Cenozoic Geology of the

By CHARLES B. HUNT

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director '

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C. - Price 75 cents (paper cover)
Abstract. __________________________________________

Tn troduction_______________________________________

Purpose of report and acknowledgments____-________

General geographic setting of the Colorado Plateau.__ 

Pre-Cambrian basement rocks._______________________

Summary of Paleozoic and Mesozoic stratigraphy._____

Cenozoic deposits.__________________________________

Lower Tertiary deposits (Paleocene and Eocene)______

Uinta Basin and High PJateaus___________________

Nor tli Horn formation _________________________

Flagstaff limestone and Wasatch formation in High 

Plateaus.__________________________________

Tuscher, Ohio Creek, and DeBeque formations. __ 

Colton and Wasatch formations in Uinta Basin._ 

Green River formation________________________

Bridger formation.____________________________

Uinta formation._____________________________

Duchesne River formation _____________________

San Juan Basin_________________________________

Animas formation.__________________________

Nacimiento formation (Puerco and Torrejon faunal 

zones) _____________________________________

Wasatch (San Jose) formation, .(and Tiffany beds)_ 

Mogollon Rim....._______________________________

Deposits in adjoining areas_---_---_---_----__-_-_

San Juan Mountains-_________________________

Rio Grande Valley.___________________________

Southern Arizona.____________________________

Upper Tertiary deposits (Miocene and Pliocene) _____

High Plateaus.-.-____________-_--------____-___

Brian Head formation.._______________________

Sevier River and Parunuweap formation_______._

Southern part of the Colorado Plateau. ___________

Bidahochi formation __________________________

Chuska sandstone.____________________________

Datil formation_______________________________

Deposits at Peach Springs, Ariz________________

Interior of the Plateau. __ _______________________

Deposits around the edges of the Colorado Plateau__ 

Uinta Basin area_________-_-_____-_-___--____

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Cenozoic deposits Continued

Upper Tertiary deposits (Miocene and Pliocene) Con. 

Deposits around the edges of the Colorado Plateau 

Continued 

San Juan Mountains.___-_--_----_-_-----___-_

Rio Grande Valley____________________________

Grand Wash trough_____________________._____

Quaternary deposits____ ~__________________________

Pre-Wisconsin deposits. _________________________

Wisconsin deposits._____________________________

Recent deposits._._____________________________

Cenozoic igneous rocks________.._____-_-_--__________

General features._________________________________

Early Tertiary igneous rocks.______________________

Late Tertiary igneous rocks. _______________________

Laccolithic mountains-_______-----____-_-_-_____

Large central-type volcanoes- _ ___________________

Volcanic rocks and intrusions in the central part of the 

High Plateaus._______________________________

Basalt and alkalic basalt series._-________--_--___

Quaternary igneous rocks._________________________

Structural geology._________-_-____-_-____-----_____

General features._________________________________

Pre-Cenozoic structural elements___--______----____

Cenozoic erogenic structures._______..__-____--____-

Early Tertiary structures.___-_-_--_______--__-__

Late Tertiary structures.________________________

Quaternary structures.____-__-_---_______-___-__

Cenozoic igneous structures._______________________

Cenozoic epeirogenic structures.____________________

Physiography._______________!_____________________

Climate and water supply-__-_-------_---------___-

Anteposition_ _ ___________________________________

Colorado and Green Rivers-_______________________

Tributary streams._______________________________

Erosion and geologic time.________________________

Soils.___________________________________________

Cenozoic history of the Plateau a hypothesis__--_-_._- 

Bibliography__ ___________________________________

Index._____________________________________________

ILLUSTRATIONS

Page

FIGURE 1. Index map of the Colorado Plateau. _______

2. Diagrammatic view of the Henry Mountains 

region._______________________________

3. Diagrams showing formation of natural 

bridges.______________________________

4. Climatic maps of Colorado, Utah, Arizona, 

1 and New Mexico_---_-_-------_-_-----_

5. Vegetation map of the Colorado Plateau.___

FIGURE 6. Soil formations on the Colorado Plateau.._.

7. Mineral deposits on the Colorado Plateau. __

8. Isopach map showing thickness of Paleozoic 

formations on the Colorado Plateau._____

9. Cross section of basin under Black Mesa and 

of San Juan Basin______________________

10. Isopach map showing thickness of Mesozoic 

formations on the Colorado Plateau._____

in

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Cross section of Mogollon Rim, illustrating 

overlap of Upper Cretaceous formations 

southward onto Permian form;ations______

Correlation chart of Cenozoic formations on, 

and adjacent to, the Colorado Plateau____

Diagrammatic section of formations exposed 

in the western part of the Wasatch Plateau.

Cross section of Grand Hogback, near Meeker, 

Colo________________________________

Diagrammatic cross section of the Uinta 

Basin north from Green River, Utah_____

Stratigraphic relations of the subdivisions of 

the Green River formation in Colorado and 

Utah.________________________________

Sections from northwest to southeast in the 

Green River Basin, Wyo. and Colo., showing intertonguing of the Wasatch and Green 

River formations.______________________

Diagrammatic section across the San Juan 

Basin from Durango, Colo., to Pueblo 

Bonito, N. Mex________________________

Diagram showing inferred Stratigraphic relations of Paleocene and Eocene formations 

on east side of San Juan Basin.__________

Map showing outcrop of Bidahochi formation

Cross section of the Defiance uplift_________

Geologic map and cross section of part of 

Grand Wash trough.___________________

Cross section of valley fill in vicinity of Grand 

Wash trough. _________________________

Diagrams illustrating four stages in the development of pediments in the Colorado 

Plateau _______________________________

Diagrammatic sections illustrating some 

common Stratigraphic relationships in the 

alluvial deposits on the Colorado Plateau.

Sketch map illustrating distribution of Cenozoic igneous rocks on the Colorado Plateau.

Variation diagrams showing proportions of 

alkalis and silica in the igneous rocks in 

four parts of the Colorado Plateau_______

Diagrams illustrating the relationship between the stocks and the domes at the 

laccolithic mountains on the Colorado 

Plateau ________-__-_____-__-_-_----___

Structure-contour map of the Henry Mountains --_______-___--__----_---__-_____

Ground plan of intrusions around the Mount 

Ellen stock in the Henry Mountains____

Diagrams illustrating shapes of laccoliths and 

bysmaliths on the Colorado Plateau______

Schematic section through a nonporphyritic 

stock in the La Plata Mountains_________

Diagrammatic view of part of the Mount 

Taylor volcanic field____________________

Map of San Francisco volcanic field, showing 

distribution of cones----____---__-___-__

CONTENTS

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FIGURE 35.

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PageGeologic cross sections of San Francisco

Mountain and vicinity_________________ 48

Maps of some volcanic necks in the NavajoHopi fields.___________________________ 50

Structure-contour map of the Colorado Piateau________________________________ 52

Section across the Zuni Mountain upwarp,

N. Mex_____________________________ 53

Sections across the Gallup-Zuni Basin, N.

Mex_.________________________________ 54

Generalized m.ap of part of eastern Utah and

western Colorado ______________________ 55

Cross section of fault blocks in High Plateaus

southeast of Salina, Utah. ______________ 56

Block diagrams showing that part of Utah 

north of latitude 39° 30' at four stages in 

Late Cretaceous time.__________________ 56

Block diagram illustrating the faulted cast 

edge of the Colorado Plateau, east of Mount 

Taylor, N. Mex________"________________ 58

Tectonic map of part of the San Juan Basin

and the Rio Grande depression __________ 59

Diagrammatic section illustrating faulting

east of Mesa Lucero____________________ 59

Sequence of late Tertiary and Quaternary

events in the Mount Taylor volcanic field. 60

Structure sections across the Hurricane fault 

zone showing four stages in its development- _-_-__-_--_--_--_--_-__-___-_-._ 61

Block diagrams illustrating stages in the development of Lodore Canyon____________ 66

Diagrams illustrating anteposition_________ 67

Generalized view of south-central Utah looking north from the Utah-Arizona boundary 

line______________________________ 69

Generalized block diagrams representing 

stages in the physiographic history of upper 

Paria Valley...___ __-_-_-_-___-__._-_._ 70

Block diagram of the San Juan Canyon across

the Monument Upwarp_________________ 71

The Colorado Plateau area in late Cretaceous

time__ ______________________________ 74

The Colorado Plateau area in early Paleocene

time__________________________________ 75

The Colorado Plateau area in late Paleocene

time____ _ _____________________________ 76

The Colorado Plateau in. early and middle

Eocene time___________________________ 78

The Colorado Plateau in late Eocene time___ 79

The Colorado Plateau in Oligocene time____ 80

The Colorado Plateau in early Miocene time. 81

The Colorado Plateau in middle Miocene

time __-_______-___---_-___--__--_--_-_ 83

The Colorado Plateau in late Miocene to

middle Pliocene time___________________ 84

The Colorado Plateau in late Pliocene to

Recent time..._-______-____-_____---__ 86
CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

By CHARLES B. HUNT

ABSTRACT

The pre-Tertiary structural history of the Colorado Plateau 

undoubtedly controlled its Cenox-oic history to considerable 

extent. 'The pre-Tertiary history seems to have been one of 

comparative stability because during most of Paleozoic and 

Mesozoic time the Colorado Plateau was a shelf area and was 

without deep geosynclinal basins except during Pennsylvanian time. Thus, the general plateau structure, which is of 

Ccnozoic age, appears to be an inherited feature.

Deposits of early Cenozoic age are well represented on, or 

adjacent to, the Colorado Plateau, but deposits of late Cenozoic age are scarce. As a result, the early Cenozoic.history is 

known fairly well but there are major gaps in the record for 

late Cenozoic time. In adjoining parts of the Basin and Range 

province the reverse is true; there, deposits of early Tertiary 

age are scarce but deposits of late Tertiary age are extensive.

Paleocene and Eocene deposits in the Uinta Basin and San 

Juan Basin record that the Plateau area was a basin or trough, 

probably near sea level, and was surrounded by newly formed 

mountains. The trough or basin was the product of folding that began in late Cretaceous time and continued intermittently during the first half of the Tertiary. In the lower 

ports of the trough, several thousand feet of lacustrine and fluviatile sediments were deposited.

After Eocene time, conditions changed markedly. General 

aggradation of the Plateau area ceased, and general degradation began. Igneous activity, in the form of volcanism and 

intrusion, became extensive. There was extensive faulting, 

especially along the west and south edges of the province, and 

epeirogenic uplift began. The erosion, igneous activity, 

faulting, and uplift have continued to the present time.

It is inferred that exterior drainage started when the Plateau began to be uplifted, and that the major courses of the 

streams probably were established before epeirogenic uplift 

had progressed very far. Also, it is believed that the canyon 

cutting began when the uplift started and that it lias progressed 

to the present time.

Cenozoic intrusive rocks, believed to be of late Tertiary age, 

in the Colorado Plateau occur as stocks, laccoliths, and bysmaliths in the dozen or so laccolithic mountains. Upper Tertiary 

eruptive rocks occur at the large central-type volcanoes at 

Mount Taylor and San Francisco Mountain and as extensive 

sheets of basaltic lavas and pyroclastic rocks. The volume of 

igneous rocks is considerable but is only a percent or so of the 

volume of eruptive rocks in the San Juan Mountains or of adjoining parts of the Basin and Range province.

As a petrographic province, the Colorado Plateau is high in 

alkalies and alumina. Four subprovinces can be distinguished 

within the Plateau. In the interior, in the laccolithic mountains, 

the percentage of soda greatly exceeds that of potash. In the 

High Plateaus, soda and potash are about equal. In the Navajo

and Tuba volcanic fields, potash exceeds soda. Along the 

southern edge of the Plateau, soda exceeds potash.

At the end of Cretaceous time the Plateau was a piedmont 

area extending eastward and northeastward from the foot of 

mountains that had been built by thrust faulting and folding 

in the adjacent parts of the Basin and Range province. When 

the Rocky Mountains were raised the Plateau area became a 

structural basin or trough.

The orogenic structures on the Plateau are believed to have 

formed during early Tertiary time. The structures associated 

with the igneous activity are believed to have been formed 

while the area was being uplifted epeirogenically in middle or 

late Tertiary time.

The meandering course of the Colorado River across the 

various orogenic structures led to the concept of antecedence, 

and later to that of superposition. Actually, neither theory 

alone seems adequate to explain all the anomalies of the Colorado River drainage, but a combination of the two processes, 

for which the term "anteposition" is suggested, offers explanations for many of them. Anteposition refers to arching of a 

canyon so that a stream becomes ponded and deposits sediment 

upstream from the arch. When dowucutting is resumed, a new 

superposed course is developed in the stretch represented by 

the reservoir. But the low point on the rim of the reservoir is 

the raised portion of the old valley; this becomes the new spillway and downstream from this point the new valley has the 

aspects of antecedence.

INTRODUCTION 

PURPOSE OF REPORT AND ACKNOWLEDGMENTS

Geologically, the Colorado Plateau ranks as one of 

the better known parts of the United States. Much 

geological work has been done there and, on the whole, 

exposures are superb. Yet, despite these favorable conditions, the Cenozoic history of the Plateau is known 

only very incompletely because datable Cenozoic deposits are feAV. This report endeavors to summarize 

what is known about the Cenozoic geology of the Plateau and to present an historical interpretation of the 

available data. But in view of the scarcity of Cenozoic 

deposits, much, indeed most, of the historical interpretation must be based on subjective inference, and therefore the history presented is in the form of a hypothesis.

An attempt to summarize and interpret the Cenozoic 

geology of an a:rea as large as the Colorado Plateau 

constitutes an ambitious undertaking, in which, of necessity, one must lean heavily on assistance from his
CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

colleagues. In particular, I received many suggestions 

and constructive criticisms from John B. Reeside, Jr., 

James Gilluly, and Henry G. Ferguson of the Geological Survey, Aaron C. Waters of Johns Hopkins University, and Chester R. Long-well of Yale University. 

The report was written very largely because of urging 

by L. C. Craig of the Survey. In acknowledging this 

assistance, however, it is not to be implied that the individuals agree with the interpretations that are offered. 

Because the descriptive data in this report have been 

abstracted from previous publications, many sentences 

and, in some instances, entire paragraphs are direct quotations. Quotation marks have not been used but the 

earlier reports from which the information was taken 

have been cited.

GENERAL GEOGRAPHIC SETTING OF THE 

COLORADO PLATEAU

The Colorado Plateau covers above 150,000 square 

miles in southeastern Utah, northern Arizona, northwestern New Mexico, and southwestern Colorado. 

About 90 percent of this area is drained by the Colorado 

River and comprises about one-half the drainage basin 

of the river. Figure 1 shows the outlines of the 

Plateau and the principal geomorphic subdivisions.

The Colorado Plateau differs from neighboring provinces in stratigraphy, in mode of occurrence and composition of the igneous rocks, and in structure. Its 

C/enozoic history differed from that of the adjoining 

provinces. As a result of all these factors, the geomorphic forms on the Colorado Plateau differ from those 

of the adjoining provinces. And as a result of differences in these factors within the Plateau, there are 

major differences in the geomorphic forms from one 

part to another. On the basis of these differences, the 

Plateau as a geomorphic province has been subdivided 

into 6 sections (Fenneman, 1928, p. 338-342). (See 

fig. 1.)

At the north edge of the Plateau is the Uinta Basin, 

the central part of which is about 6,000 feet above sea 

level but the surface rises northward to the Uinta 

Mountains and southward to the rims of the cliffs 

that face southward and overlook the Canyon Lands. 

The Uinta Basin resembles the Wyoming Basin to the 

north but is set apart from it by the Uinta Mountains 

and by rough topography along a structural arch 

extending eastward from the mountains. The Uinta 

Basin is structurally the lowest part of the Colorado 

Plateau and still retains a thick section of Tertiary 

rocks. The drainage on these Tertiary rocks accords 

with their structure and shows no important anomalies. 

The Duchesne River is an example.

The north edge of the Uinta Basin is along the hogbacks where the formations are turned up at the south

foot of the Uinta Mountains and along a structural 

arch extending eastward from the mountains. The 

east edge is along the Grand Hogback at the west foot 

of the White River Plateau. The southern edge is 

along the southward-facing Book Cliffs, the great 

southward-facing cuesta of Upper Cretaceous and early 

Tertiar}7 formations retreating northward off the 

epeirogenic upwarp in southeastern Utah.

Just south of the Uinta Basin is the Canyon Lands 

section, a plateau surface most of which is 5,000 to 

7,000 feet above sea level. This area has been epeirogenically upwarped, and on top of the upwarp are several huge folds. Throughout this area the drainage is 

deeply incised in canyons in the pre-Tertiary rocks. 

Geomorphic features of the area are the elevated plateaus on the up folds, hogbacks on their flanks, lower 

plateaus betAveen the upfolds, laccolithic mountains 

rising above the plateau surfaces, and an intricate set 

of deep canyons (fig. 2). Among the unusual 

geomorphic features are the natural bridges (fig. 3) and 

the related alcove arches (Hunt, 1953) that provide 

huge shelters along the canyon walls. Except for a few 

local deposits, like those believed to be of Pliocene age 

in the salt anticlines, no deposits of Tertiary age remain 

in the Canyon Lands section. At a prior period, however, there may have been extensive deposits similar to 

the Browns Park and Bidahochi formations along the 

main valleys.

Because of the general discordance between the drain- o

age and the erogenic structures it is easy to overemphasize this particular geomorphic feature. Actually, 

the courses of the Green and Colorado River in the 

Canyon Lands section are rather accordant with the 

principal erogenic structures.

The Canyon Lands section ends, at the north, at the 

foot of the Book Cliffs. On the east, it ends where the 

formations rise onto the San Juan Mountains. On the 

west, it ends at the base of the High Plateaus and commonly, but not always, along a fault. On the south, 

it is bounded by the less folded Navajo section which 

embraces the basin under Black Mesa and the San Juan 

Basin. Most of the laccolithic mountains, but almost 

none of the volcanic rocks, are in the Canyon Lands 

section.

The Navajo section of the Colorado Plateau is about 

as high as the Canyon Lands but much less dissected 

it is an area of mesas and broad open valleys. The 

formations are similar to those in the Canyon Lands 

section, but they have been less folded. Locally, the 

drainage is deeply incised into the rocks, but examples 

are few as compared with the Canyon Lands section. 

The San Juan Basin contains deep Tertiary fill, and 

the landforms are similar to those in the Uinta Basin.
INTRODUCTION

_Cisco

0 rX

J^tJpf 

T| U

i 

kCororaclo\_^-V5#' 

\^'S ^JWi j

-J \L, VIM»\C x -iy

FIGURE 1. Index map of the Colorado Plateau.
^^^^^^.--^z^S^s^ri

Length of view about 36 miles; width about 40 miles

O

After Hunt 1954

1 Fairview

2 Jukes Butte

3 Horseshoe Ridge

4 Table Mtn

5 Stephens Mesa

6 Thompson Mesa

7 Wildcat Mesa

8 Steele Butte

9 Bromide Basin

10 Copper Ridge

11 Eagle City

12 Maze Arch

13 Ragged Mtn

14 The Horn

15 Straight Creek Benches

16 Trachyte Ranch

17 Black Mesa

18 Gold Creek

19 Star Creek

20 Shootaring Creek

21 Eggnog

22 Lost Spring

FIGUHK 2. Diagrammatic view of the Heury Mountains region, a view that is typical of the Canyon Lands section.
INTRODUCTION

After Gregory, 1938

o 

-zAfter Gregory, 19$% 

KIGUKE 3. Diagrams showing formation of natural bridges. (A) Sipapu Natural Bridge, (B) Kachina Natural llridgo.

347620 50 2
6 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

These basin-folded Tertiary formations, and the basinfolded Mesozoic formations in the Black Mesa area, are 

bordered by strike valleys, as is the Defiance upwarp 

(fig. 37). The structures are open, as compared with 

those in the Canyon Lands section, and the drainage 

on the whole is well adjusted to them. Whereas the 

Canyon Lands section is characterized by the laccolithic 

mountains, the Navajo section is characterized by an 

abundance of volcanic necks, dikes, and remnants of 

volcanic cones and small lava flows.

The JSTavajo section has alcove arches as large as 

many of those in the Canyon Lands, and some of these, 

as at Betatakin and Kiet Siel in northern Arizona, 

were used as sites for cities by the prehistoric Puebloan 

Indians.

The northern edge of the Navajo section is at the 

southern limit of the folded rocks of the Canyon Lands 

section, approximately at the Arizona-Utah Boundary 

line. The northeast edge is located where the formations rise onto the uplifts at the San Juan and Nacimiento Mountains. To the south and southwest the 

Navajo section ends about at the north limit of great 

sheets of lava that characterize the southern and southwestern rims of the Colorado Plateau.

The Datil section, which comprises the southeast rim 

of the Colorado Plateau, is extensively and deeply covered with lavas. The boundary between the Plateau 

and adjoining Basin and Range province is sharply 

defined by the westernmost faults of the Rio Grande 

depression east of Mount Taylor, but it is highly arbitrary in west-central New Mexico.

Principal geomorphic features of the Datil Section 

are Mount Taylor, the Zuni Mountains, and the lavacapped mesas and benches to the south. The eruptives 

are of late Tertiary and Quaternary age; a few are 

Recent.

The Grand Canyon section is similar to the Datil 

section in geomorphic and structural form, but the 

Grand Canyon section is higher and more sharply set 

apart from the areas about it. It includes the San 

Francisco Mountain and the extensive lava fields to 

the south, and the Kaibab upwarp and the faulted 

blocks to the west. Except for the Colorado River, 

none of the streams is incised deeply into this part of 

the Colorado Plateau. This is structurally the highest 

part of the Plateau, partly because of ^the Kaibab upwarp and partly because of the southward and southwestward rise of the formations towards the Plateau 

rim.

The southern boundary of the Grand Canyon section 

is along the south-facing cliffs of the Mogollon Rim 

that overlook the belt of faulted and folded preCambrian rocks to the south and along; the Grand

Wash Cliffs on the west. The Little Colorado River 

valley separates this section from the Navajo section. 

A series of plateaus bounded by faults north of Grand 

Canyon are structurally part of the High Plateaus, 

but topographically they belong Avith the Grand 

Canyon section.

Along the west edge of the Colorado Plateau is the 

section known as the High Plateaus of Utah, which 

consists of long, north-trending plateaus, many higher 

than 9,000 feet and some as high as 11,000 feet. The 

north and south ends of the High Plateaus are 

capped by lower Tertiary formations; the central part 

is capped by volcanic rocks, and the lower Tertiary formations are missing. Between the plateaus are broad, 

open, north-trending valleys, most of them draining 

to the Sevier River. The plateaus and intervening 

valleys are defined by the faults of late Tertiary age. 

But, although the topography is fault-controlled, some 

of the escarpments are fault-line scarps where, as at 

Bryce Canyon, the downthrown block now stands 

topographically higher than the upthrown block 

(fig. 51 f.

Like the Datil and Grand Canyon sections, the High 

Plateaus are structurally and topographically a high 

part of the rim of the Colorado Plateau. The major 

uplift in the High Plateaus section is post-Wasatch 

and probably is of late Tertiary and Quaternary age.

In terms of annual precipitation, most of the Navajo 

section^ the High Plateaus, Uinta Basin, and the higher 

parts of the Canyon Lands are semiarid (fig. 4). The 

lowest parts of the Canyon Lands are arid. The Datil 

and Grand Canyon sections are mostly dry subhumid. 

The upper parts of many of the mountains throughout 

the Colorado Plateau are humid, although these areas 

are too small to show on figure 4. However, the precipitation effectiveness in the Colorado Plateau is low, 

especially during the growing season (fig. 4). Because 

of high temperatures and high evaporation the greater 

part of the Plateau has an arid climate during the 

growing season.

The natural vegetation on the Plateau consists mostly 

of northern desert shrub species. The higher parts of 

the Plateau are wooded or forested; many of the mountain tops and highest plateaus are forested with spruce 

and fir (fig. 5).

Soils are shallow and mostly Recent gray desert or 

lithosols that differ greatly in short distances depending on the parent materials (fig. 6). The soils below an 

altitude of about 8,000 feet are of the pedocal type 

that is, they have a limey subsoil. Above 8,000 feet are 

found acid pedalfer (non-limey) types, including graybrown podsolic soils. Recent alluvial soils occur along 

the valleys. Along the Colorado-Utah boundary is
INTRODUCTION

EXPLANATION

More than 30 in.

Less than 10 in.

A. Annual precipitation, in inches (from U. S. Weather Bureau)

EXPLANATION

O-15 16-31 32-47 48-63 64-127 More than 128 P-E INDEX

Arid Semiarid Dry Moist Humid Superhumid CLIMATIC TYPE

subhumid subhumid

B. Normal distribution of climatic types on annual basis (after Thornthwaite, 1941)

EXPLANATION

07 815 1623 24-31 32-63 P-E INDEX

Arid Semiarid Dry Moist Humid CLIMATIC TYPE .

subhumid subhumid

C. Normal distribution of climatic types during growing season, March through August 

(after Thornthwaite, 1941) .. -. ':.-'- ,

Note: P E index is a measure of precipitation effectiveness and is based

; . . ,: . on a formula that evaluates the effectiveness of precipitation in ... ...

.,',.." """., ..- terms of the temperature at which it fell . '.; ",. . " - ; . "

FIGURE 4. Climatic maps of Colorado, Utah, Arizona, and Now Mexico. (Colorado Plateau shown by lioavy lino.)
8 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

N

A

C 0 L O R A D O

W MEXICO

EXPLANATION

Mostly yellow pine forest; includes

spruce-fir forest on some mountain tops

Northern desert shrub, mostly sagebrush

After. Shantz and Zon, 1924

FIGUUE 5. Vegetation map of the Colorado Plateau.
INTRODUCTION 9

COLORADO 1

MEXICO

EXPLANATION

Gray-brown podsolic soils

Lithosois and rough, stony land; 

includes some red desert soils 

in southeastern Utah

From U. S. Dept. Agriculture soil map, 1938

FIGURE 6. Soil formations on the Colorado Plateau.
CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

N

A

LOR D 0

M E X 1 C 0

EXPLANATION

Oil shale deposits. Most of the 

important bitumen or asphalt 

deposits are in this area

Coal

Oil and (or) gas fields

Manganese

Uranium and (or) vanadium

Antimony

Magnesium

Clay

Phosphate

Potash

Salt

Gypsum

Sulfur

Silver

Carbon dioxide

Gold

Copper

Pumice, perlite

Asbestos 

Fluorspar

FIGORB 7. Mineral deposits on the Colorado Plateau.
SUMMARY OF PALEOZOIC AND MESOZOIC STRATIGRAPHY 11

an extensive area of chestnut soils that are developed 

largely on Pleistocene loessial and alluvial upland 

deposits.

The Colorado Plateau has considerable mineral resources, and the Cenozoic history of the Plateau has 

considerable bearing on their occurrence. The most 

developed resource is coal; Gallup, New Mexico and 

Price, Utah are tAvo major coal-producing centers. 

Some of the mineral resources are unusual and have 

posed perplexing problems as to their origin and mode 

of occurrence. Among these are: the sandstone deposits of uranium and vanadium, manganese, and copper-lead ; the gases helium and carbon dioxide; and the 

hydrocarbon gilsonite. Oil shale resources are tremendous. Other deposits include oil, potash, salt, gypsum, pumice, semiprecious stones, and placer and lode 

gold (fig. 7).

PRE-CAMBRIAN BASEMENT ROCKS

The structure of the pre-Cambrian basement rocks 

undoubtedly has been a major factor affecting the 

Cenozoic history of the Colorado Plateau, but data 

about the pre-Cambrian rocks are few. Pre-Cambrian 

rocks crop out extensively south, east, and north of the 

Plateau, but within the Plateau they are exposed only 

in the Uncompahgre Plateau, Grand Canyon, Zuni 

Mountains, and at one small locality on the Defiance 

uplift.

Generally, in these areas the pre-Cambrian consist 

of one or more very thick series of metasedimentary 

and metavolcanic rocks and a series of large and extensive intrusions. The troughs in which the metasediments and metavolcanics were deposited were deep, but 

data are not available to determine their trends or 

Avhet her they were narrow or broad. Nor is the trend of 

the foliation in the pre-Cambrian rocks known at 

enough places to cast light on the grain of the basement 

rocks beneath the Colorado Plateau.

At this stage in our knoAvledge the principal interest 

in the pre-Cambrian rocks, so far as Cenozoic history 

is concerned, is the fact that the pre-Cambrian igneous 

rocks, like the Cenozoic ones, are dominantly subalkalic 

although they include some alkalic types. Also, amphibolite, a common inclusion in Cenozoic intrusions, is 

abundant in the pre-Cambrian rocks.

Principal references to studies of pre-Cambrian rocks 

on the Colorado Plateau are as follows: Grand Canyon area, Noble and Hunter (1917), Campbell and 

Maxson (1938) ; Defiance upwarp, Gregory (1917, p. 

17) ; Zuni Mountains, Lindgren, Graton, and Gordon 

(1910, p. 136) ; Uncompahgre Plateau, Dane (1935). 

Some references to studies of the pre-Cambrian rocks 

around the Plateau are: Hunter (1925); Cross and

Larson (1935) ; Anderson (1951) ; and Calkins and 

Butler (1943).

SUMMARY OF PALEOZOIC AND MESOZOIC 

STRATIGRAPHY

During most of Paleozoic and Mesozoic time the 

Colorado Plateau was a shelf area and was without 

deep geosynclinal basins except during Pennsylvania!! 

time (figs. 8, 10). Pre-Tertiary rocks on the Plateau 

are very much thinner than they are to the east, north, 

and west of the Plateau. This pre-Tertiary history of 

comparative stability no doubt was an important factor 

controlling the events during Cenozoic time, which 

resulted in the Colorado Plateau becoming a distinctive 

province.

Cambrian to Devonian sedimentary rocks are thin or 

absent on the Plateau. They are absent on the Uncompahgre, Zuni, and Defiance upwarps. They are a 

few hundred feet thick and thicken westward in the 

Grand Canyon, along the southwest rim of the Plateau, 

and along the north edge of the Uinta Basin. A moderate thickness of lower Paleozoic rocks may underlie 

some of the basins on the Plateau.

By contrast, in the Basin and Range province, immediately west of the Plateau, the lower Paleozoic 

rocks are 10,000 to 20,000 feet thick. The lower 

Paleozoic deposits also thicken southward across southern Arizona and southern New Mexico. To the east, 

in the Rocky Mountain Province, the lower Paleozoic 

rocks are mostly thin, but in central Colorado there 

was a basin in which 1,000 feet of lower Paleozoic sediments was deposited (Levering, 1932, pi. 2). Therefore, during Cambrian to Devonian time the Plateau 

seems to have been a stable shelf area bordered on at 

least three sides by deep troughs.

Mississippian to Permian rocks on the Plateau also 

are thin by comparison with those to the west, but in 

the north-central part of the Plateau a deep trough 

developed during Pennsylvania!! time. This trough, 

which is known as the Paradox Basin and which apparently is elongated northwestward, lay southwest of 

the Uncompahgre Plateau. The plateau was an unstable area which was uplifted intermittently during 

the late Paleozoic and early Mesozoic time, as well as 

later. At least 7,000 feet of Pennsylvania!! marine 

shale and iiiterbedded salt or other evaporites were 

deposited in the Paradox Basin. These salt deposits 

in the Paradox Basin have resulted in salt plugs and 

salt anticlines (fig. 40). Northeast of the Colorado 

Plateau, in Colorado, there seem to have been other 

Pennsylvanian troughs similar to the Paradox Basin. 

All of these troughs are continuations of the Pennsylvania!! troughs that extended in a northwesterly
12 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

j A R ' Z o N

N

A

0 R A D 0

EXICO

EXPLANATION

" -2^-

- . a- - 

Isopach lines, showing 

thickness of Paleozoic 

formations, in thousands 

of feet

Outline of Colorado Plateau

1

Modified after McKee, 1951

FIGUHK S. Isopach map showing thickness of Paleozoic formations on the Colorado Plateau.

direction across the Rocky Mountain System. With 

the exception of the Paradox Basin, the Mississippian 

to Permian rocks on the Plateau do not exceed 2,500 

feet in thickness.

The upper Paleozoic rocks thicken tremendously 

westward in the Basin and Range province. They are 

more than 20,000 feet thick in northwestern Utah 

(Gilluly, 1932, p. 7) and become much thicker eastward. In the central Colorado Basin they are 5,000 

feet thick (Lovering,. 1932, pi. 2), and in the Sangre 

de Cristo Range they are 12,000 feefc thick (Johnson, 

1929, p. 5).

During late Paleozoic time, therefore, most of the 

Colorado Plateau seems to have been a stable shelf area 

between deep troughs that lay to the east and to the 

west. In Pennsylvanian time the east-central part of
SUMMARY OF PALEOZOIC AND MESOZOIC STRATIGRAPHY 13
14 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

the Plateau was downfolded in a northwestward-trending trough. In addition, there seems to have been an 

arch trending northwestward across the south-central 

part of the Plateau, because in the Zuni Mountains and 

in the Defiance upwarp Permian strata rest directly on 

the pre-Cambrian rocks (figs. 9, 38).

Variations in total thickness of the Paleozoic formations on the Colorado Plateau are illustrated in

The Colorado Plateau continued to be a stable area 

during most of the Mesozoic (fig. 10). The Triassic 

formations throughout the Plateau are redbeds, and at 

most places they aggregate about 1,000 feet in thickness. 

Neither the lithology nor the thickness vary markedly 

within the Plateau, but westward in the Basin and 

Range province they thicken to more than 3,000 feet.

The Jurassic formations thicken westward across the 

Plateau from less than 1,000 feet near the Rocky MounC 0

N

A

0

R A D 0

''MEXICO

EXPLANATION

Isopach lines, showing 

thickness of Mesozoic 

formations, in thousands 

of feet

Outline of Colorado Plateau

__________J

Based largely on McKee, 1951

FIGUKE 10. Isopach map showing thickness of Mesozoic formation oil the Colorado Plateau.
CENOZOIC DEPOSITS 15

tains to more than 3,000 feet along the west edge of the 

Pl'ateau (Baker, Dane, and Reeside, 1936, pi. 10), and 

immediately west of the Plateau they are at least 11,000 

feet thick (Spieker, 1946). An angular unconformity 

at the base of the Carmel formation along parts of the 

Defiance upwarp records folding in that area during 

Jurassic time (Wright and Becker, 1951, p. 609, fig. 2). 

Prior to Late Cretaceous time the part of the Colorado 

Plateau southwest of the Little Colorado River was 

tilted northeastward with the result that the Upper 

Cretaceous formations overlap southwestward across 

the older Mesozoic and later Paleozoic formations 

(fig. 11).

tions that have been recognized on, or adjacent to, the 

Colorado Plateau.

LOWER TERTIARY DEPOSITS (PALEOCENE 

AND EOCENE)

Lower Tertiary deposits in the Uinta Basin and 

High Plateaus include a large proportion of lacustrine 

sediments in addition to fluviatile sediments. These 

deposits record a downwarping to accommodate the 

lakes, a filling of these lakes with sediments derived 

from adjoining highlands, and a building-up of the 

surface by deposition of fluviatile sediments. Furthermore, they record many stages of deformation during

s

8000'-! MOGOLLON PLATEAU

Upper 

Cretaceous

11. Cross section of Mogollon Rim, illustrating overlap of Upper Cretaceous formations southward onto Permian formations.

Upper Cretaceous strata in the southeastern and 

northwestern parts of the Colorado Plateau aggregate 

6,000 to 7,000 feet in thickness. They appear to thin 

somewhat southwest\vard, and they thicken considerably at the northeast corner of the Plateau. On the 

whole, however, the Plateau seems to have been submerged as a unit block under the marine waters of the 

Late Cretaceous sea. There may have been a slight 

tilt northeastward. In general, the thickness of the 

Upper Cretaceous rocks is fairly constant, and the types 

of offshore, nearshore, and continental deposits are 

alike in different parts of the Plateau. However, the 

mountains that furnished the Upper Cretaceous sediments that were deposited across the area of the Plateau 

were developing immediately to the west and south.

CENOZOIC DEPOSITS

Early Cenozoic and late Cenozoic deposits are well 

represented on, or adjacent to, the Colorado Plateau 

but middle Cenozoic deposits are scarce. As a result, 

the early Cenozoic and late Cenozoic history of the 

Plateau can be reconstructed fairly satisfactorily but 

there are large gaps in the record for middle Cenozoic 

time. The accompanying chart (fig. 12) shows the 

probable correlation of the principal Cenozoic formaearly Cenozoic time a continuation and extension east- 

- ward of the deformation that, along the west edge of 

the Plateau, had begun in Cretaceous time. The lithology and paleontology of the deposits indicate that the 

northern and western parts of the Plateau continued 

at, or near, sea-level until the end of Eocene time.

In the early reports on the Uinta Basin and High 

Plateaus the oldest deposits were classed as Wasatch 

formation, and this name still is applied to the deposits 

in the southern High Plateaus and in the Uinta Basin 

east of the Green River. West of the Green River and 

in the Wasatch Plateau the term "Wasatch" has been 

replaced by other names. Spieker (1946, p. 137) has reviewed the difficulties in connection with the use of the 

term "Wasatch" for the earliest Eocene deposits in 

central Utah.

The lower Tertiary formations now recognized in 

this part of the Colorado Plateau are the fluviatile 

North Horn formation of Late Cretaceous and Pal eocene age, the lacustrine Flagstaff limestone of Paleocene (?) age, the fluviatile Colton formation, the lacustrine Green River formation, the fluviatile Bridger and 

Uinta formations of Eocene age, and the fluviatile 

Duchesne River formation of Eocene or Oligocene 

age (figs. 13, 16).
16

Provincial age 

(Wood and 

others 1941)

Western Colorado Northwest New Mexico Northeast Arizona

Historic alluvium 

Pre-pottery alluvium 

Dune sand

Naha alluvium. 

Tsegi alluvium 

Dune sand

Historic alluvium 

Pre-pottery alluvium

Alluvium

and 

other deposits

Moraines 

Cerro stage till

Moraines

Sevier River formation; 

conglomerate in Castle 

Valley; and ? Parunuweap 

formation

Hualpai 

limestone

(of 

Longwell)

Bidahochi fm. 

Chuska ss. 3/

? Browns Park fm. 

? Bishop cong.

? Brian Head 

formation

? Creede formation 

? Potosi volcanic series 

? Silverton volcanic series 

? San Juan tuff 

? Lake Fork quartz latite 

? Telluride conglomerate and 

	Blanco Basin formation

? Datil formatio 

VAbiqui (of Smith)

(of Cabot) tuffs 

?Popotosa format 

?E1 Rito formatio 

?Chicoma volcani

(of Smith) 

?Espinosa vole

(of Stearns)

Whitneyan

Orellan 

Chadronian

Protoceras

Oreodon 

Brontotherium

Bridger formation 

Green River formation

San Jose fm. 

(of Simpson)

Wasatch and Colton 

formations formation

(of Wood

and others) Canyon Largo 

Flagstaff group limestone 

? Tuscher formation

? Ohio Creek 

conglomerate

(of Wood 

nd others)

Torrejon faunal zone o 

formation

| Dragon local 

fauna (of Wood 

I and others)

? Gravel on Mogollon Rim

Jfuerco taunal zone of

Nacimiento

formation North Horn formation

Upper Animas formation

Cretaceous Hunter Canyon formation

Ojo 

Alamo 

sandstone

1 Duchesne River formation is considered to be either Eocene or Oligocene.

2 The age of the Datil formation is in doubt. It has been considered Miocene(?) by some authors.

3 Chuska sandstone which crops out on the east side of the Defiance upwarp may correlate with part of the Bidahochi 

formation on the west side of the upwarp. Alien (1953) designated the age as Pliocene(?).

Provincial ages, faunal zones, and many of the correlations are after Wood and others, 1941. The stratigraphic position and correlation of queried formations are highly uncertain. Major gaps in the section 

are indicated by shading

FIGURE 12. Correlation chart of Cenozoic formations on, anil adjacent to, Ilie Colorado Plateau.
CENOZOIC DEPOSITS 17

Emery sandstone After Spieker, 1946 

memberof Mancos

Horizontal scale Vertical scale 

10 0 20 Miles 1000 0 5000 Feet

I , i , , I_________,_________| Mill i i i i I

.13. Diagrammatic section of formations exposed in the western part of tlie Wnsatcli Plateau, and tlieir relations eastward to Green Kiver.

UINTA BASIN AND HIGH PLATEAUS 

NORTH HORN FORMATION

The North Horn formation includes an assortment 

of lithologic types variegated shale, sandstone, conglomerate, and fresh-water limestone. In general, the 

formation records rapidly shifting flood-plain and lacustrine conditions. It thins southwestward from 

about 2,500 feet (between Castlegate and Soldier Summit) to about 500 feet (Salina Creek). See figure 13. 

In the eastern part of the AVasatch Plateau, freshwater limestone and other lacustrine beds are irregularly scattered throughout the formation, and in places 

it is impossible to define a contact Avith the overlying 

Flagstaff limestone. A few thin beds of poor coal are 

also present. (Spieker, 1946, p. 133,140.)

The North Horn formation grades downward into the 

conglomerate or sandstone of the Price River formation, with no evidence of break, at all places where the 

two formations are known. Also, it passes transitionally upward into the Flagstaff limestone in most of 

central Utah. On the western margin of the Wasatch 

Plateau, howe\7 er, the formation was tilted and truncated by erosion before the deposition of the Flagstaff. 

The disturbance that produced this angular unconformity was apparently confined to a narrow zone that 

is now roughly coincident with Sanpete Valley. 

Throughout the Avestern piedmont of the Wasatch 

Plateau the Flagstaff overlies all older rocks in angular 

contact. Locally, the basal Flagstaff overlies steeply 

folded Jurassic and Cretaceous rocks in angular unconformity. Thus, despite the regional appearance of

transition in the passage from North Horn to Flagstaff east of the Wasatch Plateau, in the western districts the two formations were unmistakably separated 

by a physical disturbance. (Spieker, 1946, p. 134).

Variegated lower Cenozoic deposits similar to the 

North Horn formation are extensive in the Rocky Mountain region and may record deep weathering under the 

influence of a warm, humid climate, erosion of the resultant soils, and their redeposition as lacustrine or 

fiuviatile sediments (Van Houten, 1948). If this interpretation is correct, we may assume that the effects of 

climate controlled the kind of sediments that were 

deposited during the early Cenozoic, and we may further assume that the structural deformation controlled 

the continuity of the sedimentation.

The North Horn formation contains fresh-water 

mollusks and vertebrates. The latter, found in the 

lower and upper part of the formation, include dinosaurian, chel.on.ian, and crocodilian remains. (Spieker, 

1946, p. 134). The dinosauria-n remains come from the 

lower 500 feet of the formation. The middle part has 

yielded no vertebrate fossile diagnostic of age, but the 

upper part contains mammalian bones of unquestionable 

Paleocene age. (Gazin, 1938.)

The North Horn formation thus embodies strata of 

latest Cretaceous and earliest Tertiary ages, probably 

to be correlated in some part with the Lance and Fort 

Union formations of the northern plains, and with the 

Ojo Alamo, Puerco, and Torrejon formations of the San 

Juan Basin. It is of especial interest and significance 

that the passage from Cretaceous to Paleocene is recorded by an apparently transitional succession of
18 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

strata. No physical basis for regional subdivision of 

the strata grouped in the North Horn formation has 

been recognized, and in the present state of knowledge a boundary between Cretaceous and Paleocene 

cannot be mapped. The record is apparently even more 

complete than in Montana and Wyoming, where distinction between Lance and Fort Union has been the 

subject of much discussion. (Spieker, 1946, p. 1353.)

FLAGSTAFF LIMESTONE AND WASATCH FORMATION IN 

HIGH PLATEAUS

The Flagstaff limestone, a lacustrine deposit, is present throughout the Wasatch Plateau and has been 

traced about 30 miles to the east. Its extent northward 

and westward from the Wasatch Plateau is not known, 

but probably the limy lacustrine deposits that have been 

classed as Wasatch formation of the Wasatch Plateau 

are correlative with the Flagstaff.

In the Wasatch Plateau, the Flagstaff limestone consists chiefly of fresh-water limestone of many kinds, 

with interbedded shale and minor amounts of sandstone, gypsum, oil shale, and volcanic ash. In the western part of the Wasatch Plateau it contains some coal. 

The limestone in part is dense, homogeneous, exceedingly fine grained, and in part is cellular, like a compacted limy spring deposit. Some beds contain abundant ostracod or other fresh-water shells. The formation ranges from 200 to 1,500 feet in thickness and 

thickens westward and southwestward. (Spieker and 

Reeside, 1925; Spieker, 1931, 1946).

East of the Wasatch Plateau the Flagstaff limestone 

intertongues with the lower part of the Colton formation and grades into the variegated beds of that formation (fig. 13).

In the southern part of the High Plateaus, beds of 

early Tertiary age, 1,000 feet thick, have been referred 

to the Wasatch formation (Gregory and Moore, 1931, 

p. 114). These beds lithologically resemble the Flagstaff limestone and may be a southward extension of 

it. At their base, locally, is a conglomerate a few feet 

thick consisting of unusually well-rounded and 

smoothed pebbles of white and red quartzite, black 

chert, rhyolite, porphyry, and many kinds of dense

igneous rocks. About 50 percent of the pebbles exceed 

4 inches in diameter, which suggests that they have 

not been transported great distance however, their 

source is not known. (Gregory and Moore, 1931, 

p. 114-115).

Overlying the conglomerate is a few hundred to more 

than a thousand feet of highly lenticular, limy beds. 

They include dense limestone, brecciated limestone, 

shaly limestone, and calcareous shale or sandstone. 

The unweathered rock is white or light pink, but the 

weathered surfaces are deep pink or red. Fossils contained in the dense and brecciated limestone include 

Pliysa pleuromatis, probably P. bridgereiwis, and a 

small discoid shell that may be a Valvata or Planorbis. 

The surfaces of some of the calcareous sandstone beds 

are covered with plant impressions. (Gregory and 

Moore, 1931, p. 114-116).

The Flagstaff limestone, and the beds correlative with 

it, rest with angular unconformity on the older rocks 

along the west side of the Wasatch Plateau. At places 

in the southern part of the High Plateaus the Flagstaff 

limestone or Wasatch formation overlap all of the 

Cretaceous and many of the Jurassic formations where 

they have been sharply folded. (Spieker, 1946, p. 137). 

In the central and eastern parts of the Wasatch Plateau, 

and along the south and east rims of the Uinta Basin, 

the beds above and below the unconformity are parallel 

and apparently gradational (fig. 14).

These lacustrine deposits record Paleocene deformation at the extreme western edge of the Colorado Plateau and downwarping of the nortlnvestern part of the 

Plateau. The limestone may be in part the product of 

spring or fumerole activity associated with the early 

Tertiary volcanism (p. 42), or it may be the result of 

erosion of Paleozoic limestone in the area immediately 

west of the Colorado Plateau.

TUSCHER, OHIO CREEK, AND DEBEQUE FORMATIONS

Along the southeastern rim of the Uinta Basin is a 

set of beds, mostly sandstone, overlying undoubted 

Upper Cretaceous formations and underlying undoubted Eocene formations. In the southeastern part

4 000' F^^1^ ==--=

After Gale, 1910

FIGURE 14. Cross section of Grand Hogback, near Meeker, Colo. The beds shown as Wasatch probably include strata of Paleocene age.
CENOZOIC DEPOSITS 19

of the Uinta Basin these sandstone deposits have been 

described as the Tuscher formation (Fisher, 1936, p. 

20). Farther east in the Uinta Basin they have been 

mapped but not named (Erdmann, 1934, p. 53) ; still 

farther east, in west-central Colorado, is the Ohio Creek 

conglomerate (Eldridge, 1894), which may be equivalent to these early Tertiary (?) sandstones. These 

formations probably are early Tertiary in age and may 

correlate with Wood's DeBeque formation (Wood and 

others, 1941) of Paleocene and early Eocene age in 

western Colorado.

The thicknesses reported for the Tuscher and Ohio 

Creek formations range from 130 to 600 feet. Their 

base is commonly conglomeratic sandstone containing 

well-rounded pebbles of black, gray, or brightly 

colored chert and quartz. Limestone pebbles are 

scarce. The sizes range from y± to 2 inches in diameter ; a few cobbles 6 inches in diameter are quartzite. 

(Erdmann, 1934, p. 54).

The beds above the conglomerate are mostly lenticular 

and crossbedded sandstone but they include some shale. 

Generally, there is an unconformity at the base of these 

beds, and it may mark a considerable hiatus, perhaps 

the first half of Paleocene time, but the contact with the 

overlying Wasatch formation seems to be gradational. 

Nevertheless, the beds above and below the unconformity are essentially concordant structurally; presumably 

therefore, there was little or no local folding here in 

earliest Tertiary or latest Cretaceous time.

COLTON AND WASATCH FORMATIONS IN UINTA BASIN

The Col ton formation, a fluviatile deposit in the 

northern part of the Wasatch Plateau and southwestern 

part of the Uinta Basin, consists of lenticular sandstone, siltstone, and shale with little or no limestone 

and no coal. The colors are variegated brown, 

yellow, and deep red. The formation has a maximum 

thickness of about 2,000 feet along Green River, but 

westward it thins by intertonguing with,, and grading 

into, the shale of the Green River formation and the 

limy beds of the Flagstaff limestone (fig. 13). Eastward, the upper part of the Col ton intertongues with, 

and grades laterally into, the Green River formation. 

The beds that are referred to as Wasatch in the eastern 

and northern parts of the Uinta Basin are, in part at 

least, correlative with the Colton formation. Alone;

o

Green River, the formation rests unconformably, but 

concordantly, on the Paleocene North Horn formation 

and is overlain conformably by the Green River formation. (Spieker and Reeside, 1925; Spieker, 1931,. 

1946).

Early Tertiary fluviatile deposits in the eastern 

part of the Uinta Basin have been referred to as the

Wasatch formation. The Wasatch rests conformably 

on the Upper Cretaceous formations. At the Grand 

Hogback along the east side of the Uinta Basin the 

beds that have been mapped as Wasatch, probably including some beds of Paleocene age, are turned up 

steeply and concordantly with the Upper Cretaceous 

formations (Hancock and Eby, 1930). See figure 14. 

The Wasatch formation in the northwestern part of the 

Colorado Plateau presumably is equivalent in part to 

the Colton, but it may include some strata of Paleocene 

age. The formation thins eastward in the Uinta Basin 

and comprises only 400 feet of drab mudstone with 

thin bands of red where it crosses the arch separating 

the Uinta Basin and Piceance Creek Basin (fig. 37). It 

thickens again eastward to more than 3,000 feet in the 

Piceance Creek Basin, where it consists chiefly of 

variegated mudstone with a subordinate amount of 

friable, medium-grained sandstone and some conglomerate. (Bradley, 1931,, p. 8, 9).

The lower part of the Wasatch formation is very 

conglomeratic in the eastern part of the Piceance Creek 

Basin and south of Grand Mesa, but it becomes less 

conglomeratic westward and passes from conglomerate 

to sandstone and variegated mudstone. Pebbles in the 

conglomerate include acidic and basic igneous rocks, 

flint, vein quartz, and red and light-colored quartzite. 

Conglomerate is scarce at the western edge of the 

Piceance Creek Basin, but occasional lenses of pebbles 

include some limestone that may have been derived 

from the Flagstaff limestone to the west (Lee, 1912; 

Hancock and Eby, 1930, p. 209; Erdmann, 1934, p. 56); 

but probably most of the Wasatch formation in the 

Piceance Creek Basin was derived from the east.

The extensive conglomerate in the lower Cenozoic 

formations on the Colorado Plateau generally has been 

interpreted as the result of vigorous dissection,, presumably fluviatile dissection, of newly uplifted tectonic 

blocks. Without doubt, some of the deposits are essentially tectonic in origin, although the evidence points 

to repeated small movements rather than to one of 

catastrophic dimensions. On the other hand, it seems 

quite possible that the gravels represent outwash 

resulting from glacial or periglacial activity in the 

mountains. There is evidence of early Tertiary 

glaciation in the San Juan Mountains (p. 26). 

Furthermore, alpine glacial or periglacial activity is 

a common source for gravel Avhereas tectonic breccias 

rarely are extensive. Lastly, it is doubtful that large 

volumes of rocks and rock fragments would be supplied 

to streams in the absence of frost action.

GREEN RIVER FORMATION

Conformably overlying the Wasatch and Colton formations, and grading laterally into them, is the lacus-
20 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

J.-I3A3SOO&

30NVU

M3AIU M33MO\
CENOZOIC DEPOSITS 21

trine Green River formation of middle Eocene age. It 

underlies the Uinta Basin (fig. 15) and extends northward into the Wyoming Basin.

The Green River formation can be divided into four 

members (fig. 16). At the base is the Douglas Creek 

member, which is composed of 200 to 800 feet of buff 

or yellow-brown shale containing considerable sandstone, inarlstone, algae reefs, and oolite. Overlying this 

is the Garden Gulch member, which is composed of 200 

to 700 feet of marl stone or organic-rich shale in paperthin laminae and some fine-grained sandstone and siltstone. Next higher is the Parachute Creek member, 

which is 1,000 feet thick and which con tains most of the 

oil-shale beds in the formation. The Evacuation Creek 

member, at the top of the Green River formation, is 

2,000 feet thick in the Avestern part of the Uinta Basin, 

but thins eastward to 500 feet. It consists chiefly of 

barren shale and marlstone. (Bradley, 1931, p. 9-14.)

In the northeastern part of Uinta Basin, a shore and 

delta facies of the Green River formation, 1,100 to 

1,200 feet thick, consists of sandstone and shale that 

grade southward into finer-grained offshore facies. 

Other deltaic deposits in the central and western parts 

of the Uinta Basin, where the formation is at least 4,000

feet thick, intertongue with the Colton or Wasatch formations (fig. IT). (Bradley, 1931, p. 14-19.)

The change from nearshore to offshore lake beds 

southward in the Uinta and Piceance Creek Basins 

shows that the Uinta Mountains were a source of the 

Green River formation. Considerable upwarp of the 

Uinta Mountains preceded deposition of the Green 

River formation but there also was a later upwarp 

(p. 57). An interpretation of the climatic conditions 

that prevailed while the Green River formation Avas 

being deposited is given on page 64.

It is not possible to accurately determine the southern limit of the Green RiA^er lake. Southeastern Utah, 

during Green River time, Avas at the northern: end of an 

epeirogenic platform that included most of the Colorado Plateau south of the Uinta Basin (p. 64). SouthAvard, the lake probably ended against the north flank 

of this platform (fig. 56). It probably extended southAvard in great bays located in structural basins similar 

to the Henry Mountains basin. The Uncompahgre 

Plateau is assumed to have been a peninsula dividing 

the bay in Piceance Creek basin from shalloAver bays in 

southeastern Utah. Uplifts, such as the San Rafael 

and Monument upAvarp, may have stood above

Vicinity of 

Lookout Mountain, 

Colo.

Vicinity of

Little Snake River,

Colo.

Bridger Wasatch Green River ^_ 

formation <j_j 

Bridger 

formation

:inity of 

en Wyo. River, 

 "~ ^-~*-~~~

1

=^- 

:;.TrrT;\i;.v

itf

^iH1^ ^:

_^- -" Laney shale member of 

 , . ,., , __ """" Green River formation 1< luviatile and _^. - 

lake deposits ^,~-^"

1,350± :~~~^~ 

,-, , .11 -~^=~=^~ Cathedral Bluffs tongue 1' resh-water lake _- - of Wasatch formation 

deposits, including _____ _ _:^==*" oil shale °- ~~ =^=-^- _ ___ 

Tipton tongue of Green River formation

Fluviatile deposits ,,-. , , .. Mam body of 

Wasatch formation

< 70 miles > 

_ r^r^.

:H=tiSi^

 

_ =

 -

^m

g^gf^

^^ a

5=^^.=

mmmm

=£Lfb=^3=

;?:#»;#!? k

fcii bo-S

T3 *< 'C £ 

«g<4H 

!M 

2 C

1,200' *|J

<u £ <u o ^ t*H

1,200' 

300^ ~--=- o

p

^ 

_c

-t-»s 

CO

Coal bearing « 

< 20 miles 

m

=r=^=!=

 _

i^S3==

~.-~vf

...."......,......

- -=

[VHriv.'vX

=--===

Fluviatile and 

fresh-water 

lake deposits

1,100'

Fresh-water 

lake deposits 

and oil shale

Fluviatile 

deposits

After Sears and Bradley, 1924

FiGUitu 17. Sections from northwest to southeast in the Green River Basin, Wyo. and Colo., showing intertoiiguing of the Wasatch and Green

River formations.
22 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

water level. There is no reason to suppose that the 

Arizona or New Mexico segments of the Colorado 

Plateau were more than slightly higher than the lake.

BRIDGER FORMATION

Overlying the lacustrine Green River formation is the 

fluviatile Bridger formation, which consists of about 

1,000 feet of sandstone and subordinate amounts of 

shale and conglomerate. Beds of sandstone are thick, 

brown, massive or crossbedcled, and medium- to coarsegrained. The shale is greenish-gray sandy mudstone.

In most places, the Bridger rests with apparent conformity on the Green River formation. Locally, however, the contact is very irregular with a relief of 50 

feet, but this irregularity is attributed to differential 

compaction rather than to an erosional unconformity 

(Bradley, 1931, p. 20).

Although there is no angular discordance between the 

Bridger and Green River formations along the southern edge of the Uinta Basin, an angular unconformity 

at the base of the Bridger is inferred along the northern edge of the basin where the contact is concealed by 

the.northward overlap of the Uinta formation. The 

overlap of the Uinta formation onto Green River and 

older formations along the northern edge of the basin 

establishes the existence of an angular unconformity, 

and it seems probable that this unconformity is between 

the Bridger and Green River rather than between the 

Uinta and Bridger, because the Bridger and Uinta formations are very similar lithologically whereas they are 

very different from the Green River formation. Moreover, on the northern side of the Uinta Mountains there 

is an angular unconformity at the base of the Bridger. 

(Sears and Bradley, 1924, p. 96; Bradley, 1931, p. 22.)

It is probable that the Bridger and younger Eocene 

fluviatile deposits extended southward at least as far as 

the southern limit of the Green River formation. 

Play a, or perhaps lake, conditions may have existed 

in the Henry Mountains basin while the fluviatile formations were being deposited in the Uinta Basin (fig. 

57). This late Eocene drainage probably had no outlet, 

because at this time the Colorado Plateau area was low, 

and, except for the San Juan Basin, all the basins were 

surrounded by mountains or other highlands, at least 

until the end of Eocene time.

UINTA FORMATION

The Uinta formation, also a fluviatile deposit, is 

about 1,000 feet thick and is lithologically similar to 

the 'Bridger and separable from it only on the basis of 

vertebrate fossils. Along the southern edge of the 

Uinta Basin the Uinta formation conformably overlies 

the Bridger, but along the northern side of the basin 

it overlaps onto the Mesaverde formation of Late

Cretaceous age. As pointed out in the preceding section, however, an angular unconformity between the 

Uinta and Bridger formations seems unlikely, but the 

Bridger might be expected to rest with angular discordance on the Green River formation.

In the northwestern part of the Uinta Basin, the 

lower Tertiary deposits, which are several thousand 

feet thick, unconformably overlie folded and faulted 

Mesozoic rocks including the Currant Creek formation, 

which probably is of Late Cretaceous or Paleocene age 

(Bissell, 1952, p. 614) but possibly Eocene age (Williams, 1950, p. 106). The definitely Tertiary deposits, 

however, have not been traced laterally into the other 

Tertiary formations in the Uinta Basin and have been 

mapped as Uinta(?) formation (Kay, 1934, p. 357- 

372; Walton, 1944, p. 122 and pi. 2). It seems likely 

that these deposits include nearshore lacustrine or 

fluvial facies, or both, of the Green River formation 

and equivalents of the Bridger formation.

The original extent of the Uinta formation probably 

was similar to that of the Bridger.

DUCHESNE RIVER FORMATION

The fluviatile Duchesne River formation consists of 

about 1,300 feet of cliff-forming, reddish-brown sandstone. Along the southern side of the Uinta Basin the 

sandstone conformably overlies the soft clays of the 

Uinta formation, but northward it is unconformable 

on the older formations.

Opinions differ as to whether the Duchesne River 

formation should be classed as latest Eocene or earliest 

Oligocene, but in any case the Duchesne River fauna 

generalty is regarded as transitional between the Uintan and the Chadronian (Wood and others, 1941).

The limits of the Duchesne River formation are not 

well known. It may be more extensive than has been 

supposed and may be represented in the deposits that 

elsewhere have been mapped as the Uinta formation.

The lower part of the Duchesne River formation consists of 500 feet of variegated clay alternating with 

brown and gray sandstone (Randlett Horizon of Kay, 

1934). Overlying this is 500 feet of conglomerate, 

sandstone, and shale (Halfway horizon of Kay, 1934). 

Above this is 300 feet of conglomeratic sandstone, 

sandy clay, and coarse conglomerate (Lapoint horizon 

of Kay, 1934).

The original extent of the Duchesne River formation 

probably Avas similar to that of the Bridger. However, 

the fact that strata younger than Duchesne River do 

not occur in the Uinta Basin suggests that a major 

change in drainage conditions occurred at about this O o

time. Either the supply of sediments became cut off, 

or the streams hereafter transported most of their loads 

past the areas that had been aggraded during Eocene
CENOZOIC DEPOSITS 23

time. It is very likely that both happened. The Uinta 

and other mountains that were eroded during Eocene 

time must have become greatly reduced by Oligocene 

time; and it seems probable that the Colorado Plateau 

began to be raised during Oligocene time (p. 64).

Deposits of early Tertiary age in the San Juan Basin 

include the upper part of the Animas formation, the 

Puerco and Torrejon formations, and the Wasatch formation (including the so-called Tiffany beds). Unlike 

the lower Tertiary deposits in the Uinta Basin, all these 

deposits are of fluviatile origin. Their aggregate 

thickness in the northern part of the basin, near the 

San Juan Mountains which was a source area, is nearly 

5,000 feet, but in the southern part of the basin they are 

only about 1,000 feet thick (fig. 18).

The youngest Upper Cretaceous deposits under these 

lower Tertiary formations, the Ojo Alamo sandstone 

and lower part of the Animas formation, are believed 

to be correlative with the lower part of the North Horn 

formation of the High Plateaus. The upper part of 

the Animas, the Puerco and Torrejon formations, and 

part of the Wasatch formation, including the so-called 

Tiffany beds, are equivalent to the Paleocene formations 

represented in the Uinta Basin. The vertebrate fauna 

of the Wasatch formation in the Uinta Basin is correlative with the fauna of the Wasatch formation in the 

San Juan Basin. However, deposits of Bridgerian, 

Uintan and Duchesnean age (terminology of Wood and 

others, 1941) are not represented in the San Juan Basin.

The Wasatch formation is upturned against the San 

Juan and Nacimiento Mountains, thus indicating postWasatch uplift of these mountain areas. In addition, 

an angular unconformity at the base and top of the 

Animas formation in the northern part of the basin

indicates two earlier stages of upwarp in the San Juan 

Mountains. The northward dip of these formations in 

the southern flank of the San Juan Basin indicates 

that it too was raised in post-Wasatch time.

ANIMAS FORMATION

The fluviatile Animas formation is restricted to the 

northern end of the San Juan Basin where it attains 

a maximum thickness of about 2,700 feet. The lower 

part is coarse conglomerate; the upper part is mostly 

shale and sandstone but contains numerous thin layers 

of conglomerate. A high proportion of the pebbles are 

andesitic. Vegetable debris is common, and locally it 

is sufficiently abundant to form thin coal beds, especially eastward across the northern end of the San 

Juan Basin (Eeeside, 1924, p. 32-34).

In the northwestern part of the San Juan Basin the 

Animas formation is unconformable on the McDermott 

formation, which is of Late Cretaceous age and which 

also is composed very largely of andesitic debris. 

Locally, the unconformity between the two formations 

is an angular unconformity, as along the Animas River. 

EastAvard, the Animas formation overlaps successively 

onto the McDermott formation, Kirtland shale, and 

part of the Fruitland formation. The top of the 

Animas formation in the northwestern part of the basin 

also is an unconformity, and it is overlapped by the 

Torrejon formation and by the Wasatch formation. 

(Reeside, 1924, p. 32-34; Silver, 1951, p. 118). On the 

other hand, in the northeastern part of the basin the 

Animas apparently intertongues with Upper Cretaceous formations as old as the Lewis shale (Dane, 

1946). See figure 19. Thus, the lower part of the 

Animas is regarded as Late Cretaceous age, and the 

upper part is Paleocene.

 I s.

Modified after Reeside. 1924

Tw, Wasatch formation; Tn, Nacimiento formation (Puerco and Torrejon faunal zones): Tan, Animas formation; Koa; Ojo 

Alamo sandstone; Kmd, McDermott formation; Kkf, Fruitland formation and Kirtland shale; Kpc, Pictured Cliffs 

sandstone; Kle, Lewis shale; Km, Mesaverde group; Kmc, Mancos shale

FIGURE IS. Diagrammatic section across the San Juan Basin from Durango, Colo., to Pueblo Bonito, N. Mex.
24 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

. . . . :. :. : . Nocimiento formation (Pyerco ond"Torrejon 

"ojo Alomo sandstone. ' """ """'''''°u"^: ':?^.;.- ;

Kirtlond"" 'shale ^jgJ" 

Pictured Clifts sandstone

Lewis shale

After Dane, 1946

Vertical exaggeration about 25 times

FittuuK 19. Diagram showing inferred stratisrapliic relations of Paleocene and Eocene formations on east side of San Juan Basin.

The andesitic debris in the Animas formation apparently was deposited by streams flowing southward from 

the San Juan Mountains. Some of the siliceous 

material in the formation, however, is similar to that 

in the Ojo Alamo sandstone (an Upper Cretaceous formation that does not extend to the northern part of the 

San Juan Basin) and to that in the McDermott formation, which unconformably underlies the Animas. 

These siliceous materials are unlike any that are known 

in the San Juan Mountains and must have been derived 

from some other source.

NACIMIENTO FORMATION (PUERCO AND TORREJON 

FAUNAL ZONES)

The Puerco and Torrejon fauna! zones, which have 

previously been described as formations, have been referred to (jointly) as the Nacimiento formation. They 

are quite alike in lithology, but their faunas are sufficiently different that vertebrate paleontologists believe they are separated by an important hiatus although the stratigraphic position of the hiatus has not 

yet .been discovered. (Reeside, 1924, p. 35-44; Dane, 

1936, p. 122-124).

In the northern part of the San Juan Basin the 

Nacimiento formation consists of brown conglomeratic sandstone interbedded with red and gray shale. In 

the southern part of the basin it consists largely of 

banded and sandy clays of dull colors with some interbedded sandstone. The formation is about 1,500 feet 

thick along the western side of the basin, about 400 feet 

thick along parts of the north rim, and about 800 feet 

thick in the southeastern part of the basin. Presumably, the thinning is due, in part at least, to unconformities at the base, top, or within, the formation. (Reeside, 

1924, p. 35-44; Dane, 1936, p. 122-124.)

The mammalian faunas of the Puerco and Torrejon 

faunal zones are marked by the abundance of primitive 

mammals, turtles, and crocodiles and by the absence 

of dinosaurs. Although there is no discernable stratigraphic break between the two zones, the two faunas 

do not have a single species in common, and only three 

or four genera are in common. The younger fauna has 

been judged to be a lineal descendant of the older, and, 

because of the physical geology gives no basis for attributing the faunal difference to facies change of 

migration, a hiatus is inferred. (Reeside, 1924, p. 35- 

44.) The Puerco fauna is regarded as earliest Paleocene.

Both the physical geology and the paleontology indicate that the Nacimiento formation represents deposits that accumulated on. the surface of floodplains 

or on broad, gently sloping, coalesced alluvial fans. 

The mammal bones generally are not articulated and 

occur with the remains of fish, crocodiles, and turtles, 

thus leading to the belief that the bones had been washed 

into streams. A heavy growth of vegetation along the 

streams and in the interstream areas is indicated by 

the abundant remains of leaves of figs, plane trees, 

poplars, relatives of the breadfruit, and various shrubs. 

The invertebrate fauna includes both terrestrial and 

fresh-water shells. (Sinclair and Granger, 1914, p. 309, 

313.) The drab beds may have been deposited in forest 

swamps and heavily wooded areas of a savanna environment, while the redbeds were accumulating in the 

more open country (Van Houten, 1948, p. 2084). The 

absence of gravel attributable to sources in the San
CENOZOIC DEPOSITS 25

Juan Mountains suggests that tlvose mountains had become reduced in height and presumably were below the 

level of much frost action. Perhaps a part of the Nacimiento formation was derived from the west as a 

result of erosion of Upper Cretaceous and other formations uplifted in the Defiance npwarp.

WASATCH (SAN JOSE OF SIMPSON) FORMATION (AND SO-CALLED 

TIFFANY BEDS)

The Wasatch formation in the San Juan Basin is 

at least 2,000 feet thick and probably exceeds 2,500 

feet. In the northern part of the basin it is composed 

chiefly of variegated shale with beds of coarse arkose 

containing abundant pink feldspar. In the western 

and southern parts of the basin, at the base, is a 

massive and persistent gray to brown conglomeratic 

sandstone, 150 to 300 feet thick, locally containing some 

interbedded shale. Above, is mostly variegated red 

shale. Because the upper part of the formation has 

been eroded, the original variations in thickness in 

different parts of the basin are not known. (Reeside, 

1924, p. 44-48; Dane, 1936, p. 125; 1946.)

The Wasatch formation seems to be conformable on 

the Torrejon fauna! zone, but locally along the contact 

there are irregularities, such as channeling; however, 

in general, the litliologi.es of the two formations are 

gradational. The upper part of the formation in the 

San Juan Basin contains the fauna that includes 

Eoliipfms (now called Hyracothevmmi) and its associated forms, and in general it is similar to the Wasatch 

and Colton formations in the Uinta Basin (Reeside, 

1924; Dane, 1936).

In the northeastern part of the San Juan Basin the 

lower part of the Wasatch formation contains the socalled Tiffany fauna, which is intermediate between 

that of the Torrejon and that of the higher Wasatch 

beds intermediate in the sense that it includes genera 

found in the typical Torrejon but not in the typical 

Wasatch, and genera found in the typical Wasatch but 

not in the typical Torrejon (Simpson, 1935, p. 3-8). 

The beds containing the so-called Tiffany fauna have 

been mapped as part of the Wasatch and may occur 

as much as 1,000 feet above the base of the formation. 

The Wasatch formation, therefore, as mapped in the 

San Juan Basin, includes an undetermined thickness 

of Paleocene strata. (Dane, 1946.) Because of the 

uncertain range in age of the Wasatch formation in 

the San Juan Basin and because of the difficulty of 

correlating it with the type Wasatch, Simpson (1948) 

proposed that its name be changed to San Jose 

formation.

The Wasatch formation in the San Juan Basin seems 

to have been derived from the San Juan Mountains.

The occurrence of conglomerate at the base of tho 

Wasatch suggests that the San Juan Mountains may 

have become raised above frost line at the beginning of 

Wasatch time. The occurrence of variegated beds in 

the upper part of the Wasatch suggests restoration of 

the conditions that prevailed during ISTaciiniento time. 

The fact that the Wasatch rises northward towards the 

San Juan Mountains indicates that those mountains 

were further uplifted in post-Wasatch time. The Nacimiento Mountains and the south flank of the San 

Juan Basin also were uplifted after the Wasatch formation had been deposited, although they may have 

started to rise earlier than this. In any case, the Wasatch formation seems to have been deposited by streams 

that drained southward or southeastward across the 

San Juan Basin, and they seem to have discharged in 

the general area of what later became the Rio Grande 

depression. Sometime after the Wasatch formation 

had been deposited, aggradation ended in the San Juan 

Basin, and thereafter the streams transported their 

loads bsyond the limits of the basin. It is possible that 

the early Eocene aggradation of the San Juan Basin, 

coupled with post-Wasatch uplift of the east and south 

flanks of the basin, turned the drainage westward across 

the top, or around the ends, of the Defiance upwarp 

and thus into the basin under the Black Mesa of Arizona. We know that the drainage ultimately took a 

westward course, but we have no basis for guessing ' O O

when it first did so.

MOGOLLON RIM

On the Mogollon Rim, in Arizona, at the very south 

edge of the Colorado Plateau are some bouldery gravel 

deposits that may be of early Tertiary age. The gravel, 

exposed west of Show Low, Ariz., where it overlies 

Cretaceous formations (fig. 11), evidently was derived 

from pre-Cambrian rocks and must have been transported northward from lofty mountains that lay south 

of the Plateau. The age of the gravel is not known. 

It may be of Late Cretaceous age and analogous to 

seme of the conglomerate in central Utah that had 

been regarded as Tertiary until Spieker (1946) demonstrated the age as Late Cretaceous. The deposits on the Mogollon Rim may be of early Tertiary 

age. If they were derived from the south it seems unlikely that they are much, if any, younger than Eocene 

because there does not appear to be any suitable source 

for the pre-Cambrian debris after early Tertiary time. 

. Moreover, these deposits are not known to contain much, 

if any, volcanic debris, and in this respect they differ 

markedly from the later Tertiary deposits on the 

Plateau, such as the Datil (p. 29) or Bidahochi formations (p. 29).
26

DEPOSITS IN ADJOINING AREAS

SAN JUAN MOUNTAINS

Till, believed to be of Paleocene or Eocene age, underlies Oligocene deposits at several localities in the San 

Juan Mountains. The deposit, as much as 100 feet thick, 

contains fragments derived from the pre-Cambrian and 

Paleozoic formations and from volcanic tuff and 

porphyries.

The presence of abundant fragments of volcanic rocks 

in the till wherever it has been found shows that the 

glaciation took place before the Cretaceous and early 

Tertiary volcanic pile had been completely removed 

by erosion. The fact that the post-Animas beds of the 

San Juan Basin lack volcanic material indicates that 

the volcanic pile had been largely or completely removed before the deposits of the Puerco faunal zone 

were laid down. (Atwood, 1915, 1917; Atwood and 

Atwood, 1926; Cross and Larsen, 1935, p. 47).

The later Tertiary formations in the San Juan Mountains are described on pages 31-32.

RIO GRANDE VALLEY

Deposits of early Tertiary age in the Rio Grande depression along the east side of the southern part of the 

Colorado Plateau include the Galisteo sandstone, the 

upper part of which has been correlated with the Duchesne River 'formation. The Galisteo sandstone consists of from 900 to at least 4,000 feet of variegated sandstone and clay with minor amounts of conglomerate, 

fresh-water limestone, and water-laid tuff. Pebbles in 

the conglomerate were derived from the Paleozoic and o

pre-Cambrian rocks that must have formed highlands 

adjoining the basin of deposition. (Stearns, 1943, 

p. 301-319).

The Galisteo sandstone, known only on the east side 

of the Rio Grande depression, is older than, and cut by, 

the intrusions at the Cerrilos Hills. Its composition 

indicates that it was derived from ancestral highlands, 

presumably in the southern Rocky Mountains and at 

the east edge of the Colorado Plateau. But the Galisteo, although much faulted and folded, is largely concordant, although unconfomiable, on the Upper Cretaceous formations on the flanks of the folds at the northeast end of Sandia Mountain; therefore it may predate 

the block faulting and tilting there. (Stearns, 1943, 

p. 301-319).

SOUTHERN ARIZONA

Te'rtiary formations south of the Colorado Plateau, 

in the Basin and Range province in Arizona, are illustrated by exposures in the vicinity of the Artillery 

Mountains, Arizona. These exposures include the 

Artillery formation of early Eocene (?) age, volcanic

rocks of Miocene (?) age, the Chapin Wash formation 

and overlying Cobwebb basalt of early Pliocene (?) age, 

and the Sandtrap conglomerate of late Pliocene (?) age. 

(Lasky and Weber, 1949.) Although the dating of 

these formations involves many uncertainties they record a sequence of structural movements that bear on 

the history of the Colorado Plateau. They record early 

Tertiary (but post-Artillery formation) thrust faulting, middle Tertiary vulcanism and block faulting of 

the Basin and Range type, and late Tertiary (late 

Pliocene ?) folding and later block faulting.

TJPPEK TEBTIARY DEPOSITS (MIOCENE AND 

PLIOCENE)

Upper Tertiary deposits are abundant around the 

periphery of the Colorado Plateau but they are scarce 

and not at all well dated within the Plateau. In the 

southern part of the High Plateaus are the Brian Head, 

Sevier River, and Parunuweap formations. In the 

basin under Black Mesa, Ariz., is the Bidahochi formation. Elsewhere within the Colorado Plateau, deposits 

believed to be of late Tertiary age consist of scattered 

gravel deposits on erosion surfaces, similar to deposits 

south of the Defiance upwarp, the Datil formation, and 

in the salt anticlines.

North of the Plateau, in the Wyoming Basin, are the 

Bishop conglomerate..and Browns'Park formation. To 

the east, in the San Juan Mountains, is a thick volcanic 

sequence of late Tertiary age. East of Mount Taylor, 

N. Mex., is the Santa Fe formation. Along the southwest edge of the Plateau are the Muddy Creek formation and Hualpai limestone (of Longwell). In central 

Utah, west of the High Plateaus, is the Sevier River 

formation. Much of the late Tertiary history of the 

Colorado Plateau must be inferred from the record of 

the deposits around it; the deposits within the Plateau 

are not complete enough for satisfactory reconstruction 

of the history.

JSToiie of these deposits has been dated with certaint}^. 

All of them lie with angular unconformity on the older 

rocks, including the lower Tertiary deposits where they 

are present, and intraformational unconformities are 

common. The upper Tertiary deposits are mostly 

fluviatile but include some sediments that were deposited in ephemeral lakes or ponds; most of them are 

associated with vulcanism or other igneous activity.

HIGH PLATEAUS

BRIAN HEAD FORMATION

Generally, along the western edge of the Aquarius,. 

Sevier, and Markagunt Plateaus, the pink, compact 

limestones of the Wasatch formation are overlain unconformably by white, regularly stratified calcareous
CENOZOIC DEPOSITS 27

and siliceous beds, and they in turn are overlain by 

gray conglomerate and agglomerate, which in places 

extend upward to sheets of lava capping the plateaus. 

On the southern part of the Aquarius, Paunsaugunt, 

and Markagunt Plateaus the white beds are essentially 

limestone that include varying amounts of quartz, 

chalcedony, and decomposed lavas. On the northern 

Aquarius, southern Sevier, and central Markagunt 

Plateaus, beds in the same stratigraphic position consist chiefly of pyroclasti.es and highly siliceous limestone. Thus, the quartzose and volcanic debris increase 

from south to north, but the change from dominant 

limestone to dominant tuff and ash is not regularly 

progressive. These deposits, which are 500 to 1,000 

feet thick, have been named the Brian Head formation. 

(Gregory, 1945, p. 105-110.)

The sources of materials in the Brian Head formation have not been identified. Some of the loosely compacted, regularly stratified, and dominantly calcareous 

beds may represent the reworking of the underlying 

Wasatch formation,, but their chalcedony and tuffaceous 

conglomerate are out of place in the normal Wasatch 

formation. The pyroclastic beds are not local in origin. 

They are water-laid sediments derived from the disintegration of lavas that are not exposed in southern 

Utah. (Gregory, 1945,..p. 109.)

The Brian Head formation is tentatively considered 

to be of Miocene age, but the evidence for this assignment is far from satisfactory. The rare fossil snails 

and fragmental turtle bones belong to genera that 

range throughout the Tertiary, and few have been identified specifically. On the Markagunt Plateau, the 

Brian Head overlies rocks of Eocene possibly middle 

or even late Eocene age and underlies Tertiary volcanic rocks, which in turn underlie Quaternary basalt 

and glacial deposits. It is older than the Sevier River 

formation, which contains fossils of Pliocene (?) age. 

The formation predates the late Tertiary and 

Quaternary movements along the Hurricane, Sevier, 

and Paunsaugnnt faults. (Gregory, 1945, p. 110.)

SEVIER RIVER AND PARUNUWEAP FORMATION

The Sevier River formation is exposed along the 

Sevier River and is extensive in the valleys of the Basin 

and Range province west of the High Plateaus. Diatoms and gastropods obtained from the formation north 

of Marysville, Utah, establish its age as late Pliocene (?) 

or early Pleistocene(?). (Callaghan, 1938).

The formation is fanglomerate composed of poorly 

sorted pebbles, cobbles, and boulders, which range in 

diameter from y2 inch to 4 feet and which are cemented 

with reddish sand, silt, and clay, and some calcareous

material. Most of the debris is angular or subangular 

andesite, basalt, and quartzite. (Gregory, 1945, p. 115; 

1949, p. 987).

In the southern High Plateaus, in the valleys at 

heights of 10 to more than 200 feet above the surface 

of the late Pleistocene and Recent alluvial fills, are 

consolidated or partly consolidated masses of boulders, 

gravel, and stratified sand, which are classed as part 

of the Parunuweap formation and believed to be correlative with the Sevier River formation. These deposits lie midway up, or at the top of, the walls of some 

of the canyons; they completely fill some short, shallow 

valleys, and they extend onto some low interstream 

divides. (Gregory, 1945, p. 110-111).

The ParuniiAveap formation includes conglomerate 

and alluvial or lacustrine silt; the composition varies 

Avidely from place to place. In the valleys farthest 

Avest, the conglomeratic facies consists chiefly of angular slabs of gray sandstone, 1 to 4 feet long; partly 

worn pebbles of limestone; elongated iron concretions, 

1 to 12 inches in diameter; and rounded pebbles of 

quartz, quartzite, and chert, generally less than 3 inches 

in diameter. North of Ivanab, the conglomerate includes chunks of basalt and many mud balls. In Coal 

Creek valley are slabs of pink and red limestone, gray 

sandstone, and rhyolite 1 to 3 feet in diameter; angular 

and rounded pebbles of quartzite and chips of chalcedony. EveryAvhere, the cement of the conglomerate 

is calcareous and includes enough iron oxides to produce in places a tint of broAvn or yelloAv. The lacustrine 

facies, apparently restricted in extent, consists of thin 

layers of fine-grained sand interlaminated with calcareous and gypsiferous silt. (Gregory, 1945, p. HI114).

The Sevier River formation is unconformably overlain by basaltic lavas, believed to be of Quaternary age, 

and unconformably rests on the deeply eroded surface 

of the Brian Head formation. Farther to the Avest, 

along the Avest foot of the Pavant Range, the Sevier 

River formation is much faulted and is tilted southeastAvard as steeply as 35°. The ParumiAveap formation 

also is older than the Quaternary basalt flows and fossiliferous Pleistocene sediments and is older than some 

of the faulting and uplift in the southern High Plateaus. It is younger than the Avidespread rhyolite, andesite, and latite of probable Miocene age and predates 

much of the canyon cutting. (Gregory, 1945, p. 114; 

1949, p. 987; Maxey, 1946, p. 341.) The stratigraphic 

position and regional relations of both the Sevier RiA^er 

and ParunuAveap formations are comparable to those 

of the Pliocene Bidahochi formation in the basin under 

Black Mesa.
28 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

110° 30' K AYE NT A

110° 109"30'

//V^rff Rough Roc 

LACK/MESA\ ^ ,,,i %===.

7-c .'i?"1"'///.-- j> . .^%V

%,$$?" VBalakai 

"».^ \ Mesa

y rnVji*/^£Polqcca \

\5;-. /«%g9r^-4mf»._

Indian. 

Wells T.PCy

r

ft/tf^/C?

I P C XV ' .' / .V '.» '

L!- ^'-.V;;.'. V^,'.-/.\.v.^ide RuinT.P

Ill" 110°30' WIN SLOW 110°

EXPLANATION

109° 30'

After Hack. 1942

Outcrop of Bidahochi formation

Contours on base of Bidahochi 

formation (on Hopi Buttes surface). 

 Contour interval 200 feet

Trading post or settlement

10 20 Miles 

I

FIGURE 20. Map showing outcrop of Bidahochi formation.
CENOZOIC DEPOSITS 29

SOUTHERN PART OF THE COLORADO PLATEAU

BIDAHOCHI FORMATION

In the basin under Black Mesa, Ariz., are Pliocene 

deposits, known as the Bidahochi formation, which consist of interbedded calcareous sand, claj^, marl, tuff and 

other pyroclastic material and which are interbedded 

with lavas. (Fig. 20.) The deposits extend from the 

Hopi Buttes eastward to the Avest flank of the Defiance 

upAvarp and southeastward to the Zuni area, N. Mex.; 

a maximum thickness of about 400 feet has been reported. (Hack, 1942b, p. 336-340.)

The lithology varies considerably in short distances. 

In the vicinity of the Hopi Buttes, pyroclastic rocks 

that range from fine ash to coarse agglomerate locally 

make up the entire Bidahochi formation. North of the 

Buttes, on Black Mesa, the formation contains material 

derived from the Mesaverde group and is chiefly calcareous sand. Eastward and southeastward, the beds 

contain considerable sandy conglomerate or gravel. Locally, there are beds of ripple-marked and mud-cracked 

sand and clay. In general, the formation thickens and 

becomes coarser to the north and northeast and seems 

to have been deposited by streams flowing from that 

direction. (Hack, 1942b, p. 340-244.)

Fresh-water shells obtained from some of the finer 

beds have been identified as Unio, Planorbis trivolis 

Say, and Limnaea stagnalis appressa Say, and these 

have been interpreted to indicate an age no older than 

Pleistocene (Reagan, 1932, p. 258). Vertebrate remains, however, indicate the age to be middle or late 

Pliocene, probably middle Pliocene. These remains 

include fish vertebrae, pieces of bird and amphibian 

bones, the broken jaw of a new species of beaver, and 

a huge species of camel (Williams, 1936, p. 130).

The formation is interpreted as having been deposited by south westward flowing streams on a low,

wet, swampy floodplain. The vegetation was lush, and 

the climate must have been warm and moist at least 

part of the year. Since deposition, there seems to have 

been southward tilting of about 10 feet per mile (Hack, 

1942b,p. 344-345).

The Gallup-Zuni basin also contains Tertiary deposits very similar to, and probably correlative with, 

the Bidahochi formation. These sediments consist of 

nonfossiliferous, tuffaceous, loosely consolidated alluvial and lacustrine beds of white sandstone, lightgray clay shale, gravel, limestone, marl, bentonite, and 

tuff having a maximum thickness of about 350 feet. 

The pebbles that are found in the gravel are largely 

derived from the Zuni Mountains to the east, and the 

deposits evidently were deposited by streams draining 

westward from those mountains. The deposits overlie 

an erosion surface that slopes westward from the Zuni 

Mountains. Figure 39 illustrates the general structural setting but does not show these deposits. Since 

deposition, the beds seem to have been tilted westward 

as a result of roughly 700 feet of additional uplift at 

the Zuni Mountains (McCann, 1938). South of Zuni, 

N. Mex., similar beds extend beneath lavas of the 

Mogollon volcanic field.

CHUSKA SANDSTONE

The Chuska sandstone outcrops at the east edge of 

the Defiance upwarp and may correlate with the 

Bidahochi formation. It rests on Tohachi shale, which 

is thought to be of Late Cretaceous age (Alien, 1953; 

Alien and Balk, 1954). The Chuska sandstone, about 

700 feet thick, is well-bedded, medium-grained sandstone containing some volcanic ash. Locally, the base 

is conglomeratic (Gregory, 1917, p. 80-81). The 

Chuska sandstone unconformably overlaps the tilted 

Mesozoic rocks along the east side of the Defiance upwarp (fig. 21).

CHUSKA MOUNTAINS

DEFIANCE PLATEAU Te

10 

[_

10 Miles 

I

Modified after Gregory, 1917

Te, late Tertiary lavas; T, Chuska sandstone; Kmv, Mesaverde group; Kmc, Mancos shale; Jm, Morrison 

formation and San Rafael group; Jgc, Glen Canyon group; ~R, Triassic formations; P, Permian formations

FIGURE 21. Cross section of the Defiance uplift.

DATIL FORMATION

In the Datil section^ New Mexico, along the southeastern part of the Colorado Plateau is the Datil formation, which consists of highly lenticular, well347620 56 3

indurated tuff, rhyolite, crossbedded sandstone, and 

conglomerate. The formation is 2,000 feet thick and 

is* probably of late Tertiary age, although no fossils 

have been found to support this interpretation. (Win-
30 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

Chester, 1920, p. 4, 5, 9y 10). At most places the formation is practically horizontal and imconformably 

overlies the older, folded Upper Cretaceous formations.

DEPOSITS AT PEACH SPRINGS, ARIZ.

At the southwest edge of the Colorado Plateau, at 

Peach Springs, Ariz., is a depression draining southsouthwestward and alined with a 20-mile stretch of 

Grand Canyon. It is many hundreds of feet lower 

than the rims of Paleozoic rocks and is about half as 

deep as Grand Canyon. This depression may represent a former course of the Colorado River.

The depression evidently is an erosion feature, although its location and trend may have been controlled 

originally by faulting. Deposits in the bottom of the 

depression consist of water-laid stratified volcanic rocks 

overlain by fanglomerate and lavas.

The deposits resemble the Muddy Creek formation 

and are assumed to be of late Tertiary age. They are 

reddish, tuffaceous, and partly conglomeratic. Pebbles 

in the conglomerate are mostly granite; some are lavas, 

but only a few are limestone. In the lower part of the 

deposits are some porphyritic lavas. These volcanic 

sediments and lavas, at least 150 feet thick, have been 

folded and probably have been faulted.

Overlying the volcanic sediments are .fanglomerate, 

some interbedded basaltic lavas and scoria, and alluvium. These younger deposits are deeply dissected 

but the}* relate to the present topography and do not 

appear to be folded.

The Peach Springs depression was formed before 

the volcanic sediments were deposited. Regardless of 

whether the Colorado River ever flowed through the 

depression, it has not taken this course since the volcanics were deposited. If the depression marks an 

ancient course of the Colorado River, the canyon upstream from the depression must .antedate the volcanic 

deposits, although at that time the canyon would have 

been only half as deep as it-is now.

INTERIOR OF THE PLATEAU

At the northwest foot of the La Sal Mountains, 

Utah, in a salt anticline A^alley known as Castle Valley 

(fig. 4.0), is a fanglomerate, aggregating 1,000 feet thick, 

derived from the La Sal Mountains. The pebbles and 

cobbles in the deposit were derived from the intrusions 

and sedimentary rocks in the mountains. However, at 

the foot of the mountains the gravels are vertical at the 

foot of the intrusions from which they Avere derived. 

The gravels probably Avere deposited on top of salt that 

had been squeezed upAvard in the anticline, and the 

gravel beds became doAvnfolded as a result of removal 

of the underlying salt by solution or lateral floAA~age.

In any case, the gravels indicate that Castle Valley Avas 

in existence Avheii the fanglomerate Avas deposited, but 

because of the deformation resulting from salt movement it is not possible to determine to Avhat extent the 

A'alley subsequently has been deepened. It may be assumed that the A*alley AAr as half as deep then as it is IIOAA' 

(Hunt and Waters, in preparation).

The .deposit in Castle Valley probably is of late Pliocene age, although it may be early Pleistocene. No 

fossils have been found in it, but it is Avell consolidated 

and overlain by a sequence of two pre-Wisconsin tills 

or glacial outAvash (Richmond, in preparation). Similar deposits occur in the A*alleys east of the La Sal 

Mountains (Cater, 1955a). A feAV hundred feet of 

alluvial fill in Fisher valley directly north of the La 

Sal Mountains also may be of late Tertiary age (Dane,

1935. p. 156).

ElseAvhere in the interior of the Colorado Plateau are 

extensive gravel deposits that probably in part are as 

old as late Pliocene. Such deposits haA'e been reported 

on the Green River desert (Baker, 1946, p. 92-94) and 

in the Henry Mountains region (Hunt, 1953b).

One of the deposits in the Henry Mountains region, 

on the Avest rim of the canyon of the Dirty Devil RiA*er, 

contains cobbles of diorite porphyry from the Henry 

Mountains. It is, therefore, younger than those intrusions but antedates most, if not all, of the cutting 

of the adjoining canyon, Avhich is 3,000 feet deep 

(Hunt, 1953b).

DEPOSITS AROUND THE EDGES OF THpE COLORADO 

PLATEAU

UINTA BASIN AREA

Bishop conglomerate. The Bishop conglomerate, believed to be of Miocene age, is rather extensive along 

the northern side of the Uinta Mountains and along the 

southern part of the Wyoming Basin. Although the 

formation has not been recognized in the Uinta Basin, 

its history contributes to the history of the Plateau.

The Bishop conglomerate consists predominately of 

boulders and gravels of reddish quartzite and sandstone derived from the pre-Cambrian core of the Uinta 

Mountains. Mixed with the quartzitic material is a 

moderate quantity of cherty limestone and light-colored 

quartzite from the hogbacks of Paleozoic rocks that 

flank the core. The formation becomes less coarse northward from the mountains; the upper part nearly everywhere is less coarse than the loAver part. (Bradley,

1936. p.172-173).

The Bishop conglomerate reaches its maximum thickness, about 200 feet, near the Utah-Wyoming boundary 

line. It thins northward into the Wyoming Basin and 

southward to the Uinta Mountai us. The erosion surface
CENOZOIC DEPOSITS 31

on which the formation rests slopes northward from a 

maximum altitude of 13,000 feet in the Uinta Mountains to an altitude of 7,300 feet in the Wyoming Basin. 

(Bradley, 1936, p. 169,172).

The erosion surface beneath the Bishop conglomerate 

has been interpreted as a pediment; the change in 

stream, regimen, represented by the change from planation to deposition of the thick conglomerate, is attributed to a slight change in climate towards greater aridity 

rather than to a renewal of mountain uplift or other 

structural movements. (Bradley, 1936, p. 178-179; 

Rich, 1910, p. 619-620; Sears, 1924). On the other 

hand, the erosion surface may be a series of closely 

spaced pediments that were cut and aggraded in the 

manner of those along the foot of the Book Cliffs and 

around the foot of the Plenry Mountains (fig. 24). 

(Rich, 1935; Hunt, 1953b).

The Bishop conglomerate is younger than the main 

uplift of the Uinta Mountains, although it predates the 

collapse at the eastern end of the mountains. No fossils 

have been obtained from the conglomerate, but probably it is Miocene in age. It is older than the Browns 

Park formation, which is regarded as late Miocene or 

early Pliocene in age.

Browns Park formation. The Browns Park formation, of late Miocene or early Pliocene age, outcrops 

in a belt 6 to 10 miles wide extending from the Green 

River at the north foot of the Uinta Mountains nearly 

to Craig, Colo., a distance of about 100 miles. This is 

in the Wyoming Basin rather than in the Colorado 

Plateau, but the history of this formation bears on the 

history of the Plateau.

The formation, at least 1,200 feet thick and probably 

originally thicker, rests with angular unconformity on 

rocks that range in age from pre-Cambrian to Bridger. 

The formation is composed principally of white, wellbedded quart/ sandstone having a calcareous cement. 

Locally, there is an angular unconformity within the 

formation (Sears, 1924, p. 295).

The base of the formation is a conglomerate that 

ranges in thickness from a few inches to 300 feet, but 

it has very different characteristics in the eastern and 

western half of the outcrop area. In the east, the pebbles rarely exceed 2 inches in diameter and consist of 

metamorphic and igneous rock, quartzite, chert, and 

vein quartz. In the west, conglomerate consists predominantly of red quartzite pebbles and boulders, 

which reach, a maximum diameter of several feet, and 

which were derived from the pre-Cambrian core of the 

Uinta Mountains anticline. (Sears, 1924, p. 295).

The Browns Park formation contains a considerable 

amount of volcanic material including some interbedded basalt (Hancock, 1915, p. 187). The sandstone

is tuffaceous, and there are numerous beds of tuff. The 

formation is regarded in part as an eoliaii deposit that 

was transported not far from its source (Bradley, 1936, 

p. 182-184).

Mammalian fossils collected near Grey stone, Colo., 

indicate that the formation is of late Miocene or early 

Pliocene age. (Peterson, 1924, 1928).

The Browns Park formation overlaps an extensive 

erosion surface on the northern side of the Uinta Mountains. Aridity, at the time that the Browns Park formation was deposited, is suggested by the occurrence of 

halite crystal molds in part of the formation and by 

the occurrence of wind-blown sand, including some 

wind-faceted cobbles in other parts of the formation. 

The formation was involved in the graben faulting at 

the north foot of the Uinta Mountains; father east, it 

was tilted. (Bradley, 1936, p. 184).

SAN JUAN MOUNTAINS

Unconformably overlying the early Tertiary till in 

the.San Juan Mountains is the Telluride conglomerate 

of probable Oligocene age. It ranges from a thin, 

coarse conglomerate in the eastern part of the San Juan 

Mountains to a sandstone, shale, and fine conglomerate 

1,000 feet thick in the western part of the San Juan 

Mountains. Volcanic rocks are lacking. No fossils 

have-been- found in the Telluride conglomerate, but 

Oligocene(?) age is indicated by its apparently conformable relation to the overlying San Juan tuff, which 

is probably Miocene. (Cross and Larsen, 1935).

Along the southern side of the San Juan Mountains, 

is the Blanco Basin formation, which consists of several 

hundred feet of arkosic sandstone, conglomerate, and 

other sediments. The Blanco Basin formation, like the 

Telluride conglomerate, lacks volcanic materials. It 

unconformably overlies folded Cretaceous formations: 

and the Animas formation and is apparently conformable beneath the Miocene volcanic sequence. It is, 

thought to be of Oligocene age, but it could be late 

Eocene, Oligocene, or early Miocene. (Cross and 

Larsen, 1935, p. 48-50).

The conglomeratic deposits in these formations suggest that their source area in the San Juan. Mountains, 

was high enough to be in a zone of vigorous frost action,, 

and perhaps it was high enough to be in a zone of periglacial or glacial action.

The younger Tertiary deposits in the San Juan Mountains comprise a thick and extensive series of volcanic 

rocks. This volcanic activity began in the Miocene 

and continued, with interruptions, into Pleistocene or 

Recent time. It built a volcanic dome more than 100; 

miles wide and probably several miles high. This dome 

has been faulted, tilted to the east and north, folded,.
32 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

and deeply incised by erosion to form the present San 

Juan Mountains. (Cross and Larsen, 1935, p. 50).

The earliest of the eruptive formations, the Lake 

Fork andesite,1 built a volcanic mountain about 15 

miles wide and 4,000 feet high on the north flank of the 

San Juan Mountains. The Lake Fork andesite is composed mostly of andesitic breccia with some basalt and 

quartz latite. (Cross and Larsen, 1935, p. 50).

Before the Lake Fork volcano had been greatly modified by erosion it was in large part buried by much more 

widespread andesitic tuff-breccia, the San Juan tuff. 

This tuff, made up almost entirely of bedded clastic 

material, was deposited by water and probably was derived from explosive vents located west of the Lake 

Fork volcano, although that volcano contributed very 

little of the material. The San Juan tuff still is preserved in an area nearly 100 miles wide from southwest 

to northeast; its thickness commonly exceeds 1,000 feet. 

(Cross and Larsen, 1935, p. 51).

After some erosion, the San Juan tuff was partly 

buried by the Silverton volcanic series, which consists 

of quartz latite, rhyolite, and pyroxene andesite lavas 

and pyroclastics. These, in turn, were followed by 

local, water-laid tuff. Well-preserved plant remains 

in some of the tuff beds are of Miocene age. The Silverton eruptives built a dome 40 miles wide and 3,000 feet 

high. (Cross and Larsen, 1935, p. 51).

Following eruption of the Silverton volcanic series, 

there seems to have been a period when erosion cut deep 

canyons in the volcanic mountains and in the bedrock 

formations on which the volcanics rest. Towards the 

end of this period of erosion, a volcano northeast of the 

Silverton area erupted a considerable volume of rhyolite. (Cross and Larsen, 1935, p. 51-52).

This period of erosion was followed by a long series 

of great eruptions that filled the canyons and finally 

buried all of the mountains. The resulting low, broad 

dome of the Potosi volcanic series makes up the main 

part of the volcanic rocks of the region. It was 150 

miles across, and over a very large area it was a mile 

thick. The eruptions alternated between andesitic and 

rhyolitic materials. Three periods of erosion that interrupted the accumulation of volcanic rocks were sufficiently long to allow the development of canyons comparable in depth to the present canyons. (Cross and 

Larsen, 1935, p. 52).

Erosion continued after the Potosi eruptions ceased. 

During this period, the Creede formation, which is a 

thick deposit of fine rhyolitic tuff containing plant remains of Miocene age, was deposited in a lake in one 

of the canyons. After further erosion, the Fisher latite-

*In a more recent publication, in press, Cross and Larsen call this 

formation the Lake Fork quartz latite.

andesite was erupted, and this was followed by a longperiod of erosion during which an erosion surface developed throughout most of the region the San Juan 

peneplain of Atwood and Mather (1932, p. 21-26). 

(Cross and Larsen, 1935, p. 53).

Overlying the San Juan peneplain is the Hinsdale 

formation, which probably is of late Pliocene age. The 

basal part of the Hinsdale is sand and gravel with local 

flows of latite-andesite. This is overlain by rhyolite, 

and the rhyolite in turn is overlain by andesite and 

basalt. The resulting basaltic plateau was then tilted 

to the east, faulted, and folded at about the end of the 

Pliocene. (Cross and Larsen, 1935, p. 54, 95, 100).

During Pleistocene time, minor eruptions of basalts 

flowed into some of the canyons. (Cross and Larsen, 

1935, p. 54).

Associated with these eruptives are intrusives that fall 

into two groups the laccoliths and stocks that intrude 

chiefly the sedimentary rocks in the western part of the 

mountains, and the stocks and associated dikes that 

intrude the earliest Potosi rocks in the eastern part of 

the mountains. (Cross and Larsen, 1935, p. 101).

RIO GRANDE VALLEY

Post-G-alisteo and pre-Santa Fe deposits. At many 

places in the Rio Grande Valley there have been recognized deposits, which underlie the Santa Fe formation but which are younger, or apparently younger, 

than the Galisteo sandstone. These deposits include a 

high proportion of volcanic rocks in the form of waterlaid breccia, conglomerate, agglomerate, tuff, and lava 

flows. Numerous local names have been given to them.

The Galisteo sandstone is conformably overlain by 

1,000 feet of water-laid breccia, conglomerate, and tuff, 

with massive flows and pyroclastic material in subordinate amount. These have been referred to by Stearns 

(1943, p. 309) as the Espinaso volcanics. Northeast of 

the Nacimiento Mountains, the earliest Tertiary formations consist of several thousand feet of andesite and 

latite flows, with some basalt, rhyolite, and volcanic 

breccia that have been referred to as the Chicoma volcanic formation of Smith (1938). Younger than these 

is a unit consisting of 200 feet of sandstone, conglomerate, and breccia that has been referred to as Smith's 

El Rito formation. Unconformably on his El Rito 

formation is the Abiquiu tuff of Smith, which consists 

of 1,200 feet of stream-laid tuff and volcanic conglomerate with a few small interbedded lava flows and 

which apparently was derived from the north. On the 

east side of the Rio Grande depression and at the west 

foot of the Sangre de Cristo Range, 1,200 feet of beds 

similar to Smith's Abiquiu tuff have been referred to
CENOZOIC DEPOSITS 33

by Cabot (1938, p. 91) as Picuris tuff. At the east edge 

of the Mount Taylor district, tuffaceous fan deposits 

unconformably underlie the Santa Fe formation 

(Bryan and McCann, 193T, p. 817-818). Farther 

south, on the east side of Sierra Ladron, between 3,500 

and 5,000 feet of tuffaceous sandstone, conglomerate, 

and tuff overlie the Miocene(?) volcanic rocks and. in 

turn, are overlain with angular unconformity by the 

Santa Fe formation. These tuffaceous sediments have 

been referred to as the Popotosa formation (Denny, 

1940a). Pebbles of granite, schist, quartzite, and sandstone in these beds indicate that there were highlands 

in the Sierra Ladron while these beds Avere being 

deposited.

Santa Fe formation. The most extensive of the Tertiary formations in the Rio Grande Valley is the Santa 

Fe formation, which extends across New Mexico from 

Colorado to Texas. Along the valley the formation 

consists of a few thousand feet of sand, silt, and gravel, 

which were deposited by the ancestral Rio Grande 

between broad alluvial fans which, in turn, were deposited by tributaries from the east and from the west. 

Locally, there are discontinuous thin beds of tuff. 

Southeast of the San Juan Basin the gravels include 

some pre-Cambrian rocks, apparently derived from the 

Nacimiento or Zuni uplifts; andesite and other volcanic 

rocks are also common. (Bryan and McCann, 1938; 

Wright, 1946).

Vertebrate fossils obtained from the Santa Fe formation north of Santa Fe indicate that these beds are late 

Miocene or early Pliocene in age, and possibly younger. 

Fossils obtained from deposits in the San Acacia area 

indicate a middle or late Pliocene age. (Denny, 1940a, 

p. 93-94).

Immediately east of the Colorado Plateau, and east 

of Mount Taylor, the Santa Fe formation overlies the 

much faulted and tilted Upper Cretaceous formations 

(.fig. 43) with strong angular unconformity. This edge 

of the Colorado Plateau was faulted before the Santa 

Fe formation was deposited, but the formation itself is 

broken by many faults, which parallel the edge of the 

Plateau and which, in part at least, represent renewed 

movement along the faults of pre-Santa Fe age (Hunt, 

1938, p. 56, 57, 77, 78). Pre-Santa Fe uplift of the 

Sierra Ladron portion of the Plateau is indicated by 

the gravels in Denny's Popotosa formation, which unconformably underlies the Santa Fe (Denny, 1940a, 

p. 77-84). It seems probable that the Santa Fe formation will be found to contain numerous angular unconformities as do the other upper Tertiary deposits in the 

basins of the Basin and Range province. Apparently, 

downfaulting of the basins was synchronous with 

deposition.

GRAND WASH TROUGH

Upper Tertiary deposits in the Grand Wash trough 

and other basins immediately west of the Grand Wash 

Cliffs lie across the course of the Colorado River. These 

deposits include one or more thick series of clastic 

fluviatile sediments, referred to as the Muddy Creek 

formation, and a thick series of lacustrine limestone, 

referred to as the Hualpai limestone of Longwell (1936, 

p. 1429). See figure 22. The deposits are assumed to 

be of late Miocene and Pliocene age.

The oldest exposed deposits include a coarse breccia 

that rests with erosional unconformity, but concordantly (locally at least), on highly tilted Kaibab limestone. The breccia, about 350 feet thick, contains angular blocks of Kaibab limestone as much as 10 feet long 

(Longwell, 1936, p. 1,414-1,415'). The occurrence of 

such breccia suggests that it was being deposited while 

the faulting progressed along the western edge of the 

Colorado Plateau.

Unconformably overlying the breccia is fanglomerate 

and siltstone, which locally have been faulted and folded 

and which in places have been turned up as steeply as 

70°. In most of the basin the fanglomerate consists 

almost entirely of granitic and gneissic debris from 

the Virgin Mountains. Some blocks of granite, which 

must have been moved 12 to 15 miles, are 15 to 20 feet 

long. Fanglomerate, containing limestone and sandstone derived from Paleozoic formations on the Colorado Plateau, occurs at the mouth of Grand Canyon 

and overlaps eastward onto the pre-Cambrian and Cambrian formations in the Grand Wash Cliffs (fig. 22). 

(Longwell, 1936, p. 1434-1436). .

In the middle of the basin, the fanglomerate grades 

upward into several hundred feet of playa deposits, 

consisting mostly of siltstone and clay with a few thin 

beds of volcanic ash. These, in turn, are overlain conformably by Longwell's Hualpai limestone (Longwell, 

1936, p. 1435). See figure 23.

Presumably, the scarcity of Paleozoic debris in the 

fanglomerate derived from the Virgin Mountains indicates an earlier uplift of those mountains to allow removal of the Paleozoic strata that must have extended 

across them. The Virgin Mountains may have been a 

source for some of the Upper Cretaceous sediments on 

the Colorado Plateau. Therefore, at least three stages 

of deformation are recorded one or more antedating 

the fanglomerate, one that caused the fanglomerate to 

be deposited, and one that caused the post-fanglomerate faulting and folding.

The Hualpai limestone of Longwell, which is more 

than 1,000 feet thick, overlaps the edges of the fanglomerate and extends onto the pre-Cambrian rocks along 

the east and west sides of the trough. Not only is the
34 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

'^ ' ^ ' } 

-L NOO W V7^,V-V~ N
CENOZOIC DEPOSITS 35

WNW. ESE.

Hualpai limestone

Fanglomerate of 

pre-Cambrian debris

w.

Hualpai limestone 

T~*r

Coarse fanglomerate,--^^ ^<=»C5__ ~~- ^

After Longwell, 1936

FIOUUB 2:-'.. Cross suctions of valley fill in vicinity of Grand Wash trough. (A) Fanglomerate of pre-Cambrian debris intertongues with Hualpai 

liinostont1 and indicates a steep scarp directly to the east while the limestone was accumulating. (B) Faulted fanglomerate and red siltstone of Muddy Creek formation and Hualpai limestone.

limestone thick and widely distributed, it is regularly 

stratified and a large part contains remarkably little 

impurity even \vhere it"lies against the Grand Wash 

Cliffs or similar steep slopes. It appears to have been 

deposited in a lake, or perhaps in several connected 

lakes. Locally, where the limestone has been faulted 

against pre-Cambrian rocks, it includes fragments of 

them, therefore it is probable that the faulting in the 

Grand Wash trough continued while the limestone was 

being deposited. (Longwell, 1936, p. 1432-1434, 1438- 

1439).

QUATERNARY DEPOSITS

Quaternary deposits on the Colorado Plateau include 

glacial and peri glacial deposits of various kinds on and 

near the higher mountains, fanglomerate on pediments 

and in alluvial fans, gravel or alluvium both on cut 

terraces and in fill terraces along streams, colluvial and 

talus deposits on the valley walls, and eolian deposits 

and residual soils on uplands. Although fossils are 

scarce, several different ages of deposits generally can 

be distinguished by supplementing the scanty paleontologic data with information about the physical sequence, interbedded soils, and archeological remains. 

Generally, it is possible to distinguish pre-Wisconsin 

from the Wisconsin deposits, and these deposits of Pleistocene age usually are distinguishable from Recent ones.

PRE-WISCONSIN DEPOSITS

Pre-Wisconsin glacial deposits have been recognized 

in the mountains along the north and east sides of the 

Colorado Plateau and in the southern part of the 

Plateau, but curiously they are lacking to the west in 

the High Plateaus. In the TJinta, San Juan, and La 

Sal Mountains pre-Wisconsin glacial deposits extend 

to altitudes as low as 7,000 feet (Atw>ood, 1909; Atwood 

and Mather, 1932; Richmond, in preparation). No 

pre-Wisconsin glacial deposits have been recognized 

in the Aba jo Mountains, but probably snow or ice fields 

were there and on some of the nearby ridges"whose altitude is about 8,500 feet. On the San Francisco Mountain, pre-Wisconsin glacial deposits extend downward 

to an altitude of 8,000 feet (Sharp, 1942, fig. 1). On 

the High Plateaus, similar deposits are scarce, although
36 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

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The courses of Bull Creek and Nazer Creek are not changed. The grave I-covered surfaces on which these streams flowed during Stage 1 have been greatly reduced. A strea

word along the east edge of the surface on which Nozer'Creek flowed during Stage 1, threatens to capture Bull Creek. McClellon Wash is a youthful valley west of this p

Birch Creek and Coaly Wash have maintained their courses but their tributaries have greatly reduced the grave I-covered Stage 1 surface of Birch Creek. 

Oak Creek has maintained its course. Its abandoned surface (Stage 1) has been eroded further and is cut through by a stream from the west.

Bull Creek has been diverted westward onto the pediment that developed during Stage 3 and is aggrading that pediment. Another minor diversion occurred above the 

Creek and was caused by a tributary cutting headword along the foot of the mountain isolating a small remnant of the surface on which Bull Creek flowed during St< 

The lower end of Nozer Creek was diverted into a tributary of the pediment now being aggraded by Bull Creek. i ne lower ena 01 i^ozer ^reex was atverrea into a iriDurary or me peaimeni now oemg a__

Bull Creek is about to be diverted onto a pediment along McClellon Wash. The two drainages are separated by 

ley at the head of the wash has nearly captured Nazer Creek at a place where the west bank of Nazer Creek 

The lower part of Birch Creek has been diverted into a youthful valley which is now being aggraded.

10-foot divide and the pediment is considerably Ic 

S'-jfeet high and the wash is 55 feet lower.

The lower part of Birch Creek has been diverted into a youthful valley which is now being aggraded.

A broad pediment has developed along the lower port of Coaly Wash and a deep volley, known as Jet Sasin, extends headword cl

The head of this volley is several hundred feet lower than Birch Creek and the divide between them is 

Oak Creek has been diverted to the west. A new grovel-free pediment is developing between ' - - " '

, only 20 feet high. 

i and tSe abandoned course

3Se to where Birch Creek 

of Cak Creek.

ver. A 

from 

FIGURE 24. Continued.
38 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

some of the catchment basins are between 10,000 and 

11,000 feet in altitude, and there are extensive areas 

higher than 9,000 feet (Spieker and Billings, 1940, 

p. 1193-1196).

This distribution of the pre-Wisconsin glacial deposits is anomalous. It is unlikely that pre-Wisconsin 

glaciation was less extensive at high altitudes in the 

High Plateaus than at similar altitudes in the other 

mountains, one of which lies 300 miles farther south. 

In addition, it is unlikely that erosion completely destroyed the stratigraphic and physiographic record in 

and around the High Plateaus but so clearly preserved 

it in the other highlands. The anomaly could be attributed to Pleistocene upwarp of the High Plateaus, 

(p. 61).

Deeply weathered pre-Wisconsin fluvial and loessial 

deposits several feet thick are extensive on the plateau 

surfaces east of the Abajo Mountains and at the northwest foot of the San Juan Mountains. The pre-Wisconsin soils on these deposits are classed as chestnut 

soils (fig. 6) and are productive for farming.

The only assuredly pre-Wisconsin fill terrace that 

has been found along the Colorado River is located in 

a cut-off meander of the river east of Hite. The alluvial fill is at least 130 feet thick. Its base is at least 

300 feet higher than the present river. Overlying the 

fill is f anglomerate believed to be of late Pleistocene age.

Some of the higher pediments and the f anglomerate 

lying on them around the foot of the Henry Mountains and along the foot of the Book Cliffs also appear 

to be of pre-Wisconsin age. Th-e^pediments around the 

foot of the Plenry Mountains extend into, and therefore 

are younger than, the canyons tributary to the Dirty 

Devil and Colorado River Canyons east of the Henry 

Mountains. Figure 24 illustrates a common process of 

pediment development on the Colorado Plateau. The 

extensive gravel deposits on the pediments probably 

were derived from glacial or periglacial debris in the 

mountains.

Remnants of a soil that is wholly unlike that on any 

of the Wisconsin, or younger, deposits occur on the 

pre-Wisconsin deposits (Hunt and Sokoloff, 1950). 

This soil consists of a reddish clayey upper layer, a few 

feet thick, over several feet of a strongly lime-enriched 

layer of weathered parent material. At higher altitudes the limy layer is missing and the soil is acid. 

Wherever it occurs this soil is associated with subdued 

land forms that are in striking contrast to the rugged, 

youthful land forms that are developing under the Recent climatic environment.

WISCONSIN DEPOSITS

Wisconsin glacial deposits are extensive on the mountains and plateaus on all sides of the Colorado Plateau,

including the High Plateaus. Two sets of Wisconsin 

glacial deposits, representing an early and a late stage 

of Wisconsin glaciation, have been recognized. 

(Spieker and Billings, 1940; Gould, 1939; Atwood, 

1909; Atwood and Mather, 1932; Sharp, 1942; Richmond, in preparation; Flint and Denny, in preparation. ) In the Plenry Mountains, Abajo Mountains, and 

Mount Taylor no moraines have been recognized, but 

periglacial deposits, mostly in the form of boulder 

fields, are extensive.

Talus cones and colluvial aprons of periglacial origin, judged to be of Wisconsin age, are extensive along 

canyon walls in southeastern Utah, xllong the canyons 

east of Hite are some spectacular debris avalanches that 

certainly are no younger than Wisconsin and may be 

older. All these canyon-wall deposits now are deeply 

dissected, but they record a time when the climate was 

more moist than now and when the canyon country 

developed smooth contours.

Fluvial deposits of Wisconsin age include glacial outwash near the mountains and alluvial fill in valleys 

remote from the mountains. Along the Colorado River, 

for example, about a mile upstream from Hite, alluvial 

gravel, believed to be of early Wisconsin age, comprises 

a fill more than 100 feet thick. Interbedded with the 

fill are thick spring deposits of calcium carbonate. The 

deposits reveal that Glen Canyon was about as deep 

then as it is now, that there Avas considerable spring 

activity apparently reflecting a high groundwater table, 

and that since the deposits were formed the history of 

this canyon consisted alternately of deposition of fill 

and of erosion of the fill without major changes in the 

depth and shape of the canyon. Nearer the mountains 

other canyons probably became deepened and extended 

headward during Wisconsin time.

The alluvial deposits of late Wisconsin age resemble 

the Recent deposits, except that they tend to be thicker, 

more extensive, more clayey and more compact. The 

regimen of the late Wisconsin streams seems to have 

been somewhat different from that of the Recent streams 

(p. 39). Also, the late Wisconsin alluvium contains 

the remains of mammoth or of extinct longhorn bison. 

(Hunt, 1953a).

RECENT DEPOSITS

The earliest Recent deposits on the Colorado Plateau 

are represented by dune sand. Overlapping the dune 

sand is alluvium that was deposited before pottery was 

introduced among the prehistoric inhabitants of the 

region. This pre-pottery alluvium in northeastern 

Arizona has been referred to by Hack (1942a, p. 51) 

as the Tsegi alluvium. Much of the pre-pottery alluvium apparently was deposited during the first and 

second millennia B. C. Towards the close of the 13th
CENOZOIC IGNEOUS ROCKS 39

century A. D. this alluvium was cut by deep arroyos, 

and these in turn were partly filled by younger alluvium 

that apparently was deposited during the 16th and 17th 

centuries. The present-day arroyo cutting began in 

the period 1880-1895. Figure 25 illustrates some typical sequences of late Pleistocene and Recent alluvial 

deposits in the Colorado Plateau.

The early Recent dunes became stabilized during the 

comparatively moist period or periods when the prepottery alluvium was deposited. The old dune sand is 

moderately firm and stained with iron oxide. Locally, 

the area sustained vegetation that today characterizes 

somewhat higher areas. Most of the dune sand that 

was active later during the Recent, as well as the sand 

that is active today on the Colorado Plateau, is derived 

from the early Recent stabilized dunes (Hack, 1941, 

p. 261), but the volume of sand being moved today is 

small compared to that of the early Recent.

Late Wisconsin 

alluvium

EXPLANATION

ill

Pre-pottery Recent 

alluvium

Historic 

alluvium

FIGUUH 25. Diagrammatic sections illustrating some common stratigraphic relationships in the alluvial deposits on the Colorado 

Plateau.

The pre-pottery, Recent alluvium generally occurs as 

fill in arroyos cut in the Wisconsin alluvium, but in 

some valleys the pre-pottery alluvium overtops the older 

deposits. The pre-pottery alluvium represents coalescing alluvial fans built in the main valleys at the 

mouths of the tributaries. Thus, the surface of this 

alluvium is broadly rolling, and the texture and composition of the alluvium vary according to the kind of 

material brought into the valley by the tributaries. 

The Wisconsin alluvium, on the other hand, generally 

represents a smooth fioodplain built by the main stream 

itself; not only is its surface smooth, but the composition 

and texture of the alluvium commonly vary only 

slightly from the mouth of one tributary to another. 

Evidently, the regimen of the streams that deposited 

the pre-pottery, Recent alluvium was different from 

the regimen of the streams that deposited the Wisconsin 

alluvium. Generally, this difference in regimen also 

is reflected in differences in the molluscan fauna in the

two alluvial deposits. The total list of species in the 

two faunas may be alike, but the proportion of different 

species, and the number and size of the individuals, 

generally are very different when comparisons are made 

between deposits in nearby localities.

Mammalian remains in the pre-pottery alluvium are 

those of modern forms. The associated artifacts are 

those of pre-pottery lithic cultures. Hearths and charcoal are abundant at many places in the alluvium and 

help to distinguish it from the older and younger deposits. Building foundations, irrigation systems, and 

other structures constructed by the pottery-making 

Anasazai and related prehistoric cultures are found on 

and in the uppermost part of the alluvium. Denclrochronologic and radiocarbon data indicate that this 

Anasazai occupation began early in the Christian era 

and ended towards the close of the 13th century, when 

deep arroyos were cut in the alluvium.

In these younger arroyos was deposited still younger 

alluvium that, in the Navajo country, has been referred 

to by Hack (1942a, p. 53) as the Naha alluvium. Presumably, deposition occurred during the period of 

Spanish occupation in the southwest. The present-day 

arroyo cutting began during the 1880's (Bryan, 1925).

CENOZOIC IGNEOUS ROCKS

GENERAL FEATURES

Cenozoic intrusive rocks in the Colorado Plateau occur as stocks, laccoliths, and bysmaliths in the dozen or 

so laccolithic mountains. Eruptive rocks occur at the 

large, central-type volcanoes at Mount Taylor and the 

San Francisco Mountain, and as extensive sheets of 

basaltic lavas and pyroclastic rocks (fig. 26). Laccolithic types of intrusions and large, simply constructed, 

central-type volcanoes generally are lacking in the 

structurally more complex provinces surrounding the 

Colorado Plateau; the development of these igneous 

forms on the Plateau was favored by the simplicity of 

its regional structure.

The volume of the basaltic lavas and associated pyroclastic rocks, including the alkalic basalts, greatly exceeds the volume of other igneous rocks. Roughly 

15,000 square miles of the Plateau are covered by these 

eruptives; if they average about 75 feet in thickness, 

their A^olume amounts to about 200 cubic miles. The 

San Francisco Mountain and Mount Taylor together 

aggregate about 50 cubic miles of eruptive rocks, and 

there is about 50 cubic miles of intrusive rocks in the 

laccolithic mountains. These volumes are considerable, but they are very small as compared with the 

volumes of eruptives in the San Juan Mountains and 

in the adjoining parts of the Basin and Range province.
40 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

A

ADO

x i c o!

EXPLANATION

Cenozoic igneous rocks 

Outline of Colorado Plateau

i

_..._ .- I

FIGURE 26. Sketch map illustrating distribution of.Cenozoic igneous rocks on the Colorado Plateau. The laccolithic mountains are mostly 

in the central part of the Colorado Plateau ; the volcanic centers are mostly around the edges.

The laccolithic mountains are clustered in the central It is of interest to note that the pre-Cambrian rocks in

and east-central part of the Colorado Plateau. The adjoining areas, especially in the San Juan Mountains,

volcanic centers are mostly around the edges of the also include considerable bodies of alkalic rocks. The

Plateau, and especially around the southern edges. igneous rocks of the Plateau can be grouped into four

The Colorado Plateau is a petrographic province high subprovinces based on the proportions between the alin alkalis and alumina and low in zirconium. In com- kalis (fig. 27). In the interior of the Plateau, in the

mon with the Great Basin, the content of BaO is high, laccolithic mountains, soda greatly exceeds potash. In
CENOZOIC IGNEOUS ROCKS 41

OACCOLTHIC MOUNTAINS

LA SAL MOUNTAINS

63 67 7!

>1 62164 66168 701

75 7?

74 78182

73 76 il

, CENTRAL HIGH PLATEAUS. SAN RAFAEL 

SWELL, AND YAMPA RIVER DISTRICT

43

'/"'

_</

44 45

/#=

/

46

KjO

>-

NajO ^V

47 48

^

+

49 ^1 5

x^x

253

V:

54

:^T ~~

\

!

' '- 

y

5 56

^,__-- °%

+

58

57159

PERCENT OFNajO AND KiO

34

NAVAJO AND TUBA

_ 

VOLCANIC

 

FIELDS

- 

s

^

1 '<

35 3

^ 

0

NajO

37

,#n 

^ - 

sluo t I 42

__ 

I I I I MOUNT TAYLOR, SAN FRANCISCO MOUNTAIN, 

HOPI BUTTES, AND MOUNT TRUMBELL FIELDS

1. Monchiquite, Hopi Buttes

2. Analcite basalt, Hopi Buttes

3. Apatite-rich monchiquite, Hopi Buttes

4. Limburgite, Hopi Buttes

5. Basaltic (?) lava, near Mt. Trumbell

6. Augite basalt, Kendrick Peak, San Francisco field

7. Basalt, near Grants, N. M., Mt. Taylor field

8. Augite basalt, Cedar Ranch Mesa, San Francisco field

9. Augite andesite basalt, Bill Williams Mtn., San Francisco field

10. Hornblende soda andesite basalt inclusion in hornblende soda dacite,

Bill Williams Mtn., San Francisco field 

U. Augite andesite, San Francisco Mtn

12. Augite andesite, Kendrick Peak, San Francisco field

13. Pyroxene-hornblende latite, San Francisco Mtn

14. Hypersthene dacite, Kendrick Peak, San Francisco field

15. Pyroxene latite, Mormon Peak, San Francisco field

16. Pyroxene dacite, Kendrick Peak, San Francisco field

17. Hornblende dacite, O'Leary Peak, San Francisco field

18. Hypersthene soda dacite, San Francisco Mtn

19. Cerro Colorado, Mt. Taylor field

20. Andesite, Mt. Taylor

21. Quartz latite, Mt. Taylor

22. Hornblende soda dacite, Bill Williams Mti m Francisco field

23. Hypersthene-hornblende soda dacite, Elden Mtn., San Francisco field

24. Biotite-hornblende dacite, San Francisco Mtn

25. Hornblende soda dacite, Mormon Mtn., San Francisco field

26. Biotite dacite, O'Leary Peak, San Francisco field

27. Mount Taylor

28. Biotite dacite, Kendrick Peak, San Francisco field

29. Riebcckite soda granite porphyry, San Francisco Mtn

30. Riebeckite soda rhyolite, San Francisco Mtn

56 58

PERCENT OF SiOi

Nos. refer to localities and rock types listed below

31. Biotite rhyolite, Sugarloaf Hill, San Francisco field

32. Biotite soda granite porphyry, Marble Hill, San Francisco field

33. Biotite soda rhyolite, San Francisco Mtn

34. Nepheline monchiquite, Wildcat Pk., Tuba field

35. Olivine leucitite, Todilto Park, Navajo field

36. Minette, Black Rock, Navajo field

37. Minette, Chaistla Butte, Navajo field

38. Minette, Shiprock, Navajo field

39. Trachy basalt, Washington Pass, Navajo field

40. Minette, dike at Shiprock, Navajo field

41. Trachy basalt. Palisades, Navajo field

42. Pale minette, Mitten Rock, Navajo field

43. Analcite diabase, San Rafael Swell

44. Analcite basalt, Craig, Colorado

45. Alkalic olivine basalt Marysvale, Utah

46. Analcite syenite, San Rafael Swell

47. Dike rock, Fortification Rocks, Craig, Colorado

48. Intrusive calcic latite, Marysvale, Utah

49. Calcic latite flow, Marysvale, Utah

50. Andesite breccia, Marysvale, Utah

51. Quartz monzonite, intrusive, Marysvale, Utah

52. Latite, Marysvale, Utah

53. Latite, Marysvale, Utah

54. Quartz latite, Marysvale, Utah

55. Rhyolite tuff, Marysvale, Utah

56. Rhyolite glass or pitchstone, Marysvale, Utah

57. Banded gray rhyolite, Marysvale, Utah

58. Granular gray rhyolite, Marysvale, Utah

59. Tuffaceous red rhyolite, Marysvale, Utah

60. La Plata Mts

61. Monzonite, Babcock Peak, La Plata Mts

62. Monzonite porphyry, Mt. Pennell stock, Henry Mts

63. Diorite porphyry, Mt. Hillers, Henry Mts

64. Monzonite porphyry, sill on Mt Pennell, Henry Mts

65. Noselite syenite porphyry, La Sal Mts

66. Porphyritic augite-diorite, Lone Cone, San Miguel Mts, Colorado.

67. Hornblende porphyrite, Ute Peak, El Late Mts

68. Diorite porphyry, Black Mesa bysmalith, Henry Mts

69. Monzonite porphyry, La Plata Mts

70. Diorite porphyry, sill, Mt Pennell, Henry Mts

71. Diorite porphyry, Deadwood Gulch, La Plata Mts

72. Diorite porphyry, Tukuhnikiwatz laccolith, La Sal Mts

73. Diorite porphyry, sill on Mt. Holmes, Henry Mts

74. Diorite porphyry, Mt Ellen stock, Henry Mts

J5. Oiorite porphyry, Mt. Pennell stock, Henry Mts

76. Diorite porphyry, Mt Ellsworth stock, Henry Mts

77. Soda syenite porphyry, La Sal Mts

78. Diorite porphyry. South Creek Laccolith, Henry Mts

79. Diorite porphyry, interior of Table Mtn. bysmalith, Henry Mts-.

80. Quartz diorite, Mt Ellen stock, Henry Mts

81. Diorite porphyry, dike on Mt Hillers, Henry Mts

82. Hornblende porphyrite, Carrizo Mts

83. Soda syenite porphyry, La Sal Mts

84. Diorite porphyry, roof of Table Mtn. bysmalith, Henry Mts.

85. Soda rhyolite dike, La Sal Mts

86. Soda rhyolite dike, La Sal Mts

87. Aegirine granite, La Sal Mts

FIGURE 27. Variation diagrams showing proportions of alkalis and silica in the igneous rocks in four parts of the Colorado Plateau..
42 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

the High Plateaus, soda and potash are about equal. 

In the Navajo volcanic fields, potash exceeds soda. In 

the volcanic fields along the southern edge of the Colorado Plateau, soda exceeds potash.

Probably the igneous rocks on the Plateau are closely 

 related genetically despite very different modes of occurrence and regional variations in composition. The 

rocks at the laccolithic mountains and large centraltype volcanoes are similar porphyries. The chemical 

average of these basalt and alkalic basalt series is less 

basic than would appear at first, because considerable 

quantities of rhyolitic ash are associated with these 

eruptive rocks. Assuming that the rhyolitic tuffs were 

derived from vents on the Plateau, it is possible that 

the original average composition of these eruptive rocks 

approximated that of the porphyries. In any case, 

there remains the question of whether the differences 

in rock types are the cause or the effect of their different modes of irruption. That both the composition 

of the rocks and their mode of irruption are dependent 

variables is suggested by a striking reversal in proportion of soda and potash at the North La Sal Mountain 

where the intrusions breached the surface and erupted. 

The aegirine-granite (no. 8Y in fig. 27) contains more 

potash than soda and became emplaced during or just 

after the eruptive stage (p. 43).

EARLY TERTIARY IGNEOUS ROCKS

Igneous activity during the early Tertiary on, or 

around, the Colorado Plateau is recorded by the tuff 

beds and other volcanic detritus in the lower Tertiary 

sedimentary formations. Practically all the lower 

Tertiary formations are tuffaceous; the Animas formation in the San Juan Basin contains a larger amount 

of coarse volcanic debris. The igneous centers on the 

Colorado Plateau are regarded as Miocene, or younger, 

and the volcanic activity recorded in the lower Tertiary 

sedimentary formations is attributed to activity in adjoining provinces. There must have been considerable 

volcanic activity during the early Tertiary in the San 

Juan Mountains, and there certainly was volcanic activity in the Basin and Range province. These areas 

probably are the sources of the volcanic materials that 

occur in the lower Tertiary formations on the Colorado 

Plateau. Some of the earliest igneous rocks in the central part of the High Plateaus may be of early Tertiary 

age, but they probably are younger.

LATE TERTIARY IGNEOUS ROCKS 

LACCOLITHIC MOUNTAINS

The laccolithic mountains on the Colorado Plateau 

include the Henry Mountains, Navajo Mountain, the

La Sal, Aba jo, El Late, and Carrizo Mountains. Tothe east, on the flank of the San Juan Mountains, are 

the La Plata, Eico, and San Miguel Mountains, all of 

which also are laccolithic. The intrusive rocks, intrusive forms, structures, and sequence of intrusive events 

are much alike at all these centers, and the mountains 

therefore are regarded as representing one intrusive 

process, involving one type of magma, intruded into 

very similar host rocks and pre-existing structures. 

The differences between the mountains represent differences in the stage reached by the intrusive process.

The least-advanced stage in the process is illustrated 

by Navajo Mountain. No igneous rocks are exposed at 

Navajo Mountain, but the similarity of this structural 

dome to the domes at the other laccolithic mountains, 

and the differences bet\veen this dome and the evident 

orogenic structures, provide almost certain evidence 

that it is due to intrusion.

The large mountain domes at the laccolithic mountains, including the dome at Navajo Mountain, are attributed to the physical injection of stocks rather than 

to arching over buried laccoliths (fig. 28). Laccoliths 

develop around the stocks where the stocks are wide and 

where the doming around the stocks is higher than at 

Navajo Mountain.

The next stage in the process is illustrated by Mount 

Holmes and Mount Ellsworth in the Henry Mountains. 

The doming there is higher than at Navajo Mountain; 

stocks are exposed at the centers of the domes, and 

around them are sills, dikes, and small laccoliths.

The next more advanced stage is illustrated by Mount 

Killers. The structural dome there has a relief of 8,000 

feet; the stock at the center is a mile or more in diameter, and radiating from it are huge tongue-shaped laccoliths (figs. 29, 30, 31).

The geologic structure at these mountains is such that 

it is possible to estimate the volume of intrusive rock in 

them, including intrusions that are not exposed at the 

surface. As the volume of instrusive rock increases, 

the deformation is increased, and changes develop in 

the type of intrusive rock. The earliest intrusions at 

each of the mountains, and the greatest in volume 

as much as 5 or 6 cubic miles is diorite porphyry. As 

the intrusive process continues, however, monzonite 

porphyry becomes intruded, as at Mount Pennell in the 

Henry Mountains and the southernmost La Sal Mountain. And this porphyry, in turn, is followed by syenite porphyries, as at the North La Sal Mountain and 

La Plata Mountains. The volume of monzonite 

porphyry is less than one-half that of the diorite 

porphyry, and the volume of syenite porphyry is less 

than one-half that of the monzonite porphyry.
CENOZOIC IGNEOUS ROCKS 43

Alter Hunt, 1954

Scole 6 miles

FicuitK 28. Diagrams illustrating the relationship between the stocks and the domes at the laccolithic mountains on the Colorado Plateau.

The chemical composition of the average rock intruded at the laccolithic mountains is estimated (in percent) as follows:

SiO,______________________________ 62.50 

Al aOs_________________________________ 17. 75 

Fe,03 ___________________.______________ 2. 50 

FeO_______________________________ 

MgO_______________________________ 

CaO___________________.__________________

NaaO. 

K2 0_. 

other.

2.00

1.50

5.00

5.00

2.50

1.25

Total______________._____________ 100. 00

The ratio of K2 0 to CaO + Na^O increases eastward.

It is smallest in the Henry Mountains; somewhat

greater in the La Sal, 351 Late, and Carrizo Mountains;

and greatest in the La Plata Mountains.

Laccoliths and bysmaliths (fig. 31) were formed during the diorite and monzonite porphyry stages, but 

there are no syenite porphyry laccoliths. Through the 

monzonite porphyry stage the mode of intrusion was 

physical injection. The magma evidently was highly 

viscous, and judging by slight alteration of coal xe.noliths, and of organic-rich shale at the contacts, the 

magma was at low temperatures (Hunt, 1953b). The 

later syenite porphyry and some nonporphyritic intrusions became emplaced in part by assimilation or replacement of the earlier rocks (tig. 32). These later 

intrusions were more fluid and apparently were at 

higher temperature than the earlier ones, perhaps because of endothermic reactions. Whatever the reason, 

they contain high-temperature quartz (Hunt and Waters, in preparation).

At the La Sal Mountains, the latest intrusions 

breached the surface and erupted explosively; in the 

eruptive rocks the potash greatly exceeds soda, whereas 

in the earlier intrusive rocks the reverse was true. It 

seems likely that most of the larger stocks in the laccolithic mountains reached the surface and erupted, although probably none of them extruded any great 

quantity of lava or pyroclastic materials. At least, 

there is no evidence of low-pressure, oxygen-rich conditions at these stocks.

Hydrothermal activity and mineralization become 

progressively more extensive and more intensive 

around the stocks representing the more advanced 

stages of the intrusive process. The alteration culminates in the mineral deposits associated with the laccolithic mountains on the flanks of the San Juan 

Mountains.

The intrusive structures at the laccolithic mountains 

seem to be younger than the orogenic structures. The 

drainage is superimposed on the orogenic structures, 

and its pattern is indifferent to them. But the drainage
44 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

MOUNT

HOLMES'

7OOO 

Structure contours

The contours are drawn on the base of the 

Perron sandstone member of Mancos shale 

Interval 200 feet

The Perron sandstone member was selected 

as the datum to show .the structure across 

the tops of the laccoliths

MOUNT 

ELLSWORTH

FIGUUE 29. Structure-contour map of the Henry Mountains.
CENOZOIC IGNEOUS ROCKS 45

After Hunt, 1946

FJGUKB 30. Ground plan o:f intrusions around the Mount Ellen stock 

in the Henry Mountains, illustrating radial distribution of the 

laccoliths.

Side toward 

stock

Distal side

After Hunt, 1946

FIGUKK 31. Diagrams illustrating shapes of laccoliths and bysmaliths 

on the Colorado Plateau. iThe laccoliths (A) are tongue-shaped and 

arc bulged linearly and radially from the stocks. The distal ends 

are blunt; the sides are tapering. In general, the strata rise toward 

the stocks, and the laccoliths cut discordantly to younger beds away 

from the stocks. The laccoliths commonly are 1 or 2 miles long, % 

to 1 mile wide, and at least 1,000 feet thick along the axial bulge. 

The bysmaliths (B) have their roofs faulted on the sides away from 

the stocks. In other respects they resemble the laccoliths.

mostly is consequent, and strikingly so, around the laccolithic mountains, as if it had been monoclinally 

shifted during the doming. Thus, the Dirty Devil 

River swings in a wide arc around the Henry Mountains, as does the Dolores around the La Sals. The 

San Juan River follows the syncline between the El 

Late and Carrizo Mountains. Possibly, the headward 

part of the Dolores River once flowed southwestward 

to join the San Juan River and then was diverted northward by the intrusions at the La Plata and Ute Mountains. On the other hand, the dome at the Rico Mountains is breached by the Dolores River, which seems to 

be superimposed on the structure.

After Eckel, 1949

FIGURE 32. Schematic section through a nonporphyritic stock in the 

 La Plata Mountains. Existing structures are not disturbed, and 

stock narrows where it passes through a thick bed of sandstone. The 

.bulging part of the stock is 1 mile wide.

Doming at the Rico Mountains is younger than the 

San Juan peneplain, which is either late Miocene or 

Pliocene age (Atwood and Mather, 1932, p. 66-67). It 

is believed that most of the laccolithic mountains are 

of late Miocene or early Pliocene age. In any case, they 

antedate the canyons. Gravels derived from the Henry 

Mountains intrusions occur on the rims of the canyons 

of the Dirty Devil and Colorado Rivers. Gravels derived from intrusions in the La Sal Mountains occur on 

the rims of the canyons in that part of the Plateau.

The locations of the intrusions seem to be completely 

independent of the regional structures on the Colorado 

Plateau (p. 63), but most of the mountains are located 

in a vaguely defined belt extending from the San Juan 

Mountains to the volcanic field in the central part of 

the High Plateaus. Moreover, the belt coincides with 

the north edge of the structural platform that breaks 

off northward into the Uinta Basin (fig. 37).
46 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

CaO _. .

Na2 0

K2O _ _ .

Other

1.20

5.40

4.40

LARGE CENTRAL-TYPE VOLCANOES

The Mount Taylor volcano erupted subsequent to the 

major movements of folding and faulting in that district, probably in late Miocene time. The volcano broke 

out in a syncline. The eruption, which occurred in a 

fairly well denned compositional sequence, began with 

rhyolitic tuff. This was followed by relatively quiet 

eruptions of porphyritic lavas in which two and possibly three series are distinguishable on the basis of 

their content of potash feldspar. The oldest of these 

is porphyritic trachyte, but the volume is very small. 

The next eruption was a large volume of porphyritic 

latite, interrupted, however, by at least one more flow of 

porphyritic trachyte. The latite, in turn, was followed 

by a slightly smaller volume of po.rphyritic andesite. 

(Hunt, 1936, p. 63-64.)

The total volume of the tuffs and lavas is about 12.5 

cubic miles, of which about 5 cubic miles is rhyolitic 

tuff, 4 cubic miles is latite, and 3.6 cubic miles is porphyritic andesite. (Hunt, 1938, p. 64.) Following is an 

estimate of the average composition (in percent) of 

these eruptives:

SiO__________ 66.50 

AUG. ___________ 17. 40 

Fe,O?,___________ 2.60 

FeO___________ 1.50 

MgO___________ .45

Total________ 100. 00

The rhyolite and trachyte and most of the latite seem 

to have been erupted from the central crater, but most 

of the porphyritic andesite and perhaps the latest latite 

were erupted by dikes intruded radially around the 

main pipe. ' (Hunt, 1938, p. 64.) Part of the rhyolite 

may have been erupted from other centers (Callaghan, 

oral communication).

The volcano is a cone 3,000 feet high whose base is 

more than 10 miles in diameter. It is on a pedestal 

of sedimentary rocks about 2,000 feet higher than the 

general level of the surrounding country (fig. 33) ; 

erosion has lowered the surrounding country by this 

amount since the volcano was active. The original volcano probably was about 1,000 feet higher than the 

present cone. The original crater probably had a diameter of somewhat less than a mile, but it has been 

greatly enlarged by erosion. (Hunt, 1938, p. 58.)

Except for some local flows of basaltic lava, the earliest eruptions in the district were from Mount Taylor. 

The erosion surfaces that subsequently were developed 

around the base of the cone later became flooded with 

sheets of nonporphyritic basaltic and andesitic lavas 

erupted from the scores of vents that comprise the volcanic field. A few of the sheets were erupted prior to 

the latest eruptions on Mount Taylor, but most of them
CENOZOIC IGNEOUS ROCKS 47

were erupted after Mount Taylor had become quiescent 

and they overlap the outer edges of the Mount Taylor 

cone. (Hunt, 1938, p. 58.)

San Francisco Mountain is much larger than Mount 

Taylor. At the close of its activity its summit stood 

8,800 feet above the surface of the surrounding country, 

the base had a diameter exceeding 10 miles, and the cone 

had a volume of almost 40 cubic miles. Whereas the 

Mount Taylor volcano lies in a structural basin, San 

Francisco Mountain is on a broad dome. Five stages 

of activity are recognized. The earliest eruptions, aggregating 21 cubic miles of material, consisted of latitic 

lava, tuft', and breccia. This was followed by 13 cubic 

miles of pyroxene dacite lava. This was followed, in 

succession, by eruption of lavas that formed 0.5 cubic 

mile of hornblende dacite, 0.5 cubic mile of rhyolite, 

and 3.0 cubic miles of andesite (Robinson, 1913, p. 52). 

The Mount Taylor volcano stands on a pedestal, and 

the surrounding country lias been lowered considerably 

since the volcano formed; however, the general level of 

the country around the San Francisco volcano has been 

lowered no more than a few hundreds of feet since that 

volcano was active. The difference probably is not one 

of age. The Permian formations, on which the San

Francisco volcano was built, are more resistant to erosion than the Upper Cretaceous formations that underlie Mount Taylor. Also, basaltic rocks are more extensive around the base of San Francisco Mountain than 

around the base of Mount Taylor.

The eruptions at San Francisco Mountain were preceded by eruption of about 30 cubic miles of sheet basalt, 

and were followed by sheet flows of basaltic lavas and 

pyroclastic materials covering 1,200 square miles aggregating 20 cubic miles and erupted from about 200 

vents (Robinson, 1913, p. 52, 87). See figure 34.

There are several other large, central-type volcanoes 

clustered near San Francisco Mountain and belonging 

to the same general period of activity (fig. 35). Kendrick Peak, 11 miles northwest of San Francisco Mountain, built a cone 4,800 feet high covering 40 to 50 square 

miles, and aggregating more than 6 cubic miles. It 

began by erupting 5 cubic miles of rhyolite, followed 

in succession by lesser amounts of pyroxene dacite, hypersthene dacite, and andesite. Bill Williams Mountain, 33 miles south of west San Francisco Mountain, 

erupted 3 cubic miles of lavas. The earliest eruptions 

were andesitic; these were followed by a much larger 

volume of dacite. O'Leary Peak, 9 miles northeast of

EXPLANATION

Basalt of third period 

(inside dashed line)

Cones and lavas of second period

Sitgreave

. Pk»*. . ,

 ^'Basalt cones of first and third 

periods of eruption

/Basaltic cones and

^recent lavas not\\^SSSSSS:

After Robinson, 1913

FIGUKE 34. Map of San Francisco volcanic field, showing distribution of cones.
48 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

' ... Sugorloaf Hill O'Leary Pk

= IL;====I; jr;;:|r=-^sfefe^n^p^;;j ^ L^^

After Robinson, 1913

1, Alluvium (Quaternary); 2. Pennsylvania!! formations (undivided); 3, Mississippian (including some Pennsylvanian); 

4, pre-Mississippian (undivided); 5, basalt (third general period of eruption); 6, andesite (second general period of 

eruption; 7, rhyolite, (second general period of eruption); 8, hornblende dacite (second general period of eruption"); 

9, pyroxene dacite (second general period of eruption); 10, latitedacite (secondgeneral period of eruption); 11, dacite 

of Elden Mountain (intrusive portion); 12, granite porphyry of Marble Hill; 13, basalt (first general period of eruption)

FIGURE 35. Geologic cross sections of San Francisco Mountain and vicinity.

San Francisco Mountain, is a double cone built of lavas 

during two separate stages of activity. These lavas 

aggregate 2 cubic miles and are about equally divided 

between an earlier rhyolite and later dacite. Sitgreaves Peak and Sugar loaf Hill (fig. 35) erupted 

rhyolite; Mormon Mountain erupted latite and dacite 

(Robinson, 1913, p. 58, 63, 65, 66-70).

The calculated chemical composition (in percent) of 

the average lava from these central-type volcanoes in 

the San Francisco district (Robinson, 1913, p. 159), is 

as follows:

SiO2 . 

A1 2O3

FeO_. 

MgO. 

CaO_. 

Na»O. 

K3O_.

63.8

16.3

2.6

2.8

1.5

3.3

4.7

3.2

BaO

0.4 

.3 

.8 

.3 

.1

Total________ 100.2

The overall proportion of rock types is rhyolite, 38.5 

percent; andesite, 43.5 percent; trachyte, 18.0 percent. 

(Robinson, 1913, p. 160.)

The average lava from the large cones in the San 

Francisco district and from Mount Taylor contains 

less CaO and more K2O than does the average rock in 

the laccolithic mountains.

In the laccolithic mountains the differentiation sequence progressed from basic to acid, but at the large 

central-type volcanoes the sequence generally was reversed and progressed from acid to basic.

VOLCANIC ROCKS ANI> INTRUSIONS IN THE CENTRAL 

PART OF THE HIGH PLATEAUS

The igneous rocks in the central part of the High 

Plateaus are dominantly latite or rhyolite but range 

from basalt to rhyolite. Volcanic breccias and tuffs 

make up the greater volume of material. Four stages 

of igneous activity are distinguished. The earliest is 

volcanic and formed a group of latitic breccias, tuffs,, 

and flows, at least 5,000 feet thick. The second stage 

produced intrusive quartz monzonite, in stocks. After 

deformation and erosion, additional vulcanism occurred, 

the resulting rocks consisting of rhyolite, quartz latite,. 

latite, and tuff, at least 7,000 feet thick. These volcanic 

rocks are overlain by the Sevier River formation of 

late Pliocene or early Pleistocene age. The fourth stage 

of igneous activity formed scattered thin basalt flows,, 

most of which are associated with the Sevier River 

formation (Callaghan, 1938, 1939).

The table below gives the estimated average composition (in percent) of each of the igneous series in thecentral High Plateaus (after Callaghan, 1939, p. 443).
CENOZOIC IGNEOUS ROCKS 49

Si02~ --- - -

A\a 03 -. --------

Fe2 03 -------

FeO

MgO--_-------

CaO... ______ _.

NajO.-_-------

KjO --------

Other.. __.._.._

Total.. __

1

(Early)

57. 00

13. 75

5. 20

2. 50

3. 55

5. 70

3. 70

2. 75

5. 85

100. 00

2

(Intrusive 

quartz 

monzonite)

59. 40

16. 50

3. 40

1. 75

2. 40

3. 90

4. 00

4. 50

4. .15

100. 00

3

(Volcanics)

71. 00

13. 00

1. 60

. 20

. 40

1. 40

3. 50

4. 20

4. 70

100. 00

4

(Late 

basalt)

48. 65

10. 40

7. 45

6.05

5. 55

8. 10

2. 77

3. 40

7. 63

100. 00

All these are saturated with respect to silica, and they 

tend to be alkalic. Throughout the group the alkalis 

are essentially equal and lime content is low. It has 

been inferred that these rocks, despite the considerable 

range in their ages, are differentiates of a monzonitic 

magma, rather than a representative of the basaltic 

substratum. They differ from average basalt in their 

high content of potash and low content of alumina. 

These rocks are much less sodic than those in the laccolithic mountains. (Callaghan, 1938, p. 450-451.)

BASALT AND ALKALIC BASALT SERIES

The upper Tertiary basalt and alkalic basalt series 

of eruptive rocks on the Colorado Plateau include the 

extensive flows in the Mount Taylor district and in the 

Datil section, the equally extensive flows in and south 

of the San Francisco district, the eruptives at the Hopi 

Buttes and, in the Navajo field, the flows on the High 

Plateaus and western part of the Grand Canyon section, 

the .intrusions in the San Rafael Swell, and the eruptives at Grand and Battlement Mesas, Colo.

In the Mount Taylor district some of the sheet lavas 

preceded the last flows from Mount Taylor, but most 

of tliem were poured out after Mount Taylor had be- 

.come quiescent. Most of the lavas were erupted from 

central vents, although a few came from fissures. The 

sheets spread on erosion surfaces developed on Cretaceous formations around the base of the Mount Taylor 

cone; by the time these eruptions occurred, the Tertiary 

formations and uppermost Upper Cretaceous formations had already been eroded back to a position north 

of Mount Taylor. Erosion has lowered the general 

land surface 1,500 to 2,000 feet since these eruptions 

occurred (fig. 33). (Hunt, 1936, p. 64.)

Where erosion has removed the lava cap and lowered 

the country rock the vents are marked by picturesque 

necks columns of lava and breccia that solidified in 

the pipes without reaching the surface. Some of these 

are 1,800 feet high. There are all gradations from the

lava cones, completely surrounded by lava sheets, 

through cones with the lava removed on one side, thus 

exposing a natural cross section of the cone and pipe in 

its center, ' to necks from which the surrounding: Olava

sheets have been completely removed. There are scores 

of these eruptive centers, but their distribution seems to 

be independent of the preexisting structures. (Hunt, 

1938, p. 64.)

These basaltic lavas contain very few phenocrysts, 

mostly olivine. The feldspar is either calcic andesine 

or sodic labradorite. The ground-mass commonly is 

glassy. (Hunt, 1938, p. 64.)

Widespread and similar eruptive deposits cover the 

southern edge of the Colorado Plateau in west-central 

jSTew Mexico and extend westward into east-central 

Arizona. They overlap and conceal the boundary between the Colorado Plateau and the Basin and Range 

province. No satisfactory way of distinguishing between the Tertiary and Quaternary lavas in this area 

has been found.

In the San Francisco district and to the south are extensive basaltic lava flows that antedate the San Francisco volcano. The lava occurs predominantly as flows; 

fragmental material is largely restricted to the cinder 

cones. The scattered lava and cinder cones, in general, 

do not exceed 700 feet in height, although a feAv are 

more than 1,000 feet high. It is estimated that the 

eruptions were supplied by at least 100 vents distributed 

in an area covering 3,000 square miles. (Robinson, 

1913, p. 39.)

The flows commonly are 25 to 75 feet thick, and none 

exceeds 200 feet. Their thinness is impressive considering the large area they cover. Few of the flows have 

scoriaceous surfaces; most of them are dense and 

jointed in columns. Presumably, the lava had a high 

degree of fluidity to enable it to spread so widely and so 

thinly. (Robinson, 1913, p. 39.)

The basalt contains about 10 percent of olivine phenocrysts in an aphanitic groundmass. A partial analysis 

(in percent) is as folloAvs (Robinson, 1913, p. 39) :

Si02 _ _ __ .

A12O3 _

Fe O

FeO

MgO

CaO __

47 7

_ 15. 3

5.9

4. S

7.3

11. 8

Na.,O __________ 2.5

K2 6 __________ 0.6

CO2 ___________ 1. 9

TICK ____________ 1.4

Total________ 99. 2 

Other basaltic eruptions occurred subsequent to the 

eruptions at San Francisco Mountain. These were 

provided by about 200 basalt cones; about 20 cubic miles 

of lava spread over an area of 1,200 square miles. The 

lava, a normal basalt, is almost identical in chemical 

composition with the basalts of pre-San Francisco 

Mountain age. It has a very fine texture, and pheno-
50 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

crysts are rare. Most of it occurs as flows, but cinder 

deposits are common locally. As compared with the 

basalt of the earlier period, these lavas tend to form 

thicker and rougher flows of smaller extent, thus indicating greater viscosity. (Robinson, 1913, p. 87.)

These basalts overlie an erosion surface of very low 

relief, cut on Permian and Triassic formations. The 

Jurassic and Cretaceous formations had been stripped 

from this area, and their outcrop belts had retreated 

northeastward into Black Mesa basin, by the time these 

eruptions occurred. Also, the fact that many of the 

flows spread toward the Little Colorado River indicate 

that its valley was in existence at that time.

The Navajo-Hopi volcanic districts comprise scores 

of necks, dikes, and lava-capped mesas (fig. 36). The 

largest cluster are the Hopi Buttes. The surface on 

which the eruptions occurred-was one of IOAV relief, but 

it was several hundred and perhaps more than a thousand feet higher than the present surface. The typical 

Hopi vent was opened by the explosive drilling of a 

cylindrical pipe, and doubtless a pyroclastic cone or 

maarlike depression was formed about the orifice. Subsequently, upwelling lava filled the crater and finally

spilled over the rim in broad floods. (Williams, 1936, 

pp. 117-118).

Explosive ejecta from the Hopi vents probably exceed the lava flows in volume. Typically, the ejecta. 

consist of angular and subangular chips of black limburgite and monchiquite in a sedimentary matrix. True 

bombs and scoriaceous lapilli blown out in a viscous 

state are uncommon. Great volumes of pulverized 

sandstone and shale were erupted Avith the fragments 

of lava, but debris of plutonic rocks, so common among 

the tuffs of the Navajo volcanoes to the north, is very 

rare. (Williams, 1936, p. 119.)

The igneous rocks in the Hopi Buttes area are studded 

with phenocrysts of augite, and many carry recognizable crystals of olivine. Few of these rocks contain 

biotite and still fewer contain hornblende. Feldspar 

is generally absent; where present, it is in the form of 

microlithic sanidine. Normal plagioclase basalt occurs 

only along the southern margin of the area, in the direction of the basalt fields along the southern edge of 

the Colorado Plateau. The scarcity of feldspar among 

the Hopi Buttes rocks sets them apart from those of 

the Navajo field to the north, in which orthoclase and

After Williams, 1936

FIGURE 36. Maps of some volcanic necks in the Navajo-Hopi fields. (1) Buell Park. Arcuate dike of leucite minette ; other dikes of minette ; 

lava cap on Sterrett Mesa ends southward in a depression among pyroclastic rocks ; tuff-breccias, stippled. (2) Tuff-breccia neck, 5 miles 

north of Flying Butte, Hopi country. Rises through horizontal shales of the Chinle formation. Bordered by thin dikes of monchiquite. 

Diagrammatic only. (3) Shiprock. Neck of minette tuff-breccia and dikes of minette. ,(4) Boundary Butte. .Similar neck bordered by arcuate, vertical dikes. (5) Wildcat Peak. Tuff-breccias neck associated with dikes of alnoite, monchiquite, and related rocks.
CENOZOIC IGNEOUS ROCKS 51

sanidine are almost ubiquitous. Of the colorless constituents in the Hopi ]avas, analcite, a mineral rare in 

the rocks of the Navajo field, is by far the chief constituent. Leucite, sporadically present in the Navajo 

field, is not known in the Hopi Buttes area. The typical lavas in the Hopi Buttes area are superficial equivalents of monchiquite; the lavas of the Navajo area are 

equivalents of minette. Petrographically, the rocks 

can be classified as most!}7 limburgite, analcite basalt, 

and monchiquite; some olivine-augite basalt can be 

found toward the south. Chemically, the rocks are 

very much alike. An average of three analyses (in percent) is given in the following table (Williams, 1936, 

p. 124-128, 166).

SiO,___________ 39.80 

AUOa___________ 12.00

FCaOa________________ 4. 30

FeO____________ S. 70 

MgO ___________ 10. 23

CaO____________ 11.21 

Na,O___________ 3.96 

K2O____________ 1.19 

TiQ.____________ 4. 01

Iii these rocks, there is less silica, and more soda and 

potash, than in the basalt in the San Francisco district.

Several clusters of volcanic centers north and east 

of the Hopi Buttes are described together as the Navajo 

volcanic fields. In contrast to the Hopi Buttes, they 

are at once distinguished by the paucity of lava flows. 

Most of the Navajo volcanic necks are composed of 

coarse tuff breccia, or agglomerate (not of columnar 

lava) and are crowded with fragments of plutonic 

rocks chiefly of a granitic type. Also, whereas monchiquitic rocks are typical of the Hopi Buttes, in the 

Navajo fields these rocks are far subordinate to minette. 

And Avhereas the vents in the Hopi Buttes area have a 

northwest-southeast alignment (Hack, 1942, p. 67), 

those in the Navajo field are similar to those in the 

Mount T ay lor district and seem to be scattered without 

regard to pre-existing structures. None is located along 

a fault. (Williams, 19'36, p. 130-131.)

The average of eight analyses (in percent) of rocks 

from the Navajo volcanic field is given in the following 

table (Williams, 1936, p. 166) :

SiO2 ____________ 51.88 MgO

AlsOa,___________ 11,45 CaO_

FeaO;!___________ 3. 00 3ST a2O

FeO____________ 3.56 K,O_

8.76

8.45

2.26

5.41

The rocks of the Navajo volcanic field are potassic, 

whereas those in the Hopi Buttes area to the southwest, 

and in the laccolithic mountains to the north, are sodic. 

On the other hand, the diorite porphyry of the Carrizo 

Mountains, located in the midst of the Navajo volcanic 

field, is chemically like the diorite porphyry of the other 

laccolithic mountains to the north and is unlike the 

rocks in the Navajo field.

The rocks involved in the explosive eruptions that 

terminated the igneous activity at the North La Sal 

Mountain had an unusually large potash content. A 

similar relationship is found in the volcanic fields. The 

potash-rich Navajo volcanic field produced fewer lava 

flows and more explosive eruptions than did the sodarich volcanic fields. We can only conjecture as to 

whether the presence of more potash led to greater 

explosive activity, or Avhether the greater explosive activity resulted in the liberation of more potash and soda.

In the northern part of the Colorado Plateau there 

are other alkalic basalts similar to those in the NavajoHopi region. These lie north of the laccolithic mountains. In the San Eafael Swell are dikes and sills of 

analcite diabase and analcite syenite. An average (in 

percent) of two analyses, one of each type, is as follows 

(Gillury,1927,p.205) :

SiO, ____ _______ 46. 65

Al 2 0n ____ . ____ : __ 15. 75 

Fe,O:< __ __. _______ 3.58 

FeO ____ _______ 4.36

MgO 

CaO

6. SO 

8. 95 

3.78 

3.46

Similar sodic-potassic rocks are associated with the 

Browns Park formation just northeast of the Colorado 

Plateau in the vicinity of Craig, Colorado. In this 

part of Colorado there are normal basalts also (Ross, 

1926) .

In the High Plateaus are numerous lavas and volcanic 

cones ; these are of several different ages, probably many 

of late Tertiary, but some of Quaternary age. The 

older lavas and volcanic cones antedate the faulting; 

some of them overlie the Wasatch formation with angular unconformity. (Gregory, 1950, pi. 2).

The lava flows along the Hurricane fault in southwestern. Utah (fig. 47) are part of a volcanic field that 

extends westward into the Basin and Range province. 

Some of the lavas that were erupted from centers west 

of the Hurricane fault became displaced by the Hurricane fault, and they now cap the cliffs formed by the 

upthrown block. However, the displacement of these 

lavas is not so great as the displacement of the underlying rocks; therefore it is clear that there was prevolcanic, as well as postvolcanic, mo\7 ement on the Hurricane fault. In general, the eruption of lavas in the 

southern part of the High Plateaus was contemporaneous with the horst and graben faulting that developed those plateaus. So far as known, all these lavas 

in the southern High Plateaus are normal basalt consisting of labradorite, olivine, augite, and magnetite. 

Many of the flows are less than 50 feet thick. Cinders, 

lapilli, and other pyroclastic deposits occur at some of 

the cones, but the quantity of these is small compared to 

similar deposits in the Navajo Or Hopi Buttes fields
52

 112

Structure contours on top of 

Kaibab limestone. Contou 

interval is 1000 feet

Outline of Colorado Plates

0 100 Miles

* i i . i i i i i i . _ _ _i Compiled by James Gilluly and Charles B. Hunt. Mostly afte 

Baker, 1935; Dsrton. 1925; Sears, Hunt, and"Dane, 1936

34

FIGURE 37. Structure-contour map of the Colorado Plateau.
STRUCTURAL GEOLOGY 53

where the rocks are alkali c. (Gregory, 1950, p. 133- 

140.)

Farther north in the High Plateaus (in central Utah) 

the lavas are largely latite and rhyolite, and these are 

older than the basaltic lavas (see p. 49); an analysis 

of one of these basaltic lavas in the central High Plateaus is given on page 49.

QUATERNARY IGNEOUS ROCKS

The igneous rocks of Quaternary age are of interest 

in this report chiefly because of their recency. So far 

as known all of them are normal basalt. These rocks 

occur as flows along the bottoms of present-day valleys; 

some of them are so fresh that they appear to have been 

erupted in historic time. Among them are the flows 

along the San Jose River south of Mount Taylor, 

N. Mex. Others are south of the Zuni Mountains. 

Similar flows in Arizona occur near the Mogollon Rim, 

in the San Francisco Mountain district, in Grand Canyon, and at Peach Springs. There is a fresh-looking 

flow on the bottom of a canyon Johnson Canyon east 

of Ivanab, Utah. Quaternary basaltic lavas just north 

of the Colorado Plateau include some that are associated with the Lake Bonneville deposits in western 

Utah, and one that is in the valley of the Eagle River 

near its junction with the Colorado River at Dotsero, 

Colo. No doubt many of the lava flows along the southern rim of the Colorado Plateau in New Mexico and 

Arizona are of Pleistocene or Recent age.

One of the most recent eruptions occurred at Sunset 

Crater (fig. 1, 34) in the San Francisco field, Arizona. 

This eruption, dated 1160 A. D., buried a Pueblo II occupation layer under 6 feet of cinders. (McGregor, 

1936; Colton, 1945). The flow at McCartys, south of 

Mount Taylor, may be less than 1,200 years old 

(Nichols, 1946, p. 1049-1086).

Many of the lava flows in the southern part of the 

High Plateaus are of Quaternary age; some of the 

lavas, and perhaps most of the cones, are of very late 

Pleistocene age and may be Recent. At several places,

thin narrow flows follow the stream beds. Many of the 

flows have been faulted. (Gregory, 1950, p. 133-140).

STRUCTURAL GEOLOGY

GENERAL FEATURES

The Colorado Plateau is part of the geanticline that 

extends from Kansas to California, including the 

High Plains, Rocky Mountains, and Basin and Range 

province. The Basin and Range province can be interpreted as a collapsed segment of the geanticline, and 

this collapsed segment ends along fractures at the edges 

of the Colorado Plateau. Except along the Rio Grande 

depression, which is part of the collapsed area, the 

Colorado Plateau has remained "fastened" to the Rocky 

Mountains.

The principal structural elements of the Plateau are 

of five kinds (fig. 37). The first, and most extensive, 

are the broad basins represented by the Uinta, San 

Juan, and Navajo Basins. Together, they comprise a 

quarter of the Plateaus. They trend toAvard the west 

or north west. The Uinta Basin is the lowest, and the 

Navajo Basin (shown as Black Mesa in fig. 37) is the 

highest.

Between these large basins are clusters of upwarps 

(the second kind of feature) including the San Rafael 

Swell, Circle Cliffs, Kaibab, Monument, Defiance (fig. 

21), and Zuni upwarps (fig. 38), and between these upwarps are basins such as the Henry Mountains and 

Gallup-Zuni Basins (fig. 39). These are asymmetrical 

folds, some trend northward, others trend northwestward. All of the upwarps, except that at the Zuni 

Mountains, have their steep flanks facing eastward.

The third kind of structural feature is represented 

by the nortliAvestward-trending anticlines and faults in 

east-central Utah, in the area underlain by thick salt 

deposits (fig. 40).

The fourth kind is represented by the northwardtrending fault blocks of the High Plateaus. These 

features represent a zone transitional between the Colorado Plateau and Basin and Range province (fig. 41).

wsw. E.NE.

Recent £ 

lava, O

HORIZONTAL SCALE:

0 5

5,000

VERTICAL SCALE 

0 5,000 10,000 FEET

Old lava

After Darton, 1922

^Tqclilto limestone 

-Wingate sandstone 

nle formation 

nkoPi formation 

o and San Andre's 

formations

FIGURE 38. Section across the Zuni Mountain upwarp, N. Mex.
54 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

Horizontal scale Atter Darton. 1922

K, Cretaceous formations; Kmv, Mesaverde group; Kms, Mancos shale; Kd, Dakota sandstone; 

, Jn, Navajo sandstone; "Rw, Wingate sandstone; "fie, Chinle formation; "fis, Shinarump 

conglomerate; "Rm, Moenkopi formation; PAL, Upper Paleozoic rocks

FIGURE 39. Sections across the Gallup-Zuni Basin, N. Mex. (A) near Zuni; (B) near Atarque.

And fifth, and last, there are the domes and other folds 

related to the intrusions at the laccolithic mountains, 

most of which are in the central part of the Colorado 

Plateau (figs. 29, 30).

Although these five structural elements of the Colorado Plateau are the product of Cenozoic deformation, 

they were in large part controlled by pre-Cenozoic 

structures.

PRE-CENOZOIC STRUCTURAL ELEMENTS

The pre-Cenozoic structural elements of the Colorado 

Plateau mostly have northwesterly trends, and these 

elements undoubtedly controlled the direction, and 

probably the location of those Cenozoic elements that 

trend northwestward. Development of these northwest-trending features started at least as early as Paleozoic time, and they may date from the pre-Cambrian. 

They persisted through the Mesozoic and guided the 

depositional basins and facies changes in the Mesozoic 

formations.

The best known of these features is that of the Uncompahgre Plateau and the basin to the southwest, 

known as the Paradox Basin. The Uncompahgre 

Plateau, part of a larger ancient highland area that 

extends southeastward into the Southern Eocky Mountains, was anticlinally raised in late Mississippi an or 

early Pennsylvania]! time. The lithology, thickness, 

and distribution of the Pennsylvania!!, Permian, and 

Triassic sedimentary rocks adjacent to this highland 

show that the uplift began at least as early as early 

Pennsylvania!! time and continued through Permian 

and into Triassic time. Paralleling this uplift, on the 

southwestern side, was a trough in which the salt-bearing sediments of the Pennsylvania!! Paradox member 

of the Hermosa formation accumulated (Baker, 1935, 

p. 1495).

In the Zuni Mountains (fig. 38) and Defiance upwarp 

(fig. 9), Permian redbeds rest on pre-Cambrian crystalline rocks, thus suggesting that these areas also Avere 

uplifted in Pennsylvania!! time. These uplifts probably are part of a northwestward-trending arch that 

marked the northeast limit of the early Paleozoic formations in the southern and southwestern parts of the 

Colorado Plateau.

The present Grand Canyon seems to be near the crest 

of a broad arch created during Pennsylvania!! time, 

because Pennsylvania!! formations thin out by overlap 

on its northeast flank (Baker, 1935, p. 1495).

Three Mesozoic features have been recognized on the 

Colorado Plateau and probably there are others. One 

of these is the early Triassic uplift at the Uncompahgre Plateau. Another is represented by the unconformity that is reported to be between the Carmel formation and Navajo sandstone along the eastern side 

of the Defiance upwarp (p. 15). The third known 

Mesozoic feature is along the south rim of the Plateau 

and is recorded by the overlap of the Upper Cretaceous 

formations onto Jurassic, Triassic, and Permian formations southwestward from Zuni to the Mogollon Rim 

south of Holbrook, Arizona (fig. 11). This overlap 

indicates northeastward tilting of the southwestern 

part of the Colorado Plateau prior to Late Cretaceous 

time. Perhaps the northeast change in facies of the 

Upper Cretaceous formations in the San Juan Basin 

(Sears, Hunt, and Hendricks, 1941) also is a result of 

this tilting; the strandline marking the edge of the
STRUCTURAL GEOLOGY 55

T^== Outcrop of Paradox member 

of Hermosa formation

After Dane, 1935

40. Generalized map ol: part of eastern Utah and western Colorado, showing relation of principal faults to outcrops of the Paradox 

formation, the La Sal Mountains, and the southwest flank of the Uncompahgre Plateau.

Lute Cretaceous geosyncline in that part of the Plateaus 

trended northwestward and parallel to the strike of the 

pre-Cretaceous tilting.

Reconstruction of pre-Cenozoic structural features 

along the western edge of the Colorado Plateau is difficult. There Avere deep geosynclinal troughs AN7 est of the 

Plateau during Paleozoic time, but there Avere none 

Avithin the area of the Plateau. The AA^estern edge of 

the late Cretaceous geosyncline in Utah AAras approximately at the position of the present Avestern edge of 

the Plateau.

In genera], the Colorado Plateau constituted a shelf 

area during Paleozoic and Mesozoic time, and the differences betA\7 een it and the Basin and Range province 

therefore, in large part, are inherited. On the other

hand, the Paleozoic and Mesozoic structures of the Plateaus resemble those in adjoining parts of the Wyoming 

Basin and Southern Rocky Mountain provinces, and the 

differences between, the Plateau and those provinces to 

the north and east seem to have originated in large part 

during the Cenozoic.

At various times during late Paleozoic and Mesozoic 

time in the Paradox Basin, southwest of the Uncompahgre Plateau, there Avas movement of salt and deformation of the overlying strata (Prommel and Crum, 

1927; Harrison, 1927). But these pre-Cenozoic disturbances seem to be less significant than the Cenozoic 

deformation (Baker, 1933, p. 74-76).

At the end of Cretaceous time the Colorado Plateau 

Avas a piedmont area extending east\vard and northeast-
56 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

.f

ward from the foot of mountains that had been built 

by thrust faulting and folding in the adjoining parts 

of the Basin and Range province (fig. 42). When the

A. Early Colorado time

C Late Montana time (Castlegate)

D. Early Lance t,rr,8 (North Horn) Afte[ Spieker, , 946

FIGURE 42. Block diagrams showing that part of Utah north of latitude 

39°30' at four stages in Late Cretaceous time.

Uinta Mountains and Rocky Mountains were raised, beginning in early Paleocene time, the area of the Plateau 

became a structural basin ringed by mountains on at
57

least three sides (fig. 54). It may have been a trough 

open to the south or southeast.

CENOZOIC OROGENTC STRUCTURES 

EARLY TERTIARY STRUCTURES

Early Cenozoic deformation, recorded by an angular 

unconformity at the base of the Wasatch or older Tertiary formations, is known at four places in the Colorado Plateau. These are: the south flank of the San 

Juan Mountains, west flank of the Circle Cliffs upwarp, 

northeast flank of the upwarp at the head of the Fremont River, and Avest side of the Wasatch Plateau. 

The beds above the unconformity at the Circle Cliffs 

upwarp probably are of early Eocene or late Paleocene 

age. At the north rim of the San Juan Basin and at 

the west side of the Wasatch Plateau there is reasonable 

certainty about the age of the beds above the unconformity. It .also is certain that uplift of the Uinta 

Mountains began during, if not prior to, Wasatch time 

because, although the unconformity is concealed by 

overlap of younger formations, the facies changes in 

the Green River and other formations in the Uinta 

Basin show that the Uinta Mountains were in existence 

and were a major source of the sediments in those Terti ary formations.

Probably the Circle Cliffs, Defiance, and Zuni upwarps date from the same period because they lie along 

the same pre-Cenozoic arch.

The unconformable overlap of the Animas formation 

onto the McDermott and older formations on the north 

flank of the San Juan Basin indicates uplift of that 

flank in Late Cretaceous or earliest Tertiary time. The 

andesitic debris in the McDermott and Animas formations indicates that the uplift was accompanied by vulcanism in the San Juan Mountains. Post-Wasatch 

uplift of the San Juan Mountains is indicated by the 

southward dip of the Wasatch formation into the San 

Juan Basin.

On the western side of the Wasatch Plateau, the Flagstaff limestone rests with angular unconformity on 

folded older rocks. The limestone is younger than the 

Animas, and therefore this deformation recorded on 

the western side of the Wasatch Plateau could be 

younger than that recorded on the southern flank of 

the San Juan Mountains. However, there was earlier 

folding during Cretaceous time to the west of the 

Wasatch Plateau (fig. 42).

The lacustrine Flagstaff limestone and Green River 

formation record down warping, first along the northwestern edge of the Colorado Plateau and slightly later 

in the Uinta Basin area. This downwarping is regarded as a part of the epeirogenic episode and is discussed more fully on page 63.

Although the Uinta Mountains began rising long before Green River time, there was post-Green River 

upwarp also, as recorded by the overlap of the Uinta 

formation onto the Mesozoic formations that are turned 

up along the southern side of the mountains. There is 

some uncertainty about the position of this unconformity, but it is inferred to be at the base of the Bridger; 

there is an angular unconformity at the base of the 

Bridger on the northern side of the Uinta Mountains 

(Sears and Bradley, 1924, p. 96). Later upwarp of 

the Uinta Mountains is recorded by the folding of the 

Duchesne River formation; this post-Duchesne River 

upwarp may have occurred during Oligocene time.

The northward dip of the Bridger and younger fluviatile Eocene formations into the Uinta Basin is assumed to indicate subsequent upwarp of the area to the 

south, instead of continued downwarping of the Uinta 

Basin. The Wasatch formation and equivalent Colton 

formation are arched around the north end of the San 

Rafael Swell and around the northward-trending anticline that separates the Uinta and Piceance Creek basins 

(fig. 37). Moreover, the Qreen River formation is 

warped downward in the syncline that plunges northward from Green River, Utah. Perhaps the Bridger, 

Uinta, and Duschesne River formations also are affected by this syncline, but this is not certain. The 

syncline is assumed to reflect late Eocene or Oligocene 

upwarp on the San Rafael Swell and on the anticline 

separating the Uinta and Piceance Creek basins. There 

also appears to have been at least two earlier stages of 

upwarp of these anticlines. The first upwarp probably 

was pre-Wasatch; and there probably was post-Green 

River and pre-Bridger upwarp also. The amount of 

upwarp in early Tertiary time must have been slight 

considering the concordance between the early Tertiary 

and Cretaceous strata around the north ends of these 

northward-trending folds. The apparent superposition of the San Rafael and Muddy Rivers across the 

San Rafael Swell suggests deposition of a layer of Tertiary deposits unconformably on the older folded rocks; 

this layer probably was no older than the Bridger 

formation.

Mention has already been made of the late Cretaceous 

and early Tertiary upwarp in the San Juan Mountains 

as recorded by the lowermost Tertiary formations in 

the northern part of the San Juan Basin. PostWasatch upwarp of the flanks of the San Juan Basin is 

recorded by the basinward dips of that formation. Upwarp of the Zuni Mountains is assumed to have started 

in pre-Wasatch time, but there also must have been 

later upwarp to.produce the northward dip of the Wasatch formation. There was post-Wasatch upwarp of 

the Nacimiento Mountains along the eastern side of the
58 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

San Juan Basin, and along the Defiance upwarp along 

the western side. The post-Wasatch upwarps probably 

were the result of repetitive movements in Eocene and 

Oligocene time, such as occurred in the northern part 

of the Colorado Plateau. The Nacimiento Mountains 

may have contributed debris to the late Eocene (or 

Oligocene) Galisteo formation. Folding and faulting 

of the salt anticlines southwest of the Uncompahgre 

Plateau may be assumed to have occurred contemporaneously with the movements of upwarp on the Uncompahgre Plateau. Deformation there is believed to 

have resumed in early Eocene time and to have recurred 

in later Eocene and in Oligocene time. The folding 

was accompanied, or immediately followed, by graben 

faulting. In late Tertiary time, when canyons were 

cut into the salt beds, the salt flowed laterally from 

under the anticlines, and collapse structures became 

superimposed on the anticlinal structures. (Cater, 

F. W., 1955b).

The principal unwarp at the Grand Hogback at 

Meeker (fig. 14), and at some anticlines northwest of 

Meeker, are post-Green River in age.

The major orogenic structural features in the interior 

of the Colorado Plateau seem to have been developed

almost completely before late Tertiary (Miocene and 

Pliocene) time. The Bidahochi formation, for example, 

is younger than the Defiance upwarp. There is some 

evidence that the Bidahochi and related deposits have 

been warped slightly, but late Tertiary deformation in 

the interior of the Plateau probably amounted to no 

more than Avarping, perhaps as a result of slight further 

uplifting of the upwarps but more likely as a result of 

differential movements of an epeirogenic sort (p. 63). 

In contrast, there was extensive and considerable deformation around the edges of the Colorado Plateau during late Tertiary time.

In the Mount Taylor district, the general northward 

tilt and the minor folding occurred after deposition of 

the Wasatch formation but before the eruptions of 

Mount Taylor and the eruptions of the basalt on its 

flanks. Twenty-five miles east of Mount Taylor, however, the San Juan Basin structures abruptly terminate 

at a faulted monocline marking the west edge of the 

Rio Grande depression (figs. 43, 44, 45). East of this 

monocline, the Upper Cretaceous formations are abundantly faulted in blocks that roughly parallel the 

faulted monocline. The Santa Fe formation overlaps 

these faulted beds and is itself much faulted. The 

deposition of the Santa Fe formation and the faulting 

that accompanied its deposition are younger than the

Horizontal and vertical scale

Jm, Morrison formation; Ku, Upper Cretaceous formations After Hunt, 1938

FIGURE 43. Block diagram illustrating the faulted east edge of the Colorado Plateau, east of Mount Taylor, N. Mex. The Alamoso. 

fault provides a sharp boundary between the Colorado Plateaus (represented by the San Juan Basin) and the faulted Basin and 

Range province (Rio Grande depression) east of the fault.
STRUCTURAL GEOLOGY 59

10

"""" Modified after Kelley, 1951 

20 Miles

fl 44. Tectonic map of part of the San .Juan Basin and the Rio Grancle depression.

structures of the San Juan Basin immediately west of 

the monocline. The sequence of events in this area is 

illustrated in figure 4.6.

Lucero Mesa

, Sheet bosolt (Pliocene?)

Pliocene(?)

Ir'H.TitH 45. Diagrammatic suction illustrating faulting east of Mesa 

Lucero. The basalt and the erosion surface on which it lies are 

probably younger than the fault at the right.

Similar late Tertiary deformation at the edge of the 

Colorado Plateau occurred along the Hurricane Cliffs 

in southwestern Utah. Displacement on the Hurricane 

fault, which marks the western edge of the Plateau, 

apparently started in Miocene time but continued intermittently into Pliocene time. The sequence of 

events is illustrated in figure 47.

The horst and graben faulting in other parts of the 

.High Plateaus is post-Wasatch in age (fig. 41) and

probably is mostly of late Tertiary age. This faulting 

may have continued into Quaternary time (p. 61). 

The Sevier and Paunsaugunt faults (fig. 37) had a history similar to that of the Hurricane fault. They displace the Wasatch and Brian Head formations and some 

of the overlying lavas. The Sevier River formation in 

central Utah also is faulted.

The Grand Wash Cliffs and Grand Wash trough, 

marking the west edge of the Colorado Plateau at the 

mouth of Grand Canyon, were faulted while the fill in 

the trough was being deposited (fig. 22). This fill has 

been correlated with the Muddy Creek formation and 

presumably is no older than late Miocene and may be 

somewhat younger than early Pliocene; deformation 

continued, however, while the fill was being deposited.

In the depression at Peach Springs, Ariz., are highly 

tilted, tuffaceous sandstone and conglomerate containing volcanic rocks that lithologically resemble the Muddy Creek formation. Apparently there was late 

Tertiary and perhaps early Quaternary deformation in 

this trough too.

At the north edge of the Colorado Plateau deformation immediately preceded deposition of the Browns
60 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

Time of 

eve'nts

s s

IS

<b 

C ill 

U 

O

E a

c

<u 

o

i

2

Elevation of drainage around base of Mount Taylor 

cone with respect to present stream levels

Drainage at present level

Drainage about 100 feet above present level

Drainage about 750 feet above present level

drainage developed around Mount Taylor

Irregular topography with drainage about 2000 

feet above present level

Probable irregular topography with drainage 

more than 2000 feet above present level

Structural movements

i Is

ci ** £

"3 £ >

 2 c u

° .5 "8

n

.

:

1! °

a f« a "

ffli £ m i>" o u

rt c '*H c

^ u c .5 c

' i i g1

ll « is i§

m ^ 3 c ca

"E,"2-^ o1^=4

I

i

1

i §

ft) CJ -In

ago.

i21

111 n

Volcanic activity

Sheet basalt

Mount Taylor

IP "IP

S a, 1- S u *; o o 

 a ~ a !>.

c « u x 

< J H K

1

1

After Hunt. 1938

FICUKK 46. Sequence of late Tertiary and Quaternary events in the Mount Taylor volcanic field. The length of line represents approximately 

the duration of each activity ; solid lines indicate fairly defini te information; dotted lines indicate considerable uncertainty.
STRUCTURAL GEOLOGY 61

F- Mohove erosion surface, lote Tertiary or early Quaternary

G-Fourth disturbance; Quaternary. (Present topography) 

a 4 Miles

After Gardner, I

FIG UK in 4.7. Structure sections across the Hurricane fault zone showing four stages In Its development. The basalt lavas (Qb) west of 

the fault have been bent and dropped almost 2,000 feet below the 

undlstorted remnant of the same flow east of the fault. Downturning of Miocene (?) lavas (Tv) is even greater, thus indicating two 

periods of downflexing.

Park formation, deformation that must have controlled 

the lithology and distribution of the formation. The 

collapse of the Uinta Arch preceded deposition of the 

Browns Park formation, but later movements affected 

that formation as well as the older rocks. Some of the 

domes immediately northeast of the Piceance Creek 

Basin formed in late Tertiary time, but prior to deposition of the Browns Park formation. They affected the 

Green River formation but are overlapped by the 

Browns Park.

In the San Juan Mountains late Tertiary folding and 

faulting were accompanied by volcanism and intrusions. 

Part of the domal uplift of the formations in the adjoining part of the Colorado Plateau probably is of this 

date.

347G20 5G 5

QUATERNARY STRUCTURES

The only recorded Quaternary deformation in the 

interior of the Colorado Plateau is in the area underlain 

by the salt deposits and is due to movement of the salt. 

One such example is the development of normal faults 

and grabens along the Colorado River near its junction 

with Green River. The drainage is poorly developed 

through the area of graben faulting, and well-defined 

old drainage channels are cut off by the faults, showing 

that the faulting occurred after the surface had been 

eroded to essentially its present position. In Salt Valley (fig. 40), a caliche-capped erosion surface has been 

faulted (Baker, 1935, p. 1500). In Castle Valley, 

Fisher Valley, Sinbad Valley, and Paradox Valley (fig. 

40), Recent alluvial deposits are faulted and locally 

folded.

Also, in Castle Valley and in Gypsum Valley is 

strongly folded conglomerate believed to be of late 

Pliocene age (p. 30). The folding of the conglomerates is attributed to salt movement.

Upwarp of the High Plateaus undoubtedly continued 

into Pleistocene time. Much of the deformation in the 

High Plateaus is younger than the late Pliocene or 

early Pleistocene Sevier River formation (Callaghan, 

1938, p. 103). A number of lava flows, believed to be 

of Pleistocene age, are faulted. South of the Paunsaugunt Plateau, in a canyon northwest of Kanab, alluvial fill that probably is of Recent age is displaced 

by a fault that extends downward to a slickensided 

fracture in the underlying rocks (Gregory, 1950, p. 

143). Some drainage changes in the High Plateaus 

have been attributed to Pleistocene tilting (Hardy and 

Muessig, 1952). Late Pleistocene upwarp of the 

Wasatch Mountains, which are alined with, and are 

north of, the High Plateaus, is recorded by the tilted 

and faulted Lake Bonneville deposits (Hunt, Thomas, 

and Varnes, 1953). Also, the High Plateaus have been 

seismically active in historic time. Since settlement in 

1851, several earthquakes have been recorded; those at 

Kanab in 1885 and 1891, and at Tropic, Glendale, and 

Panguitch in 1902, 1924, 1930, and 1931 were of special 

note (Gregory, 1950, p. 143).

The amount of Pleistocene upwarp in the High Plateaus may have been sufficient to account for the scarcity 

of pre-Wisconsin glacial deposits there (p. 35) ; 2,000 

feet of Pleistocene upwarp is a quite reasonable 

inference.

Some of the faulting around the edges of the Colorado Plateau, affecting formations like the Santa Fe, 

Muddy Creek, and Sevier River, probably also is of 

late Quaternary age, because Quaternary deformation 

has been extensive in the Basin and Range province,
62 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

both to the west and south of the Colorado Plateau. 

For example, the Lake Mead area, immediately west of 

the Grand Wash Cliffs, now is undergoing southwestward tilting in addition to basin subsidence related to 

loading by Lake Mead (Longwell, in preparation). 

The Wyoming Basin and the Rocky Mountains seem to 

have been more stable than the Basin and Kange province, but less stable than the interior of the Colorado 

Plateau.

CENOZOIC IGNEOUS STRUCTURES

The typical laccolithic mountain on the Colorado 

Plateau is a structural dome several miles in diameter 

and a few thousand feet high (figs. 28, 29). In general, 

the domes have smooth flanks, but most of them have 

many small superposed anticlinal noses that were produced by the laccoliths. At the center of each of the 

domes is a stock, around which the laccoliths are clustered. The stocks are cross-cutting intrusions, most 

of them surrounded by a shatter zone consisting of 

highly indurated sedimentary rocks irregularly intruded by innumerable dikes, sills, and irregular masses 

of porphyry (Hunt, 1953b). Through the monzonite 

and diorite porphyry stages the mode of intrusion of 

both the stocks and laccoliths is assuredly by physical 

injection. However, in those mountains where the intrusive process reached the syenitic stages the shattered 

rocks around the stock are in part replaced or assimilated by the stock.

The anticlinal noses clearly are the result of arching 

over the laccoliths, which extend radially from the 

stocks as tongue-shaped masses. The big mountain 

domes are attributed to deformation accompanying 

physical injection of the stocks, because the sedimentary 

formations turned up around the stocks cover the same 

area as they did in their original horizontal position. 

This evidence is especially forceful because of the fact 

that although the stocks are of different widths at the 

different mountains, the amount of upwarp at the domes 

is almost in direct ratio to the width .of the stocks 

(Hunt, 1946, p. 11, 12). (See fig. 28.)

The laccoliths are concordant injected masses that 

lifted their roofs by arching. Many of the laccoliths 

possess a very simple, linearly bulged, tongue-shaped 

form, but where the intrusions are crowded the forms 

are complex. This is especially true in the La Sal 

Mountains. Also, some of the intrusions have steep 

sides along which the roof rocks were faulted upward. 

These intrusions are bysmaliths, but they are similar 

to the laccoliths in all respects except this faulting 

(fig. 31).

Coherence and competency of the invaded rocks appear to have been a major factor in controlling the stratigraphic distribution of the laccoliths. Incompetent

formations were favorable. In the Henry Mountains, 

Abajo, and El Late Mountain the laccoliths spread 

mostly in the incompetent Upper Cretaceous shaly 

strata. The intrusions at the middle mountain of the 

La Sal Mountains did likewise, but the North and South 

La Sal Mountains rose in salt anticlines and spread 

mostly in the salt beds of the Pennsylvania!! Paradox 

member. At the North La Sal Mountain the intrusions 

breached the overlying rocks and erupted (Hunt and 

Waters, in preparation).

Because the stratigraphy and structure of the Colorado Plateau is fairly uniform, the similarity in form 

of intrusion, geologic structure, and rock types at the 

several laccolithic mountains in the Plateau reflect close 

similarities of the igneous processes involved. The 

mountains seem to represent a series of examples of one 

igneous process that was arrested at various stages of 

its development (Hunt, 1946, p. 16). Figure 28 illustrates some of the differences in stage represented in the 

different mountains.

The volcanoes, in contrast, did not produce major 

structures in the country rocks. Mount Taylor volcano 

is located in a syncline; San Francisco Mountain is on 

a dome, or broad arch, but neither of these underlying 

structures is believed to be related to the igneous activity. The fact that the pipes that fed these volcanoes 

did not dome the rocks around them indicates that their 

mechanism of intrusion was notably different from that 

of the stocks that produced domes at the laccolithic 

mountains, yet the rock types in the stocks and volcanoes are similar, both chemically and mineralogically. 

The diameters of the pipes feeding the volcanoes are not 

known, but they probably are comparable to some of the 

stocks; for example, the stock at Mount Holmes is only 

1,000 feet in diameter. The sequence of rock types 

erupted by the volcanoes is the reverse of the sequence 

intruded at the laccolithic mountains. In the latter, 

diorite porphyry was intruded first, followed by monzonite porphyry, and later by sj^enite porphyry. At 

the volcanoes, the first eruptions were rhyolitic and 

progressed through latite to andesite. Apparently, the 

reason for the difference in structure between the volcanoes and the stocks at the laccolithic mountains must 

be sought in some subcrustal phenomena that also produced a difference in the sequence of the differentiates 

that were pushed upward.

Little is known about Mount Trumbull and the small 

eruptive centers around it. They rest on a pedestal of 

rocks that had been deformed before the mountains 

erupted, and they are surrounded by centers of basaltic 

eruptions, some of which are of Quaternary age. In 

these ways, Mount Trumbull resembles Mount Taylor 

and San Francisco Mountain.
63

The A^olcanoes in the Navajo and Hopi Buttes fields 

(fig. 26) were mostly of the explosive type known as 

diatremes. On the other hand, in the volcanic fields 

where normal basalt was erupted the amount of pyroclastic material is small in proportion to the amount of 

lavas. The differences between these volcanoes may be 

due to differences in the physical-chemistry of the eruptives, because the volcanoes in the Navajo and Hopi 

areas are alkalic. However, the structural and hydrothermal effects of these small volcanoes, either of the 

alkalic type or normal basalt, are restricted to drageffects and minor baking along the walls of the pipes 

or dikes.

Neither the laccolithic mountains nor the volcanic 

centers show any distributional correlation with the 

erogenic structural features on the Colorado Plateau. 

The Henry Mountains are in a structural basin, the 

Abajo Mountains are to one side of an upwarp, the 

La Sal Mountains are in the midst of the salt anticlines, 

El Late Mountain and Navajo Mountain are in areas 

of gentle homoclinal dips, the Carrizo Mountains are at 

the nortliAvard-plunging end of an upwarp, the La 

Plata, Rico, and San Miguel Mountains are on the flank 

of the San Juan Mountain dome. A more diversified 

set of structural environments would be hard to find in 

an area of structural features as simple as those on the 

Colorado Plateau. The volcanoes seem equally independent of the orogenic structures.

Nevertheless, there is an apparent order in the regional distribution of the different kinds of igneous 

centers. The laccolithic mountains are clustered in the 

central part of the Plateau, and most of them lie in a 

belt between the San Juan Mountains and the volcanic 

pile in the High Plateaus (fig. 26). The normal basalt 

volcanoes are distributed around the edge of the Plateau. The volcanoes and minor intrusions of the alkalic 

basalt type lie in a belt between the laccolithic mountains and the belt of normal basalts.

CENOZOIC EPEIROGENIC STRUCTURES

Among the epeirogenic events in the structural history of the Colorado Plateau are the downwarping 

of the north part (and southern part of the Wyoming 

Basin) to produce the Green River lake, the broad arching or doming of the central part of the Plateau in 

southeastern Utah, the upward warping of the southern 

and southwestern rims of the Plateau, and the general 

upwarp and northeastAvard tilting of the Plateau as a 

whole.

At the close of Late Cretaceous time the area coA^ered 

by the Colorado Plateau must haA^e stood at, or near, 

sea level because it Avas a coastal plain. The west edge 

of the Colorado Plateau (the part represented by the

High Plateaus) must have been dowmvarped to accommodate the lakes in which were deposited the Flagstaff limestone and lacustrine beds of the Wasatch formation in the southern part of the High Plateaus. The 

Avestern part of the Uinta Basin also Avas doAVIIwarped, 

because Flagstaff limestone extends eastAvard nearly to 

the Green River. The dowmvarped area includes most 

of the northwest quarter of the Plateau; the amount of 

doAviiAvarping probably equaled the thickness of the 

Flagstaff limestone, which is about 1,500 feet. The 

gradational contact between these lacustrine deposits 

and the OA^erlying fluviatile deposits of the Wasatch 

formation suggests that the cessation of deposition in 

the lakes Avas a result of filling rather than a result of 

upAvarp.

DoAviiAvarping, hoAvever, spread eastAvard across the 

north end of the Colorado Plateau to accommodate the 

Eocene lake in Avhich the Green RiA^er formation Avas 

deposited (fig. 56). This doAvmvarping, which must 

have amounted to as much as 5,000 feet, embraced all 

the Uinta Basin and extended an unknoAvn distance to 

the south. If it extended halfAVay from the Uinta 

Basin to the southern borders of Utah and Colorado 

it involved the northern quarter of the Colorado Plateau. It extended far to the north into the Wyoming 

Basin, although it Avas interrupted by the Uinta Mountains which had begun to rise in early Eocene time.

The San Juan Basin portion of the Colorado Plateau 

Avas aboA^e sea level in earliest Tertiary time, Avhen the 

upper beds of the Animas formation Avas deposited 

in the northern part of the basin. The north flank of 

the San Juan Basin had been raised by doming of the 

San Juan Mountains, and this doming must also have 

raised the east-central part of the Colorado Plateau. 

There is no evidence that the San Juan Basin Avas high 

aboA^e sea leA^el. The Wasatch formation of the San 

Juan Basin, Avhich lithologically resembles the Wasatch 

formation of parts of the Uinta Basin, probably Avas deposited before the region Avas upAvarped to any great 

extent. In early Eocene time, in the San Juan Basin, 

the drainage probably Avas toAvard the south or southeast.

What Avas happening in the way of regional upAvarp 

in the Arizona portion of the Plateau is pure conjecture, 

but the occurrence of gravels containing pre-Cambrian 

quartzite on the Mogollon Rim suggests that this part 

of the Plateau Avas IOAV lying and Avas receiving debris 

from mountains to the south.

DoAviiAvarping of the Uinta Basin ceased in middle 

Eocene time, and thereafter fluviatile sediments represented by the Bridger, Uinta, and Duchesne River formations Avere deposited. Presumably this deposition 

helped aggrade some of the structural depressions that
64 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

were being developed between the orogenic upwarps to 

the south. Absence of deposits younger than the 

Duchesne River formation suggests erosion, at least 

non deposition, beginning in Oligocene time.

The structural elevation of the Colorado Plateau in 

southeastern Utah averages about the same as in the 

basin under Black Mesa. The southeastern Utah and 

northern Arizona portions of the Plateau therefore 

represent a platform that is considerably higher than 

the San Juan or Uinta Basins'. This platform, which 

is as old as early Eocene and perhaps older, may have 

been a highland that contributed to the Eocene sediments in the Uinta Basin and to the Nacimiento formation in the San Juan Basin (p. 24). It seems likely 

that the north flank of this platform roughly marked 

the southern limit of the Green River lake, but the Green 

River formation and the fluviatile Bridger, Uinta, and 

Duchesne River formations probably extended in a 

southerly lobe at least as far as the southern edge of the 

Henry Mountains structural basin. The laccolithic 

mountains seem to be clustered near the north edge of 

this structural, platform.

The upwarping of the southwestern and southern 

rims of the Colorado Plateau is assumed to have been 

contemporaneous with the general uplift of the Plateau 

block as a whole, and perhaps of the entire geanticline. 

The uplifting is thought to be contemporaneous with 

the late Tertiary and Quaternary block faulting that 

seems to represent the collapse of the Basin and Range 

segment of the geanticline. As a result of this uplifting and accompanying warping, the Colorado Plateau 

became saucer shaped and was tilted northeastward. 

From the Uinta Basin and San Juan Basin the strata 

rise southward and south west ward to the high rims 

bordering the Plateau on those sides (fig. 37). The 

High Plateaus can also-be thought of as a high rim, 

but they were lifted by faulting instead of by epeirogenic warping.

The process by which a block of the earth's crust as 

large as the Colorado Plateau is raised so many thousands of feet is even more uncertain than the time of 

uplift. The elevation might be due to the lateral transfer of materials into the subcrust beneath the Plateaus. 

It might be due to melting and expansion of subcrustal 

layers. It might be due to arching caused by lateral 

compression.

PHYSIOGRAPHY

CLIMATE AND WATER SUPPLY

The greater part of the Colorado Plateau is now 

semiarid (fig. 4), but earlier in the Cenozoic the climate 

was very different. At the beginning of Tertiary time 

the Colorado Plateau area was essentially at sea level

and was bordered by mountains on the north, east, west, 

and southwest sides. In Eocene (?) time the San Juan 

Mountains were high enough for the development of the 

glaciers that deposited the Ridgeway till. Presumably, 

there was glaciation on the other bordering ranges during this time.

In Paleocene and Eocene time the climate of the 

Plateau area, which was at sea level, appears to have 

been humid, warm temperate or sub-tropical, and the 

flora of the Green River and Bridger beds indicates a 

climate similar to that in the present-day southeastern 

United States (Berry, 1925). It has been estimated 

that during the middle Eocene time the northern part 

of the Colorado Plateau was characterized by cool, moist 

winters and relatively long warm summers, that .the 

mean annual temperature fluctuated seasonally from 

a mean that was about 65° F., and that the rainfall 

varied seasonally from a mean annual precipitation of 

about 38 inches (Bradley, 1929, p. 93-95). Throughout the Paleocene an.d Eocene the low-lying Plateau 

area had lakes and marshy floodplains, and received the 

discharge from the mountains; such conditions are indicated not only by the physical geology but also by the 

heavy-footed, amblypod fauna of that period.

However, if the adjoining mountains had been 10,000 

feet high we might expect them to have had a mean 

annual temperature of about 32° F. and a mean annual 

precipitation of about 60 inches. At such high altitudes, there could have been ice fields, or glaciers, during 

the time of the early Tertiary lakes. Early Tertiary 

glaciation in the San Juan Mountains is recorded by 

the Ridgeway till. The widespread conglomeratic 

gravels, other than those of volcanic origin, in the lower 

Tertiary formations also could be interpreted as the 

product of alpine glacial or periglacial activity because 

it is difficult to imagine how such gravel deposits would 

form in the absence of vigorous frost action.

By middle Oligocene time, judging by evidence from 

neighboring regions, the climate of the Colorado Plateau had become semiarid. Beginning in Miocene time, 

and continuing through middle Pliocene time, the climate of the western United States seems to have become 

drier and more continental (Axelrod, 1950, p. 228, 266).

Very likely, as this change occurred, the influence of 

the topography on the local climate became increasingly 

important. For example, the epeirogenic rise of the 

Colorado Plateau during late Cenozoic time probably 

resulted in a climate that was less dry and cooler than 

that of the Basin and Range province to the southwest, 

which, then as now, was arid and semiarid. The orogenic rise of the High Plateaus probably caused a rain 

shadow that, as at present, kept the interior of the Colorado Plateau as dry as the Basin and Range province,
PHYSIOGRAPHY 65

but, because of its greater altitude, it was cooler and the 

effective moisture Avas greater. Such local conditions 

reflecting physiographic controls may have largely 

masked the general change in world climate towards 

cooler and moister conditions in late Pliocene time.

Fossil vertebrates of late Pliocene age from southern 

Arizona suggest that the climate there was warm and 

moist, similar to that now existing in southern Mexico 

(Gidley, 1922). However, to the degree that the plateau had been raised epeirogenically towards its present 

level by late Pliocene time, the climate on the plateau 

may be inferred as cooler than that in southern Arizona.

During Pleistocene time the effective moisture on the 

Colorado Plateau must have been considerably greater 

than at the present time, because during some of the 

glacial stages snow accumulated at altitudes as low as 

6,000 feet. These accumulations were seasonal and in 

sufficient volume to produce debris avalanches like those 

east of Hite (p. 38). Further evidence of much more 

effective.moisture during the Pleistocene is provided by 

the spring deposits interbedded with the Pleistocene 

valley fill in the vicinity of Hite, Utah (p. 38).

The Recent epoch started with a period that was drier 

and warmer than the present. During this early dry 

period, extensive dunes developed and extensive arroyo 

cutting occurred. It was followed by a period when 

effective moisture was greater than at present the 

period when the prepottery, Recent alluvium was deposited. This, in turn, was followed by a dry period 

around 1300 A. D., during which arroyo cutting was 

resumed. Dry, warm conditions have prevailed during 

the last 600 years, except for one brief interruption 

represented by the deposition of alluvium during the 

16th and 17th centuries.

Rates of weathering probabry are roughly proportional to the effective moisture. Therefore, weathering 

must have been greater during the early Tertiary than 

during the later Tertiary or Quaternary. Weathering 

was at a minimum during the Miocene and early 

Pliocene. During the Pleistocene, weathering was 

most effective during the interglacial stages. Since 

the beginning of Wisconsin time, weathering has been 

of little effect on the Colorado Plateau.

Erosion probably is at a maximum when'there is a 

climatic change that causes a decrease in effective moisture, because it is the weathered products that are most 

easily eroded. We might assume therefore, that the 

rate of general lowering of the land surface by erosion 

was greater during early Tertiary time than it was during late Tertiary time. On the other hand, the relatively arid conditions that prevailed during the Miocene 

and Pliocene would have favored erosion in those parts 

of the Plateau where the surface formations were unconsolidated or weakly consolidated, and would have 

favored erosion along the main stream courses.

During the latter part of Pleistocene time the erosion 

history of the valleys seems to have an alternation of 

deposition of fill and removal of that fill. The canyons, 

of course, became extended headward, and in the mountains the valleys that contained glaciers became deepened, but the general land surface does not seem to have 

been lowered much, and the main stream courses seem 

to have been cut essentially to their present depths before late Pleistocene time.

The ground waters in latest Cretaceous time probably were saline with the residue of the marine waters 

of the Late Cretaceous sea. During early Tertiary 

time, conditions were moist, the .ground-water table 

must have been high and was freshened by the introduction of fresh water. In Miocene time, as the Plateau 

became raised epeirogenically, and as the climate became less humid, the water table presumably was lowered, was divided into basins by the upwarps, and probably became alkaline. During late Pliocene and Quaternary time, the water table has fluctuated. During 

periods when moisture was effective, there must have 

been considerable movement of ground water down the 

flanks of the upwarps into the basins. These groundAvater movements produced some large springs, as along 

the Colorado River near Hite, and they must have raised 

the water table in the basins and reduced the alkalinity 

of the water.

ANTEPOSITION

The streams of the Colorado River system (fig. 1) 

cross the Plateau seemingly indifferent to the various 

orogenic structures encountered. This fact has been 

commented upon frequently in geologic literature. 

PoAvell attributed the lack of adjustment to antecedence. He postulated that the river and its principal 

tributaries Avere able to maintain their course across 

uplifts by dowiiAvard cutting while the uplifting was 

in progress. Later, Davis provided reasons for doubting the antecedence of the drainage and postulated that 

it had been superimposed from strata that unconformably lay across the folds. Actually, neither theory 

alone seems to be adequate to explain all the anomalies 

of the Colorado River drainage system, but a combination of the tAvo concepts, which I refer to as "anteposition," seems to offer explanations for most of the anomalies. The process, illustrated in figure 49, can be applied to the Colorado Plateau only by inference. The 

process, however, has been recognized elsewhere, as 

along the Ventura RiA^er in California (Putnam, 1942).

The canyons through the uplifts that lie across the 

Colorado River drainage system are thousands of feet 

deep. If these canyons are entirely the result of super-
66 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

A. Block diagram

showing the probable

topography of the east end of the

Uinta Range after the erosion of the Bear

Mountain surface (a) and the Browns Park Valley (c)

but before the deposition of the Browns Park formation

The diagram also shows 

Cold Spring Mountain 

(b), Diamond Peak (d), 

Cascade Creek and Summit 

Valley (e), Lodore Branch of 

Cascade Creek and site of Lodore 

Canyon (f), and Red Creek (g)

B. Block diagram

showing the east end of

the Uinta Range after the Browns

Park Valley had been filled with the Browns

Park formation and after the east end of the range

had collapsed to form the Umta Mountain graben and theGreen

River (c) had been diverted into the Browns Park Valley

In the foreground the trace of the Uinta fault(h) is

shown by the southward-facing escarpment.

Lodore Branch of Cascade Creek (f) is ^*^"

shown about to capture the Green ,^^?^

River (near c) and divert it /

southward along its own .^A^,'

course

Cold Spring 

Mountain is buried 

beneath the Browns 

Park formation and Vermilion Creek has established 

its course across the east end of 

this mountain (near b).

The diagram also shows the Bear 

Mountain surface (a), Diamond Peak (d), 

Cascade Creek and Summit Valley (e), and 

Red Creek (g)

C. Block diagram

showing the east end of

the Uinta Range after the Green

River (c) had been diverted southward by

capture so as to occupy the old valley ot Lodore

Branch of Cascade Creek (f) and Cascade Creek. The river

has entrenched itself in the soft beds of the Browns Park formation

and thus accelerated the dissection of the adjacent region. Vermilion Creek

at (b) has discovered Cold Spring Mountain through which it has begun to cut Irish Canyon

Both Vermilion 

Creek and Cottonwood 

Creek (g) have changed 

their courses in response to 

the diversion of the Green River. 

The diagram also shows the 

dissected Bear Mountain surface 

(a). Diamond Peak (d), and Cascade Creek 

in Summit Valley (e)

FIGURE 48. Block diagrams illustrating stages

After Bradley, 1936

in the development of Lodore Canyon, as interpreted by Bradley.
PHYSIOGRAPHY 67

position the fills deposited upstream must have been 

built as high as the canyon rims on top of the uplifts. 

Such an amount of fill upstream from many of the canyons is unlikely. Bradley (1936, p. 188-189) recognized 

this difficulty in offering his interpretation for the origin 

of Lodore Canyon (fig. 48). He points out that the 

Browns Park formation probably was not deposited 

to the height of the rim of Lodore Canyon, and he attributed the canyon to headward cutting by drainage 

on the south side of the Uinta Mountains. However, 

it is equally possible, and in my judgment it is more 

probable, that Lodore Canyon antedates the Browns 

Park formation, a condition analogous to stage 1 in 

figure 49. As a result of downfaulting of the Browns 

Park area, the floor of Lodore Canyon stood about a 

thousand feet higher than the area upstream, the drainage became ponded, and the Browns Park formation 

was deposited in this basin (analogous to stages 2 and 

3 in fig. 49). The old canyon floor would be a natural 

spillway when the fill upstream was built to that level. 

When that stage was readied (stage 4 in fig. 49), aggradation upstream would cease, and canyon cutting 

would be resumed. The new stream course upstream 

from the spillway can become superposed; the course 

below the spillway has the aspects of antecedence. Such 

a combination might be referred to as anteposed.

COLORADO AND GREEN RIVERS

The courses of the Colorado and Green Rivers and 

their tributaries provide evidence that superposition or 

anteposition (or both) of the drainage onto the bedrock 

structures has occurred during at least two stages widely 

separated in time. The younger stage of superposition 

:is judged to have been from formations equivalent in 

age to the Browns Park or Bidahochi formations. The 

older stage of superposition was from formations older 

tlian these, possibly as old as the Bridger.

The Colorado River enters the Colorado Plateau at 

Rifle, Colorado, where it crosses the Grand Hogback 

(fig. 1). From there, it cuts across the eastern end of 

the Uinta Basin in a southwesterly course to Grand 

Junction (its junction with the Gunnison River). At 

Grand Junction, the river turns westward in a strike 

A'alley along the north side of the Uncompahgre Plateau, turns southwestward into a canyon that crosses 

the end of the Plateau, and then continues a southwesterly course into southeastern Utah.

The course from Rifle to Grand Junction could be 

due to superposition. If this is true, the surface of 

superposition probably was at the level of the Tertiary 

lavas capping Grand and Battlement Mesas, roughly a 

mile higher than the present level of drainage.

Stage 1. Stream course established in a canyon across an upwarp

Stage 2. Renewed upwarp arches stream bed causing aggradation 

upstream (black area)

Stage 3. Aggradation continues until fill has been constructed to 

level of the floor of the arched canyon

Stage 4. Canyon cutting is resumed when stream begins spilling 

over the elevated canyon floor. Upstream from the high point in 

the arched bed of the canyon the new stream course may be superimposed. Downstream from the high point the course is antecedent

FJGUEB 49.- Diagrams illustrating anteposition.

Transversely across the Uncompahgre Plateau, and 

alined with the Colorado River above Grand Junction 

is a broad abandoned river valley know as Unaweep 

Canyon, 500 to 1,000 feet deep in pre-Cambrian rocks, 

and 2',500 feet higher than the Colorado River to the 

north and the Dolores River to the south. Peale (1877, 

p. 58-59) considered the possibility that it represented 

a former northward course of the Dolores River, but 

decided that it was more probable that it represented a 

former southward course of the Gunnison or the Colorado River. The occurrence of basaltic pebbles in 

gravel in Unaweep Canyon, 4 miles above Gateway
68 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

(Cater, oral communication), and the absence of basaltic pebbles in the gravels along the Dolores River and 

its tributaries, also suggests that the canyon drained 

southward rather than northward. If so, the abandonment of Unaweep Canyon probably resulted from capture of the Colorado River by a stream that drained 

towards the Henry Mountains basin and eroded headward in the soft rocks around the northwest end of the 

Uncompahgre Plateau. This stream became incised 

into a canyon that cuts across the northwestwardplunging end of the Plateau, probably by superposition. 

The floor and rims of this canyon are much lower than 

Unaweep Canyon, however, both evidently are due to 

superposition. They provide evidence of two stages of 

superposition in this area, and the younger stage must 

represent superposition from deposits at least as old 

as the Browns Park formation.

. The Colorado River, below its junction with Green 

River, obliquely crosses the Henry Mountains basin. 

In late Eocene time this part of the Colorado Plateau 

was structurally between 5,000 and 10,000 feet higher, 

on the average, than the Uinta Basin, but the deposition 

of nearly 10,000 feet of Eocene deposits in the Uinta 

Basin probably raised its surface to a level equal to, or 

above, that of the Henry Mountains basin. The Henry 

Mountains basin probably received drainage from the 

Uinta Basin, as well as from the uplifts to the east and 

west. In any case, regardless of its sources, the ancestral drainage would have aggraded the Henry Mountains basin until a low point of the rim was reached. 

Structurally, the lowest point on the rim is at the south 

end of the Waterpocket fold, and this is where the Colorado River leaves the basin.

The course of the Green River across the southern 

part of the Uinta Basin is along the axis of a synclinal 

trough that involves the upper Eocene formations. 

This part of the river's course therefore, may have been 

inherited from the stage when the folding occurred. 

Southward drainage along this syncline could have been 

started as early as Oligocene time.

The present course of the Colorado River, after it 

leaves the Henry Mountains basin, is southwestward to 

the Kaibab up warp (Strahler, 1948) and across the 

high southwest flank of the Colorado Plateau. This 

flank is high, both structurally and' topographically; 

in fact, it is one of the highest places on the southern 

rim of the Colorado Plateau. How the river established its course across the Grand Canyon section is 

one of the major problems of Cenozoic history.

TRIBUTABY STREAMS

The Yampa River (fig. 1) emerges from the foothills 

of the Rocky Mountains, enters rather open country, 

and crosses two anticlinal upwarps with apparent disregard for rock structure. At one of the anticlines, instead of continuing its course in soft beds around one 

end of the upwarp, the river turns into a short canyon 

through hard Paleozoic rocks in the upwarp. Fifteen 

miles downstream the river cuts across the second upwarp instead of taking an easy course around it. (Hancock, 1915, p. 184.)

These upwarps crossed by the Yampa River are preBrowns Park in age, because that formation lies essentially horizontally around their base. That they 

were once buried by the Browns Park formation is suggested by occurrences of that formation at elevations 

equal to, or greater than, that of the highest Paleozoic 

beds along the rim of the river canyon in the upwarp. 

There is little reason, therefore, to doubt that the 

Yampa River was superimposed on these folds from the 

Browns Park formation, and that the canyons through 

these folds are post-Browns Park in age. (Hancock, 

1915, p. 186-188.)

The western tributaries of the Green and Colorado 

Rivers illustrate several quite different relationships.

In the western part of the Uinta Basin is the Duchesne River, which flows eastward approximately 

along the trough of the Uinta Basin. Its position 

seems to be that of a normal consequent stream on the 

folded upper Eocene formations. Minnie Maud Creek, 

the stream next south of the Duchesne River, also seems 

to be a normal consequent stream in a strike valley in 

the northward-dipping Eocene formations.

However, the western tributaries next to the south 

the Price, San Raf ael, and Muddy Rivers have courses 

that are the result of superposition. Price River flows 

obliquely across the north end of the San Raf ael Swell. 

San Rafael and Muddy Rivers cross the structurally 

highest parts of the swell. These courses probably are 

due to superposition from Tertiary strata that overlapped unconformably across the swell, or their history 

may be more complex and may involve one or more periods of anteposition. In either case, the Tertiary beds 

were of Bridger age or younger, because the older Tertiary formations seem to have been domed by uplift of 

the San Rafael Swell.

The Dirty Devil and Fremont Rivers illustrate another condition, because they flow in a wide arc around 

the north end of the Henry Mountains; this part of 

their course is attributed to monoclinal shifting as a 

result of the Henry Mountains intrusions. The headward part of the Fremont River has been eroded into an 

upwarp the Capitol Reef uplift probably by headward erosion.

A strike valley, 35 miles long, on the eastern side of 

the Waterpocket fold (fig. 50) is a consequent structurally controlled valley, but the creek in the valley,
From Gregory and Moore, 1931 

KK 50. Generalized view of south-central Utah looking north from the Utah-Arizona boundary line.

Halls Creek, leaves the strike valley at two places and 

meanders into canyons cut into the fold. These anomalous canyons, evidently the product of superposition, 

obviously are younger than the consequent strike valley, and, in turn, this strike valley probably is younger 

than the canyons of the streams that are incised across 

the high parts of the big upwarps. Perhaps the canyons along Halls Creek correlate with the post-Browns 

Park canyons along the Yampa River and with .the canyon along the Colorado River at the northeast end of 

the Uncompaghre Plateau.

The Escalante River (fig. 50) crosses the Circle Cliffs 

upwarp in a course similar to the courses of the streams 

that cross the San Rafael Swell, and it probably was 

superposed from the early Tertiary formations that occur in the basin west of the upwarp. The headward 

part of the Paria River is discordant to the structure 

and may be the result of superposition or headward 

erosion (.figs. 50,51) ; the lower part of the river's course 

seems to be in a normal strike valley.

Most of the tributaries on the east side of the Colorado River axe longer than those on the west, and they 

illustrate similar physiographic relationships. The 

Gunnison and San Miguel Rivers follow strike valleys 

on the sides of the Uncompaghre uplift but the course 

of the Dolores River is anomalous. It flows southwestward down the flank of the San Juan Mountains and 

then turns 135° to the north. Perhaps the river 

originally continued southwestwarcl but became di347620 5G 6

verted when the La Plata and El Late Mountains were 

domed by the intrusives.

The course of the San Juan River also is anomalous. 

The San Juan Basin, structurally, is one of the lowest 

parts of the Colorado Plateau. In Animas time, there 

was drainage from the San Juan Mountains southward 

into the basin. In Puerco and Torrejon time, there 

seems to have been drainage into the basin from the 

west. In Wasatch time, there was drainage southward 

from the San Juan Mountains, and this drainage seems 

to have continued southward across the southern part 

of the San Juan Basin. By middle Eocene time, several thousand feet of Tertiary sediments had been deposited in the basin. At some later time, though, the 

land surface in the San Juan Basin was higher than the 

basin of the Colorado River in southeastern Utah, and 

the drainage off the south side of the San Juan Mountains was turned westward to join the Colorado River. 

To reach the Colorado River, this drainage had to cross 

the Monument Upwarp (fig. 52). If it be assumed that 

the river was superimposed across the upwarp, the 

surface from which it was superimposed was as high or 

higher than the rim of the canyon through the upwarp, 

which is about 6,000 feet in altitude and about 2,500 

feet higher than the river. Such a surface could have 

been cut by the Dolores River before the intrusions 

formed at El Late Mountain. In any case, the westward course of the San Juan River appears to be at 

least as old as the volcanics in the Mount Taylor field
70 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

From Gregory and 

Moore, 1931

a, A short time after displacement of beds along Paunsaugunt fault; 

consequent north ward drainage on the west (downthrown) side, and 

possibly also on east side, b, Recession of Tertiary cliffs on upthrown side through headward cutting of the Paria River drainage favored by steep gradient to the Colorado River and weak 

Cretaceous rocks below Tertiary, c, A later stage, showing 

erosion of the block west of the fault as well as further recession 

of cliffs on the upthrown block, d, Present stage. Not much 

headward cutting is needed for the Paria to capture the waters 

of the upper East Fork of the Sevier River. Tw, Wasatch formation; Kk, Kaiparowits formation; Kws, Wahweap and Straight 

Cliffs sandstones; Kt, Tropic shale; Kd, Dakota(?) sandstone; 

Jsr, San Rafael group; Jgc, Glen Canyon group

FIGURE 51. Generalized block diagrams representing stages in the 

physiographic history of upper Paria Valley.

and the other volcanics alone the south and east sides D

of the San Juan Basin.

A much younger set of superimposed canyons occurs 

along Chinle Creek and Chaco. River. Chinle Creek 

follows a strike valley northward along the west side 

of the Defiance Upwarp, but it joins San Juan River 

by turning into a canyon on the flank of the Monument 

Upwarp. The course of Chaco River is similar to that 

of Chinle Creek. Below Pueblo Bonito, the river flows 

north Avar d along a strike valley, but it joins San Juan 

River by turning into a canyon in the upturned rocks 

to the west. The strike valleys along Chinle Creek and 

Chaco River are consequent and are the result of general 

degradation after the San Juan River had become superimposed across, and incised into, the upwarps that lie 

across its course. The canyon at the mouth of each 

strike valley evidently is the result of superposition 

from a fill or erosion surface that was developed during 

the cutting of the strike valley, and these canyons must 

postdate the incision of the San Juan River into the 

upwarps. The later stage of superposition probably 

was from deposits equivalent to the Bidahochi formation, which occurs as fill in nearby valleys. However, 

the superposition of the San Juan River across the big 

upwarps occurred earlier probably much earlier.

Another condition is illustrated by the Little Colorado River, which is in a strike valley with long, consequent-like tributaries draining northward to it from 

the Mogollon Rim. This valley is older than the Bidahochi formation. It must be nearly as old as the volcanoes in the San Francisco Mountain area because the 

Mesozoic formations, whose escarpments form the strike 

valley, had been eroded from the volcanic district before 

the eruptions occurred. Moreover, the Bidahochi formation records that the plateau surface in that area 

had been eroded nearly to its present form by the time 

the Hopi Buttes volcanoes were erupting.

In general, it appears that the drainage is fairly well 

adjusted to the orogenic structures in the San Juan 

Basin and in northeastern Arizona; it is fairly well 

adjusted to the Tertiary deposits in the Uinta Basin. 

It is strikingly inconsequent on and apparently superimposed or anteposed (or both) across the folds in the 

other parts of the Plateau. At several localities there 

is good evidence of at least two stages of superposition. 

The younger stage occurred about the time that the 

Browns Park or Bidahochi formations were deposited; 

the older stage preceded this by sufficient time for erosion of the general level of the Plateau a thousand feet 

or more lower than the tops of the upwarps.

In contrast to the lack of adjustment of the drainage 

to many of the orogenic structures is the rather complete adjustment of the drainage to the structural fea-
PHYSIOGRAPHY 71

Width of view about 50 miles After Miser, 1924, W-SP 538

PIGUKIO 52. Block diagram of tlic San Juan Canyon across tho Monument Upwarp.

tures produced by the igneous intrusions. The Fremont and Dirty'Devil Rivers swing in a wide arc around 

the nortli end of the Henry Mountains. The Dolores 

River S'wings in a similar arc around the La Sal Mountains. The San Juan River follows the syncline between El Late and Carrizo Mountains. The headward 

parts of the San Miguel and Dolores Rivers are separated by the intrusions and igneous structures at the 

San Miguel Mountains. Chinle Creek and Chaco River 

are in strike valleys on each side of the Carrizo Mountains. The general effect of these drainage adjustments 

is that the stream, courses were monoclinally shifted

 off 'the"igneous" structures. Only at the Rico .Mountains is drainage superimposed on an igneous structure 

in a, manner analogous to that of the Yampa, .Muddy, 

or San Rafael Rivers. The drainage also is consequent 

around the A'olcanoes at Mount Taylor and San Francisco Mountain.

The relatio.nsli.ip, or lack of relationship, of the Colorado River to the epe.iroge.nic or regional, structure of 

the plateau as a whole is anomalous and seems to be 

that of an antecedent or anteposed stream. The plateau tilts northeastward, and the Colorado and Green 

Rivers enter it at the Uinta Basin, which structurally 

is the lowest part of the plateau. From here, the rivers 

flow southwest/ward onto the epeirogenic platform in 

southeastern Utah and northeastern Arizona. At 

Grand Canyon, the Colorado River flows across one of 

the structurally highest parts of the rim of the plateau. 

This relationship is not that of a superposed stream,

 unless it be postulated that virtually the entire Colorado Plateau, and all the ranges crossing the lower 

Colorado River, are exhumed. It seems more likely 

that the river's course is partly the result of antecedence 

and partly the result of anteposition dating from an 

early stage in the epeirogenic upwarp of the Plateau.

EROSION AND GEOLOGIC TIME

About 80 percent of the Colorado Plateau has been 

eroded to formations below the middle of the Upper

Cretaceous; about 60 percent is lower than the base of 

the Cretaceous; about 35 percent is lower than the base 

of the Jurassic; and about 25 percent is lower than the 

base of the Triassic. It is judged therefore, that about 

8,000 feet of Mesozoic rocks has been removed from the 

Plateau. To this amount must be added the thickness 

of Paleozoic rocks and the thickness of those Tertiary 

rocks, especially the lower Tertiary, that were transported onto the Plateau from the bordering mountains. 

The total Cenozoic degradation on the Plateau therefore must average about 10,000 feet.

The rate of erosion of bedrock on the Colorado Plateau during the period 1935-48, as determined by sedimentation studies at Lake Mead, has been at the rate of 

1 foot every 2,150 years (Gould, report in preparation). 

At this rate, 21% million years would be required to 

erode 10,000 feet of rock from the Plateau.

On the basis of lead-uranium ratios in radioactive 

minerals the duration of the Cenozoic era is calculated 

to have been 60 million years. The Paleocene and 

Eocene epochs are estimated to comprise the first 23 

million years of this era, and an age of 31 million years 

has been calculated for the early Oligocene. (Bradley, 

1929, p. 109-110.) ' . *

Through Paleocene and Eocene time, and perhaps 

into Oligocene time, the Colorado Plateau was subject 

to aggradation rather than degradation, because it wasa low-lying trough surrounded by newly formed mountains. Degradation was dominant during about half 

of Cenozoic time; at the present rates of erosion, about 

a third of Cenozoic time would be required to accomplish the erosion on the Colorado Plateau.

SOILS

The dependence of soils upon the geologic history of 

their locale, and upon the geologic formations from 

which they are derived, is well illustrated on the Colorado Plateau where soils of three quite different ages 

can be recognized. The youngest soils are those that 

have developed during Recent time. Next oldest are
72 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

those that developed during Wisconsin time, and the 

oldest recognizable soils 'are pre-Wisconsin. In the Recent and Wisconsin soils, the degree of weathering is so 

slight that the parent material still dominates those 

profiles; there are, therefore, about as many varieties of 

these soils as there are variations in the parent materials.

Recent soils characteristically are shallow, and their 

profiles are only weakly developed. They are best developed on alluvial parent materials, and generally 

they consist of no more than a darkened layer, enriched 

in organic matter, above very slightly oxidized and 

lighter-colored parent material. The depth of this 

layer commonly is less than 6 inches, and only infrequently does it exceed about 18 inches. Other Recent 

soils have profiles similar to those of the alluvial soils 

only at those places where the parent material is not 

consolidated. Soils that are similar to those on alluvium 

are found on upland flats, on some of the Tertiary formations, or on some of the older formations where they 

have been blanketed by eolian deposits. Dune sand 

that was deposited during early Recent time commonly 

is weathered and the old dunes are stabilized. They 

are more compact and more stained with iron oxide 

than the sand in the younger dunes.

On the Colorado Plateau, during Recent time, erosion in general has been more vigorous than weathering. 

Soil development has not been able to keep pace with 

the erosion, and, as a result, vast areas on the Plateau 

are bare rock. This is especially true in the Canyon 

Lands section. It has been estimated, for example, 

that about 25 percent of the Henry Mountains region 

is bare rock. In the Uinta Basin and Navajo sections 

many of the formations are poorly consolidated as compared with those in the Canyon Lands, and Recent soils 

blanket a high proportion of these sections. The High 

JPlateaus, Grand Canyon, and Datil sections receive 

much more moisture than do the sections in the interior 

of the Colorado Plateau, and these areas also have extensive Recent soils. However, all of them are shallow 

and weakly developed.

The next older group of soils are those that developed 

during Wisconsin time. These are even less extensive 

than the Recent soils. Where developed on unconsolidated parent materials they commonly are 3 feet deep. 

In these soils the organic-rich, darkened, top layer 

generally is more than a foot thick and is underlain by 

a somewhat reddish zone and (at altitudes below about 

8,500 feet) by a lime-enriched zone 2-3 feet thick. The 

lime in the subsoil may occur as nodules, as veinlets, 

or it may be finely disseminated throughout the subsoil. 

It forms a conspicuous layer, although not so conspicuous as the lime zone under the pre-Wisconsin soils.

The climate of Wisconsin time was much more moist 

than that of Recent time, and the soils of that period 

are deeper and their profiles more fully developed.

Still thicker and more fully developed than the Wisconsin soils are those that formed in pre-Wisconsin 

time. In general, these consist of an upper layer, a few 

feet thick, of reddish clay that is mostly hydromica. 

Below this clay layer is strongly lime-enriched, weathered parent material; the lime occurs both as carbonate 

and as sulphate. At altitudes above about 8,500 feet 

there is no lime zone and the old soils are acid. PreWisconsin soils are preserved only locally in the Colorado Plateau. The most extensive remnants are on the 

uplands between the Abajo and El Late Mountains and 

on the uplands southwest of the San Miguel River 

where extensive areas are covered by several feet of 

pre-Wisconsin eolian or alluvial deposits on which has 

developed a pre-Wisconsin soil. Pre-Wisconsin soils 

also are extensive on the pediment graArels around the 

foot of the mountains; good examples can be found 

around the Henry Mountains, along the foot of the 

Book Cliffs, in the Uinta Basin, and in southwestern 

Utah. Where these soils have been mapped, they have 

been classed as the Mesa or Harrisburg [soil] series 

(Youngs and Jennings, 1939; Hendrickson and others, 

1925; Strahorn and others, 1924, Youngs and others, 

1942). Weathering of basalt in the San Francisco area 

has yielded 2 feet of residual clay having the following 

chemical composition, in percent. (Analyst, F. N. 

Guild; after Robinson, 1913, p. 39, 150.)

SiO2 _____ ____ 54.28 CaO __________ 2.08

A12O3 ___________ 18.16 Na2O+K,O _______ 2. 24

Fe2O3 ______ _ 9.52 H.O+CO, _______ 13.01

MgO ___________ 1. 53 Total ________ 100. 82

An analysis of the basalt from which this clay was derived is given on p. 49. In southwestern Utah the soils 

developed on deeply weathered basalt are classed as 

the Veyo soil series (Youngs and others, 1942).

The fuller development of the pre-Wisconsin soils 

as compared to the Wisconsin soils, and the fuller development of the Wisconsin soils as compared to the 

Recent soils, immediately suggests that the differences 

between them are due to differences in age. But until 

more is known about the climates and other conditions 

under which the soils developed there is no justification 

for attributing their differences solely to age. There 

are parallels between soil development and glacial deposits; in each case, the older ones are more fully developed than the younger ones. In glacial deposits this 

difference certainly is not due to difference in age; indeed, if the reverse were true, the record of the earlier 

and lesser 'ice advance would have been destroyed by 

the later one. The same reasoning can be applied to
CENOZOIC HISTORY OF THE PLATEAU A HYPOTHESIS 73

soils. The considerable depth and development of the 

pre-Wisconsin soils, even where buried by younger deposits, probably reflects the intensity of the processes 

involved; the length of time that the processes operated 

may have been no greater than the duration of the processes that gave rise to the younger and less well developed soils.

The variegated early Tertiary fluviatile sediments 

may have been derived from red soils developed on the 

surrounding uplands and deposited in a humid warmtemperate to subtropical loAvland. The red stain would 

be presented where little organic matter was incorporated in the flood-plain deposits of the aggrading 

streams, whereas drab colors would result from reduction of the ferric oxide in sediments rich in decomposing 

plant debris (Van Houten, 1948, p. 2084).

CENOZOIC HISTORY OF THE PLATEAU A HYPOTHESIS

The foregoing description of the Cenozoic sedimentary deposits, igneous rocks, and structural and physiographic features of the Colorado Plateau reveals tremendous gaps in the record, but also reveals the gross 

outlines of the Cenozoic history.

In pre-.Cenozoic time, the Colorado Plateau province 

had been a shelf area. At the beginning of Cenozoic 

time, and during the early Tertiary, the Plateau area 

was a basin or trough probably not far above sea-level 

and surrounded by newly formed mountains whose 

higher parts were subjected to glacial, or periglacial, 

conditions. The trough, or basin, was the product of 

folding that began in "Late Cretaceous time and continued during the early Tertiary. In its lower parts, 

several thousand feet of lacustrine and fluviatile sediments were deposited. After Eocene time conditions 

changed markedly. General aggradation ceased and 

general degradation began. Igneous activity, in the 

form of volcanism and intrusions, became extensive. 

There was extensive faulting, especially along the west 

and south edges of the province; and epeirogenic uplift 

began. The erosion, igneous activity, faulting, and uplift have continued to the present time.

It is supposed that exterior drainage started when 

tire Plateau began to be uplifted epeirogenically, and 

that the major courses of the streams probably were established before this uplift had progressed very far. 

It also is supposed that the canyon cutting began at that 

time and that it has continued to the present time. The 

history of sedimentation in the Colorado Plateau is almost the opposite of that in the Basin and Range province. The Basin and Range province appears to have 

been a highland, which was undergoing erosion during 

Paleocene, Eocene, and Oligocene time, and which was 

extensively aggraded during late Miocene and early Pliocene time. The Plateau, on the other hand, was aggraded during the early Tertiary and was degraded 

later.

To fill in details in this gross outline of the Cenozoic 

history of the Plateau requires much interpretation, 

and the following effort therefore is a hypothesis.

Figure 53 is a diagrammatic representation of the 

Colorado Plateau area just before Cenozoic time. During Late Cretaceous time the area had been submerged 

beneath the sea. The axis of the Late Cretaceous geosyncline lay east of the Plateau area, but the sea spread 

westward to about the western edge of the Plateau. 

Mountains in western Utah and in southern Arizona 

were the source of the sediments that accumulated on 

the coastal plain and in the sea. By Late Cretaceous 

time the area had become a coastal plain, and the sea 

lay to the east. At this stage, volcanism in the area 

of the Rocky Mountains may have produced volcanic 

islands, but major uplift of the Rockies had not yet 

started.

In early Paleocene time (fig. 54), folding, which had 

started much earlier in western Utah, progressed eastward to the area of the Plateau. The northwestwardtrending Circle Cliffs upwarp was formed, and apparently fully so, because its folded rocks are truncated by 

nearly horizontal Paleocene lake beds (Flagstaff limestone). Formation of a volcanic highland, probably 

accompanied by upwarping, had started in the San 

Juan Mountains in latest Cretaceous time and continued 

to groAv during Paleocene time. This highland shed 

volcanic sediments (Animas formation) on the Colorado Plateau. Pre-Wasatch deposits in the Uinta 

Basin indicate that mountains were forming to the east O

and to the west of the basin, and also at the Uinta 

Mountains. A mountainous area south of the Plateau 

that may be of this age is recorded by the deposits of 

gravel on the Mogollon Rim which were derived from 

pre-Cambrian rocks.

Presumably, other folds within the Plateau also began to form at this time. These include the San Rafael 

Swell, Uncompahgre Plateau, and the Monument, 

Kaibab, Defiance, and Zuni upwarps. As a result of 

Paleocene folding, earlier eastward drainage on the 

Late Cretaceous coastal plain became disintegrated and 

ponded in the basins between the upfolds.

Slightly later, the western part of the Plateau was 

downwarped and became the site of a lake in which 

was deposited the Flagstaff limestone (fig. 55). Presumably, bays of the lake spread eastward in basins 

between the upwarps. The limits of the lake, as shown 

on the diagram (fig. 55), are wholly conjectural except 

in the area of the Uinta Basin, where the lacustrine 

sediments have been found to grade eastward into the
74 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

LATE CRETACEOUS

LATE 

CRETACEOUS

COASTAL PLAIN

FIGURE 53. The Colorado Plateau area in Late Cretaceous time. The area was part of a coastal plain that extended eastward from the foot of 

mountains in central Arizona and central Utah. The edge of the Late Cretaceous Sea was to the east in Colorado.
CENOZOIC HISTORY OF THE PLATEAU A HYPOTHESIS 75

EARLY PALEOCENE

	EXPLANATION

C Circle Cliffs upwarp

D Defiance upwarp

K Kaibab upwarp

M Monument upwarp

SJ San Juan Mountains

SR San Rafael Swell

Da Uinta Mountains

Un Uncompahgre upwarp

Z Zuni upwarp

FIGURE 54. The Colorado Plateau area hi early Puleocune time. The principal folds on the Plateau had begun to form. There were volcanic

mountains and (perhaps) uplifts in the area of the Rocky Mountains.
76 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

LATE PALEOCENE

- "j^^=-'^,:..^.:'

EXPLANATION

Circle Cliffs upwarp 

Defiance upwarp 

Kaibab upwarp 

Monument upwarp 

San Juan Mountains 

San Rafael Swell 

Uinta Mountains 

Uncompahgre upwarp 

Zuni upwarp

FIGURE 55. The Colorado Plateau area in late Paleocene time. The Flagstaff lake was formed along the western edge of the Plateau area.
CENOZOIC HISTORY OF THE PLATEAU A HYPOTHESIS 77

fluviatile Wasatch formation. Presumably, the Arizona 

part of the Plateau drained northward into this lake 

but the New Mexico portion seems to have drained 

southeastward because the Naciraiento formation in the 

San Juan Basin can be attributed to erosion of uplifted 

Upper Cretaceous formations on the south side of the 

San Juan Mountains and on the east side of the Monument, Defiance, and Zuni upwarps. The Nacimiento 

Mountains had not yet been uplifted.

In early and middle Eocene time the downwarping 

of the northern part of the Plateau spread eastward, 

and the huge Green River lake was formed (fig. 56). 

This lake spread far northward into Wyoming and may 

have drained eastward into the area of the Great Plains 

province. The Uinta Mountains may have been completely surrounded, or they may have been a peninsula 

connected by an isthmus with the Rocky Mountains. 

The eastern edge of the lake was at the west foot of the 

Rocky Mountains, in Colorado. The south shore probably was in southeastern "Utah along the north flank of 

the structural, platform that comprises southernmost 

Utah and northern Arizona. Bays probably extended 

southward in the basins between the upfolds. The lake 

also may have spread westward between the early Tertiary mountain ranges in northwestern Utah. The 

catchment area of the Colorado Plateau portion of the 

Green. River lake probably was not very different from 

that of the Flagstaff lake.

At some stage during the early Tertiary, glaciation 

in the San Juan Mountains deposited the Ridgway till. 

Perhaps the Green River lake was maintained in part 

by glacial meltwaters. The paleobotanical and other 

evidence of a mild climate around the shores of the lake 

is not inconsistent with the occurrence of glaciers in 

the mountains if the mountain summits were 10,000 

feet higher than the lake.

The Green River lake came to an end in middle Eocene time, in part perhaps because of uplift; in part 

because of filling. Thereafter, fluviatile sediments 

were deposited in the northern part of the Colorado 

Plateau (fig. 57). In late Eocene time, uplift was renewed at the Uinta Mountains, the San Rafael Swell, 

and on the Douglas Creek anticline (Avhich is a northward extension of the Uncompahgre uplift). To what 

extent the renewed uplift was synchronous with the deposition of the Bridger, Uinta, and Duchesne River formations is not clear, but the Green River formation and 

the earliest of the late Eocene formations were involved 

in this deformation. The Nacimiento upwarp occurred 

at about this time, and presumably there was renewed 

upwarp at some of the other folds too.

Deposition in the Uinta Basin of 5,000 feet of sediments of the Green River formation, and of some addi347620 56 7

tional thousands of feet of later Eocene fluviatile deposits, probably built the surface ol this part of the 

Colorado Plateau higher than that of the Henry Mountains basin and other basins to the south. These basins 

probably became the site of relicts of the Green River 

lake; the fill deposited in them would partly bury the 

adjoining upf olds. By Oligocene time, the basins may 

have become the sites of playas, and perhaps many of 

the uplifts had largely become buried (fig. 58).

The next events in the history of the Plateau are 

wholly conjectural because Oligocene and early Miocene 

deposits have not been recognized on the Plateau, and 

deposits of this age are scarce in the adjoining areas.

During Oligocene time, block faulting had begun in 

the Basin and Range province, and the resulting basins 

could have captured some streams near the edges of the 

Colorado Plateau. The Plateau must have continued 

to receive sediments from the Rocky Mountains, Uinta 

Mountains, and from any remnant highlands that persisted along the southwest and west sides. Parts of 

the southeastern portion no doubt drained into basins 

along the Rio Grande valley, where basin deposits such 

as the late Eocene or Oligocene Galisteo formation were 

deposited.

During early Miocene time, as block faulting progressed in the Basin and Range province, the Colorado 

Plateau probably became well defined as a structural 

unit and reached an altitude distinctly higher than the 

basins, though perhaps not so high as the ranges (fig. 

59). Epeirogenic uplift of the Plateau began at this 

stage, and as the Plateau broke away from and was 

raised higher than the basins to the west, south, and 

southeast, large areas on the Plateau must have begun 

draining to those basins. At this point, aggradation 

on the Plateau ended and degradation began. o o

The superposition of the main streams across the 

large upwarps is presumed to have occurred at about 

this stage in the history of the Plateau. Among these 

superposed streams are the courses of the San Rafael 

and Muddy Rivers across the San Rafael Swell, and 

the course of Unaweep Canyon across the Uncompahgre 

upwarp. Also, at some early stage (presumably about 

this time) there must have been drainage westward 

across the Monument upwarp, no doubt in the form of 

a stream rising on the west or southwest side of the 

San Juan Mountains. Perhaps the Dolores River 

originally flowed southwestward across the Monument 

upwarp. Tributaries to it, eroding headward in the 

strike valleys south of the San Juan Mountains, could 

have captured streams that formerly had taken southerly and southeasterly courses. Some such explanation 

must be found for the San Juan River (fig. 60), which
78 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

1 EARLY AND MIDDLE EOCENE

-^\Tj^\ Ua ;;;>^ wly-,. V-.>>x-d*ii^u..-' v^,^^^

Green River Lake

Circle Cliffs upwarp 

Defiance upwarp 

Kaibab upwarp 

Monument upwarp 

San Juan Mountains 

SR San Rafael Swell 

Ua Uinta Mountains 

Un Uncompahgre upwarp 

Z Zuni upwarp

FIGURE 56. The Colorado Plateau area in early and middle Eocene time. Down warping of the Uinta Basin produced the Green River lake, which 

covered most of the north part of the Plateau area. Most of the uplifts, like the San Kafael Swell, probably stood higher than the lake and 

shed sediments into it.
CENOZOIC HISTORY OF THE PLATEAU A HYPOTHESIS 79

1 LATE EOCENE

c

D

dc

K

M

SJ

SR

Ua

Un

Z

EXPLANATION

Circle Cliffs upwarp 

Defiance upwarp 

Douglas Creek anticline 

Kaibab upwarp 

Monument upwarp 

San Juan Mountains 

San Rafael Swell 

Uinta Mountains 

Uncompahgre upwarp 

Zuni upwarp

FIGURH 57. The Colorado Plateau arta in late Eocene time. Deposition of 5,000 feet of sediments iu Green River lake, and deposition of a few 

thousand feet of fluviatile sediments, probably raised the surface of the Uinta Basin higher than some of the basins farther south on the 

Plateau. The Henry Mountains Basin between the Circle Cliffs and Kaibab uplifts, or the Escalaute basin, may have been the lowest parts 

of the area. The Nacimiento Mountains were raised in middle or late Eocene time.
80 CENOZOIC HISTORY OF THE PLATEAU A HYPOTHESIS

OLIGOCENE

EXPLANATION

Circle Cliffs upwarp 

Defiance upwarp 

Kaibab upwarp 

Monument upwarp 

Nacimiento Mountains 

San Juan Mountains 

San Rafael Swell 

Uinta Mountains 

Uncompahgre upwarp 

Zuni upwarp

58. The Colorado Plateau in Oligocene time. The beginning of block faulting in the Basin and Range province may have developed 

some basins that were lower than the area of the Plateau, and drainage around the edge of the Plateau may have been diverted into the 

basins. Presumably, this occurred although the Plateau area was still in part a trough and was still receiving sediments from the surrounding mountains.
CENOZOIC HISTORY OF THE PLATEAU A HYPOTHESIS 81

EARLY MIOCENE

C

D

K

Ic

M

mr

N

SJ

SR

sr

Ua

uc

Un

Z

EXPLANATION

Circle Cliffs upwarp 

Defiance upwarp 

Kaibab upwarp 

Little Colorado River 

Monument upwarp 

Muddy River 

Nacimiento Mountains 

San Juan Mountains 

San Rafael Swell 

San Rafael River 

Uinta Mountains 

Unaweep Canyon 

Uncompahgre upwarp 

Zuni upwarp

FIGURE 59. The Colorado Plateau in early Miocene time. By early Miocene time, block faulting iu the Basin and Range province had started ;: 

the basins are assumed to have been lower than the Colorado Plateau, but the ranges probably continued to be higher. Considerable move-- 

ment had taken place along the boundary faults, and epeirogenic uplift presumably was started. The Little Colorado River was- in existence- 

(see fig. 60) and presumably drained westward approximately along the present course of the Colorado River. The High Plateaus werebecoming outlined.
82 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

takes a course westward across a high upwarp on the 

Colorado Plateau instead of a southward course across 

the San Juan Basin to the Rio Grande.

The laccolithic intrusions in the interior of the Plateau and the beginning of volcanism in the southern and 

western parts of the Plateau are assigned to middle 

Miocene time (fig. 60). The drainage system gives 

every indication of having shifted monoclinally in adjustment to the laccolithic intrusions, except at Rico 

Dome. The detour made by the Dolores River around 

the La Sal Mountains, the detour of the Dirty Devil 

River around the Henry Mountains, the relation of 

Chinle Creek and San Juan River to the Carrizo Mountains, and the course of the San Juan River along the 

structural trough between the Carrizo and El Late 

Mountains are examples of the Avay the drainage is 

adjusted to the igneous structures. The abrupt northward bend in the Dolores River at the southwest foot of 

the San Juan Mountains may be due to diversion as a 

result of the intrusions at El Late and La Plata 

Mountains.

The La Plata Mountains form part of the divide between the Animas and Dolores Rivers. The San Miguel Mountains form part of the divide between the 

headwaters of the Dolores and San Miguel Rivers. The 

incision of the Dolores River into the dome at Rico 

might be attributed to superposition from one, or more, 

of the series of Miocene volcanic rocks in the San Juan 

Mountains, or from an erosion surface extending southward f rom the San Miguel Mountains, where the intrusions are at much higher elevations.

Clearly, the drainage pattern on the Colorado Plateau bears a very different relation to the igneous structures than it does to the orogenic structures. Therefore, the stream courses may in general be assumed 

to antedate the igneous intrusions.

The Little Colorado River valley was in existence before the eruptions in the San Francisco volcanic district. Formations overlying the Permian had already 

been stripped from that area before the eruptions occurred, and a valley had been eroded between the area 

of volcanism and the cliffs of Jurassic and Upper Cretaceous formations to the northeast. There is no evidence that the Little Colorado River has shifted its 

course more than slightly (in a down-dip direction) 

since the eruptions occurred.

In the Mount Taylor area the eruptions had been 

preceded by northward tilting of the south flank of the 

San Juan Basin, and on this south flank the Tertiary 

formations had been stripped back to a position north 

of the area of eruptions. The San Juan River has not 

drained southward since the eruptions occurred in the

Mount Taylor district; presumably, that drainage already was turned to the west.

There is no obvious reason why igneous activity in 

the interior of the Plateau took the form of intrusive 

stocks and laccoliths, whereas the activity around the 

margins of the Plateau took the form of volcanism. 

Nor is there evident reason why the differentiation sequence at the large, central-type volcanoes progressed 

from acid to basic, whereas the differentiation sequence 

in the intrusive stocks and laccoliths progressed from 

basic to acid. Lastly, there is no evident reason for the 

grossly different ratios of soda and potash in the intrusions and eruptives in different parts of the Plateau.

In the High Plateaus, upwarp accompanied by extensive volcanism and some intrusive activity apparently began during Miocene time, but both upwarp and 

volcanism continued into Quaternary time. There 

could have been some westward drainage across the 

area of the High Plateaus until the upwarps and volcanism began, but we can be sure that there has been 

no significant drainage westward since that time.

Epeirogenic upwarp of the Plateau also is judged to 

have started at about this stage because faulting began 

along the Grand Wash Cliffs, Hurricane Cliffs, and Rio 

Grande depression.

The conditions call for exterior drainage from the 

Colorado Plateau, and there seems to be no possible 

course for the drainage other than the course now followed by the Colorado River. Yet, there is evidence 

that the Colorado River did not discharge into the 

trough west of Grand Wash Cliffs while the Miocene 

and Pliocene (?) formations were being deposited there. 

This raises one of the major, and still unsolved, problems of Cenozoic history the problem of the age of 

the Colorado River.

Blackwelder (1934) and Longwell (1946) have 

pointed out that the Colorado River could not have 

emerged from the foot of Grand Canyon while the 

Muddy Creek formation was being deposited there, because the formation in that area is locally derived and 

contains no Colorado River gravels. They concluded 

that the Grand Canyon stretch of the river must be 

younger than the deposits in Grand Wash trough. This 

problem, therefore, has certain parallels with the problem of the irresistible force and the immovable object. 

The Muddy Creek formation in Grand Wash trough is 

the immovable object; the irresistable force is the evidence upstream that the Colorado River must have discharged through Grand Canyon before late Tertiary 

time. The possibility that the river may once have discharged from the Plateau through the depression at 

Peach Springs (p. 30) does not help solve the main
CENOZOIC HISTORY OF THE PLATEAU A HYPOTHESIS 83 1 MIDDLE MIOCENE

c

Ca

CO

cr

D

dd

do

El

GW

Animas River 

Circle Cliffs upwarp 

Carrizo Mountains 

Colorado River 

Chinle Creek 

Defiance upwarp 

Dirty Devil River 

Dolores River 

El Late Mountain 

Grand'wash Cliffs

EXPLANATION

H Henry Mountains

He Hurricane Cliffs

K Kaibab upwarp

L La Sal Mountains

Ic Little Colorado River

Lp La Plata Mountains

M Monument upwarp

MT Mount Taylor

N Nacimiento Mountains

R Rico Dome

Rd Rio Grande depression

Heavy stippling indicates lava fields

SF San Francisco Mountain

SJ San Juan Mountains

sj San Juan River

SJB San Juan Basin

SM San Miguel Mountains

sm San Miguel River

SR San Rafael Swell

Ua Unita Mountains

Un Uncompahgre upwarp

Z Zuni upwarp

FiOUiti'j CO. The Colorado Plateau in middle Miocene time. The laccolithic mountains Avere formed, and there were eruptions at Mount Taylor, 

San Francisco Mountain, and at the volcanic pile in the central High Plateaus. The main streams were already superimposed on the uplifts, but these streams shifted monoclinically in adjustment to the intrusions. The valley of the Little Colorado River was in about the 

same position and about as deep as it is today. A considerable canyon already had formed in Grand Canyon.
84 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

1

LATE MIOCENE 

TO MIDDLE PLIOCENE

^:v-^'^'V' 

/^fe^VvC^

-'"He""/-- ^vr^r :."-f:|'.=> (-

/^>C -^-j I -"-"_ : k" v^i ":"r"-Y \

^..;r: /GW.-v::- - : * V-J/j:, \

S^>-'? "~ r -* -- "- .-"" -"-S" ";?-"

/ 

** 7 "'^v^^O '^^r 0 "'

EXPLANATION

A Abajo Mountains H

Al Alamosa Fault He

be Book Cliffs K

bg Battlement and Grand Mesas L

C Circle Cliffs upwarp Lp

Ca Carrizo Mountains M

D Defiance upwarp MT

El El Late Mountain N

GW Grand Wash Cliffs R 

FIGURE 61. The Colorado Plateau in late Miocene to middle Pliocene time. Displacement 

cane, Grand Wash, and Alamosa faults. The Plateau rose epeirogenically and became 

ponded and to deposit formations such as the Browns Park and Bidahochi formations 

and Santa Fe formations were deposited in the basins around the edges of the Plateau, 

basalt and alkalic basalt.

Henry Mountains 

Hurricane Cliffs 

Kaibab upwarp 

La Sal Mountains 

La Plata Mountains 

Monument upwarp 

Mount Taylor 

Nacimiento Mountains 

Rico Dome

Heavy stippling indicates lava fields

SF San Francisco Mountain

SJ ' San Juan Mountains

SM San Miguel Mountains

SR San Rafael Swell

Ua Unita Mountains

Ub Unita Basin

Un Uncompahgre upwarp

V Virgin Mountains

Z Zuni upwarp

continued on the boundary faults, such as the Hurritilted northeastward, causing the drainage to become

(stippled area). Formations such the Muddy Creek

At this time, there occurred extensive eruptions of
CENOZOIC HISTORY OF THE PLATEAU A HYPOTHESIS 85

problem, because similar and probably correlative deposits also occur in that depression.

There seems to be only two possible ways that the 

Colorado River could have established its Grand Canyon course in post-Muddy Creek time by capture by 

a stream eroding headward from the Grand Wash 

trough, or by superposition. Neither of these interpretations seems tenable.

Capture by a stream eroding headward from the 

Grand Wash trough requires unusual circumstances. 

The Grand Wash Cliffs north and south from the foot 

of Grand Canyon are straight for many miles, and have 

not been cut deeply by the streams draining westward 

to the basins. It would indeed have been a unique and 

precocious gully that cut headward more than 100 miles 

across the Grand Canyon section to capture streams 

east of the Kaibab upAvarp.

Superposition also seems to be out of the question. 

The southwest rim of the Colorado Plateau was substantially higher than the interior of the Plateau when 

the Bidahochi formation and the fill in Grand Wash 

trough Avere deposited. Thus, the erosion surface, or 

.fill, from Avhich superposition Avould haA^e to occur 

would have been as high as the rim of Grand Canyon 

noAv about 9,000 feet in altitude and of course, this 

surface would have to rise upstream and be still higher 

in Utah and Colorado. HoAvever, at much lower eleA^ations upstream, there are Pliocene or Pliocene(?) deposits, such as the Bidahochi formation, indicating that 

the Pliocene topography of the Plateau Avas not greatly 

different from that of today. The canyons along the 

river may be antecedent, but it is more probable that 

they are the product of anteposition, as suggested in 

figure 61.

During late Miocene to middle Pliocene time (fig. 

61) Avhile formations such as the Muddy Creek and 

Santa Fe were being deposited, the Colorado Plateau 

rose higher 

CJ 

above the basins of the Basin and RangeO

province. As a result of this general uplift, the Plateau Avas tilted northeastAvard. The Grand Canyon 

course of the Colorado River could have formed earlier 

than the deposits in Grand Wash trough if the river 

had become ponded and later anteposed in its old course 

as a result of regional tilting northeastAvard of the 

Plateau.

The BroAvns Park formation, Bidahochi formation, 

and the 1,000 feet of fanglomerate at the nortliAvest foot 

of the La Sal Mountains record a stage or stages of aggradation on the Plateau, Avhich supposedly took place 

at about the same time that the Miocene to Pliocene (?) 

formations were being deposited in Grand Wash trough. 

Deposits such as these may haA^e been a common occurrence in the valleys on the Plateau, as suggested in

figure 61. TAVO thousand feet of differential up warp 

resulting from northeastAvard tilt, could easily have 

caused the aggradation. This amount of tilt, or even 

more, is suggested by the structure-contour map 

(% 37).

The ponding and aggradation, Avhether it occurred 

at one place or at many places, Avould have to haA^e been 

for the duration of Muddy Creek sedimentation in the 

Grand Wash trough. Drainage out of the bed of the 

old canyon would be resumed Avhen the Avater Avas raised 

to that level by ponding and aggradation. The first 

Avaters over the spilhvay could have supplied the lake 

that formed in Grand Wash trough AAThen the Hualpai 

limestone of Long-well Avas deposited. Indeed, because 

the climate of that period Avas not conducive to lake deA^elopment, an outside source like the Colorado River 

seems to be necessary to supply the Avater for this Amst 

lake.

Sediments deposited when the Plateau Avas tilted 

could have produced the younger set of superposed 

drainage features, such as the canyon of the Colorado 

RiA^er across the northwest end of the Uncompahgre 

Plateau, the meanders that Halls Creek has incised into 

the Waterpocket fold on the flank of the Circle Cliffs 

up warp, and the curious manner in which Chinle Creek 

and Chaco River turn out of strike valleys and into 

canyons to join the San Juan River (fig. 62). These 

features could readily be the product of superposition 

from late Tertiary deposits.

Under this interpretation, the late Pliocene to Recent 

history of the Colorado Plateau has Avitnessed no great 

change in the pattern or position of the drainage. The 

canyons have been deepened, but only along existing 

courses. UpAvarping has continued in the High Plateaus. If upAvarping has continued in the rest of the 

Colorado Plateau, the rise has been sloAv enough for the 

Colorado RiA7 er to maintain an antecedent course across 

the Plateau. The maximum of igneous activity on the 

Colorado Plateau occurred when the extensive sheets of 

basalt and andesite Avere erupted onto the southern and 

western rims of the Plateau the rims that overlook the 

Basin and Range province. The greatest volume of 

these eruptions occurred after upAvarpmg Avas Avell 

under way. The last volcanic eruptions occurred Avithin 

the past 1,000 years.

During Pleistocene time the canyons along the main 

stream courses have been deepened. The late Pleistocene history of the canyons has .been an alternation of 

deposition of deep fill in the canyons and erosion of that 

fill; the amount of late Pleistocene canyon cutting in 

the bedrock has not been great, even along headAvater 

courses in the mountains.
86 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

LATE PLIOCENE 

TO RECENT

A

Al

be

BM

C

Ca

ch

CO

cr

D

El

Abajo Mountains

Alamosa fault

Book Cliffs

Black Mesa

Circle Cliffs upwarp

Carrizo Mountains

Chaco River

Colorado River

Chinle Creek

Defiance upwarp

El Late Mountain

GW

H

h

He

K

L

Ic

Lp

M

MT

N

EXPLANATION

Grand Wash Cliffs 

Henry Mountains 

Halls Creek 

Hurricane Cliffs 

Kaibab upwarp 

La Sal Mountains 

Little Colorado River 

La Plata Mountains 

Monument upwarp 

Mount Taylor 

Nacimiento Mountains

Heavy stippling indicates lava fields

R Rico Dome

re Roan Cliffs

SF San Francisco Mountain

SJ San Juan Mountains

sj San Juan River

SJB San Juan Basin

SM San Miguel Mountains

SR San Rafael Swell

Ua Unita Mountains

Un Uncompahgre upwarp

Z Zuni upwarp

FIGURE 62. 'The Colorado Plateau iu late Pliocene to Recent time. The canyons become reoccupied and cut deeper when the ponded water

reaches the level of the uplifted stream beds.
BIBLIOGRAPHY 87

The Recent history of the Plateau has included some 

structural deformation, some volcanism, and a succession of stages of alluviation and arroyo cutting that 

apparently reflect climatic changes. Since about 1880, 

arroyo cutting on the Plateau lias been vigorous. There 

is some evidence that this erosion was hastened by overgrazing, but there is good reason to believe that the 

hastening of erosion is attributable primarily to climatic change another example of history repeating 

itself.

BIBLIOGRAPHY

Abel, Otheuio, and Cook, H. J., 1925, A preliminary study of 

early mum ma Is in a new fauna from Colorado: Colo. Mns. 

Nat. History Proc., v. 5, p. 33-36.

Alien, C. A., 1925, Coal mining in Utah: U. S. Bur. Mines Tech. 

Paper 345.

Alien, .T. E., 1953, Tohatchi formation of Mesaverde group, western San Juan Basin, N. Mex.: Am. Assoc. Petroleum 

Geologists Bull., v. 37, no. 11, p. 2569-2571.

Alien, J. E., and Balk, Robert, 1954, Geology and mineral resources of the Fort Defiance and Tohatchi quadrangles, 

Arizona and New Mexico: N. Mex. Bur. Mines Bull. 36.

American Association for the Advancement of Science, 1922, 

Problems of the Colorado River [Symposium] : Am. Assoc. 

Adv. Sci., Salt Lake City, Utah.

American Association of Petroleum Geologists, 1929, On Pennsylvanian-Perinian stratigraphy of southwestern United States 

[Symposium] : Am. Assoc. Petroleum Geologists Bull., v. 

13, no. 8, p. 883-1033.

Anderson, C. A., 1951, Older pre-Cambrian structure in Arizona : 

Geol. Soc. America Bull., v. 62, p. 1331-1346.

Andrews, D. A., and Hunt, C. B., 1948, Geologic map of eastern 

and southern Utah : U. S. Geol. Survey Prelim. Map 70, Oil 

and Gas Inv. Ser.

Antevs, Ernst, 1938, Post-pluvial climatic variations in the 

Southwest: Meteorol. Soc. Bull., v. 19, p. 190-193.

Atwood, W. W., 1905, The glaciation of San Francisco Mountain, 

Ariz.: Jour. Geology, v. 13, p. 276-279.

 1909, Glaciation of the Uinta and Wasatch Mountains: 

U. S. Geol. Survey Prof. Paper 61.

 1915, Eocene glacial deposits in southwestern Colorado: 

U. S. Geol. Survey Prof. Paper 95, p. 12-26.

 1917, Another locality of Eocene glaciation in southwestern Colorado : Jour. Geology, v. 25, p. 684-686.

Atwood, W. W., and Atwood, W. R., 1926, Gunnison tillite of 

Eocene age: Jour. Geology, v. 34, p. 612-622.

Atwood, W. W., and Atwood, W. W., Jr., 1938, Working hypothesis for the physiographic history of the Rocky Mountain 

region : Geol. Soc. America Bull., v. 49, p. 957-980.

Atwood, W. W., and Mather, K. F., 1932, Physiography and 

Quaternary geology of the San Juan Mountains, Colo.: U. S. 

Geol. Survey Prof. Paper 166.

Axelrod, D. I., 1940, Late Tertiary floras of the Great Basin and 

border areas: Torrey Bot. Club Bull., v. 67, no. 6, p. 477-487.

 1948, Climate and evolution in western North America 

during middle Pliocene time: Evolution, v. 2, no. 2, p. 127- 

144.

 1950, Evolution of desert vegetation in western North 

America: Carnegie Inst. Washington Pub. 590, Contr. 

Paleontology, p. 217-306.

Babenroth, D. L., and Strahler, A. N., 1945, East Kaibab monocline, Arizona and Utah: Geol. Soc. America Bull., v. 56, 

p. 107.

Bailey, R. S., 1935, Epicycles of erosion in the valleys of the 

Colorado Plateaus province: Jour. Geology, v. 43, p. 337-355.

Bailey, R. W., Forsling, C. L., and Becraf t, R. J., 1934, Floods and 

accelerated erosion in northern Utah: U. S. Dept. Agr. 

Misc. Pub. 196.

Baker, A. A., 1933, Geology and oil possibilities of the Moab 

district, Grand and San Juan Counties, Utah: U. S. Geol. 

Survey Bull. 841.

 1935, Geologic structure of southeastern Utah: Am. 

Assoc. Petroleum Geologist Bull., v. 19, p. 1472-1507.

 1936, Geology of the Monument A7 alley-Navajo Mountain 

region, Utah: U. S. Geol. Survey Bull. 865.

 1946, Geology of the Green River desert-Cataract Canyon 

region, Utah: U. S. Geol. Survey Bull. 951.

 1947, Stratigraphy of the Wasatch Mountains in the

vicinity of Provo, Utah: U. S. Geol. Survey Prelim. Chart 

30, Oil and Gas Inv. Ser.

Baker, A. A., Dane, C. H., and Reeside, J. B., Jr., 1933, Paradox 

formation of eastern Utah and western Colorado: Am. 

Assoc. Petroleum Geologists Bull., v. 17, p. 963-980.

 1936, Correlation of the Jurassic formations of Utah,

Arizona, New Mexico, and Colorado: U. S. Geol. Survey

Prof. Paper 183. 

Baker, A. A., Duncan, D. C., and Hunt, C. B., 1952, Manganese

deposits of southeastern Utah: U. S. Geol. Survey Bull.

979-B. 

Baker, A. A., Huddle, J. W., and Kiuney, D. M., 1949, Paleozoic

geology of north and west sides of Uinta Basin, Utah: Am.

Assoc. Petroleum Geologists Bull., v. 33, p. 1161-1197. 

Baker, A. A., and Reeside, J. B., Jr., 1929, Correlation of the

Permian of southern Utah, northern Arizona, northwestern

New Mexico, and southwestern Colorado : Am. Assoc. Petroleum Geologists Bull., v. 13, p. 1413-1448. 

Baker, A. A., and others, 1927, Notes on the stratigraphy of the

Moab region, Utah: Am. Assoc. Petroleum Geologists Bull.,

v. 11, p. 785-808. 

Baker, C. L., 1911, Notes on the later Cenozoic history of the

Mojave Desert region in southeastern California: Calif.

Univ., Dept. Geol. Sci., Bull., v. 6, p. 333-383. 

Bartram,*J. G., 1939, Summary of Rocky Mountain geology : Am.

Assoc. Petroleum Geologists Bull., v. 23, p. 1131-1152. 

Bass, N. W., 1945, Correlation of basal Permian and older rocks

in southwest Colorado, northwest New Mexico, northeast

Arizona, and southeast Utah: U. S. Geol. Survey Prelim.

Chart 7, Oil and Gas Inv. Ser. 

Bauer, C. M., 1916, Stratigraphy of a part of the Chaco River

valley : U. S. Geol. Survey Prof. Paper 98, p. 271-278. 

Beckwith, E. G., 1855, Report of exploration of a route for the

Pacific Railroad near the 38th and 39th parallels of latitude

from the mouth of the Kansas to Sevier River in the Great

Basin: U. S. Congress Documents, 33d Cong., 1st sess., H.

Doc. 129.

 1859, U. S. Pacific Railroad Reports, v. 11: U. S. Congress

Documents, 33d Cong., 2d sess., S. Doc. 78, pt. 11. 

Berry, E. W., 1925, Flora and ecology of so-called Bridger beds

of Wind River Basin, Wyo.: Pan-Am. Geologist, v. 44, p.

357-368. 

Bissell, H. J., 1952, Stratigraphy and structure of northeast

Strawberry Valley quadrangle, Utah : Am. Assoc. Petroleum

Geologists Bull., v. 36, no. 4, p. 575-634.
88 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

Blackwelcler, Eliot, 1909, Cenozoic history of the Laramie region: 

Jour. Geology, v. 17.

 1910, New light on the geology of the Wasatch Mountains, Utah: Geol. Soc. America Bull., v. 21, p. 518-542.

 1915, Post-Cretaceous history of the mountains of central 

western Wyoming: Jour. Geology, v. 23, p. 193-202.

 1934, Origin of the Colorado River: Geol. Soc. America 

Bull., v. 45, p. 551-566.

 1939, Pleistocene mammoths in Utah and vicinity: Am.

Jour. Sci., v. 237, p. 890-894. 

Brady, L. F., 1936, The arroyo of the Rio de Flag, a study of an

erosion cycle : Mus. Northern Arizona Mus. Notes, v. 9, no. 6,

p. 33-37. 

Bradley, W. PI., 1929, The varves and climate of the Green River

epoch: U. S. Geol. Survey Prof. Paper 158-E. /

 1931, Origin and microfossils of the oil shale of the 

Green River formation of Colorado and Utah: U. S. Geol. 

Survey Prof. Paper 168.

 1936, Geoniorphology of the north flank of the Uinta

Mountains: U. S. Geol. Survey Prof. Paper 1S5-I. 

Brandenburg, F. H., 1919, The Colorado River : Monthly Weather

Rev., v. 47, p. 309-311. 

Brown, Barnnm, 1914, Cretaceous-Eocene correlation in New

Mexico, Wyoming, Montana, Alberta: Geol. Soc. America

Bull., v. 25, p. 355. 

Brown, R. W., 1929, Additions to the flora of the Green River

formation: U. S. Geol. Survey Prof. Paper 154 J. 

Bryan, Kirk, 1925, Date of channel trenching (arroyo cutting) in

the arid Southwest: Science, new ser., v. 42, p. 338-344.

 1926, Recent deposits of Chaco Canyon, N. Mex., in relation to the life of the prehistoric peoples of Pueblo Bonito 

[abs.] : Washington Acad. Sci. Jour., v. 16, p. 75-76.

 1927, Channel erosion of Rio Salado, Socorro County, 

N. Mex.: U. S. Geol. Survey Bull. 790.

 1928, Historic evidence on changes in the channel of 

Rio Puerco, a tributary of the Rio Grande in New Mexico: 

Jour. Geology, v. 36, no. 3, p. 265-282.

 1939, Stone cultures near Cerro Pedernal and their 

geological antiquity : Texas Archeol. and Paleont. Soc. Bull., 

v. 11, p. 9-42.

 1940, Erosion in the valleys of the Southwest: N. Mex.

Quart., p. 227-232. 

Bryan, Kirk, and LaRue, E. C., 1927, Persistence of features in an

arid landscape, Navajo Twins, Utah: Geol. Rev., v. 17,

no. 2, p. 251-257. 

Bryan, Kirk, and McCanu, F. T., 1937, The Ceja del Rio Puerco :

Jour. Geology, v. 45, no. 8, and v. 46,1938.

 1943, Sand dunes and alluvium near Grants, N. Mex.: 

Am. Antiquity, v. 8, no. 3.

Bryan, Kirk, and Toulouse, J. H., Jr., 1943, The San Jose nonceramic culture and its relation to a puebloan culture in 

New Mexico : Am. Antiquity, v. 8, no. 3.

Burke, J. J., 1935, Preliminary report on fossil mammals from 

the Green River formation in Utah: Carnegie Mus. Annals, 

v. 25, p. 13-14.

Burma, B. H., and Hardy, C. T., 1953, Pre-North Horn orogeny 

in Gunnisoii Plateau, Utah: Am. Assoc. Petroleum Geologists Bull., v. 37, no. 3, p. 549-553.

Butler, B. S., 1920, The ore deposits of Utah: U. S. Geol. Survey 

Prof. Paper 111.

 1929, Relation of the ore deposits of "the southern Rocky 

Mountain region to the Colorado Plateau: Colo. Sci. Soc. 

Proc., v. 12, p. 23-36.

Cabot, E. C., 1938, Fault border of the Sangre de Cristo Mountains north of Santa Fe, N. Mex.: Jour. Geology, v. 46, 

p. 88-105.

Calkins, F. C., and Butler, B. S., 1943, Geology and ore deposits of 

the Cottonwood-American Fork area, Utah: U. S. Geol. 

Survey Prof. Paper 201.

Callaghan, Eugene, 1938, Preliminary report on the alunite deposits of the Marysvale region, Utah: U. S. Geol. Survey 

Bull. S86-D.

 1939, Volcanic sequence in the Marysvale region in southwest central Utah: Am. Geophys. Union Trans., 20th Ann. 

Mtg., pt. 3, p. 438-452.

Campbell, lan, and Maxson, J. H., 1938, Geological studies of 

the Archean rocks at Grand Canyon, Ariz.: Carnegie Inst. 

Washington Pub., Yearbook, 1937, p. 359-364.

Campbell, M. R,, 1922, Guidebook of the western United States, 

part E., The Denver and Rio Grande Western Route: U. S. 

Geol. Survey Bull. 707.

Cater, F. W., 1955a, Geology of the Gypsum Gap quadrangle,. 

Colorado : U. S. Geol. Survey geol. quadrangle mapGQ 59.

 1955b, Geology of the Paradox quadrangle, Colorado: 

U. S. Geol. Survey geol. quadrangle map GQ 72.

Chancy, R. W., 1940, Tertiary forests and continental history: 

Geol. Soc. America Bull., v. 51, p. 469-488.

 1944, A fossil cactus from the Eocene of Utah : Am. Jour,

Botany, v. 31, p. 507-528. 

Ohaney, R. W., and Elias, M. K., 1936, Late Tertiary floras from

the High Plains: Carnegie Inst. Washington Pub. 476,

p. 1-72. 

Childs, O. "E., 1948, Geoniorphology of the valley of the Little

Colorado River, Ariz.: Geol. Soc. America Bull., v. 59, p. 353.

 1950, Geologic history of the Uinta Basin: Utah Geol. 

and Mineral Survey Guidebook 5, p. 49-59.

Clark, F. R., 1928, Economic geology of the Castlegate, Wellington, and Snnnyside quadrangles, Carbon County, Utah: 

U. S. Geol. Survey Bull. 793.

Colton, H. S., 1937, Some notes on the original condition of the 

Little Colorado River: a sidelight on the problems of 

erosion: Mus. Northern Arizona Mus. Notes, v. 10, no. 6, 

p. 17-20.

 1945, Sunset Crater: Plateau (Mus. of Northern

Arizona), v. 18, no. 1. 

Cook, PI. J., 1926a, A new genus of uintatheres from Colorado:

Colorado Mus. Nat. History Proc., v. 6, no. 2, p. 7-11.

 1926b, New Eocene titanotheres from Moffat County, 

Colo.: Colorado Mus. Nat. History Proc., v. 6, no. 3, p. 12-18.

Cope, E. D., 1875, Report on the geology of that part of northwestern New Mexico examined during the field season of

1874. in U. S. [War Dept.] Chief Engineer's Ann. Rept. for

1875. pt. 2, app. G 1, p. 1008-1017.

 1876, On the geologic age of the vertebrate fauna of the 

Eocene of New Mexico: Am. Jour. Sci., 3d ser., v. 12, p. 

297-298.

 1884, The vertebrata of the Tertiary formations of the

west: U. S. Geol. and Geog. Survey Terr. (Hayden) 3d Ann 

Rept.: 35, 1009 p.

Craig, L. C., and others, 1955, Stratigraphy of the Morrison and 

related formations, Colorado Plateau region, A preliminary 

report: U. S. Geol. Survey Bull. 1009-E.
BIBLIOGRAPHY 89

Cross, Whitman, 18S6, Petrography, in Emmons, S. F., Geology 

and mining industry of Leadville, Colo.: U. S. Geol. Survey 

Mon. 12, p. 359<-362.

 1894, The laccolitic mountain groups of Colorado, Utah, 

and Arizona: U. S. Geol. and Geog. Survey Terr. 14th Ann. 

Kept., pt. 2, p. 152-241.

 190S, Wind erosion in the plateau country: Geol. Soc.

America Bull., v. 19, p. 53-62. 

Cross, Whitman, and Larsen, E. S., 1935, A brief review of

the geology of the San Juan region of southwestern Colorado : U. S. Geol. Survey Bull. 843. 

Cross, Whitman, and Spencer, A. C., 1900, Geology.of the Rico

Mts., Colo.: U. S. Geol. and Geog. Survey Terr. 21st Ann.

Kept, pt. 2, p. 7-165. 

Cuminings, Byron, 1910, The great natural bridges of Utah : Nat.

Geog. Mag., v. 21, p. 157-167. 

Dane,' C. I-L, 1931, Uncompaghre Plateau and related structural

features [abs/l : Washington Acacl. Sci. Jour., v. 21, p. 28.

 1932, Notes on the Puerco and Torrejon formations, San 

Juan Basin, N. Miex.: Washington Acad. Sci. Jour., v. 22, 

p. 406-411.

 1935, Geology of the Salt Valley anticline and adjacent 

areas, Grand County, Utah: U. S. Geol. Survey Bull. 863.

 1936, The La Ventana-Chacra Mesa coal field (San Juan

Basin, N. Hex.) : U. S. Geol. Survey Bull. 860-C.

 1940, Stratigraphic relations of Eocene, Paleocene, and 

latest Cretaceous formations of eastern side of San Juan 

Basin, N. Mex.: U. S. Geol. Survey Oil and Gas Inv. Prelim. 

Chart 24.

 1948, Geologic map of part of eastern San Juan Basin, 

Rio Arriba County, N. Mex.: U. S. Geol. Survey Prelim. Map 

78, Oil and Gas Inv. Ser.

Darton, N. II., 1915, Guidebook of the western. United States, 

part C, The Santa Fe Route: U. S. Geol. Survey Bull. 613.

 1922, Geologic structure of parts of New Mexico: U. S. 

Geol. Survey Bull. 726-E.

 1925, A re'sume' of Arizona geology : Ariz. Univ. Bull. 119, 

Geol. Ser. no. 3.

 1928, "Red Beds" and associated formations in New

Mexico: U. S. Geol. Survey Bull. 794.

Davis, AV. M., 1900, The fresh water Tertiary formations of the 

Rocky Mountain region: Am. Acad. Arts Sci. Proc., v. 35, p. 

345-373.

 1901, An excursion to the Grand Canyon of the Colorado : 

Harvard Coll. Mus. Conip. Zoology Bull., v. 38, p. 107-200.

 1903, An excursion to the Plateau province of Utah and

Arizona: Harvard Coll. Mus. Comp. Zoology Bull., v. 42. 

Denny, C. S., 1940a, Tertiary geology of the San Acacia area, 

New Mexico: Jour. Geology, v. 48, p. 73-106.

 1940b, Santa Fe formation in the Espanola valley, 

N. Mex.: Geol. Soc. America Bull., v. 51, p. 677-694.

v__

Dixon, Helen, 1935, Ecological studies on the High Plateaus of

Utah: Bot. Gazette, v. 97, p. 272-320. 

Dutton, C. E., 1880, Geology of the High Plateaus of Utah: U. S.

Geog. and Geol. Survey Rocky Mtn. Region1 Rept.

 18S2a, The physical geology of the Grand Canyon district : U. S. Geol. and Geog. Survey Terr. 2d Ann. Rept.

 18S2b, The Tertiary history of the Grand Canyon district : U. S. Geol. Survey Mon. 2.

 1885, Mt. Taylor and the Zuni Plateau: U. S. Geol. and 

Geog. Survey Terr. 6th Ann. Rept., p. 165-182.

 1925, On some greater problems of physical geology:

Dyar, W. W., 1904, The colossal bridges of Utah: Century Mag.,

v. 68. 

Eardley, A. J., 1931, A limestone chiefly of algal origin in the

Wasatch conglomerate, southern Wasatch Mountains, Utah:

Michigan Acad. Sci., Arts, and Letters Paper, v. 16, p. 399-

414.

 1949a, Paleotectonic and paleogeographic maps of central 

and western North America: Am. Assoc. Petroleum Geologists Bull., v. 33, p. 655-682.

 1949b, Structural evolution of Utah, in Hansen, G. H.,

Washington Acad. Sci. Jour., v. 15, no. 15, p. 359-369.

and Bell, M. M., The oil and gas possibilities of Utah: Utah 

Geol. and Mineral Survey, p. 10^23.

Eardley, A. J., and Beutner, E. L., 1934, Geomorphology of 

Marysvale Canyon and vicinity, Utah: Utah Acad. Sci. 

Proc., v. 11.

Eckel, E. B., 1937, Mode of igneous intrusion in La Plata Mountains, Colo.: Am. Geophys. Union Trans., pt. 1, p. 258-260.

 1949, Geology and ore deposits of the La Plata district, 

Colorado: U. S. Geol. Survey Prof. Paper 219.

Eldridge, G. H., 1894, Description of the sedimentary formations : U. S. Geol. Survey Geol. Atlas, Anthracite-Crested 

Butte folio, no. 9.

Emery, W. B., 1916, The igneous geology of Carrizo Mountain: 

Am. Jour. Sci., 4th ser., v. 42, p. 349-363.

Einmons, S. F., 1897, The origin of the Green River: Science, 

new ser., v. 6, p. 19-21.

Erdmauu, C. E., 1934, The Book Cliffs coal field in Garfield and 

Mesa Counties, Colo.: U. S. Geol. Survey Bull. 851.

Fenneman, N. M., 1928, Physiographic divisions of the United 

States: Assoc. Am. Geographers Annals, 3d ed., v. 18, no. 4.

 1931, Physiography of western United States : New York,

McGraw-Hill Book Co., p. 274-326. 

Fieldner, A. C., and others, 1925, Analyses of Utah coals: U. S.

Bur. Mines Tech. Paper 345.

Fischel1 , R. P., 1937, Sedimentary deposits of copper, vanadiumuranium, and silver in southwestern United States: Econ.

Geology, v. 32, p. 906-951. 

Fischer, R. P., and Hilpert, L. Si, 1952, Geology of the Uravan

mineral belt: U. S. Geol. Survey Bull. 9S8-A. 

Fisher, D. J., 1936, The Book Cliffs coal field in Emery and

Grand Counties, Utah : U. S. Geol. Survey Bull. 852. 

Flint, R. F., and Denny, C. S., 1956, Pleistocene geology of northeastern Aquarius Plateau, Utah: U. S. Geol. Survey (in

preparation). 

Forrester, J. D., 1937, Structure of the Uinta Mountains: Geol.

Soc. America Bull., v. 48, no. 5, p. 631-666. 

Gale, H. S., 1910, Coal fields of northwestern Colorado and

northeastern Utah: U. S. Geol. Survey Bull. 415. 

Gardner, F. D., and Jensen, C. A., 1901, Soil survey in the Sevier

Valley, Utah: U. S. Dept. Agr. Soil Survey. 

Gardner, J. H., 1910, The Puerco and Torrejou formations of

the Nacimiento group: Jour. Geology, v. IS, p. 702-741. 

Gardner, L. S., 1941, The Hurricane fault in southwestern Utah

and northwestern Arizona: Am. Jour. Sci., v. 239, no. 4,

p. 241-260. 

Gazin, C. L., 193S, A Paleocene mammalian fauna from central

Utah: Washington Acad. Sci. Jour., v. 28, p. 271-277.

 1939, A further contribution to the Dragon Paleocene

fauna of central Utah: Washington Acacl. Sci. Jour., v. 29,

p. 273-286. 

Giclley, J. W., 1922, Preliminary report on fossil vertebrates of

the San Pedro Valley, Ariz.: U. S. Geol. Survey Prof. Paper

131-E.
90 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

Gilbert, G. K., 1875, Report on the geology of portions of Nevada, 

Utah, California, and Arizona: U. S. Geog. and Geol. Surveys W. 100th Mer. Kept. (Wheeler), v. 3, p. 17-187.

 1876, July-August, The Colorado Plateau province as a 

field for geological study: Am. Jour. Sci., 3d ser., p. 16-24, 

85-103.

 1877, Report on the geology of the Henry Mountains: 

U. S. Geog. and Geol. Survey Rock Mtn. Region Rept.

 1878, The Wasatch, a growing mountain: Philos. Soc. 

Washington Bull., v. 2, p. 195.

 1883, Pre-Bonneville climate: Science [2d ser.], v. 2, 

p. 170.

 1928, Studies of Basin-Range structure: U. S. Geol.

Survey Prof. Paper 153.

Gilluly, James, 1927, Analcite diabase and related alkaline 

syenite from Utah: Am. Jour. Sci., 5th ser., v. 14, p. 199-211.

 1929, Geology and oil and gas prospects of part of the 

San Rafael Swell, Utah: U. S. Geol. Survey Bull. 806-C.

 1932, Geology and ore deposits of the Stockton and Fairfield quadrangles, Utah : U. S. Geol. Survey Prof. Paper 173. 

Gilluly, James, and Reeside, J. B., Jr., 1928, Sedimentary rocks

of the San Rafael Swell and some adjacent areas in eastern

Utah: U. S. Geol. Survey Prof. Paper 150-D. 

Gilmore, C. W., 1916, Vertebrate faunas of the Ojo Alamo,

Kirtland, and Fruitland formations: U. S. Geol. Survey

Prof. Paper 98-Q, p. 279-308.

 1946, Reptilian fauna of the North Horn formation of 

central Utah : U. S. Geol. Survey Prof. Paper 210-C.

Gould, H. R., 1955, Chapter on secliinentology, in Smith, W. O., 

Vetter, C. P., Cummings, G. B., and others, Lake Meade 

comprehensive survey, 1948-49: U. S. Geol. Survey (manuscript report in files of U. S. Geol. Survey).

Gould, L. M., 1925, A "laccolite in the air" (La Sal Mountains) : 

Michigan Acad. Sci. Papers, v. 5, p. 253-256.

 1926a, The geology of La Sal Mountains of Utah : Michigan Acad. Sci. Papers, v. 7, p. 55-106.

 1926b, The role of orogenic stresses in laccolithic intrusions : Am. Jour. Sci., 5th ser., v. 12, p. 119-129.

 1939, Glacial geology of Boulder Mountain, Utah: Geol.

Soc. America Bull., v. 50, p. 1371-1380. 

Graham, E. H., 1937, Botanical studies in the Uinta Basin of

Utah and Colorado: Carnegie Mus. Annals, v. 26. 

Granger, Walter, 1914, Lower Eocene of New Mexico and

Wyoming: Am. Mus. Nat. History Bull., v. 33, p. 201-207.

 1917, Notes on Paleocene and lower Eocene mammal 

horizons of northern New Mexico and southern Colorado: 

Am. Mus. Nat. History Bull., v. 37.

Gregory, H. E., 1911, The San Juan oil field: U. S. Geol. Survey 

Bull. 431, p. 11-29.

 1916, The Navajo Country, a geographic and hydrographic reconnaissance of parts of Arizona, New Mexico, 

and Utah: U. S. Geol. Survey Water-Supply Paper 380.

 1917, Geology of the Navajo Country, a reconnaissance of 

parts of Arizona, New Mexico, and Utah : U. S. Geol. Survey 

Prof. Paper 93.

 1933, Colorado Plateau region: Internal. Geol. Gong., 

XVI Sess., Guidebook 18.

 1938, The San Juan country: U. S. Geol. Survey Prof. 

Paper 188.

 1944, Geologic observations in the upper Sevier River 

valley, Utah: Am. Jour. Sci., v. 242, p. 577-606.

 1945, Post-Wasatch Tertiary formations in southwestern

Gregory, H. E., 1949, Geologic and geographic reconnaissance of 

eastern Markagunt Plateau, Utah : Geol. Soc. America Bull., 

v. 60, p. 969-997.

 1950, Geology and geography of the Zion Park region, 

Utah and Arizona: U. S. Geol. Survey Prof. Paper 220.

 1951, The geology and geography of the Paunsaugunt 

region, Utah: U. S. Geol. Survey Prof. Paper 226.

Gregory, H. E., and Moore, R. C., 1931, The Kaiparowitz region, 

a geographic and geologic reconnaissance of parts of Utah 

and Arizona: U. S. Geol. Survey Prof. Paper 164.

Hack, J. T., 1939, The late Quaternary history of several valleys 

of northern Arizona, a preliminary announcement: Mus. 

Northern Arizona Mus. Notes, v. 11, no. 11.

 1941, Dunes of the western Navajo country: Geog. Rev., 

v. 31, p. 240-263.

 1942a, The changing physical environment of the Hopi 

Indians of Arizona: Harvard Univ., Peabody Mus. Archeol. 

and Ethnologic Papers, v. 35, no. 1.

 1942b, Sedimentation and volcauism in the Hopi Buttes,

Ariz.: Geol. Soc. America Bull., v. 53, p. 335-372.

Hager, Dorsey, 1953, Crater Mound (Meteor Crater), Ariz., a 

geologic feature: Am. Assoc. Petroleum Geologists Bull., 

v. 37, p. S21-S57.

Hains, C. F., Van Sickle, D. M., and Peterson, H. V., 1952, 

Sedimentation rates in small reservoirs in the Little Colorado River basin: U. S. Geol. Survey Water-Supply Paper 

1110-D.

Hancock, E. T., 1915, The history of a portion of Yampa River, 

Colo., and its possible bearing on that of Green River: 

U. S. Geol. Survey Prof. Paper 90-K, p. 183-189.

Hancock, E. T., and Eby, J. B., 1930, Geology and coal resources 

of the Meeker quadrangle, Moffat and Rio Blanco Counties, 

Colo.: U. S. Geol. Survey Bull. 812-C.

Hardy, C. T., and Muessig, Siegfried, 1952, Glaciation and drainage changes in the Fish Lake Plateau, Utah: Geol. Soc. 

America Bull., v. 63, p. 1109-1116.

Harrell, M. A., and Eckel, E. B., 1939, Ground-water resources 

of the Hoi brook region, Arizona: U. S. Geol. Survey WaterSupply Paper 836-B.

Harrison, T. S., 1927, Colorado-Utah salt domes: Am. Assoc. 

Petroleum Geologists Bull., v. 11, p. 111-133.

Hayden, F. V., 1877, U. S. Geol. and Geog. Survey Terr. 9th Ann. 

Rept., for the year 1775.

 1881, Geological and geographical atlas of Colorado and

portions of adjacent territory : U. S. Geol. and Geog. Survey

Terr. Sheets 14 and 15. 

Heatou, R. L., 1933, Ancestral Rockies and Mesozoic and late

Paleozoic stratigraphy of the Rocky Mountain region: Am.

Assoc. Petroleum Geologists Bull., v. 17, p. 1-68.

 1937, Stratigraphy versus structure in Rocky Mountain 

region: Am. Assoc. Petroleum Geologists Bull., v. 21, 

p. 1241-1267.

 1950, Late Paleozoic and Mesozoic history of Colorado

Utah: Jour. Geology, v. 53, no. 2, p. 105-115.

and adjacent areas: Am. Assoc. Petroleum Geologists Bull.,

v. 34, p. 1659-1698. 

Henderson, Jnnius, 1913, Geology and topography of the Rio

Grande region in New Mexico: Bur. Am. Ethnology Bull.

54, p. 25-39. 

Hendrickson, B. H., and others, 1925, Soil survey of the Uinta

River valley area, Utah: U. S. Dept. Agr., Bur. Soils. 

Hill, J. M., 1913, Notes on the northern La Sal Mountains,

Grand County, Utah: U. S. Geol. Survey Bull. 530, p. 99-

118.
BIBLIOGRAPHY 91

Hills, R. C., 1895, Types of past eruptions in the Rocky Mountains : Colorado Sci. Soc. Proc., v. 4, p. 14-32.

Hinds, N. E. A., 1936, Uncompahgran and Beltian deposits in 

western North America: Carnegie lust. Washington Pub. 

463, p. 53-136.

Holmes, W. H., 1877, Geological report on the San Juan district: 

U. S. Geol. and Geog. Survey Terr. 9th Ann. Kept., for the 

year 1775, p. 241-276.

 1878, Report on geology of the Sierra Abajo and west San 

Miguel Mountains: U. S. Geol. and Geog. Survey Terr. 

(Hayden) 10th Ann. Rept, p. 189-196.

Howell, E. K, 1875, Report on the geology of portions of Utah, 

Nevada, Arizona, and New Mexico examined in the years 

1872 and 1873 : U. S. Geog. and Geol. Surveys W/lOOth Mer. 

Rept., v. 3, p. 227-301.

Huddle, .1. W., and Dobrovolney, Ernest, 1945, Late Paleozic 

stratigraphy and oil and gas possibilities of central and 

northeastern Arizona: U. S. Geol. Survey Prelim. Chart 10, 

Oil and Gas Inv. Ser.

Huddle, J. W., and McCann, F. T., 1947, Geologic map of 

Duchesne River area, Wasatch and Duchesne Counties, 

Utali: U. S. Geol. Survey Prelim. Map 75, Oil and Gas 

Inv. Ser.

Huddle, .T. W., Mapel, W. J., and McCann, F. T., 1951, Geology 

of the Moon Lake area, Duchesne County, Utah: U. S. 

Geol. Survey Map OM 115, Oil and Gas Inv. Ser.

Hunt, C. B., 1934, Tertiary structural history of parts of northwestern New Mexico: Washington Acad. Sci. Jour., v. 24, 

p. 188-189.

 1936, The Mount Taylor coal field: U. S. Geol. Survey 

Bull. S60-B, p. 31-80.

 193Sa, A suggested explanation of the curvature of columnar joints in volcanic necks: Am. Jour. Sci., 5th ser., 

v. 36, p. 142-149.

 193Sb, Igneous geology and structure of the Mount 

Taylor volcanic field, N. Mex.: U. S. Geol. Survey Prof. 

Paper 1S9-B, p. 51-79.

 1942, New interpretation of some laccolithic mountains 

and its possible bearing on structural traps for oil and gas : 

Am. Assoc. Petroleum Geologists Bull., v. 26.

 1946, Guidebook to the geology and geography of the 

Henry Mountains region: Utah Geol. Soc. Guidebook 1.

 1953a, Pleistocene-Recent boundary in the Rocky Mountain region: U. S. Geol. Survey Bull. 996-A.

 19531), Geology and geography of the Henry Mountains

region, Utah : U. S. Geol. Survey Prof. Paper 228.

Hunt, C. B., and Dane, C. H., 1954, Map showing geologic structure of the southern part of the San Juan Basin, N. Mex.: 

U. S. Geol. Survey Map 158, Oil and Gas Inv. Ser.

Hunt, C. B., and Sokoloff, V. P., 1950, Pre-Wisconsin soil in the 

Rocky Mountain region, a progress report: U. S. Geol. Survey Prof. Paper 221-G.

Hunt, C. B., Thomas, H. E., and Varnes, H. D., 1953, Lake 

Bonneville Geology of northern Utah Valley, Utah: U. S. 

Geol. Survey Prof. Paper 257-A.

Hunt, C. B., and Waters, A. C., 1956, Igneous geology and 

structure of the La Sal Mountains, Utah: U. S. Geol. 

Survey Prof. Paper (in preparation).

Hunter, J. F., 1925, Pre-Cambrian rocks of Gunnison River, 

Colo.: U. S. Geol. Survey Bull. 777.

Huntington, Ellsworth, and Goldthwait, J. W., 1904, The Hurricane fault in the Toquerville district, Utah: Harvard Coll. 

Mus. Comp. Zoology Bull., v. 6, p. 1-208.

Jefferson, M. S. W., 1897, The antecedent Colorado River; 

Science, new ser., v. 6, p. 293-295.

 1902, Limiting width of meander belts: Nat. Geog. Mag.,

v. 13, p. 373-383. 

Johannsen, Albert, 1914, Petrographic analyses of the Bridger,

Washakie, and other Eocene formations of the Rocky

Mountains: Am. Mus. Nat. History Bull., v. 33, p. 209-222. 

Johnson, D. W., 1907, Volcanic necks of Mount Taylor region:

Geol. Soc. America Bull., v. 18, p. 303-324.

 1909, A geological excursion in the Grand Canyon district : Boston Soc. Nat. History Proc., v. 34, p. 135-161.

Johnson, J. H., 1929, Contributions to the geology of the Sangre 

de Cristo Mountains of Colorado : Colo. Sci. Soc. Proc., v. 12, 

p. 3-21.

Jones, M. E., 1910, The origin and distribution of the flora 

of the Great Plateau: Western Botany, Contr., no. 13, p. 

46-68.

Kay, J. L., 1934, Tertiary formations of the Uinta Basin, Utah: 

Carnegie Mus. Annals, v. 23, p. 357-372.

Kelley, V. C., 1950, Regional structure of the San Juan Basin: 

N. Mex. Geol. Soc. Guidebook of San Juan Basin, N. Mex. 

and Colo., p. 101-108.

 1951, Tectonics of the San Juan Basin : N. Mex. Geol. Soc. 

Guidebook of the south and west sides of San Juan Basin, 

N. Mex. and Ariz., p. 124-131.

 1955, Regional tectonics of the Colorado Plateau and relationship to the origin and distribution of uranium: N.

Mex. Univ. Pub. Geology; Meteoritics, no. 5. 

Kelley, V. C., and Wood, G. H., 1946, Lucero uplift, Valencia,

Socorro, and Bernalillo Counties, N. Mex.: U. S. Geol.

Survey Oil and Gas Inv. Prelim. Map 47. 

Kiucer, J. B., 1919, The seasonal distribution of precipitation:

Monthly Weather Rev., 47, p. 624-631. 

King, Clarence, 1870, The Green River coal basin, Utah: U. S.

Geol. Expl. 40th Par. Rept., v. 3, p. 451-473. 

Kinney, D. M., 1951, Geology of the Uinta River and Brush

Creek-Diamond Mountain areas, Duchesne and Uintah

Counties, Utah: U. S. Geol. Survey Map OM 123, Oil and

Gas Inv. Ser.

Kinney, D. M., and Rominger, J. F., 1947, Geology of the Whiterocks River-Ashley Creek area, Uintah County, Utah : U. S.

Geol. Survey Prelim. Map 82, Oil and Gas Inv. Ser. 

Knowlton, F. H., 1914, Cretaceous-Tertiary boundary in the

Rocky Mountain region; Geol. Soc. America Bull., v. 25,

325 p.

 1916, Flora of the Fruitland and Kirtland formations: 

U. S. Geol. Survey Prof. Paper 9S-S, p. 327-354.

 1930, The flora of the Denver and associated formations 

of Colorado : U. S. Geol. Survey Prof. Paper 155.

Koons, E. D., 1945, Geology of the Uinkaret Plateau, northern 

Arizona: Geol. Soc. America Bull., v. 56, p. 151-180.

LaRue, E. C., 1916, Colorado River and its utilization: U. S. 

Geol. Survey Water-Supply Paper 395.

 1925, Water power and flood control of Colorado River

below Green River, Utah: U. S. Geol. Survey Water-Supply

Paper 556. 

Lasky, S. G., and Weber, B. N., 1949, Manganese resources of the

Artillery Mountains region, Mohave County, Ariz.: U. S.

Geol. Survey Bull. 961. 

Lee, W. T., 1907, The Iron County coal field, Utah: U. S. Geol.

Survey Bull. 316, p. 359-375.

 1912a, Coal fields of Grand Mesa and West Elk Mountains : U. S. Geol. Survey Bull. 510.
92 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

Lee, W. T., 1912b, Stratigraphy of the coal fields of northern 

central New Mexico: Geol. Soc. America Bull., v. 23.

 1918, Early Mesozoic physiography of the southern Rocky 

Mountains: Smithsonian Misc. Coll., v. 69, no. 4.

Leopold, L. B., and Snycler, C. T., 1951, Alluvial fills near Gallup, 

N. Mex.: U. S. Geol. Survey Water-Supply Paper 1110-A.

Lindgren, Waldemar, 1915, The igneous geology, of the Cordilleras and its problem, in Problems of American geology: 

New Haven, Conn., Yale Univ. Press, p. 246.

Lindgren, Waldemar, Graton, L. C., and Gordon, C. H., 1910, The 

ore deposits of Newi Mexico: U. S. Geol. Survey Prof. 

Paper 68.

Longwell, C. R., 1925, The Pre-Triassic unconformity in southern Nevada: Am. Jour. Sci., 5th ser., v. 10, p. 93-106.

 1936, Geology of the Boulder Reservoir floor, ArizonaNevada : Geol. Soc. America Bull., v. 47, p. 1393-1476.

 1946, How old is the Colorado River?: Am. Jour. Sci.,

v. 244, p. 817-835. 

Long-well, C. R., Miser, H. D., Moore, R. C., and others, 1923,

Rock formations in the Colorado Plateau of southeastern

Utah and northern Arizona: U. S. Geol. Survey Prof. Paper

132-A. 

Looniis, F. P>., 1907, Origin of the Wasatch deposits: Am. Jour.

Sci., 4th ser., v. 23, p. 356-364. 

Loughlin, G. F., and Koschmann, A. H., 1942, Geology and ore

deposits of the Magdalena mining district, New Mexico:

U. S. Geol. Survey Prof. Paper 200, 168 p. [1943]. 

Lovering, T. S., 1932, Geology of Colorado : Internat. Geol. Gong.

Guidebook 19, p. 8-26. 

Luptou, C. T., 1912, Notes on the geology of the San Rafael

Swell, Utah: Washington Acad. Sci. Jour., v. 2, p. 185-188.

 1916, Geology and coal resources of Castle Valley, in 

Carbon, Emery and Sevier Counties, Utah: U. S. Geol. Survey Bull. 628.

McCann, F. T., 1938, Ancient erosion surface in the Gallup-Zuni 

area, New Mexico: Am. Jour. Sci., 5th ser., v. 36, p. 260^278.

McGregor, J. C., 1936, Dating the eruption of Sunset Crater, 

Ariz.: Am. Antiquity, v. 2, no. 1, p. 15-26.

McKee, E. D., and Schenk, E. T., 1942, The lower canyon lavas 

and related features at Toroweap, Grand Canyon: Jour. 

Geomorphology, v. 5, p. 245-273.

 1951, Sedimentary basins of Arizona and adjoining

areas: Geol. Soc. America Bull., v. 62, p. 481-506. 

McKnight, E. T., 1940, Geology of area between Green and

Colorado Rivers, Grand and San Juan Counties, Utah:

U. S. Geol. Survey Bull. 908. 

Marsell, R. E., 1949, The Quaternary system in Utah, in Hanseu,

G. H., and Bell, M. M., The oil and gas possibilities of Utah :

Utah Geol. and Mineral Survey, p. 109-118. 

Martin, W. P., and Fletcher, J. E., 1943, Vertical zonation of

great soil groups on Mount Graham, Ariz., as correlated with

climate, vegetation, and profile characteristics: Ariz. Univ.

Agr. Expt. Sta. Tech. Bull. 99. 

Matthew, W. D., 1909, Faunal lists of the Tertiary mammalia of

the West, in Osborn, H. F., Cenozoic mammal horizons of

western North America: U. S. Geol. Survey Bull. 361,

p. 92-95.

 1914, Evidence of the Paleocene vertebrate fauna on the 

Cretaceous-Tertiary problem: Geol. Soc. America Bull., 

v. 25, 381 p.

 1915a, The Tertiary sedimentary record and its problems, 

in Problems of American geology: New Haven, Conn., Yale 

University Press, p. 377-478.

Matthew, W. D., 1915b, A revision of the lower Eocene Wasatch 

and Wind River faunas part IV, Ehtelonychia, Primates, 

Insectivora (part) : Am. Mus. Nat. History Bull., v. 34, 

p. 429-483.

 1921, Fossil vertebrates and the Cretaceous-Tertiary 

problem: Am. Jour. Sci., 5th ser., v. 2.

1937, Paleocene faunas of the San Juan Basin, N. Mex.:

Am. Philos. Soc. Trans., new ser., v. 30, p. 8, 510. 

Matthew, W. D., and Granger, Walter, 1921, New genera of

Paleocene mammals: Am. Mus. Novitates, no. 13, p. 51-62. 

Maxey, G. B., 1946, Geology of part of the Pavaut Range, Millard

County, Utah: Am. Jour. Sci., v. 244, p. 324-356. 

Maxon, J. H., 1950, Lava flows in the Grand Canyon of the

Colorado River, Ariz.: Geol. Soc. America Bull., v. 61,

p. 9-16. 

Meek, F. B., 1S70, List of fossils from Utah with some notes:

U. S. Geol. Expl. 40th Par. Rept., v. 3, p. 459^66. 

Melton, F. A., 1925a, The ancestral Rocky Mountains of Colorado and New Mexico: Jour. Geology, v. 33, no. 1, p. 84-89.

 1925b, Correlation of Permo-Carboniferous red beds in

southwestern Colorado and northern New Mexico: Jour.

Geology, v. 33, no. 8, p. 807-815. 

Merriam, J. C., 1918, Evidence of mammalian paleontology

relating to the age of Lake Lahontan: Calif. Univ., Dept.

Geol. Sci., Bull., v. 10, p. 517-521. 

Miser, H. D., 1924a, The San Juan Canyon, southeastern Utah,

a geographic and hydrographic reconnaissance: U. S. Geol.

Survey Water-Supply Paper 538.

 1924b, Geologic structure of San Juan Canyon and adjacent country, Utah : U. S. Geol. Survey Bull. 751.

 1925, Erosion in San Juan Canyon, Utah: Geol. Soc. 

America Bull., v. 36, p. 365-378.

 1927, Shapes of stream pebbles in San Juan Canyon,

Utah [abs.] : AVashington Acad. Sci. Jour., v. 17, p. 270-271. 

Miser, H. D., Trimble, K. W., and Paige, Sidney, 1923, The

Rainbow Bridge, Utah: Geog. Rev., v. 13, p. 518-531. 

Montgomery, Arthur, 1953, Pre-Cambrian geology of the Picuris

Range, north-central New Mexico: N. Mex. Bur. Mines

Bull. 30. 

Moore, R. C., 1923a, Structural features of the Colorado Plateau

and their origin: Geol. Soc. America Bull., v. 34, p. 88.

 1923b, Physiography of the Paria River valley, southern 

Utah: Geol. Soc. America Bull., v. 34, p. 94.

 1925, Geologic report on the inner gorge of the Grand 

Canyon of the Colorado River: U. S. Geol. Survey WaterSupply Paper 556, p. 125-171.

 1926a, Origin of enclosed meanders on streams of the 

Colorado Plateau: Jour. Geology, v. 34, p. 29-57.

 1926b, Significance of enclosed meanders in the physiographic history of the Colorado Plateau country: Jour.

Geology, v. 34, p. 97-130. 

Nace, R. L., 1936, Summary of the late Cretaceous and early

Tertiary stratigraphy of Wyoming: Wyo. Geol. Survey Bull.

26, p. I-VI, 1-271. 

Newberry, J. S., 1876, Report of the exploring expedition from

Santa Fe, N. Mex., to the junction of the Grand and Green

Rivers of the Great Colorado of the West in 1859: Engineer

Dept., U. S. Army. 

Nichols, R. L., 1946, McCartys basalt flow. Valencia County,

N. Mex.: Geol. Soc. America Bull., v. 57, p. 1049. 

Noble, L. F., 1914, The Shinumo quadrangle, Grand Canyon

district, Arizona: U. S. Geol. Survey Bull. 549. 

Noble, L. F., and Hunter, J. F., 1917, A reconnaissance of the

Archean complex of the Granite Gorge, Grand Canyon,

Ariz.: U. S. Geol. Survey Prof. Paper 98, p. 95-113.
BIBLIOGRAPHY 93

Nolan, T. B., 1943, The Basin and Range province in Utah,

Nevada, and California: U. S. Geol. Survey Prof. Paper

197-D. 

Osborn, H. F., 1929, The Titanotheres of ancient Wyoming,

Dakota, and Nebraska: U. S. Geol. Survey Mon. 55. 

Osborn, H. F., and Matthew, W. D., 1909, Cenozoic mammal

horizons of western North America, with faunal lists of

Tertiary mammalia of the West: U. S. Geol. Survey Bull.

361, p. 1-138. 

Pack, F. J., 1919, Wonders of Utah geology: Utah Univ. Bull.,

v. 10, no. 12. 

 1922a, Natural bridging in the High Plateaus: Pan-Am.

Geologist, v. 37, p. 213-225. 

 1922b, Outstanding geological features of Colorado River

basin: Pan-Am. Geologist, v. 38, p. 289-298. 

Parsons, T. S., 1907, Some unknown American natural bridges:

Mineral Collector, v. 14, p. 103-104. 

Pattersou, Bryan, 1939, New Pantodonta and Diuocerata from

the upper Paleoceue of western Colorado: Field Mus. Nat.

History Pub., Geol. ser., v. 6, no. 24, p. 351-384. 

Peale, A. C., 1877a, On a peculiar type of eruptive mountain in

Colorado: U. S. Geol. and Geog. Survey Terr. Bull., no. 3,

p. 550-564.

 1877b, Geological report on the Grand River district: 

U. S. Geol. and Geog. Survey Terr. 9th Ann. Rept.

 1878, Geological report on the Grand River district, embracing Colorado and parts of adjacent territories: U. S. 

Geol. and Geog. Survey Terr. 10th Ann. Rept., p. 163-182.

 1879, Report on the geology of the Green River district:

U. S. Geol. and Geog. Survey Terr. (1877) llth Ann. Rept., 

p. 511-646.

Peterson, O. A., 1924, Discovery of fossil mammals in the Browns 

Park formation of Moffat County, Colo.: Carnegie Mus. 

Annals, v. 15, nos. 2 and 3.

 1928, The Browns Park formation: Carnegie Mus. Mem.,

v. 11, no. 2. 

Pierce, R. C., 1917, The measurement of silt-laden streams:

U. S. Geol. Survey Water-Supply Paper 400, p. 39-52. 

Pike, W. S., Jr., 1947, Intertonguing marine and nonmarine

Upper Cretaceous deposits of New Mexico, Arizona, and

southwest Colorado: Geol. Soc. America Mem. 24. 

Powell, J. W., 1872, Survey of the Colorado River of the West:

U. S. Congress Documents, 42d Cong., 2d sess., H. Misc.

Doc. 173.

 1873a, Geological structure of the country north of the 

Grand Canyon of the Colorado : Am. Jour. Sci., 3d ser., v. 5, 

p. 456-465.

 1873b, Report of the survey of the Colorado River of the 

West: U. S. Congress Documents, 42d Cong., 3d sess., H. 

Misc. Doc. 76.

 1874a, Remarks on the structural geology of the valley of 

the Colorado of the West: Philos. Soc. Washington, Bull. 1, 

p. 48-51.

 1874b, Report of explorations in 1873 of the Colorado of the West and its tributaries: U. S. Congress Documents, 43d Cong., 1st sess., H. Misc. Doc. 265.

 1875a, Exploration of the Colorado River of the West and 

its tributaries : Smithsoniau Inst. Ann. Rept.

 1875b, Physical features of the Colorado valley: Pop. Sci. 

Monthly, v. 7, p. 385-399, 531-542, 670-680.

Powell, J. W., 1876, Report on the geology of the eastern portion 

of the Uinta Mountains and a region adjacent thereto: U. S. 

Geol. and Geog. Survey Terr., 2d div.

 1879, Report on the lands of the arid regions of the 

United States, with a more detailed account of the lands of 

Utah: U. S. Congress Documents, 45th Cong., 2d sess., H. 

Ex. Doc. 73, 179 p.

 1895, Canyons of the Colorado: Meadville, Pa., Flood

and Vincent. 

Prommel, H. W. C., 1927, Salt domes, fractures and test wells in

southeast Utah: Oil Weekly, v. 45, p. 691-745. 

Prommel, H. W. C., and Crum, H. E., 1927a, Structural history

of parts of southeastern Utah from interpretation of

geologic sections: Am. Assoc. Petroleum Geologists Bull.,

v. 11, p. 809-820.

 1927b, Salt domes of Permian and Pennsylvanian age in 

southeastern Utah and their influence on oil accumulation: 

Am. Assoc. Petroleum Geologists Bull., v. 11, p. 373-393.

Putnam, W. C., 1942, Geomorphology of the Ventura region, 

California: Geol. Soc. America Bull., v. 53, p. 691-754.'

Rausome, F. L., 1915, The Tertiary orogeny of the North American Cordillera and its problems, in Problems of American 

geology: New Haven, Conn., Yale Univ. Press, p. 287.

Reagan, A. B., 1932, The Tertiary-Pleistocene of the Navajo 

Country: Kansas Acad. Sci. Trans., v. 35.

Reeside, J. B., Jr., 1923, Notes on the geology of Green River 

valley between Green River, Wyo., and Green River, Utah: 

U. S. Geol. Survey Prof. Paper 132, p. 35-50.

 1924, Upper Cretaceous and Tertiary formations of the 

western part of the San Juan Basin: U. S. Geol. Survey 

Prof. Paper 134.

 1944, Maps showing thickness and general character of

the Cretaceous deposits in the western interior of the 

United States: U. S. Geol. Survey Prelim. Map 10, Oil and 

Gas Inv. Ser.

Reiciiel, Eberhard, 1928, Der wasserhaushalt des Coloradogebietes ini siidwestlichen Nordamerika: Geog. Abh., 2 

reihe, heft 4, p. 1-74. With supplement: Leiter, M. M., 

Untersuchungen liber die denudation dieses gebietes.

Reuick, B. C., 1931, Geology and ground-water resources of 

western Sancloval County, N. Mex.: U. S. Geol. Survey 

Water-Supply Paper 620.

Rich, J. L., 1910, The physiography of the Bishop conglomerate, 

southwestern Wyoming: Jour. Geology, v. 18.

 1935, Origin and evolution of rock fans and pediments:

Geol. Soc. America Bull., v. 46, p. 999-1024. 

Richardson, G. B., 1906, Coal in Sanpete County, Utah: U. S.

Geol. Survey Bull. 285, p. 280-284.

 1907a, The Book Cliffs coal field : U. S. Geol. Survey Bull. 

316, p. 302-320.

 I907b, Underground water in Saupete and central Sevier 

valleys, Utah: U. S. Geol. Survey Water-Supply Paper 199.

 1909a, Reconnaissance of the Book Cliffs coal field, between Grand River, Colo., and Sunnyside, Utah: U. S. Geol. 

Survey Bull. 371.

 I909b, The Harmony, Colob, and Kanab coal fields, southern Utah: U. S. Geol. Survey Bull. 341, p. 379^00.

 1927, The Upper Cretaceous section in the Colob Plateau,

southwest Utah: AVashington Acad. Sci. Jour., v. 17, no. IS, 

p. 464-475.

Richmond, G. M., 1956, Pleistocene and Recent geology of La Sal 

Mountains, Utah, U. S. Geol. Survey (in preparation).
94 CENOZOIC GEOLOGY OF THE COLORADO PLATEAU

Robinson, H. H., 1907, The Tertiary peneplain of the plateau 

district and all adjacent country in Arizona and New 

Mexico: Am. Jour. Sci., 4th ser., v. 24, p. 109-129.

 1910, A new erosion cycle in the Grand Canyon district: 

Jour. Geology, v. IS, p. 742-763.

 1911, The single cycle development of the Grand Canyon 

of the Colorado: Science, new ser., v. 34, p. 89-91.

 1913, The San Franciscan volcanic field, Ariz.: U. S.

Geol. Survey Prof. Paper 76, p. 74-85. 

Rocky Mountain Association of Geologists, and others, 1951,

Possible future petroleum provinces of North America:

Am. Assoc. Petroleum Geologists Bull., v. 35, no. 2. p. 274-

315. 

Romer, A. S., 1933, Pleistocene vertebrates and their bearing

on the problem of human antiquity in North America, in

Jenness, Diamond, The American aborigines: Toronto,

Univ. Toronto Press, p. 49-83. 

Ross, C. S., 1926, A Colorado lamprophyre of the verite type:

Am. Jour. Sci., 5th ser., v. 12, p. 217-229. 

Schrader, F. C., 1909, Mineral deposits of the Cerbat Range,

Black Mountains, and Grand Wash Cliffs, Mohave County,

Ariz.: U. S. Geol. Survey Bull. 397. 

Schultz, A. R., 1920, A geological reconnaissance of the TJinta

Mountains, northern Utah, with special reference to phosphate : U. S. Geol. Survey Bull. 702. 

Scott, W. B., 1937, A history of land mammals in the AArestern

Hemisphere, 2d ed.: New York, Macmillan Co., p. xiv, 786. 

Sears, J. D., 1924a, Relations of the Browns Park formation and

the Bishop conglomerate and their role in the origin of

Green and Yampa Rivers: Geol. Soc. America Bull., v. 35,

p. 279-304.

 1924b, Geology and oil and gas prospects of part of 

Moffat County, Colo., and southern Sweetwater County, 

Wyo.: U. S. Geol. Survey Bull. 751-G, p. 269-319.

 -- 1925, Geology and coal resources of the Gallup-Zuni 

Basin, N. Mex.: U. S. Geol. Survey Bull. 767.

 1934, The coal field from. Gallup eastward toward Mount

Taylor (San Juan Basin) : U. S. Geol. Survey Bull. 860.

Sears, J. D., and Bradley, W..H., 1924, Relations of the Wasatch 

and Green River formations in northwestern Colorado and 

southern Wyoming with notes on oil shale in the Green 

River formation: U. S. Geol. Survey Prof. Paper 132-F, 

p. 93-107.

Sears, J. D., Hunt, C. B., and Hendricks, T. A., 1941, Transgress Lve and regressive Cretaceous deposits in southern 

San Juan Basin, N. Mex.: U. S. Geol. Survey Prof. Paper 

193-F.

Shantz, H. L., and Zon, Raphael, 1924, Natural vegetation : Atlas 

Am. Agriculture, part 1, sec. E.

Sharp, R. P., 1942, Multiple Pleistocene glaciation on San Francisco Mountain, Ariz.: Jour. Geology, v. 50, p. 481-503.

Shenon, P. J., 1935, Utah earthquake of March 24, 1934 [abs.] : 

Washington Acad. Sci. Jour., v. 23, p. 508-509.

Shoemaker, E. M., 1956, Geology of the Roc Creek quadrangle, 

Colorado: U. S. Geol. Survey geol. quadrangle map (in 

preparation).

Silver, Caswell, 1950, The occurrence of gas in the Cretaceous 

rocks of the San Juan Basin: N. Mex. Geol. Soc. Guidebook 

of the San Juan Basin, N. Mex. and Colo., p. 109-123.

 1951, Cretaceous stratigraphy of the San Juan Basin: 

N. Mex. Geol. Soc. Guidebook of the south and west sides 

of the San Juan Basin, N. Mex. and Ariz., p. 104-118.

Simpson, G. G., 1933, Glossary and correlation charts of North 

American Tertiary mammal-bearing formations : Am. Mus. 

Nat. History Bull., v. 67, p. 79-121.

Simpson, G. G., 1935, The Tiffany fauna., upper Paleocene: Am. 

Mus. Novitates 795, p. 1-19 ; 816, p. 1-30; and 817, p. 1-28.

 1948, The Eocene of the San Juan Basin, N. Mex.: Part 1,

Am. Jour. Sci., v. 246, no. 5, p. 257-282; Part 2, no. 6, p. 363-

385. 

Sinclair, W. J., and Granger, Walter, 1914, Paleocene deposits of

the San Juan Basin, N. Mex.: Am. Mus. Nat. History Bull.,

v. 33, p. 297-316.

Smith, H. T. U., 1938, Tertiary geology of the Abiquiu quadrangle, New Mexico: Jour. Geology, v. 46, p. 933-985. 

Smith, J. H., 1900, The Eocene of North America west of the

100th meridian (Greenwich) : Jour. Geology, v. 8, p. 444-

471. 

Smith, W. O., Vetter, C. P., Cummings, G. B., and others, 1955,

Lake Mead comprehensive survey, 1948-49: U. S. Geol.

Survey (manuscript report in .files of U. S. Geol. Survey). 

Spieker, E. M., 1931, The Wasatch Plateau coal field, Utah:

U. S. Geol. Survey Bull. 819.

 1946, Late Mesozoic and early Cenozoic history of central 

Utah: U. S. Geol. Survey Prof. Paper 205-D, p. 117-161.

 1949, The transition between the Colorado Plateau and

the Great Basin in central Utah: Utah Geol. Soc., Guidebook to the Geology of Utah, no. 4.

Spieker, E. M., and Baker, A. A., 1928, Geology and coal resources of the Saliua Canyon district, Sevier County, Utah: 

U. S. Geol. Survey Bull. 796-C, p. 125-170.

Spieker, E. M., and Billings, M. P., 1940, Glaciatiou in the Wasatch Plateau, Utah : Geol. Soc. America Bull., v. 51, p. 1173- 

1198.

Spieker, E. M., and Reeside, J. B., Jr., 1925, Cretaceous and 

Tertiary formations of the-Wasatch Plateau, Utah (with 

discussion by Charles Schuchert) : Geol. Soc. America Bull., 

v. 36, no. 3, p. 435-454.

 1926, Upper Cretaceous shoreline in Utah : Geol. Soc.

America Bull., v. 37, p. 429-438. 

Stagner, W. L., 1941, The paleogeography of the eastern part of

the Uinta Basin during Uinta B (Eocene) time: Carnegie

Mus. Annals, v. 28, p. 273-308. 

Stauton, T. W., 1914, Boundary between the Cretaceous and

Tertiary as indicated by stratigraphy and invertebrate

faunas: Geol. Soc. America Bull., v. 25, p. 341. 

Stearns, C. E., 1943, The Galisteo formation of north-central

New Mexico: Jour. Geology, v. 51, no. 5.

 1953, Tertiary geology of the Galisteo-Tongue area, 

New Mexico: Geol. Soc. America Bull., v. 64, p. 459-508.

Stock, Chester, 1921, Later Cenozoic mammalian remains from 

the Meadow Valley region, southeastern Nevada : Am. Jour. 

Sci., 5th ser., v. 2, p. 250-264.

Stokes, W. L., and Hansen, G. H., 1937, Two Pleistocene muskoxen from Utah: Utah Acad. Sci. Proc., v. 14, p. 63-65.

Stoyanow, A. A., 1942, Paleozoic paleogeography of Arizona: 

Geol. Soc. America Bull., v. 53, p. 1255-1282.

Strahler, A. N., 1948, Geomorphology and structure of the west 

Kaibab fault zone and Kaibab Plateau, Ariz.: Geol. Soc. 

America Bull., v. 59, p. 513-540.

Strahorn, A. T., and others, 1924, Soil survey of the Ashley 

valley, Utah: U. S. Dept. Agr., Bur. Soils.

Thomas, C. R., McCann, F. T., and Ramon, N. D., 1945, Mesozoic 

and Paleozoic stratigraphy in northwest Colorado and 

northeast Utah: U. S. Geol. Survey Prelim. Chart 16, Oil 

and Gas Inv. Ser.

Thomas, H. D., and Krueger, M. L., 1946, Late Paleozoic and 

early Mesozoic stratigraphy of the Uinta Mountains, Utah: 

Am. Assoc. Petroleum Geologists Bull., v. 30, p. 1255-1293.
BIBLIOGRAPHY 95

Thorpe, M. R., 1919, Structural features of the Abajo Mountains, 

Utah: Am. Jour. Sci., 4th ser., v. 48, p. 379-389.

 1938, Structure of the Abajo Mountains, in Gregory, H. 

E., The San Juan country: U. S. Geol. Survey Prof. Paper 

188, p. 89-91.

Tidestroin, Ivan, 1925, Flora of Nevada and Utah : U. S. Nat. 

Herbarium, Contr., v. 25, Smithsonian Inst, Wash.

United States Geological Survey, 1917, Profile surveys in the 

Colorado River basin in Wyoming, Utah, Colorado, and 

New Mexico: U. S. Geol. Survey Water-Supply Paper 396.

United Stnt.es National Park Service, 1946, A survey of the 

recreational resources of the Colorado River basin: Washington, D. C.

United States v. St.ate of Utah (283 U. S. 64), on the navigability of the Green, San Juan, and Colorado Rivers: U. S. 

Supreme Court, Oct. term, 1930.

United States Bureau of Reclamation, 1919: 18th Ann. Kept, 

p. 404.

 1946, The Colorado River: Washington, D. C. 

Untennann, G. E., and Untermann, D. R., 1949, Geology of

Green and Yninpa River canyons and vicinity, Dinosaur

National Monument, Utah and Colo.: Am. Assoc. Petroleum

Geologists Bull., v. 33, p. 683-694. 

Van Houten, F. B., 1948, Origin of red-banded early Cenozoic

deposits in Rocky Mountain region: Am. ASSOC. Petroleum

Geologists Bull., v. 32, p. 2083-2125.

 1952, Sedimentary record of Cenozoic erogenic and

erosional events, Big Horn basin, Wyo.: Wyo. Geol. Assoc.

7th Ann. Field Conf. Guidebook. 

Veatch, A. C., 1909, Coal deposits near Pinedale, Navajo County,

Ariz.: U. S. Geol. Survey Bull. 491, p. 239-242. 

Ver Wiebe, W. A., 1930, Ancestral Rocky Mountains: Am. Assoc.

Petroleum Geologists Bull., v. 14, no. 6, p. 765-788. 

Walcott, C. D., 1890, Study of a line of displacement in the

Grand Canyon of the Colorado in northern Arizona: Geol.

Soc. America Bull., v. 1, p. 49-64. 

Walton, P. T., 1944, Geology of the Cretaceous of the Uinta

Basin, Utah: Geol. Soc. America Bull., v. 55, p. 91-130. 

Ward, L. F., 1901, Geology of the Little Colorado valley: Am.

Jour. Sci., 4th ser., v. 12, p. 401-413. 

Weeks, A. D., and Thompson, M. E., 1954, Identification and

occurrence of uranium and vanadium minerals from the

Colorado Plateaus: U. S. Geol. Suvey Bull. 1009-B.

Weeks, F. B., 1907, Stratigraphy and structure of the Uinta

Range: Geol. Soc. America Bull., v. 18, p. 427^148. 

Williams, Howel, 1936, Pliocene volcanoes of the Navajo-Hopi

country: Geol. Soc. America Bull., v. 47, p. 111-172. 

Williams, M. D., 1950, Tertiary stratigraphy of Uinta Basin:

Utah Geol. and Mineral Survey Guidebook, no. 5, p. 101-114. 

Wilson, E. D., 1939, Pre-Cambrian Mazatzal revolution in central Arizona: Geol. Soc. America Bull., v. 50, p. 1113-1164. 

Winchell, N. H., 1904, The colossal bridges of Utah: Am.

Geologist, v. 34, p. 189-192. 

Winchester, D. E., 1920, Geology of Alamosa Creek valley,

Socorro County, N. Mex.: U. S. Geol. Survey Bull. 716-A. 

Wodehouse, R. P., 1933, Tertiary pollen, part 2, The oil shales of

the Eocene Green River formation : Torrey Bot. Club Bull.,

v. 60, p. 479-524. 

Wood, H. E., and others, 1941, Nomenclature and correlation of

North American continental Tertiary: Geol. Soc. America

Bull., v. 52, p. 1. 

Woodruff, E. G., I9l2a, Marsh gas along Grand River near Moab,

Utah: U. S. Geol. Survey Bull. 471, p. 105.

 1912b, Geology of the San Juan oil field, Utah : U. S. Geol.

Survey Bull. 471, p. 76-109. 

Woodruff, E. G., and Day, D. T., 1914, Oil shale of northwestern

Colorado and northeastern Utah: U. S. Geol. Survey Bull.

581-A, p. 1-21. 

Woolley, R. R., 1930, The Green River and its utilization:

U. S. Geol. Survey Water-Supply Paper 618. 

Wortman, J. L., 1895, in Osborn, H. F., and Earle, Charles,

Fossil mammals of the Puerco beds, collection of 1892 : Am.

Mus. Nat. History Bull.,, v. 7.

 1897, in Matthew, W. D., A revision ot! the Puerto fauna:

Am. Mus. Nat. History Bull., v. 9. 

Wright, H. E., 1946, Tertiary and Quaternary geology of the

lower Rio Puerco area, New Mexico: Geol. Soc. America

Bull., v. 57, p. 383-456. 

Wright, H. E., and Becker, R. M., 1951, Correlation of Jurassic

formations along Defiance monocline, Arizona-New, Mexico:

Am. Assoc. Petroleum Geologists Bull., v. 35, p. 607-614. 

Youngs, F. O., and Jennings, D. S., 1939, The Price area, Utah:

U. S. Dept. Agr. Bur. Cheni. and Soils, Soil Survey ser.

1934, no. 13. 

Youngs, F. O., and others, 1942, The Virgin River valley area,

Utah-Arizona: U. S. Dept. Agr. Bur. Plant Industry, Soil

Survey ser. 1936.

INDEX

	Page 

Abajo Mountains, a luccolithic group.-----..- 42

position in relation to structural features.. 63

strata penetrated by Igneous intrusions 62

Abiquiu tuff of Smith, description... . 32

Acknowledgments...--.----.--------. ..-.. 1-2

Alluvial deposits, Wisconsin age .-.-.-.. 38

Alluvium, Recent, prc-pottcry, description..- 38-39

Anasazai culture, relation to Recent alluvium. 39

Animas formation, description .-.- -.-.. 23

indications of upliL and vulcanism... 57

silicious material.__ _.- - - _ 24

volcanic debris....--.-------------------- 42

Anticlines and faults, northwestward-trending 53

Artifacts, prc-pottcry lithic cultures.--------- 39

Artillery formation. ..........-.--------- 26

Artillery Mountains_...------.-----..-..... 26

B

Basalt and alkalic basalt scries, extent, description. -. . ... .-. 49-53 

Basin and Range province, evidences of early

Tertiary volcanic activity..------ 42

place in geologic history....... ........ 73

Tertiary formations ------------ .... 26

volcanic field extending into... .. 51 

Basins, as structural element-..-.... .--... 53

Bidahochi formation, age in relation to structural features....-....------ -. 58

description.-._. ..................... 29

one of few of late Tertiary age ------------ 26

stratigraphic position..................... 27

Bill Williams Mountain, a large central-type

volcano .-....---.------.--.-. 47

Bishop conglomerate, description............. 30-31

occurrence__............................ 26

Bison, extinct longhorn ------- .--.--.-.. 38

Black Mesa, Ariz.._...__._____---__----__.-.. 20,29

Blanco Basin formation, description----.---.. 31

Book Cliffs, pro-Wisconsin pediments and

fanglomcrato--------------------- 38

Brian Head formation, description-..--.....- 26-27

displacement by faulting..--------- ... 59

Bridgcrformation, description................ 22

evidence of cpcirogcnic structural movement......____________... 63,64

Browns Park formation, associated sodicpotassic rocks........_..-__. 51

deformation preceding deposition ... 59,61 

description and relation to plateau _..__ 31 

occurrence..-----------------. --------- 26

Bysmaliths_..._.__-_--.___._-___.-.._ 43

Cambrian sedimentary rocks, occurrence...-. 11 

Canyon Lands section, a gcomorphic subdivision.. ,.-..- ..--.. .---.- 2

Carrizo Mountains, a laccolithic group.-.-.-. 42

position in relation to structural features.. 63

Castle Valley, description and history-------- 30

faulting in Recent alluvial deposits....... 61

Chaco River......................__........ 70

Chinlc Creek................................. 70

Circle Clin's.------.--------.----.-------.--.. 57

Chapin Wash formation.-------.-.-----------

Chicoma volcanic formation of Smith, description. --.-.-_.------.-------------.

Chuska sandstone, description. ---------------

Circle Cliffs upwarp, place in geologic history. 

Climate, early Tertiary to Recent.. ....._-..

Coal............ - -.-.-...--------.----

Cobwebb basalt..----------------------------

Colluvial aprons, Wisconsin age - -- - 

Colorado River, drainage system... ._ .

age.... ... ---...-------..--...--..

Colton formation, description ---.-.....

Copper-lead, sandstone deposits of. -------

Crcede formation, description.........-------

Cretaceous doposits _ - 

Page 

26

32 

29 

73

64-65

11

26

. 38

67-68

82,85 

19 

11 

32

15,23

D

Datil formation, description.- ........--.-.. 29-30

Datil section, a geomorphic subdivision ... 6 

DeBeque formation.-.._------------------- 19

Defiance upwarp, age-.---.----------.-u----- 57

place in geologic history,...-------------- 73

Deformation, early Cenozoic, recorded by

angular unconformity...--------- 57

Devonian rocks, occurrence----...-.--........ 11

Diatoms, in Sevier River formation._..--.-.- 27 

Diorite porphyry...............---...-----.-. 42

Dirty Devil River............................ 68

Dirty Devil River canyon, significance of

cobbles of diorite porphyry....... 30

Dolores River-.---------.------------------.. 69

Domes and folds associated with laccolithic

mountains._...----------.---.-. 54

Douglas Creek member, Green River formation. . _ _ 21

Drainage, antcposition... - __ _ 65,67

Colorado River........................... 67-68

Green River..--.---...-------.-..-..--.-- 68

tributary streams_--------------------- 68-71

Duchesne River-.----.-------................ 68

Duchesne River formation, description.------ 22

evidence of cpcirogcnic structural movement--.__..-......-.--.....-.- 63-64

Dune sand, Recent..------------------------- 38-39

E

Earthquakes recorded since 1851-----.----.--- 61

El Late Mountain, features of igneous rocks... 62 

position in relation to structural features.. 63 

Ellsworth, Mount, a stage of igneous intrusion. .__._._..._...__.. 42,43 

El Rito formation of Smith, description...... 32

Eohippus (Hyracotherium), in Wasatch formation, San Juan Basin.---.-...-.-. 25 

Epcirogenic structure-.--------..--..._.-.. 63-64

Erosion, geologic time..----------------------

Escalante River..............................

Espinaso volcanics of Stearns, description..-.

Evacuation Creek member, Green River

formation- -------------- ....

F

Fanglomerate, Tertiary 

'trough_....

age, Grand Wash

33

Page

Fault blocks ------------------------------ 53

Faulting, near junction of Colorado and Green

Rivers . - - 61

Fisher Valley, faulting in Recent alluvial deposits__.--.--.----.-- .----.. 61

Flagstaff limestone, description_. ---_. 18 

evidence of cpeirogenic structural movement----------------------------- 63

origin __ .__ --------- 73

records of dovmwarping.---------------- 57

Flora, Animas formation.-------------------- 23

Nacimiento formation..-- .---- .---- 24

Fluvial deposit, Animas formation----------- 23

Bridger formation.----------------------- 22

Colton formation.------..--------------.. 19

Duchesne River formation_..--.--.---.. 22 

pre-Wisconsin age..---------------------- 38

Uinta formation- ---------- ------- 22

Wisconsin age,.-------------------------- 38

Fluvial sediments in lower Tertiary deposits, _ 15

Fossils, extinct bison and mammoth, in Wisconsin alluvium.---------------.- 38

Fremont River.-----.-----------------.------ 68

Fruitland formation, contact with Animas

formation.--.------------------ 23

G

Galisteo sandstone, description.-------------- 26

reference to stratigraphic sequence-------- 32

Gallup-Zuni basin, Tertiary deposits------- 29

Garden Gulch member, Green River formation....-----------------------.-. 21

Gastropods, in Sevier River formation .-.. 27

Geomorphic subdivisions, list of, descriptions. 2-11

Glacial deposits, pre-Wisconsin, an anomaly.. 38

pre-Wisconsin, occurrence. ---------- -- 35

Wisconsin age. ----------------------- 38

Glen Canyon, history during Wisconsin time 38

Glendale, Utah, earthquakes recorded 61

Gold.--------------------------------.----. 11

Grand Canyon section, a geomorphic subdivision.------------------------- 6

Grand Wash Cliffs, age of faulting . . 59

Grand Wash trough, faulting__ 59

upper Tertiary deposits-----.----------.- 33

Green River desert. --.- - 30

Green River drainage system -------------- 68

Green River formation, affected by late Tertiary deformation_.............. 61

description....--_---------------------- 21

evidence of epcirogenic structural movement__-._.--._-______ 63,64 

records of downwarping. __. .,. 57

Green River lake, origin_--------_-------- 77

probable extent ----- - . 21

Greystone, Colo- . - __...-. 31

Gunnison River_..____ _.__ _ 69

Gypsum__-.....---...._................. 11

Gypsum Valley, folded conglomerate of late

Pliocene age________...__ 61

H

Halls Creek.--.-.....----.-..-------..-- 68-69

Helium_.__ ____._ 4

97
98 INDEX

Page

Henry Mountains, features of intruded rocks. 62 

a laceolithic group.---------.------------- 42

position in relation to structural features.. 63 

pre-Wisconsin pediments and fanglomerate_--------__---------.--.-_--- 38

Henry Mountains region..................... 30

High Plateaus, faulting__------------------- 59

lavas and volcanic cones..---------------- 51, 53

rocks described.--.------.---------------- 48-49

scarcity of pre-Wisconsin glacial deposits.. 35,38 

seismic activity_.------_-__.-----_-.--- 61

High Plateaus section, a geomorphic subdivision.-..------------------------ 6

Hillers, Mount, a stage of igneous intrusion_ 42,43 

Hinsdale formation, description..-.-----.---- 32

History, Ceiiozoic...--_-------_....-.-_ 73-86

Holmes, Mount, a stage of igneous intrusion. 42,43 

Hopi Buttes area, basalt and alkalic basalt

series.____.--.__-_---..--_-------- 50-51

Hopi Buttes volcanic field.................... 63

Hualpai limestone of Longwell..-..--.------. 33,35

Hurricane Cliffs, late Tertiary deformation... 59 

Hurricane fault, lava flows along-_........... 51

I-lyracotherlum (Eohippus) -------------------- 25

I

Igneous centers, apparent order in regional

distribution......---------------- 63

Igneous rocks, Ccnozoic, description, chemical

composition, subprovinces........ 39-42

Quaternary_____________-- ----------- 53

Igneous structures, Ceiiozoic, description.---. 62-63 

Intrusive processes, description.-------------- 42,43

Intrusive rocks, San Juan Mountains_...... 32

.. Jphnson. Canyon, Quaternary'igneous flow... 53 

Jurassic rocks, occurrence and thickness...... 14-15

Kaibab limestone, Grand Wash trough....... 33

Kaibab upwarp, place in geologic history....- 73

Kanab, Utah, earthquakes recorded-..------- 61

Kendrick Peak, a large central-type volcano,

description __._------_.----------- 47

Kirtlancl shale, contact with Aninias formation....--------.----------------- 23

Laccolithic mountains, age of intrusive structures indicated by drainage pattern..-...........-.---.---------. 43,45

chemical composition of average rock-.,.. 43 

lack of correlation with orogenic structural

features._---------------------- 63

list of, general description ..---..-.--- 42-45 

location.---.......-.-.--..-.--.....--.--- 40

structure.......--..----.---.-...-.----..- 62

Laccoliths, intrusive stages.-..--------------- 43

Lacustiine deposit, Flagstaff limestone.-.---- 18

Green River formation...---------------- 19,21

Lacustrine sediments in lower Tertiary dejjosits__.---. ----.-.--------- 15

Lake Fork andesitc, description....-.-..-.... 32

La Plata Mountains, position in relation to

structural features. -------------- 63

La Sal Mountains, complex intruded rocks... 62 

description of intrusion.-.---------------- 43

position in relation to structural features.- 63 

pre-Wisconsin glacial deposits in.--------- 35

Limnaea stagnalis appressa, In Bidahochi formation .-------.-------.---------- 29

Little Colorado River--.-.------------------- 70

Loessial deposits, pre-Wisconsin age.-------. 38

Page 

McDermott formation, indications of uplift

and vulcanism.._............... 57

unconformably overlain by Animas formation. ---------................. 23

Mammalian fossils, in Browns Park formation....-.-.--.-...._............. 31

in Recent pre-pottery alluvium.-------_ 39

Mammoth, fossils, in alluvium of Wisconsin

age...----------__----....----_... 38

Manganese -------------.-------------.....-.. 11

Mcsozoic history of area._____________________ 11

Mineral resources.-----------.------------.,-- 11

Minnie Maud Creek--------...---------.-.-- 68

Mississippian rocks, occurrence.-_---------- 11

Mogollon Rim, evidence of epeirogenic structural movement..--.------------- 63

location of gravel of possible Tertiary age. 25 

Quaternary igneous flows__--_.----.-.-. 53

Monument upwarp, place in geologic history. 73 

Monzonite porphyry.------------.-- --------- 42

Mormon Mountain, a large central-type volcano .----- ,--------.-----_-_._- 48

Muddy Creek formation, description.-._-.._ 33 

occurrence.-.--------- ------------...-- 26

Muddy River-----.-.----.-.--------- -....I. 68

N

Nacimiento formation, description.. ..-.-.-- 24 

origin.-------------------__.___-.---_.-- 77

Nalia alluvium of Hack.-----.....--------.--- 39

Navajo-Hopi volcanic districts, basalt and

alkalic basalt series.--- ----------- 50-51

Navajo Mountain, intrusive stage.-----.----- 42

position in relation to structural features.. 63 

Navajo section, a geomorphic subdivision.....

Navajo volcanic neld----.--..----.-----------

North Horn formation/correlation._________.- 

description and fauna.---------_--.-...

North La Sal Mountain, reversal of soda-potash proportion. _ _---------------

0

2,6 

63 

 23 

17

42

Oliio Creek conglomerate.----------- ------- 19

Oil -__ - -- --._--_-.-_-- 11

Oilshale -------- - --- .- 11

Ojo Alamo sandstone, correlation with North

Horn formation.---.-.. -------- 23

O'Leary Peak, a large central-type volcano.- 47-48 

Orogenic structural features, lack of correlation 

with laceolithic mountains and 

volcanic centers.----------------- 63

Paleozoic history of area--_---.___-- ....... 11

Panguitch, Utah, earthquakes recorded.... 61

Parachute Creek member, Green River formation.----------.. ...... .-- 21

Paradox Basin, a pre-Cenozoic structural

feature----.--.-----.------------- 54

Pennsylvanian marine sediments deposited In...--------------------- 11-12

Paradox Valley, faulting in Recent alluvial

deposits.----------------------..- 61

PariaRiver........-.-....-.-----.------.-... 69

Parunuweap formation, age and description.. 26-27 

Paunsaugunt fault------.-------.----------.-- 59

Peach Springs, Ariz.------------------------- 59

Peach Springs depression, Tertiary deposits in- 30 

Pennell, Mount--------.-----.---.----------- 42,43

Pennsylvanian rocks, occurrence....---.-.-.-. 11-12

Periglacial deposits, Wisconsin age...-------- 38

Permian rocks, occurrence-.-----.-.-.-------- 11

Physapleuromatis, in Flagstaff limestone--..- 18

Page 

Piceance Creek Basin, description of Wasatch

formation. _._..____._..._________ 19

Picuris tuff of Cabot, description.------------ 32-33

Planorbis trivolis, in Bidahochi formation..--. 29 

Plant remains, in Silverton volcanic series.-.. 32 

Popotosa formation of Denny, description.... 33

Porphyry, diorite. See Diorite porphyry.

monzonite. See Monzonite porphyry.

syenite. See Syenite porphyry. 

Potash...._._....._._........._.... ]1

Potosi volcanic series, description_...._.__._ 32

Pottery culture, remains in Recent alluvium.. 39 

Pro-Cambrian rocks, description and effect on

Cenozoic history__.___..-.----.---- 11

Precipitation....................._-----...... 6

Prehistoric cultures, remains in Recent alluvium........................... 39

Price River...._.....--.-.-..-_.._-.._ 68

Puerco fauna! zone.-------------------------- 24

Puerco formation, equivalent to Pal eocene formations in Uinta Basin._....... 23

Pumice--...-............-........------.-.... 11

Quaternary deposits, description.------------ 35

Quaternary igneous rocks, description........ 53

Quaternary structures, description....-.-..-.. 61-62

Recent deposits, description......-.-----..... 38-39

molluscan fauna.......................... 39

Rico Mountains, a laccoHthic group.-------.. 42

position in relation to structural features.. 63

Rio Grandc depression.---...-.-------------- 58

S

Salt....---.---....---.....-----.------------- 11

Salt deposits, Quaternary deformation duo to

movement of salt...-------------- 61

Salt Valley, Quaternary faulting._.......... 61

Sandtrap conglomerate....................... 26

San Francisco district, basalt and alkalic basalt

series__._.................... 49-50

San Francisco Mountain, a large central-type

volcano_---.-----.-..----.---.-. 47

pre-Wisconsin glacial deposits...... -.-... 35

volume of eruptive rocks..--------------- 39

San Francisco Mountain volcano, effect on

structure of country rocks.------- 62

San Jose River, Quaternary igneous flows.-.. 53 

San Juan Basin, description of formations-... 23 

structures terminated at faulted monocline.---------------------------- 58

San Juan Mountains, early Tertiary volcanic

activity..---.-..-----.----------- 42'

folding and faulting accompanied by volcanism and intrusions.----------- 01

pro-Wisconsin glacial deposits.-.--------- 35

results of hydrothennal activity and mineralization on flanks.------------- 43

till deposits.- --------------------------- 26

San Juan peneplain.------------------------- 32

San Juan River _-------------------------- 69-70

San Juan tuff, position and description.------ 31-32

San Miguel Mountains, a laceolithic group... 42

position in relation to structural features.. 63

San Miguel River.--------------------------- 69

San Rafael River..-.__.._..^....... --- 68

San Rafael Swell, dikes and sills, description-. 51 

place in geologic history.----------------- 73

Santa Fe formation, description...----------. 33

faulting___------.-..--..--------------- 58

occurrence _ __.-------.----..------------ 26 

stratigraphic sequence-------------------- 32,33-
INDEX 99

Page 

Sevior fault...-....-.------.----------------.- 59

Scvior River fonnation, ago and description.. 20-27 

faulting... -..----.-.-.........-.......- 59

relation to Igneous rocks.....--..--------- 48

Show Low, Ariz_.--_-...-....-.-...--...... 25

Siliceous material, Animas forinutlon.-------- 24

Sllverton volcanic series, description--------- 32

Sinbad Vulloy, faulting in Recent alluvial deposits__.... -------------------- 61

Sitgroavos Peak, a large central-type volcano.. 48 

Soil, overlying pro-Wisconsin deposits...----- 38

relation to geology_--.............-----. 71-73

types-----.--.-.------------------------ G

Stones, semiprecious_...................... 11

Structural elements-__....----...---....-.. 53-54

Structural history, prc-Ccnozolc.------------- 54-57

Structures, cftrly Tertiary.------------------- 57-58

epcirogcnie.................-.-..-.L...... 03-04

igneous, Ccnozoic_---------------------- 02-03

late Tertiary.-......-...---------------.- 58-01

Quaternary............................... 01-02

Sugarloaf Hill, a large central-type volcano... 48 

Sunset Crater....-------------------.-------- 53

Syenite porphyry__.----------------------- 42

Talus cones, Wisconsin age.------------------ 38

Taylor, Mount, district, basalt and alkalic

basalt series.--.------------------ 49

late Tertiary structures.------------------ 58

Taylor, Mount, volcano, description, types 

and chemical composition of oruptives.--------------------------- 40

effect on structure of country rocks. ------ 02

volume of eruptive rocks.---------------- 39

Telluride conglomerate, description.. ------- 31

Tertiary formations, listed.----.-------------- 15,20

	Page 

Tiffany beds, equivalent to Paleocenc forma

tions in U inta Basin... ----------- 23

in Wasatch formation, San Juan Basin... 25

Till, San Juan Mountains..-.--------- --.-.. 20,31

Tohachi shale, overlain by Chuska sandstone. 29

Torrejon fatuial zone.__-.---.--.-------_-.-- 24,25

Torrejon formation___-------__......... 23

Triassic rocks, occurrence and thickness.----- 14

Tropic, Utah, earthquakes recorded.--------- 61

Trumbull, Mount, description.-...---------- 62

Tsegi alluvium of Hack__.--------.------.- 38

Tuschcr formation_..---....-...-....-..-.. 18

U

Ulnta Arch. ------------------------------- 61

Uinta Basin, description of formations_----- 18-23

Uinta Basin section, a geomorphic subdivision....-------------.-----------. 2

Uinta formation, description_.............. 22

evidence of epcirogeuic structural movement..-..--.-------------------- 03,04

Uinta Mountains, pro-Wisconsin glacial deposits in..-..-.------------------- 35

structural history_------------_---.-.--. 57

Uncompahgre Plateau, a pre-Cenozoic structural feature_................... 54

place in geologic history.----------------- 73

Unio, in Bidahochi formation-.--------------- 29

Up warps ---.----------------------------.-.-- 53

Uranium.----...-----------------------.----- 11

Vanadium..--..----------..------------------ 11

Vegetation-.-.--.-------------------------.-. 0

Vertebrate fossils, in Bidahochi formation.... 29

in North Horn fonnation.---------------- 17

Page 

Vertebrate fossils Continued

in Santa Fe formation..-.--------.------- 33

Volcanic activity, in San Juan Mountains.--- 31-32 

Volcanic centers, lack of correlation with orogenicstructural features.--------- 63

Volcanoes, central type------------.--------. 40-48

W

Wasatch fonnation, angular uncomformity at

base.-.--.-...-..-.-..--.-..-..--- 57

character in Uinta and Piceancc Creek

basins....---------------.-..--.-- 19

correlation with Flagstaff limestone___- 18 

displacement by faulting......----....... 59

equivalent to Paleocenc formations in

Uinta Basin.--.-------------.---. 23

evidence of epeirogenic structural movement.- .---...-.-------------.-.-. 03

in San Juan Basin, description........... 25

name replaced in certain areas..-.-----_-. 15

Wasatch Plateau, description of Colton formation ...--------------.--------. 19

description of Flagstaff limestone.-------- 18

description of North Horn formation..... 17

Wisconsin deposits, general description......- 38

molluscan fauna.......................... 39

Wyoming Basin-.---------------.-.---------- 30-31

Yampa River....----...-..--..-.-------.-.-- 08

Zuni upwarp, age.---.---.-------------------- 57

place in geologic history.........--..--... 73

o