groups in the 

Paleozoic rocks at any one place. A close and accurate comparison and correlation of the thickness and character of the Paleozoic 

formations from place to place in the Grand Canyon must therefore 

depend on the results of future detailed work at many points.

i Walcott, C. D., Pre-Cambrian igneous rocks of the Unkar terrane, Grand Canyon of the Colorado, Arizona, with notes on the petrographic character of the lavas, by J. P. Iddings: U. S. Geol. Survey Fourteenth Ann. Kept., pt. 2, pp. 520 et seq., 1894.

»See Bibliography, pp. 13-15.
PALEOZOIC BOCKS. 61 

GENERAL SUCCESSION OF THE PALEOZOIC HOCKS.

At the base of the Paleozoic is the Tonto group, of Cambrian age. 

This group is divisible into three formations. At the base, resting 

in some places upon Archean and in other places upon Algonkianrocks, is the Tapeats sandstone. Overlying the sandstone is the 

Bright Angel shale, containing Middle Cambrian fossils. The highest 

formation of the group is the Muav limestone. No representatives 

of the Ordovician, Silurian, or Devonian were discriminated in the 

area studied, the Muav limestone being succeeded without apparent 

stratigraphic break by the Redwall limestone, of Carboniferous age. 

The Kedwall limestone is overlain by the Aubrey group, which is also 

of Carboniferous age, and is divisible into three formations. At the 

base of the Aubrey group is the Supai formation composed of sandstone and shale, which is in turn overlain by the Coconino sandstone. 

The highest formation of the group, and likewise of the Paleozoic in 

the quadrangle, is the Kaibab limestone, containing a Pennsylvanian 

fauna. (See PL XVIII, p. 86.)

CAMBRIAN SYSTEM.

TONTO GKOUP. 

TAPE ATS SANDSTONE.

The Tapeats sandstone rests upon an eroded surface which bevels 

the upturned and truncated edges of the Vishnu schist and Grand 

Canyon series. This unconformity is in plain view in the walls of 

the Granite Gorge throughout the entire Kaibab division of the 

canyon and is probably the clearest and most spectacular illustration 

of such a geologic feature in the world. Except in localities where 

remnants of Algonkian strata are preserved, the Tapeats sandstone 

in this division everywhere rests upon Archean rocks, yet we know 

from the record in the Vishnu quadrangle that at least 12,000 feet of 

Algonkian strata was deposited horizontally upon the Archean and 

that these Algonkian rocks were profoundly tilted and faulted before 

they were eroded away. So vast was the erosion that all but a few 

remnants of Algonkian strata were removed and the Archean rocks 

make the greater part of the floor on which the Tapeats sandstone 

was laid. down. This floor, like that upon which the basal strata of 

the Unkar group were deposited, represents a surface base-leveled 

by erosion. This surface was not nearly so even as that represented 

by the more ancient pre-Unkar unconformity, yet it formed a comparatively level plain. Here and there a knob of more resistant 

Archean rock projects into the Tapeats sandstone, and in Monadnock 

amphitheater the rocks of the Unkar monadnock project 600 feet
62 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

above the base of the sandstone, almost cutting out the overlying 

Bright Angel shale, but the relief of even these exceptional projections is small in comparison with the horizontal extent of the floor.

The name Tapeats sandstone is derived from Tapeats Creek, below 

the mouth of which, just north of the Shinumo quadrangle, the bed 

of the Colorado River lies within this formation.

The Tapeats sandstone shows little variation in lithologic character in the Kaibab division. The following is a typical section in the 

Shinumo quadrangle (reading from the top downward, A being the 

top bed, underlain by B and C):

Section of Tapeats sandstone.

Feet. 

A. White cross-bedded sandstone containing "Scolithus".......... . 35

B. Shaly brown or greenish sandstone............................ 50

C. Brown slabby sandstone or pebbly grit, composed chiefly of 

particles of quartz and characterized by cross bedding. The 

basal portion generally includes beds of coarser grit, or con-- 

glomerate, made up of the harder fragments of the underlying 

rocks. Most of the pebbles are rounded. The member contains here and there thin lenses of shale. The sandstone is 

commonly indurated to quartzite and the entire member is 

very resistant to erosion and makes a conspicuous brown cliff 

along the rim of the Granite Gorge. The thickness depends 

on the relief of the underlying surface; where greatest it is... 200

285

No fossils were found in the formation.

Within the Tapeats sandstone is a record of marine planation that 

in these vertical sections, which include no soil, is preserved with a 

clearness that is almost beyond belief. The long southwestern face 

of the Unkar island monadnock was undercut by the waves of the 

sea in which the sandstone was deposited, and a cross section of this 

old sea cliff preserved in the Tapeats sandstone in the southern wall 

of Hotauta Canyon near the Colorado reveals clearly every detail of 

the structure; at the base of the cliff huge angular blocks of Shinumo 

quartzite are incorporated in the Tapeats sandstone in the places 

where they fell and lodged; farther out lie masses of bowlders, worn 

and rounded by the pounding of the waves; and these bowlders run 

into lenses of fine pebbly conglomerate, representing the shingle of 

the ancient beach, dragged out by the undertow. No more striking 

example of a fossil sea cliff can be imagined.

BRIGHT ANGEL SHALE.

The name of the Bright Angel shale is derived from Bright Angel 

Canyon, in the walls of which the formation is well exposed.

The section following was measured on the north side of Colorado 

River between Hakatai and Burro canyons, in the central part of 

the Shinumo quadrangle.
PALEOZOIC ROCKS. 63

Section of Bright Angel shale on north side of Colorado River between Hakatai and Burro

canyons.

A. Upper division (alternating layers of shale and purplish-brown 

sandstone in upper part; soft, greenish, micaceous sandy 

shales below; the lower part makes a moderate slope and the

upper part a steep slope):

Feet.

1. Shale...................................................... 16

2. Sandstone................................ 1............... 2

3. Shale...................................................... 16

4. Sandstone................................................ 3

5. Shale..................................................... 6

6. Sandstone..........................................:.... 1

7. Shale..................................................... 5

8. Sandstone................................................ 2

9. Shale...................................................... 80

131

B. Middle division (locally known as "Snuffy limestone" ; two 

cliffs of resistant limestone separated by a slope of soft shale; 

see PI. XVIII, p. 86): .

1. Dense snuff-colored limestone, somewhat sandy, with platy 

partings................................................ 10

2. Very dense, snuff-colored crystalline limestone............. 12

3. Soft shales, including a very thin layer of glauconite(?) containing linguloid brachiopods........................... 25

4. Limestone like 2.......................................... 10

57

C. Lower division (soft, green, micaceous sandy shales with occasional thin layers of resistant sandstones, which form small 

cliffs; the entire division makes a very gentle slope):

1. -Cross-bedded greenish sandstone ........................... 6

2. Extremely soft shales with a few very thin interbedded layers 

of fossiliferous sandstone and phosphatic limestone, made 

of the shells of linguloid brachiopods. A layer of glauconite (?) a few inches thick occurs in the center of the shales. 75

3. Sandstone, containing fossils.............................. 1

4. Shale..................................................... 7

5. Sandstone................................................ 2

6. Shale..................................................... 9

7. Cross-bedded brown sandstone, containing fossils............ 3

8. Shale..................................................... 55

9. Reddish-brown quartzite, in many places conglomeratic..... 2

160 

Total thickness of Bright Angel shale................... 348

Most of the fossils were found in certain layers of brown sandstone, indicated in the section, but some were collected from the 

shales, through which fossils are also scattered, though much less 

abundantly. All the specimens found in the sandstones bear marks 

of grinding and attrition.
64 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

The following forms were identified: By Prof. Schuchert: Worm 

trails; Lingulepis spatulus; Lingulella acutangula. By Mr. Walcott: 

Obolus westania, var. themis. By Mr. Bassler: Phyllopod Indiana 

fala U. and B.

In addition, Mr. Walcott collected at the same horizon in the Shinumo quadrangle in 1901 numerous worm trails, Lingulella limolata, 

Lingulella perattenuata, and Lingulepis spatulus.

These fossils show that the Bright Angel shale is of Middle Cambrian age. Whether the underlying unf ossiliferous Tapeats sandstone 

represents the Middle or the Lower Cambrian system is not yet known. 

Walcott* thinks it probable that the erosion interval represented by 

the unconformity at the base of the Tapeats sandstone represents 

the whole or a large part of the Lower Cambrian.

The Bright Angel shale, like the formations of the Unkar group, 

is characterized by curious circular or elliptical spots that appear 

throughout all the shaly and sandy strata, some caused by local 

leaching, some by local addition of a ferruginous mineral.

MUAV LIMESTONE.

The name of the Muav limestone is derived from Muav Canyon, 

in the lower part of which the formation is particularly well exposed. 

(See PI. XV, A.) It designates the predominantly calcareous part of 

the Tonto group.

The limestones of the formation are of a peculiar and distinct type. 

Characteristically, they are impure thin-bedded bluish-gray limestones which have a mottled appearance, imparted by infinitely 

numerous thin bands or lenses of buff or greenish shaly material. 

By this mottling and the thin banding the formation can be readily 

distinguished at a distance. On closer inspection the limestones are 

seen to contain numerous imperfect coralloid or fucoidal markings. 

The upper part of the formation contains layers of sandstone and 

some layers of massive buff crystalline limestone, but most of the 

beds are slightly impure and mottled. The shaly material of the 

mottlings is locally finely micaceous, and in places the rock comprises 

more shale than limestone. In other places the formation contains 

layers that have the appearance of a shale conglomerate, made up 

of rounded, flattened fragments of shale and limestone. Some of the 

fucoidal mottlings are composed of buff or green shale and some 

layers of the limestone are cherty. Infinite variations of all phases 

occur throughout the formation. The sandstones and the purer portions of the limestones make cliffs and the impure portions make 

slopes. The upper part of the formation unites with the layers at 

the base of the overlying Redwall limestone to form the lower part 

of a single great cliff.

i Walcott, C. D., Pre-Cambrian igneous rocks of the UrLkar terrane: U.S. Geol. Survey Fourteenth Ann. 

Kept., pt. 2, p. 518,1894. . - .
U. S. GEOLOGICAL SURVEY 

A. MUAV LIMESTONE IN MUAV CANYON. B. F
PALEOZOIC BOCKS. 65

The following section was measured in Bass Canyon:

Section of Muav limestone.

Feet.

Massive layers of buff crystalline limestone (cliff)................. 30

Fine-grained calcareous buff sandstone (cliff)..................... . 90

Sandy mottled limestone (steep slope)............................ 85

Fine buff sandstone............................................. 5

Mottled limestone (cliff)......................................... 200

Impure shaly mottled limestone,.fine-grained buff sandstone, and 

snuff-colored crystalline limestone in thin laminae............... 45

 455 -

No fossils were found in the Muav limestone in the Shinumo 

quadrangle. The similarity in lithologic character, however, leaves 

little doubt that the beds are the same as those of the "mottled 

limestone" (earlier nomenclature), from which Walcott collected an 

abundant Middle Cambrian fauna both in Kanab Canyon, farther 

west, and in the eastern part of the Kaibab division.

CORRELATION OF TONTO GROTTO.

According to Ransome, 1 the Tapeats sandstone is apparently 

equivalent to the Apache group of the Globe district, to the Coronado 

quartzite of the Clifton district, and to the Bolsa quartzite of the 

Bisbee district. The Bright Angel shale and the Muav limestone 

are apparently represented by the Abri'go limestone of the Bisbee 

region.

UNCONFORMITY.

In certain parts of the .Grand Canyon, both east and west of the 

Shinumo quadrangle, the Cambrian Muav limestone is separated from 

the overlying Carboniferous Redwall limestone by a peculiar unconformity of erosion without unconformity of dip. The studies that 

revealed the presence of this unconformity were made by Walcott.

In Kanab Canyon, 20. miles west of the Shinumo quadrangle, 

Walcott 2 reports the presence of Devonian beds separated by a 

strong line of erosion from the underlying Cambrian and by a similar 

line of erosion from the overlying Redwall. The writer had the 

privilege of examining sketches made by Mr. Walcott showing the 

details of these unconformities. In one place canyons 80 feet deep 

were eroded in the "mottled limestone" (Muav limestone) and these 

depressions were filled by limestones and sands containing a Devonian 

fauna.

1 Ransome, F. L., A comparison of some Paleozoic and pre-Cambrian sections in Arizona: Science, new 

ser., vol. 27, p. 69,1908.

aWalcott, C. D., The Permian and other Paleozoic groups of the Kanab Valley, Arizona: Am. Jour. Sci.,. 

3d ser., vol. 20, pp. 221-225,1880.

29745° Bull. 549 14 5
66 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

The observations of Walcott at the east end of the Kaibab division 

reveal a similar condition. He writes: 1

In places the Devonian is entirely absent, either through erosion or nondeposition, 

so that the Red wall limestone rests directly upon the massive calciferous strata of 

the upper Tonto. It rarely has a thickness of more than 100 feet. v

In the south wall of the Grand Canyon between Ruby Canyon, in 

the Shinumo quadrangle, and Pipe Creek, in the Bright Angel quadrangle, the unconformity between the Muav limestone and the 

Eedwall is well marked and in many places Devonian beds lie in 

small hollows eroded in the Muav limestone. These Devonian beds 

are clearly separated from the underlying Muav and from the overlying Redwall by unconformities of erosion. In the Shinumo 

region, however, this double unconformity is not clearly evident, 

and in order to determine the stratigraphic relations in Bass Canyon 

with certainty it will be necessary to trace the beds at the horizon 

of the unconformity westward from Ruby Canyon into the Shinumo 

region.

CARBONIFEROUS SYSTEM.

REDWALL LIMESTONE.

The type locality for the Redwall formation is Redwall Canyon, 

in the Shinumo quadrangle. The name was applied to the formation 

long ago by Gilbert.

Because of the lack of fossils and the failure to detect the line of 

erosion that would mark a division between the Muav limestone and 

.the Redwall in Bass Canyon it has been necessary to fix tentatively 

the base of the Redwall by means of lithology. The Muav limestone 

is here overlain by alternating layers of calcareous sandstone and 

dense blue-gray crystalline limestone, which have a thickness of 

110 feet. These layers are taken arbitrarily as the base of the Redwall. The remainder of the formation comprises beds of pure, 

dense, bluish-gray crystalline limestone, the bedding of which is 

generally so obscure that they have the appearance of a single 

stratum. The bedding is thinner in the lower than in the upper part 

of this limestone. These beds of limestone appear in a single great 

cliff, the highest in the Grand Canyon. The face of the cliff is generally 

stained red by the weathering of the overlying red shales of the 

Supai formation. These obscurely bedded limestones are about 

500 feet thick in Bass Canyon.

- The cliff-making limestone of the Redwall formation has produced 

some of the most remarkable scenery in the canyon. Throughout 

the canyon the faces of the cliffs it forms are recessed with great 

niches and alcoves and are penetrated by many caves. The niches

1 Walcott, C. D., Pre-Carboniferous strata in the Grand Canyon of the Colorado, Arizona: Am. Jour, 

gci., 3d sen, vol. 26, p. 438,1883.
PALEOZOIC BOCKS. ' 67

and alcoves are described, but left unexplained, by Dutton * and are 

explained by Davis.2 Their grandest development in the region is 

found in the walls of Walthenberg Canyon, in the Shinumo quadrangle. Two of the largest caves in the Redwall are found in Bass Canyon and in the upper part of Muav Canyon.

The total thickness of the Redwall limestone in Bass Canyon is 

610 feet, of which at least 30 feet at the base is probably of Devonian 

age. , ,

The only fossils obtained in this formation by the writer were some 

obscure forms collected about 325 feet above its base in Bass Canyon. 

These comprise some cross sections of a cyathophylloid coral and 

some small brachiopods, which were identified by Prof. Schuchert 

as Schuchertella. They may belong to either a Mississippian or a 

Pennsylvanian fauna.

In Kanab Canyon, 20 miles west of the Shinumo quadrangle, 

Gilbert 8 found abundant fossils in the Recbvall and concluded that 

the base of the formation in that locality represents "Lower Carboniferous" (Mississippian) and the summit "Upper Carboniferous" 

(Pennsylvanian), time, the transition taking place without break.

Similar evidence was obtained later by Lee 4 in the western part 

of the Grand Canyon region. The paragraphs presenting this evidence 

are here quoted:

In Truxton Canyon two small collections of fossils were obtained from the Redwall 

limestone. These were examined by G. H. Girty, of the Geological Survey, who 

reports the following lists:

At Yampai, near the top of the exposed section, the following were obtained: 

Derbya (?) sp. 

Composita. 

Aviculipecten.

Myalina sp. aff. M. Meliniformis and M. cogeneris. 

Edmondia (?) sp.

These fossils, according to Girty, indicate a Pennsylvanian or "Coal Measures" age. 

Lower in. the section, near Nelson, Ariz., Mississippian forms were obtained, as 

follows:

Menophyllum excavum. 

Schuchertella inequalis. 

Spirifer centronatus. 

Spirifer striatus var. madisonensis. 

Straparollus sp.

Girty states that this is the Eo-Mississippian fauna, which has a wide range over the 

West, correlating it with the lower "Wasatch limestone of Utah, the Madison limestone of Yellowstone Park, and the Chouteau limestone of Missouri."

Lee believes that in the locality described by him the upper part 

of the Redwall is Pennsylvanian and the lower part is Mississippian,

i Button, C. E., Tertiary history of the Grand Canyon district: U. S. Gcol. Survey Mon. 2, chap. 14,1G82.

» Davis, W. M., An excursion to the Grand Canyon of the Colorado: Harvard Univ. Mus. Comp. Zool. 

Bull. 38, vol. 5, No. 4, p. 178, 1901.

« Gilbert, G. K., op. cit., p. 178.

«Lee, W. T., Geologic reconnaissance of a part of western Arizona: U. S. Gool. Survey Bull 352, p. 15, 

1908.
68 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, AEIZ.

the line of division being drawn between the upper massive and the 

lower laminated members of the formation.

The fossils found by the writer of the present report in the lower 

part of the formation in the Shinumo quadrangle are apparently 

similar to forms found in the part of Lee's section which is referred to 

the Mississippian by Girty, but correlation can not be based upon 

evidence so doubtful.

The limestone beds in which Pennsylvanian fossils were found by 

Gilbert and Lee may be the correlatives of the layers of cherty limestone that lie at the base of the Supai in the Shinumo region, and the 

line of separation between the Mississippian and Pennsylvanian may 

consequently be the base of the Supai formation in Bass Canyon, but 

until this question has been decided by further study the base of the 

Redwall may be assigned to the Mississippian and the summit to the 

Pennsylvanian.

. AUBREY GROUP.

All the strata above the Redwall limestone in the canyon wall belong to the Aubrey group. The group is divisible into three formations the Supai, the Coconino, and the Kaibab.

SUPAI FORMATION.

Liihology. This is the basal formation of the Aubrey group. The 

name was given by Darton1 and is derived from the Indian village of 

Supai in Cataract Canyon, which is designated as the type locality. 

The Supai formation is easily distinguished by its color, for it contributes most of the red to the canyon landscape. Its upper part is made 

of soft red shale, which appears in a gentle, waste-covered slope beneath the Coconino sandstone cliff. Its lower part consists chiefly 

of layers of hard sandstone, which make a long, steplike succession 

of cliffs, each of which corresponds in height to the thickness of the 

bed that determines it. The shale of the upper part wastes back from 

the summit of the sandstone of the lower part and leaves the Esplanade platform. (See Pk. VI and VII, A and B, pp. 21, 22.)

Sandstone of the Supai formation. The.basal member of the lower 

division of the Supai formation in Bass Canyon, which is about 100 

feet thick, consists of red shales alternating with beds of massive bluegray crystalline limestone containing bands and nodules of red chert. 

These beds waste back from the summit of the Redwajl, leaving a 

narrow ledge. The remainder of the lower division consists almost 

entirely of fine-grained cross-bedded sandstone. At a horizon 575 

feet above the summit of the Redwall, however, some remarkable 

beds of limestone conglomerate are here and there interbedded with 

the sandstones. The conglomerate occurs in lenses, which alternate

i Darton, N. H., A reconnaissance of parts of northern New Mexico and northern Arizona: U. S. Geol. 

Survey Bull. 435, p. 25, 1910.
PALEOZOIC BOOKS. s 69

with beds of fine red shaly sandstone. The total thickness of the 

beds that carry the conglomerate lenses is 20 feet. The pebbles, 

which are derived from a rock of much the same character as the 

massive part of the Redwall limestone, are well rounded and their 

average diameter is about an inch. The matrix is red mud. The 

thickness of the sandstone division of the Supai formation is 850 feet 

in Bass Canyon and shows little variation in the quadrangle.

SJiale of the Supai formation. The upper member of the higher 

division of the Supai formation consists chiefly of soft red shaly sandstones, which make a slope rising from the Esplanade platform and 

are largely masked by fans of gray waste shot down from the overlying Coconino sandstone. In the walls directly above Bass Canyon 

the formation is 400 feet thick but its thickness varies greatly in the 

quadrangle.

The total thickness of the Supai formation in this locality is 1,250 

feet.

In the Shinumo region the Supai formation appears to be separated 

from the underlying Redwall limestone by a slight unconformity of 

erosion. According to Darton 1 it is " distinct from the gray sandstone, [Coconino] throughout northern Arizona, but their separation 

from the underlying Redwall is not everywhere so clear as could be 

desired."

COCONINO SANDSTONE.

Darton writes: 2

The name Coconino sandstone is proposed for the cross-bedded gray to white sandstone of the Aubrey group, which is so conspicuous in the walls of the Grand Canyon. 

It underlies the entire Coconino Plateau, as well as the extensive plateau country 

north of the Grand Canyon.

The Coconino sandstone is buff to creamy-white, is of uniformly 

fine grain, and is characterized throughout by -cross-bedding. It 

forms a single great, massive bed, which makes the highest cliff in the 

upper wall of the canyon, whose white color presents a striking contrast to the red color of the shales of the Supai formation in the slope 

beneath. The huge scale of the cross-bedding is remarkable. The 

inclined beds dip in a general southerly direction and each layer is 

evenly truncated above, so that it forms a wedge. Many of the 

wedges attain a thickness of 100 feet. No ripple marks or sun cracks 

have ever been found in the Coconino sandstone and, with the exception of the Tapeats sandstone, it is the only Paleozoic formation of the 

canyon wall in which fossils have not been found. Its thickness varies 

considerably in the quadrangle and is everywhere in inverse ratio to 

that of the underlying shale of the Supai formation. Under Havasupai Point, near Bass Canyon, its thickness is 335 feet. . ...

» Darton, N. H., idem. 2 Darton, N. H., idem, p. li.
70 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

KAIBAB LIMESTONE.

Tke name Kaibab has been applied to the next highest formation 

by Darton * from the fact that it forms the surface of the Kaibab 

Plateau. The Kaibab limestone overlies the Coconino sandstone 

and is the highest formation in the canyon wall. Upon it are developed the surfaces of all the plateaus of the Grand Canyon district. 

The upper portion of the formation consists of layers of dense buff 

or cream-colored limestone, which are composed largely of the remains of sea- animals and contain great quantities of lumpy flint or 

chert. Fossil Mountain (PL VII, B, p. 22), near Havasupai Point, is 

so named because of the abundance of fossils on its southwest slope. 

The layers of limestone are very resistant to erosion and make the 

first elm0 that drops away at the rim of the canyon. The middle and 

lower portions of the formation consist of beds of sandy limestone, 

which decay more easily and make a series of weak cliffs and steep 

slopes in the wall.

The unequal hardness of the upper and middle parts of the formation has produced a curious scenic feature in the north wall of the 

canyon. Rain erosion has carved the rock into colossal pillars or 

"hoodoos," which stand like sentinels along the rim of Shinumo 

Amphitheater (PI. XVI, A, p. 78). Each pillar is preserved by a cap 

of the hard summit limestone, which protects the softer sandy limestone beneath.

The absence of surface streams on the Kaibab Plateau is due to the 

fact that its floor is made of limestone. As is usual in limestone 

regions of abundant rainfall, the rock is honeycombed by a system 

of underground drainage channels which have been dissolved by 

rain water that descends along lines of joint and fracture. In only 

a few places do the surface waters flow far before they sink and join 

this underground system, in which they continue southwestward 

with the dip of the strata and burst out as springs in the north wall 

of the canyon, feeding the perennial streams of the amphitheaters. 

The map shows small circular depressions here and there on the 

plateau. These are sink holes, each of which has in its bottom an 

outlet that communicates with the underground channels. Where 

the outlets become clogged up the sinks hold small ponds in wet 

weather. Fen Lake is one of these ponds.

Section of Kaibab limestone near Fossil Mountain, Coconino Plateau.

A. Crystalline limestone, containing many nodules of chert in its 

upper portion. The cherty layer caps the remarkable "pinnacles of erosion " along the northern rim of the canyon in the Feet. 

Kaibab division.......................................... 75

i Darton, N. H., idem, p. 28.
C PALEOZOIC ROCKS. " 71

i

j ' Feet. 

B. Very fossiliferous white crystalline limestone, forming a cliff... 200 

C. Bed of soft and crumbling calcareous sandstone, locally a conglomerate made up of fragments of soft calcareous sandstone. 20 

D. Calcareous red and white sandstones......................... 135

E. Buff, crystalline, siliceous limestone, making a cliff............ 40

F. Calcareous white sandstone, making a ledge and slope at the

summit of the Coconino sandstone ......................... 50

520

The fossils of division B are abundant wherever the beds of that 

horizon are exposed in the quadrangle. A collection made at Fossil 

Mountain and in the Muav Saddle was examined by G. H. Girty, of 

the Geological Survey, who reports that the forms comprise all those 

which are included in a similar collection in his possession obtained 

at the same horizon in the Kaibab 'limestone at Parusi-Wompats 

Spring, just north of the Shinumo quadrangle, on the Kaibab Plateau.

The list from Parusi-Wompat is as follows:

Sponges. Productus aff. irginse.

Lophophyllum n. sp. Productus subhorridus var. rugatulus?

Crinoid stems. Productus sp.

Fistulipora sp. Pugna osagensis var.

Meekopora sp. Heterelasma n. sp.

Stenopora sp. Squamularia guadalupensis?

Septopora sp. ' Spiriferina campestris?

Polypora sp. Composita subtilata.

Lingulidiscina convexa? Aviculipecten 2 sp.

Derbya sp. Acanthopecten occidentalis.

Meekella pyramidalis. Pseudomonotis aff. hawni. 

Chonetes aff. hillianus. ' Pseudomonotis? sp.

Productus occidentalis. Anisopyge perannulata? 

Productus ivesii.

In a letter concerning this fauna Girty writes:

The list is typical of the fauna of the upper Aubrey, the general character of which 

has long been known through similar lists made up by Meek and others. I have been 

tentatively .correlating the Aubrey with the Manzano group of New Mexico and with 

the upper part of the Hueco formation of western Texas. Consequently, it would be 

older than the Guadalupe group, which overlies the Hueco formation. The fauna 

listed above, however, contains a number of species which are very similar to or identical with species that occur in the Guadalupian fauna, and in spite of the fact that 

most of the Guadalupian species have not been found in the Aubrey group, it seems 

less improbable than it did several years ago, when the Guadalupian fauna was under 

investigation, that the Kaibab limestone is of the same geologic age.

VARIATION IN THE THICKNESS OF THE PALEOZOIC STRATA.

The table following shows the variations in thickness of the Paleozoic strata in the quadrangle.
Approximate thickness, infect, of the Paleozoic formations in different parts of the 

[.The letters (as NE. NW.) after each locality indicate the part of th

Supai formation : 

Shale ............................................

Bright Angel shale ...................................

Thompson 

Point 

(NW.).

600

250

550

850

700

475

375

4,065

Apache 

Point 

(W.).

600

300

550

Wheeler 

Point 

(NW. 

center).

550

300

550

850

Button 

Point, 

Masonic 

Temple 

(N. center).

600

250

450

900

700

450

375

280

4,005

Tyndall 

Dome 

(center).

625

350

285
PALEOZOIC ROCKS. 73

The Kaibab limestone varies considerably in thickness from place 

to place, but this variation is only apparent, being due to the fact 

that the summit of the formation has undergone unequal erosion in 

different parts of the quadrangle. The original thickness was probably nearly uniform. .

The Coconino sandstone decreases steadily in thickness toward the 

north and west.

The shale of the Supai formation increases steadily in thickness in 

the same directions.

The sandstone of the Supai formation varies only slightly, its 

thickness decreasing toward the west.

The Redwall limestone increases in thickness toward the north and 

west.

The Muav limestone becomes slightly thicker toward the west.

The Bright Angel shale is nearly uniform in thickness throughout 

the quadrangle except in places where the Unkar monadnock projects 

into it. Its texture becomes firmer toward the west.

The thickness of the Tapeats sandstone depends entirely on the 

relief of the underlying eroded surface and therefore shows an exceedingly irregular variation.

The total thickness of the Paleozoic system increases gradually 

toward the north and west.

EFFECT OF THE VARIATION IN THE THICKNESS OF THE PALEOZOIC STRATA UPON THE TOPOGRAPHY OF THE CANYON WALL.

The profile of the canyon wall in the Paleozoic strata everywhere 

shows a direct relation to the variations in thickness and character 

of the strata of this era. It has been emphasized that each resistant 

stratum makes a cliff and each weak stratum a slope, and that each 

ledge in the wall is made by the wasting back of weak strata from the 

summit of a resistant, cliff-making stratum below. The width of a 

ledge invariably increases with the thickness of the weak strata, and is 

also controlled by the relative thickness and strength of the overlying 

s trata which defend the retreat of the wall above. Although this relation has always been recognized in. the smaller ledges in the canyon 

wall, a different explanation of the two widest ledges, the Esplanade and 

Tonto platforms, is found in most geologic literature an explanation 

based on a theory advanced by Dutton.

Dutton * explains the Esplanade (PI. VI, p. 21) by a pause in the 

uplift of the region during the cutting of the Grand Canyon. By this 

pause a temporary base level of erosion was produced, the topographic expression of which was a mature valley whose floor was the 

Esplanade.

Again the country was hoisted, this time more than before * * *. Swiftly the 

inner gorge was scoured out and the chasm assumed its present condition.

i Dutton, C. E., op. clt., p. 121.
74 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

The reader is led to infer that the Ton to platform (PL V, p. 20) 

represents the prolongation of the same base level into the Kaibab 

division.

The physiographic studies of Davis in the canyon region, however, 

have made it clear 1 that .the Esplanade is associated with the same 

changes in character and thickness of strata that produced the 

smaller benches in the canyon; that the Esplanade may be regarded 

simply as a structural bench; and that it is not therefore necessary 

to postulate more than a single cycle for the cutting of the Grand 

Canyon.

The writer of the present report is entirely in accord with Davis. 

The Shinumo quadrangle is the critical area for the study of the 

origin of the platforms, for the profile of the canyon wall here changes 

from that which is characteristic of the Kaibab division to that 

which is characteristic of the Kanab. This change, which takes 

place opposite Havasupai Point, has already been described, and the 

variations in thickness and character of the Paleozoic strata have 

just been outlined. The perfect correlation of the character of the 

rocks with the topography in the two greatest platforms will now 

be shown.

In the Kaibab division the Bright Angel shale of the Tonto group 

is uniformly weak and has wasted back rapidly from the summit of 

the Tapeats sandstone, leaving the wide ledge known as the Tonto 

platform. As the Bright Angel shale is traced westward into the 

Shinumo quadrangle, layers of resistant snuff-colored limestone begin 

to a,ppear in the middle of the formation. These layers, known 

locally as the "Snuffy limestone" (PL XVIII, p. 86), gradually increase 

in thickness toward the west, making two delicate parallel cliffs 

which form a conspicuous feature in the interior of the canyon. 

Similarly the overlying Muav limestone and the massive Eedwall

limestone become gradually thicker toward the north and west, and 

the innner canyon narrows as these strata become more and more 

effective in defending the retreat of the wall.

In the Kanab division the Supai formation of the Aubrey group 

consists of weak red shales in its upper portion and resistant sandstone below. The shales waste back from the summit of the sandstone, leaving the Esplanade platform. In the western part of the 

quadrangle, where the Esplanade is developed, the thickness of these 

shales is 550 feet, whereas that of the overlying massive Coconino 

sandstone, which defends the retreat of the outer wall, is only 250 

feet. East of Havasupai Point, in the Kaibab division, the thickness of the shale of the Supai formation decreases to 300 feet, whereas

1 Davis, W. M., An excursion to the Grand Canyon of the Colorado: Harvard Univ. Mus. Comp. Zool. 

Bull. 38,geol. ser., vol. 5, No. 4, pp. 181 et seq., 1901; An excursion to the Plateau province of Utah and 

Arizona: Harvard Univ. Mus. Comp. Zool. Bull. 42, geol. ser., vol 6, pp. 31 et seq., 1904.
STRUCTURAL GEOLOGY. 75

that of the Coconino sandstone has increased to nearly 400 feet. The 

Esplanade fades to a narrow ledge in this part of the canyon.

If the Esplanade and Tonto platforms represent base levels of 

erosion there is no reason why every bench in the canyon wall should 

not represent a similar base level. In the Kaibab division at least 

two benches are better developed than the bench that locally represents the Esplanade. . The writer agrees with the conclusions of 

Robinson, who, in discussing the same problem from observations 

made in the Bright Angel quadrangle, says: *

It is hardly reasonable to expect such, a nice adjustment of base levels, three or 

four in number, to suit definite structural horizons. It must be concluded, rather, 

that the benches are simply what they appear to be the stripped surfaces of resistant 

formations which have been successively exposed in the progressive downcutting o'f 

the Colorado River through the plateau.

The facts that the Esplanade and Tonto platforms are both widely 

developed in the central part of the Shinumo quadrangle and that 

they are there vertically over 2,000 feet apart show that they do not 

represent a common base-level of erosion.

STRUCTURAL GEOLOGY.

WEST KAIBAB FAULT.

Perhaps the most interesting structural feature in the quadrangle 

is the West Kaibab fault, in the Muav-Flint canyon, where the line 

of the fault is laid open to study for a vertical mile by the deep cutting of the gorge, which has revealed three separate displacements 

along the same line. These displacements occurred at widely separated periods of geologic time. (See PI. I, sections, in pocket.)

The earliest of these displacements is recorded in the pre-Cambrian 

rocks in the depths of the canyons of Shinumo and Flint creeks, and 

is the great fault that limits the Unkar wedge on the northeast, 

bringing up the Vishnu schist on the opposite side of the fault plane.

The strike of the fault in this part of the Muav-Flint canyon is in 

general northwest-southeast, but its extension is undulatory, as may 

be seen from the geologic map. The dip of the fault plane is 60° 

SW. in the only locality where a vertical cross section could be 

observed. The strata of the Unkar group are dragged.up against the 

fault line throughout its exposure, the "drag sharply reversing their 

usual northeasterly dip. The fault plane is marked by cemented 

breccia wherever it crosses the harder beds of the Vishnu schist or the 

quartzites of the Unkar group. Between the Dox sandstone and the 

Vishnu schist it is characterized by a soft talcose selvage.

The pre-Cambrian age of the fault is established by the fact that 

the entire structure is truncated by the base-leveled surface of erosion

i Robinson, H. H., The single-cycle development of the Grand Canyon of the Colorado: Science, new 

ser., vol. 34, No. 864, p. 90,1911.
76 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

at the base of the Tapeats sandstone. The total amount of displacement can never be known; the highest beds of the Unkar group 

which abut against the fault belong to the Dox sandstone, lying 

stratigraphically 5,800 feet above the Archean, surface upon which 

the Unkar group rests, but this can be only a minimum measure 

because of the truncation of higher beds by the pre-Tonto unconformity, as explained above.

The two later displacements which took place along the same line 

are recorded in the Paleozoic strata.

The earlier of these displacements is a monoclinal flexure, which 

dips northeastward. This flexure is clearly defined throughout the 

Muav-Flint Canyon, from Muav Saddle to the gap between Point 

Sublime and Sagittarius Ridge, a distance of 10 miles, in which it 

displays everywhere about the same amount of throw and the same 

radius of curvature. The throw ranges from 400 to 500 feet and the 

curvature is accomplished within a quarter of a mile. Southeast of 

Point Sublime the flexure diminishes in throw to about 50 feet and 

crosses the river near the eastern boundary of the quadrangle at the 

mouth of Slate Creek. Boucher trail, in the Bright Angel quadrangle, 

-ascends the canyon wall for a part of the way in the line of the 

flexure.1 The course of the displacement north of Muav Saddle is 

described on page 79.

The deep Muav Canyon affords an excellent opportunity to study 

the effect of folding in the Paleozoic beds. The beds of the massive 

formations the Kaibab limestone, Coconino sandstone, Supai 

formation (sandstone division), Muav limestone, and Tapeats sandstone bend downward in a graceful arc. The entire Redwall limestone curves downward as a single stratum. The soft sandstones of 

the Supai formation and the Bright Angel shale, however, are greatly 

mashed and crumpled.

The later displacement is a fault along the line of flexure. In the 

upper part of Muav Canyon the strata west of the fault are dropped; 

farther down the canyon the fault dies out for about half a mile and 

reappears with the throw reversed, the strata this tune dropping on 

the northeast side of the fault, which finally dies out under Point 

Sublime, at the head of the canyon of Flint Creek.

The compound displacement gives a peculiar profile to the walls 

of the Muav-Flint Canyon: On the northeast side of the canyons of 

Shinumo and Flint creeks the combined throw of the fault and flexure 

drops the Tonto platform 500 feet below the level at which it stands 

on the opposite side, but in the upper part of Muav Canyon the 

throw of the fault just compensates that of the flexure. (See PI. I, 

sections, in pocket.)

1 Davis, W. M., An excursion to the Grand Canyon of the Colorado: Harvard Univ. Mus. Comp. Zool. 

Bull. 38, geol. ser., vol. 5, No. 4, p. 165,1901. . .
STRUCTURAL GEOLOGY. 77

A description of this fault in Muav Saddle is given by Dutton,1 

whose observations, however, did not extend southward into the 

canyon. North of the Muav Saddle the fault crosses Tapeats Amphitheater and its throw increases greatly until it becomes the immense 

break which drops the strata nearly 2,000 feet to the west and forms 

the western boundary of the Kaibab Plateau.

The flexure probably originated when the Paleozoic rocks were 

buried under a considerable load of Mesozoic strata, for the thick and 

massive Paleozoic beds yielded by bending rather than by breaking, 

as is shown in Muav Canyon. This movement must have occurred 

not long after erosion began in the region and therefore early in 

Tertiary time. The fault that breaks the flexure may have occurred 

at any time after the greater part of the mass of the Mesozoic strata 

had been eroded away.

FAULTS OF THE UNKAR WEDGE.

In addition to the great fault that limits the wedge on the northeast, a large number of smaller faults traverse the Unkar strata. 

(See PL I, sections.) These faults are exceedingly numerous, there 

being in some places as many as 30 to the mile. The amount of displacement ranges from almost nothing up to 400 feet, but by far the 

greater number have a throw of less than 50 feet. Only those whose 

throw exceeds 50 feet are recorded on the map. The general trend 

of the faults is northwest-southeast, parallel to that of the limiting 

West Kaibab fault and to the strike of the strata. The fault lines 

are very crooked, owing to the fact that they traverse a rugged 

region (PL XVII, £).

All the faults are of the normal type and divide the strata into 

crustal blocks. At many places two fault planes dip toward each 

other, a vertical wedge of strata lying between them. The fault 

blocks and wedges are of all sizes, ranging from those included 

between the larger faults down to those formed by the innumerable 

faults of small throw. A cross section of one of the wedges is clearly 

exposed in the cliff of the west wall of Shinumo Canyon about half a 

mile above its junction with Burro Canyon. (See PL XV, B, p. 64.) 

Every detail of the wedge is revealed from its summit, where it is 

truncated by the pre-Tonto unconformity down to its apex, a 

vertical distance of 1,000 feet.

" Where the fault planes traverse the harder strata they are characterized by fault breccia and slickensided surfaces. The breccia 

is usually cemented with milky quartz and in nearly all such places 

a small amount of copper has been deposited, so that the weathered 

fault planes have a greenish stain.

1 Dutton, C. E., op. cit., p. 162.
78 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

In Bass Canyon a sharp monoclinal flexure has been formed in the 

Unkar strata as a result of a compressive force acting from the southeast. This flexure runs northeastward through Bass Canyon, crossing 

the Colorado just above the mouth of Hotauta Canyon. It has long 

been known to visitors as the "Wheeler fold." (See Pis. XVI, B, 

and XVII, A.) Its throw is about 300 feet. It is finely displayed 

in cross section in the wall of the Granite Gorge on the north side of 

the Colorado. Here the diorite that intrudes the Vishnu schist has 

been buckled and shoved into the limestones, shales, and jaspers of 

the lower Unkar and the flexure is passing into a thrust fault.

All these smaller faults, like the great limiting fault, are truncated 

by the pre-Tonto unconformity (see PL I, sections) and were likewise 

undoubtedly formed by the great crustal movements that uplifted 

the Algonkian mountains.

DISPLACEMENTS OF THE PALEOZOIC STRATA.

In addition to the West Kaibab faulted flexure a number of smaller 

displacements of various types are recorded in the Paleozoic strata.

Flexures. A number of yery gentle flexures run northwestsoutheast parallel to the strike of the southwestward warping of the 

strata. All dip southwestward and are hardly more than slight 

swells upon the warped surface. The most prominent of these 

flexures may be traced through Powell Plateau, near the head of 

Walthenberg Canyon. -It runs southeastward through the great 

butte of Redwall limestone that stands between Hakatai and Burro 

canyons, and is exactly on the line of strike of the Unkar monadnock. 

A similar swell may be detected in the strata between Fossil Mountain and Bass Camp. These swells are in the zone of maximum southwestward warping heretofore described, and many similar swells may 

be detected in the quadrangle.

Faults. In this part, as in other parts of the Grand Canyon, a 

number of minor faults are found which have no apparent relation 

to the greater lines of displacement that bound the blocked plateaus. 

They are haphazard in trend, have small throws, and most of them 

persist for only a few miles. The long straight gorge of Slate Creek 

coincides with a fault of about 125 feet. Another fault of this character runs through Bass Canyon and has guided the erosion of that 

gorge. It is directly on the line of the Algonkian displacement 

known as the Wheeler fold.

At least two displacements in the adjoining Bright Angel quadrangle are on the line of Algonkian faults, and in each the throw of 

the Paleozoic displacement reverses that of the Algonkian fault. 

One of these is the well-known Bright Angel fault, in the canyon of 

Garden Creek; the other is a faulted flexure which runs southeastward across the quadrangle in the gorges of Phantom, Cremation, and
U. S. GEOLOGICAL SURVEY 1ULLETIN 549 PLATE XVI

A. PINNACLES OF EROSION IN KAIBAB LIMESTONE ALONG RIM OF KAIBAB PLATEAU.

These pinnacles or "hoodoos" are characteristic features of the scenery along the north rim of the Grand Canyon 

in the Kaibab division. They are carved in the Kaioab limestone by ram erosion. Each column is capped by 

a portion of the resistant cherty layer at the summit of the formation, which protects the softer and more easily 

eroded beds beneath. Although the cherty layer is also present on the south side of the Grand Canyon, the 

pinnacles are rarely formed there, for the rainfall is less.

B. WHEELER FOLD IN BASS CANYON. . '. '. ' .. ;

View down Bass Canyon from summit of Tapeats sandstone. The strata in the fold are beds of the Bass limestone. Trie fold is overlain uncomformably by the Tapeats sandstone, which appears in tne upper right corner 

of "the view.
\

A. NEAR VIEW OF WHEELER FOLD FROM BED OF BASS CANYON.

Photograph by N. W. Carkhuff.

IN STRATA OF THE UNKAR WEDGE IN BURRO CANYON.

d, Diabase intrusive; H, Hakatai shale; Sh, Shinumo quartzite; T, Tapeats sandstone; BA, Bright Angel 

shale; Sn, "Snuffy limestone" in Bright Angel shale; M, Muav limestone; E, Redwall limestone. Photograph by N. W. Carkhuff. . . .
STRUCTURAL GEOLOGY. 79

Grapevine creeks and limits the mass of Algonkian strata at the 

mouth of Bright Angel Creek in the same way that the West Kaibab 

fault limits a similar mass in the Shinumo region. This displacement is the northwestern extension of the great flexure that bounds 

the Coconino Plateau on the northeast and is known as the Coconino 

fold. If to these are added the Butte fault on the line of the East 

Kaibab monocline in the Vishnu quadrangle it becomes apparent 

that the,reopening of a line of displacement after the lapse of a very 

long time is common in the Grand Canyon district.

The faults in the Grand Canyon have exerted a marked influence 

on the topography, as they form lines of weakness which, under the 

searching action of erosion, have determined the location of side 

gorges, such as the lateral gorge of the Muav-Flint canyon and the 

gorges between Sagittarius Ridge and Point Sublime, on the line of 

the West Kaibab fault. North of the Muav Saddle, beyond the 

boundary of the quadrangle, a similar lateral gorge in the line of the 

same fault runs northward entirely across the head of Tapeats Amphitheater, at right angles to the main course of Tapeats Creek, the master stream. Examples of the same phenomenon in the Bright Angel 

quadrangle are the canyons of Monument, Horn, Garden, Bright 

Angel, Phantom, and Cremation creeks and the upper part of the 

 canyon of Grapevine Creek. Among other examples in the Vishnu 

quadrangle are Red Canyon, the canyon of Vishnu Creek, and the 

gorges in the line of the Butte fault.

Lines of fracture without displacement. In addition to the faults 

the lines of fracture in the Shinumo quadrangle (and presumably in 

other parts of the canyon) have exerted a. marked influence on the 

topography, although their importance has not been recognized in 

the literature of the Grand Canyon. In tracing many of the side 

gorges of the Grand Canyon to the walls at their heads the writer 

found in the Paleozoic strata lines of shattering that were directly 

on the main axes of the gorges. These lines of fracture can not be 

classed as faults, for they exhibit no appreciable throw, yet along each 

of them a sufficient amount of shattering has taken place to constitute a line of weakness, which has guided the erosion of the gorge. 1 

The peculiar arrangement of the drainage lines of the Shinumo 

Amphitheater, heretofore described, affords a striking example of this 

phenomenon, for Merlin Abyss and the similar parallel lateral gorge 

that crosses the amphitheater between Lancelot Point and Elaine 

Castle lie along lines of fracture, and many other examples occur in 

the quadrangle.

Many of the buttes and temples in the Grand Canyon owe their 

isolation to lines of fracture. Elaine Castle is a good example, and

1 Mr. Francois Matthes, of the Geological Survey, made an extensive study of these fracture lines in the 

Kaibab division several years ago and reached the same conclusions as to their significance. Oral communication.
80 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

another is the great butte, capped by sandstone of the Supai formation, which forms the north arm of Monadnock Amphitheater. 

Among other examples are Explorers Monument, at the south end of 

Marcos Terrace, and Castor, Pollux, Diana, and Vesta temples, along 

the rim of the Coconino Plateau.

GEOLOGIC HISTORY.

THE SEDIMENTARY AND EBOSIONAL RECORD.

The earliest decipherable record of the geologic history of the 

Shinumo quadrangle a blurred and mangled record is found in the 

Vishnu schist. Far back in geologic time a thick series of more or 

less arkose sands and muds was accumulating upon the subsiding 

floor of a great mediterranean sea. So much may be reasonably 

inferred from the mineralogic character of the quartz-mica and quartzhornblende schists of the Vishnu formation. So dim and vague is 

the record that the base of the series, the floor upon which it was laid 

down,- its thickness, and the location of the land mass from which 

it was derived must perhaps remain forever unknown. After a long 

period, in which sediments were accumulated and buried, a mountain-making movement wrote its story across the older manuscript 

in a later and bolder hand, blurring the ancient chronicle with a 

record of deep-seated regional metamorphism and imparting to the 

manuscript the aspect of a palimpsest. The regional metamorphism 

is conceived to have been brought about by deep burial of the sediments and by their subsequent folding and compression, which in 

slow process of time engraved upon them the characters of recrystallization and schistosity and were accompanied by their elevation 

into lofty mountains. Somewhat later the cores of these mountains 

were penetrated and their summits were farther uplifted by intrusions 

of great masses of igneous rock, here becoming quartz diorite, the 

injection of which was followed by injections of magma of pegmatite. 

Doubtless while this mountain-making movement was still in progress 

the forces of denudation were already at work, beginning a cycle of 

widespread erosion, which was carried through to a remote end and 

which planed away the ancient mountains to. their bases and reduced 

hard and soft rocks alike to a flat, unbroken plain. This ancient 

surface is represented by the unconformity at the base of the Unkar 

group and marked the final cycle of this great unknown and unnamed 

eon of Archean time.

.The next event is the beginning of another great cycle of sedimentation, which resulted in the deposition of the Grand Canyon 

series, of Algonkian age. This cycle was ushered in by the invasion 

of the land by a shallow sea, which swept over the featureless surface 

of the Vishnu plain.
GEOLOGIC HISTORY. 81

The Hotauta conglomerate, at the base of the Unkar group, was the 

first formation deposited in this sea and was made from the mantle 

of loose rock and soil that covered the surface of the plain. The 

lithology of the formation is a possible clue to the climate of that 

time. Its lack of chemical weathering; locally shown by the freshness 

and the arkose nature of its component fragments and the red color 

of its matrix, indicating a lack of vegetation and of abundant moisture 

to decompose the soil and to reduce the iron which imparts to it its 

red color, point, to an arid climate. It is therefore possible that the 

Vishnu plain was a vast desert at the incoming of the sea. The lack 

of transportation, sorting, and rounding of pebbles in the Shinumo 

region indicates that the waves had little chance to rework the 

soil mantle. It seems impossible to account for these phenomena 

except by supposing a sudden invasion of the sea across the Vishnu 

plain. If we seek to interpret the past in the light of the present our 

only means of gaining an understanding of the conditions that then 

existed is to try to picture some present condition on the earth which 

is comparable with that preserved in the geologic record. A possible 

clue may lie in the present conditions about the Caspian Sea, where 

there is a desert that lies below the present level of the Black Sea, so 

that a sudden rise in the level of the ocean might cause that sea to 

overflow the low barrier which separates it from the Caspian and 

suddenly inundate the desert.

The succeeding Bass limestone was deposited in a permanent body 

of water into which mud was frequently washed. The section of 

this formation shows that the alternations in the character of its 

beds are almost innumerable. The exact cause of these alternations 

is unknown and is still a subject of speculation. Possibly they were 

due to climatic oscillation, for a change from an arid to a semiarid 

climate would load the rivers with sediment and arid intervals would 

retard their flow or dry them up entirely, resulting in a temporary 

clarifying of the sea and the deposition of limestone. Whether these 

limestones were formed by organic agencies or by purely chemical 

precipitation is also a matter of speculation, as the rocks contain no 

traces of life. The water was probably for the most part shallow, for 

sun cracks appear in the shales in the upper part of the member below 

the highest limestone stratum.

The most striking feature of the Hakatai shale is the great 

abundance of sun cracks in the shaly strata and of ripple marks and 

of cross bedding in the sandstones. Eesearch by Prof. Joseph Barrell 

has shown that extensive sun cracking is most likely to be preserved 

on broad flood plains or deltas in an arid climate. 1 In the opinion of

i Barrel!, Joseph, Relative geological importance of continental littoral and marine sedimentation: 

Jour. Geol., vol. 14, pp. 524-568, 1906.

29745° Bull. 549 14 6
82 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

the writer of the present report the extreme abundance of these 

cracks in the formation is hard to account for except by postulating 

wide delta flats or flood plains. Furthermore, the bright-red color 

of the shaly strata, taken in connection with the mud cracks, seems 

to bespeak an arid climate, with little or no vegetation to reduce the 

iron. It is certain that the Hakatai shale was deposited in very 

shallow water, which often evaporated entirely, leaving broad mud 

flats exposed to a hot sun. In the upper part of the formation, as 

may be seen from the section, the alternations of shale and sandstone 

are notably regular. The sandstone layers are composed of fine, 

cleanly sorted, and rounded quartz grains and are ripple marked and 

cross bedded, and the shales were a fine red mud. The cleanness of 

the sandstone in this alternating series is probably a mark of climatic 

oscillation. A climatic movement toward a wetter climate, if increasing the ratio of run-off to erosion, causes the rivers to flow on a lower 

grade and to sweep seaward the piedmont deposits of sand and gravel, 

and as the clay was largely sorted from those deposits when they 

were first laid down, their redistribution and their secondary sorting 

on a delta surface or sea bottom would be marked by extreme 

cleanness. '

Great thickness, clean sorting, and extreme fineness and roundness 

of grain are the characters that distinguish the Shinumo quartzite, 

which is .composed entirely of sandstones and quartzites. Most of 

the beds show cross bedding and ripple marks, bespeaking shallow 

water. Clean sorting and extreme fineness indicate long transportation, so the rivers that carried this material to the sea may have 

flowed through a great desert of dune sands, picking up and carrying 

material such as is to-day deposited in the delta of the Indus from a 

similar source. Scattered lenses of fine conglomerate within some of 

the strata suggest scoured and filled stream channels.

The Dox sandstone, again, bears all the marks of shallow-water 

origin; it is throughout characterized by mud cracks, ripple marks, 

. and cross bedding. The addition of micaceous material and of some 

feldspar gives a slightly arkose character to the rocks; so possibly a 

crustal movement rejuvenated the land mass that supplied the 

sediments. Here, again, are marks of aridity, seen in the vermilion 

color and the vast development of mud cracks.

In the Shinumo quadrangle all subsequent Unkar and Chuar 

deposits have been removed by the truncation of the pre-Cambrian 

structure, by the plane of the base-leveled surface of erosion beneath 

the Tapeats sandstone. In the Vishnu quadrangle, where these 

subsequent deposits are preserved, they also bear evidence of deposition in shallow water. . It is not unlikely that a considerable portion 

of the Grand Canyon series was deposited in deltas or in the flood 

plains of rivers. The evidence obtainable from the Unkar group in
GEOLOGIC HISTORY. 83

the Shinumo region indicates that an arid climate prevailed at least 

during the greater part of Unkar time.

The predominance of clastic sediments in the part of Walcott's 

section in the Vishnu quadrangle that corresponds to the Bass limestone in the Shinumo quadrangle suggests that the Vishnu region was 

nearer the shore line of the early shallow sea. The close correspondence in the lithology of the succeeding formations in both regions 

indicates uniform conditions of deposition over at least the distance 

between these quadrangles.

The next event that can be deciphered in the geologic record in 

the Shinumo quadrangle is the invasion of the Unkar strata by sheets 

of diabase. If these invasions are to be regarded as contemporaneous 

with the lava flows of the Vishnu quadrangle, they must have taken 

place before the deposition of the Chuar strata, which are assumed to 

have once overlain the Unkar group in the Shinumo region.

After at least 12,000 feet of Unkar and Chuar strata had accumulated, a mountain-making movement of block faulting and tilting, 

accompanied or succeeded by elevation, broke the Algonkian strata 

into great crustal blocks, which must have formed high ranges of 

mountains. Doubtless these mountains were in character and aspect 

at one time not unlike the faulted ranges of the Great Basin or the 

desert ranges of Arizona and California at the present day.

Then began a second long period of erosion that gnawed slowly but 

surely into these faulted mountains, reducing them in slow process of 

time through stages of youth, maturity, and old age, and finally 

eating down into the Archean rocks beneath and planing away all 

but the stumps of the faulted mountains, leaving the broad expanse 

of a base-leveled surface. This surface is the spectacular unconformity at the base of the Paleozoic. The remnants of the tilted and 

faulted Algonkian strata were left inset as wedges in this plain of 

Archean rocks. The monotony of the surface was broken here and 

there by a monadnock of Shinumo quartzite, which resisted the forces 

of erosion in that ancient plain by the same adamantine hardness by 

virtue of which these strata to-day wall in the deep box canyon of the 

Shinumo. These monadnocks of the Cambrian plain may be compared with the Baraboo ridges of Huronian quartzite, which by 

virtue of their homogeneity and hardness still stand as prominences 

that have weathered repeated cycles of erosion. This cycle of erosion 

was probably not completed until Cambrian time. 

,^ The next notable event in the region is the sinking of the plain and 

/die incoming of the Tonto sea, which probably spread over a surface 

that strongly resembled the present surface of the great Laurentian 

peneplain of Canada, with its broad areas of crystalline rocks, in 

which are inset occasional blocks of sedimentary strata, and above 

which stand scattered monadnocks of quartzite.
84 SHINUMO QUADRANGLE, GRAND CANYON DISTBICT, ARIZ.

The Tapeats sandstone is a deposit formed on the beach of the 

invading sea. When the sea came in over the ancient plain the 

mantle of rock waste that covered the surface was ground and reworked by the waves until only its most durable particles remained, 

making a quartz sand. The conglomerates in the basal part of the 

formation represent the coarse shingle of the beach, worn and rounded 

by the pounding of the waves; the grits and sandstones are the shifting sands along the ancient shore. The monadnocks of Shinumo 

quartzite stood as islands in the sea. The striking record of marine 

planation revealed in the cliff faces of these monadnocks has already 

been described.

After the deposition of the Tapeats sandstone, quantities of micaceous sand were washed into the gradually deepening sea. These 

sands formed the Bright Angel shale. Twice during this epoch the 

sea became locally clear and the layers of the so-called "Snuffy limestone" were deposited. The highest islands of quartzite of the Unkar 

group were finally buried by the uppermost sands of the Bright 

Angel shale. The fossils found in the Bright Angel shale are the 

first clear evidence of life in the Paleozoic sea; the fauna of Middle 

Cambrian age which they represent belongs far down in the scale of 

the world's life history.

After the deposition of the Bright Angel shale the sea became 

clearer and the Muav limestone was laid down. Small quantities of 

mud were still being washed into the sea, imparting to the limestone 

its mottled appearance.

Then followed an interval in regard to which the record is nearly 

silent a period lasting through Silurian and Devonian time. During 

the first part of that period the sea retreated and the upper part of 

the Muav limestone was exposed to erosion, probably as a low-lying 

land. During the Devonian period the sea came in over this land 

and deposited material that formed sandstone and limestone. Again 

the land was gently uplifted without deformation and was subjected 

to erosion which removed nearly all the Devonian strata except those 

that lay in depressions in the Muav limestone. So. much may be 

learned from the study of the unconformity at the base of the Redwall limestone in the Grand Canyon region.

The next recorded event, coming in early Carboniferous (Mssissippian) time, is a submergence in a sea that first received deposits 

of material that formed sandstone and limestone but rapidly became 

clear, depositing material that formed the massive Redwall limestone. 

The purity of this limestone is evidence of the clearness of the waters, 

and the presence of large cup corals indicates that the sea was warm.

After the deposition of the Redwall limestone the sea became very 

shallow, and into it large quantities of sand and mud were alternately 

washed. These sands and muds are the alternating red shales and
GEOLOGIC HISTORY. 85

sandstones of the Supai formation, the lowest of the Aubrey group 

of strata. In some parts of the Grand Canyon region the sea was 

clearer and layers of limestone are there interbedded with the shales 

and sandstones of the lower part of the formation. A fauna of 

late Carboniferous (Pennsylvanian) age lived in that clearer portion of the sea. It is probable that the pebbles of the limestone 

conglomerate in the sandstone division of the Supai formation of the 

Shinumo region were derived from these limestones by erosion.

The origin of the overlying Coconino sandstone is an interesting 

problem. A counterpart of this formation in the Plateau province is 

the great sandstone 50 miles north of the Shinumo quadrangle, in the 

terraces of southern Utah, to which Huntington and Goldthwait 

have given the name Colob sandstone. The origin of this sandstone 

is discussed by Huntington and Goldthwait as follows: l

The white sandstone is cross-bedded on a scale so large that a single layer attains a 

thickness of from 5 to 50 feet. * * * Everywhere the deposit consists of uniformly 

fine white sand without a trace of pebbles or coarser sand so far as has yet been observed. The uniformity of texture is emphasized by the total lack of ripple marks, 

which, as Cornish has shown, result from the mixture of sand grains of different sizes. 

That such a formation could be due to marine or lacustrine action of any kind seems 

contrary to what we know of such agencies. It is generally recognized that crossbedding of a marked type is a proof that the deposits were formed close to the shore 

or on land. The uniform thickness of the Colob sandstone over so great an extent 

renders it antecedently improbable that it is a shore deposit; the total absence of 

ripple marks, rill marks, and other characteristic shore features lends support to .this, 

and lastly the perfect smoothness and horizontality of the planes which truncate the 

tops of the strata render this still more improbable. * * * The same facts of 

structure, together with the total absence of gravel, of fossil stream beds, and of lateral 

unconformities render it equally improbable that the Colob was deposited by fluviatille 

processes. The only remaining possible agent is the wind. We can not yet be certain that the Colob sandstone is a wind formation; nevertheless none of its characteristics seem to oppose such an hypothesis. The uniformity and fineness of the component quartz grains, the steepness of the cross bedding, its general uniformity with 

interesting minor variations, the even truncation of the successive cross-bedded strata, 

and the tangency of the overlying layers to the plane surface thus formed suggest a 

series of great white dunes marching forward to the east and south from the base of the 

Basin Range Mountains. * * * It seems to be a fair question whether the crossbedded strata of the Kanab and Colob formations may not be continental deposits laid 

down by the wind.

The Coconino sandstone differs little, except by its lesser thickness, 

from the sandstone just described, and many beds of sandstone in 

the underlying Supai formation resemble the Coconino sandstone, 

but are still smaller. It seems probable that whatever may have 

been the origin of these sandstones it must have been analogous to 

that of the sandstone of southern Utah described by Huntington and 

Goldthwait. If their interpretation is correct the region must have 

become land during the deposition of the Coconino sandstone and at

i Huntington, Ellsworth, and Goldthwait, J. W., The Hurricane fault in the Toquerville district, Utah: 

Harvard Mus. Comp. Zool. Bull 42, geog. ser., vol. 6, No. 5, pp. 214 et seq., 1904.
86 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

intervals during the deposition of the Supai formation, and the sandstones represent deposits of dune sand.

Again the sea invaded the land and laid down the sandy, calcareous 

sediments forming the base of the Kaibab limestone. The clarifying 

of the sea resulted in the deposition of the pure and richly fossiliferous limestones in the upper part of the formation. The fossils represent the typical fauna of the western sea in Pennsylvanian time. 

Life was easy, for the forms are fat and well nourished, as well as exceedingly abundant. The waters were probably shallow and warm 

as well as clear, for the rocks deposited in them contain great quantities of bryozoa, which possibly even formed reefs, and with the 

bryozoa are mingled the remains of echinoids, corals, crinoids, brachiopods, gasteropods, and sponges.

So much of the geologic history may be read from the actual rock 

record in the Shinumo quadrangle.

One who looks across the broad plateaus on either side of the Grand 

Canyon finds it difficult to realize that the deposition of strata did not 

end with that of the Kaibab limestone, upon which he stands, but the 

cliffs and terraces that rise to higher and higher levels along the 

northern border of the Grand Canyon district, as well as Echo Cliffs, 

on its eastern border, represent the eroded edges of strata that were 

once deposited horizontally bed upon bed upon the Kaibab limestone, 

and that once extended continuously across the whole region where 

the Grand Canyon lies. 1 At the base of the cliffs on the north lie 

strata of the Permian epoch, completing the record of the Carboniferous and also of the Paleozoic'; above lie strata of Mesozoic age 

Triassic, Jurassic, and Cretaceous. The highest beds belong at the 

base of the Tertiary.

After the deposition of the Kaibab limestone, the accumulation of 

the Mesozoic and Tertiary strata went on quietly and almost continuously. The presence of occasional unconformities of erosion without unconformity of dip shows that whatever uplifts occurred were 

unattended by horizontal deformation. The strata were deposited 

"with almost rigorous horizontality."2 By the end of Mesozoic time 

these strata had accumulated to a thickness considerably greater than 

that of the entire Paleozoic section of the canyon wall.

During the early part of the Tertiary period, after the accumulation 

of 6,000 feet or more of strata, deposited bed after bed above the 

Kaibab limestone, the Grand Canyon district began to be uplifted high 

above the surrounding country, and a period of erosion was begun 

which has lasted to the present day. This erosion was not continuous; 

there were pauses in the uplift of the region, during which the forces 

of erosion worked far along toward producing a mature topography;

1 Button, C. E., op. cit., pp. 61 et seq. * Button, C. E., idem.
U. S. GEOLOGICAL SURVEY

GEOLOGIC HISTORY OF THE SHINUMO QUADRANGLE AS REVEALED BY THE 

V, Vishnu schist; Au, Unconformity, separating the Archean and Aleonkian systems; 7?, Bass lim

quartzite; Pu, Paleozoic unconformity, separating Algonkian and Paleozoic rocks; T, Tapeats 

Bright Angel shale; M, Muav limestone; R, Redwall limestone; Ss, sandstone of Supai form

K, Kaibab limestone. A vertical mile of strata is in view. Photograph by N. W. Carkhuff.
GEOLOGIC HISTORY. 87

then again the country would rise and the attack be renewed more 

vigorously. Out of all these vicissitudes of uplift and erosion two 

major cycles stand clearly forth, and the result of the work in each is 

stupendous.

The work of the earlier ana greater cycle is known as the " great 

denudation." As a result of the erosion in this period nearly all the 

6,000 feet of Mesozoic and basal Tertiary strata was removed from 

the surface of the Grand Canyon district, their edges retreating to a 

line 50 miles north of the Shinumo quadrangle, to the cliffs along the 

border of Utah. Toward the end of the great denudation the surface 

of the region was reduced to a base-level of erosion. Fragments of 

this peneplain are preserved beneath the San Francisco Mountains, 

Red Butte, and the hills of the Uinkaret Plateau by floods of lava that 

were poured out upon the plain during the last stages of its formation. 

This resistant lava has protected the underlying strata from subsequent erosion.

The work of the second and lesser cycle is the cutting of the Grand 

Canyon by Colorado River and the removal of whatever remnants of 

soft strata were left upon the surface of the plateaus at the end of the 

great denudation. This cycle, which is still in progress, is known as 

the "canyon cycle" of erosion.

The course of Colorado River across the region became established 

before the beginning of the uplift which began the canyon cycle of 

erosion. As the land rose the river entrenched itself in its original 

course, continuing to cut deeper and deeper. The present stage of 

the valley is the Grand Canyon, which is thus wholly a product of 

erosion. It has been excavated by Colorado River and is deep, 

because the land is high and because in this arid region the river, fed 

by the snows of the Rocky Mountains, has cut down its bed much 

faster than the erosion due to strictly local agencies could, lower the 

adjacent plateau. The walls have retreated slowly in comparison 

with those of most valleys, because the strata that determined them 

are unusually massive and because the forces that attacked them 

have been comparatively weak and have worked in the way characteristic of arid regions.

By far the most impressive feature of this wonderful country, to 

the traveler and the geologist alike, is the mile-deep pathway of the 

Colorado River of the West across the great plateaus. The stupendous and glaring record of erosion revealed in the cutting of this 

mighty gorge has almost blinded us to the immensity of the vastly 

greater record revealed in its walls (PL XVIII), but the erosion of 

the canyon becomes only an episode in the geologic history of the region in comparison with the story told by the two intersecting unconformities in the bottom of the gorge. These unconformities represent
88 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

two ancient cycles of sedimentation, uplift, and erosion carried to a 

remote end, separated by long intervals of time whose record is hopelessly lost, resulting twice in the planing down of lofty mountain 

ranges to their very cores, written vaguely at first on a blurred and 

time-worn record and later in an increasingly clearer and bolder 

hand, telling of the slow accumulation of the strata of the canyon 

wall on the floor of the Paleozoic sea, of the subsequently erased record 

of the accumulation of vast thicknesses of Mesozoic and Tertiary 

strata, at times separated by great intervals of erosion, and even 

telling of the "great denudation," which has stripped these later 

strata back 50 miles to the terraces of Utah ^all these events representing a lapse of time which compared with that consumed in the 

cutting of the Grand Canyon is but as the passing of a summer afternoon compared to the procession of a season; for in the light of present 

knowledge according to the fossil record, it may be said that the 

Grand Canyon was all cut since man has inhabited the earth.

THE PLATEAU PROBLEM.

Since the history of the region from early Tertiary to the present 

time is entirely a record of uplift and erosion, that record should be 

interpreted wholly by means of the science of physiography. The 

salient events, as outlined above, were established beyond a doubt 

by the work of Dutton 'and Powell. The science of physiography, 

however, has grown remarkably since the work of these pioneer 

observers was done.

In 1900, 1901, and 1902 the region was visited by Davis,1 whose 

studies confirmed the broader conclusions of Dutton, but brought 

to light evidence that the history of erosion in the region is far more 

complex than was formerly supposed.

It was shown that the great denudation was complicated by repeated movements of uplift, after each of which erosion may have 

reached an advanced stage.

It was discovered that the great displacements of the region began 

at an earlier date than was formerly supposed. The absolute antecedence of the Colorado River to the displacements, regarded by 

Dutton and Powell as proved, is therefore open to question.

It was made clear that the exact dates of the various events of the 

Tertiary and recent history are still unknown.

It was shown that these problems can be solved only by a great 

amount of further detailed observation, not only in the Grand Can- 

.yon district but in the neighboring regions.

Since the work of Davis, parts of the region have been studied in 

detail by Robinson, Huntington and Goldthwait, and Johnson,1 and

i See Bibliography, p. 14.
GEOLOGIC HISTORY. 89

many data bearing on these problems have been accumulated. 

Owing to the vastness and inaccessibility of the region a great amount 

of work of this kind still remains to be done.

The detailed interpretation of this complex erosional history has 

become known as "the plateau problem."

The most absorbing question of the plateau problem is that which 

concerns the date and the method of the establishment of the course 

of the Colorado Kiver across the region. Two theories have been 

entertained.

The earlier theory is found in the writings of Dutton and Powell. 

These observers found that the general course of the river lies across 

the great lines of displacement that bound the blocked plateaus and 

were led to the conclusion that the course of the river was established 

before the first movements along the lines of displacement occurred. 

As the displacements came into existence the river continued to cu{; 

down in its original channel faster than they rose across its path. 

It was thought that the displacements did not begin until the end 

of the great denudation..

An alternate theory has been advanced by Davis and supported 

by Robinson, Huntington, and Johnson. The work of these men 

brought to light evidence that the first movements along the lines 

of displacement had begun early in the period of the great denudation; 

that the peneplain developed in the later part of this period represented a stage of erosion so far advanced that hard and soft rocks 

alike were reduced to a nearly even level and the initial relief produced by the displacements was almost effaced. The drainage 

system of the Colorado first became established upon this peneplain, 

the configuration of the surface of that time guiding the course of 

the river. The fact that the relief produced by the displacements 

was largely effaced in the peneplain would account for the course 

of the river across them.

In order to confirm this later theory that the Colorado is a superposed stream let down from the surface of an ancient peneplain 

it is necessary to restore in imagination the topography of the 

region as it existed in the later stages of the peneplain that is, 

the topography to which the ancestral drainage system of the 

Colorado adjusted itself, and this restoration can be made only by 

careful detailed study. A study of the structural irregularities 

that date back to the tune of the great denudation may afford a 

partial restoration of the ancient topography. Even the smallest 

folds or faults may have influenced the adjustment of the drainage 

by exposing strata of unequal resistance. Since practically all the 

Permian and higher strata that may have affected this adjustment 

of the drainage have been removed by erosion, it is obvious that
90 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT. ARIZ.

these structural irregularities are open to study only in the Paleozoic 

rocks of the present plateau surface. The writer of this report believes 

that such detailed study may show that the course of Colorado River 

between Kanab Creek and the Little Colorado, at least, is related to lines 

of structure. Davis 1 has shown that such a relation probably exists 

in the Kaibab division immediately west of the Little Colorado.

If similar speculation concerning the Bright Angel and Shinumo 

quadrangles is undertaken, it seems significant that the northwesterly 

course of the river is parallel to the strike of the northeastwarddipping flexures of the Coconino fold and of the West Kaibab fault. 

The great loop of the river around Powell Plateau is a local deflection from this general northwesterly course and it is of interest to 

note that just beyond the boundary of the quadrangle, west of the 

end of Alarcon Terrace, there is a faulted flexure which trends northeast-southwest and resembles on a smaller scale the West Kaibab 

faulted flexure in Muav Canyon. The river apparently flowed westward until it encountered this displacement, and its course was then 

deflected toward the north and northeast, possibly following a belt 

of weak Permian rocks on the thrown side of the displacement. 

Doubtless the river was held up for a time at this displacement, and 

the loop around Marcos Terrace may represent a meander, subsequently entrenched, which dates back to that time.

It is now thought that the greater lines of displacement of the 

Grand Canyon district were blocked out in the first broad uplift that 

started the erosion known as the great denudation. More and more 

evidence has been found of movements that have taken place along 

these lines at intervals throughout all succeeding time. Each successive faulting is correlated with a fresh uplift and a revival of the 

forces of erosion, necessitating the recognition of more and more 

cycles in the erosional history of the region.

An interesting feature of these displacements is their location upon 

ancient lines of displacement in the basement rocks. This coincidence is the rule in the Kaibab division, as has been shown in this 

bulletin, and it therefore seems probable that it applies to other 

faults in the district whose prolongation into the basement rocks can 

not be studied. The history of the displacements thus has its beginning in the mountain-making movements of Algonkian time.

The dating of the numerous events of the complex erosional history 

in geologic time is the most difficult riddle of the plateau problem. 

A discussion of this subject has no place in the present report, for the 

Shinumo quadrangle affords no evidence whatever concerning it. 

A brief outline, however, will show how complex the interpretation 

has become since the publication of Button's monograph.

i Davis, W. M., An excursion to the Grand Canyon of the Colorado: Harvard Univ. Mus. Comp. Zool. 

Bull. 38, geol. ser., vol. 5, No. 4, pp. 164-165,1910.
SCENIC INTEREST OP SHINUMO QUADRANGLE. 91

A summary of the Tertiary history as worked out by Button is as 

follows:

I. The period of great denudation, lasting until the close of the Miocene.

II. Uplift by folding (?) and faulting at close of Miocene.

III. Canyon cycle of erosion:

(a) Cutting of outer gorge of Grand Canyon during the Pliocene..

(6) Uplift by faulting at close of Pliocene.

(c) Cutting of inner gorge of the canyon during the Quaternary.

The following summary, given by Robinson 1 in a recent publication, is the most recently published interpretation of the Tertiary 

history. The dates of the events are assigned tentatively by that 

writer:

I. Period of folding and flexing during the later half or at the close of the Eocene.

II. Erosion period during the Miocene.

III. First period, of faulting at close of the Miocene. A period of extensive faulting. 

It is correlated with, the faulting that gave rise to the Basin Eanges of southern Nevada 

as tilted block mountains.

IV. The peneplain cycle of erosion during the Pliocene. The Miocene and Pliocene 

. erosion, which are considered as constituting the later and greater part of the period 

of the great denudation, closed with the widespread development of a peneplain. 

This is correlated with the mature topography and local peneplains of the Basin Range 

country of southern Nevada and of Arizona. Relief produced by previous faulting 

(III) largely and at some localities entirely obliterated. Widespread volcanic activity, 

marked by the eruption of basalt, occurred shortly after the development of the peneplain and most probably while the region still stood close to sea level.

V. The second period of faulting at the close of the Pliocene. Movements probably 

of less magnitude than those of the first and third periods.

VI. The post-peneplain cycle of erosion during the first part of the Quaternary. 

Widespread stripping of Permian and Triassic strata and development of a mature 

topography of low relief, principally on the upper Aubrey limestone, at a horizon 

ranging from zero to 1,000 feet below the level of the peneplain. Further retreat of 

the high cliffs on the north and east sides of the district. Land stood at no great 

height above the sea.

VII. The third period of faulting, with broad regional uplift, during the middle or 

latter part of the Quaternary. Region raised from 4,000 to 6,000 feet above the position 

it occupied at the close of the post-peneplain cycle of erosion.

VIII. The canyon cycle of erosion during the latter part of the Quaternary. Marked 

by the development of a canyon system of drainage of extreme youthfulness. Refreshing of cliff profiles. Erosion otherwise very slight. Colder atmospheric conditions 

prevailed during part- of this cycle, at least as indicated by the existence of a small 

.glacier on San Francisco Mountain.

SCENIC INTEREST OF THE SHINUMO QUADRANGLE.

The views from the northern wall of the Grand Canyon in the 

Shinumo quadrangle have long been famous through the descriptions 

of Dutton. 2 The most celebrated outlook is Point Sublime, the 

promontory that forms the eastern arm of the Shinumo Amphi1 Robinson, H. H., A new erosion cycle in the Grand Canyon district, Arizona: Jour. Geology, vol. 18, 

No. 8 (Nov.-Dec., 1910), pp. 763fl. 

a Tertiary history of the Grand Canyon district: U. S. Geol. Survey Mon. 2, chaps. 8 anu J, 1382.
92 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ.

theater. The view from this point is the subject of the three magnificent panoramic drawings by Holmes which illustrate that part of 

Button's monograph that is devoted to the scenery of the canyon.

A scarcely less comprehensive view may be obtained from Havasupai Point (PL VII, B, p. 22), on the south side of the canyon. The 

view within the canyon itself from this point is even more extensive 

than that from Point Sublime, directly across the canyon. Point 

Sublime, however, like all points on the northern rim in the Kaibab 

division, has the advantage of greater altitude, which extends the 

outlook far over and beyond the southern rim of the canyon.

By far the most interesting scenic ground in the quadrangle is Powell 

Plateau (PI. IV, A, p. 18), on the north side of the canyon, accessible 

by trail from the Muav Saddle. The scenic advantage possessed by 

this great butte is due to its peculiar situation with reference to the 

course of the Grand Canyon and to its great altitude. As it lies 

almost in the middle of the canyon, just at the elbow of the great 

bend where the general course of the river changes from northwest to 

southwest, directions maintained in either direction for over 50 miles, 

the views from the north and south ends of the high eastern portion 

command a greater stretch of the interior of the canyon than can be 

seen from any other place in the region. And since this eastern portion of the plateau is higher than any land in the quadrangle outside 

of the Kaibab, it is possible to obtain from these two places an outlook in every direction except to the northeast over an expanse of 

country extending nearly a hundred miles to the horizon and including the greater part of the Grand Canyon district.

The outlook from Button Point, at the south end of Powell Plateau 

includes the entire Kaibab division of the canyon, seen along the 

very center of the pathway of the river. Below, on the northeast, 

is Muav Canyon, where the consequences of the West Kaibab fault 

are clearly revealed. Birectly below, to the east, in the interior of 

the canyon, is the wedge of Unkar strata about the mouth of the 

Shinumo. To the south, in the canyon, the topography of the wall 

is changing from east to west, the Esplana'de appearing and the 

Tonto platform fading gradually. Beyond the southern wall the 

Coconino Plateau slopes away from the canyon rim, merging gradually 

into the broad expanse of the San Francisco Plateau, upon whose 

surface the San Francisco Mountain volcanic group is in full view, 

80 to 100 miles away.

The north end of Powell Plateau lies just beyond the northern 

border of the map. Here the outlook is still more extended. To the 

southwest the canyon is visible through the Kanab division for 50 

miles; beyond are the white outer walls of the outer canyon in the 

Uinkaret and Shivwits plateaus. South of the canyon the San 

Francisco Plateau stretches far away into central Arizona; across it
COPPER DEPOSITS OF SHINUMO QUADEANGLE, 93

may be seen the walls of Cataract Canyon. North of the Grand 

Canyon lies the surface of the Kanab Plateau, broken only by the 

gorge of Kanab Creek; along the western border of the Kanab 

Plateau, beyond the mouth of Toroweap Valley, rise the mountains 

of the Uinkaret, a group of lava flows and recent cinder cones dominated by Mount Trumbull; many of the cinder cones are clearly 

visible. Along the northern border of the Kanab are the cliffs and 

terraces of Mesozoic strata, beginning with the Vermillion Cliffs, 

composed of Triassic strata, and receding step by step to Pink Cliffs, 

which are composed of Tertiary strata. To the northwest the 

promontories of Vermillion Cliffs fade below the horizon 100 miles 

away.

In the foreground, directly below, is Tapeats Amphitheater, an 

expanse of Esplanade 12 miles across, trenched by the single gorge 

of Tapeats Creek and by two arms of the great lateral gorge which 

runs northward from Muav Saddle across the head of the Amphitheater in the line of the West Kaibab fault. Along Colorado River 

above the mouth of Tapeats Creek may be seen the mass of Unkar 

strata which lies in the Lower Granite Gorge and represents the 

prolongation of the Shinumo wedge northwestward underneath 

Powell Plateau.

To the geologist these two views from Powell Plateau are encyclopedic. The rocks that are visible represent in turn a portion of every 

great geologic age, and the stratigraphic position of each system of 

rock is apparent at a glance. Every great earth-making process is 

illustrated; sedimentation by a thickness of over 16,000 feet of 

unaltered strata reaching from Algonkian to Tertiary; regional 

metamorphism by the Archean rocks; contact metamorphism by 

certain Unkar strata; vulcanism by deep-seated invasions in the 

Archean, by intrusive sheets in the Unkar strata, and by surface 

eruptions in the San Francisco Mountains and the hills of the Uinkaret 

Plateau; deformation by the mashed and crumpled Archean rocks, 

by -the faulted Algonkian rocks, and by the great displacements that 

traverse the Paleozoic strata. Perhaps the most impressive record of 

all is that of the processes of uplift and erosion the ancient cycles 

denoted by the unconformities that separate the systems of rock; 

the later cycles by the removal of vast thicknesses of strata and the 

production of the surface of the region in its present aspect.

The panorama is probably the most complete geologic revelation 

in the world.

COPPER DEPOSITS OF THE SHINUMO QUADRANGLE.

Occurrence. With one exception all the copper deposits in the 

quadrangle are found in the Archean and Algonkian rocks in the 

depths of the canyon.
94 SHINUMO QUADRANGLE, GRAND CANYON DISTRICT, ARIZ,

History. The discovery and exploration of the deposits is the work 

of Mr. W. W. Bass and Mr. John Walthenberg. A large amount of 

prospecting has been done and claims have been located in Copper 

Canyon, Bass Canyon, Granite Gorge near Cable Crossing, Shinumo 

Canyon between White Creek and Flint Creek, along the line of the 

West Kaibab fault, and on Muav Saddle.

The most valuable bodies of ore so far found are in Copper Canyon, 

from which about 25 tons of ore were taken in 1908. The ore was 

carried to the rim of the Grand Canyon on burros, and hauled thence 

20 miles by wagon to Grand Canyon, a station on the Grand Canyon 

Railway, of the Santa Fe system. Some exploratory work has been 

done at the other localities, but so far no attempt has been made to 

take out ore for shipment.

Geology. The claim in the Muav Saddle is the only one in the 

Paleozoic rocks. It is just at the point where the trail up Muav 

Canyon enters the saddle, at an elevation of 6,700 feet. Some copper 

mineralization occurs along the contact of the Supai formation and 

Coconino sandstone, where the beds are shattered by the West 

Kaibab fault, and this mineralized zone is now being explored by an 

open cut. The copper here is doubtless of the same age and origin as 

that of the deposits found on the surface of Kaibab and Coconino 

plateaus in other parts of the Grand Canyon district.

The deposits in Copper Canyon are, in method of occurrence, a fair 

type of all the deposits in the Archean and Algonkian rocks in the 

quadrangle. As they are the only ones now accessible to underground 

study a description of them will also serve in a general way for those 

at the other localities.

The country rock of the interior of Copper Canyon beneath the 

Paleozoic is the Vishnu schist, of the Archean system. At the end of

the great pre-Cambrian erosion .the basal strata of the Unkar group

of the Algonkian extended part way across the Granite Gorge of 

Copper Canyon, terminating there as the apex of the Algonkian wedge. 

Only a few layers of. these strata in that locality, however, have 

escaped the present cycle of erosion. These lie high up under the 

cliff of Tapeats sandstone, in the eastern wall of the Granite Gorge of 

Copper Canyon.

The ore bodies in Copper Canyon all lie in the rocks of the Vishnu 

schist which in this locality ..are quartz-mica schists and pegmatites. 

The ores are found in two main veins, which will be described.

The outcrop of the first vein runs northwestward across the Granite 

Gorge of Copper Canyon. The vein is almost vertical, dipping 

slightly southwestward. On the east side of the creek, at the bottom 

of the canyon, a tunnel has been driven in southwestward for over 

100 feet along the strike of the vein. This tunnel is about half a mile 

from Colorado River, at an elevation of about 2,800 feet. . A vertical
. COPPEE DEPOSITS OF SHINUMO QUADRANGLE. 95

shaft has also been sunk 50 feet on the vein which it followed down 

the dip from the surface outcrop. This shaft intersects the tunnel 

at a point 15 feet below the surface of the ground and 25 feet from the 

mouth of the tunnel. All the ore that has been taken from Copper 

Canyon for shipment has come from these workings.

The ore minerals of the vein in this locality are cuprite, bornite, and 

chalcocite. The first two minerals make by far the greater proportion of the, ore mined. The chalcocite has come from the most recent 

workings at the bottom of the shaft. The gangue of the vein is 

chiefly brecciated mica schist cemented by milky quartz and some 

calcite. The vein shows the usual pinches and swells, and averages 

about 1 to 2 feet in width. The minerals on the outcrop of the vein 

are considerably weathered, making incrustations of malachite and 

green silicate of copper.

The second vein crosses the creek bed a few hundred feet north of 

the first vein. Its strike is nearly east and west and its dip is about 

60° N. About 200 feet above the level of the bed of the creek where 

it is crossed by the vein a tunnel, known as the Hakataia tunnel, has 

been driven westward along the strike of the vein for 75 feet. The 

vein at the tunnel in about a foot wide. The ore minerals taken from 

the tunnel include cuprite, bornite, chalcopyrite, and argentiferous 

galena. The gangue is quartz. Near the surf ace the ores are leached 

of their values by weathering but grow richer underground.

The two veins converge toward the west in the western wall of 

Copper Canyon. Their inclined dip would also cause them to converge upward on the eastern side of the canyon, but this part of their 

apex has been removed by erosion.

The second vein was traced upward in the eastern wall of Copper 

Canyon to the base of the Unkar strata and was found to be on the. 

prolongation downward into the Archean rocks of one of the Algonkian faults. It is therefore a simple mineralized fault fissure. The 

first vein was similarly traced upward but was found to be truncated 

by the pre-Tonto unconformity just beyond the apex of the Algonkian 

wedge, so that its relation to the Algonkian faulting could not be 

positively determined. It represents, however, a filled fissure produced by a normal fault of small throw, the evidence of which is 

found in the offset of certain pegmatite veins that are sheared by the 

fault. This fissure is doubtless the downward prolongation of an 

Algonkian fault like that on which the other vein is located.

All the other deposits in the Archean and Algonkian rocks occur 

either in similar fissure veins, which represent" the mineralized fault 

planes of normal Algonkian faults, or in the zone of shattering along 

the line of the Algonkian displacement of the West Kaibab fault. 

All the faults belong to the same period of disturbance, the one in 

which the great mountain-making movement came at the end of 

Algonkian time.
96 SHINUMO QUADRANGLE, GEAND CANYON DISTRICT, ARIZ.

Age. The primary ore deposition undoubtedly occurred in 

Algonkian time, as all the ore-bearing fissures are truncated by the 

unconformity at the base of the Paleozoic.

Origin. The origin of the primary ore deposition is not clear. The 

event with which it is obviously connected is the Algonkian mountainmaking movement, but the specific causes that set up the circulation 

of the mineral-bearing solutions are a matter of speculation. It is 

possible that some sort of a genetic connection may have existed 

between the mineral-bearing solutions and the igneous activity manifested by intrusions of diabase in the Unkar strata of the Shinumo 

region, although it is clear that the intrusions in this locality were 

earlier than the faulting that gave rise to the mineral-bearing fissures.

Value. The deposits in Copper Canyon are locally of high grade, 

but not enough work has been done to give, an accurate idea of their 

extent and quantity.
INDEX.

A. Page.

Acknowledgments to those aiding........... 15

Algonkian rocks, occurrence and character

of....................... 30-31,37-60,61

Altitudes, data on........................... 24-25

Archean rocks, occurrence and character of. 29-30,

31,32-37 

Asbestos, occurrence of................... 13,58-59

origin of................................. 59-60

Asbestos mine, section at.................... 58

Aubrey group, distribution and character of. 68-71 

geologic relations of...................... 61

subdivisions of........................... 61,68

Aztec Amphitheater, altitude of............. 25

B.

Bass, W. W., copper prospecting by......... 94

Bass Camp, location of...................... 11-12

Bass Canyon, cirque at head of....... 22 (PI. VII)

folds and faults in............ 78,78 (PI. XVI)

rocksin...................... 40,55(PI.XIV)

section in................................ 65

tank in ............................. 11 (PI. I)

Bass limestone, character of..... 30 (PI. IX), 43-48

deposition of............................. 81

geologic relations of...................... 41

section of.......................... 44-46,55,58

views of........................... 38(P1.X),

39 (PI. XI), 54 (PI.

XIII), 86 (PI. XVIII)

Bedrock Tank, view at.................. 11 (PI. I)

Bibliography...........;..................". 13-15

Bright Angel Creek, rocks on........ 38,38 (PI. X)

Bright Angel fault, location of............... 78

Bright Angel shale, deposition of............ 84

distribution and character of...... 30 (PI. IX),

62-64,74 

fossils in................................. 64,84

section of................................ 63

views of................ 20 (PI. V), 38 (PI. X),

39 (PI. XI), 79 (PI. XVII), 86 (PI. XVIII) 

Burro Canyon, view in ............. 79 (PI. XVII)

Butte fault, character of..................... 79

C.

Cable crossing, description of................ 11,

16 (PI. Ill), 54 (PI. XIII) 

Cambrian system, distribution and character

of............................. 31,61-65

Camps, locations of.......................... 11-12

Canyons, description of...................... 17

Carboniferous rocks, occurrence and character

of............................. 31,66-71

Carkhuff, N. W., photographs by............ 20

21,38,39,54,79,86 

Cataract Canyon, location of................. 19

Chuar group, distribution of............... 37,38,40

geologic relations of...................... 7-8

See also Grand Canyon series.

29745° Bull. 549 14 7

Climate, character of........................ 25-27

Coconino fold, description of................. 78-79

Coconino Plateau, climate of................. 26-27 . description of...................... 19,24-25,27

location of............................... 17

Coconino sandstone, deposition of........... 85

distribution and character of.... 30 (PI. IX),69

thickness of.............................. 72-73

views of........................... 20 (PI. V),

21 (PI. VI), 38 (PI. X),

39 (PI. XI), 86 (PI. XVIII)

Colorado Plateau, description of....'......... 15-16

Colorado River, canyons of.................. 17

cutting of.......................... 87-88,89-90

description of............................ 22-24

Copper, deposits of.......................... 93-96

Copper Canyon,copper in.................... 94-95

Crystal Creek, rocks on...................... 38

D. 

Barton, N. H.,cited......................... 68,69

work of.................................. 60

Darwin Plateau, altitude of................. 25

Davis, W. M., cited..................... 74,89-90

Denudation, the great, occurrence of.... 87,88,90

'Diabase, age of............................. 60

asbestos in. See Asbestos.

invasion of.............................. 83

lower contact of................. 55 (PI. XIV)

metamorphism of....................... 57-58

occurrence and character of............. 55-60

views of......................... 639(P1. XI),

52 (PI. XII), 54 (PI. XIII),

55 (PI. XIV), 64 (PI. XV),

79 (PI. XVII), 86 (PI. XVIII)

Diller, J. S., on asbestos.............. 13,14,58-60

box sandstone, character of........ 30 (PI. IX), 53

deposition of........................... 82

geologic relations of..................... 41

section of............................... 53,55

views of............ 39 (PI. XI), 54 (PI. XIII)

Dutton, C. E., cited.... 1....... 20,38-39,73,89-91

work of............................... 7,13,14

Dutton Point, view from................... 92

E. 

Echo Cliffs, location of...................... 17

Erosion, record of................... 22 (PI. VII),

26-27, 30, 70, 78 (PI. XVI), 80-88 

Esplanade, description of....... 18,21-22,25,27-28

origin of................................ 73-75

view of........................... 21 (PI. VI)

Evans, R. T., work of...................... 8

F.

Faulting, description of..................... 75-80

effect of, on topography................. 79-80

occurrence of................ 79 (PI. XVII), 83

Field work, extent of....................... 13

97
98 INDEX.

Folds, description of........................ 76-80

views of......... 78 (PL XVI), 79 ( PL XVII)

Fossil Mountain, rocks of................... 70

section near............................ 70-71

viewof.......................... 22(P1.VH)

Fossils, occurrence of......... J............. 84,86

See also particular formations.

. G.

' Geography, description of.................. 11-12

Geologic history, account of. 80-91,86 (PI. XVIII) 

Geologic map of Shinumo'quadrangle........ PI. I,

in pocket. 

Geology, description of..................... 20-75

Gilbert, G. K., work of...................... 15,60

Girty, G. F., fossils determined by.......... 71

Goldthwait, J. W.,and Huntington, E.,on

Colob sandstone................ 85

Grand Canyon, age of....................... 88

climate in............................... 25-26

description of..................... 17-18,21-25

exploration in........................... 7-8

history of................................ 89-91

map of...................... 8, PL I, in pocket.

strata revealed by...................... ' 7

travel in..... i................ 11 (PL I), 11-12

Grand Canyon district, description of. ...... 16-21

Grand Canyon series, age and correlation of.. 54-55 

distribution and character of............ 37.

geologic relations of...................... 7

history of............................... 80-83

intrusions in............................ 55-60

name of................................. 37

structure of............................. 39,40

unconformity in......................... 37

See also Unkar group; Intrusive diabase. 

Granite Gorge, description of............. 18,21,23

rocks of............ 23,29,32,35,36,38,39-40,61

views in............ 16 (PL III), 28 (PL VIII)

H.

Hakatai Canyon, rocks in................ 43,57-58

section in............................... 48

Hakatai shale, character of...... 30 (PI. IX), 48-51

- deposition of............................ 81-82

geologic relations of...................... 41

section of............................. 48-50,55

views of............... 38 (PL X), 39 (PL XI),

52(PLXn),54(Pl.XIH),64(Pl.XV),

79 (PL XVII), 86 (PL XVIII)

Havasupai Point, description of............. 24-25

views of and from....................... 21,

21 (PL VI), 22 (PL VH), 92 

Hindu Amphitheater, rocks in.............. 38

Holy Grail Temple, description of........... 25

Hoodoos, occurrence of........... 70,78 (PL XVI)

Hotauta Canyon, rocks in..'...... 38 (PL X), 42-47

section in.............................42,43-46

Hotauta conglomerate, character of.......... 30

(PL IX), 42-43 

deposition of............................ 81

geologic relations of...................... 41

Huethawali, Mount, view of.......... 22 (PL VII)

Huntington, E., and Goldthwait, J. W., on

Colob sandstone................. 85

fluxley Terrace, view of.............. 22 (PL VH)

Indian ruins, distribution and character of... 28-29 

K.

Kaibab limestone, character and distribution

Of............. 16,21,30 (PL IX), 70-71

deposition of............................ 86

fossils of.................................. 71

pinnacles of...................... 78 (PL XVI)

section of................................ 70-71

thickness of.............................. 72-73

viewsof..........:.... 18 (PL IV), 21 (PL VI),

39 (PL XI), 86 (PL XVHI) 

water in, flow of........................ 27,70

Kaibab Plateau, climate on.................. 25

description of...................... 17,18,19,27

Grand Canyon in..................... 18,21,22

Kanab Plateau, description of............ 17,18,19

Grand Canyon in........................ 22

L. 

Lava, deposition of................:......... 87

Lee, W. T., cited............................ 67-68

Literature, list of............................ 13-15

Location of quadrangle....................... 11,12

Lower Aubrey sandstone, changed name of.. 32

M.

Map of Shinumo quadrangle... 8 PL I (in pocket) 

Map, index, showing location of quadrangle. 12 

Marble Canyon, description of............... 17

Marble platform, description of.............. 17

Matthes, F. E., work of..................... 8

Mesozoic rocks, deposition of................. 86

Monadnock, survival of...................... 83

Monadnock Amphitheater, rocks of....... 40,61-62

Muav-Flint canyon,description of.. 1........ 24

faultsin................................. 75-77 .

rocks of.................. 33,39,40,64 (PL XV)

Muav limestone, deposition of............... 84

distribution and character of 30 (PL IX), 64-65 

section of................................ 65

thickness of............................. 72-73

views of.. 20 (PL V), 39 (PL XI), 54 (PL XIII),

64 (PL XV), 79 (PL XVII), 86 (PI. XVIII)

Muav Saddle, copper in..................... 94

description of............................ 19

viewof............................ 18 (PL IV)

N.

Needle Mountains group, character and correlation of......................... 54-^55

Noble, L. F., work of........................ 8-9

Nomenclature, changes in................... 32

O. 

O ttoman Amphitheater, rocks in........... 38

P.

Paleozoic rocks, displacements of............ 78-SO

occurrence and character of........... 31,61-71

previous work on........................ 60

thickness of............................. 71-73

variation in, effect of................ 73-75

Pegmatite, distribution and character of..... 36-37

Physiography, account of.................... 15-21
INDEX. 99

Page.

Plateaus, description of...................... 17

problem of.............................. 88-91

Point Sublime, description of............... 24

view from............................... 91-92

Powell, J. W., cited......................:.. 39,89

work of.................................. 7

Powell Plateau, climate of................... 26

description of......................... 19,20,27

flexures in............................... 78

views on..................... 18 (PI. IV), 92-93

Proterozoicrocks, occurrenceandcharacterof. 32-60

Q.

Quartz diorite, distribution and character of. 35 

R.

Rainbow Plateau, valleys of................. 20

Rainfall, occurrence of....................... 25-26

Ransome, F. L., cited.................... 35,57,65

preface by............................... 7-9

Redwall limestone, deposition of............. 84

distribution and character of. 30 (PL IX), 66-68 

fossils in................................. 67-68

geologic relations of......%................ 61

thickness of....'......................... 72-73

views of.... 20 (PI. V), 38 (PI. X), 39 (PI. XI),

54 (PI. XIII), 79 (PI. XVII), 86 (PI. XVIII) 

Robinson, H. H., cited...................... 75,91

Rock formations, age and character of........ 29-32

columnar section of................ 30 (PI. IX)

S.

San Francisco Plateau, location of........... 18

Scenic features, interest in................... 91-93

Sedimentary and erosional record, data of.... 80-88

Shinumo Amphitheater, description' of....... 22,

24,25,28,79 

Indian ruins in.......................... 28-29

Shinumo Creek, canyon of........... 28 (PI. VIII),

64 (PI. XV) 

canyon of, section in............... 51-52,53,57

description of............................ 23,24

rocks on..... I........................... 38,

52 (PI. XII), 55 (PI. XIV), 64 (PI. XV) 

section on............................... 42

Shinumo quartzite, character of.. 30 (PI. IX), 51-53 

deposition of............................ 82

geologic relations of...................... 41

monadnocks of.......................... 83,84

section of................................ 51-52

views of........ 38 (PI. X), 39 (PI. XI),

52 (PI. XII), 64 (PI. XV),

79 (PI. XVII), 86 (PI. XVIII)

Shinumo wedge, description of........... 40,41,77

See also Unkar wedge. 

Shivwits Plateau, description of............. 17,19

Slate Creek, fault on......................... 78

Snow, occurrence of.......................... 25

Snuffy limestone, distribution and character

of................................ 74

viewsof....................... 79(P1. XVII),

86 (PI. XVIII) 

Springs, source of............................ 27

Structure, description of..................... 75-80

sections showing.............. PL I, in pocket.

Page. 

Supai formation, deposition of............... 84-85

distribution and character of...... 30 (PL IX),

68-69,74 

sandstone of............................. 68-69

shale of.................................. 67

thickness of............................. 72,73

viewsof.............. 20 (PL V), 21 (PL VI)<

38 (PL X), 39 PL XI), 86 (PL XVIH)

T. 

Tapeats Creek, description of................ 22

Tapeats sandstone, deposition of............. 84

distribution and character of.. 30 (PL IX, 61-6 

section of................................ 62

thickness of............................. 72-73

views of............................ 20 (PL V),

38 (PL X), 39 (PL XI), 54 (PL XIII),

55 (PL XIV), 79 (PL XVII), 86 (PL XVIH)'

Tertiary rocks, deposition of................. 86

Tertiary time, history of..................... 91

Timber, growth of........................... 27-28

Tonto group, deposition of................... 83-84

distribution and character of............ 61-65

Tonto platform, description of......... 18,22,25,28

origin of.............................. 73,75,78

view from.............. 18 (PL IV), 20 (PI. V)

Tonto sandstone, changed name of........... 32

Tonto shale, changed name of............... 32

Trails, routes of..................... 11-12,18,19,29

Uinkaret Plateau, description of............. 17,19

Unconformities, occurrence and character

of.......... 30(PLIX),30,31,61,65-66,

84, 86 (PL XVHI), 87-58 

Unkar group, character of'................... 40-53

deposition of............................. 81-83.

geologic relations of....................... 7-S(

intrusive diabase associated with........ 55-60,

See also Diabase, 

name of................................. 37

section of............................. 42,44-^53

structure of.............................. 39-40

subdivisions of.......................... 41-42,

See also particular subdivisions. 

views of.... 16 (PL III), 20 (PL V), 38 (PL X)

Unkar monadnock, description of............ 61,62

Unkar Valley, section in..................... 53-54

Unkar wedge, faults in............... 64 (PI. XV),

77-78,79 (PL XVTI) 

view of............................ 18 (PL IV)

V. 

Valleys, beheaded, occurrence and character

of................................ 20

Vegetation, character of..................... 27-28

Vishnu Creek, rocks in...................... 38

Vishnu schist, age and correlation of......... 33

distribution and character of. 30 (PL IX), 32-33 

geologic relations of................. 7-8,29,31

intrusions in............................. 35-37

name of................................. 32

origin of.......................:...... 34-35,80

types of................................. 33-34

viewsof.......................... 16 (PL HI),

20 (PL V), 38 (PI. X), 

39 (PL XI), 86 (PL XVHI)
INDEX.

W. Page.

Walcott,C.D.,cited.................. 32,37,65-66

work of................................ 7,15,60

Walthenburg, John, copper prospecting by.. 94 

Warping, occurrence and character of........ 20-21

See also Faulting; Folding.

Page. 

West Kaibab fault, age of................. 75-76,77

description of...................... 20,39,75-77

effect of....................:....... 18 (PI. IV)

line of............................. 39 (PI. XI)

Wheeler fold, description of......... 78 (PI. XVI),

79 (PI. XVH)

o