Geology of the Uinta 

River-Brush Creek Area 

Duchesne and Uintah 

Counties, Utah 

By DOUGLAS M. KINNEY 

GEOLOGICAL SURVEY BULLETIN 1007 

UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 195 5 
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary 

GEOLOGICAL SURVEY 

W. E. Wrather, Director 

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

Washing, ton 25, D. C. - Price $3.50 (paper cover) 
CONTENTS 

Page 

Abstract__________________________________________________________ 1 

Introduction______________________________________________________ 4 

Location and extent of the area_________________________________ 4 

Purpose and scope of the work__________________________________ 5 

Fieldwork____________________________________________________ 5 

Acknowledgments_____________________________________________ 7 

Topography, drainage, and water supply_________________________ 7 

Climate______________________________________________________ 10 

Vegetation____________________________________________________ 16 

Population____________________________________________________ 16 

Accessibility and routes of traveL_______________________________ 17 

Previous publications__________________________________________ 18 

Stratigraphy______________________________________________________ 20 

Pre-Cambrian_________________________________________________ 20 

Uinta Mountain group_____________________________________ 20 

Cambrian system______________________________________________ 22 

Lodore formation_______ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 22 

Carboniferous system__________________________________________ 24 

Mississippian series_____________________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 25 

Limestone unit________________________________________ 25 

Black shale unit_______________________________________ 33 

Pennsylvanian series_______________________________________ 38 

Morgan formation_____________________________________ 38 

VVebersandstone______________________________________ 45 

Permian sy8tem _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 48 

Park City formation_______________________________________ 48 

Triassic system________________________________________________ 55 

Lower Triassic series__________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 56 

Moenkopi formation___________________________________ 56 

Upper Triassic series_______________________________________ 63 

Shinarump conglomerate_______________________________ 63 

Chinle formation______________________________________ 67 

Jurassic ( ?) system _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 7 3 

Navajo sandstone_________________________________________ 73 

Jurassic system_____ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 7 7 

Middle and Upper Jurassic series____________________________ 77 

San Rafael group_______________________________________ 77 

Carmel formation____________________________________ 77 

Entrada sandstone___________________________________ 81 

Curtis formation__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 85 

Upper Jurassic series_______________________________________ 90 

Morrison formation____________________________________ 90 

III 
IV CONTENTS 

Stratigraphy-Continued Page 

Cretaceous system______________________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 95 

Lower(?) and Upper Cretaceous series________________________ 95 

Dakota sandstone_____________________________________ 95 

Upper Cretaceous series____________________________________ 97 

Mancos shale_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 97 

Mowry shale member_______ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 98 

Frontier sandstone member_________________________ 102 

Upper shale member_______________________________ 107 

Mesaverde formation__________________________________ 110 

Tertiary system_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ 114 

Bishop conglomerate___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 114 

Structure_________________________________________________________ 116 

Methods of representing structure_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 116 

Generalfeatures_______________________________________________ 117 

Folds________________________________________________________ 118 

Island Park syncline_______________________________________ 118 

Split Mountain anticline____________________________________ 119 

Section Ridge anticline_____________________________________ 119 

Daniels Draw syncline_____________________________________ 120 

Neal dome________________________________________________ 120 

Little Mountain synclines__________________________________ 121 

Coal Mine syncline________________________________________ 121 

Mosby Mountain syncline or fault___________________________ 121 

Whiterocks anticlinal nose__________________________________ 122 

Dry Fork anticlinal nose___________________________________ 122 

Ashley Creek anticlinal nose________________________________ 122 

Davis Spring anticlinal nose________________________________ 123 

Brush Creek anticlinal nose_________________________________ 123 

Barker Spring anticlinal nose_________________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 124 

Faults________________________________________________________ 124 

South Flank fault zone_____________________________________ 124 

Deep Creek fault zone_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 124 

Age of· deformation_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 125 

Geomorphology___________________________________________________ 126 

General features_______________________________________________ 126 

Gilbert Peak surface____________________________________________ 126 

Lake Mountain surface_________________________________________ 128 

Jensen surface_________________________________________________ 128 

Younger erosion surfaces_______________________________________ 129 

Glacial deposits_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 130 

Canyon development_____________________________ _ _ _ _ _ _ _ _ _ _ _ _ _ 135 

Economic geology_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 136 

Coal_________________________________________________________ 136 

Oil and gas____________________________________________________ 150 

Metallic mineral deposits_______________________________________ 159 

Copper___________________________________________________ 159 

Lead_____________________________________________________ 161 

Iron_____________________________________________________ 161 

Gold_____________________________________________________ 162 

Phosphate____________________________________________________ 162 

Sand and gravel_______________________________________________ 173 

Refurences cUed___________________________________________________ 176 

Index____________________________________________________________ 181 
Pr~ATE 1. 

2. 

3. 

4. 

5. 

6. 

FIGURE 1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

CONTENTS v 

ILLUSTRATIONS 

Page 

Geologic map and structure sections of the Uinta River-Brush 

Creek area, Utah__________________________________ In pocket 

Correlation chart of detailed sections from Whiterocks River 

to Green River, Utah _______________________________ In pocket 

Map of erosion surfaces and late Cenozoic deposits_______ In pocket 

Map and sections of the coal in the Frontier sandstone 

member_________________________ _ _ _ _ _ _ _ _ _ ______ :. _ _ _ In pocket 

Character and composition of rocks in the lower part of the 

Park City formation ________________________________ In pocket 

General section of rock formations in area between Uinta 

River and Brush Creek _____________________________ In pocket 

Index map of Utah______________________ ________________ 4 

West wall of upper Ashley Creek_________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 27 

Small anticlinal fold in the Morgan formation____________ _ _ _ _ 39 

Crossbedding in the Weber sandstone_______________________ 47 

Lower part of the Park City formation_______________________ 49 

Formations on north side of Cocklebur Wash__ _ _ _ _ _ _ _ _ _ _ _ _ _ 57 

Shinarump conglomerate channel in top of Moenkopi formation_ 61 

Chinle, Shinarump, and Navajo formations on Red Mountain_ 68 

Carn~_el formation in syncline north of Neal dome____________ 75 

Formations along east side of Steinaker Draw_______________ 90 

Mowry shale member on lower Brush Creek________________ 99 

Sul:surface structure-contour n:ap of Ashley Creek oilfield____ 157 

Outline map showing Phospbate Withdrawal No. 24, Utah 

No.3__________________ _____________________ ______ ___ 171 

GEOLOGY OF THE UINTA RIVER-BRUSH CREEK AREA, 

DUCHESNE AND UINTAH COUNTIES, UTAH 

By DouGLAs M. KrNNEY 

ABSTUACT 

The area described in this report includes 870 square miles of almost uninlmbited country on the south flank of the Uinta .Mountains lying in Duchesne 

and Uintah Counties, north and east of Roosevelt and Vernal, Utah. U. S. 

Highway 40 crosses the southeastern part of the area and continues westward 

to Vernal, Roosevelt, Heber, and Salt Lake City. Utah State Highway 44 connects Vernal with :Manila, Utah, and with other towns on the north flank of 

the Uinta Mountains. The area lies on the northern border of the Colorado 

Plateau. 

The oldest exposed rocks are quartzitic sandstone and sandy shale of Proterozoic age that belong to the Uinta Mountain group. They crop out on the 

northern border of the area. The Lodore formation of· Cambrian age overlies 

the Uinta :Mountain group from Brush Creek eastward to the Green River. The 

formation consists of coarse-grained sandstone and arkose and thickens eastward. Both the Lodore formation, east of Brush Creek, and the Uinta :Mountain group, west of Brush Creek, are overlain by 1,000 to 1,200 feet of light-gray 

cherty limestone, with some sandstone near the top, which is mapped as the 

limestone unit of :Mississippian age. This limestone unit is of early, or, in part, 

late :Mississippian age. It is succeded by black shale of late Mississippian age. 

'l'he black shale unit thins toward the east from 280 feet to 25 feet or less. The 

next overlying formation is the :Morgan formation of Pennsylvanian age, which 

consists of a lower light-gray cherty limestone member and an upper member of interbedded red sandy shale, light-buff to gray sandstone, and gray fossiliferous limestone. The lower member is 300 to 400 feet thick, and the upper 

member is 700 to 1,000 feet thick. The Morgan formation grades upward into 

the massive, crossbedded 'Veber sandstone of Pennsylvanian age, which ranges 

from 1,000 to more than 1,200 feet in thickness. 

The Park City formation of Permian age, 100 to 200 feet thick, overlies the 

·weber sandstone and grades upward into the Moenkopi formation. The Park 

City formation consists of gray slabby limestone, gray shale, sandstone, and 

greenish-gray phosphate rock. The Moenkopi formation, of Early Triassic age, 

consists of reddish-brown and greenish-gray, fine-grained sandstone and siltstone and is 800 to 1,000 feet thick. The lower 300 feet of the Moenkopi, east 

of Red :Mountain, rapidly changes in color from red to gray. The :Moenkopi is 

unconformably overlain by the Shinarump conglomerate, of Late Triassic age, 

which is as much as 95 feet thick. The Shinarump grades upward into the 

Chinle formation, which consists of varicolored shale overlain by red to tan 

ripple-marked sandstone. The Chinle, 230 to 260 feet thick, grades upward into 

the tangentially crossbedded, light-gray Navajo sandstone of Jurassic ( ?) age. 

The Navajo sandstone is 700 to more than 1,000 feet thick. 
2 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

The San Rafael group overlies the Navajo sandstone and is composed of the 

Carmel formation of Middle and Late Jurassic age, and the Entrada sandstone 

and Curtis formation of Late Jurassic age. The Carmel consists of red and 

white fine-grained silty sandstone and siltstone, gray platy mudstone, fossiliferous limestone, and pink gypsum. It thins from almost 400 feet in the west to 

120 feet on the Green River. The Entrada, a light-gray, massive, crossbedded, 

fine- to medium-grained, friable sandstone, thins eastward from 240 feet on 

Whiterocks River to 105 feet at Split Mountain. The Curtis formation consists 

of greenish-gray, medium- to coarse-grained, thin- to massive-bedded, highly 

glauconitic sandstone overlain by dark greenish-gray shale with thin beds of 

fossiliferous, glauconitic, sandy, oolitic limestone. The Curtis varies from 150 

to 270 feet in thickness. The San Rafael group is overlain by the continental 

Morrison formation of Late Jurassic age, which consists of variegated red and 

light-gray siltstone and shale, red and gray fine-grained silty sandstone, and 

fine- to coarse-grained sandstone. The Morrison is 800 to 900 feet thick. 

In the area studied, the basal formation of the Cretaceous system is the Dakota 

sandstone of Early ( ?) and Late Cretaceous age, which ranges from 50 to 135 feet 

in thickness. The formation is comprised of light-gray to tan, fine- to coarsegrained sandstone, with pebbles of dark-gray and black chert. The Dakota is 

overlain by the Mancos shale of Late Cretaceous age, which is divided into 

three members, the thin Mowry shale member at the base, the thin Frontier 

sandstone member, and a thick upper shale member of light-gray siltstone and 

shale. The Mowry shale member, 30 to 125 feet thick, consists of dark brownishgray clay shale overlain by dark-gray, fissile, siliceous shale containing abundant fish scales. The Frontier sandstone member of the Mancos, 140 to 270 

feet thick, consists of tan-weathering, gray sandy shale overlain by tan, fine- to 

medium-grained, calcareous sandstone. The upper shale member of the Mancos 

is 4,900 feet thick east of the Green River. Thin limy sandstone beds are present 

in the top part of the upper member. The Mancos shale is overlain by the Mesaverde formation, of Late Cretaceous age, which is found only in the southeastern 

part of the area. The Mesaverde consists of light-gray, fine- to medium-grained, 

partly crossbedded, speckled sandstone overlain by dark-gray shale, dark-brown 

lignitic shale, and brown lignite. Two miles east of the Green River, the formation is 1,175 feet thick. 

The older Tertiary rocks (Eocene and Oligocene) overlying the Mesaverde 

formation consists of light-gray sandstone, marl, sandy shale, and tan-weathering pebble conglomerate. To the west, the Tertiary rocks, which overlie the 

Mancos shale and older rocks, consist of tan to red, fine- to medium-grained 

sandstone. The younger Tertiary rocks are referred to the Bishop conglomerate 

and are tentatively assigned a Miocene age. The Bishop ·consists of lighttan to red conglomerate in a matrix of coarse-grained sandstone. Chalky-white 

tuffaceous sandstone is found in the lower part of the Bishop in the Mosby 

Mountain-Lake Mountain area, and white tuffaceous sandstone is prominent on 

Diamond Mountain. 

Glaciers descended into the valleys of Dry Gulch, Uinta River, Pole Creek, 

Whiterocks River, and Dry Fork of Ashley Creek, and occupied the headwaters 

of Farm Creek, East Fork of Dry Fork, Black Canyon, and Ashley Creek. Three 

ice advances, respectively termed the Earliest, Maximum, and Latest glaciation 

periods, are recognized; corresponding outwash gravels of these periods are 

also present. 

The area is divided into two parts by Dry Fork of Ashley Creek and by a line 

trending S. 60° E. across Ashley Valley. Faulting is dominant south of this line, 

although sharp folds are also present. East and northeast of Dry Fork, faulting 
ABSTRACT 3 

is of minor importance and open folding is predominant. The strata dipping 

southward from the main Uinta Mountain axis are folded into sharp southsoutheast plunging anticlinal noses. South of the principal Uinta Mountain 

axis and separated from it by the Island Park syncline, are two parallel westward-plunging anticlines, the Split Mountain anticline and the Section Ridge 

anticline. These anticlinal folds are separated by the shallow Daniels Draw 

syncline. To the west of Dry Fork of Ashley Creek, the northwest-trending 

faults, comprising the Deep Creek fault zone, intersect the South Flank fault 

zone that generally bounds the pre-Cambrian core of the mountains. 

Three periods of deformation are indicated in the area. The first deformation involved the faulting of pre-Cambrian rocks and occurred prior to the deposition of the limestone unit of Mississippian age. The second deformation 

followed the deposition of the Moenkopi formation and included gentle westward tilting of the area prior to the deposition of the Shinarump conglomerate. 

The third and principal deformation of the area followed the deposition of the 

youngest Cretaceous rocks and continued during the deposition of the early 

Tertiary rocks. Deformation of the area had almost ceased by the time the 

Bishop conglomerate was deposited in Miocene ( ?) time. 

Three widepread erosion surfaces, the Gilbert Peak surface, the Lake Mountain surface, and the Jensen surface, were developed during late Tertiary and 

Quaternary time. The Gilbert Peak surface underlies the Bishop conglomerate 

and bevels all older rocks. The Lake Mountain surface was cut on the Bishop 

conglomerate, and the Jensen surface was formed by coalescing pediments late 

in the erosion period of the Tertiary sedimentary rocks of the Uinta Basin. 

Two strath terraces, the Vernal and Thornburg surfaces, were formed along 

major streams during the glaciation of the Uinta Mountains in Pleistocene time. 

Lenticular coal beds, 14 inches or more in thickness, occur in the upper part 

of the Frontier sandstone member of the Mancos shale. The coal is high-volatile 

C bituminous in grade. Coal is reported in the black shale unit of latE> 

Mississippian age, and lignite is present in the Mesaverde formation of Late 

Cretaceous age. Approximately 240,000 tons of coal has been mined from 

the Frontier sandstone member of the Mancos shale. Sixty million tons of coal 

under less than 1,000 feet of overburden, 54 million tons under 1,000 to 2,000 feet 

of overburden, and 29 million tons under 2,000 to 3,000 feet of overburden are 

considered as indicated reserves. 

A. number of oil and gas wells have been drilled in the area. Commercial 

gas was discovered on the Ashley Creek structure in 1925 and was produced from 

1929 to 1940. The producing horizon was a sand in the lower part of the Morrison 

formation. Five hundred and thirty-six million cubic feet of gas were produced. 

Oil was discovered in the Weber sandstone on the Ashley Creek structure at a 

depth of 4,152 feet in September 1948. Twenty-eight commercially producing 

wells had been drilled by February 1950. One of the wells is producing from 

a sand in the Park City formation. 

Small quantities of copper, lead, and iron have been produced from the 

Carbonate district (T. 1 S., R. 21 E.), which is located in the limestone unit of 

Mississippian age. 

Low-grade phosphate rock occurs in the lower part of the Park City formation. 

The phosphate rock averages 20 percent of P205 for a thickness of 18 feet 

in the Ashley Creek-Brush Creek area. Two hundred and fifty million tons of 

phosphate rock under 43 feet or less of overburden, 650 million tons under 78 

feet or less of overburden, 1,800 million tons to stream level, and 2,450 million tons 

to 1,000 feet below stream level are listed as indicated reserves in .the Ashley 

Creek-Little Brush Creek area. 
4 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Sand and gravel for concrete and road construction occur in terrace deposits 

adjoining the major streams. Reserves are adequate for the normal demands of 

the area. 

FIGURE 1.-Iondex map of Utah showing location of Uinta River-Brush Creek area. 

INTRODUCTION 

LOCATION AND EXTENT OF THE AREA 

The Uinta River-Brush Creek area is in northeastern Duchesne 

County and northern Uintah County in the northeastern part of Utah. 

It lies on the south flank of the Uinta Mountains between longitude 

109° 15' and 110° 15' and includes an area of about 870 square miles. 

The location and extent of the area are shown on figure 1. 
INTRODUCTION 5 

The northern boundary of the area roughly corresponds to the northern lilnit of rocks of Paleozoic age, and the southern boundary of the 

area corresponds to the northern extent of the overlapping Tertiary 

rocks of the Uinta Basin. The eastern boundary of the area lies north 

and east of Vernal, the county seat and principal town in Uintah 

County, and the western boundary lies north and west of Roosevelt, the 

largest town in Duchesne County. The rectangular indentation on the 

eastern boundary of the area is the extreme western part of the Dinosaur National Monument, which lies partly in northwestern Colorado 

and partly in northeastern Utah. By agreement with G. E. Tintermann and B. R. Unter1nann of Vernal, Utah, who have studied the 

geology of the monument for the U.S. Park Service, this rectangular 

area was excluded from the present investigation. 

PURPOSE AND S.COPE OF THE WORK 

The study of this area by the United States Geological Survey is 

part of a plan to portray the geologic setting of the great Uinta 

Basin, an irregularly shaped and structurally depressed area that 

underwent sedimentation throughout 1nuch of Tertiary time. The 

Uinta Basin is bounded on the north by the Uinta Mountains, on the 

south by the Book Cliffs, on the east by a structurally high area near 

the Rangely and Douglas Creek anticlines, and on the west by the 

Wasatch Mountains. 

The geology of the Book Cliffs region has been published in United 

States Geological Survey Bulletin 852 by D. J. Fisher, Bulletin 819 

by E. M. Spieker, and Bulletin 793 by F. R. Clark. These bulletins, 

which deal primarily with the coal resources, cover an area extending 

from the Colorado State line westward to longitude 111°. The 

·western boundary of the Uinta Basin, theW asatch Mountains, is being 

studied by A. A. Baker. The western portion of the south flank of 

the lTinta Mountains has been studied by John W. Huddle. Huddle's 

area bounds the Uinta River-Brush Creek area on the west along 

longitude 110° 15'. In 1943, impetus was given to the study of the 

south flank of the Uinta Mountains by the development of petroleum 

production in the Weber sandstone on the large Rangely anticline in 

northwestern Colorado. Increased prospecting activity in adjacent 

areas in northeastern Utah led to the discovery of oil deposits in the 

'Veber sandstone (Pennsylvanian) at the Ashley Creek field in September 1948. Interest in the Uinta Basin as a petroliferous province 

has been further justified by the discovery of oil in the Green River 

formation, Eocene) in the northern part of the Uinta Basin, near 

Roosevelt, Utah. 

FIELD WORK 

Part of the area between 109° 30' and 110° 00' was mapped in 1945 

by A. J. Crowley and Joseph M. Gorman of the Geological Survey. 
6 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Their field work was terminated in November 1945 before their study 

was complete. Their mapping has been incorporated, with modifications, in the field work carried on by the writer between April and 

November 1946. Joseph F. Rominger and Ralph S. Brown served as 

assistants between June and September, P. Veraste.gui M. from August 

to October, and Robert W. Blair in October 1946. The pre-Tertiary 

geology of the area between 109° 30' and 110° 00' was briefly described 

by the writer and J. F. Rominger in Preliminary Map 82, Oil and Gas 

Investigations~ U. S. Geological Survey, December 1947. The areas 

between 110° 00' and110° 15' and between 109° 15' and 109° 30' were 

studied from April to October, 1947, with Joseph Rominger as field 

assistant (June to September). This area was described in U. S. 

Geological Survey Oil and Gas ~fap 123, September 1951. The location and altitudes of many control points in the area between longitude 

109° 30' and110° 00' were established in 1945 by means of plane-table 

triangulation by Howard Clark and Wn1. P. Clark of the Geological 

Survey. Additional locations and altitudes in the remaining areas 

were established by Joseph F. Rominger in 1947 by 1neans of planetable triangulation using primary triangulation stations of the United 

States Coast and Geodetic Survey. In 1946 and 1947, altitudes of key 

beds were obtained at many places by angles determined with the 

tele.seopic alidade frmn stations established by three-point intersection 

from eontrol stations and by distances measured on the photographic 

lllOSalCS. 

That part of the area north of latitude 40° 30' and between longitude 109° 30' and 110° 15' is shown on the topographic maps of the 

Marsh Peak and Gilbert Peak quadrangles of the U. S. Geological 

Survey at a scale of 1: 125,000 (or approximately 2 miles to the inch). 

These maps, surveyed in 1904-1906, show the 1najor features of the 

land surface, but they are not adequate as a base for detailed mapping 

of thin stratigraphic units. 

Geologic 1napping was done on aerial photographs, on a scale of 

1 : 31,680 (or 1 mile to 2 inches), and later was compiled on photograph mosaics supplied by the Soil Conservation Service, U. S. 

Department of Agriculture. A s1nall area north of 40° 37' 30" and 

west of 109° 45' was assembled from photographs by the radial line 

method of compilation. The land net, shown on plate 1, is based on 

land plats of the General Land Office, on section corners identified on 

the photographs, and on section corners located by alidade and plane 

table, using three-point intersection from known triangulation stations and stadia traverses from triangulation stations. Three detailed 

stratigraphic sections at intervals across the area (see pl. 2) were 

measured by plane table and telescopic alidade. A few thin units were 

measured by hand level or Brunton clinometer. 
INTRODUCTION 7 

As part o£ a coordinated study o£ the phosphate and associated 

minor metals in Idaho, "'\-Vyoming, Montana, and Utah, the Mineral 

Deposits Branch o£ the Geological Survey under V. E. McKelvey 

(geologist in charge o£ the northwest phosphate investigations) cooperated in the detailed study o£ the phosphate unit o£ the Park City 

£ormation. Following the bed-by-bed description o£ the phosphatic 

unit by J. F. Rominger and the author, R. P. Sheldon cut channel 

sa1nples, Helmuth W edow made numerous statigraphic-paleontologic 

collections, and L. E. Smith subdivided the £ormation into three members and 1napped their distribution. 

ACKNOWLEDGMENTS 

The writer is indebted to his field assistants, Messrs. Rominger, 

Brown, V erastegui, and Blair £or their capable aid in the field. To 

G. E. Untermann and B. R. Untermann, o£ the Utah Field House o£ 

Natural History; Charles Neal; Philip Williams, geologist £or the 

Carter Oil Co.; and }larry Ratli:ffe, resident manager £or the Humphreys Phosphate Co., all o£ Vernal, the writer is deeply indebted £or 

geologic information ltnd discussion o£ problems. James Steele Williams, Ralph I1nlay, and Lloyd Henbest o£ the Paleontology and 

Stratigraphy Branch; V. E. McKelvey, L. E. Smith, Helmuth 

'Vedow, and R. P. Sheldon o£ the Minerals Deposits Branch; and 

A. A. Baker, J. W. Huddle and N. W. Bass o£ the Fuels Branch, all 

members o£ the United States Geological Survey, visited the writer 

during the course o£ the field work and contributed valuable aid. 

Messrs. James Steele Williams, Ralph Imlay, Willia1n Hass, John B. 

Reeside, James M. Schop£, and Miss Helen Duncan, all o£ the Geological Survey; and Messrs. David H. Dunkle and G. Arthur Cooper, 

o£ the U. S. National Museum, identified fossils and made age determinations o£ collections £rom the area. 

During the preparation o£ the report, the writer has been aided by 

criticism and suggestions £rom Jack E. Schoellhamer o£ the Geological Survey. 

The writer wishes to express appreciation to the Director o£ the 

Geological Survey £or his permission to submit a part o£ this report 

to Yale University as a dissertation in partial fulfillment o£ the requirements £or the degree o£ doctor o£ philosophy. He also acknowledges with thanks the helpful criticism o£ Pro£. C. R. Longwell and 

Pro£. C. 0. Dunbar o£ the departlnent o£ geology at Yale University. 

TOPOGRAPHY, DRAINAGE AND WATER SUPPLY 

The Uinta River-Brush Creek area lies on the south flank o£ the 

elongate Uinta Mountain range, which trends eastward across northeastern Utah and southeastward in northwestern Colorado. To the 
8 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

west, the mountains are separated from the north-trending Wasatch 

Range by the narrow Heber Valley. To the east, they die out in Cross 

Mountain and the Danforth Hills, which extend to the White River uplift. The crest of the Uinta Mountains lies to the north of the median 

line and result in a relatively gentle south slope and a steep north slope. 

The crest slopes eastward and westward in a gradual manner from 

an average altitude of 13,000 feet near the central portion of the 

range. The higher peaks, Kings Peak and Mt. Emmons, lie slightly 

south of the crest and to the north and west of the northwestern corner 

of the area. The mountains do not give the impression of great height 

because they are smoothly contoured and rise frmn a high plateaulike surface which slopes gently away frmn the crest. This high surface, which on the south flank in large part defines the boundaries of 

the Uinta Mountains, not only slopes southward frmn the crest, but 

it also slopes eastward to the Green River and the eastern border of 

the area. The Uinta Basin lies south of the Uinta Mountains and 

extends in a southerly direction for 60 to 100 miles to the Book Cliffs: 

The most important topographic feature in the area is the widespread gently rolling surface that fonns the tops of Jefferson Park, 

Pole Mountain, Mosby Mountain, Lake Mountain, Dry Fork Mountain, the upland area between Ashley Creek and Brush Creek and 

Diamond Mountain. The crests of Little Mountain and Split Mountain, and the Yampa Plateau, which lies east of the Green River, also 

are remnants of this surface that have been isolated by erosion. The 

surface slopes at a rate of 120 to 180 feet to the mile southward from 

the crest and slopes 50 feet to the 1nile toward the east. It descends 

from an altitude of more than 10,000 feet at Jefferson Park, west of the 

Uinta River, to 7,300 feet at a few points on Diamond Mountain. On 

Mosby Mountain, the surface is at an altitude of about 9,400 feet; on 

Lake Mountain, it is at 9,050 feet, and on Little Mountain, at about 

8,050 feet. 

Limestone and quartzite hills rise above this widespread surface on 

Taylor Mountain, Brush Mountain, Little Brush Mountain, and in the 

line of peaks that extend east and southeast across the northern border of Diamond Mountain and separate Diamond Mountain from the 

valley of Pot Creek. These hills reach an altitude of 10,250 feet on 

Brush Mountain and an altitude of 8,500 feet on the peaks north of 

Diamond Mountain. 

Split Mountain and Section Ridge enter the area on the eastern 

boundary. The maximum altitude of points on these features is only 

500 to 600 feet above the level of the Green River, but to the east, Split 

Mountain and Section Ridge merge to fonn Blue Mountain whose 

upper surface, an altitude of 7,500 feet, forms the Yampa Plateau. 

South of the termination of the high surface, the average altitude 

drops almost 2,000 feet in a distance of 3 or 4 miles. West of Little 

Mountain, from Little Mountain east to Diamond Mountain, and on 
INTRODUCTION 9 

the flanks of Split Mountain and Section Ridge, the 1nore resistant 

sandstone strata form hogbacks rising 300 to 400 feet above the stream 

courses that have developed in the more easily eroded strata. Between Diamond Mountain and Split Mountain, west and south of 

Split Mountain, and south of Section Ridge, easily eroded gray shale 

forms low hills, some of which are capped by gravelly benches sloping away from the mountains. Northwest of Split Mountain, the 

barren, gray Buckskin Hills are capped with coarse gravel and rise 

to an altitude of 6,800 feet. South of Section Ridge and east oJ 

Green River, there is a low sandstone escarpment called The Rirrt 

Rock. This is a continuation of Asphalt Ridge, the north-facing 

escarpment that increases in altitude northwestward to merge into 

the gravel-capped surface sloping south from Little Mountain. This 

escarpment, and its continuation westward frmn Little Mountain to 

Mosby Mountain, marks the northern boundary of the Uinta Basin. 

'Vest of Mosby l\iountain, the flat-lying Uinta Basin sediments encroach farther north and the change from mountains to basin has no 

intervening belt of sandstone hogbacks and gray shale hills. 

Green River, the master stream of the region, enters the eastern 

boundary of the area after it emerges frmn Split Mountain Gorge 

and flows southwesterwarcl across the Uinta Basin to Desolation 

Canyon, where it passes through the Tavaputs Plateau and the Roan 

and Book Cliffs in a deep gorge. Below Jensen, the Green River lies 

about 4,700 feet above sea level; this is the lowest altitude in the area. 

The rolling upland surface is cut by steep-walled gorges, which 

are 2,000 to 2,500 feet deep and trend south to southeast from the crest 

of the range. Uinta River, \Vhiterocks River, Ashley Creek, Brush 

Creek, and Little Brush Creek are perennial streams draining the 

central part of the range. These streams obtain their maximum discharge from melting snow in late spring. Dry Fork of Ashley Creek 

is perennial in its upper course, but after the flood stage of late spring 

the lower course of the boulder-covered strean1bed is dry. Whiterocks River and Deep Creek join the Uinta River south of Whiterocks settlement, and the Uinta River, in turn, joins the Duchesne 

River 10 miles above the junction of the Duchesne with the Green 

River. Neither the Uinta River nor the Whiterocks River has a 

clearly defined single channel after leaving the mountain front; each 

river separates into a series of distributary channels flowing over 

boulder-choked alluvial plains. Dry Fork of Ashley Creek join~, 

Ashley Creek east of Little Mountain, and Ashley Creek flows southeastward through the broad Ashley Valley to join the Green River 

south of Jensen. Little Brush Creek joins Brush Creek in the eastcentral part of T. 3 S., R. 22 E., and the latter strearn enters the 

Green River a few miles above Jensen. Diamond Mountain and the 

area to the north of Diamond Mountain are drained by Diamond 

·Gulch and Pot Creek, which are tributary to Green River. 
10 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

The perennial streams flowing southward from the crest of the 

Uinta Mountains have been partly diverted by irrigation canals, 

which carry the water southward by gravity flow into the arid, but 

potentially fertile, Uinta Basin. Water from Uinta River is diverted 

toward the southwest to irrigate the farmlands between Neola and 

Roosevelt. Water from Whiterocks River is diverted toward the 

southeast to irrigate the farmland from Whiterocks southeast to 

Tridell and Lapoint, and water from Ashley Creek irrigates the 

Ashley Valley around Vernal. The small flow of Brush Creek is 

used to irrigate land near Jensen. The Green River is used for. irrigation by only one large farm that raises the water by pumps to 

irrigate the bottomland along the river northeast of Jense.n. Sma11 

ranches that raise grass for hay and pasture use the water within 

the borders of the mountains; however, the amount of irrigated land 

is small. Water from Brush Creek, normally lost as surface flow by 

passing underground at Brush Creek Cave, is stored in the Oak Park 

Heservoir, and part of it is diverted westward into the Ashley Creek 

watershed by a canal that skirts Taylor Mountain. This water is 

then used to irrigate a portion of the Ashley Valley. Much of the 

water that goes underground at Brush Creek Gave probably reappears 

in the spring 5 miles downstream. 

Hydroelectric power is produced at the mouth of Uinta Canyon by 

water diverted from Uinta River in sec. 4, T. 2 N., R. 2 W., and carried 

by open ditch and iron pipe to the generating station. Hydroelectric 

power is also. generated at the mouth of Ashley Creek for use in 

Vernal. 

Small springs are common a few hundred feet below the high surface that forms the tops of J e:fferson Park, Pole Mountain, Mosby 

Mountain, Lake Mountain, Little Mountain, Dry Fork Mountain, and 

Diamond Mountain. Many of these springs run dry in late summer, 

but others provide a small flow of water suitable for livestock throughout the year. In addition to the springs that feed Brush Creek below 

Brush Creek Cave, a large spring is located in the Elf2 sec. 31, T. 2 S., 

R. 22 E., west of the mouth of Brush Creek Gorge. The principal 

water supply of the town of Vernal is brought by pipe from a large, 

covered spring, half a mile above the mouth of Ashley Canyon. A 

large spring is located on the east side of Uinta River at the end of 

the automobile road; a smaller spring, in SE"%,SE:!4 sec. 34, T. 3 N., 

R. 2 W., feeds Pole Creek. 

CLIMATE 

Because the amount of rainfall increases with an increase in altitude, the records of the U.S. Weather Bureau at Jensen and Elkhorn 

Ranger Station are supplemented by records taken at other stations 

in the Uinta Basin and on the south flank of the Uinta Mountains in 

the following table : 
t-:> Average monthly and annual mean precipitation (in inches) at seven stations 'in the northern part of the Uinta Basin 01· on the south 

g; flank of the Uinta Mountains 

""" ~ 

I I I Length g: Stations Altitude (~~:~~)~I Jan. I Feb. I Mar. I Apr. I May I June I July I Aug. I' Sept. I Oct. I Nov. I Dec. I Annual I ____ f _____________ _ 

>o ~'§~~.,.,- -1 i~ Duchesne _________________________ ------------1 5, 520 I 

~~~~ ~ake--~~ ~ ~= =~ ~= =~ ~= =~ ~~ =~ = ~=~~~ ~~~~ ~ ~ ~~ ~ 1 ~: ~~6 

27 0. 52 0. 49 0. 59 0. 94 0. 75 0. 61 0. 40 0. 71 0. 92 0. 93 0.36 o. 54 7. 96 

61 . 45 .40 .54 . 62 . 69 . 43 . 97 . 68 1. 03 . 76 .38 .46 6. 99 

25 . 33 . 79 . 75 . 61 . 57 .45 . 81 . 91 . 98 . 78 . 37 .96 6. 93 

51 . 63 . 58 . 78 .90 . 91 .43 . 62 .71 1. 09 . 93 . 62 . 54 8.74 

43 . 59 . 65 . 78 . 67 . 73 . 72 1.01 1. 25 1.13 . 97 . 50 . 53 9. 53 

35 . 95 1. 08 2. 68 1. 28 1. 31 4.03 1. 22 1.17 1. 62 1. 98 . 78 2. 76 13.63 

13 1. 40 1. 74 1. 70 1. 48 1. 48 1. 63 1. 50 2.08 1. 80 2.15 1. 00 4. 50 19.00 

I Record ends in 1948. 

H 

z 

~ 

:::0 

0 

t;:j 

q 

0 

~ H 

0 

z 

~ 

~ 
12 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Most of the area below the 8,500-foot contour has a sen1iarid 

climate with a mean annual rainfall of 20 inches or less. Below the 

5,600-foot contour the rainfall is 10 inches or less. Localities along 

the south flank of the Uinta Mountains at the same altitude should 

have similar precipitation, because prevailing Ert,orms come frmn the 

west, and no high mountains are sufficiently close to form a "rain 

shadow" on the western side of the Uinta Basin. No measurements 

of precipitation in the higher parts of the mountains have been made, 

although incomplete records from the Trout Creek Ranger Station, 

at an altitude of 9,200 feet northwest of the area, suggest that the 

precipitation at Elkhorn and Moon Lake 1nay be relatively high 

because of their location in, or at, the mouths of canyons surrounded 

by high mountains. Rainfall usually accompanies thunderstorms and 

is heavier from the middle of July through October. 

From the first of November, through March, most of the precipitation is in the fonn of snow. Both rainfall and snowfall tend to 

increase at greater altitude. The following table, compiled from 

records of the U.S. Weather Bureau, shows the average monthly and 

annual snowfall at stations in the general area. 
Avera.ge monthly and annual snowfall (in inches) at five stat·ions in the nm·thern part of the Uinta Basin o1· on the south flank of the 

Uinta Mountains 

Stations 

Fort Duchesne _______________________________ _ Myton ________________________________________ _ VernaL _______________________________________ _ Duchesne _____________________________________ _ Elkhorn ______________________________________ _ 

I Record ends in 1948. 

Length 

Altitude I of record I Jan. 

(years) I 

4, 739 5, 030 

5, 280 5, 520 

6, 657 

WI 13 

~ ul 13 

~211 

~1 

&4 &21 

Feb. I Mar. 

a91 an2 as ~3 a7 RR ~0. 

i~l i~l 

AP'· I May I Juno I July I Aug. I S•pt. I Oct. I Nov. I Dec. I Annual 

1.0 01 0.0 ----~~r--;~r~ 1.0 2.1 4.1 19.0 .1 T .0 .0 .0 .0 T 1.2 2. 9 14.3 .9 .2 .0 .0 .0 T .8 2. 7 4. 4 23.1 .9 .4 .0 .0 .0 T .8 3. 3 5.3 28.5 

6. 1 3. o . o I . o 1 . o 1 . 7 2. 2 9. 7 10.9 58.6 

z 

8 

::0 

0 

t;:; 

~ 

0 

8 

H 

0 

z 

1---l 

eN 
14 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

The lesser a1nount of snowfall at Myton, as compared with that at 

Fort Duchesne, is due to the higher average and annual temperature 

at Myton. 

The daily and annual variations in tmnperature show a wide range. 

At lower altitudes ( 5,000 to 7,000 feet) during the summer, the days 

usually are hot, but the nights invariably are cool. At higher altitudes, the direct midday sun is wann, but shady areas are relatively 

cool and nights are cold. At a lower level, a similar range in temperature exists during the winter months. July is the hottest month, 

and August is a few degrees cooler. January is the coldest month, 

and December averages ahnost 5° warmer. Extrmnes of temperature 

at Vernal ranged from a maximum of 103° F. in July to a minimu1n of 

-38° F. in January. The average date of the last killing spring frost 

at Jensen or Vernal is late in May, and the earliest elate of killing 

frost in the fall is late in Septmnber, thus giving a minin1um growjng season of approximately 4 months. The U. S. \Veather Bureau 

has furnished the following tables of temperature. 
:Mean monthly and annual tetnperatures ( o F.) at four stations in the nor·ther·n part of the Uinta Basin or on the south flank of the 

Uinta Mountains 

Stations 

Jon.%n ...... ---. -- .. --------.----· .. -.-------. -~ 

Fort Duchesne -------------------------------

~lr~~t====== = = == = = == = = === = = == = = == = = == = = = = = = == = I 

I Record ends in 1948. 

Length Altitude I of record I Jan. (yeats) I 

Feb. I Mar. Apr. I May I June I July I Aug. I Sept. I Oct. I Nov. I Dec. I Annual 

l--l--l--l--1--1--,--,--,--,--,--,--_, __ _ 

~n'l 141 161 I 1861 ". I .. 'I , 'I 65.2 ' 

72.7 7LG I 6131 ''-'1 ~·I 22.6. 46.4 4, 951 57 13.3 20.6 35.5 47.9 .55. 5 64.1 72.0 70.0 61.0 47.8 33.6 19.9 44.2 5, 030 33 15.4 24.4 37.0 47.6 57.2 65.5 72.2 70.4 61.5 49.4 33.6 20.9 46.3 5, 280 44 16.8 23.2 35.3 46.6 55.3 63.9 70.2 67.9 58.8 46.9 34.1 19.9 44.9 

Highest and lowest monthly and annual tempet·ature ( o F.) recot·ded at three stations in the northern part of the Uinta Basin ot· on the 

s01ah flank of the Uinta Mountains 

Length Stations Altitude of record Jan. Feb. Mar. Apr. May 

(years) I 

--------------------------

Max. 59 65 82 86 95 

Fort Duchesne ---------------------------- 4, 951 58 Min. -40 -36 -14 4 18 Max. 54 62 79 85 93 VernaL ____________________________________ 5, 280 48Min. -38 -32 -16 0 12 Max. 57 60 74 83 92 Duchesne ______________________________________ 5, 528 43Min. -43 -32 -16 9 18 

1 Record ends in 1948. 

June July Aug. Sept. 

------------

101 104 101 98 21 31 31 17 99 103 99 94 24 25 32 17 95 99 98 93 25 35 26 16 

Oct. Nov. 

------

88 76 4 -19 

86 72 11 -13 84 72 4 -17 

Dec. 

---

61 -33 

61 -32 

60 

-39 

Annm 

---

10 

-4 

10 

-3 

~ 

-4 

5 

0 

3 

8 

9 

3 

z 

8 

~ 

0 

t:1 

q 

0 

8 

~ 

-

~ 
16 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

The relatively higher monthly and annual temperatures for Jensen 

and Myton, in comparison with Fort Duchesne and Vernal, can be 

explained by the proximity of the two stations to large streams, Jensen 

is located near the Green River, and Myton is near the Duchesne River. 

VEGETATION 

The vegetation in the Uinta River-Brush Creek area is typical of 

the Rocky Mountain states. The lowlands are treeless except along 

watereourses and near springs, where cottonwoods and willows abound. 

Sagebrush and the commonly associated desert shrubs, rabbitbrush, 

shadscale, and salt sage are common at altitudes as high as 9,000 feet. 

Greasewood flourishes on the alluvial flats, particularly in areas that 

have been under cultivation. Pifion and juniper are common on the 

flanks of the higher mountains between 6,000 and 8,500 feet, and thick 

~tands of juniper are present on well-drained rocky soils underlain 

by sandstone or slabby limestone. Above 8,000 feet, and partieularly 

on the high surface that cmnprises the top of Mosby Mountain, Dry 

Fork Mountain, and parts of Diamond Mountain, aspen grow in thiek 

clumps interspersed with grass-covered meadows or "parks." Mixed 

f,tands of pine and aspen appear on all exposures at 8,500 feet; these 

stands continue above 9,000 feet on south slopes. Above 9,500 feet, on 

the flanks and summits of n1ountains, and as low as 7,500 feet in eanyons, pine and fir are the dmninant types. The high plateau land, 

known as Diamond ~fountain, has only a few clumps of aspen; the 

remaining area is covered with native grass and sagebrush. The mountain "parks" support a continuous sod cover, but the lowlands are so 

sparsely covered that they make poor grazing land. Diamond Mountain contains some o£ the best grassland in the area; it has been dryfarmed successfully for grain during the years of high grain prices 

following W oriel "\V ars I and II. 

POPULATION 

The permanent population of the Uinta River-Brush Creek area 

is concentrated along perennial streams, where irrigable land is available. Exce.pt for temporary lumber camps maintained on Pole Mountain, Mosby Mountain, and Dry Fork Mountain, and occasional U. S. 

Forest Service cabins at protected locations, no permanent habitation 

is maintained at high altitudes. During the summer the high mountains within the Ashley National Forest are visited by itinerant sheep 

camps that are moved with the flocks toward the crest of the range 

in July and August and are returned to lower altitudes in early September. A few farms are located on the gently sloping land at the 

mouth of Whiterocks River and Farm Creek southwestward to Uinta 

River, in the valley of Mosby Creek and Deep Creek, along Dry Fork 
INTRODUCTION 17 

of Ashley Creek and Ashley Creek, in the lower part of Steinaker 

Draw, and in the valley of Brush Creek and Little Brush Creek. The 

largest community in the area is located on the rich bottomland of the 

Green River at Jensen, where two general stores, gasoline stations, and 

cafes are grouped at the western approach of the highway bridge over 

the river. The raised terraces of the Green River frmn Little Brush 

Creek southward for a distance of 4 miles to Ashley Creek, and the 

terraces of lower Ashley Creek, are the most highly cultivated areas. 

However, much of this land is used for pasture or the growing of hay. 

Farming and stockraising are the principal occupations. Coal mining has been of considerable importance in the past, but only one 1nine 

in the Deep Creek area and one n1ine at Coal Mine Draw, west of 

Ashley Creek, were active during 1947. Oil is produced at the Ashley 

Creek oil field in T. 5 S., R. 22 E., and some oil from the Rangely field 

in northwestern Colorado is processed at a small refinery on the east 

side of the Green River at Jensen. Lmnbering operations in the Ashley National Forest include cutting 1nine-prop timbers for the mines 

of Carbon County. Vernal, the county seat of Uintah County, is the 

shopping center for the eastern part of the area, and the town of 

Roosevelt is the shopping center for the area from Whiterocks River 

to Dry Gulch. The nearest railheads are at Heber and Helper, Utah, 

and at Craig, Colo. ; therefore, all supplies must be brought into the 

area by truck. 

ACCESSIBILITY AND ROUTES OF TRAVEL 

Paved U. S. Highway 40 enters the area from the east, southeast 

of Jensen, and runs northwestward to Vernal, where it turns southeastward to Roosevelt. This highway provides the principal means 

of access to the area from Craig, Steamboat Springs, and Denver on 

the east, and from Duchesne, Heber, and Salt Lake City on the west. 

Utah State Highway 121 lies a short distance south of the area and 

leads west from Vernal. It connects Vernal, Lapoint, Hayden, and 

Neola, and then turns southward to join U.S. Highway 40 at Roosevelt. Utah State Highway 44 goes north frmn Vernal across the 

Uinta Mountains to l\fanila, Utah, and to Green River, Wyo. The 

route of access to Uinta River Canyon is northward on a graded road 

from Neola. From the mouth of Uinta Canyon, roads lead westward 

to Dry Gulch and southeastward clown the northeast bank of the 

Uinta River to Whiterocks. Whiterocks and Whiterocks Canyon can 

also be reached by means of a graded road leading northward from 

U.S. Highway 40 and 1Jtah State Highway 121. 

An unimproved road, leading northward from Lapoint, supplies 

access to the coal mines on Deep Creek, which are also connected westward with the Whiterocks road by an unimproved, rocky road, and 
18 GEOLOGY OF UINrrA RIVER-BRUSH CREEK AREA, UTAH 

eastward with the settlement of Dry Fork on Dry Fork of Ashley 

Creek. From Vernal, an asphalt paved road leads northwestward to 

the com1nunity of l\iaeser and from there by unsurfaced roads northward to Taylor Mountain and northwestward up Dry Fork of Ashley Creek and East Fork of Dry Fork to Dry Fork Mountain. Access 

to Upper Brush Creek and Ashley Creek is gained by the graded 

Iron Springs road, which branches westward from Utah State Highway 44 after reaching the upland surface above Brush Creek. Two 

roads lead into the Dia1nond Mountain area; the first road branches 

toward the east frmn State Highway 44, 2 miles above the Little Brush 

Creek crossing, and the other road leads northeastward from Vernal 

to Brush Creek and then scales the west slope of Diamond Mountain 

by a series of switchbacks and dugways. Branch roads and trails 

lead from these roads to almost all parts of the area. No single point 

on the map is more than a few miles from a passable automobile road. 

All roads shown on plate 1 were passable for ordinary passenger car 

travel during 1946 and 194:7. 

PREVIOUS PUBLICATIONS 

The earliest published description of the geology of the area is the 

report of J. W. Powell on the eastern Uinta Mountains, published 

in 1876. This report described the structure of the area, and named 

and described geologic formations with such accuracy that all units 

separated on the map are clearly identifiable with present-day stratigraphic nomenclature. Smne fonnations still bear the names given 

by Powell, and (in the opinion of the author) others might better 

have been left with Powell's names than included in formations named 

and described in adjacent areas. 

Geologists of the Fortieth Parallel Survey mapped the geology of 

the area in a reconnaissance in 1869 and 1871 (Emmons, 1877) but 

they added very little to the total knowledge of the area. In 1906, 

F. B. Weeks made a reconnaissance investigation of the geology of 

the Uinta Mountains and published a revised, but crude, map of the 

area. 

The coal deposits of the area, extending as far westward as Little 

Mountain, were described by H. S. Gale and party in 1906, and more 

coal deposits in the Deep Creek area to the west of Little Mountain 

were described by C. T. Lupton in 1910. In 1915, A. R. Schultz made 

a reconnaissance examination of the phosphate deposits and adjacent 

rocks along the flanks of the Uinta Mountains. 

Geologic investigations of the area and adjacent regions have been 

more intensive during the past 20 years, because the possibilities of 

the Uinta Basin as an oil-producing province have been realized. 
INTRODUCTION 19 

The chronological list of publications included here consists of only 

those titles that specifically refer to the mapped area. Other publications dealing with the stratigraphy and structure of adjacent 

regions are cited at appropriate places in the report, and all cited 

publications are given in the principal bibliography. 

Listed in chronological order, these pertinent publications are as 

follows: 

1876. Powell, J. W., Report on the geology of the eastern portion of 

the Uinta Mountains: U. S. Geol. and Geog. Survey Terr., 

2d div. 

1877. Emmons, S. F., Green River Basin: Report of the Geological 

Exploration of the Fortieth Parallel, v. 2, p. 198-202; 291-

300. 

1907. Weeks, F. B., Stratigraphy and structure of the Uinta Range: 

Geol. Soc. Ameriea Bull., v. 18, p. 427-448. 

1910. Gale, H. S., Coal fields of northwestern Colorado and northeastern Utah: U. S. Geol. Survey Bull. 415, p. 204-219. 

1912. Lupton, C. T., The Deep Creek district of the Vernal coal field, 

Uintah County, Utah: U. S. Geol. Survey Bull. 471, p. 

579-594. 

1919. Schultz, A. R., A geologic reconnaissance of the Uinta Mountains, northern Utah, with special reference to phosphate: 

U. S. Geol. Survey Bull. 690, p. 31-94. 

1930. Spieker, E. M., Bituminous sandstone near Vernal, Utah: U. S. 

Geol. Survey Bull. 822, p. 77-98. 

1933. Heaton, R. L., Ancestral Rockies and Mesozoic and late 

Paleozoic stratigraphy of Rocky Mountain region: Am. Assoc. 

Petroleum Geologists Bull., v. 17, p. 109-168. 

1937. Forrester, J. D., Structure of the Uinta Mountains: Geol. Soc. 

America Bull., v. 48, p. 631-666. 

1939. Williams, J. S., "Park City" beds on southwest flank of Uinta 

Mountains, Utah: Am. Assoc. Petroleum Geologists Bull., 

v. 23, p. 82-100. 

1939. Williams, J. S., Phosphate in Utah: Utah Agr. Exper. Bull. 

290, p. 1-44. 

1943. Williams, J. S., Carboniferous for1nations of the Uinta and 

northern Wasatch . Mountains, Utah; Geol. Soc. America 

Bull., v. 54, p. 591-624. 

1944. Walton, P. T., Geology of the Cretaceous of the Uinta Basin, 

Utah: Geol. Soc. America Bull., v. 55, p. 91-130. 

1945. Thomas, C. R., McCann, F. T., and Raman, N. D., Mesozoic 

and Paleozoic stratigraphy in northwestern Colorado and 

northeastern Utah: U. S. Geol. Survey, Oil and Gas Investigations, Prelim. Chart 16. 
20 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

1946. Thmnas, H. D., and l{rueger, M. L., Late Paleozoic and early 

Mesozoic stratigraphy of Uinta Mountains, Utah: Am. 

Assoc. Petroleum Geologists Bull., v. 30, p. 1255-1293. 

1947. Kinney, D. M., and Rominger, J. F., Geology of the Whiterocks River-Ashley Creek area, Uintah County, Utah: U. S. 

Geol. Survey, Oil and Gas Investigations, Prelim. Map 82. 

1949. Unter1nann, G. E., and Untermann, B. R., Geology of Green 

and Yampa River Canyons :tnd vicinity, Dinosaur National 

Monument, Utah and Colorado: Am. Assoc. Petroleum Geologists Bull., v. 33, p. 683-694. 

STRATIGRAPHY 

The sedimentary rocks exposed within the area range in age from 

Proterozoic to Cenozoic; the latter beds were studied only where they 

directly overlie the older formations. Three thousand to 4,000 feet 

of pre-Cambrian strata are present in the area shown on plate 1. 

Formations of Paleozoic and :1\;Iesozoic age total 14,000 feet and include beds of both marine and continental origin. The older rocks are 

located to the north, and progressively younger strata are exposed 

towards the south except in Split Mountain and in the area to the east 

of Jensen where folding brings older fonnations to the surface. 

Rocks of Paleozoic and Mesozoic age are well exposed in canyons of 

south-flowing streams which cross the general strike of the strata at 

right angles. 

The lithologic characteristics, succession, and variation of thickness 

of the formations are summarized in tabular form on plate 6 (in 

pocket). 

PRE-CAMBRIAN 

UINT.A MOUNTAIN GROUP 

Definition.-The oldest rocks exposed in the area are 1nassive quartzitic sandstones and interbedded shales of the Uinta Mountain group 

of Proterozoic age. J. ""\V. Powell (1876, p. 141-145) named these 

rocks the Uinta sandstone or lTinta group, but because that name was 

preoccupied by Marsh ( 1871, p. 196) for lake beds of Eocene age, 

Burbank, Lovering, Goddard, and Eckel in the Geologic Map of 

Colorado (1935) adopted the present name, Uinta Mountain group, 

for the pre-Cambrian rocks for1nerly called "Uinta sandstone," 

"Uinta group," and "Uinta quartzite." 

Dlstrib~ttion and clw'l'acter.-West of Ashley Creek, the pre-Cambrian rocks are limited to a small strip on the northern edge of the 

map area near the South Flank fault zone; to the east of Ashley Creek 

the pre-Cambrian rocks lie north of the escarpment formed by the 

lin'lestone unit of Mississippian age. They form the central mass and 
STRATIGRAPHY 21 

higher peaks of the L"~inta Mountain range. Large outcrops of the 

group are located in the upper canyons of the Uinta River, Whiterocks 

River, Dry Fork of Ashley Creek, Ashley Creek, Brush Creek, and in 

the higher peaks north of the exposures of the limestone unit of Mississippian age. The n1assive quartzitic sandstones yield large angular blocks and 1nany bare rock exposures, but the sandstone areas are 

generally well forested with stands of pine and spruce. Interbedded 

shales are poorly exposed except along \Vhiterocks River and Ashley 

Creek. 

Lithology and thickness.-Massive to thick-bedded sandstone, 

partly quartzitic, and ranging in color from light tan to dull reel or 

purplish reel, is the dominant lithology of the Uinta Mountain group. 

Some intervals are coarse grained and arkosic, with poorly rounded 

pebbles as 1nuch as one-half inch in diameter. The interbedded tan to 

dark-gray or greenish-gray sanely shale, which weathers to drab or tan, 

constitutes less than one-third of the group. Lenticular beds of coarse 

pebbly sandstone and beds of glauconitic sandstone are present in the 

shale. Ripple marks, cross-laminations, and rain-drop (?) impressions 

have been noted in the sandstone. 

Powell's graphic seetion (1876, p. 141 and 143) shows 1nore than 

12,000 feet of the Uinta l\{ountain group in Reel Canyon, of Green 

River, on the north flank of the mountains where the base of the group 

is not exposed. The shale in the upper part of the group on the south 

flank has been studied in 1nore detail than the rest of the formation 

in an attempt to establish its age. At least 3,000 feet of beds are present south of the South Flank fault zone in Uinta Canyon, more than 

1,800 feet in Whiterocks Canyon, 500 feet along Ashley Creek, and 

only 265 feet north of Dia1noncl Mountain. At Loclore Canyon on 

the Green River, east of the area studied, no shale is present in an 

equivalent stratigraphic position. This eastward thinning is believed 

to be due to erosion that occurred prior to Upper Cambrian time, but 

it may be clue to a facies change from shale to 1nassive quartzite. 

Stratigraphic relations and age.-The Uinta Mountain group rests 

unconformably upon a cmnplex series of quartzites, schists, and intrusive rocks (the Red Creek quartzite) exposed in a sn1all area north 

of Browns Park. Powell (1876, p. 140) records about 10,000 feet 

of red sandstone beds deposited against the Red Creek quartzite and 

obviously derived frmn the older rock. In the western part of the area, 

the Uinta Mountain group is overlain by the lin1estone unit of Mississippian age but east of Brush Creek it is succeeded by the Lodore 

formation of probable Late Cambrian age. 

The interbedded shales, especially the well-exposed section along 

vVhiterocks River, offer the best possibilities for the preservation of 

fossils but repeated searches have failed to reveal evidence of ancient 

life. In the absence of paleontologic evidence, the age of the Uinta 
22 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Mountain group is dependent upon its stratigraphic position beneath 

the Lodore formation of Late ( ~) Cambrian age and above highly 

metamorphosed Red Creek quartzite. The rocks of the Uinta Mountain group were originally assigned to the Devonian by Powell ( 1876, 

p. 70), but were later placed in the pre-Cambrian by Gale (1910, p. 47), 

Schultz (1920, p. 24), and Burbank, Lovering, Goddard, and Eckel 

( 1935), and are so considered in the present report. 

Conditions of deposition.-The great thickness and general coarsegrained character of the beds suggest rapid accumulation of sediments 

in a subsiding basin. The presence of ripple marks, cross-lan1inations, 

and rain-drop ( ~) impressions in the sandstones indicate that son1e of 

the beds were deposited in water subject to current action and sometimes were exposed to the air. Glauconitic sandstone beds in the thick 

shale unit on 'Vhiterocks River are probably of marine origin, "\vhich 

suggests sea encroachment late in the deposition period of the lTinta 

Mountain group. Eardley ( 1940, p. 830-831) has suggested that rocks 

of similar stratigraphic position and appearance in the northern 

vV asatch Mountains accumulated between the highland of northern 

lTtah (represented by the outcrops of the Reel Creek quartzite), and 

the highland of central Utah (represented by the igneous and metamorphic rocks of the lTncompahgre Plateau 100 miles to the south). 

CAMBRIAN SYSTEM 

LODORE FORMATION 

Definition.-The only Cambrian fonnation in the area "\vas named 

by Powell (1876, p. 41, 147) for exposures in Loclore Canyon on the 

Green River about 15 miles east of the area 1napped. At the type section in Dunn's Cliff (now known as Limestone Ridge), the formation 

is 460 feet thick and consists of soft sandstone and shale with conglomerate at the base. A section 1 mile north of Hells Half Mile 

on the Green River and 2 miles west of the type locality, is approxilnately 440 feet thick. At this locality, the lower 290 feet of tan to 

reddish sandstone is very feldspathic at the base, and grades upward 

into green micaceous sandy shale and sandstone 150 feet thick. The 

color of the upper sandy shale and sandstone is due to glauconite which 

is present in the shale and is extremely abundant in the interbedded 

sandstone. 

Distrib~ttion and character of outcrop.-Within the mapped area 

the lower arkosic coarse-grained sandstone is well exposed beneath 

the limestone unit of Mississippian age on the peaks north of Diamond 

Mountain and east of State Highway 44. The upper green shale 

does not crop out but is believed to be present in a covered interval 

between the arkosic sandstone and the overlying limestone unit of 

Mississippian age. West of Highway 44 the Lodore formation is thin; 

it is not known to extend west of Brush Creek. 
STRATIGRAPHY 23 

Lithology and thickness.-East of State Highway 44 the lower part 

of the Lodore formation is light gray to pink, coarse-grained arkosic 

sandstone. The bedding of the forn1ation ranges from massive to 

thick bedded; cross-lamination is common. The feldspar fragments 

are salmon colored, one-half inch to 1 inch 1naximum diameter, and 

generally slightly rounded; some pieces represent only slightly worn 

cuhedral crystals derived from a coarse-grained granite or pegmatite. 

Feldspar of similar appearance is present in the pegmatites intrusive 

into the Red Creek quartzite and in the coarser grained arkosic beds 

of the Uinta Mountain group. On Little Brush Mountain, a short distance west of State Highway 44, the basal arkosic sandstone was not 

noted in outcrop, but blocks of pink arkosic sandstone, probably representing the lower part of the Lodore, occur as float resting on shale 

of the Uinta Mountain group. From the size of these blocks it is 

probable that the lower sandstone has thinned to about 6 feet. Thin 

slabs of pink arkosic sandstone cemented by tan dolomitic limestone 

were noted on the west side of Brush Mountain. 

At the Iron Springs road bridge on Brush Creek, beds of greenish 

micaceous sandstone, and coarse-grained to pebbly, cross-laminated, 

thick-bedded, light-gray quartz sandstone (which underly the limestone unit of Mississippian age) were first believed to correlate with 

the Lodore formation, but the absence of pink feldspar grains suggests that these beds belong to the Uinta Mountain group. Similarly, 

a 25- to 60-foot bed of massive, white, coarse-grained sandstone with 

well-rounded pebbles of vein quartz and quartzite (underlying the 

limestone unit of Mississippian age on Ashley Creek and in the headwaters of East Fork of Dry Fork), is interpreted as being part of a 

bed locally occurring at the top of the Uinta Mountain group. 

The Lodore formation thins frmn 155 feet north of Dian1ond Mountain to a thickness of less than a foot on Dyer Mountain. The 

upper part of the formation is only 32 feet thick north of Diamond 

~fountain and wedges out a short distance east of Highway 44. 

Fossils and age.-N o fossils were found within this area, but G. E. 

Untermann and B. R. lJntermann ( 1949, p. 690) report a fauna from 

the upper part of the Lodore formation within the Dinosaur National 

~Ionun1ent that has been identified by G. Arthur Cooper and Christina 

Lockman Balk as of Late Cambrian age. To the west of the Uinta 

River-Brush Creek area, in the vicinity of Peterson's Sawmill north 

of Rock Creek, John Huddle (personal communication, 1948) has 

eollected a poorly preserved. Late Cambrian fauna from the sandy 

shales above the thick Pine Valley conglomerate, which was named 

and assigned to the Ordovician system by Forrester (1937, p. 638). 

Stratigraphic relations and correlation.-Along the Green River, 

Powell (187'6, p. 144-145) states that the Lodore formation rests on a 

very irregular erosional surface cut in massive quartzite of the Unita 
24 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Mountain group. A discordance of dip from 4° to 6° has been 

measured in the strata above and below the unconforn1ity. In the area 

of this report, the bm{ndary between the Lodore and the Uinta Mountain group appears regular, and no divergence of clip has been detected. 

It is only in the eastward thinning of the shale, at the top of the 

underlying group, that evidence is found for unconformable relations; 

this thinning n1ay be due to facies change from shale to massive 

quartzite. 

Without identifiable fossils, the Lodore formation cannot be definitely correlated with formations of Late Cambrian age in adjacent 

areas. The lo\ver arkosic sandstone might be correlated with the 

Sawatch sandstone of central Colorado and the Ignacio quartzite of 

southwestern Colorado, and the upper glauconitic shale might correspond with the limestones of Late Cambrian age recorded from 

adjacent mountain ranges. 

Conditions of deposition.-The lower arkosic sandstone is believed 

to have been derived from highlands to the north, which are represented by outcrops of Red Creek quartzite in the Browns Park area 

of northwestern Colorado. The feldspar closely resmnbles crystals in 

the pegmatites of the ancient metan1orphic terrane, and the occasional 

fresh, unweathered euhedral crystals could not have been transported 

far. The lower sandstone was probably deposited by streams flowing 

frmn an area underlain by Red Creek quartzite. The abundant 

glauconite and the marine faunas in adjacent areas indicate occasional 

marine environment for some of the upper shale. 

CARBONIFEROUS SYSTEM 

The Carboniferous rocks offer pecular problems of subdivision and 

nmnenclature in the eastern Uinta Mountains. In ascending order, 

they consist of (1) 900 to 1,200 feet of light- to dark-gray, cherty limestone and dolmnitic limestone with intercalated beds of tan sandstone 

near the top; (2) 80 to 280 feet of black shale with thin beds of black 

argillaceous limestone; ( 3) 300 to 415 feet of light-gray cherty limestone ; and ( 4) 735 to 960 feet of red sandstone, shale, and argillaceous 

limestone with intercalated beds of gray limestone, grading upwards 

into ( 5) 1,015 to 1,275 feet of fine- to medium-grained light-gray 

sandstone. 

The basal part of the thick limestone unit has an early Mississippian 

fauna typical of the Madison limestone of Montana (Peale, 1893, p. 

32-33), but the upper part, which has a fauna that is poorly preserved 

and, for the most part, uncliagnostic, may be of early or, in part, of 

late Mississippian age. Because fossil evidence points to the early 

Mississippian age of the lmver part of the limestone unit and to the 

possibility for a late Mississippian age for the upper part, the whole 
STRATIGRAPHY 25 

unit has been assigned to the lower and upper J\IIississippian in this 

report. The black shale unit overlying the thick basal limestone is 

poorly exposed and its upper boundary is not visible. It carries a 

late Mississippian fauna, and west of vVhiteroeks River it rests on 

reel sandstone which may have been derived frmn the solution of the 

underlying sandy limestone during a period of subaerial erosion. 

The light-gray cherty limestone overlying the blaek shale unit is 

remarkably consistent, in both thickness and lithology. It earries a 

fauna, which, although it ineludes many undiagnostic forms, has an 

early Pennsylvanian aspect. In this report, it is considered the basal 

men1ber of the Morgan formation because it resembles the basal nlember of the Morgan formation of the central vVasatch Mountains (Calkins and Butler, 19±3, p. 28-29) and may have a counterpart (Calkins, 

F. C., personal communication, 1949) in the type locality of the Morgan on Weber River (Blackwelder, 1910, p. 529-530). The overlying 

red sandstone, shale and argillaeeous limestone appear to be conforlnable with the underlying li1nestone and grade upward into tan to 

light-gray, crossbeclded sandstone, with thin beds of light-gray, cherty 

limestone. The upper boundary of the Morgan formation is drawn at 

the top of the highest limestone bed in the predominantly massive 

sandstone sequence. 

The highest formation of the Carboniferous system, a massive, 

partly crossbedded, Jine- to medimn-grained, light-gray sandstone, is 

the Weber sandstone. The entire unit is probably Pennsylvanian in 

age and is overlain by the Park City formation of Permian age. 

MISSISSIPPIAN SERIES 

LIMESTONE UNIT 

Definition.-In this area the limestone unit of Mississippian age 

ineludes probable equivalents of the Madison limestone, the Deseret 

limestone, and the Humbug formation, as recognized in the vVasatch 

Mountains (Calkins and Butler, 1943, p. 23-28) and in the western 

Uinta J\IIountains (Huddle and McCann, 1947). These subdivisions of 

the li1nestone unit of Mississippian age are tentatively recognized in 

the detailed section measured at Whiterocks River, but are not sufficiently distinctive in the rest of the area to n1ake possible the mai>ping 

of the units at the seale of the aerial photograph contact prints, 2 inches 

equal 1 1nile. · · 

_Distribution and topographic expression.-The limestone unit of 

Mississippian age is present at isolated exposures in the headwaters of 

Dry Gulch, on Uinta River, Pole Creek, and Farm Creek, and as a11 

escarpment on the southwest side of Whiterocks River. East of 

Whiterocks River, the limestone is broken by the Deep Creek zone of 

faulting so that it occurs only in fault blocks, and farther to the 
26 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

east, in the tributaries of Dry Fork of Ashley Creek and in Black 

Canyon, the limestone is only incompletely exposed south of the 

South Flank fault zone. Virtually complete exposures are present 

from Ashley Creek (fig. 2) eastward across Brush Creek and Little 

Brush Creek to the peaks that separate the valley of Pot Creek from 

Diamond Mountain (the plateaulike area to the south). It also 

appears along the Green River in the center of Split Mountain within 

the Dinosaur National Monument. 

The limestone n1akes ahnost vertical cliffs along strean1s in the 

western part of the area, but in interstream areas it is unconformably 

overlain for the most part by Bishop conglomerate or glacial debris. 

East of Ashley Creek, however, lilnestone ridges rise more than 1,000 

feet above the upper surface of the Bishop and form the higher 

peaks in the area. Beds of cherty limestone form prominent dip 

slopes in this area. 

Lithology arnd thickness.-The lower 215 feet of the limestone 

unit of Mississippian age on Whiterocks River is dark-gray, fine- to 

coarse-grained, massive to thin-bedded cherty limestone with some 

interbedded light-gray, fine- to medium-grained dolomitic limestone. 

The chert is light to dark gray, and occurs as small porous masses or 

as thin lenticular beds. To the east, in equivalent stratigraphic position, are light-gray to tan, fine- to medium-grained, 1nassive to thinbedded cherty limestone and dolomitic limestone. The chert is 

brown to light gray, and for a short distance east of Ashley Creek 

and in the SWl)t sec. 11, T. 1 S., R. 22 E., it forms a massive bed 20 

to 40 feet thick. Beds of coarse-grained limestone in the lower part 

of the sequence on Whiterocks River are crinoidal and moderately 

fossiliferous ; fossils also occur in finer grained rock eastward as far 

as Brush Creek. The dark-gray, coarse-grained cherty limestone on 

Whiterocks River is typical of the Madison limestone as recognized 

in the western Uinta Mountains and Wasatch Mountains, but eastward the lithologic similarity of the lower part of the unit disappears. 

On Whiterocks River, the 750-foot limestone unit that overlies the 

probable Madison limestone equivalent is light-gray, fine- to nlediumgrained cherty limestone with thin beds of reddish sandy limestone 

and tan shale. The chert is light to dark gray and occurs as nodules 

or lenses. One 30-foot bed of coarse-grained crinoidal limestone is 

located 250 feet above the base. Beds of brecciated limestone are 

characteristic of the unit, and some of the breccias appear to have 

been formed in place because the stratification in adjacent fragments 

may be only slightly disturbed. The breccia beds grade·upward into 

massive limestone and appear to have been cemented by material 

similar to the over lying bed. Evidence of disconformity in the sequence is found in the Whiterocks River section, 400 feet above the 

base, where clark-gray, fine- to medium-grained limestone with peb~ 
"' ~ 

CJ• 

1-' 

~ 

co 

I 

<:){ 

r 

"~ 

FIGURE 2.-West wall of upper Ashley Creek canyon from south of Red Pine Setting, showing the Uinta Mountain (Peu) limestone unit of 

~fississippian age (Clu), the black shale unit of Mississippian age (Cbs), and the Morg~n formation [upper member (Cmou), lower member 

(Cmol)]. 

U1 

8 

~ 

H 

~ 

0 

~ 

> "d 

~ 

tv 

""' 
28 GEOLOGY OI<' UINTA RIVER-BRUSH CREEK AREA, UTAH 

bles of chert, sandstone, and iron oxide rest on a slightly irregula ;· 

surface. The entire unit is probably equivalent to the Deseret limestone of the Duchesne River area in the western Uinta ]\fountains. 

The upper 250 feet of the limestone unit of Mississippian age 01~ 

Whiterocks River consist of tan, fine- to medium-grained sandstone 

with beds of brecciated, light-gray, fine-grained limestone. For the 

most part, the unit is not as well exposed as the underlying gray 

cherty limestone, but just east of Brush Creek about 110 feet of interbedded, tan, fine- to medium-grained sandstone, light-gray finegrained limestone, and some dark-gray to reddish shale are exposed 

along the road in NE1,4SE:14 sec. 29, T. 1 S., R. 21 E. On Diamond 

Mountain, in SvVl,i sec. 27, T. 1 S., R. 23 E., a massive red sandstone 

is located beneath the covered interval correlated with the black shale 

unit of J\tiississippian age. In the measured stratigraphic section in 

the \Vlj2 sec. 20, T. 1 S., R. 23 E., the sandstone unit is covered, but 

on the eastern border of the mapped area, in the NWl,i sec. 32, T. 1 

S., R. 24 E., tan-weathering light-gray fine-grained sandstone forms 

good outcrops. The stratigraphic unit at Split Niountain, called 

"Beds of undetermined age" by J\1:cCann, Raman, and Henbest (1946, 

p. 3, 15-17), probably represents this sandstone facies of the limestone 

unit of Mississippian age. These sandstones are believed to be equivalent to the Humbug formation mapped by Huddle and McCann 

(1947) in the Duchesne River area of the western Uinta Mountains. 

The detailed lithology and thickness of the limestone unit of Mississippian age, measured at intervals across the mapped area, IS as 

follows: 

Section of the limestone unit of M~ ississippian a.r;e on the west sicle of IVhiterock.'? 

River in W% sec. 7, T. 2 N., R. 1 E. 

[Measured by D. M. Kinney, J. F. Rominger, R. S. Brown, and P . Verastegui M.] 

Black shale unit: Fine- to medium-grained red sandstone and red shale. 

Limestone unit: Feet 

Limestone, gray, coarse-grained__________________________________ 4 

Shale, gray, platy___ ____ ___ __________ __ __________________________ 2 

Limestone, gray, fine-grained_______ __ ____________________________ 2 

Sandstone, tan, fine- to medium-grained; and limestone, light-gray, 

fine-grained, brecciated_______________ ____ _____ __ __________ _____ 244 

Limestone, light-gray, fine-grained, brecciated_ _____________ ______ __ 152 

Limestone, light-gray, fine-grained, thin-bedded______ ____ ________ __ 30 

J . ...imestone, light-gray, fine-grained, with rare solitary corals________ 83 

Limestone, brecciated, light-gray, fine-grained, tan-weathering; chert, 

dark-gray; and shale, tan, contorted_________________________ ___ 4() 

Limestone, dark-gray, fine- to medium-grained; pebbles of chert, sandstone, and iron oxide pellets at base marking a possible disconformity_________ _________________ _________ ___ ______ ________________ 4~ 

Limestone, light-gray, fine- to medium-grained, jointed______________ 2 

Limestone, light-gray, fine-grained, brecciated and recemented ; grades 

upward into undisturbed limestone______________________________ 112 

Limestone, red, fine-grained_______________________________________ 5 
STRATIGRAPHY 29 

S('ction of the limestone unit of M·ississippian age on the west side of 1Vhiterockg 

River in Wlh sec. 7, T. 2 N., R. 1 E.-Continued 

Limestone unit-Continued 

Limestone, light gray to tan, coarse-grained, crinoidal, with few reddish streaks __________________________________________________ _ 

Limestone, light-gray, fine-grained, with lenses of chert, light-gray __ _ 

Limestone, light-gray, fine-grained; nodules and lenses of light-gray chert; top 8 feet very cherty _________________________________ _ 

Limestone, light-gray, fine-grained, with nodules of light-gray cherL_ 

Limestone, light-gray, medium-grained ___________________________ _ 

Limestone, light- to medium-gray, brecciated; breccia fragments to 2 

feet in diameter ______________________________________________ _ 

Limestone, dark-gray, fine-grained, styliolitic, with lenses of dark-gray 

chert; breaks into angular blocks ______________________________ _ 

Limestone, dolomitic, gray, fine- to medium-grained: forms cliffs ___ _ 

Limestone, light-gray, fine-grained ; makes recess in cliff ___________ _ 

Limestone, dolomitic, light-gray, fine- to medium-grained ; contains 

small solutional cavities to% inch in diameter ___________________ _ 

Limestone, dark-gray, medium-grained; thinly banded on weathered 

surface ______________________________________________________ _ 

Limestone, light-gray, fine-grained, tan-weathering; with beds of limestone; dark-gray, coarse-grained, fossiliferous and thin beds of lightFeet 

30 

56 

97 

30 

36 

28 

25 

35 

3 

3 

gray chert~---------------------------------------------------- 72 

Limestone, dark-gray, massive, fossiliferous, with white chert in small 

lace-like masses: contains solitary corals, coiled gastropods, and 

brachiopods -------------------------------------------------- 28 

Limestone, dark-gray, massive, crystalline_________________________ 14 

Limestone, dark-gray, fine-grained________________________________ 3 

Limestone, gray, fine-grained, thin-bedded ·with unconformity at base_ 7 

Sandstone, tan, fine- to medium-grained, calcareous; and shale, reddish-brown, sanely in thin streaks; contains vugs filled with calcite__ 2 

Limestone, dark-gray, with calcite-filled fractures_________________ 3 

Sandstone, tan to reddish, fine-grained, thin-bedded: interbedcled "\Vith 

limestone, dark-gray, brecciated_________________________________ 11 

1,235 

Section of the limestone ·unit of Missis8ipp·ian age on Diamoncl Mountain north 

of Diamond Gulch f1·om theSE% sec. 7 to the SE1j1 8CC. 1fJ, T. 1 S., R. 23 E. 

[Measured by D. M. Kinney and J. F. Rominger] 

Black shale unit: Covered. 

Limestone unit : 

Limestone, light-gray to mottled tan, fine-grained haekly weathering__ 22 

Covered : probably limestone and sandstone interbedded: Diamond 

Mountain road passes through swale made by this intervaL_______ Hl8 

Limestone, light-gray, fine-grained, with tan to reddish chert nodules_ 43 

Sandstone, tan to gray, fine-grained, caleareous: forms ledge________ fl 

Limestone, light-gray to pink, fine-grained ; 0.5 foot of pink chert 

at base________________________________________________________ 13 

Limestone, light-gray to tannish-gray, fine-grained, slightly eherty ____ 110 

Limestone, light-gray. fine-grained, cherty, with few thin beds of limestone, dark-gray, fine-grained: weathers brown; fossiliferous near 

top ---------------------------------------------------------- 77 
30 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

SeaUon of the li'mestone 'ltnit of Mississippian age on, Diamond Mountain north of 

Diarnonfl Gulch fro'm the BElJ± sec. 7 to the SElf4 sec. 19, T. 1 S., R. 23 E.-Con. 

Limestone unit-Continued Feet 

Limestone, light- to clark-gray, mottled, brecciated_________________ 30 

Limestone, light-gray, fine-grained, slightly dolomitic, thin-bedded, 

fossiliferous, with tan to light-gray reticulated chert____________ 72 

Limestone, light-gray, medium- to coarse-grained, crinoidal and fossiliferous, thin-bedded with light-gray to tan cher~ concretions; 

forms ledge--------------------------------------------------- 52 

Limestone, light-gray, fine- to medium-grained and limestone, coarse, 

crinoidal, thin-bedded; forms slope_____________________________ 73 

Limestone, light-gray, fine- to coarse-grained, crinoidal, thin-bedded; 

forms slope____________________________________________________ 29 

Limestone, light-gray, fine-grained, with lenses of tan chert_________ 4 

Limestone, light-gray, coarse-grained, fossiliferous_________________ lfi 

Limestone, light-gray, slightly porous; limestone, coarse-grained, 

crinoidal; and chert, tan, porous interbedded____________________ 2H 

Limestone, light-gray to brown; oolitic, fossiliferous; solitary horn 

corals abundant; forms ledge___________________________________ 5 

Limestone, light-gray, fine-grained, in part dolomitic, massive; shows 

fine banding and crossbedding on weathered surface; vugs to 1 foot 

in diameter fillecl with calcite; fossils poorly preserved and probably fragmental. Some light-gray chert concretions_____________ 67 

Limestone, light-gray, thin-bedded and brown chert concretions showing "liesegang ring" banding___________________________________ 90 

Limestone, pink to gray, sanely, thin-bedded; poorly exposed_________ 31 

965 

Fossils and age.-The lower 50 to 100 feet of the limestone unit of 

Mississippian age in the western part of the area is abundantly fossiliferous at certain places. A collection (USGS 10,335) frmn the west 

side of Whiterocks River, submitted to James Steele Williams of the 

Geological Survey, was reported as follows : "This is a typical Madison 

limestone assemblage, containing Spi1'ifer centronatrztS Winchell, 

Chonetes loganensis Hall and Whitfield and Schuchertellas? represented by brachial valves." Concerning a second collection (USGS 

10,328) frmn the Wlh see. 36, T. 1 S., R. 20 E., east of Red Pine Setting, Mr. Williams states, "Though none of the species definitely recognized is restricted to the Madison limestone, the assemblage is typical 

of that formation." The upper part of the unit is only sparingly fossiliferous, although poorly preserved cup corals are present at anumber of horizons, crinoidal colmnnals are locally present, and poorly 

preserved and 1nostly fragmental brachiopods are recognizable i1J 

cross section on weathered surfaces. In regard to a large collectior.t 

(USGS 10,359) of brachiopods and corals fron1 the s1nall hill near the 

quarter-section corner bet\veen sections 30 and 31, T. 1 S., R. 24 E., 

close to the northeastern border of the map on Diamond Mountain 

and a short distance belo\Y the base of the interbedded sandstone and 
STRATIGRAPHY 31 

lin1estone at the top of the limestone unit of Mississippian age, Mr. 

'Villiams and Miss Helen Duncan report : 

The Spirifer that is so abundant is, unfortunately, probably a new species. 

It has some affinities with types commonly found in upper Mississippian and 

lower Pennsylvanian rocks in the West but is also allied to a species S. vernonens'is 

Swallow, which has also been reported in upper Mississippian rocks in the West 

but is typically in rocks in the midcontinent that would probably be correlated 

with the Madison limestone. The other brachiopods consist of a few incomplete 

specimens that are tentatively identified as immature individuals of Punctospirifet· subellipticus (McChesney), a large but generically indeterminate shell tentatively referred to Ot·thotetes sp. indet., and two productids that preserve so little 

of the ornamentation that they cannot be generically identified. The assemblage 

looks more like an upper Mississippian one for this area than a typical Madison 

assemblage, but the age could be of Madison. 

Several types of corals are present, but they are so much altered by recrystallization and replacement that it is difficult to interpret internal structures. 'Vhat 

are believed to be two species of Syringopora are each represented by several 

specimens. They resemble, at least superficially, types that are common in the 

Madison but that have been reported from the Ul)per Mississippian as well. 

There is one specimen of a lithostrotionid coral that has been partly silicified, 

partly dissolved, and much recrystallized. I rather think it is a Lithost1·otionella, 

but I have not been able to demonstrate the presence of columellas, so it might 

be a Thysanophyllum. These lithostrotionids are not entirely unknown in the 

lower Mississippian but are much more characteristic of Meramecian and later 

rocks. There are also a number of specimens, mostly fragmentary, of zaphrentoid 

corals. Most of these are small forms, though a few are medium sized. Details 

of internal structure are not clear, and I do not wish to make even a tentative 

guess as to what genera may be represented. 

No marine fossils were noted in the sandstone and interbedded limestone at the top of the limestone unit of Mississippian age, although 

a 1nold of a plant stem almost 5 inches in diameter, in fine-grained red 

sandstone, was collected from the NE%,SW~i sec. 27, T. 1 S., R. 23 E. 

This specimen (USGS 10,341) was identified by James S. Schopf of 

the Geological Survey as a root stock of Stigmaria ficoides Brongniart. 

It suggests that continental, or very near shore conditions, were necessary for deposition of the upper part of the unit to the east. Commonly, S. ficoides ranges from late Mississippian to late Permian in 

age, but it could occur in rocks of early Mississippian age. 

The age of the lower part of the thick limestone sequence is indicated as early Mississippian according to 1negafossil collections which 

were obtained 40 to 100 feet above the top of the shale of the Uinta 

~1ountain group on Whiterocks River. Collection USGS 10,359 

frmn the upper part of the unit on Diamond Mountain has conflicting 

elements, but it is probably of late Mississippian age. The black shale 

that overlies the limestone unit is definitely of late Mississippian age. 

The age of the entire li1nestone unit of Mississippian age, therefore, 

has been assigned as "early and late Mississippian." 
32 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Stratigraphic relations and correlations.-The limestone unit of 

Mississippian age rests unconformably upon the pre-Cambrian Uinta 

l\1ountain group 'from Dry Gulch eastward to Brush Creek, and upon 

the Lodore formation of Late ( ~) Cambrian age frmn Brush Creek 

to Diamoncll\1ountain. The dip and strike of the underlying pre-Cambrian and Upper(~) Cambrian rocks and the limestone unit of Mississippian age are very similar except on the south and west side of 

'V"hiterocks River, where the limestone unit of Mississippian age overlaps and cuts out more than 300 feet of the shale at the top of the 

Uinta Mountain group. No other physical evidenee of an unconformity was noticed, although the importanee of the break is proved by 

the absenee of Cambrian, Ordovieian, Silurian, and Devonian rocks 

in the western part of the area, and by the lack of the Orclovieian, 

Silurian, and Devonian rocks in the area \vhere the Lodore formation of Late ( ~) Cambrian age is present. The pronouneed thinning 

of the upper shale unit of the Uinta Mountain group eastvmrd from 

Whiterocks River suggests that eonsiderable erosion of the pre-Cambrian rocks oceurred during the time represented by the hiatus, but, 

as has been pointed out in the discussion of the pre-Cambrian rocks, 

the thinning of the shale at the top of the Uinta Mountain group 

may be clue to facies ehange from shale to red quartzitie sandstone. 

Some evidence is present on the divide between vVhiterocks River 

and Farin Creek that the reel sandstone at the base of the overlying 

Mississippian black shale unit is an accumulation formed by the solution of lime from calcereous sandstone and sandy limestone, although 

karst topography, as reported by Henbest (McCann, Raman, and 

Hen best, 1946, p. 3) in northwestern Colorado, was not recognized. 

It is probable that the time break at the top of the limestone unit of 

Mississippian age is of small duration. The disconformity, 400 feet 

above the base of the limestone on Whiterocks River, and the abundance of limestone breccias at intervals throughout the upper twothirds of the unit, suggest frequent temporary interruptions of sedimentation. 

The limestone unit of Mississippian age includes probable equivalents of the Madison limestone, the Deseret limestone, and the Humbug fonnation of the western Uinta and '::V asatch Mountains, and the 

Madison limestone in Wyoming, southeastern Idaho, and northwestern 

Colorado. A n1uch thinner limestone in central and southwestern 

Colorado, the Leadville limestone, is equivalent to the lower 200 feet 

of the Mississippian strata on vVhiterocks River. In the Grand Canyon area of Arizona, the correlative Mississippian unit is the Redwa1l 

limestone. No Mississippian rocks are present in the area directly 

south of the Book Cliffs, although Dane (1935, p. 24) reports a Madi-
STRATIGRAPHY 33 

son fauna from boulders in a conglomerate of early Pennsylvanian (?) 

age in the Salt Valley area. These boulders could not have been transported far, so the Madison limestone equivalent must have been present in the area and must have bee11 eroded prior to the deposition of 

the Pennsylvanian rocks. 

Conditions of depos-ition.-The limestone unit of Mississippian age 

is predominantly of marine origin, although the tan to reel sandstone 

(in which a mold of a rootstock of Stigmaria ficoides was found on 

Diamond Mountain) n1ay be of continental origin. The crossbedding 

visible on weathered outcrops of limestone, the frequency of occurrence of broken or worn fossil fragments in the upper part of the 

unit, and the abundance of limestone breccia beds, suggest that much 

of the li1nestone accumulated under shallow water and conditions 

suggestive of deposition in an epeiric sea. Deposition was frequently 

interrupted by storms whose waves broke the already consolidated 

lin1estone, but did not disarrange or transport the fragn1ents so that 

they were later recemented by deposition of calcimn carbonate now 

represented by the overlying li1nestone and dolomitic limestone. No 

subaerial conditions are believed to have existed in the western part 

of the area; the only observed case of a surface of scour overlain by 

pebbles of chert, sandstone, and iron oxide is believed to be 

subaqueous. 

BLACK SHALE UNIT 

Definition.-The black shale unit as used in this report is a thin, 

topographically weak sequence of strata of late Mississippian age 

above the limestone unit of Mississippian age and below the lower 

member of the Morgan formation. At Split Mountain, the shale has 

been included in the Morgan formation by Brill ( 1944, p. 632), and 

by McCann, Raman and Hen best ( 1946, p. 2, 3, 13, 14). The shale at 

Split Mountain occupies the same stratigraphic position as the black 

shale unit to the west, but it 1nay be slightly younger. The blac.k 

shale unit is not given a formal formation na1ne here because of the 

lack of a well-exposed section to serve as a type locality. 

Distrib,ution and topographic expression.-The black shale unit is 

present in a fault block in sees. 34 and 35, T. 3 N., R. 2 W., east of 

Pole Creek; in sees. 3, 10, 11, and 12, T. 2 N., R. 1 \V., and sees. 

7, 8 and 5, T. 2 N., R. 19 E., on Farm Creek and Whiterocks River; 

in T. 2 S., R. 19 E. (nnseetionized), in the headwaters of tributaries 

of Dry Fork of Ashley Creek; in sees. 1, 2, 3, and 11, T. 2 S., R 20 E., 

on Ashley Creek at Red Pine Setting; and from sec. 32, T. 1 S., 

R. 21 E., eastward across Brush Creek and Little Brush Creek to 

Diamond Mountain. 
34 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

The black shale unit is not completely exposed at any point in the 

area. The better exposures are along Fann Creek in sec. 11, T. 2 N., 

R. 1 W.; on the east fork of Dry Fork of Ashley Creek in sec. 10, 

T. 2 S., R. 19 E. (unsectionized); !lncl on the Iron Springs Road, 

east of Brush Creek in sec. 29, T. 1 S., R. 21 E. Generally, a heavy 

dark soil mantles the area of outcrop, and blocks of limestone from 

the overlying Morgan formation litter the surface. In places, it has 

been necessary to 1nap the black shale unit by using stratigraphic 

position and the lack of exposures as the only criteria. The shale 

fonns swales or low places in ridges and under lies small subsequent 

streams. Along Ashley Creek, the shale was eroded more rapidly 

than the strata above and, as a result, massive limestone of the 

Morgan formation is undennined and retreats as an almost vertical 

wall. The retreat of the Morgan formation and the weathering of 

the shale has developed a ledge on top of the underlying limestone 

unit of Mississippian age that is almost covered by large angular 

blocks of Morgan limestone. ~Jong Dry Fork of Ashley Creek, the 

black shale forms a similar narrow ledge which slopes gently southward with the dip of the strata. 

Lithology and thickness.-On Farm Creek and on the divide between Fann Creek and Whiterocks River, the black shale unit consists of 14 feet of red sandstone and shale over lain by 6 feet of lightgray to pink limestone and 259 feet of dark -gray to black highly 

organic and pyritiferous shale with beds of greenish sandstone, green 

to tan sandy limestone, and black fossiliferous limestone. Some lignitic shale is present in the upper part of the unit, and analyses of 

bituminous coal samples, reportedly collected from Carboniferous 

strata on Farm Creek, are given in the section on Economic Geology. 

Eastward, a black to dark-gray shale is the most abundant lithologic 

constituent, however, beds of tan-weathering, coquinalike limestone, 

black chert, and thin beds of dark-greenish sandstone are commonly 

the only lithologic criteria present in outcrop because the shale disintegrates to a black clay soil. Black shale fragments have been 

definitely identified east of State Highway 44 near the bridge over 

Little Brush Creek. 

The detailed lithology of the black shale unit at one of the better 

exposures, where the formation is of maximum thickness, is given 

in the following section. 
STRATIGRAPHY 35 

Section of black shale unit in the NW1A, sec. 12, T. 2 N., R. 1 W., on the divide 

between Farm Ot·eek and Whitet·ocks Ri'L•er 

[Measured by D. M. Kinney and J. F. Rominger] 

Morgan formation: 

Lower member : Feet 

Limestone, light-gray, ftne- to coarse-grained, fossiliferous, with 

nodules of light-gray chert______________________________________ 50 

Black shale unit : 

Shale, dark-gray to black, pyritiferous; lignitic shale or lignite beds 

near the top. Streaks of argillaceous, fossiliferous limestone and 

0.5 feet of greenish sandstone at base____________________________ 162 

Shale, dark-gray to black, pyritiferous, with thin bed of green to tan 

sandy limestone near the middle_________________________________ 36 

Shale, dark-gray to black, thin beds of greenish sandstone________ 30 

Sandstone, gray-green, medium-grained____________________________ 12 

Covered, probably black to dark-gray shale_________________________ 19 

Limestone, light-gray to pink, fine-grained__________________________ 6 

Sandstone, red, fine- to medium-grained, and shale, red, sandy______ 14 

279 

The black shale unit decreases in thickness from 279 feet (as 

measured in the above section) to not more than 25 feet in the Nlh 

sec. 36, T. 1 S., R. 23 E., on Diamond Mountain. The eastward thinning appears to be gradual because 125 feet of black shale was measured in the SEl4 sec. 29, T. 1 S., R. 22 E., and 80 feet of shale was 

measured in the SElM, sec. 19, T. 1 S., R. 23 E. The unit seems to 

thicken south of Diamond Mountain because a thickness of 16:5 feet of 

shale was measured at Split Mountain (Thomas, McCann, and Raman, 

1945); however, part of this shale may be of Pennsylvanian age (McCann, Ra1nan, and Hen best, 1946, p. 3). The Tidewater Associated 

Oil Co.-Mohawk Oil Co. well1-58-7, located in the SW14SW14SE14 

of sec. 7, T. 3 S., R. 20 E., passed through 147 feet of black shale 

between 2,588 feet and 2,735 feet depth. 

Fossils and age.-Fossil collections frmn two localities of the black 

shale unit were made in the course of the field work. Because of their 

importance, both localities were visited twice to obtain large, diagnostic collections. The first locality is on the east side of Farm Creek 

near the center of sec. 11, T. 2 N., R. 1 W., lTintah County, Utah. The 

original collection (USGS 10,321) from this locality was submitted to 

James Steele vVillian1s of the Geological Survey, who n1ade the following report in 1949 : 

The most common form and only identifiable species in this collection is 

Dictyoclostus injlatus (McChesney). The genus Chonetes is represented by immature or incomplete individuals that cannot be specifically identified. Other 

genera that have been tentatively identified include: Oom,posita?, Diaphragmus?, 

Atnbocoelia?, and Leiorhynchus?. The Leim·hynchw;?, if it is a Leiorhynchus, is 

of about the same size as L. carbonifenun Git·ty. Several unidentified aviculo-
36 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

pectenoid pelecypods are also in the collection. The age cannot be given with 

certainty because so many of the elements in it are not determinable. The resemblances are more with Mississippian faunules of nearby areas than with 

nearby Pennsylvanian faunnles. 

The second group of colleetions, obtained frmn the sa1ne locality 

in August of 1947, was made by Williams, Mendes, Rominger, and 

IGnney. Mr. vVillian1s made the following report in 1949 on 1naterial 

in Collections USGS 10,350, 10,351 and 10,352: 

These lots contain good brachial valves of Diaphmgmus that show the internal 

characters that typify that genus. The collections also contain Dictyoclostus 

in;fiatus (McChesney), a Scllizoplwria cf. ~'1. su;allotoi (Hall), probably two species 

of Cho-netes, both of the general type of C. illinoisensis Worthern, at least one 

species of Lin[!Ula or of a closely related genus, a smalllinoproductid, at least two 

genera of aviculopectenoids and a few other pelecypods, and two pieces of fish 

remains. 

The fish remains were exa1nined by Dr. David H. Dunkle of the U.S. 

National Museum who reports: 

Specimen No. 1-An unassociated operculum of a palaeoniscoid fish. The 

specimen is not generically and specifically identifiable, but its general habit is 

strongly reminiseent of the corresponding part in members of the Carboniferous 

family Rhadinichthyidae. 

Specimen No. 2-A. typical crossopterygian scale of the cycloid type. In all 

observable characters this specimen suggests identification as the late Devonian 

Holoptychius gigantens. The same attributes, however, permit the assumption 

that the specimen might pertain to either of the Carboniferous rhizodont genera 

Strepsodus or Rhizodopsis. Strepsodus is confined to Mississippian strata in 

various parts of the world. One species, arenos-us, has been described from near 

the base of the lower Mississippian in north-central Pennsylvania. It differs 

from the present specimen in being much smaller and having a greater length 

than breadth. Rhizodopsis is an exclusively Pennsylvanian genus and differing 

similarly in small size and greater length than breadth has been reported in the 

United States from the Allegheny group in Illinois and Ohio. The only other 

published occurrence of a Mississippian crossopterygian is a mandible from the 

St. Louis limestone in Missouri. In the absence of associated seales, this single 

specimen has been referred to the osteolepid lJI egalichthys. 

Of the age of Collections USGS 10,350, 10,351, and 10,352, Mr. 

"\Villiams com1nented, "There is little, if any, doubt that this collection 

is of late Mississippian age, probably Chester, but it 1nay be slightly 

older." 

The second locality frmn which a black shale fauna was collected 

is in the swale in the NEl!t,SEl!t, sec. 29, T. 1 S., R. 21 E., one-half 

1nile east of Brush Creek. Collection USGS 10,348, obtained from a 

thin, brown limestone in the black shale, was submitted to ~ir. Williams who reported as follows: "It contains fragments of brachiopods, possibly representing Spirifers, Punctospirifers, and Compositas, but nothing determinable. No age significance. Mr. Haas 

examined material frmn this collection for conodonts and obtained 
STRATIGRAPHY 37 

an indeterminate species of the genus Oavusgnathus, which genus 

ranges from Mississippian into Pennsylvanian." 

On a second collection from the same locality, ~fr. Williams reports, 

Collection USGS 10,35~. This collection contains nothing that is determinable 

except possibly some immature Cleiothyridinas. Fragments of brachiopods resembling dictyoclostids of the Dictyoalostus inflatu,s type, and possibly Compositas 

are present, as are crinoid columnals and a few very small and incomplete horn 

corals that are not determinable. No age data of value are provided by the collection, but nothing \Vas seen that conflicts with a late Mississippian age. Mr. 

Hass found several fragments of conodonts belonging to the genera Cavusgnathus 

and Ligonodlna and one specimen that may be Gnathodus. 

Stratigraphic relations and correlation.-The stratigraphic relations of the black shale unit to the underlying limestone unit of Mississippian age and overlying lower member of the Morgan forn1ation 

are poorly known because of the lack of exposures. On the divide between Whiterocks River and Farm Creek, the red sandstone included 

in the black shale appears to rest conformably upon the underlying 

gray li1nestone of Mississippian age and to be overlain conformably 

by light-gray to pink fine-grained limestone which is succeeded by a 

covered interval presun1ed to be black shale. The boundary between 

the limestone unit and the black shale unit 1night have been drawn 

equally well at the top of the light-gray to pink fine-grained linlestone, because some tan to red sandstone is characteristic of the upper 

part of the limestone unit. To the east, the boundary of the limestone 

unit of Mississippian age and the black shale unit is on a dip slope of 

limestone; the stratigraphic relations are not exposed. The upper 

boundary of the black shale is covered throughout the area. 

The black shale has been recognized in all sections that were measured along the south flank of the Uinta Mountains. From the faunal 

evidence derived frmn study of the collections made by Huddle in the 

Duehesne River area, there seems little doubt that the entire unit is 

of uniform age. A black limestone and black shale unit occupying a 

similar stratigraphic interval in the Cottonwood-American Fork area 

of the Wasatch Mountains was included in the Hmnhug formation by 

Calkins and Butler (1943, p. 27). Fossils collected frmn the black 

limestone-shale unit in Big Cottonwood Canyon were assigned to 

the upper Mississippian by G. H. Girty (Baker, Huddle, and Kinney, 

19±9, p. 1177). It is probable that this unit in the eentral Wasatch 

Mountains is continuous with the black shale unit on the south flank 

of the Uinta Mountains. Lithologically, the post-Hmnbug roeks 

north of the thrust fault, which passes through Heber Valley, closely 

resemble the basal part of the Great Blue lin1estone south of the fault 

and these units have been tentatively correlated by Baker. It is possible, nevertheless, that the black shale unit of the Uinta Mountains is 

to be eorrelated with the lower part of the Manning Canyon shale 
38 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

(upper Mississippian, lower Pennsylvanian) which overlies the Great 

Blue limestone. 

Oonditimus of deposition.-The presence of a normal marine fauna, 

in the black shale unit on Farm Creek and east of Brush Creek, indicates that marine conditions existed over the major portion of the area 

during most of the period of shale deposition. Swan1p conditions 

during the deposition of the upper part of the shale are suggested by 

streaks of lignitic shale and the reported occurrence of a coal prospect 

along Farm Creek. The source of the black n1uds and the calcareous 

1nuds, which for1ned the shale unit, was probably smnewhere west of 

the Wasatch Mountains because the formation thickens in that direction. The attenuated black shale unit along the south flank of the 

Uinta Mountains probably represents a foreland facies of the thicker 

sections to the west. 

PENNSYLVANIAN SERIES 

MORGAN FORMATION 

Definition.-The name "Morgan formation" was originally given to 

exposures of red sandstone and shale with intercalated limestone in 

the upper canyon of the Weber River, near the town of Morgan in 

the Wasatch Mountains (Blackwelder, 1910, p. 529). At that location, it rests on the cavernous weathered surface of a gray limestone, 

whose fauna was assigned by Girty to the early Pennsylvanian (Blackwelder, 1910, p. 530), and it grades upward through alternate gray 

shale, limestone, and sandstone into the \V eber quartzite. A fauna 

from the intercalated li1nestone is also early Pennsylvanian in age 

(Blackwelder, 1910, p. 530). A formation, tentatively correlated 

with the Morgan in the central Wasatch Mountains, 35 miles south 

of the type locality (Calkins and Butler, 1943, p. 28-29, and Baker, 

1947), consists of 250 feet of cliff-forming blue-gray cherty limestone 

over lain by 100 feet of thin-bedded 1naroon limestone and calcareous 

shale, and some gray limestone. It is separated from the underlying 

limestone unit of late Mississippian age by an erosional unconformity. 

The Morgan formation is also identified in the Duchesne River area of 

the western Uinta Mountains, where 240 feet of gray cherty limestone 

is overlain by 210 feet of red sandstone (Huddle and McCann, 1947). 

In the Uinta River-Brush Creek area, the formation includes 300 to 415 

feet of light-gray cherty li1nestone overlain by 250 to 440 feet of red 

sandstone, shale, and argillaceous li1nestone with intercalated beds 

of gray limestone. 

Distribution and topographic empressions.-The Morgan formation is well exposed in the cliffs on the west side of Whiterocks River 

(fig. 3), along Ashley Creek (fig. 2), along Dry Fork of Ashley Creek, 

and at isolated places in the northern part of Diamond Mountain. 
FIGURE 3.-Small anticlinal fold in the upper member of the Morgan formation (Cmou) on the west side of Whiterocks River. Upper mem- ber of Morgan formation overlain by Weber sandstone (Cw) and underlain by lower member of Morgan formation (Cmol). 

U1 

t-3 

::tl 

H 

~ 

0 

::tl 

~ 

c:,.., 

~ 
40 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

The lower gray cherty limestone member forms cliffs or steep slopes 

and is generally well exposed throughout the area. The over lying 

red sandstone, shale, and argillaceous limestone member is relatively 

soft, disintegrates into a red sandy soil, and rarely forms good exposures. 

Lithology and thickness.- The lower member of the Morgan forn1ation includes beds of light- to dark-gray, fine- to coarse-grained, thinto thick-bedded, cherty limestone. The chert is generally light gray, 

but in certain beds it is red to orange red. The base of the upper member is soft, red sandy shale, fine-grained sandstone, and argillaceous 

limestone with intercalated beds of light-gray to pink coarse-grained 

fossiliferous limestone. It grades upward into calcareous, fine- to 

medium-grained, crossbedded or massive, tan to red sandstone with 

occasional thin beds of light-gray to pink, medium- to coarse-grained 

limestone. The sandstone is similar to that in the overlying Weber 

sandstone, but it contains more calcareous cement, is slightly darker 

in color, and is crossbedded in thinner beds. 

The lower 1nember of the Morgan formation thins from 415 feet 

on Whiterocks River to 296 feet on Split Mountain. The upper member is remarkably constant in thickness, ranging from 960 feet in the 

west to 900 feet on Diamond lVIountain. However, in the section at 

Split Mountain measured by McCann, Raman, and Hen best ( 1946, 

p. 5- 13), it is only 711 feet thick. 

The following sections measured on Whiterocks River, Ashley 

Creek, and Diamond Mountain show the detailed lithologic variaation in the ~{organ formation. 

Section of Morgan formation in cliff on west side of Whiterocks River SW:Y4 

sec. 7 and NW:l4 sec. 18, T. 2 N., R. 1 E., Uintah County, Utah 

[Measured by D. M. Kinney, J. F. Rominger, P. Verastegui M., and R. S. Brown] 

w· eber sandstone : 

Sandstone, light-gray, fine-grained, massive, crossbedded, slightly calcareous. 

Morgan formation : Feet 

Sandstone, red to tan, fine-grained, in part calcareous, with a few 

sandy limestone beds and lenses of red chert___________ _________ 517 

Breccia, sandstone, tan and limestone, light-gray-- - ---- ----------- 4 

Sandstone, red, shaly and shale, red, sandy, interbedded with a few 

thin beds of sandy red limestone___________________ ___________ 378 

Limestone, light-gray with lenses of light-gray chert________________ 9 

Sandstone, tan, fine- to medium-grained__________________________ 6 

Sandstone, red, shaly with beds of limestone, reddish-gray, finegrained --------------- ----- ----- ------- ----- - ----- ------------ 49 

Limestone, gray, with lenses of light-gray chert___________ __ _____ 109 

Limestone, white, cherty, rough-weathering___ _______ ____ _____ ____ 10 

Shale, reddish-brown__ ____ ___ __ _____ ______ __ ___________ ______ ____ 2 

1,084 
STRATIGRAPHY 41 

Section of the Ume:stone tt,nit of Mi.<i:si:s:sip]Jian age on the 'lDe:st :side of Whiterock:s 

cliff on east side of Ashley Greek 1lh 'miles west of the 'U'est boundar·y of sec. 

8, T. 2 S., R. 21 E. Upper part of :section rneasur·ed in cliff on west side of 

A_shley Greek in the SElf± sec. 2 and NE¥4 sec. 11, T. 2 S., R. 20 E. (unsectionized), Uintah County, Utah 

Pleasured by D. M. Kinney, J. F. Rominger, P. Verastegui M., and R. S. Brown] 

'V eber sandstone : 

Sandstone, light-gray, tan-weathering, crossbedded, thick-bedded to massive, 

fine-grained, calcareous. 

Morgan formation: Feet 

Limestone, gray, medium-grained, with fossils and a few chert concretions ------------------------------------------------------ 16 

Limestone, light-gray, sandy, rough-weathering____________________ 6 

Sandstone, tan, calcareous, slab by-------------------------------- 22 

Limestone, light-gray, massive, thick-bedded, fine-grained, with poorly 

preserved fossils_______________________________________________ 14 

Sandstone, tan, fine-grained, crossbedded, with streaks of crinoidal 

limestone ----------------------------------------------------- 190 

Sandstone, red to tan, fine-grained, crossbedded with thin beds of fossiliferous crinoidal limestone___________________________________ 301 

Sandstone, tan, fine- to medium-grained, crossbedded, calcareous____ 191 

Shale, red, sandy, with a few thin beds of fossiliferous limestone____ 134 

Sandsto11e, light-gray to pink, qtlartzitic, thin-bedded______________ 5 

Shale, red, sandy, with a few thin beds of fossiliferous limestone____ 44 

923 

Section of Morgan fonnation on north side of Diamond Gulch, Dianwnd 

Mountain. SEl;~ :sec. 29, to NW lf± :sec. 32, T.1 S., R. 23 E. 

[Measured by D. l\L Kinney and J. F. Rominger] 

\Veber sandstone : 

Sandstone, light-gray, tau-weathering, fine-grained, crossbedded, thickbedded. 

l\Iorgau formation: Feet 

Limestone, sandy, light-gray to pink, fine-grained, thin-bedded, 

cherty; weathers to slabs______________________________________ 18 

Limestone, light-gray, fine-grained, fossiliferous, with ovoid tau to 

red chert concretions to 6 inches in diameter____________________ 8 

Sandstone, tan, calcareous, crossbedded, fine-grained______________ lHi 

Limestone, light-gray to pink at top, fine- to medium-grained crinoidal 

and fossiliferous at base, with lenses of tan chert to 2 feet in length_ 6 

Sandstone, tau, fine-grained, crossbedded, calcareous______________ 35 

Limestone, fine- to coarse-grained, light-gray, criuoidal, with abundant 

light-gray ovoid chert nodules _______ -------------------------- 27 

Sandstone, light-gray, tan-weathering, fine-grained________________ 51 

Limestone, light-gray, coarse-grained, fossiliferous________________ 10 

Sandstone, light-gray, tan-weathering, fine-grained, crossbedded, 

calcareous _________________________________________ ~---------- 40 

Sandston~ red, fine-grained_____________________________________ 20 

Limestone, gray, coarse-grained, with nodules of red chert__________ 6 

Sandstone, light-gray to tau, fine-grained__________________________ 119 

Limestone, dark-gray, with concretions of red chert________________ 3 

Sandstone, light-gray, fine-grained________________________________ 90 
42 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Section of Morgan formation on north side of Diamond Gulch, Diamond 

Mou.ntain. SE1j1 sec. 29, to NW~ sec. 32, T. 1 S., R. 23 E.-Continued 

Morgan formation-Continued Feet 

Sandstone, light-gray, fine-grained, calcareous, with some pink to 

white chert___________________________________________________ 10 

Limestone, gray to red, coarse-grained____________________________ 66 

Sandstone, tan and red interbedded, fine-grained__________________ 30 

Shale, red and sandstone, thin-bedded, red, interbedded____________ 59 

Limestone, red and purple to gray, argillaceous__________________ 194 

Standstone, light-gray, tan-weathering, fine-grained, cherty-------- 1 

908 

Fossils and age.-Certain limestone beds in the Morgan formation 

are abundantly fossiliferous. Collections 1nade at a number of places 

and at different stratigraphic positions were submitted to James Steele 

Williams of the Geological Survey. Collection USGS 10,332, which 

was obtained near the base of the lower limestone member on the west 

side of vVhiterocks River, and collection USGS 10,338, from about 

the middle of the lower li1nestone member at the same locality, were 

reported as follows : 

Collection USGS 10,.')32.-This collection contains a horn coral tentatively 

identified by Miss Duncan as Gan,inia cf. C. flaccida Easton, Dictyoclostus cf. 

D. in/latus (McChesney), a linoproductid represented by fragments, a small 

Juresania ?, Spirifers of the S. occidentalis type, Compositas, and unidentified 

fragments of other brachiopods. Caninia flaccida is so far known only from 

the Mississippian, but the identification is not certain and the range of the 

species has not been adequately tested. The Jm·esania? suggests Pennsylvanian 

age, whereas the other fossils are types that occur in both Mississippian and 

Pennsylvanian rocks. The evidence is perhaps slightly stronger for a Pennsylvanian age than for a reference to Mississippian. 

Collect·ion UBGB 10,338.-This collection is a large one, but it is not varied, as 

only a small number of species are represented. Included in it are Spirifer oc· 

cidentalis ( Girty) ; a species of the Bpirifer opim1ts type; a productid that probably represents the form commonly identified in this region as Jttresania nebrascensis (Owen), but I cannot be sure that it actually belongs to that genus: 

a Composita; and a JJiyalina.. That is very probably Pennsylvanian in age, but 

the possibility that it might be Mississippian cannot be ruled out. 

These determinations are the basis for separating the limestone 

from the underlying black shale unit which carries an upper Mississippian fauna. 

Collections USGS 10,329, 10,330, and 10,331, from limestone beds 

near the top of the Morgan formation in sec. 1, T. 3 S., R 20 E., on 

the west side of Ashley Creek, and collection USGS 10,337, from near 

the base of the upper member on the west side of Whiterocks River, 

were reported a! follows : 

Collection UBGS 10,329.-This collection consists of Spirifers of the S. 

opimus type and some crinoid stems. The collection is of Des Moines or older 

Pennsylvanian age. 
STRATIGRAPHY 43 

Collection USGS 10,330.-This collection contains bryozoans tentatively 

identified as belonging to the genera Tabulipora, Polypora, Fenestella, and 

MeekopoTa. There is also a rhomboporoid form. (Identified by Miss Helen 

Duncan). The brachiopods include species close to Pt·oductus ( Dictyoclostus) 

hermosanus Girty and one that is probably a Prodttcttts (Linoproductus) coloradoensis Girty. There are also Spirifers of the S. opimus type. The age is 

Des Moines or older Pennsylvanian. 

Collection USGS t-0,331.-This collection contains Bryozoa belonging to the 

genera Septopora, Fenestella, and Polypora as well as a rhomboporoid form. 

The brachiopods are referable to the genera Composita, Spit·ifer, and Productus 

s. 1. The Spirifers are of the S. occidentaUs type. One of the productid species 

is probably P. (Dictyoclostus) hermosanus Girty, and the other is a linoproductid 

of larger size. The assemblage suggests. Pennsylvanian age. 

Collection USGS 10,337.-The fossils include crinoid columnals, stenoporoid ( ? ) bryozoans, a Spirifer cf. S. occidentalis ( Girty), a part of a brachial 

valve of a Derbya ?, and many immature compositids. A fragment of a trilobite 

pygidium was referred to Dr. J. Marvin Weller, of the Universeity of Chicago, 

who identified it as Paladin? sp. indet. This collection has a Pennsylvanian 

aspect. 

From these determinations, it is evident that the lower member of 

the Morgan formation may be early Pennsylvanian or late Mississippian, but that Mr. Williams favors an early Pennsylvanian age. The 

limestone, therefore, has been considered as the lower member of the 

Morgan formation and separated from the underlying black shale unit 

that definitely is of late Mississippian age. 

A fusulinid collection from 50 feet below the top of the upper member of the Morgan formation in the NW14 sec. 18, T. 2 N., R. 1 E., 

on Whiterocks River collected by M. N. Bramlette in 1949 was reported by L. G. Henbest as follows : 

The following fusulinidae are identifiable: lV edekindelUna aff. lV. euthysepta 

and a species of Fusttlina-. The early half of the Des Moines epoch is indicated. 

The preservation is poor, but the identifications seem rather secure. 

A second fusulinid collection from 50 feet below the top of the upper member of the Morgan formation near the E1;4 corner of sec. 6, T. 

3 S., R. 20 E., on DTy Fork of Ashley Creek, made by M. N. Bramlette in 1948, was submitted to L. G. Henbest of the Geological Survey. 

Mr. Hen best reports as follows : 

Textularians, Tetratamis sp., and a species of fusulinid that belongs to the se- ries represented by Fusulina girtyi and F. distenta were identified in this sam- ple. Also present are two sections rather definitely identifiable as Prismopora. 

Middle Des Moines age is definitely indicated and approximately the middle or slightly lower part of that epoch is strongly suggested. 

These age assignments are consistent with the fusulinid faunas collected by Henbest (McCann, Ra1nan and Henbest, 1946, p. 5-9) from the 

upper part of the Morgan formation in Split Mountain canyon. Mr. 

Henbest reports that all of these faunas are of "early Des Moines 

forms," except for one that was located 32 to 57 feet from the top of 

295163-55--4 
44 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

the upper Morgan, which he classified as "upper or possibly middle 

Des Moines form." 

The upper member of the Morgan is herein considered of Pennsylvanian age, probably Des Moines. 

Stratigraphic ~relations and correlation.-The contact of the limestone mmnber of the Morgan with the underlying black shale unit is 

not exposed in the area. However, both at Split Mountain (Thomas, 

~1cCann, and Raman, 19±5) and in the Duchesne River area (Huddle 

and ~lcCann, 1947), the limestone is conformable with the shale. The 

limestone grades upward into the soft red sandstone, shale, and argillaceous limestone, with thin stringers of reel sandy shale occurring 

smne distance below the top of the limestone, and thin beds of fossiliferous limestone occurring in the red unit. Sin1ilar conditions exist at Split Mountain, but in the Duchesne River area an erosional 

break is suggested by "a relief of 1 to 2 feet in a horizontal distance of 

4 feet" and "large 1nasses of chert in the lower member projecting into 

the overlying red sandstone" (Huddle and McCann, 194 7). In the 

upper part of the fonnation, the deposition appears to be continuous 

except at Whiterocks River where a breccia bed, 4 feet thick and 857 

feet above the base, includes angular pieces of sandstone and gray 

limestone. The upper boundary of the Morgan formation is arbitrarily taken at the top of the highest limestone and the overlying 

vVeber sandstone is conformable upon this bed. Frmn the above fusulinid detenninations, all frmn a stratigraphic horizon approxilnately 50 feet below the top of the upper member of the Morgan fonnation, it appears that the upper part of the Morgan formation is progressively younger as it is traced eastward. In other words, the Morgan fonnation at Split Mountain is in part equivalent in age to the 

vVeber sandstone at Whiterocks River. 

The Morgan fonnation is correlated with part of the Tensleep sandstone of central Wyoming, the Hennosa formation of western Colorado, and the lower part of the Oquirrh formation in the Provo area of 

the Wasatch Mountains (Baker, Huddle, and Kinney, 19±9, p. 1185). 

Conditions of deposition and origin.-The basalli1nestone member 

o± the l\1:organ fonnation is of marine origin, as shown by its abundant 

invertebrate fauna. The lower part of the upper 1nen1ber, however, 

was fonned partly under marine conditions (as shown by the interbedded fossiliferous lin1estone), and partly under conditions approaching modern offshore deltas (shown by the well-bedded, fine-grained 

reel sandstone, and shale). From the recurrent character of the fossiliferous li1nestones, it is probable that the area of deposition was close 

to sea level, which allowed the sea to enroach over considerable areas 

with a slight change of sea level. The fine- to medium-grained lightgray calcareous sandstone, which (with the intercalated limestones) 

make up most of the upper member of the Morgan, are believed to be 
STRATIGRAPHY 45 

beach sands or dune sands that grew behind the beach and were reworked into thick n1assive beds of crossbedded sand with the succeeding marine encroaclunent. The calcareous cmnenting 1naterial probably came frmn shell frag1nents incorporated in the beach and dune 

sands. 

The pronounced red color in the lower part of the upper mmnber 

of the Morgan formation is believed to be clue to the original red 

color of the sedin1ent; it is not believed to be caused by environmental 

conditions during, or since, deposition. The great preponderance of 

uniform-sized sand grains, and a lack of finer gained sediments in 

che general area, suggest a source area in which the erosion of preexisting quartzites and sandstones provided the bulk of the material. 

The probable equivalence of the upper part of the upper member of 

the }\forgan formation at Split Mountain to the lmcver part of the 

vVeber sandstone at Whiterocks River to the west suggests that the 

source of the red sedi1nents included in the upper men1ber of the 

Morgan formation was to the east or southeast, probably in the Uncmnpahgre Plateau and other areas in central and western Colorado, 

which are underlain by pre-Cambrian, or younger, crystalline rocks 

mnergent during Pennsylvanian time. As indicated by the great 

thickening of the Pennsylvanian rocks in the Provo area of the 

Wasatch Mountains (Baker, 1947), it is probable that there was a 

western source for at least some of the sediment. 

WEBER SANDSTONE 

Definition.-The Weber sandstone (originally defined as a quartzite 

at the type locality, the formation throughout the Uinta Mountains 

and most of the Wasatch Mountains is more correctly referred to as 

a sandstone) was named by Clarence l(ing ( 1876, p. 480-481) and 

geologists of the Fortieth Paralle:i Survey in 1876, for exposures in 

Weber Canyon in the Wasatch Mountains. It was defined as including the strata that were later differentiated by Blackwelder (1910, p. 

529) as the Morgan formation. In the Uinta Mountains, geologists 

of the Fortieth Parallel Survey 1nistakenly applied the name to the 

great thickness of pre-Ca1nbrian rocks, now known as the Uinta 

Mountain group, instead of the less extensive sandstone of Pennsylvanian age. J. W. Powell (1876, p. 149), in his report on the eastern 

Uinta Mountains, named the 1nassive sandstone of Pennsylvanian age 

the Yampa sandstone for the Yampa River which enters the Green 

River from the east in northwestern Colorado. The Yampa sandstone 

was correlated with the 1nore widely used VV eber standstone by A. R. 

Schultz (1920, p. 24) in his report on the Rock Springs uplift. Since 

1920, the na1ne "Weber sandstone" has been used instead of the name 

"Yampa sandstone," which has been rejected by the U. S. Geological 

Survey (Wilmarth, 1938, p. 2381). 
46 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Distribution and topogTaphic eo; pression.-The Weber sandstone 

crops out at intervals between the valley of Pole Creek east of Uinta 

River and Diamond ~fountain. Good exposures can be seen in the 

canyon of Whiterocks River, where the steeply dipping white sandstone of the formation forms the '"gates," that give rise to the name 

"Whiterocks" in the canyon walls of Dry Fork of Ashley Creek, Ashley 

Canyon, Brush Creek (fig. 4), Little Brush Creek, and in discontinuous outcrops on Dia1nond Mountain. The spectacular scenery of Split 

Mountain and Green River Gorge within the Dinosaur National Monument has also been carved from this sandstone. 

Because of its calcareous cement and n1assive character, the Weber 

sandstone is a very resistant fonnation that forms almost vertical 

walls in defilelike canyons on Dry Fork, Ashley Creek (fig. 9), Brush 

Creek, and Little Brush Creek. The deep canyons and steep walls, 

however, may be due as n1uch to the rapid cutting by proglacial 

strean1s during Pleistocene time as to the resistance of the sandstone. 

The 'V eber sandstone, veneered with the Bishop conglomerate of late 

Cenozoic age, forms the southern boundary of the topographically 

high area included in the Uinta Mountains; the area to the south is 

marked by a drop of 1,500 to 2,000 feet in elevation. 

Lithology and thickness.-The Weber sandstone is a uniform, massive, fine- to 1nedium-grained, light-gray, slightly calcareous, quartzose sandstone. Individual grains are not well rounded except in the 

upper 300 to 400 feet of the formation in the Brush Creek area, where 

well-rounded, 1neclimn-to-coarse grains are concentrated along planes 

of crossbedding. In this area (fig. 4), the crossbedding extends between bedding planes 30 to 50 feet apart. However, such crossbedding is relatively rare in the main n1ass of the sandstone exposed on 

Ashley Creek. The massive character of the Weber makes it very difficult for the investigator to detect clips and to accurately measure the 

thickness of the formation. The sandstone possesses relatively small 

amounts of heavy minerals. Quartz grains are clear, and feldspar 

is rare. Although the Weber sandstone has a calcareous cement, no 

beds of limestone are present. 

The Weber sandstone ranges in thickness from 1,015 to 1,275 feet 

in this area, with an average of 1,150 feet. The thicker sections (in 

Ashley Creek and on Dia1nond Mountain) are adjacent and are located in the area in which the upper 300 to 400 feet of the Weber is 

particularly cross bedded. 

Fossils and age.-No fossils have been found in the Weber sandstone and, therefore, the age of the fonnation is open to question. 

The apparent absence of depositional breaks from the upper part of 

the Morgan formation to the top of the Weber sandstone, and the 

Des ~oines (Pennsylvanian) age of the upper part of the Morgan 

for1nation (reported by Bramlette and based on fusulinid determina-
S'rRATIGRAPHY 47 

FIGURE 4.-Crossbedding in the upper part of the Weber sandstone (Ow) at The Seeps, 

Ppc, Park City formation. 

tions by Henbest) strongly suggest that theW eber is entirely of Pennsylvanian age. 

Stratigraphic relations and correlation.-The Weber sandstone is 

believed to correlate with part of the Tensleep sandstone of central 

Wyoming, the Hermosa formation of central Utah, the lower part 

of the Oquirrh formation of the Wasatch Mountains (Baker, 1947), 

the Wells formation in southeastern Idaho, and the Quadrant formation in Montana. The vV eber sandstone of this area has been recognized on Yellowstone Creek, Rock Creek, the Duchesne River in the 

western Uinta Mountains, and in the Big Cottonwood-Park City district of the Wasatch Mountains (where it is thicker and more calcareous, but otherwise identical). 

Conditions of deposition and origin.-The low percentage of heavy 

minerals, the scarcity of clay and micaceous minerals, and the great 

thickness and widespread distribution of the vVeber sandstone, suggest that erosion of preexisting sandstone was the source of the 

formation. The Weber is believed to have been deposited under 

shallow marine waters, where currents winnowed out fine-grained 

constituents and formed tangential crossbedding in certain beds. 

The principal source area of sediments of the vVeber sandstone in 

the eastern Uinta Mountains is believed to have been the highlands 

of eastern Nevada which provided the clastics for the thick sequence 

of Pennsylvanian and Permian rocks assigned to the Oquirrh formation in the Oquirrh (Gilluly, 1932, p. 34) and Wasatch Mountains 

(Baker, 1947). Other sources, however, may have been the Algonkian 

type strata and crystalline rocks of the Uncompahgre Plateau and a 
48 GEOLOGY OF UINTA RIVER- BRUSH CREEK AREA, UTAH 

westward extension of the Front Range highlands in western Colorado, and the sedimentary rocks of earlier Paleozoic age exposed in 

adjacent land areas. 

PERMIAN SYSTEM 

PARK CITY FORMATION 

Definition.- The Park City formation was named for exposures in 

the Park City n1ining district (Boutwell, 1912, p. 443-444) in the 

central Wasatch Mountains, Utah. It consists of three divisions in 

that area, an upper and a lower member of cherty limestone and interbedded limy sandstone, separated by a middle member consisting of 

black phosphatic shale. Fossils collected from the lower member of 

the formation were referred to the upper Pennsylvanian by G. H. 

Girty and the fauna of the n1iddle and upper members to the Permian. 

In the course of detailed n1apping and stratigraphic studies in the 

southeastern Idaho phosphate district, Richards and Mansfield (1912, 

p. 684-689) defined the Phosphoria formation to include only those 

beds equivalent to the middle and upper members of the type Park 

City formation; that is, the part assigned to the Permian. Subsequently, vVilliams (1939, p. 85-86) suggested abandoning the Park 

City formation or restricting it to the lower, presumably Pennsylvanian, member of the original formation. However, recent work in 

the Provo area of the 'iV asatch ~1ountains, south of the type section, 

proved that the lower member of the Park City formation is also 

of Permian age because it can be correlated with the Kaibab limestone, thus reestablishing the Park City formation as an acceptable 

stratigraphic unit (Baker and Williams, 1940, p. 625). 

Park City formation has been used in the western Uinta ~1ountains 

in preference to Phosphoria formation (Huddle and ~1cCann, 1947) 

because the type section of the Park City is only a few miles to the 

west, the formation in both areas is tripartite, and the rocks are lithologically similar. The formation is exposed at intervals along the 

south flank of the Uinta J\1ountains, but east of Lake Fork, the lower 

sandstone and limestone n1ember is not present. The first use of 

Park City formation in the Uinta Mountains was by Schultz (1919, 

p. 46- 53) and the present definition conforms to his usage. 

Distrib~ttion and topographic expression.-The Park City formation is exposed along the Whiterocks River, at two localities near the 

head of Mosby Creek, in a fault block in the Deep Creek area, and almost continuously eastward from north of Little Mountain to Diamond Mountain where rocks of Paleozoic and Mesozoic age are covered by the Bishop conglomerate. The phosphatic shale member of 

the Park City formation overlies the vV eber sandstone and generally 

forms a poorly exposed bench mantled with pieces of chert and fragments of phosphate rock. The upper member of the Park City formation, in part correlative with the Rex member of the Phosphoria for-
STRATIGRAPHY 49 

mation of southeastern Idaho, is well exposed in the Ashley CreekLittle Brush Creek area where the soft red and gray sandstone of the 

lVIoenkopi formation has been stripped away. 

Lithology and thickness.-East of Lake Fork, the Park City formation consists of a lower light gray-green to olive-green phosphatic 

shale and rock phosphate member, overJain by an upper member of 

slabby-weathering light-gray cherty lin1estone, dolon1ite, limy sandstone and light-gray shale. A considerable proportion of the phosphate occurs as pellets or other small irregular phosphate particles. 

The color of the phosphatic member varies from light gray-green on 

\Vhiterocks River to dark olive-green in the vicinity of Brush Creek. 

The darker color is probably due to the higher organic content of the 

beds in the Brush Creek area which contain the highest grade phosphate rock in the eastern Uinta Mountajns. The phosphatic member 

ranges from 20 to 30 feet in thickness ; the maximum thickness is 

found in the vicinity of Brush Creek (fig. 5). The phosphatic 

shale is discussed in detail in the section on Economic Geology. The 

upper, interbedded light-gray, cherty limestone and shale member 

ranges in thickness from 175 feet on vVhiterocks River to 80 to 100 

feet between Red Mountain and Little Brush Creek. Some of the 

cherty limestone beds are very sandy ; in some places, they are almost 

FIGURE 5.- Lower part of the Park City formation at Brush Creek 

Gorge. 
50 GEOLOGY OF UIN TA RIVER-BRUSH CREEK AREA, UTAH 

a limy sandstone. One such locality, in SW14 sec. 12, T. 2 S., R. 21 E., 

carries a well-preserved Phosphoria fauna. A thin band of red siltstone or very fine grained sandstone is present near the middle of the 

Park City formation. Its occurrence in the southwestern Uinta 

Mountains was named the lVIackentire "red beds" tongue of the Phosphoria formation by Williams (1939, p. 93). The tongue appears to 

thin toward the east in the Red Mountain-Brush Creek area and it 

seems to be split into two tongues by a limestone bed in the White· 

rocks River section. 

The detailed lithology of the Park City formation is shown in the 

following sections : 

Section of the Parle City formation on w est side of Whiterocks River SWlA, 

see. 18, T . 2 N., R. 1 E ., Uinta Special Base and Meridian 

[Measured by D. M. Kinney and J . F. Rominger] 

Moenkopi formation : 

Sandstone, reddish-brown, very fine grained, poorly exposed. 

Park City formation: Feet 

Limestone, light-gray, cherty and light-gray bedded chert____ __ ____ 60 

Siltstone, red, sandy, and red, very fine grained sandstone__________ 8 

Limestone, light-gray to pink, fine-grained, cherty- ------ --------- 17 

Siltstone, red_______ ______________ __________________ _____________ 15 

Covered, probably light-gray shale_______ _______ _____ _____________ 38 

Sandstone, tan, fine-grained, with calcareous vugs_______________ _ 3 

Limestone, light-gray, tan-weathering, very cherty; fossiliferous at 

top_______ ________ ______ _____ ___ ___________ __ ___ ____ _____ __ ___ _ 34 

Shale, greenish-gray, siliceous, and olive-gray phosphate rock with 

light-gray chert. One and one-half feet of limestone, tan, sandy 

with vugs of light-gray chert, at toP --- -- --- --- -- ---- 20 

Section of Parle City formation on north side of Red Mountain NElJ± 

sec. 3-1, T. 2 S., R. 21 E., Salt Lalcc Base and Meridian 

[Measured by D. M. Kinney, J . F . Rominger, R. S. Brown, and P. Verastegui M.] 

Moenkopi formation : 

Shale, light-gray, sandy. 

Park City formation: 

Limestone, light-gray, sandy, slab by------ --- --------------------- Sandstone, red, fine-grained _____ _____ __ ____ _____ ____ ____________ _ 

Sandstone, light-gray, speckled; contains angular medium- to coarsegrained sand grains. One-half foot chert conglomerate at top __ _ _ 

Limestone, lightly-gray with thin streaks of light-gray chert_ _______ _ 

Limestone, light-gray, fine-grained, with calcite-filled vugs _________ _ 

Shale, light-gray, conf:retionary -------------- - --- - -------- ------ -

Limestone, light-gray, fine-grained with calcite-filled vugs ______ __ _ _ 

Shale and phosphate rock, greenish-gray to olive-gray oolitic, fossili195 

Feet 

14 

27 

11.5 

18 

6 

2 

1.5 

ferous_________________________________________________________ 17 

97 
STRATIGRAPHY 51 

Section of Park City fonnation in canyon. 1 mile west of Little Brush Greek. 

NEY.t sec. 22, T. 2 S., R. 22 E. (unsectionized) 

[Measured by D. M. Kinney and J. F. Rominger] 

:Vloenkopi formation: 

Siltstone, light-gray, with thin streaks (0.1 to 2.0 feet) of light-gray, calcareous siltstone. 

Park City formation: Feet 

Limestone, light-gray, thin-bedded, sandy-------------------------- 22 

Shale, light-gray and thin beds of light-gray, sandy limestone________ 6 

Limestone, light-gray, thin-bedded, cherty, in part porous__________ 7 

Shale light-gray and thin beds of light-gray, sandy limestone_________ 20 

Sandstone, red, very fine-grained__________________________________ 2 

Sandstone, light-tan, fine-grained__________________________________ 10 

Limestone, light-gray, sandy (covered)---------------------------- 6 

Limestone, light-gray, thin-bedded, slabby _____________ _____________ 6.5 

Sandstone, light-tan, very fine grained, calcareous, fossiliferous 

(Phosphoria fauna)------------------------------------------- 4 

Limestone, light-gray, with uneven bedding, vugs, nodules of white to 

purplish calcite, and angular particles of dark-brown chert______ 12 

Limestone, tan, massive, with vugs, and nodules of light-gray chert___ 3.5 

Chert, gray, nodular in matrix of gray-shale_______________________ 1.0 

Shale, gray-green to olive-green, and olive-green, oolitic phosphate 

rock with chert________________________________________________ 19 

119 

Fossils and age.-The phosphatic member of the Park City formation, especially in the Brush Creek area, carries an abundant phosphatized fauna limited to a few genera. The phosphate replacing the 

shell material adds eonsiderably to the phosphate eontent of the rock 

but sinee it does not preserve shell ornamentation, specific identification is difficult. 

A collection 1nade by J. Steele vVilliams of the Geological Survey 

was reported as follows : 

No conodonts were found. Quite a few immature gastropods that preserved 

no ornamentation and could not be identified were present. One or two individuals that might be ostracodes and fragments possibly of very small pelecypods or 

brachiopods were also present. No data of worth-while age significance have 

been found. 

Large eollections made by Helmuth W eclow of the Geological Survey were sub1nitted to l{enneth McLaughlin for identification. Mr. 

McLaughlin reported two ostracodes, Geisina sp. and F-I ollinella? sp., 

and a conodont referred to Gondolella. Mr. McLaughlin reports in 

a letter elated January 1950: 

It is difficult to place any age significance on the specimens in question. The 

probable taxonomic affinities of the ostracodes, as well as the nature of their 

occurrence in the Brush Creek samples, suggest that they are reworked specimens. Geisina is closely similar to species reported from both lower and middle 

Pennsylvanian; the genus is not a particularly diagnostic one, but is generally 
52 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

considered to be strictly Pennsylvanian. Hollinella? is a prominently nodose 

form which, according to Betty Kellet Nadeau, is characteristic of lower Pennsylvanian and Mississippian time. It is also similar to those which oecur in the 

DesMoinesian Glen Eyrie formation of Colorado. 

The single conodont specimen was not identified except as belonging to the 

gondolellid group, which are considered to become abumlant at about middle 

Pennsylvanian. 

More impressive than the above possible relationships, however, is the following: 

( 1) Out of a sizable sample only three single specimens were found. 

(2) All three shovv evidence of physical wear. 

( 3) The ostracodes are casts composed of the same material as clastic grains 

making np a large part of the sample in which they occurred. 

( 4) The abundance of fossil fragments of this material among the clastic 

grains. 

In short, these three specimens are noncliagnostic, but suggest that the Park 

City formation may have a rather complex stratigraphic-tectonic history. 

Sehultz ( 1919, p. 53), in his reeonnaissance of the Uinta Mountains, 

made two fossil eollections from the phosphate interval in the NEl;t 

see. 8, T. 3 S., R. 19 E., Salt Lake 1neridian. The first eollection from 

the "upper phosphate bed" was submitted to G. H. Girty who reported, Yoldia 1nacchensneya:na and small undetermined gastropod. 

In the seeond eollection from the "lower phosphate bed," Mr. Girty 

identified Ling1tlidisci na ulahens is. 

From these fossil and stratigraphic age determinations, it is evident that no definite age ean be assigned to the phosphatic 1nember 

from fossils. McLaughlin's suggestion of middle or early Pennsylvanian or even Mississippian age for the recognized1niero-fauna, and 

the evident abrasion by transport, implies that the source of the phosphatie sediments was some earlier formed Carboniferous rock. 

The eorrelation of the upper part of the Park City formation with 

the Phosphoria formation of southeastern Idaho is based on a fauna 

present in the section 35 to 50 feet above the base of the for1nation. 

,J. Steele 'iVilliruns reports on the silieified fauna collected in the SWl;t 

sec. 12, T. 2 S., R. 21 E., as follows: "This is a typic.al Permian fauna 

of this region, eontaining Plagioglyptas, Euphemites, Ledas." 

Considerable difference of opinion has been shown by investigators 

in regard to the time element that is represented by the Phosphoria 

formation and its general equivalent, the Park City fonnation. In 

southwestern Wyoming (Sublette Range), a eephalopocl fauna from 

a horizon 60 feet below the Rex chert n1en1ber of the Phosphoria formation, is characteristic of the Word fonnation (middle Permian) 

and eertain elements suggest possible eorrelation with the Leonard 

series (Miller and Cline, 1934, p. 283-285). Fusulinids from limestone 

strata overlying the Quadrant formation (Frenzel and Mundorff, 

1942, p. 675-684) in Montana, classified as Phosphoria, suggest an 

age as old as W olfca1np (lower Permian~), but Thompson and 

Wheeler (1946, p. 8) believe that these strata are younger than the 
STRATIGRAPHY 53 

type section of the vVolfeamp fonnation. The physieal-ehemieal aspeets of the problem of preeipitation of the phosphate (Mel{elvey, 

V. E., personal eommunieation) re.quire a very long period of time 

for an aeemnulation of great thieknesses of phosphate rock, which 

substantiates, in part, the above fusulinid determinations. However, 

1·eeent work by A. A. Baker ( 1947) in the Provo area of the Wasateh 

~1ountains shows that almost 3,000 feet of the Oquirrh formation, 

as well as the IGrkman limestone and the Diamond Creek sandstone, 

intervene between the horizon of the fusulinicl eollections of middle 

or late W olfeamp age and the basal beds of the Park City formation, 

whieh are highly phosphatie. Considerable time must have been required for the deposition of more than 5,500 feet of strata (Baker, 

1947), therefore only a relatively short period of time is available for 

the deposition of the phosphatie shale of the Park City formation. 

StJYdigraph-ic relations and correlation.-The lower boundary ofthA. 

Park City formation is easily recognized in the area; the easily eroded 

phosphatie shale weathers backward, leaving a beneh at the top of 

the vV ebe.r sandstone. However, many problems have been eneountered in choosing the boundary between the Park City and the 

overlying Moenkopi formation. From "'\Vhiteroeks River eastward to 

Reel ~fountain the boundary originally was taken at the base of the 

reel beds vvhich eorrespond to the top of the light-gray limy sandstone and interbedded shale. This boundary, easily reeognizable in 

the field, appeared to be remarkably eonsistent aeross the area. l\1apping between Red Mountain and Utah State Highway 44 at Brush 

Creek, however, showed that the lower part of the red beds grade into 

light greenish-gray sandy shale and thin-bedded sandstone, and the 

base of the red beds rises more than 150 feet stratigraphieally in 3 

miles. This rising eolor eontact is believed to continue in a northeasterly direction beyond Split ]\;fountain, for n1ore of the roeks at the 

base of the l\1oenkopi are gray at Skull Creek in northwestern Colorado than at Split Mountain, and at Vermilion Creek the entire unit 

is gray. In order to use a eonsistent boundary throughout the area, 

the top of the highest slabby, light-gray cherty limestone or limy sandstone '"as taken as the top of the Park City formation. As the upper 

limestone beds thin and grade into light-gray sandy shale towards 

the east, the bmmdary probably descends stratigraphieally in that 

direetion. 

Although the boundary that was adopted is believed to be best for 

the purposes of mapping in the area, the possibility rmnains that, in 

the absence of evidenee of erosion at this horizon, the boundary should 

be taken somewhat lower, at the base of the eoarse-grained, angular, 

in places conglomeratic, tan sandstone that lies 54 feet above the base 

of the Park City formation on Whiterocks River, 44.5 feet above the 

base at Reel Mountain, and 35.5 feet above the base at Little Brush 
54 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Creek. Permian fossils have not been found above this sandstone 

and the sandstone is the only denwnstrable physical evidence of erosion found between the top of the "'\¥ eber sandstone and the base of 

the Shinarump conglomerate. If this sandstone bed marked the base 

of the overlying Moenkopi formation, some of the slabby whiteweathering limestone, heretofore considered typical of the Park City 

formation, would be included in the overlying Moenkopi, and the 

boundary between the two fonnations would be lowered 138 feet on 

"\Vhiterocks River, 55.5 feet at Red Mountain, and 83 feet on Little 

Brush Creek. 

The lower member of the Park City fonnation (Willia1ns, 1939, 

p. 93-94), as represented on Duchesne River in the western Uinta 

Mountains, is not recognized within this area. The absence of the 

lower member of the Park City formation in the eastern part of the 

area can be interpreted in either of two ways: (1) The member has 

been rmnoved by erosion and is now represented by an unconformity 

at the top of the Weber sandstone in the area frmn Whiterocks River 

eastward (Thomas and l{rueger, 1946, p. 1264), or (2) the lower 

member of the Park City formation grades laterally into the upper 

part of the Weber sandstone, (Williams, 1939, p. 96). The upper 300 

feet of the Weber strata on Whiterocks River is 1nore thinly bedded 

and calcareous than the underlying massive sandstone, and it weathers 

to shades of tan. A similar thickness at the top of the Weber sandstone in the Brush Creek area is more strongly crossbedded than the 

underlying sandstone, and this unit may be correlative with the thinbedded, tan-weathering calcareous sandstone on Whiterocks River 

and the lower member of the Park City formation of the Duchesne 

River section. However, no physical evidence is known to exist that 

would indicate interruption of sedimentation within the mapped 

boundaries of the Weber sandstone. 

The Park City formation of this area is correlated with the Phosphoria formation and with the middle and upper 1nembers of the 

Park City fonnation in the section at Park City, Utah. Thin tongues 

of cherty limestone have been recognized in northwestern Colorado 

(Thomas, McCann, and Ra1nan, 1945) . The Kaibab limestone in the 

San Rafael Swell carries a mixture of the Kaibab fauna as represented in southern Utah and certain forms characteristic of the Phosphoria ( Gilluly and Reeside, 1928, p. 64). The Park City fonnation 

above the phosphatic shale 1nember in the Uinta Mountains probably 

represents deposits younger than the l{aibab li1nestone of the San 

Rafael Swell area. 

Conditions of deposition.-Marine fossils in the sandy limestones 

of the upper member of the Park City formation indicate a marine 

origin for the enclosing sediments. The limited fauna in the lower 

(phosphatic) member and the abrasion to which the forms were sub-
STRATIGRAPHY 55 

jected prior to incorporation in the beds suggest that the phosphate 

pellets are not a primary marine deposit. From the evidence presented by ~fcLaughlin (seep. 51-52), it seems probable that the phosphate pellets were concentrated from a much greater thickness of 

marine Pennsylvanian rocks. This concentration might have been 

caused by wave action or by subaerial weathering with later deposition on the sea floor. However, due to the absence of ripple marks 

and crossbedding, it seems probable that the sea floor below the level 

of current action was the final place of deposition. The concentration of huge quantities of phosphate in a relatively thin interval is 

more easily explained by 1nechanical concentration than by chemical 

precipitation frmn sea water, for the latter action requires a very 

perfect balance of physical-chmnical conditions, a great length of 

time, and an almost total absence of clastic sediments. On the other 

hand, mechanical concentration more easily explains the sharp boundaries of the phosphate ocurrence, because phosphate pellets are rare 

on the north side of Split Mountain 6 to 8 miles southeast of Brush 

Creek, which has the thickest and richest deposits in the eastern Uinta 

Mountains. 

The great extent of the Park City formation and its equivalents, 

which reach frmn central Montana to northern Utah and from eastern 

Idaho almost to the Utah-Colorado border and northward into Wyoming, indicates that the sea was widespread and that the peculiar 

conditions necessary for the precipitation of phosphate were not local. 

It is possible that the phosphate deposits in the eastern Uinta Mountains may represent only a part of the time when phosphate was being 

deposited farther west in Idaho and southwestern 'Vyoming. Faunal 

evidence in southeastern Idaho suggests that the Phosphoria sea had 

connections soutlnvard into Texas, westward into California, and 

northward to Alaska and Russia (Mansfield, 1927, p. 185). 

According to evidence accmnulated by Mcl{elvey ( 1946, p. 88), the 

sea floor in western Wyoming, southeastern Idaho, and northern Utah 

was essentially flat with only minor irregularities. Similar conditions appear to have prevailed in the Uinta River-Brush Creek area 

because the top of theW eber sandstone forms a smooth surface. High 

organic content of the phosphate rock, suggesting anaerobic and fetid 

conditions, is characteristic of the Park City and Phosphoria formations farther west, but the organic content is comparatively minor in 

the area covered in this report. This fact is evident from the olivegreen to gray-green color of the phosphate rock in the Brush Creek 

area. 

TRIASSIC SYSTEM 

In his pioneer work in the eastern Uinta Mountains, J. W. Powell 

(1876, p. 41, 53) included in the Shinarump group, named for the 

Shinarump Cliffs in southern Utah, all the red beds now referred to 
56 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

the Triassic. He recognized three units, a Lower Shinarmnp sandstone and an Upper Shinarump sandstone separated by the Shinarump conglmnerate. The use of a Imine both for a group and for a 

formation within the group being contrary to good stratigraphic noInenclature, the "Lower Shinarmnp" was rena1ned the Moenkopi forInation, the "lJ pper Shinarump" was rE:named the Chinle formation, 

and the Shinarump was retained for thE· conglomerate. 

LOWER TRIASSIC SERIES 

MOENKOPI FORMATION 

Definition.-The Moenkopi formation was named by Ward ( 1905, 

p. 18-19) for Moenkopi Wash in northeastern Arizona, and the name 

has subsequently been carried northward into central Utah by the 

work of Gilluly and Reeside ( 1928, p. 65-66), Baker ( 1933, p. 3±-37; 

1936, p. 40-44), Dane (1935, p. 42-54), and Mci\:night (1940, p. 52-

en). The reasoning for the extension of the nomenclature of northern Arizona into central lTtah has been based on the stratigraphic 

position of the Moenkopi formation below the Shinarump conglomerate and the lithologic si1nilarities with the type section. The Early 

Triassic age of the Moenkopi formation has been confirmed by vertebrate remains and tracks (Welles, 19± 7, p. 285-286; Peabody, 1948, p. 

413) and by invertebrate faunas from the Sin bad limestone member 

of the Moenkopi (Gillnly and Reeside, 1928, p. 66) 200 feet above the 

base of the fonnation in the San Rafael Swell and by the interfingering of the Moenkopi formation with its marine Virgin limestone 

n1ember (Reesicle and Bassler, 1922, p. 67-68) in southern Utah and 

with the Thaynes li1nestone in northern Utah. 

The Woodside shale, Thaynes limestone, and Ankareh shale, originally described by Boutwell (1912, p. 52-59) from the Park City district in theW asatch Mountains, are recognized in the Duchesne River 

area (Thomas and I\:rueger, 19±6, p. 1284-1285; Huddle and McCann, 

1947) of the western lTinta Mountains. However, in the area between 

Duchesne River and Whiterocks River, the Thaynes limestone thins 

from a maximum of 650 feet to less than 20 feet; east of vVhiteroeks 

River, it is represented only by calcareous fine-grained red sandstone. 

vVith the disappearance of the tongue of the Thaynes limestone, the 

separation of the Woodside shale from the overlying shaly equivalent 

of the Thaynes limestone beeomes more difficult and ~ioenkopi formation is substituted for Woodside, Thaynes, and Ankareh formationf::. 

Gypsum beds on Red ]\fountain at approximately the same horizon as 

the limestone farther west are believed to have been deposited on tidelands during the maximum extent of the Thaynes sea. The upper 

part of the Moenkopi is equivalent to the Ankareh and the lower part 

to the Woodside. The rocks between the Park City formation and 
STRATIGRAPHY 57 

the Shinarump conglomerate occupy the same interval and have the 

same lithology as the Moenkopi formation in the San Rafael Swell. 

Distribution and topographic expression.- In the area shown on 

plate 1, the Moenkopi formation crops out at Whiterocks River, in 

fragmentary sections in the faulted area between Mosby Creek and 

Deep Creek, on the north side of Little Mountain south and west of 

the com_munity of Dry Fork, and in continuous outcrop from_ east of 

Dry Fork, across the north side of Red Mountain eastward to Diamond ~1ountain. The ~1oenkopi is also exposed on the flanks and nose 

of Split Mountain anticline within the Dinosaur National Monument 

and along the westward plunging Section Ridge anticline, but these 

exposures are only partially shown on the accon1panying map (pl. 1). 

The finest outcrops of the complete section of Moenkopi are on the 

north side of Red ~1ountain and along Little Brush Creek. Excellent 

exposures are also present in Dinosaur National Monument and on 

Cliff Creek (fig. 6) on the extreme eastern border of the mapped area. 

The Moenkopi formation is a thin-bedded, easily eroded sequence 

of interbedded red sandstone, siltstone, and shale which would generally make poor outcrops except for protection afforded by the overlying resistant Shinarump conglomerate. The upper part of the forrnation is generally better exposed than the lower part, which forms 

strike valleys near Dry Fork and on both sides of Ashley Creek. The 

more massive and resistant sandstone beds, and especially the thin interval of gypsum and gypsiferous sandstone near the n1iddle of the 

formation on Red Mountain, form steep cliffs, and the thin-bedded, 

FIGURE 6- 1\f oenkopi formation ( T rm), Shinarump conglomerate ( Trs), Chinle formation 

('Pre), and NaYajo sandstone (Jn) on the north side of Cocklebur Wash. 
58 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

fine-grained sandstones and interbedded shales form gentle slopes. At 

the head of Deep Creek the limy interval, which marks the maximum 

incursion of the Lower Triassic sea from the west, makes a slight escarpment. 

Lithology and thickness.- In this area the Moenkopi formation consists of thin-bedded reddish-brown siltstone or very fine-grained sandstone with thin partings of weak-red, sandy shale and thin beds of light 

greenish-gray, fine-grained sandstone. The basal 100 to 150 feet, as 

mapped in the area from Red Mountain to Diamond Mountain, is 

light-gray to light greenish-gray, sandy shale and thin-bedded, micaceous sandstone. Eastward, the light-gray facies increases in thickness 

at the expense of the red facies of the Moenkopi and at Irish Canyon 

(Sears, 1924, p. 281) on Vermilion Creek, 37 miles to the northeast, 

the Lower Triassic sedimentary rocks are all light-gray, sandy shale 

and fine-grained sandstone. 

The section of the Moenkopi formation on the north side of Red 

l\fountain is the best exposed section in the area. It is given here to 

illustrate the general character of the formation in the western twothirds of the area. 

Section of Moenkopi formation on the north side of R ed Mountain in SW14 

sec. 34, T. 2 S., R. 21 E. 

[Measured by D. M. Kinney, J. F . Rominger, a nd R. S. Brown] 

~hinarump conglomerate: 

Sandstone, conglomeratic, yellowish-gray, weak yellowish-orange weathering, massive, crossbedded, very resistant, with light-brown streaks, pebbles up to 2 inches in diameter, and silicified wood ; basal contact shows 

channels in the Moenkopi formation. 

Unconformity 

Moenkopi formation: Feet 

Sandstone, weak-red, very fine grained, thin-bedded, intercalated 

with weak-red sandy shale and light-gray, fine-grained, thin-bedded 

( 0.05 foot thick) sandstone; few thin ( 0.01 foot) lenses of gypsum. 

Forms steep slope below the cuesta formed by the Shinarump____ 126 

Sandstone, pale reddish-brown, very fine grained, thin-bedded ( 0.05 

to 0.2 foot) intercalated with light greenish-gray, fine-grained sandstone. Thin beds of gypsum 25 feet and 75 feet below top__ __ ____ 269 

Sandstone, reddish-brown, very fine grained__ ____ _____ ____ __ _____ 110 

Sandstone, reddish-brown, fine-grained, gypsiferous., with three 1 foot 

beds of gypsum; forms cliff_ __ ________ ___ ___ ___ ________________ 10 

Sandstone, reddish-brown, fine-grained, with thin band of light-gray 

sandstone at top_______________________________________________ 150 

San.dstone, interbedded reddish-brown and light-gray, fine-grained_ __ 195 

Sandstone, light-gray, very fine grained___________________ _________ 25 

Sandstone, red, very fine grained___ ___ ___ _________ ___ __ __ ___ ____ __ 12 

Shale, light-gray, sandy---- ------------------------- ------------- 7 

.Sandstone, light-gray, very fine grained, calcareous, slabby - - -------- 1 

'Shale, light-gray, sandy-----------------------------------------_ 60 

965 
STRATIGRAPHY 59 

The section measured on Little Brush Creek illustrates the thickening section of gray sandy shale and thin-bedded sandstone at the base 

of the Moenkopi formation along the tributaries of Brush Creek and 

Little Brush Creek in the eastern part of the area. The thickness o:f 

the l\!Ioenkopi formation in the rna pped area, as sho,vn by the detailed 

measured sections, ranges from 1,120 feet in the west to 725 feet on 

the east. The thinning is believed to have been caused by erosion of 

the top, which has cut out beds in exposures 1 mile west of Dry Fork; 

some thinning may occur in individual beds. 

Section of Moenkopi formation along west side of Little Brush Greek from the 

SW~SW1,4 sec. 24 to the SW1,4 sec. 25, T. 2 S., R. 2i2 E. 

[Measured by D. M. Kinney and J. F. Rominger] 

Shinarump conglomerate: 

Sandstone, light-gray to tan, coarse-grained, crossbedded, with pebbles to 

2 inches in diameter; abundant fossil wood near base. 

Unconformity 

Moenkopi formation : Feet 

Sandstone, red, very fine grained__________________________________ 17 

Sandstone, red, fine-grained, well-bedded and ripple-marked, with 

interbeds of shaly micaceous sandstone, and red sandy shale_____ __ ~5 

Sandston~ red, very fine grained________________ __________________ 255 

Gypsum, white to pink, thinly laminated, contorted_________________ 7 

Sandstone, red, fine-grained, ripple-marked, gypsiferous ; forms ledge_ 72 

Sandstone, red, fine-grained_____________ _______ ____________ __ _____ 26 

Sandstone, red and white interbedded, nne-grained thinly laminated; 

basal 1 foot slightly calcareous_____________________ ___________ __ 6 

Siltstone, red, and red very fine grained sandstone, with streaks of 

sandstone, greenish-gray, fine-grained, crossbedded, micaceous, 

laminated ( 0.2 to 0.5 foot thick) -------------------------------- 46 

Siltstone, red and red very fine-grained sandstone_______ ____________ 93 

Shale, light-tan to gray, with 0.5 foot beds sandstone, light-gray, finegrained, calcareous, slabby_________________________ ____________ 36 

Sandstone, light-gray, fine-grained, crossbedded, slabby; selenite crystals common___________________________________________________ 2 

Siltstone, light-gray---------------------------------------------- 31 

Siltstone, light-gray,· with 0.5- to 0.8-foot beds sandstone, light-gray, 

micaceous, ripple-marked, slab by-------------------------------- 24 

Sandstone, light-gray, fine-grained, with angular to semirounded 

grains -------------------------------- --- ---- ----- --~----- --- 15 

Siltstone, light-gray, with thin streaks (0.1 to 2.0 feet), siltstone, 

light-gray, calcareous___________________________________________ 60 

725 

Fossils and age.--A small collection of poorly preserved fossils from 

the limestone unit 520 feet above the base of the Moenkopi formation 

in the SW~ sec. 18, T. 2 N., R. 1 E., on the west side of Whiterocks 

River was submitted to John B. Reeside, Jr., of the Geological Survey 

who reports: 

295163-55--5 
60 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

This material has obviously been a coquina, but I am unable to get out enough 

of any single specimen to warrant an identification. Fragments of several 

gastropods, one probably a bellerophontid, and fragments of several sorts of 

pelecypods are present. I have seen similar material at a number of places in 

Lower Triassic deposits in Utah and believe the material well placed as Triassic. 

The light gray-green sandy shales and interbedded sandstones at the 

base of the Moenkopi formation in the section on Brush Creek are 

comparable to the sections described from the San Rafael Swell region 

where they have been attributed to deposition on a delta in stagnant, 

muddy pools (Gilluly, 1929, p. 86). No vertebrate fossils are known 

with the exception of the footprints of certain reptiles found in the 

upper part of the Moenkopi formation in the SE:lJ.t, sec. 32, T. 2 S., R. 

22 E. The trackways are "too distorted for diagnosis," according to 

Dr. Frank E. Peabody (personal communication, 1948), who has 

studied the reptilian and amphibian trackways in the Moenkopi formation of northern Arizona and southern and central Utah. Dr. 

Charles L. Camp (personal communication, 1948) suggests that the 

tracts are "impression of Ohirotherium made in soft mud." 

Stratigraphic relations and correlations.-The Moenkopi formation, as mapped, rests with apparent conform.ity on the Park City 

formation of Permian age. In the discussion of the stratigraphic 

relations of the Park City formation, it has been suggested that in the 

absence of evidence of erosion at this horizon, the boundary might be 

taken somewhat lower, at the base of the coarse-grained, angular, in 

places conglomeratic tan sandstone that lies 54 to 35 feet above the 

base of the Park City formation. No evaluation of a time break, 

indicated by the coarse sandstone, can be made because of the lack of 

marine fossils in the overlying slabby, sandy limestones. 

The upper boundary of the Moenkopi formation is clearly unconformable; it shows scour and fill by the streams that deposited the 

basal beds of the Shinarump conglomerate. The Shinarump rests in 

channels 40 to 50 feet wide and cuts out as much as 20 feet of red 

siltstone and shale within that distance. Excellent exposures of the 

channel fillings are present near Brush Creek on Utah Highway 44 

(fig. 7) and on the west side of Red ~fountain. Although the unconformity is evident over much of the area, very few beds of the 

Moenkopi have been removed in the area from Red Mountain eastward to Dian1ond Mountain. However, in sections 6, 7, and 8, T. 3 S., 

It. 20 E., 1 mile west of the community of Dry Fork, the Shinarump 

clearly truncates resistant sandstone beds in the upper part of the 

Moenkopi formation. The thinning of the Moenkopi, from 1,120 feet 

on vVhiterocks to 725 feet on Little Brush Creek, is believed due to 

erosion by streams whose ancient channels are filled with the basal 

beds of the Shinarump conglomerate. 
STRATIGRAPHY 61 

FIGURE 7.-Shinarump conglomerate (Trs) filling channel in the top of the Moenkopi 

formation Trm), on the West side of Brush Creek. 

The l\1oenkopi formation of this region is correlated, at least in part, 

with the Moenkopi formation of the San Rafael Swell-Moab region 

to the south, and with the Woodside and Thaynes formations of the 

western Uinta Mountains and their type sections in the Wasatch 

Mountains. The Dinwoody formation of central vVyoming and the 

tongue of the Dinwoody at the base of the red beds in the Chugwater 

formation of southeastern 'iVyoming closely resemble the lower part 

of the Moenkopi formation east of Red Mountain and are correlated 

with it. To the east of the Green River, the l\1oenkopi formation extends practically unchanged in lithology for almost 100 miles 

(Thomas, McCann, and Raman, 1945). 

Conditions of deposition.-The well-sorted, fine-grained sandstone, 

siltstone, and shale, the preponderance of uniform bedding, the a bundance of mica on the bedding planes, and the scarcity of ripplemarks, mud cracks and crossbedding, point toward deposition of the 

l\1oenkopi formation in water generally free from strong currents. 

Such conditions might prevail near the center of a large intermontane 

basin or on a wide coastal plain. In Salt Valley south of the Uinta 

Basin, Dane ( 1935, p. 52) has demonstrated that the source of the sediments that formed the l\1oenkopi formation in that area was the old 

crystalline highlands now represented by the Uncompahgre Plateau. 

Such a source for the l\tfoenkopi formation in the Vernal area is in 

harmony with what is known of the paleogeography of Early Triassic 

time and the character of the sediments on the North Douglas Creek 

anticline (Thomas, .McCann, and Raman, 1945) in Rio Blanco County: 
62 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Colo., 70 miles to the southeast, where coarse-grained sandstone and 

conglomerate are interbedded with red sandy shale and sandstone. 

The coarsening of the Moenkopi deposits to the southeast suggests 

that the Uncompahgre Plateau area was the source for at least part of 

the Moenkopi formation in the Uinta Mountains. Additional sediments might have been derived from crystalline rocks of the ancestral 

Rocky Mountains to the east, but the general thinning of the formation eastward suggests that this source was not important. With thi3 

interpretation, the Moenkopi deposits in the Vernal area represent the 

basinward or coastal-plain equivalents of coarse alluvial fans originating in highlands to the south and east. 

The tongue of marine Thaynes limestone, and its eastward continuation as a gypsiferous interval in the middle of the Moenkopi formation, suggests deposition of this thin unit as normal marine sediments 

at Whiterocks River and as lagoonal deposits east of Deep Creek. 

The incursion of the sea from the west, bringing marine organisms, 

and the deposition of marine limestone at Whiterocks River, can be 

explained by temporary dominance of subsidence over deposition in 

the area, thus allowing the sea to transgress far to the east. The 

gypsiferous interval at the horizon of the tongue of the Thaynes limestone suggests lagoonal conditions where sea water evaporated unti.l 

the calcium sulfate was precipitated. The salinity of the water is 

not known, although the lack of marine fossils, so prevalent to the 

west, suggests a brackish or very saline environment. 

The red color of the sediments may be due to oxidizing conditions 

in the transporting mediun1 or, more probably, it is due to the original 

red color of the sediments which were formed under humid subaerial 

conditions. The greenish-gray, sandy shale and fine-grained sandstone at the base of the Moenkopi formation in the Brush Creek area, 

and the increase of this facies to the east until the entire formation 

is gray on Vermilion Creek (Sears, 1924, p. 281) in northwestern 

Colorado, have their counterpart in the San Rafael Swell area, where 

Gilluly has attributed the color change to bleaching of sediments under 

reducing conditions (water high in sulfur) in stagnant, muddy pools 

on a delta ( Gilluly, 1928, p. 65). Similar conditions prevail in lagoons along low-lying coasts. However, the west-to-east color change 

of the Moenkopi formation fron1 red to gray may be due to groundwater conditions existing after deposition of the sediments, which 

allowed the red iron oxide in the sediments to the east to be reduced 

to the green ferrous state while the red facies of the Moenkopi to the 

west remained red or became gray only in the lower beds. 

·The presence of the amphibian tracks (thought to be Chirotherium) 

in the upper part of the Moenkopi formation near Brush Creek suggests a low-lying, poorly drained deltaic area with pools of shallow 

water and broad mud flats. 
STRATIGRAPHY 

UPPER TRIASSIC SERIES 

SHINARUMP CONGLOMERATE 

63 

Definition.-ln 1876, Powell inelncled the Triassic red beds and the 

thin but topographically prominent unit lying between them on the 

flanks of the Uinta Mountains in the Shinanunp group, and named 

the conglomerate the Shinarmnp conglomerate. More than 40 years 

later a Triassic tenninology borrowed from the Wasatch Mountains 

was extended east along the flanks of the Uinta Mountains (Schultz, 

1919, p. 54; 1920, pl. 1) and Woodside, Thaynes, and Ankareh formations were commonly recognized as the na1nes of Triassic formations 

in the eastern Uinta Mountains (Sears, 1924, p. 280-281 and 284). 

The extension of these nan1es beyond their geographic limits created 

confusion in regard to stratigraphic nomenclature in the Upper 

Triassic or Ankareh formation equivalents. Thomas and Krueger 

(1946, p. 1270) tried to solve the problem by substituting the new 

name "Stanaker formation" for the beds Sears referred to the Ankareh ( ~) formation, and by naming its thin lower 1nember the "Gartra 

grit." The Gartra grit is the same unit which Powell, 70 years before, 

had called the Shinarump conglomerate. The use of a single formation name for a thin unit of essentially unifonn appearance over the 

entire Colorado Plateau region provides a point of reference to those 

familiar with the fonnation in adjacent areas, and, as the Shinarump 

conglomerate has priority in the eastern Uinta Mountains, it is retained in the Uinta River-Brush Creek area. 

Topographic expression and distrUnttion.-The Shinarump conglomerate, although not inherently a resistant fonnation, crops out as 

narrow sharp pointed ridges, or caps long dip slopes because of the 

ease of erosion of the underlying thin-bedded Moenkopi formation 

and the overlying soft clays and shales of the Chinle formation. The 

Shinarump conglmnerate is present throughout the area shown on the 

map (pl. 1), although from west of Little Brush Creek eastward to 

Diamond Mountain it thins noticeably and at places is represented by 

only a few grains of sand separating typical ~foenkopi frmn the shale 

of the Chinle formation. · 

The Shinarun1p conglmnerate crops out on both sides of Whiterocks 

Hiver, as discontinuous strike ridges in the valley of Deep Creek and 

l\:fosby Creek, and crops out continuously frmn north of Little Mountain eastward to Diamond Mountain. The ridges fonned by the 

Shinarump conglomerate permit solution of the badly faulted zone 

between Mosby Mountain and Little Mountain. The formation makes 

consistently good outcrops ; some of the best exposures are on the north 

and west sides of Red Mountain where the Shinarump has a calcareous 

cement and forms almost vertical ciffs and long dip slopes that are 

covered with cedar trees. 
64 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Lithology and thickness.-The Shinarump conglomerate is a lightgray, medium- to coarse-grained, in part conglomeratic, sandstone. 

The quartz is glassy, pink to light-gray, and the individual grains are 

angular to subrounded. Quartz grains comprise more than 95 percent of the rock; the remaining 5 percent is chert and feldspar. On 

weathered surfaces, the larger and more resistant quartz grains weather in relief, thus emphasizing the pebbly, conglomeratic or coarsegrained features of the rock. The larger pebbles in the Shinarump 

conglomerate are predon1inantly light-pink quartzite similar to the 

dreikanter found at two places in the area at the top of the Navajo 

sandstone. The clasts [clast (Woodford, Moran, and Shelton, 1946, p. 

525) is used for clastic fragment. It does not have size limits as do 

granules, pebble, boulder, and cobble in the Wentworth (1922, p. 381) 

scale] are as large as 6 inches in diameter and usually are more rounded 

than the smaller grains. The relative proportion and general 

appearance of the pink, white, and gray quartz grains in the sandstone is much the same as the grains in the Navajo sandstone (Jurassic?) and the Entrada standstone (Jurassic), which suggests a comnwn source area of pre-Cambrian rocks. Dark, ferromagnesian minerals are relatively rare. 

The Shinaru1np conglomerate ranges from a knife-edge thickness 

at certain points in the Little Brush Creek area to a 1naximum of over 

90 feet on Whiterocks River; it averages between 40 and 60 feet thick. 

The variation in thickness is not uniform; thicker sections may be 

adjacent to average or thin sections. On the whole, the lower half of 

the formation has a greater concentration of pebbles than the upper 

part. The finer grained upper half is characteristically crossbedded, 

and without close exa1n1nation it 1night be taken for beds in theN avajo 

sandstone. 

The following sections measured on Red Mountain and Little Brush 

Creek give the variation and general characteristics of the formation: 

Section of the Shinm·ump conglomerate on the west side of Red Mountain 

SE¥4 sec. 17, T. 3 S., R. 21 E. 

[Measured by D. M. Kinney and J. F. Rominger] 

Chinle formation: 

Sandstone, reddish-gray to weak red-purple, shaly, with thin layers of shale, 

reddish-gray, sandy; silicified wood, manganese and iron-stained nodules 

in Shinarump-type sandstone lenses occur in basal10 feet. 

Shinarump conglomerate: Feet 

Sandstone, light-gray, fine- to medium-grained, thin-bedded (0.01 to 

1.0 feet), crossbedded, calcareous; less resistant than underlying 

unit ---------------------------------------------------------- 22 

Sandstone, coarse to very coarse grained, conglomeratic, yellowishgray, weak yellowish-orange weathering, massive, crossbedded, 

with light-brown streaks; pebbles to 2 inches in diameter and 

silicified wood generally present. Caps cuestas. Basal contact 

locally disconformable with channels extending 25 feet into the 

underlying Moenkopi formation_________________________________ 44 

66 
STRATIGRAPHY 65 

Section of the Shinantmp conglomerate on the west side of Red Mountain 

SE1f4 sec.11, T. 3 S., R. 21 E.-Continued 

Unconformity. 

Moenkopi formation: 

Sandstone, red, very fine grained. 

Sec'tion of the Shinarump conglomerate on the west side of Little 

BrusT~ Creek, SWY4 sec. 25, T. 2 S., R. 22 E. 

[Measured by D. M. Kinney and .J. !f· Rominger] 

Chinle formation: 

Shale, gray to purple. 

Shinarump conglomerate: Feet 

Sandstone, light-gray to tan, coarse-grained, crossbedded with pebbles 

to 2 inches in diameter and abundant fossil wood near the base____ 28 

Unconformity. 

Moenkopi formation: 

Sandstone, red, very fine grained. 

Section of Shina1·ump conglomerate on the west side of Whiterocks Rive1·, SW1,4 

sec.18, T. 2 N., R.1 E., Uinta Special Base and Meridian 

[Measured by D. M. Kinney, .J. F. Rominger, R. S. Brown, and P. Verastegui M.] 

Chinle formation: 

Shale, tan to red. 

Shinarump conglomerate: Feet 

Sandstone, gray to tan, medium-grained, crossbedded to massive____ 53 

Sandstone, tan, medium- to coarse-grained, conglomeratic, with quartz 

pebbles ------------------------------------------------------- 40 

Unconformity. 93 

Moenkopi formation: 

Sandstone, red, very fine grained. 

Fossils.-The Shinarump conglomerate throughout the area of 

outcrop is unfossiliferous except for the presence of silicified wood. 

Fragments and logs of silicified wood as large as 8 inches in diameter 

and a few feet long are concentrated in the basal part of the forination. The wood is especially abundant near Brush Creek, but 

generally can be found in almost any large outcrop. The petrified 

wood is usually some shade of gray in marked contrast to the warmer 

colored specimens in the overlying Chinle formation, although the 

wood in other particulars appears similar. In the type area of the 

Shinarump conglomerate the wood is believed to have affinities with 

that found in the overlying Chinle (Gregory, 1913, p. 41). 

Strat,igraphio relations, age, and oorrelation.-The contact of the 

Shinarump conglomerate and the underlying Moenkopi formation 

clearly shows erosion of the Moenkopi before deposition of the conglomerate (fig. 7). Upwards, however, the Shinarump appears to 

grade into the Chinle formation. At places, it is diffi.cult to place the 

exact contact between the two formations because lenses of coarse-
66 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

grained sandstone and pebbles appear in the lower few feet of the 

Chinle formation. For mapping purposes, the contact has been drawn 

at the top of the massive coarse-grained sandstone. In the area south 

of the Book Cliffs, where the Shinarump is thin and rocks flat lying, 

the Shinarump conglomerate has been considered the basal member 

of the Chinle formation (Dane, 1935, p. 55-56) and of Late Triassic 

age. 

Reeently, Stokes ( 1948, p. 1383), in an attempt to explain the lack 

of Middle Triassic sedilnents in the Plateau region, has suggested that 

the Shinarump conglomerate is the gravel cover of a coalescing pedi1nent surface and the unconformity and basal beds represent most, if 

not all, of Middle Triassic time. Such an interpretation permits an 

explanation of the widespread distribution of the Shinarump conglomerate, its local variation in rock types making up the pebbles, the 

channel-type deposits in the top of the Moenkopi fonnation, and the 

total lack of Middle Triassic sediments in the area. However, the 

suggestion is based entirely upon deductive reasoning, and in view of 

the close relationship of the Shinarump to the overlying Chinle and 

the unquestioned Late Triassic age of the Chinle in southern Utah and 

northern Arizona, it seems prudent to continue classifying the Shinarump conglmnerate as Late Triassic in age. 

The Shinarump conglomerate is believed to thin eastward into 

northwestern Colorado, where it maintains much the same lithologic 

character as in the Uinta Mountains (Thmnas, McCann, and Raman, 

1945). It also extends southward to northwestern New Mexico, 

northern Arizona, and southeastern Nevada. It has been recognized 

on Weber River in the extreme western end of the Uinta Mountains 

(Thomas and l{rueger, 1946, p. 1272 and 1283), and in the Park City 

district the equivalent of the Shinarump is probably represented in 

the basal part of the Nugget sandstone as mapped by Boutwell (1912, 

pl. 5). In the central vV asatch Mountains, south of the Park City 

district, it is represented by a conglmneratic sandstone unit at the 

base of the upper part of the Ankareh shale (Baker, 1947). On the 

north flank of the Uinta Mountains, the basal part of the Shinarump 

conglomerate contains seattered pebbles of limestone. In this respect, 

it resembles the conglomerates at the base of the J ehn formation in 

the Sierra Madre and Medicine Bow Mountains (Thomas and 

l{rueger, 1946, p. 1273). Limestone pebble conglomerates are characteristic of the Chinle fonnation south of the Uinta Basin. No definite 

equivalent of the Shinarump is present in the \Vincl River Range of 

central Wyoming, although the sandstone above the Alcova li1nestone 

me1nber of the Chugwater fonnation (Lower Triassic) contains fragInents of limestone and comparatively large, rounded and frosted 
STRATIGRAPHY 67 

sand grains (Love, Johnson, Nace, Sharkey, Thompson, Tourtelot, 

and Zapp, 1945). Mansfield (1927, p. 192) has suggested the correlation of the Higham grit of southeastern Idaho with the Shinarump 

conglomerate in the eastern Uinta Mountains. 

Conditions of deposition or origln.-Any explanation of the depositional conditions and origin of the Shinarump conglon1erate must 

take into consideration ( 1) the widespread occurrence of the formation, (2) the relative thinness of the unit in comparison with its great 

areal distribution, ( 3) the high degree of rounding in the large pebbles, 

(4) the angularity of the smaller grains, (5) the diversity of rock 

types, and ( 6) the erosional surface at the top of the under lying 

Moenkopi formation. 

The suggestion of Stokes that the Shinarump represents a coalescing 

pediment cover has already been discussed in connection with the age 

of the formation. The suggestion of Mansfield (1927, p. 192) that 

the Higham grit, a probable equivalent of the Shinarump in southeastern Idaho, is a series of overlapping fans also answers satisfactorily most of the field relations observed in the Uinta Mountains. 

The Shinarump is thicker than the normal pediment cover; therefore, 

, in this particular case, origin as a series of coalescing fans appears 

to be 1nore probable. The great expanse of the Shinarump conglomerate and its equivalents is difficult .to explain by coalescing fans 

or by coalescing pediments. 

CHINLE FORMATION 

Name and Definition.-The name "Chinle", for the Chinle Valley, 

northeastern Arizona, was applied by Gregory (1913, p. 42) to the 

Upper Shinarump of Powell. It has been traced from the type area 

eastward into northwestern New Niexico, westward into the Spring 

and Muddy Mountains of southeastern Nevada, and northward into 

central Utah, by a series of workers (Longwell, 1921, p. 51; Gilluly 

and Reeside, 1928, p. 67-68; Baker, 1936, p. 47-48; Baker, 1933, p. 

38-41; Dane, 1935, p. 54-65; and l\1cKnight, 1940, p. 66-70) mapping 

in contiguous areas. Throughout the Colorado Plateau region, the 

formation maintains similar lithology, stratigraphic relationships, 

and included fossils. 

The use of the name "Chinle formation" on the south flank of the 

Uinta Mountains cannot be based on lateral tracing of beds, for the 

Tertiary rocks of the Uinta Basin completely cover the area north of 

the Book Cliffs and south of the Uinta Mountains. The use of thev 

Colorado Plateau stratigraphic tern1inology for the Triassic rocks in 

the eastern Uinta Nlountains, however, was suggested by A. A. Baker~ 

who has studied the Shinarump conglomerate and Chinle formation in 
68 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

the Plateau Region from the Monument Valley-Navajo Mountain area 

in southern Utah northward to the Moab-Green River Desert country, 

and the Ankareh shale in the Provo-Park City area of the vVasatch 

Mountains. The use of Colorado Plateau terminology in the eastern 

Uinta Mountains is based on stratigraphic position and, in part, on 

lithologic similarity of the Triassic rocks in the two areas. 

Lithology and topographic ewpression.-The Chinle formation is 

divided into two members-a lower member of interbedded mudstone, fine-grained sandstone, and shale, in shades of red, purple and 

brown, and an upper men1ber of fine-grained, light-gray to weak 

yellowish-orange sandstone with thin partings of weak-red shale 

(pl. 2 and fig. 8). The lower member is remarkably consistent in 

lithology from Mosby Creek eastward to Diamond Mountain. Finegrained, reddish-gray to weak red-purple, shaly sandstone and siltstone are interbedded with dark reddish-gray to weak-red shale. The 

finer grained beds, those with the greater percentage of shale, are 

darker in color. Lenticular beds of coarse-grained, gray to dark 

purple sandstone with occasional pebbles of pink and gray quartzite, 

nodules of manganiferous iron oxide, and fragments of silicified 

wood are common in the basallO feet. A 23-to 36-foot bed of moderate yellowish-brown mudstone or siltstone, containing botryoidal 

concretions of calcite, lies 70 to 80 feet above the base of the Chinle 

in the Brush Creek-Ashley Creek area. The upper member is red 

FIGURE 8.-Chinle formation (Trc) resting on Shinarump conglomerate (Trs) and: overlain by Navajo sands;tone (Jn) on Red' Mountain. 
STRATIGRAPHY 69 

to white, fine- to medium-grained sandstone with occasional thin beds 

of red to purple siltstone. Some sandstone beds are cemented with 

calcile and show irregular solution pits. Others are crossbedded in 

beds 0.5 to 1.0 foot in thickness. The lower member forms smooth 

slopes malltled by a thin crust of weathered red sandy shale and clay. 

Out.crops are usually good because of the protection afforded by the 

more resistant upper part of the Chinle formation. The upper member generally forms vertical cliffs which retreat by spalling large 

blocks of sandstone. 

Distribution and thickness.-The Chinle formation crops out on 

"Tltilerocks River, in the faulted area between Mosby Mountain and 

Dry Fork of Ashley Creek, and on the north flank of Little Mount.aill. It appears at the crest of the Neal dome at the intersection of 

Dry Fork and Ashley Creek and crops out from the community of 

Dry Fork eastward to Dian1ond Mountain. It also is present on the 

north side of Split Mountain and along Cliff Creek in the southeastern 

part of the area. 

The lower member ranges in thickness from 120 feet to 175 feet, 

and averages 145 feet. The upper member ranges in thickness from 

85 feet to 130 feet, and averages 105 feet. 

The detailed lithology and thickness of the Chinle formation is 

shown in the following sections taken at well-exposed intervals across 

the area: 

Section of the Chinle formation on west side of Little Brush Creek SWlA, sec. 

25, and NWlA, sec. 36, T. 2 S., R. 22 Fl. 

[Measured by D. M. Kinney and J. F. Rominger] 

Navajo sandstone: 

Sandstone, light-gray, fine-grained, crossbedded. 

Chinle formation: Feet 

Sandstone, red, fine-grained, friable______________________________ 8 

Sandstone, white, fine- to medium-grained, ripple-marked__________ 3 

Siltstone, red to purple with thin beds of sandstone, light-gray, 

fine-grained---------------------------------------------------- 13 

Sandstone, red, fine-grained, massive, slightly calcareous, cavernous 

weathering____________________________________________________ 63 

Sandstone, mottled red and white, fine-grained, slightly calcareous__ 3 

Siltstone, red---------------------------------------------------- 48 

Shale, moderate yellowish-brown, with botryoidal concretions of 

calcite-------------------------------------------------~------ 23 

Sandstone, red to purple, very fine-grained, with streaks of purple 

shale__________________________________________________________ 56 

Sandstone, red, coarse-grained, crossbedded, with occasional small 

pebbles-------------------------------------------------------- 5 Shal~ gray to purple_____________________________________________ 12 

234 
70 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Shinarump conglomerate: 

Section of the Chinle formation measured on southwest side of Red Mountnin, 

SE1j4 sec.17, T. 3 S., R. 21 E., Salt Lake Base and Meridian 

[Measured by D. M. Kinney and J. F. Rominger] 

Navajo sandstone: 

Sandstone, yellowish-gray, fine- to medium-grained, crossbedded. 

in turrets and spires. 

Weathers 

Chinle formation: 

Sandstone, yellowish-gray, fine- to coarse-grained, massive, crossbedded within 0.5 foot layers, calcareous, with spherical calcareous 

nodules 5 to 10 mm. in diameter. Thin beds of weak-red shale in 

Feet 

upper 2 feet_ _____________________________________ _:____________ 13 

Sandstone, weak yellowish-orange, fine-grained, friable, thin-bedded 

(0.2 to 1.0 foot), with harder 1-foot beds of sandstone, light-gray, 

fine-grained, slightly calcareous. Weak-red shale beds 36 to 40 feet 

and 56 to 60 feet above base____________________________________ 79 

Sandstone, light-gray, fine- to medium-grained, massive crossbedded; 

forms ledge___________________________________________________ 8 

Sandstone, light-brown, tine-grained, friable_______________________ 14 

Sandstone, light-brown with streaks of light-gray to greenish-gray, 

fine-grained, thin-bedded (0.1 to 1.0 foot), slightly crossbedded; 

forms cliff. Bed of shale, sandy, pale reddish-brown, 8 to 11 feet 

· above base____________________________________________________ 22 

Shale, weak-red__________________________________________________ 22 

Siltstone, moderate yellowish-brown_______________________________ 36 

Shale, dark reddish-gray to weak-red______________________________ 58 

Sandstone, shaly, reddish-gray, to weak red-purple, with thin layers of 

reddish-gray, sandy shale; silicified wood, manganese and ironstained nodules, and Shinarump-like sandstone lenses in basal 10 

feet. Thin bed (0.5 foot) of sandstone, very coarse grained, pebbly, 

weak orange-pink, lenticular, with few fragments of silicified wood 

at top_________________________________________________________ 24 

276 

Shinarump conglomerate: 

Sect,ion of the Chinle fonnation on the west side of Mosby Ct·eek SlVl,4 sec. 8, 

T. 3 S., R.19 E., Salt Lake Base and Meridian 

[Measured by D. M. Kinney, J, F. Rominger, R. S. Brown, and P. Verastegui M.] 

Navajo sandstone: 

Sandstone, light-gray, tan-weathering, fine-grained, crossbedded, with 

rounded grains of sand. 

Chinle formation: Feet 

Sandstone, red to tan, thin-bedded, with partings of reddish-brown 

shale ________ ~------------------------------------------------- 85 

Shale, tan to red, sandy------------------------------------------ 175 

260 

Shinarump conglomerate: 

Sandstone, light-gray, crossbedded, medium- to coarse-grained, pebbly. 
STRATIGRAPHY 71 

Foss-ils and age.-The only recognized fossils in the Chinle formation in this area are fragments of silicified wood found near the base 

of the lower nH'mbe.r, although Untermann (personal communication) 

reports finding fragments of phytosaurian bone in the san1e unit on 

Red Mountain. The wood probably belongs to the genus 

Araucariowylon, the characteristic conifer of the Shinarump conglomerate and Chinle formation in northern Arizona. Evidence from 

vertebrate paleontology (phytosaurian bones) and paleobotany 

(Camp, 1930, p. 1-23; Baker, 1933, p. 38; Mcl{night, 1940, p. 66-71; 

and Daugherty, 1941) (leaf i1npressions and silicified wood) indicate 

a Late Triassic age for the Chinle in northeastern Arizona and as far 

north as Moab, Utah. On the south flank of the Uinta l\{ountains, 

the Chinle is not dated by vertebrate or botanical remains. 

Stratigraph-ic relations and coJ•relations.-Small lenses of coarsegrained pebbly sandstone in the basal few feet of the Chinle suggest 

a gradational boundary with the underlying Shinarmnp conglomerate. 

A similar relationship has been observed in the Salt Valley-Green 

River Desert region south of the Uinta Basin where the basal conglomerate of the Chinle forn1ation "has much of the same stratigraphic significance as the Shinarump and may be regarded as the 

eastern equivalent of the Shinarump" (Dane, 1935, p. 55-56). The 

boundary between the lower and upper n1en1bers of the Chinle in the 

Deep Creek-Brush Creek area is very sharp, and in the NE14 sec. 20, 

T. 3 S., R. 21 E., the upper n1en1ber appears to truncate the n1ore steeply dipping reel sanely shale of the lower 1nernber. This relationship 

was not observed elsewhere in the area, and an additional section 

n1easured in an exposure one-fourth 1nile to the north shows no change 

in thickness for the lower 1nember. The truncated beds of the lower 

member are interpreted as foreset bedding in a deltaic deposit. The 

upper boundary of the Chinle is taken at the top of the highest reddish shale beneath the 1nassive crossbedded Navajo sandstone of 

Jurassic( n age. The upper boundary 1nay not always have been 

drawn at the same horizon in measuring sections and in mapping. On 

Split Mountain, beds of reddish sandstone and red shale occur at intervals throughout the Navajo sandstone, 1naking the choice of the 

upper boundary difficult. The arbitrary choice of the highest red 

shale as the top of the Chinle seerns 1nost reasonable in the area from 

Mosby Mountain east to Dia1nond Mountain, for it groups together 

the eolian-type crossbedding of the Navajo sandstone and the dominantly water-laid sandstone and shale of the Chinle. No evidence 

of erosion of the Chinle prior to the deposition of the Navajo was 

found, and additional study of the Chinle for1nation east of the Green 

River 1nay make it more logical to group the upper 1nember with the 

overlying Navajo sandstone. 
72 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

The correlation of the Chinle formation in the eastern Uinta Mountains with the type section is made on the basis of lithologic similarity 

and stratigraphic position above the Shinarump conglomerate and 

below the cross bedded Jurassic ( ~) sandstone, here assigned to the 

Navajo sandstone. The lithology of the Chinle in the eastern Uinta 

Mountains, however, has changed slightly from that south of the 

Uinta Basin, for the crossbedding and lenticular bedding, characteristic of subaerial fluvial deposition, has been replaced by even-bedded 

siltstone and fine-grained sandstone, which are more characteristic 

of playa deposition. This change probably denotes greater distance 

from the source area. Ripplemarks and other evidence of current 

action are comparatively rare, except in the upper member of the 

Chinle where it is believed to be transitional to the overlying Navajo 

sandstone. 

In northwestern Colorado, to the east of the Uinta Mountains, the 

Chinle formation is believed to continue relatively unchanged for at 

least 100 miles (Thmnas, McCann, and Raman, 1945). To the west 

in the Wasatch Mountains, the Chinle is correlated with the upper 

part of the Ankareh shale of the Park City district. The type Ankareh includes a bed of coarse-grained sandstone near the middle of 

the section which has been correlated with the Shinarump conglomerate. In the Provo area (Baker, 1947), the twofold division of the 

Chinle into a lower fine-grained shaly member and an upper sandstone 

member persists, although the formation is almost twice as thick as 

in the eastern Uinta Mountains. In the Wind River Mountains of 

central Wyoming, the Popo Agie member of the Chugwater formation probably correlates with some part of the Chinle (Gregory, J. T., 

personal communication), although Branson and Camp have suggested 

a Middle Triassic age for the vertebrate fauna of the Popo Agie. The 

Popo Agie has a very characteristic lithology of ocher-colored, oOlitic, 

siliceous, dolomitic claystone, limestone pellet-conglomerate, purple 

and red shale, and red silty sandstone. Certain beds in the lower 

member of the Chinle of the Red Mountain-Little Brush Creek area 

closely resemble the descriptions of the Popo Agie. The Deadman 

limestone and Wood shale ( 200 to 250 feet thick) in southeastern 

Idaho, now assigned questionably to the Triassic, may correspond to 

the Chinle formation of the eastern Uinta Mountains. 

Conditions of deposition.-The prevailing thin-bedded, fine-grained 

micaceous character of the lower member of the Chinle fonnation 

together with the lack of mud cracks, raindrop impressions, and other 

evidence of subaerial conditions point to deposition in a body of 

standing water. The absence of gypsum, anhydrite, and beds of limestone associated with the shales and siltstones, together with the presence of fresh-water pelecypods and swamp-living vertebrate reptiles 

and amphibians in correlative strata in the Wind River Moun-
STRATIGRAPHY 73 

tains to the north and the San Ra£ael Swell-Moab region to the south, 

suggest deposition in £resh water. 

The lower member o£ the Chinle £ormation is in sharp contrast 

to the Chinle £ormation in the Salt Valley anticline and San Ra£ael 

Swell areas, where the beds o£ the Chinle are lenticular in shape, the 

bedding is discontinuous and irregular, and ripple marks are common. These conditions are characteristic o£ fluvial deposits. The 

upper member o£ the Chinle, however, is dominantly thick-bedded, 

fine- to medium-grained sandstone; crossbedding and ripple marks 

are common, which suggests fluvial deposition, perhaps on an advancing delta. 

The Chinle and its equivalents become finer grained toward the 

north, suggesting a southern source, perhaps in highlands in central 

Arizona. Additional sediments probably were derived £rom rocks o£ 

other areas, such as the crystalline rocks o£ the Uncompahgre Plateau 

area which was a local source £or the Chinle in the Salt Valley-Green 

River Desert area south o£ the Book Cliffs. 

JURASSIC ( P) SYSTEM 

NAVAJO SANDSTONE 

Name and definition.-The Navajo sandstone, a fine- to mediumgrained, light-gray to buff, crossbedded sandstone was named £or exposures in the "Navajo country" o£ northern Arizona (Gregory, 1913, 

p. 57). The name has been used £or rocks o£ similar appearance and 

stratigraphic position in central Utah. In central and southern Utah 

and northern Arizona, the Navajo sandstone is the upper £ormation 

in the Glen Canyon group, which also includes the Wingate sandstone 

and the Kayenta £ormation. The Wingate and Kayenta cannot be 

differentiated in the eastern Uinta Mountains, although equivalent 

beds may be present in the upper member o£ the Chinle £ormation and 

in the lower beds o£ the Navajo. For many years, the rocks here included in the Navajo sandstone have been identified as the Nugget 

sandstone, whose type section is in southwestern Wyoming. As used 

by Schultz (1920, p. 78); Sears (1924, p. 284); and Hancock (1925, p. 

8, 10) in the eastern Uinta Mountains, and especially in northwestern 

Colorado, the Nugget sandstone included equivalents o£ the Navajo 

sandstone, the Carmel £ormation, the Entrada sandstone, and the 

basal sandstone o£ the Curtis £ormation o£ the present report. 

Lithology and thiekness.-The Navajo is a light-gray to buff, fineto medium-grained sandstone composed o£ subrounded to rounded 

quartz grains. The larger particles are concentrated along planes 

o£ crossbedding and are generally better rounded than the averagesized grains. The sand is dominantly clear quartz, but a minor portion is pink and dark-gray quartz resembling the minor constituents 

o£ the Shinarump conglomerate and the Entrada sandstone. The 
7 4 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

crossbedding in the Navajo dips in a southerly direction between 

true bedding planes 10 to 30 feet apart. Dreikanter of light-pink 

quartzite exhibiting fluted carving and frosted surfaces, as much as 6 

inches in diameter, have been found at two localities in the Steinaker 

Draw area; one locality is in the SE:J4 sec. 27, T. 3 S., R. 21 E., west 

of Utah State Highway 44, and the other is located 4 miles to the 

northeast in the SEl;i sec. 5, T. 3 S., R. 22 E. In both localities, the 

dreikanter are found in the top bed of the formation. They may 

have been concentrated from a great thickness of sandstone by the 

encroaching Carmel sea during late Jurassic time or by wind ablation 

prior to submergence of the area. 

A thin, lenticular bed of fine-grained, rough- to hackly-weathering, 

gray, sandy li1nestone, 6 to 8 feet thick, is present in the middle of the 

Navajo sandstone on a sharp-pointed hill in the NvVl;i sec. 36, T. 2 S., 

R. 22 E., a short distance west of Little Brush Creek. In the San 

Rafael Swell region similar beds in the Navajo have been interpreted 

as deposits of ephemeral lakes among the dunes ( Gilluly and Reeside, 

1928, p. 72; Baker, 1946, p. 69). A bed of tan-weathering, highly calcareous sandstone is present on Neal dmne, east of Ashley Creek. This 

resistant calcareous bed appears to have been deposited at a single 

horizon and probably under conditions similar to those under which 

the lenticular li1nestone bed was deposited. The tracing of this calcareous bed has 1nade possible the structural contouring of Neal dome. 

The Navajo sandstone thins frmn 1,028 feet on the west side of 

Whiterocks River to a little over 700 feet at Split Mountain; between 

Steinaker Draw, Little Brush Creek, and Split Mountain it is remarkably constant and averages between 750 and 800 feet thick. The 

highly crossbedded nature of the Navajo and the obscurity of true 

bedding made it difficult to obtain detailed n1easurement of the thickness of the sandstone. The above thicknesses are calculated from 

sections wherein the strike and dip of the underlying well-bedded 

Chinle formation and of the overlying Carmel formation are in close 

accord. 

Distribution and topographic expression.-The Navajo sandstone 

is present on the east and west sides of Whiterocks River where it is 

heavily i1npregnated with petroleum residue, in the valleys of Mosby 

Creek and Deep Creek where it is only incompletely exposed because 

of the faulted condition of the rocks, on the north side of Little Mountain, and in continuous outcrop from west of Ashley Creek (fig. 9), 

eastward to Diamond Mountain. It is again exposed on the north 

flank of Split Mountain and in the vicinity of Cliff Creek on the 

eastern border of the area under study. Some of the finest exposures 

of the fonnation are between Ashley Creek and Steinaker Draw, 

where the "tangential" crossbedded sandstone weathers into smoothly 

rounded dmnes and sharp turrets, and is cut by steep-walled box 
STRATIGRAPHY 75 

FIGURE 9.- Carmel formation (Jca) on mass.ive crossbedded Navajo sands.tone (Jn) preserved in small syncline north of Neal dome. 

canyons eroded along northwest-southeast striking joints or :faults of 

slight displacement. It is not a particularly resistant formation 

except in the walls of Dry Fork of Ashley Creek and Ashley Creek 

where its massive, basal part forms cliffs 100 to 200 :feet high. Elsewhere the sandstone forms smoothly rounded slopes covered with 

dunes of wind-drifted, fine-grained sand. 

Stratigraphic relations and age.-The lower boundary o:f the 

Navajo sandstone has been chosen arbitrarily at the base o:f the massive, light-gray, cross bedded sandstone. No erosion o:f the Chinle 

formation prior to the deposition of theN avajo has been observed and 

the boundary is believed to be gradational. Sand derived :from the 

upper beds o:f the Navajo or :from dunes lying on the surface of the 

consolidated Navajo were reworked into a bed of light-gray, finegrained sandstone by the advancing Carmel sea during Middle and 

late Jurassic time. Except :for this thin bed of reworked sand, the 

sharp change :fron1 crossbedded Navajo to the overlying red sandy 

shale, pink to white sandstone, gypsum and interbedded marine fossiliferous limestone that make up the Carmel :formation, suggests unconformity. The upper surface o:f the Navajo shows no channeling or 

other irregularities which might have been caused by subaerial erosion. 

Of course, unconformity is shown most clearly by truncation of the 

underlying beds; this could not readily be recognized because the 

Navajo sandstone is highly crossbedded. The eastward thinning of 

the Navajo is not believed to be due to thinning by truncation o:f beds. 

29516.3- 55-6 
76 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

The age o:f the Navajo sandstone is entirely dependent upon its 

stratigraphic position below the :fossiliferous Carmel :formation which 

carries a diagnostic Middle and Upper Jurassic :fauna and above the 

Chinle :formation which, in the Uinta Mountains, is itself correlated 

by lithology and stratigraphic position with the Chinle :formation 

south o:f the Book Cliffs. The Chinle :formation, in turn, is dated as 

Late Triassic by amphibian remains :found near Moab, Utah. It has 

been suggested by Heaton (1939, p. 1176) that the "'\Vingate and 

Kayenta :formations in the San Rafael Swell were deposited in Late 

Triassic or Middle( n Jurassic time and that the Navajo sandstone 

was deposited in Middle ( ? ) Jurassic time. More recently, however, 

Imlay (1945, p. 1026), on the basis o:f ammonites, has suggested that 

the Carmel :formation o:f the San Rafael Swell region is separated 

:from the Navajo sandstone by an unconformity representing most o:f 

Middle Jurassic time. No :fossil evidence :favoring either o:f these 

suggestions is available in the Uinta River-Brush Creek area because 

the Navajo is un:fossili:ferous. 

Oorrelation.-The Navajo sandstone in the eastern Uinta Mountains is believed to correlate with the typical Nugget sandstone o:f 

southwestern Wyoming and the Wasatch Mountains (Baker, Dane, 

and Reeside, 1936, p. 5). Eastward :from the Uinta River-Brush 

Creek area, the Navajo has been traced :for more than 100 miles 

(Thomas, McCann, and Raman, 1945) by surface sections and drill 

cuttings. To the south, the sandstone is believed to be continuous with 

the Navajo o:f the San Rafael Swell, the region between the Green 

and San Juan Rivers, and the Moab area. 

Conditions of deposition.-It is agreed by all investigators working in the highly crossbedded, fine- to medium-grained Navajo sandstone that the :formation is predominantly o:f eolian origin. Water 

played a minor part in its deposition, as is shown by thin lenticular 

beds o:f fine-grained, sandy limestone and occasional horizontally 

bedded, shaly, red sandstone. 

An isopachous map o:f the Navajo sandstone in southern and central 

Utah prepared by Baker, Dane, and Reeside (1936, p. 47) strongly 

suggests a western source. Recent additional information in regard 

to the thickness o:f the Navajo sandstone in the Uinta Mountains 

coupled with the more prevalent belie£ that it is correlative with the 

Nugget sandstone o:f the Wasatch Mountains and southwestern Wyoming has justified an isopachous map which shows eastward thinning 

o:f the :formation :from the latitude o:f central Wyoming southward to 

central Arizona. This thinning towards the east suggests that the 

principal source was in the mountains o:f central and eastern Nevada. 

It is possible that additional sediments were derived :from central 

Colorado. However, the predominant southern dips o:f the crossbedding in the Uinta River-Brush Creek area indicate that the prevailing winds advanced the local dunes towards the south. 
STRATIGRAPHY 77 

JURASSIC SYSTEM 

MIDDLE AND UPPER JURASSIC SERIES 

SAN RAFAEL GROUP 

The San Rafael group (Middle and Upper Jurassic), named for 

exposures in the San Rafael Swell ( Gilluly and Reeside, 1928, p. 73), 

includes four formations in the type area, which, in ascending order, 

are the Carmel formation, the Entrada sandstone, the Curtis formation, and the Summerville formation. In the eastern Uinta Mountains, however, the Summerville fonnation is not recognized, and the 

Morrison for1nation of Late Jurassic age overlies the Curtis formation. 

CARMEL FORMATION 

Name.-The Cannel formation, the lowest in the San Rafael group, 

was proposed by Gregory and Moore (1931, p. 73) for exposures near 

Mount Carmel in southwestern Utah. Informally published by W. T. 

Thmn (1926, p. 3) in summarizing field investigations of W. T. Lee, 

W. W. Boyer, and James Gilluly, it was first published formally by 

Gilluly and Reeside ( 1928, p. 73) in their study of the San Rafael 

region. Dane ( 1935, p. 90) has suggested that only the lower marine 

part of the Cannel formation in central and east central Utah may be 

equivalent to the type Cannel. The name "Car1nel" was introduced 

into the eastern Uinta Mountains by Baker, Dane, and Reeside (1936, 

p. 14). Previously, these strata were considered a part of the Nugget 

sandstone. 

Lithology and thickness.-Within the area mapped, the Carmel formation consists of soft red sandy shale, fine-grained sandstone, a few 

thin beds of platy, light-gray, calcareous 1nudstone, and fossiliferous 

light-gray limestone. Beds of pinkish gypsum or gypsiferous finegrained sandstone are present locally in the lower part of the formation. Limestone is more abundant on Whiterocks River in the western part of the Uinta River-Brush Creek area than to the east; it disappears at the head of Steinaker Draw. 

The Carmel forn1ation thins frmn 390 feet on the west side of Whiterocks River to 244 feet in Steinaker Draw, 170 feet between Little 

Brush Creek ·and Brush Creek, ancl124 feet on the south side of Split 

Mountain. This thinning is unifonn frmn west to east, and near Skull 

Creek in north western Colorado the Cannel is present only as thin 

lenses beneath the Entrada sandstone. 

The following detailed sections, 1neasured by stadia, show the pronounced thinning and change of character of the formation from west 

to east: 
78 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Section of the Carmel fomwtion on west side of TVhiterocks River NW1,4 sec. 19, 

T. 2 N., R. 1 E., Uinta Bpecial Base and Meridian 

[Measured by D. l\L Kinney and J. F. Rominger] 

Entrada sandstone : 

Sandstone, light-gray, fine- to medium-grained, with rounded and 

frosted grains. 

Carmel formation: Feet 

Covered, probably sandstone, reddish-brown, fine-grained and shale, 

reddish-brown, and sandy---------------------------------______ 113 

Sandstone, weak yellowish-gray, very fine grained__________________ 20 

Covered, probably shale, reddish-brown to light-gray, sanely__________ 76 

Mudstone, yellowish-gray----------------------------------------- 10 

Sandstone, light reddish-brown, with veinlets of gypsum____________ 6 

Gypsum, light-gray, lenticular____________________________________ 2 

Sandstone, reddish-brown, fine-grained, with gypsum veins__________ 3 

Gypsum (60 percent) and sandstone ( 40 percent), yellowish-gray, 

interbedded____________________________________________________ 2 

Mudstone, yellowish-gray----------------------------------------- :2 

Sandstone, yellowish-gray, very fine grained________________________ 4 

Gypsum_________________________________________________________ 1 

Mudstone, reddish-brown, gypsiferous, slightly sanely, with veinlets of 

gypsum_______________________________________________________ 13 

Gypsum, white to greenish, lenticular ________ :______________________ 1 

Mudstone, yellowish-gray, thin-bedded_____________________________ 40 

Covered_________________________________________________________ 29 

Sandstone, reddish-brown, very fine grained________________________ 15 

Limestone, light-gray, very thin bedded, slabby, brittle, and ripplemarked_______________________________________________________ 3 

Sandstone, moderate reddish-brown, fine-grained___________________ 17 

Shale, light-gray, fissile, with thin beds (to 0.4 foot) of limestone, 

gray, tan-weathering, abundantly fossiliferous____________________ 26 

Navajo sandstone: 

Sandstone, dark-brown, petroleum impregnated, fine- to mediumgrained. 

383 

Section of Cannel fonnation on west side of Steinaker Draw E1,4 sec. 27 and 

W1,4 sec. 26, T. 3 B., R. 21 E. 

[Measured by D. M. Kinney, J. F. Rominger, P. Verastegui M., and R. S. Brown] 

Entrada sandstone: 

Sandstone, light-gray, fine-grained, massive, with rounded. grains. 

Carmel formation: Feet 

Covered, sandstone, red, very fine grained__________________________ 54 

Mudstone, gray, with streaks of silty sandstone____________________ 22 

Sandstone, red, fine-grained_______________________________________ 27 

Gypsum, light-pink to white. Bed thickens to 4 feet in 300 feet 

southwest_____________________________________________________ 2 

Mudstone, gray-------------------------------------·------------- 17 

Sandstone, red, fine-grained_______________________________________ 8 

Shale, gray, crinkly-bedded _________________ ----------------------- 3 
STRATIGRAPHY 79 

Section of Carmel fonnation on west side of Steinaker Draw E14_ sec. 27 and 

· W14_ sec. 26, T. 3 S., R. 21 E.-Continued 

Carmel formation-Continued Feet 

Sandstone, gray, fine-grained, platy, calcareous, fossiliferous_________ 6.5 

Shale, gray, platy________________________________________________ 6.5 

Sandstone, red, fine-grained ______________________ ._________________ 31 

Shale, light-gray, conchoidally fracturing, with 4 inches of limestone, 

light-gray, fine-grained, at base. Tdgonia replaced by red chert 

in the limestone bed____________________________________________ 7 

Sandstone, red, fine-grained, with three 1- to 2-foot beds of sandstone, 

gray, fine-grained_._____________________________________________ 39 

Sandstone, light-gray, fine-grained, turbulent-bedded, with calcareous 

cement near top. Probably reworked Navajo sandstone___________ 8 

231 

Section of tl!e Cm·mel formation south of Toacl between Bt·ush Ot·eek ancl Little 

Bntsh Ct·eek, NW1A, sec. 2, T. 3 S., R. 22 E. 

[Measured by D. M. Kinney and J. F. Rominger] 

Entrada sandstone: 

Sandstone, white fine- to medium-grained, with rounded and polished grains. 

Carmel formation: Feet 

Siltstone, red____________________________________________________ 22 

Shale, greenish-gray, and sandstone, fine-grained, interbedded______ 10 

Siltston~ red____________________________________________________ 22 

Sandstone, light-gray, fine-grained_________________________________ 9 

Shale, gray, conchoidally fracturing, in part calcareous____________ 24 

Sandstone, gray, fine- to medium-grained, with rounded and polished 

grains________________________________________________________ 1 

Sandstone, red, fine to very fine grained and shale, reeL_____________ 82 

170 

Distribution and topographic expression.-The Cannel formation 

is present along Whiterocks River, in the faulted area between Mosby 

Mountain and Ashley Creek, and eastward from Ashley Creek along 

the west side of Steinaker Draw and across the valleys of Brush 

Creek and Little Brush Creek to Dia1nond Mountain. It is present 

also on the north flank of Split Mountain and on the westward plunging Section Ridge anticline in the eastern part of the mapped area. 

Good exposures can be found on the north side of Little Mountain, 

along Steinaker Draw, and between Brush Creek and Little Brush 

Creek. 

The Carmel formation is easily eroded, and forms strike valleys 

between the Navajo sandstone and the Curtis formation, or between 

the Navajo sandstone and the n1assive crossbedded sandstone which 

comprises the Entrada sandstone in the eastern part of the area. At 

sOine places, as in the faulted area between Mosby Creek and Little 

Mountain, or in Steinaker Draw, the light-gray, conchoidally weather-
80 • GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

ing, calcareous shale and thinbedded, fossiliferous limestone in the 

basal 50 feet of the Car1nel will for1n strike ridges. 

Fossils.-Fossil collections frmn the limestone beds in the basal 50 

feet of the Cannel formation in Steinaker Draw were submitted to 

Ralph W. Imlay of the Geological Survey. Mr. Imlay reports as 

follows: 

The collections from the Jurassic of the Uinta Mountains do not allow exact 

age determinations. Collection U-4 from the Carmel or Twin Creek in sec. 

26, T. 3 S., R. 21 E., contains Trigonla q7tadrangularis Hall and Whitfield which 

has been found previously only in the Carmel, Gypsum Spring, Twin Creek and 

lower part of the Sundance. Collection U-5 from the Carmel or Twin Creek 

in sec. 12, T. 3 S., R. 21 E., contains fragmentary Camptonectes . ... 

Strat-igraphic relations and correlation.-The contact between the 

Carmel formation and the Navajo sandstone is sharp (fig. 9). Except for a thin reworked sandstone bed at the base of the Carmel, 

no gradational beds appear between the light-gray to tan, fine-grained 

sandstone of the Navajo and the overlying reel sanely shale. The 

boundary of the Carmel with the overlying Entrada sandstone appears gradational, particularly in the western two-thirds of the area. 

From Whiterocks River eastward to the measured section in Steinaker 

Draw, the boundary is generally poorly exposed. Even in the better 

exposures in this area, the change from reel siltstone and fine-grained 

sandstone of the Carmel to the fine-grained light-gray sandstone of 

the Entrada takes place over an interval of 10 or 15 feet. In the area 

from Brush Creek southward to Section Ridge anticline, the boundary 

between the two formations is sharp, but no evidence points to erosion 

of the Carmel formation prior to the deposition of the overlying 

Entrada sandstone. The two formations appear conformable 

throughout the area. 

The limestone beds in the basal 50 feet of the Cannel formation 

are tongues of the Twin Creek limestone, which progressively thickens 

to 700 or 800 feet east of the Duchesne River (Huddle and McCann, 

1947) to 1,100 feet in the Wasatch Mountains (Baker, 1947), and 

finally reaches a thickness of 3,500 to 3,800 feet in the type section 

in southwestern Wymning (Veatch, 1907, p. 56). The amount of 

Twin Creek limestone that is represented in these thin limestone beds 

is not known, but from analogy with the section in the San Rafael 

Swell, where the limestones near the base of the Carmel formation 

are early Middle Jurassic (Imlay, 1948, pl. 4), it is probable that the 

Carmel formation in the eastern Uinta Mountains is, for the most 

part, Middle Jurassic in age. 

Conditions of deposition.-The fossiliferous limestone at the base 

of the Cannel formation in the western three-quarters of the area is 

certainly of marine origin. Thin beds of gypsum, which occur in 

the lower 150 feet o:f the Whiterocks River section, also suggest 
STRATIGRAPHY 81 

deposition from sea water in shallow land-locked lagoons. Th.e upper 

part of the Carmel formation probably was deposited from water 

in lakes or ponds, on a river flood plain, or on a coastal plain near 

the sea as the Jurassic sea withdrew northward and westward into 

the central trough of the geosyncline. The gradational contact between the Carmel and the overlying Entrada sandstone marks the 

change from subaqueous to prevailing eolian deposition. Smne of 

the rock showing evidence of subaqueous deposition at the top of the 

Carmel was probably wind transported before final deposition. The 

source of the clastic sediments, fine-grained sandstone and silt, in the 

Cannel formation was probably to the east and southeast where 

Triassic and Permian red beds were being eroded from a low -lying 

land area. Smne of the Cannel fonnation, as mapped in the western 

and central parts of the Uinta River-Brush Creek area, may be 

equivalent to the reel, silty sandstone facies of the Entrada which is 

present to the west of the "white sand" facies in the San Rafael Swell 

regwn. 

ENTRADA SANDSTONE 

N wme.-The Entrada sandstone was defined by Gilluly and Reeside 

( 1928, p. 76) as a thick series of earthy sandstones and subordinate 

shale overlying the Carmel fonnation and underlying the Curtis 

formation in the northern part of the San Rafael Swell. Two 

lithologic facies of the formation are present in central Utah, the 

westerly facies is red, silty, and fine-grained, but eastward the sandstone is light-gray, "clean," and fine- to mediun1-grained. The Entrada sandstone has been recognized in the eastern Uinta Mountains 

since the work of Baker, Dane, and Reeside (1936, p. 27, 41). 

Lithology and thickness.-The Entrada sandstone, as typically developed in the eastern Uinta Mountains, is a fine- to 1nedium-grained, 

light-gray, poorly cemented sandstone. This facies of the forn1ation 

has also been decribed from east of the San Rafael Swell (McKnight, 

1940, p. 91-93; Baker, 1933, p. 49-50; Dane, 1935, p. 92-98). To the 

west, the clean, light-gray sandstone is interbedded with light-gray to 

red, very fine grained sandstone or siltstone. The fine-grained silty 

phase of the Entrada fingers out into the light-gray, fine- to mediumgrained phase near the head of Steinaker Draw. Some of the strata 

included in the upper, covered portion of the Carmel formation in 

Whiterocks Canyon and west of Steinaker Draw also 1nay be the finegrained red silty facies of the Entrada sandstone. 

The sand grains in the Entrada are sorted into two very definite 

sizes-fine and coarse. This double sorting distinguishes the Entrada 

sandstone from the Navajo sandstone (which it superficially resembles), because the coarse grains are not concentrated along planes of 

crossbedding; instead, they oeeur as isolated grains surrounded by 
82 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

finer grained sand. The coarser grains are well rounded and their 

surfaces have a matte or frosted appearance. The 1najority of the 

sand grains are transparent or colorless quartz, but 1ninor percentages 

of pink and dark-gray grains give the sandstone a characteristic 

appearance. This mixture of clear quartz with gray and pink grains 

also has been noted in the Navajo sandstone and in the Shinarump 

conglomerate, which suggests a common source area for these three 

formations. Dane (1935, p. 93) also records similar minor mineral 

constituents in the Entrada sandstone of the Salt Valley anticline 

area of west central Utah. 

The bedding in the Entrada sandstone in the eastern part of the 

area is massive and faintly crossbedded. Individual beds more than 

25 feet thick and displaying no horizontal bedding, are common. The 

crossbedding is in marked contrast to the prmnient "tangential" bedding which characterizes the Navajo sandstone. The cross-lalnination in the Entrada n1ay be subordinant because it is not highly developed or because differential solution does not emphasize the long 

sweeping false bedding as is clone in the calcareous-cemented Navajo 

sandstone. 

The Entrada sandstone thins frmn 240 feet on Whiterocks River 

to 215 feet at Steinaker Draw, 163 feet between Brush Creek and Little 

Brush Creek, and to 104 feet at Split Mountain. Heaton ( 1939, p. 

1175) records only a little more than 100 feet of Entrada on Whiterocks River, but this discrepancy is due to the choice of the lower 

boundary of the sandstone in an area where the reel silty sandstone 

facies is interbedded with the "clean" sand facies (Thomas and l{rueger,1946,p.1287). 

The following detailed sections of the Entrada sandstone give the 

lithology and thickness of the different units in n1ore detail: 

Section of the Entrada sandstone on the west side of Whiterocks Rlvet·, NTV:tA, 

sec. 19, T. 2 N., R. 1 E. 

[Measured by D. M. Kinney and J. F. Rominger] 

Curtis formation: 

Sandstone, light-gray, fine- to medium-grained, glauconitic, crossbedded. 

Entrada sandstone : Feet 

Sandstone, moderate reddish-brown, fine-grained__________________ 45 

Sandstone, yellowish, very fine grained___________________________ 34 

Sandstone, light-gray, fine- to medium-grained____________________ 28 

Covered, probably sandstone, reddish-brown, fine-grained____________ 113 

Sandstone, weak yellowish-gray, very fine grained.________________ 20 

240 

Carmel formation : 

Covered. 
STRATIGRAPHY 83 

Section of the Entrada sandstone on the 1oest side of Steinaker Draw SW14 

sec. 26, T. 3 S., R. 21 E. 

[Measured by D. M. Kinney, J. F. Rominger, P. Verastegui M., and R. S. Brown] 

Curtis formation: 

Sandstone, light-gray, fossiliferous, conglomeratic with pebbles of quartz 

and shale. 

Entrada sandstone : Feet 

Sandstone, red, fine-grained______________________________________ 10 

Sandstone, light-gray, fine-grained, with large, rounded and frosted 

sand grains___________________________________________________ 55 

Sandstone, light-gray, fine-grained, with rounded and frosted grains__ 101 

Sandstone, light gray, fine-grained, massive, with rounded and frosted' 

grains_________________________________________________________ 49 

215 

Section of the Entrada sandstone between Brush Creek and Little Brush Creek, 

SlV1,4NlV1,4 sec. 2, T. 3 S., R. 22 E. 

[Measured by D. 1\L Kinney and J. F. Rominger] 

Curtis formation : 

Sandstone, light greenish-gray, glauconitic, fine- to medium-grained, poorly 

sorted, calcareous, with pebbles to lh inch in diameter, partings of reddish shale, and dark greenish-gray shale. 

Entrada sandstone: 

Sandstone, white, fine-grained, crossbedded with rounded and pol- Feet 

lished sand grains. Basal 2 feet poorly sorted__________________ 64 

Sandstone, red, fine- to medium-grained, poorly sorted, ·with rounded 

and polished grains____________________________________________ 4 

Sandstone, white, fine- to medium-grained, with rounded and polished 

sand grains____________________________________________________ 95 

163 

Carmel formation : 

Siltstone, red. 

Distribution and topographic expression.-The Entrada sandstone 

is present on Whiterocks River, in the faulted area between Mosby 

Mountain and Ashley Creek, and eastward from Ashley Creek to 

Diamond Mountain. Also, it is present on the north flank of Split 

Mountain and on the Section Ridge anticline. In the western half 

of the mapped area, both the Carmel formation and the Entrada are 

poorly exposed; it is difficult to draw a boundary between the two 

formations because the boundary frequently lies at the bottom of a 

strike valley. Only the upper part of the Entrada is well exposed 

near the base of the escarpment, which is topped by the oolitic sandy 

limestone that is present at the top of the Curtis formation. East 

of Steinaker Draw, the Entrada commonly forms 25- to 35-foot cliffs 

topped by the basal, thin-bedded, coarse-grained, glauconitic sandstone of the Curtis fol'lnation. 

Fossils and age.-The Entrada sandstone is unfossiliferous in the 

eastern Uinta Mountains and therefore its exact age is unknown. In 
84 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

the San Rafael Swell area, Imlay ( 1948, pl. 4) considers the Entrada 

to be upper Callovian (low Upper Jurassic) and a similar age is 

probable :for the Entrada in the eastern Uinta Mountains. 

Stratigraphic relations and correlation.-The Entrada sandstone 

is apparently gradational with the underlying Carmel :formation in 

the western three-quarters o:f the Uinta River-Brush Creek area. To 

the east, it is separated :from the Carmel by a sharp lithologic boundary, but there is no evidence o:f erosion. The upper boundary o:f the 

Entrada is sharp, especially in those sections where the basal bed o:f 

the unconformably overlying Curtis :formation is a coarse-grained to 

pebbly, glauconitic sandstone. The upper surface o:f the Entrada is 

channeled and irregular east o:f Steinaker Draw. Fragments o:f shale 

and pebbles as much as one hal:£ inch in diameter are incorporated in 

the basal bed. Between Mosby Mountain and a mile west o:f Steinaker Draw, the basal bed o:f the Curtis :formation is shale and there is 

no evidence o:f interruption in sedi1nentation in exposed sections. A 

1narked change in the depositing medium is evident in this area between the Entrada sandstone and the overlying Curtis :formation because the massive Entrada sandstone is succeeded by thin-bedded, in 

part crossbedded, highly glauconitic sandstone o:f the Curtis :formation. 

The Entrada sandstone is believed to be continuous with the type 

area on the east side of the San Rafael Swell and in the Green River 

Desert to the south o:f the Uinta Basin. It has been traced westward 

into the Preuss sandstone (Heaton, 1939, p. 1173; Thomas and 

l{rueger, 1946, p. 1277), which is widely recognized in the western 

lTinta Mountains, the Wasatch Mountain, and in southeastern Idaho 

and southwestern Wyoming. In northwestern Colorado, the underlying Carmel :formation wedges out, and the Entrada has been included with the Navajo sandstone in the Nugget :formation. The 

Entrada is also recognized on the north side o:f the Uinta Mountains, 

where 201 :feet o:f the section was measured at Manila, Utah (Thomas 

n.nd Krueger, 1946, p. 1292). In central Wyoming, equivalents of 

the Entrada are probably present in the "lower Sundance." 

Conditions of deposition.-As mapped, the Entrada sandstone consists o:f two lithologic :facies-a fine-grained, red, silty sandstone and 

a fine- to medium-grained, light-gray "clean" sandstone. On Whiterocks River and in Steinaker Draw, the red and gray :facies are interbedded, but east o:f Steinaker Draw the :formation is almost exclusively massive, fine- to medium-grained light-gray sandstone. Usually, 

the red, silty sandstone is more thinly bedded and resembles the 

typical Entrada of the San Rafael Swell (which is believed to have 

been water laid). The massive light-gray sandstone, on the other 

hand, is well sorted in two general sizes and has a faint trace of 

"tangential" crossbedding (characteristics which are generally 
STRATIGRAPHY 85 

ascribed to eolian deposition). However, the faintness of the crossbedding on weathered surfaces suggests that some other agency, 

probably water, reworked the sand and destroyed some of the "tangential" bedding. 

It is known that the Entrada sandstone grades westward into the 

Preuss sandstone, which is thought to be a great deltaic deposit which 

was shed fron1 a land mass in eastern Nevada and western Utah (Neely, 1937, p. 752). The red facies of the Entrada probably was derived from this source. The average and 1naxi1num grain size of the 

light-gray, massive facies is so 1nuch greater than that found in the 

Preuss sandstone that another source, probably to the east or southeast, is indicated. Erosion of sandstone or quartzite of Mesozoic, 

Paleozoic, or even Proterozoic age in western Colorado probably contributed debris to the massive, light-colored facies of the Entrada. 

An eastern or southeastern source for this part of the Entrada closely 

agrees with the reasoning of Dane (1935, p. 102) that a northern 

source is indicated for the Entrada in the Salt Valley anticlinal area. 

CURTIS FORMATION 

Name.-The Curtis for1nation is na1ned for Curtis Point in the 

northeastern part of the San Rafael Swell ( Gilluly and Reeside, 1928, 

p. 78). It has been traced frmn the type section to a short distance 

east of the Green River, where it grades into lithology which is typical 

of the Summerville formation (Baker, Dane, and Reeside, 1936, p. 8, 

25) . As in the case of other fonnations in the region south of the 

Uinta Basin, the Curtis formation cannot be traced laterally into the 

Uinta River-Brush Creek area and its identification depends upon 

its stratigraphic position, lithology, and included fossils. Prior to 

1936 the Curtis was wrongly identified as the "Twin Creek" formation in the eastern Uinta Mountains. 

Lithology and thiokness.-ln this area, the Curtis formation is 

divisible into two members. The lower member consists of glauconitic 

sandstone of medium to coarse grain size; the upper member is soft, 

greenish-gray shale with thin intercalations of fine-grained, calcareous sandstone and sandy limestone, and hard, oolitic, sandy limestone 

at the top. The lower member is thin bedded and some beds are highly crossbedded. Concentrations of glauconite are so high that the 

sandstone is greenish gray. Glauconite also imparts a greenish-gray 

color to the upper shale member. The intercalated calcareous sandstone and sandy limestone occur as thin beds which weather into rough 

tan slabs. The calcareous oolites in the limestone beds have wellrounded nuclei of zircon, tourmaline, and apatite; these highly resistant minerals could not have been well rounded in a single sedimentary cycle. 

The Curtis formation thickens from 150 feet on Whiterocks River 

and 144 feet at Steinaker Draw to 270 feet at Split Mountain and 
86 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

263 feet between Brush Creek and Little Brush Creek. Although 

the shale and upper sandy limestone 1nember thickens slightly from 

west to east, the principal variation in thickness is in the development of the lower glauconitic. sandstone member whieh is 1.5 feet 

thick on Steinaker Draw, 37 feet thick on Whiterocks River, 91 feet 

thick between Brush Creek and Little Brush Creek, and 110 feet 

thick at Split Mountain. 

The following sections, measured by planetable and alidade, are 

representative: 

Sect·ion Of the Curtis formation on the west side of lVhifterocks Rit1er NW14 

sec. 19, T. 2 N., R. 1 E. 

[Measured by D. M. Kinney, J. F. Rominger, P. Verastegui M., and R. S. Brown] 

Morrison formation: 

Shale and siltstone, light-gray to reddish variegated.' 

Curtis formation: 

Upper member : Feet 

Limestone, oolitic, argillaceous, gray, crossbedded, fossiliferous, 

glaueonitic, with interbedded shale, dark-gray________________ 79 

Shale, dark gray-green_______________________________________ 26 

Limestone, gray, conglomeratic ( ?) , fossiliferous_______________ 1 

Shale, dark-gray_____________________________________________ 7 

Lower member : 

Sandstone, light greenish-gray, fine- to medium-grained, crossbedded, glauconitic_________________________________________ 37 

Entrada sandstone : 150 

Sandstone, moderate reddish-brown, fine-grained. 

Section. ot the Cnrtis fonnation on the 1cest side1 ot Steinaket· Draw SW14 sec. 

26, T. 3 S., R. 21 E., Salt Lake Base and JJf ed.dian 

[Measured by D. M. Kinney, J. F. Rominger, P. Verastegui M., and R. S. Brown] 

Morrison formation : 

Sandstone, light-gray, fine-grained and shale, light-gray, interbedded. 

Curtis formation : 

Upper member: Feet 

Limestone, gray to greenish-gray, oiHitic, slabby, glauconitic; 

shale, light-gray; and sandstone, light-gray, fine-grained, interbedded. Basil 2 feet of oolitic limestone forms ledg·E' at the top 

of the ridge_______________________________________________ 40 

Shale, dark-gray, fissile, with streaks of fossiliferous, oolitic 

limestone___________________________________________________ 49 

Sandstone, light-gray, fine-grained, slightly calcareous, thinbedded____________________________________________________ 30 

Sandstone, light-gray, crossbedded, with pink and gray grains___ 17 

Shale, gray, fissile___________________________________________ 8 

Lower member: 

Sandstone, light-gray, conglomeratic, fossiliferous ( Ostr·ea), 

with pebbles of quartz and shale____________________________ 1.5 

Entrada sandstone : 145.5 

Sandstone, red, fine-grained. 
STRATIGRAPHY 87 

Section ot the Curtis formation south of road between Brush Creek and Little 

Brush Creek, SW:!4 sec. 2, T. 3 S., R. 22 E. 

[Measured by D. M. Kinney and J. F. Rominger] 

Morrison formation: 

Sandstone, fine- to medium-grained, white, friable, with semi-rounded grains 

and fragments of fossil wood. 

Curtis formation : 

Upper member : Feet 

Limestone, oolitic, tan, thin-bedded, with partings of shale, dark 

greenish-gray______________________________________________ 17 

Shale, dark greenish-gray, fissile, with 3 beds 0.5 to 0.7 foot thick 

of sandstone, oolitic, tan, fine-grained, crossbedded___________ 67 

Sandstone, glauconitic, tan, fine-grained, poorly crossbedded, fossiliferous. Bed thins to 1 foot of limestone, tan, oolitic, 

glauconitic in 600 feet west_ ______________________ _:_________ 7 

Shale, dark-gray, fissile______________________________________ 38 

Limestone, tan, very fossiliferous (Belemnites densus) .,-------- 1 

Shale, dark gray-green, fissile________________________________ 42 

Lower member : 

Sandstone, gray, glauconitic, fine- to medium-grained; forms 

bench--------------------------------------~------~------- 50 

Sandstone, gray, glauconitic, fine- to medium-grained, poorly 

sorted, calcareous, with pebbles to 1h inch in diameter, streaks 

of reddish shale, and partings of shale, dark greenish-gray. 

Pebbles of green and red chert, and red and green shale are COlllillOn___________________________________________________ 41 

263 

Entrada sandstone : 

Sandstone, white, :fine-grained,· cross bedded. 

Distribution and topographic expression.-The Curtis formation 

is present on Whiterocks River, in the faulted area between Mosby 

Mountain and Little Mountain, on the north side of Little Mountain, 

in Coal Mine Draw, and eastward frmn Ashley Creek to Diamond· 

Mountain. It is also present on the flanks of Split Mountain anticline 

and Section Ridge anticline, east' of Jensen. 

The Curtis generally forms a strike ridge with the upper, resistant, 

sandy, oolitic lilnestone beds forming a dip slope. The soft, greenishgray shale and thin interbeddedli1nestone of the upper n1ember crop 

out on· the slopes beneath the ridge-fanning beds. At places, the 

lower thin-bedded, well-cemented, glauconitic sandstone member forms 

a ledge which protects the underlying 1nassive sandstone of the Entrada sandstone. 

Fossils and age.-No extensive paleontologic collections were made 

from the Curtis fonnation in the 1napped area. However, collections 

made by J. B. Reeside (1925, p. 43-44) from the "Twin Creek formation of Schultz" in Island Park on the north side of Split Mountain 

and a few miles east of the mapped area, and from the same unit near 

the Carnegie Musemn Dinosaur Quarry on the south flank of Split 
88 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Mountain within the Dinosaur National Monument, are clearly from 

the Curtis formation. The two collections as identified by Mr. Reeside 

include: 

Collection from lower 50 feet of the upper member of the Curtis formaUon (above 

the basal glauconitic sandstone) in Island Park 1 mile west of the Rttple Ranch 

Cidaris f sp. 

bryozoan 

Parallelodonf n. sp. 

Pinna sp. 

Eumicrotis curta (Hall) 

Ostrea strigilecula White 

Cardiniaf n. sp. 

Trigonia quadrangularis Hall and Whitfield 

Camptonectes platessiformis White 

M odiola pertenuis Meek and Hayden 

Pleuromya newtoni Whitfield 

Astarte packardi White 

Tancrediaf inornata Meek and Hayden 

Dosinia jurassica Whitfield 

Quenstedticeras '! hoveyi Reeside 

Cardioceras cf. C. cordiforme (Meek and Hayden) 

Cardioceras sp. 

Belemnites densus Meek and Hayden 

Collection from 1 foot limestone bed 2"1 feet above the top of the lower glauconitic 

sandstone member of the Curtis fo1·mation on south flank of Split Mountain 

anticline at Carnegie Mttseum Dinosattr Qum·ry 

Et~;microtis curta (Hall) 

Ostrea strigilecula White 

Camptonectes platessifo1·mis White 

Astarte packardi White 

Tancredia '! inornata Meek and Hayden 

Tancredia sp. 

Dosinia jurassica Whitfield? 

Cardioceras russelli Reeside 

Cardioceras hyatti Reeside 

Cardioceras cordifm·me Meek and Hayden 

Cardioceras aff. C. wyomingense Reeside 

Cardiocems sp. 

These faunas are characterized by the cardioceratid ammonites 

which were dominant during the Argovian stage of the European time 

scale. The presence of a questionable Quenstedticeras hoveyi Reeside 

suggests upper Divesian in the European scale. The Argovian and 

Divesian stages are middle Upper Jurassic. 

Stratigraphic relations and correlation.-The lower boundary of 

the Curtis formation is irregular and shows evidence of erosion prior 

to the deposition of the lower, pebbly, glauconitic sandstone member. 

Fragments of shale, and pebbles of greenish and reddish chert in the 

basal beds, suggest erosion of earlier sediments in an adjacent area. 

Because the underlying Entrada sandstone is massive, no measurement 
STRATIGRAPHY 89 

can be made of the an1ount of erosion prior to the deposition of the 

lower sandstone unit of the Curtis formation. However, it seems 

probable that at least some of the Entrada sandstone was reworked 

and incorporated in the Curtis because the upper boundary of the 

Entrada sandstone is sharply defined. The tan-weathering, oolitic, 

and glauconitic sandy limestone beds at the top of the Curtis formation are abruptly succeeded by light-gray sandstone that is the base 

of the Morrison formation. There is no clear evidence of a hiatus, 

however, and the difference in lithology may reflect merely the change 

from marine to fluvial deposition. 

The beds here referred to the Curtis formation are believed to be 

equivalent in age to the Curtis and to at least a part of the Summerville formation of the San Rafael Swell. This correlation is substantiated, in part, by the paleontological determinations of Imlay 

(1945, p. 1021), who shows the Summerville to be equivalent to the 

zone of Oardioceras, and to the determinations of Reeside, who has 

identified numerous species of 0 ardioceras from the Curtis in the eastern Uinta Mountains. The Curtis, as represented in this area, is equivalent to the Stump sandstone of southeastern Idaho and southwestern 

Wyoming, and to at least a part of the "upper Sundance" of central 

and eastern Wyon1ing. It has been traced eastward in well logs and 

surface sections to the vicinity of Meeker, Craig, and Dotsero in 

northwestern Colorado (Thomas, McCann, and Raman, 1945; Baker, 

Dane, and Reeside, 1936, p. 28), where it is still characterized by glauconite. 

0 onditions of deposition.-The Curtis formation is unquestionably 

of marine origin because of its invertebrate fauna and abundant glauconite (Takahashi, 1939, p. 503-512). The lower, 1nedium- to coarsegrained glauconitic sandstone member is poorly sorted, and shows evidence of current action in the crossbedding. It probably was formed 

in shallow water under near-shore conditions. It carries the same 

minor mineral constituents as the Shinarump conglomerate, Navajo 

sandstone, and Entrada sandstone, which are believed to have come 

from the east and southeast. The upper member of the Curtis was 

formed in deeper water and it was seldom that the currents were 

strong enough to bring sand grains and oolites into the area, or to develop oolites in sit~(;. The upper calcareous sandstone beds of the formation have abundant calcareous oolites which suggest shallow nearshore water. Grains of the resistant minerals tourmaline, zircon, and 

rutile, which n1ake up the nuclei of the oolites, n1ust have been derived 

from earlier sandstone formations, because it would take more than a 

single cycle of erosion to reach such well-rounded shapes. The upper 

part of the Curtis was probably transitional to the fluvial deposits of 

the overlying Morrison formation. 
90 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

UPPER JURASSIC SERIES 

MORRISON FORMATION 

Name.-The Morrison formation was named for exposures near the 

town of Morrison (Cross, 1894, p. 2), in the foothills of the Front 

Range southwest of Denver, Colo. It has been recognized over an 

area of 350,000 square miles (Stokes, 1944, p. 953) in the western interior where it has been applied to rocks of somewhat heterogeneous 

lithology but similar stratigraphic position. At present, the J\iorrison formation includes all continental Jurassic sediments younger 

than the San Rafael group in the Rocky Mountain region (Baker, 

Dane, and Reeside, 1936, p. 31). The nan1e was first used in the eastern Uinta Mountains by Sears (1924, p. 279-280, 285) while working 

in northwestern Colorado. 

Distribution.-The Morrison formation is present in the faulted 

area between Mosby Mountain and Little Mountain, in a fault segment 

in Coal Mine Draw on the east side of Little Mountain, and continuously fron1 east of Ashley Creek to Diamond Mountain. It is also 

present in the area shown on plate 1, north and west of Split J\iountain anticline and on the westward plunging Section Ridge anticline. 

The best exposures are west of the JVIosby J\iountain road, at the head 

of Steinaker Draw (fig. 10), between Brush Creek and Little Brush 

Creek, on the west side of Diamond Mountain, and on the Split Mountain and Section Ridge anticlines. 

FIGURE 10.-Morrison formation (Jrn), Dakota sandstone (Kd), and Mowry shale (Kmy) 

13.nd F.rontier sandstone (Kf) members of the Mancos shale along the east of Steinaker 

Draw (Kfb), base of massive sandstone. 
STHATIGRAPHY 91 

Lithology and topographic expPession.-In the area under study, 

the Morrison for1nation consists of light-gray, very fine-grained sandstone, variegated n1udstone and shale, fine- to meclimn-grained sandstone, and occasional thin lenticular beds of coarse pebbly to conglmneratic sandstone. The n1uclstone and shale beds include calcareous, 

brown-weathering concretionary zones. The formation is heterogeneous, with no single unit being present in all measured sections. It 

ranges in thickness frmn 825 to 925 feet, and averages about 850 feet. 

In the Steinaker Draw and Little Brush Creek sections, the lower part 

is 1nore sandy and the upper part includes 1nore variegated mudstone 

and shale, but this division cannot be recognized in the Split Mountain 

and Mosby Creek sections. The sandstones in the JYiorrison are generally very light gray to greenish-gray, even in beds long subjected 

to weathering. The conglomeratic beds commonly weather to shades 

of dark tan, and consist of pebbles of "\veil-rounded, dark-red and 

black chert in a matrix of tan quartz sand. 

The Morrison formation is a soft, easily eroded formation that generally forms part of the strike valleys lying between the dip slope 

fonned by the underlying Curtis fonnation and the escarp1nent 

fonnecl by the Frontier sandstone member of the Mancos shale. 

Throughout most of the area, only the upper 200 to 300 feet of the 

Morrison are well exposed on the slope beneath the resistant Frontier 

sandstone member, and only under exceptional conditions is the entire 

formation visible. 

The follo·wing sections indicate the lithology and the variability of 

the formation in the eastern Uinta l\1ountains : 

Section of thP Morrison formation on tlle 1cest side of the Mosby Mountain road, 

sec. 18, T. 3 S., R. 19 E. 

[Measured by P. Vemstegui l\I., R. S. Brown. and D. l\L Kinney] 

Dakota sandstone : 

Sandstone, light-gray, buff-weathering, medium- to coarse-grained, in part 

conglomeratic, crossbedded, massive, with pebbles of black chert common. 

Morrison formation : Feet 

Shale and mudstone, red and gray, variegated____________________ 601 

Sandstone, conglomeratic, light-brown, cross-laminated, with subangular to rounded vebbles as large as % inch in diameter_________ 5 

Sandstone, light-gray, fine- to medium-grained crossbedded__________ 16 

Shale and mudstone, light-gray to red variegated____________________ 270 

892 

Curtis formation : 

Limestone, oolitic, argillaceous, gray, tan-weathering crossbeddecl, fossiliferous, glauconitic, interbedded with dark-gray shale. 

295163-55--1 
92 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Secticm of the Morrison formation in Steinaker Draw, SW:JA, sec. 26, T. 3 S., 

R. 21 E. Detailed lithology of lower pm·t of Mort'ison formaUon from SW1A, 

sec. 7, T. 3 S., R. 22 E. 

[Measured by D. M. Kinney, J. F. Rominger, R. S. Brown, and P. Verastegui M.] 

Dakota sandstone : 

Shale, gray, interbedded with light-gray sandstone. 

Morrison formation: Feet 

Mudstone, light-gray, plastic______________________________________ 61 

Shale, variegated in pastel shades_______________________________ 39 

Sandstone, light-gray, fine-grained, with slightly calcareous concretions__________________________________________________________ 10 

Shale, light-gray, with calcareous concretions_____________________ 67 

Sandstone, light-gray to white, lenticular, medium-grained, friable___ 10 

Shale, variegated_________________________________________________ 15 

Sandstone, gray to light-gray------------------------------------- 1 

Mudstone, variegated_____________________________________________ 30 

Sandstone, light-gray, conglomeratic, lenticular-------------------- 12 

Mudstone, light-gray, sandy--------------------------------------- 15 · 

Sandstone, light-gray, very fine grained____________________________ 63 

Sandstone, brown, calcareous_____________________________________ 1 

Mudstone, variegated_____________________________________________ 65 

Sandstone, gray, fine-grained_____________________________________ 86 

Mudstone and shale, gray--------------------------------------- 45 

Sandstone, fine-grained, red--------------------------------------- 44 

Sandstone, pebbly, crossbedded------------------------------------ 3 

Sandstone, red, fine-grained______________________________________ 74 

Sandstone, pebblY------------------------------------------------ 2 

Shale, gray______________________________________________________ 7 

Mudstone, gray, with thin beds of light-gray limestone____________ 181 

Curtis formation: 831 

Limestone, gray to greenish-gray, oolitic, slabby, glauconitic, interbedded with dark-gray shale and light-gray, fine-grained sandstone. 

Section of the Morrison formation between Brush Greek and Little Brush Greek, 

SE:JA, sec. 2, T. 3 S., R. 22 E., Salt Lake Base anf1.l'rferidian 

[Measured by D. M. Kinney and J. F. Rominger] 

Dakota sandstone : 

Sandstone, light-gray, coarse-grained, with angular grains and fragments of fossil wood. 

Morrison formation: Feet 

Sandstone, white to gray, fine-grained, with angular grains_________ 138 

Sandstone, white, fine- to medium-grained, calcareous with angular 

grains_________________________________________________________ 1 

Sandstone, white to gray, fine-grained with angular grains________ 2:3 

Sandstone, white, fine-grained, with angular grains________________ 2 

Sandstone, red and gray, fine-grained, soft, and red and purple shale, 

with brown calcareous concretions______________________________ 15G 

Sandstone, white, fine- to medium-grained, calcareous______________ 3 

Sandstone, red and gray, fine-grained, and red and purple shale with 

brown calcareous concretions as large as 2 feet in diameter________ 74 

Shale, gray, plastic, with brown calcite c~ncretions in basal10 feet___ 73 
STRATIGRAPHY 93 

Section of the Morrison formation 7Jetween Brush Creek and Little Brush Creek 

SE¥4 sec. 2, T. 3 S., R. '22 E., Salt Lake Base and Meridian-Continued 

Morrison formation-Continued Feet 

Sandstone, white, fine-grained, with angular grains______________ 3 

Claystone, gray, plastic, with gypsum and thin beds of brown calcite__ 66 

Shale, light-red, with red calcareous concretions__________________ 12 

Sandstone, white, fine- to medium-grained________________________ 39 

Sandstone, brown, coarse-grained, crossbedded, with pebbles of black 

and red chert as large as 1h inch in diameter__________________ 1 

Shale, grey plastic, weathers with a hard crust, gypsiferous (?) ______ 20 

Shale, red and greenish-gray, with calcareous concretions in zone 5 

feet frOIU tOP---------------~---------------------------------- 32 

Sandstone, white, fine-grained, massive, friable_____________________ 26 

Sandstone, pebbly, coarse-grained, calcareous, with· semi-rounded to 

angular grains_________________________________________________ 2 

Sandstone, white, fine-grained, massive, friable____________________ 8 

Sandstone, tan, coarse-grained, with pebbles of black, yellow and 

red chert______________________________________________________ 1 

Sandstone, white, fine- to medium-grained, massive, friable________ 37 

Sandstone, tan, coarse-grained, with pebbles of red and black chert. 

Bed swells to 10 feet in a distance of 100 feet to the west__________ 2 

Sandstone, greenish-gray, fine- to medium-grained---------------.- 38 

Sandstone, white, fine- to medium-grained, with few beds of white, 

coarse-grained sandstone, with rounded grains__________________ 87 

Shale, red------------------------------------------------------- 5 

Sandstone, white, fine- to medium-grained, friable, with semi-rounded 

grains, and fragments of fossil wood____________________________ 7i 

Curtis formation: 926 

Limestone, oolitic, tan, thin-bedded, with partings of dark greenishgray shale. 

Fossils and age.-A very complete and well-preserved dinosaurian 

vertebrate fauna has been recovered in a sandstone and conglomerate 

lens in the upper part of the Morrison for1nation on the south flank 

of Split Mountain within the Dinosaur National Monument. The 

conglomerate lens that carries the dinosaurian remains also includes 

a thick-shelled, fresh-water bivalve which was identified by Dr. John 

B. Reeside, Jr., as Unio aff. U. felohi White, and fragments of fossil 

wood. Elsewhere in the area, only small fragments of bone and 

pieces of fossil wood have been recognized. 

The age of the Morrison formation has been the source of much 

speculation and considerable difference of opinion, because no comparable fauna is represented in the European section of the Jurassic. 

However, an evaluation of all the vertebrate eviden~ (Simpson, 

1926, p. 215) points to a late Jurassic age, probably Kimmeridgian 

or Portlandian. Stokes (1944, p. 988) has e1nphasized the possibility 

that at least some of the rocks included in the upper part of the Morrison formation in the Colorado Plateau region 1nay be Early Cre-
94 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

taceous in age. In the absence of definite faunal evidence~ however, 

it seems best to consider all of the Morrison formation in the eastern 

Uinta Mountains to be of Late Jurassic age. 

Stratigraphic relations and correlation.-The basal boundary of 

the Morrison for1nation is sharp. No erosion of the underlying Curtis 

formation is evident before the deposition of the basal sedin1ents of 

the Morrison, although the possibility exists that poorly consolidated 

and easily eroded Curtis strata may have been stripped to the resistant 

oolitic limestone bed everywhere over the area before the deposition 

of the first continental sediments. Inasmuch as the upper beds of 

the Curtis probably were deposited in very shallow 1narine waters, 

it is believed that the Morrison formation is confonnable upon the 

Curtis formation with fluvial deposition resting on the last sediments 

deposited in the retreating Sundance sea. 

The Morrison formation is believed to be overlain unconfonnably 

by the Dakota sandstone, although the precise contact generally is 

covered by blocks of massive Dakota sandstone slumped far below 

their normal stratigraphic position. The unconformity n1ay represent most of Early Cretaceous time in the places where the overlying 

Dakota is a single sandstone bed, but where the Dakota is tripartite, 

the shale and lower sandstone may be Early Cretaceous in age and 

the unconformity may be of lesser i1nportance. 

The dinosaurian fauna within the Dinosaur National Monun1ent 

indicates a fairly close correlation of the Morrison formation in the 

eastern Uinta Mountains with the type Morrison along the Front 

Range of the Rocky Mountains, with the Morrison formation at Como 

Bluff, 1Vyo., and in the San Rafael Swell region (Stokes, 1944, p. 965). 

The Morrison formation has been recognized (Baker, 1947) in the 

Wasatch Mountains, and its equivalents are recognized in the upper 

part of the Beckwith formation of southwestern Wyoming, and in the 

Ephrai1n conglomerate and perhaps other formations of the thick 

Gannett group of southeastern Idaho. East and south of the Uinta 

Mountains, the Morrison formation has been recognized by its characteristic heterogeneous and variegated lithology and by its stratigraphic position. 

Conditions of deposUion.-The Morrison formation has long been 

considered to be of fluvial origin and to have been deposited on an 

ancient flood plain. The conglmnerate lenses represent old riverchannel deposits, and the finer grained sandstones and 1nndstones 

represent the sediments deposited by the aggrading streams in areas 

of lower current velocity or in te1nporary lakes. The measured sections show no consistent increase in thickness or in coarseness of 

sands, nor in percentage of coarse- to fine-grained sediments, which 

would suggest a source area. Stokes (1944, p. 975) has suggested 

that the Morrison formation was deposited on a plain tha,t sloped 
STRATIGRAPHY 95 

gently toward the northeast, and the change to a sandstone facies 

in Arizona, reported by Baker, Dane, and Reesicle ( 1936, fig. 14, p. 51), 

suggest that such an interpretntion is logical. The inability to see the 

conglomerate lenses in the ~Iorrison in north-south section, because of 

the east-1vest strike in the eastern -Uinta Mountains and the high dips, 

makes the interpretation of the cross-laminations in conglomerate 

lenses very difficult. However, in the Dinosaur l\1onument area the 

strean1s must have been flowing eastward, because Gilmore ( 1932, p. 3) 

has shown that parts of some of the dinosaur skeletons were shifted in 

that direction before burial. It is possible, of course, that the stream 

was meandering, and that its general course was to the northeast or 

southeast. 

CRETACEOUS SYSTEM 

LOWER(?) AND Ul'"PER CRETACEOUS SE.RIES 

DAKOTA SANDSTONE 

Definition.-Over the northern Great Plains and westward into the 

Rocky Mountain region, the Cretaceous systen1 commonly begins with 

a nonmarine basal sandstone. It was named the "Dakota sandstone" 

(Meek and Hayden, 1862, p. 419-420) in northeastern Nebraska, where 

fossil plants in the upper sandstone beds indicate early Late Cretaceous age. In the type locality, lower beds of sandstone are probably 

of Early Cretaceous age (Reeside, J. B., Jr., personal communication, 

,January 1948). In the Colorado Plateau region, the initial Cretac-eous sandstone is referred to the Dakota sandstone, although it cannot be traced laterally frmn the type area and its age is generally 

unknown. It may be Late Cretaceous, or both Late and Early 

Cretaceous. 

Lithology and thickness.-In the area under study, the Dakota 

sandstone may consist of a single light-gray to tan, medium- to coarsegrained sandstone, a sandstone underlain by brownish-gray shale and 

interbedded thin sandstone, or a sandstone underlain by brown to 

greenish-gray shale and a thin, fine-grained, light-gray, basal sandstone. The main sandstone, characteristically, is cross bedded, friable, 

and noncalcareous. It is composed of angular sand grains and wellrounded chert pebbles. The pebbles consist of dark-gray to black, 

and reddish-brown chert, and are more abundant near the base of the 

unit. The brownish-gray shale is interbedded with yellow, platy 

sandstone or greenish sandstone. It contains thin lignitic layers near 

Steinaker Draw. The lmver sandstone is light gray to tan, very fine 

grained and platy. Where the lower sandstone is not present and 

the brownish-gray shale rests on the Morrison formation, the color 

change frmn light gray to dark brownish-gray marks the boundary. 

The Dakota sandstone ranges in thiekness from 50 feet to 1351 feet 

in the measured sections, and probably reaches a thickness of 200 feet 

at certain localities in the mapped area. There seems to be no sys-
96 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

tematic change in thickness and lithology across the area. Individual 

beds pinch and swell along the strike and may lens out entirely in a 

few hundred feet. The variation in thickness and lithologic character 

is well displayed along the north- and west-facing escarpment that 

is topped by the Frontier sandstone member of the Mancos shale, 

which forms the south and east sides of Steinaker Draw. 

The variation in thickness and lithology of the Dakota sandstone 

is given in the following representative sections: 

Section of the Dakota sandstone so,uthwest of Mosby Creek SlV14 sec. 13, '1'. 

3 S., R. 18 W. (unsurveyed) 

[Measured by P. Verastegui M., R. S. Brown, and D. M. Kinney] 

Mowry shale member of the Mancos shale : 

Shale, dark-gray, weathering silver-gray, fissile. 

Dakota sandstone : Feet 

Sandstone, tan, medium-grained, crossbedded______________________ 61 

Sandstone, light-gray, weathering tan to buff, medium- to coarsegrained, partly conglomeratic, crossbedded, massive with pebbles 

of black chert------------------------------------------------- 34 

Morrison formation: 95 

Shale, red variegated with gray. 

Section of the Dakota sandstone in Steinaker Dmw east of Uta,h State Highway 

44, SE1,4 sec. 25, T. 3 S., R. 21 E. 

[Measured by D. M. Kinney, J. F. Rominger, R. S. Brown, and P. Verastegui M.] 

Mowry shale member of the Mancos shale: 

Shale, dark-gray. 

Dakota sandstone : Feet 

Sandstone, light-tan, medium- to coarse-grained, with angular grains__ 33 

Shale, gray and interbedded light-gray, thin-bedded, fine- to mediumgrained sandstone______________________________________________ 102 

Morrison formation : 135 

Claystone, light-gray, plastic when wet. 

Section of the Dakota sandstone on west side of Little Brush Creek SW1,4 sec. 

1, T. 3 S., R. 22 W. 

[Measured by D. M. Kinney and J. F. Rominger] 

Mowry shale member of the Mancos shale : 

Shale, dark-gray, weathering light-gray, platy, with fish scales and a 

few thin beds of tan, fine- to medium-grained calcareous sandstone. 

Dakota sandstone : Feet 

Sandstone, light-gray, coarse-grained, with angular grains, and fragments of fossil wood___________________________________________ 50 

Morrison formation: 

Sandstone, white to gray, fine-grained, with angular grains. 

Distribution and topographic ewpression.-The Dakota sandstone 

is present from south of Mosby Mountain eastward to Little Moun-
STRATIGRAPHY 97 

tain, in Coal Mine Draw, east of Little Mountain, and continuously 

from Ashley Creek and Steinaker Draw (fig.10) eastward to Diamond 

Mountain. It is also present on the flanks of Split Mountain anticline 

and on Section Ridge anticline. 

Throughout the Colorado Plateau region, the Dakota sandstone 

commonly forms hogbacks and prominent outcrops. In the eastern 

Uinta Mountains, however, it is not well cemented, and only the more 

massive, coarse-grained sandstone is well exposed. The upper sandstone generally makes the better outcrop. 

Fossils and age.-No fossils have been found in the Dakota sandstone in the area studied, but a collection of marine fossils found west 

of Delta., Colo., 130 miles southeast of this are&, contains an Acanthoceras fauna of Cenomanian or early Late Cretaceous age (Reeside, 1927, p. 453-454). Characteristic leaves of the Dakota were 

collected by Richardson (1909, p. 14) near Elgin and Woodside, 

Utah, approximately 110 miles to the southeast of Vernal. In the 

eastern Uinta Mountains, the Dakota sandstone is believed to be nonmarine. The basal sandstone and overlying brownish shale may be 

of Early Cretaceous age, but the upper sandstone appears to be the 

initial sedimentation of the Upper Cretaceous series in the area. 

Stratigraphic relations and correlations.-The Dakota sandstone 

is believed to rest disconformably upon the Morrison formation. The 

absence of the lower sandstone and brownish-gray shale at some l«;>calities suggests erosion prior to the deposition of the upper sandstone. 

The upper boundary of the Dakota is sharp, with no transitional 

beds into the Mowry shale member of the Mancos shale. 

The Dakota sandstone probably correlates with the rocks grouped 

under the same name in north western Colorado (Thomas, McCann, 

and Raman, 1945) and in the Book Cliffs area (Baker, 1946, p. 90-91; 

Dane, 1935, p. 113-117; McKnight, 1940, p. 109-113; Erdmann, 1934, 

p. 27-28; Fisher, 1936, p. 10-11) south of the Uinta Basin. Equivalents of it are probably present in the upper part of the Beckwith 

formation ( Reeside, 1925, p. 38) on the north flank of the Uinta 

Mountains. The Dakota is believed to be of continental (probably 

fluvial) origin because of the lenticularity of the beds, the crossbedding, and the associated carbonaceous matter. 

UPPER CRETACEOUS SERIES 

MANCOS SHALE 

Name and definition.-The Mancos shale was named by Cross ( 1899, 

p. 4) for exposures in the Mancos Valley, in southwestern Colorado. 

The term was first used (Fenneman and Gale, 1906, p. 22) in the 

Yampa coalfield, northwestern Colorado, for the dark, marine shale 

of Late Cretaceous age that lithologically resembles the type Mancos 

shale and occupies the same stratigraphic position above the Dakota 
98 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

sandstone and beneath the sandstones of the Mesaverde formation. 

It was later used by Gale ( 1910, p. 61) for beds of similar lithology 

in northeastern Utah. The dark 1narine shale had previously been 

called the Sulphur Creek group by Powell (1876, p. 50), but that 

term has been shown to be unacceptable as a stratigraphic name 

(Veatch, 1907, p. 70) in southwestern Wyoming. Gale (1910, p. 61) 

recognized a threefold division of the Mancos shale in the Ashley 

Creek-Brush Creek area, a lower, dark-gray, fissile shale (which characteristically weathers very light-gray), a sandy shale and fine- to 

medium-grained sandstone, and an upper clay shale almost 5,000 feet 

thick. 

The Upper Cretaceous rocks, equivalent in age to the Mancos shale, 

are much thicker in southwestern Wyoming where Knight (1902, p. 

721-722) named the sandy shale and sandstone unit the "Frontier 

forn1ation" and the upper shale the "Hilliard formation," and Veatch 

(1902, p. 64) named the lower shale the "Aspen formation." Schultz 

(1920, p. 71-75) used this terminology in the Rock Springs uplift in 

south-central Wyoming and shows in cross section (Schultz, 1920, 

p. 37) the Aspen shale, the Frontier sandstone, and the Hilliard shale 

in the Uinta Mountain uplift to the south of Rock Springs. Subsequently, Reeside (1925, p. 44) used the terminology of southwestern 

Wymning for the Upper Cretaceous rocks along the Green River and 

south of Split Mountain. 

In this report, Mancos shale is retained for the entire thickness of 

the strata that was named by Gale (1910) in his report on the coalfields of northwestern Colorado and northeastern Utah. On the suggestion of vV. W. Rubey, the ter1n ''~iowry" is used in preference to 

"Aspen" for the lower, dark-gray, fissile shale me1nber of the Man.cos, 

because the lithology and thickness of the unit in the Mosby CreekBrush Creek area n1ore closely resmnbles the type Mowry shale of 

the Bi:£horn Mountains than the thick, highly clastic Aspen shale 

of southwestern Wyoming. For the sandy shale and the fine- to 

medium-grained sandstone that overlies the Mowry member, the name 

"Frontier" is retained as a member of the Mancos shale, although it 

is recognized that the unit n1ay not be strictly equivalent to the typical 

Frontier formation of southwestern Wymning. The thick, upper, 

gray shale unit is termed the "upper member of the Mancos shale" in 

preferei1ce to continuing the use of Hilliard shale in the eastern Uinta 

.l\1onntains. 

MOWRY SH~-\LE MEMBER 

Name and definition.-The Mowry shale, named for exposures on 

the east side of the Bighorn Mountains (Darton, 1904, p. 399-400), 

is recognized over central and eastern Wyoming, western South 

Dakota, and Montana. It is commonly a light-gray weathering, 

siliceous shale with abundant fish scales and interbedded thin sand 
STRATIGRAPHY 99 

stones. Gale ( 1910, p. 61) recognized the probable equivalence of the 

light-gray weathering, siliceous shale unit in northeastern Utah to the 

Mowry, but he did not subdivide the thick Mancos shale into members. 

Lithology and thickness.-The Mowry shale member of the Mancos 

shale is a dark-gray, hard, and fissile shale (fig. 11), weathering into 

hard silvery gray flakes. These chips are so resistant that the formation can be traced on soil-covered slopes by pieces of shale in the 

weathered mantle. The ~1owry is characterized by abundant scales of 

teleost fish; these scales are commonly used for identification purposes 

in the field. In exposures along Steinaker Draw, the lower part of the 

~1owry is less platy and resembles the strata known in vVyoming as 

the Thermopolis shale. 

FIGURE 11.- Unweathered Mowry shale member of the Mancos 

shale on lower Brush Creek. 

The Mowry shale thins from 123 feet in the Deep Creek area to 31 

and 32 feet, respectively, on Little Brush Creek and in the section that 

was n1easured south of U.S. Highway 40. This thinning is not uniform in an easterly direction, because Thomas, McCann, and Raman 

(1945) report 95 feet of Mowry shale on the south flank of Split 

Mountain, mid way between the thinner sections. 

Detailed lithology and thickness of representative sections of the 

Mowry shale member are as follows : 
100 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Section of the Mowry shale member of the Mancos shale northwest of the 

coal mines, SW1,4 sec. 13, T. 3 S., R. 18 E. ( unsectionized) 

[Measured by D. M. Kinney, J. F. Rominger, P. Verastegui M., and R. S. Brown] 

Mancos shale : 

Frontier sandstone member: 

Shale, light-gray, sandy, drab-weathering. 

Mowry shale member : Feet 

Shale, dark-gray, silver-gray weathering, fissile, with fish scales 

common ------------------------------------------------·-- 123 

Dakota sandstone : 

Sandstone, tan, medium-grained, crossbedded. 

Section of the Mowry shale member of the Mancos shale in Steinaker Draw, 

SE1,4 sec. 26, T. 3 S., R. 21 E. 

[Measured by D. M. Kinney, J. F. Rominger, R. S. Brown, and P. Verastegui M.] 

Mancos shale : 

Frontier sandstone member : 

Shale, light-gray, sandy, tan-weathering. 

Mowry shale member : Feet 

Shale, dark-gray, silver-gray weathering, siliceous, fissile, with 

abundant fish scales_______________________________________ 58 

Shale, dark-gray_____________________________________________ 32 

Dakota sandstone : 90 

Sandstone, light-tan, medium- to coarse-grained, with angular grains. 

Section of Mowry shale member of the Mancos shale on west side of Little Brush 

Creek, SE1,4 s-ec. 1, T. 3 S., R. ~~E. 

[Meas.ured by F. T. McCann and~. D. Raman] 

Mancos shale : 

Frontier sandstone member : 

Shale, gray, sandy, tan-weathering. 

Mowry shale member : Feet 

Shale, dark-gray, silver-gray weathering, fissile, siliceous, with 

fish scales common________________________________________ 31 

Dakota sandstone : 

Sandstone, light-gray, coarse-grained, with angular grains and fragments of fossil wood. 

Section of the Mowry shale member of the Mancos shale in Orchard Draw, 

Dinosaur National Monument, SW1,4 sec. ~"1, T. 4 S., R. 23 E. 

[Measured by F. T. McCann and N. D. Ramon] 

Mancos shale : 

Frontier sandstone member : 

Shale, dark-gray to black, blocky, fissile, interbedded with numerous thin ( 1h inch to 6 inch) sandstones. 

Mowry shale member : Feet 

Shale, black, siliceous, resistant, usually fissile, light-gray weathing; forms ridge-----------------·------------------------- 59 

Shale, dark-gray to dark-brown, clayey; forms slight valley____ 36 

95 
STRATIGRAPHY 101 

Section of the Mowry shale member of the Ma-ncos shale in Orchara Draw, 

DinosarUr 1Vationa.l JJ1o1~ument, SW:I4 sec. 27, 'P. 4 S., R. 23 E.-Continued 

Dakota sandstone : 

Sandstone, gray, friable, noncalcareous, massive, with minor black 

fissile shale at top of bed. Usually fine- to medium-grained but may 

be coarse-grained and conglomeratic. Minor black and gray chert. 

Limonite concentrated largely along bedding, cross-laminations, 

and joints. Intricate network of fine quartzitic veins, which stand 

out on weathered surface as tiny ridges. 

Section of the Mowry shale member of the Mancos shale sorUth of U.S. Highway 

.qo ana north of Spring Greek, NW:I4 sec. 7,, T. 6 S., R. 24: W. 

[Measured by D. l\L Kinney and J. F. Rominger] 

Mancos shale : 

Frontier sandstone member : 

Shale, gray, clayey, with thin interbeds of tan, fine-grained calcareous sandstone. Sandstone prominent in upper 10 feet. 

Mowry shale member : Feet 

Shale, dark-gray, weathering light-gray, platy, with a few thin 

(0.1 to 0.3 inch) beds of tan, fine- to medium-grained, calcareous 

sandstone with fish scales__________________________________ 32 

Dakota sandstone : 

Sandstone, tan, medium- to coarse-grained, with well-rounded quartz 

grains and a few grains of gray chert. 

Distribution.-The Mowry shale member is present in the coal-mine 

area of Deep Creek and eastward to Little Mountain, and it appears 

again in Coal Mine Draw on the east side of Little, Mountain. It is 

present continuously frmn Ashley Creek eastward to Diamond Mountain, and is exposed on the north and west flanks of Split Mountain 

anticline and on Section Ridge anticline. The Mowry shale member 

forms low rounded hills in some places, and at other points it appears 

only as a thin, light-gray line on the escarpment held up by the Frontier sandstone n1ember of the Mancos shale. 

Fossils, age, and stratigraphic relatidns.-The most common fossils 

reported from the Mowry shale mmnber of the Mancos shale are teleost 

fish scales and fragments of fish bone. Reeside (1930, p. 35-41) reports marine invertebrates from Vermilion Creek, Colo., just east 

of the present area. The fish rmnains have little stratigraphic significance, but are useful as a lithologic character for correlation. The 

invertebrates indicate a lower Upper Cretaceous horizon. Reeside 

(1944, map 3) considers the Mowry to be equivalent to a part of the 

Graneros shale of the type Upper Cretaceous section east of the Rocky 

Mountains. 

The lower boundary of the Mowry shale member of the Mancos 

shale marks an abrupt change from the underlying Dakota sandstone 

and suggests a disconformity. The variation in thickness of the 

Mowry, and especially the absence of the nonsiliceous, dark-gray shale 

at the base of the 1nember in smne sections, suggest a hiatus at the base 
102 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

of the siliceous shale. The upper boundary of the Mowry appears 

as a sharp line in the well-exposed sections in Steinaker Draw. It is 

1nore noticeable in weathered outcrop because the overlying shale of 

the Frontier sandstone member is sandy and weathers tan. The 

Mowry is believed to be conformable with the overlying Frontier. 

0 orrelation.-In the area between Mosby Creek and the eastern 

boundary of the rna pped area, the Mowry shale member of the Mancos 

shale is believed to correlate, in part, with the type section of the 

Aspen shale of southwestern Wymning (Rubey, 1929, p. 153), on the 

basis of lithologic similarity and stratigraphic position. The n1ember 

thins from the Duchesne River area (Huddle and McCann, 1947) eastward along the south flank of the Uinta Mountains, and it is thicker in 

the vicinity of Manila, Utah (Reeside, 1925, p. 38), on the north flank 

of the Uintas that it is in the Mosby Creek-Brush Creek area. The 

Mowry has been reported in northern Colorado 150 miles to the east 

and has been identified from well cuttings (Thomas, McCann, and 

Raman, 1945) more than 50 miles to the southeast on Douglas Creek 

in Rio Blanco County, northwestern Colorado. Equivalents of the 

Graneros shale that are not lithologically similar to the Mowry are 

present in the lower part of the Mancos shale south of the Book Cliffs 

in central Utah (Reeside, 1944, n1ap 3). 

Conditions of depositio,n.-The fact that the Mowry is of marine 

origin is substantiated by fossilized remains of marine forms of both 

the common fish and invertebrates. Rubey ( 1929, p. 153-170) has 

shown that the Mowry shale in the Black Hills was formed by extremely slow sedimentation and that the bulk of the material was 

originally volcanic ash. The isopachous map by Reeside (1944, map 

3) shows the center of deposition of the Mowry and Aspen equivalents 

to be in southwestern 'Vyoming, thus indicating that the source of 

the ash (the principal constituent of the unit) is to the west of .that 

area. The presence of thin bands of glassy, quartzitic sandstone in 

the Mowry shale mmnber of the Mancos in the Mosby Creek-Brush 

Creek area suggests that some clastic material was transported far 

eastward, or that it was derived locaily. The absence of the typical 

lithology of the Mowry south of the Book Cliffs and the thinness of 

the 1nember on the south flank of the Uinta Mountains suggest that 

the area is near the depositional boundary of the siliceous shale that 

is regarded as characteristic of the Mowry. 

FRONTIER SANDSTONE MEMBER 

Definition.-For many years, the sandstone, shale, and coal-bearing 

unit in the eastern Uinta ~1ountains, which occupies the stratigraphic 

position of the Frontier formation in southwestern Wyoming, has 

been known by the name "Frontier sandstone," although it is much 
STRATIGRAPHY 103 

thinner and may not be continuous with the strata at the type locality. 

In this report, it is considered as a member of the Mancos shale. 

Lithology and thickness.-The Frontier sandstone 1nember of the 

Mancos shale (fig. 10) consists of two units, an upper 1nassive sandstone and a lower sandy siltstone which, at places, includes thin beds 

of fine-grained sandstone. The upper unit, which is topographically 

prominent and forms ridges and long dip slopes, is cmnposed of massive to thick-bedded, in part crossbedded, medimn-grained, gray to 

tan sandstone with angular sand grains, thin beds of tan-weathering, 

sandy shale and bituminous coal or lignitic shale beds. Near the base, 

the sandstone is well cemented with lime and, at places, carries molds 

of Ostrea and other marine fossils. The lower unit is comprised of 

dark-gray, sandy siltstone, which weathers to shades of tan. 

The upper part of the Frontier sandstone n1ember appears to thin 

eastward and southeastward from 160 feet at Steinaker Draw to 33 

feet south of U. S. Highway 40; however, the underlying shale thiekens over the same area. In the Deep Creek area, near the coal1nines, 

the sandstone unit is only 9-± feet thick, as compared to a thickness 

of 177 feet for the underlying shale, thus indicating that the increase 

in thickness of the upper unit is not unifonn toward the west. Within the area mapped, the Frontier thins from a thickness of 273 feet 

near the coal mines west of Little Mountain to 209 feet on Little Brush 

Creek. 

The detailed lithology of the Frontier sandstone member of the 

Mancos shale at well-exposed places across the area is as follows: 

Section of the Frontier sandstone member of the .Mancos shale, northwest of 

the coal rnine area and southwest of Mosby Creek, SW1;4 sec. 13, T. 3 S., 18 E. 

[Measured by D. M. Kinney, J. F. Rominger, P. Verastegui M., and R. S. Brown] 

~1ancos shale: 

Upper shale member: 

Shale, clay, dark-gray, slightly sandy. 

Frontier sandstone member : Feet 

Sandstone, tan, fine- to medium-grained, calcareous, thick-bedded 

to massive, with fossils near base__________________________ 94 

Shale, gray, tannish-gray weathering, sandy___________________ 177 

l\fowry shale member : 271 

Shale, dark-gray, fissile, siliceous. 

Section of the Frontier sandstone rnember of the JJJ ancos shale 'in Stcinaker· 

Draw, north of Vernal, Utah, SE¥.! sec. 86, T. 3 S., R. 21 E. 

[Measured by D. M. Kinney, J. F. Rominger, P. Verastegui M., and R. S. Brown] 

Mancos shale : 

Upper shale member: 

Shale, clay, dark-gray, slightly sandy. 
104 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Section of the Frontier sandstone member of the Mancos shale in Steinaker 

Draw, north of Vernal, Utah, SE1,4, sec. 26, '1'. 3 S., R. 21 E.~Continued 

Mancos shale--Continued 

Frontier sandstone member: Feet 

Sandstone, fine- to medium-grained, calcareous, tan or buffweathering __ '---------·------------------------------------ 6 

Coal, shaly, with streaks of black, carbonaceous shale__________ 7 

Shale, dark-gray, carbonaceous_______________________________ 8 

Sandstone, fine- to medium-grained, calcareous, light-gray, tanweathering------------------------------------------------ 92 

Shale, gray, sandy, tan-weathering____________________________ 51 

l\iowry shale member: 164 

Shale, siliceous, dark-gray, light-gray weathering. 

Section of the Frontier sandstone member of the Mancos shale, 1h mile west of 

Little Brush Greek, N.W.~4 sec.11, '1'. 3 S., R. 22 JlJ 

[Measured by D. M. Kinney and J. F. Rominger] 

Mancos shale : 

Upper shale member : 

Shale, clay, dark-gray. 

Frontier sandstone member : Feet 

Sandstone, light-gray to buff, fine- to medium-grained, calcareous, 

Sandstone, light-gray to buff, fine- to medium-grained, calcareous, 

thick-bedded, fossiliferous at base with brown calcareous concretions as large as 5 feet in diameter at top__________________ 134 

Shale, gray, tan-weathering, sandy---------------------------- 75 

Mowry shale member : 209 

Shale, siliceous, dark-gray, weathering light-gray. 

Section of the Frontier sandstone member of the Mancos shale in Orchard 

Draw, Dinosaur National Monument, SW%, sec. 27, T. 4 S., R. 23 E., 1 milf3 

west of Monument Headquarters 

[Measured by F. T. McCann and N. D. Raman] 

Mancos shale : 

Upper shale member: 

Shale, clay, slightly sandy, dark-gray, weathering silver-gray. Feet 

Frontier sandstone member : 

Sandstone, very fine- to fine-grained, gray to buff, slightly 

calcareous, yellowish-brown, gray or brown-weathering, with 

glassy quartz grains and some carbonaceous materiaL_______ 6 

Shale, dark-gray to black, blocky and fissile, noncalcareous, sandy 

near top and bottom, brownish-gray weathering ___________ '"-- 44 

Sandstone, very fine-grained, gray to buff, gray to brown-weathering, massive, slightly calcareous, with grains of subangular, 

glassy to slightly frosted quartz and considerable limonite near 

base ------------------------------------------------------ 20 

Shale, dark-gray to black, blocky, fissile, noncalcareous, buffweathering, interbedded with numerous thin (% to 6 inches 

thick) beds of sandstone, very fine-grained, gray to light-buff, 

noncalcareous --------------------------------------------- 100 

Shale, dark-gray, similar to above but without sandstone beds____ 1.4 
STRATIGRAPHY 105 

Section of the Frontier sandstone member of the Mancos shale in Orchard 

Draw, Dinosaur National Monu,ment, SW* sec. '27, T. 4 S., R. 23 E., 1 mile 

west of Monument Headquarters-Continued 

Mancos shale-Continued 

Frontier sandstone member-Continued Feet 

Shale, black, similar to above, but weathering brownish-black 

and with some fish scales in lower portion__________________ 40 

Mowry shale member: 22·! 

Shale, dark-gray, silver-gray weathering. 

Section of the Frontier sandstone member of the Mancos shale, south of U. S. 

Highway 40 and north of Spring Creek, NW14 sec. 7, T. 6 S., R. 24 E. 

[Measured by D. M. Kinney and J. F. Rominger] 

Mancos shale : 

Upper shale member: 

Shale, dark-gray, light-gray weathering. 

Frontier sandstone member : Feet 

Sandstone, tan, fine- to medium-grained, calcareous______________ 32 

Shale, gray, tan-weathering, fine- to- medium-grained, sandy------ 10 

Shale, clay, dark-gray fissile__________________________________ "14 

Sandstone, tan, fine-grained, platy at top________________________ 5 

Shale, clay, dark-gray, fissile, with 1 foot bed of fine-grained, 

calcareous sandstone prominent in top 10 feet________________ 98 

Mowry shale member : 235 

Shale, dark-gray, silver-gray weathering, platy to fissile, with fish 

scales and a few thin (0.1 to 0.3 foot) beds of medium-gray, finegrained sandstone. 

Distribution.-The Frontier sandstone mmnber o:f the Mancos shale 

has the same distribution as the Mowry member. It is present in the 

coal-mine area southwest o:f Mosby Creek eastward to Little Mountain, in Coal Mine Draw on the east side o:f Little Mountain, and in 

the ridge that extends :from east o:f Ashley Creek along the east side 

o:f Steinaker Draw, across the valley o:f Brush Creek to Diamond 

Mountain. It also :forms a hogback ridge on the north and west sides 

o:f Split Mountain, with the upper massive sandstone unit :forming a 

dip slope on the west side o:f Split Mountain. The Frontier is present on the south side o:f Split Mountain within the Dinosaur National 

~fonument. It is also present on the flanks o:f Section Ridge anticline 

east o:f Jensen. 

Fossils, age, and stratigraphic relations.-A sparse :fauna o:f Ostrea 

and other pelecypods is :found near the base o:f the sandstone that 

:forms the upper part of the Frontier member. Well-preserved fossil 

molds were noted in the measured section near ·the coal mines in 

T. 3 S., R. 19 E., and east of Utah State Highway 44 in Steinaker 

Draw. No collections were made in the present area, but Walton 

(1941, p. 104, pl. 1) has shown that in the Duchesne River area on the 

south flank o:f the Uinta Mountains, 50 miles to the west, a part of the 
106 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

n1ueh thicker Frontier forn1ation contains a typical fauna of Greenhorn age. He also found the shale underlying the sandstone to be 

of pre-Greenhorn age, and he believed that the Greenhorn fauna 

ranged upward into the basal part of the upper shale member of the 

Maneos shale. Reeside ( 1930, p. 35-41) reports, from the Frontier 

member on Vermilion Creek, Colo., a fauna that indicates an equivalence to the upper part of the Carlile shale east of the Front Range; 

this zone is widespread in the Maneos shale. Reeside's isopaehous 

map (1944, map 4) of the Cretaeeous deposits in the western United 

States shows 200 to 300 feet of Greenhorn equivalent in the northeastern part of Utah, and abou:t the same thickness of upper Carlile 

equivalent. 

The lower boundary of the Frontier sandstone member is drawn at 

the abrupt eolor ehange frmn silver-gray shale of the Mowry shale 

member to tan drab-weathering sandy siltstone. The upper boundary 

of the Frontier member is drawn above the highest sandstone. It 

appears to be conformable throughout the area. 

Oorrelation.-The Frontier sandstone member of the l\{ancos shale 

is equivalent to the Frontier formation as defined ( Sehultz, 1920, p. 

73-74) on the north flank of the Uinta Mountains. Walton (1944, p. 

103) has shown that it thins progressively eastward on the south flank 

of the Uinta Mountains and that it can be definitely eorrelated with 

the Frontier sandstone of the Red Creek and Duchesne River sections 

of the western Uinta Mountains. Thin-bedded sandstones and interbedded sandy shales at the horizon of the Frontier member ean be 

traeed (Thmnas, McCann, and Raman, 19-!5) into northwestern Colorado. 1Valton (1944, p. 104) has suggested that the Frontier on the 

south flank of the Uintas correlates with the Ferron sandstone in the 

lower part of the Maneos shale south of the Uinta Basin. However, 

Clark (1928, p. 14) reports a Carlile fauna from the Ferron at Farnum 

Dome and '¥alton (194±, p. 104) has shown the Frontier of the Uinta 

Mountains to be Greenhorn in age, so it would appear that the Ferron 

sandstone member of the Maneos shale is slightly younger than the 

Frontier 1nember. Bartram (1937, p. 907) has suggested that the 

Ferron and the Frontier eould have been deposited on different deltas 

at slightly different times. 

Oondition.s of deposition.-It has been suggested (Bartram, 1937, 

p. 902-903) that the Frontier formation of southwestern 'V"yoming 

is an old delta whieh was formed by streams (flowing from mountains rising in eastern Nevada and western Utah) that deposited their 

loads of sand and silt in a great inland Cretaceous sea. When deposition exceeded subsidence of the area, the delta was built above sea 

level, and the resultant fresh-water, swampy conditions resulted in 

lush vegetation. After burial, this vegetation formed thick coal beds. 

As the subaerial portion of the delta grew, the coarser particle·s were 
STRATIGRAPHY 107 

spread farther east. The Frontier sandstone member of the Mancos 

shale on the south flanks of the eastern Uinta Mountains probably represents attenuated deltaic sediments derived frmn the west. The 

lower sandy siltstone unit was deposited under marine conditions, and 

the lower, fossiliferous part of the Frontier is of marine origin. Only 

the medium- to coarse-grained, crossbedded sandstone, and the associated coal beds in the upper part of the member, are of fresh-water 

origin. Deposition of the member was terminated by the renewal of 

subsidence and the submergence of the area during the deposition of 

the upper shale member of the Mancos. 

UPPER SHALE MEMBER 

Definition.-The Mowry shale and Frontier sandstone members of 

the Mancos shale constitute only 5 percent of the total thickness of the 

formation and the remaining strata are included in the upper shale 

member, which resen1bles, in lithology, the typical Mancos shale of 

southwestern Colorado and the Yampa eoalfield of northwestern 

Colorado. It rests on the Frontier sandstone member and is overlain 

by the sandstones of the Mesa verde formation. 

Lithology and thickness.-The upper shale member of the Mancos 

shale consists of mediun1 to dark gray, massive siltstone or clay shale 

with thin, lenticular beds of tan to brown, sandy limestone or calcareous sandstone. Along Spring Creek and northwest of fJ ensen, the 

lower 1,000 to 1,500 feet weather to light silver gray and the upper 

part weathers to a slightly darker gray. The brown-weathering, calcareous sandstone or sandy li1nestone beds are rare in the basal threequarters of the member but, as the upper boundary of the Mancos 

shale is approached, thin, fine-grained, calcareous sandstone beds become more common. The siltstone or clay shale is so massive that 

particular reliance must be placed on the sanely limestone beds in the 

lower part of the member for knowledge of the attitude of the strata 

when calculating the thickness of the measured section. 

In the area mapped, the thick upper shale member is completely 

exposed only in the Spring Creek drainage, south of U.S. Highway 

40. At this place, 4,910 feet of gray siltstone have been measured, 

but an abrupt change in clip near the middle of the member suggests 

strike-slip faulting and the possibility that some section is missing or 

duplicated. The n1easured thickness is believed to be approximately 

correct, however, because a thickness of 5,000 and 5,200 feet of shale 

is present at the Rangely oilfield and at V ern1ilion Creek (Thomas, 

McCann, and Raman, 1945) respectively, in northwestern Colorado. 

Huddle and McCann (1947) report only 1,800 to 2,600 feet of the 

upper shale member in the Duchesne River area, because at this point 

the upper part of the Mancos is replaced by coarse-grained sandstones 

of the Mesaverde formation. Because of the fact that the upper 

shale member thins toward the west, it is probable that less than 4,900 

295163-55-8 
108 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

feet of the upper member is present in the area overlapped by Tertiary 

sediments west of Little Mountain. 

Distribtttion and topographic expression.-The upper shale Inember of the Mancos shale is present from south of the coal mines in the 

Mosby Creek-Deep Creek drainage eastward to Little Mountain, 

beneath the broad Ashley Valley, in the badlands near the Buckskin 

Hills and east of Steinaker Draw, in the Island Park syncline between 

Diamond Mountain and Split Mountain, south of Split Mountain, 

around the Section R,idge nose, and southward to The Rim Rock. 

The upper shale member generally is poorly exposed; a thin soil 

mantles unweathered siltstone a few inches beneath the surface. The 

gray siltstone supports practically no vegetation and this leads to the 

development of badland topography, except where terrace gravels 

along Ashley Creek, Brush Creek and Green River protect the underlying sedimentary rock from erosion. Most of the well-developed 

erosion surfaces on the upper member are cut deeply enough to give a 

clue to the late Cenoozoic history of the area. 

The detailed lithology of the upper shale member of the Mancos 

shale, as exposed in the vicinity of Spring Creek and south of U. S. 

Highway 40, is given in the following section measured by planetable and telescopic alidade. 

Sect,ion of the ttpper shale member of the Mancos shale in the Spring Creek area, 

S¥2 sec. "1, sec. 18, and sec.19, T. 6 S., R. 24 E. 

[Measured by D. 1\1. Kinney and J. F. Rominger] 

Mesaverde formation: 

Sandstone, light-gray, tan-weathering, fine- to medium-grained, massive, 

crossbedded, with abundant grains of subangular black chert. 

Mancos shale : 

Upper shale member : Feet 

Shale, gray, tan-weathering, sandy, with two 1-foot beds of tan, 

thin-bedded, crossbedded sandstone__________________________ 79 

Sandstone, tan, fine-grained, thin-bedded______________________ 3 

Shale, sandy, gray to tan____________________________________ 248 

Shale, gray, grayish-tan weathering, sandy, with lenses (maximum 2 feet thick and 10 feet long) of tan, very fine-grained 

sandstone ------------------------------------------------- 709 

Shale, gray (grayish-tan weathering, with thin beds of tan, finegrained, calcareous, slabby sandstone_______________________ 296 

Shale, clay, gray, tan-weathering, sandy, with few tan concretionary beds. Top 5 feet of sandstone, tan, fine-grained, 

calcareous, interbedded with sandy, light-gray shale__________ 379 

Shale, clay, gray--------------------------------------------- 1170 

Shale, clay, gray, tan-weathering_____________________________ 762 

Shale, clay, gray, tan-weathering, sandy, with thin partings of 

fine-grained sandstone in top 10 feet_________________________ 506 

Shale, clay, silver-gray--------------------------------------- 704 

Shale, clay, dark gray_______________________________________ 54 

Frontier sandstone member: 4,910 

Sandstone, tan, fine- to medium-grained, calcareous. 
STRATIGRAPHY 109 

Fossils and age.-Fossils are abundant at certain horizons in the 

upper shale member of the Mancos, but the preservation is usually 

poor because of weathering in surface exposures and because of the 

fragile character of the original shells. Some of the better fossil 

localities were noted at places of structural complexity .and poor 

stratigraphic control. This discovery of fossils at places of structural 

complications is due to the greater detail with which such areas were 

studied. Similar searches of less con1plicated areas should yield more 

fossil localities. On the basis of regional isopachous maps of Reeside 

(1944, maps 6 and 7) and the work of Walton (1944, p. 105), the upper 

shale mmnber of the Mancos probably contains equivalents to the 

upper part of the Carlile shale and the Niobrara formation of the 

standard section for the western interior, as well as 2,700 to 2,900 feet 

of the Montana group. 

Stratigraphic relations and correlation.~The lower boundary of 

the upper shale member of the Mancos shale appears to be gradational 

with the underlying Frontier sandstone member, although the absence of the lower Carlile shale equivalent over the general area, as 

shown by Reeside (1944, n1ap 5), suggests that a stratigraphic break 

may be present at approximately this point in the sedimentary record. 

Certainly, no physical evidence for such a break is found in the detailed section measured on Spring Creek. However, the character 

of the outcrops is such that, although a break may exist, it can easily 

be unnoticed. The gradational relationship of the upper boundary 

with the overlying Mesaverde fonnation is indicated by more abundant sandstone beds in the upper shale member as the boundary with 

the overlying massive sandstone is approached, and by evidence (W alton, 1944, p. 109) that the Mesaverde is of Niobrara age in the western 

part of the Uinta Mountains but is of post-Niobrara age near the 

Green River. Reeside (1930, p. 35-41) has indicated the presence of 

equivalents of the Niobrara formation, Telegraph Creek formation, 

Eagle sandstone, and some post-Eagle beds in the Mancos shale on 

Vermilion Creek, Colo. 

The upper shale mmnber is correlated with the Mancos shale and 

most of the Mesaverde formation of the Duchesne River area of the 

western Uinta Mountains, the Hilliard shale of the north flank of the 

Uinta Mountains, the middle and upper part of the type section of 

the Hilliard shale in southwestern Wyoming, and the upper member 

of the Maneos shale as mapped in adjacent areas of northwestern 

Colorado. Farther east in Colorado and south of the Uinta Basin 

(Erdmann, 1934, p. 29-31), the Mancos shale may include still younger Upper Cretaceous rocks, perhaps equivalent to the Lewis shale of 

the Montana group. 

Conditions of deposition.-The upper member of the Mancos shale 

is unquestionably of marine origin throughout the Uinta River-Brush 
110 GEOLOGY OF UIN'l'A RIVER-BRUSH CREEK AREA, UTAH 

Creek area. The rapid thickening of the Upper Cretaceous sedimentary rocks toward the west, and the change frmn marine shale 

to deltaic deposits (including coal), indicate a western source for 1nost 

of the sediments. The source was probably in the rising mountains 

of western Utah and eastern N evacla. The isopachons maps of Reeside (1944, map 2) clearly show hvo centers of subsidence and deltaic 

deposition, one in southwestern vVyoming and the other in central 

Utah. The sediments deposited in the eastern Uinta ~fountains probably were derived from the center of deposition in southwestern 

Wymning. 

MESA VERDE FORMATION 

Definition.-The Mesaverde formation was named by Holn1es (1877, 

pl. 35) for the Mesaverde in southwestern Colorado. There, it underlies dark marine Lewis shale and overlies similar 1narine shale of the 

Mancos. The Mesaverde was first identified in northwestern Colorado 

by Fennmnan and Gale ( 1906, p. 22-23) in the Y a1npa coalfield and 

later, it was recognized in northeastern Utah by Gale (1910, p. 63). 

Gale recognized two 1nmnbers in the Mesaverde formation: a lower, 

primarily marine, member that is characterized by fine- to mediumgrained sandstone and an upper, brackish to fresh-water 1nember 

that includes beds of carbonaceous shale and lignitic coal seams. In 

the Axial and Monument Butte quadrangles in northwestern Colorado, 

Hancock ( 1925, p. 15-25) named these members the "lies fonnation" and the "Willia1ns Fork formation" for exposures at Iles Mountain and along Williams Fork near its junction with the Y a1npa River. 

Sears (1924, p. 289-290, pl. 35) extended these formations to the vicinity of Elk Springs, Colo., 40 miles to the east of the Green River, but 

he does not believe (personal connnunication, March 1949) that the 

Iles can be carried farther westward. Walton (1944, p. 110-111, 

114-115) has divided the lower .part of the Mesaverde, in the Vernal 

area, into the Asphalt Ridge sandstone (below) , and the Rim Rock 

sandstone (above), and he has retained the name "Williams Fork" 

for the upper part of the Mesa verde formation. If present at all 

within the area under study, the Asphalt Ridge sandstone of 'V alton 

is only poorly developed because 'Valton has shown that it feathers 

out, west of the Green River, into the upper part of the Mancos. All 

of the sandstone at the base of the Mesaverde formation in the southeastern part of the mapped area probably would be included in Walton's Rim Rock sandstone. 

Lithology arul thickness.-The lower 1nember of the Mesaverde 

formation consists of one-third light-gray, fine- to medium-grained 

sandstone and two-thirds 1nedium-grained, light-gray speckled sandstone. The sanrlstone is thick-bedded to massive and, commonly, 

crossbedded. Some beds are highly contorted. Only 5 percent, or less, 

of the member is sandy shale. The sand grains are angular to sub-
S'l'RATIGRAPHY 111 

angular. The speckled appearance of some of the beds is given by a 

large number of grains of black chert. Except for the basal beds, 

which are cemented with lime, the sandstone is friable and disintegrates readily. The upper 1nmnber of the fonnation consists of 

light-gray to brown, fine- to 1nediun1-grained sandstone, and dark-gray 

to light brownish-gray lignitic shale. Sandstone constitutes about 60 

percent of the unit. It is thin bedded to massive, but only the massive 

beds are well exposed. The lignitic shale and thin-bedded, finegrained, brown sandstone beds are soft, easily eroded, and poorly exposed, except along banks of streambeds. 

The lower member is 528 feet thick, and the upper member is 631 

feet thick at The Rim Rock and 2 1niles east of the Green River. 

More of the upper 1nember of the Mesa verde formation is exposed at 

this place than at any other place in the area. To the east, and to the 

west, the Tertiary rocks transgress farther north and rest on the lower 

member of the formation. Only 525 feet of Mesaverde formation is 

exposed at Point of Rocks on the west side of the Green River. 

The detailed lithology of the Mesa verde formation in the area of 

maximmn exposure east of the Green River is as follows: 

Section of the JJf esaverde formation 2 miles east of the Green River SW14 sec. 8 

and NW:l;.!NW14 sec. 17, T. 6 S., R. 23 E. 

[Measured by D. M. Kinney and J. F. Rominger] 

Tertiary: 

Green River(?) formation: 

Conglomerate, brown, with pebbles predominantly of well-rounded, dark 

chert and abundant fragments of silicified wood .. 

Mesaverde formation: 

Upper member: Feet 

Sandstone, light-gray, speckled, massive to contorted bedding, 

crossbedded, with angular to sub-rounded grains_________ 68 

Shale, lignitic interbedded with light-gray, massive, highly 

lenticular sandstone _________________________ .___________ 81 

Lignite, dark-gray, with selenite crystals; grades into overlying bed---------------------------------------------- 6 

Sandstone, dusky yellow-orange, specked, with a few 1 to 2 

foot beds of moderate-brown, fine- to medium-grained, 

calcareous sandstone and streaks of lignitic shale________ 73 

Sandstone, light-gray, fine- to medium-grained, calcareous____ 2 

Shale, lignitic, and lignite interbedded with light-gray, finegrained, soft sandstone_________________________________ 134 

Sandstone, light-gray, lenticular, massive to thin-bedded____ 30 

Shale, medium dark-gray, fissile__________________________ 10 

Sandstone, light-gray, fine-grained_________________________ 2 

Lignite, dark-gray, thin-bedded, interbedded with light-gray, 

massive, crossbedded sandstone_________________________ 22 

Sandstone, moderate-brown, thin-bedded, contorted, overlying 

light-gray, massive, soft sandstone; weathers into concretions_______________________________________________ 48 

Sandstone, light-gray, fine-grained, massive________________ 10 
112 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Section of the Mesaverde formation 2 miles east of the Green River SW% sec. 8 

· and NW%NW% sec.17, T. 6 S., R. 23 E.-Continued 

Tertiary-Continued 

Mesaverde formation-Continued Feet 

Sandstone, light-gray, fine- to medium-grained, speckled, massive, with a few thin beds of light brownish-gray, lignitic 

shale__________________________________________________ 91 

Sandstone, light-gray, tan-weathering, fine- to mediumgrained, thin-bedded with few thin beds of light brownishgray lignitic shale at base------------------------------ 70 

Lower member: 

Sandstone, moderate yellowish-brown, speckled, mediumgrained, poorly crossbedded with angular to subrounded 

grains, and light-gray, specked, massive, crossbedded sandstone__________________________________________________ 70 

Covered; sandstone, light-gray, fine- to medium-grained, soft, 

friable________________________________________________ 77 

Sandstone, light-gray, medium-grained, highly crossbedded 89 

Covered; 1-foot beds of sandstone, light-gray, speckled, interbedded with shale------------------------------------- 24 

Sandstone, light-gray, speckled, fine- to medium-grained, massive, crossbedded, contorted bedd~d, with angular grains__ 34 

Covered; sandstone, yellowish-gray, fine- to medium-grained, 

slabby, as float. Unit probably sandy shale_______________ 16 

Sandstone, light-gray, speckled, medium-grained, massive, 

crossbedded____________________________________________ 201 

Sandstone, light-gray, tan-weathering, speckled, fine- to medium-grained, massive, crossbedded_____________________ 18 

529 

Total thickness-------------------------~------------ 1,176 

Mancos shale : 

Shale, sandy, gray, tan-weathering. 

Distribution and topographic ewpression.-The Mesa verde formation underlies Asphalt Ridge to the south and west of Vernal, crosses 

the Green River in the NE% T. 6 S., R. 22 E., and continues a little 

south of east to the eastern border of the mapped area. East of 

the Green River it underlies The Riln Rock (a low north-facing esearpnlent). It is overlapped by Tertiary roeks east of Little Mountain and does not crop out again to the. west for almost 50 1niles. The 

lower, massive to thick-bedded sandstone member forms the escarplnent, and the upper thin-bedded lignitic shale and sandstone member, where it appears beneath the overlying Tertiary sediments, underlies an area of subdued topography to the south. 

Fossils and age.-No fossils were found in the Mesaverde formation 

during the present field work, although carbonized plant remains are 

common in the lignitic shale of the upper member. Tolmachoff (1942, 

p. 41-45) reports an Upper Cretaceous marine fauna from a sandstone bed on Asphalt Ridge; Walton (1944, p. 111) correlates this 

sandstone bed with his Asphalt Ridge sandstone. The fauna includes: 
Enchodus sp. 

Apateodus sp. 

Scapanorhynchus sp. 

Placenticeras meeki J. Boehm 

Turritella sp. 

Gyrodes sp. 

Margarita sp. 

Fissurella sp. 

Leptosolen conradi Meek 

STRATIGRAPHY 

Anatina lineata Stanton 

Cymella bella Conrad 

Lucina sp. 

Cat·dium kayi Tolmachoff 

Tellina sp. 

Cymbopora sp. 

Yoldia evansi Meek and Hayden 

Crenella burkei sp. nov. 

113 

Reeside (Walton, 1944, p. 111) reports that this fauna 1nust be considered post-Niobrara in age. Because the Asphalt Ridge sandstone 

feathers out into the upper part of the Mancos formation east of Green 

River, this fauna dates the upper part of the Mancos and does not 

date the Mesaverde near the Green River. Gale (1910, p. 66) sumInarized the species collected from the Mesa verde of northwestern 

Colorado and northeastern Utah. 

Stratigraphic relations and correlation.-The Mesaverde formation 

is confor1nable with the under lying Mancos shale and is unconformably overlain by the lowest exposed Tertiary rocks. The Lewis shale, 

which overlies the Mesaverde east of Lay in northwestern Colorado~ 

is not exposed near the Green River. 

The lower member of the Mesaverde is, in part, correlative with 

the type section of the Iles formation near Craig, Colo., with 

the Mesaverde formation of the north flank of the Uinta Mountains, 

and perhaps with the lower part of the Currant Creek formation of 

the western Uintas. According to Walton (1944, p. 114), Spieker 

and Reeside believe that the Rim Rock sandstone (basal Mesaverde) 

near Rangely, Colo., is 1,500 feet stratigraphically below the base of 

the Sego sandstone of the Book Cliffs, or about in the middle of the 

Star Point sandstone of the Wasatch Plateau section. Walton (1944, 

p. 116-117) also correlates the Mesaverde with the Adaville formation 

(described in southwestern Wyoming). The upper member of the 

Mesaverde is probably equivalent to the Blackhawk formation of 

the Wasatch Plateau and is partly equivalent, at least, to the Williams 

Fork formation of northwestern Colorado. 

Conditions of deposition.-Most of the fossils from the lower member of the Mesaverde are of 1narine origin, although some beds may 

have been deposited in fresh or brackish water. The sandstone was 

deposited near the shore, and the sand probably was derived from 

great deltas which were forming to the west. The upper member 

of the Mesaverde formation is predominantly continental, as is shown 

by the frequent interbedded lignitic shale, lignite, and included invertebrate forms. It was formed on a low-lying coast that was subject 

to occasional readvances of the sea and submergence by marine waters. 
114 GEOLOGY OF UIN'rA RIVER-BRUSH CREEK AREA, UTAH 

TERTIARY SYSTEM 

The present investigation is concerned principally with the rocks 

of Paleozoic and Mesozoic age on the south flank of the Uinta Mountains, which formed a portion of the northern border for the great 

Uinta Basin, an area of Tertiary deposition in northeastern Utah 

and northwestern Colorado. The lower Tertiary rocks on the southern border of the mapped area have been grouped together as Eocene 

and Oligocene ( ? ) strata because it was believed that the naming and 

correlation of early Tertiary forn1ations would require the mapping 

of areas and the study of sections far :removed frmn the present assignment. The Bishop conglomerate (Miocene?), which rests on 

the older rocks over considerable areas, lies almost wholly within the 

boundaries of the mountains and was studied at many places. 

Some geologists now believe that most of the coarse-grained sediments included in the Bishop conglomerate are equivalents of the 

finer grained early Tertiary sedi1nents that occupy the central part 

of the Uinta Basin. The Bishop conglomerate, however, is essentially horizontal and overlies older Tertiary rocks that dip at noticeable angles into the surface trace of the Uinta Basin syncline, located 

a few miles south of the Uinta Mountain front. 

BISHOP CONGLOMERATE 

Definition.-The Bishop conglomerate was named by Powell ( 1876, 

p. 40, 44, 62, 169) for Bishop Mountain (now known as Pine Mountain) in southwestern Wymning. On the north flank of the Uinta 

Mountains, it varies in thickness fron1 a few feet to 200 or n1ore feet 

and rests unconformably on Eocene to pre-Cambrian fonnations. 

The boulders in the conglomerate consist principally of red and white 

quartzites derived from the Uinta Mountain group. The 1nore detailed work of Bradley (1936, p. 169) on the gemnorphology of the 

north flank of the Uinta Mountains has established the fact that the 

Bishop conglmnerate rests on a widespread erosion surface, which he 

named the Gilbert Peak surface for a large remnant of the surface 

that slopes westward and northward frmn the west base of Gilbert 

Peak. The Bishop conglomerate was identified by Powell on the 

south flank of the Uintas; all subsequent workers have continued his 

nomenclature. Bradley (1936, pl. 34) reports that the Gilbert Peak 

surface extends south of the crest of tht range for a few miles. 

Distrib~ttion a,nd topographic expression.-In the area shown on 

the map (pl. 1) the Bishop conglomerate underlies J e:fferson Park, 

Pole Mountain, Mosby Mountain, Lake Mountain, Dry Fork Mountain, Little Mountain, the high plateau from Ashley Creek eastward 

to Diamond Mountain, and Diamond Mountain. An isolated patch of 

conglomerate, tentatively identified ::ts Bishop, underlies the Buckskin Hills between Steinaker Draw and Split Mountain. 
STRATIGRAPHY 115 

The Bishop conglomerate is almost flat-lying and forms broad 

gently-rolling upland surfaces covered by clumps of pine and quaking 

aspen, grassy parks, and areas of boulders with only a slight soil 

cover. The upland surface is cut into a nmnber ot isolated flat-topped 

1nountains by steep-walled canyons of perennial streams flowing 

southward frmn the crest of the rang~. The Bishop conglomerate is 

well consolidated and forms steep slopes and good exposures along the 

canyon walls and on the southern boundary of the mountains. The 

southern limit of the Bishop conglomen.te forms the boundary of the 

main mountain mass that culminates along the crest of the Uinta 

Range. On Diamond Mountain, reentrants of Bishop conglomerate 

extend north ward into the valley of Pot Creek and its tributaries. 

Lithology and thickness.-The Bishop conglomerate at Jefferson 

Park consists ahnost exclusively of light-tan to reel boulders in a 

matrix of coarse sandstone. The matrix is not prominent and in n1ost 

outcrops only the rounded boulders are visible. On Pole Mountain, 

l\fosby Mountain, and Lake Mountain, the lower bed of the Bishop is 

a characteristic basal conglomerate, 25 to 40 feet thick, composed of 

well-rounded boulders of limestone, chert, and sandstone in a matrix 

of medium- to coarse-grained sand. Overlying this basal conglomerate is a chalky-white tuffaceous sandstone, 25 to 100 feet thick, which, 

in turn is overlain by light-tan to buff conglomerate with a sand 

matrix. Eastward, the conglomerate beds are prmninent on Dry 

Fork Mountain, Little Mountain, east of Ashley Creek, and for a short 

distance east of Brush Creek. However, in the escarpment formed by 

equivalent beds on Diamond Mountain, the conglomerate appears as 

streaks or thin beds, and medium-grained, partly tuffaceous, lightgray sandstone comprises most of the forn1ation. The upper surface 

of the Bishop, from Ashley Creek eastward to Little Brush Creek, is 

dotted with occasional groups of large, angular, quartzite blocks; 

some of the blocks weigh several tons. These blocks are believed to 

be large erratic boulders that were carried far frmn their source by 

mudflows. 

The Bishop conglomerate thins unifonnly eastward from a thickness of 800 feet at Jefferson Park, on the western edge of the mapped 

area, to an approximate thickne.s of 300 feet on Diamond Mountain. 

Fossils and age.-No fossils have been found in the Bishop conglomerate within the area and it is believed that it is only in the finegrained facies on Diamond Mountain that vertebrate fossils might be 

preserved. The Bishop conglomerate on the north flank of the Uintas 

is tentatively classified as Miocene(?) by the Geological Survey (Wilmarth, 1938, p. 194) because it is believed to be older than the Browns 

Park fonnation in which vertebrate fossils of Pliocene age have been 

found at Sunbean1, northwestern Colorado. The age of the under-
116 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

lying Gilbert Peak erosion surface is accepted to be of Oligocene or 

Miocene age by the Geological Survey (Wilmarth, 1938, p. 818). 

Stratigraphic relations and correlation.-As mapped along the south 

flank of the Uinta Mountains, the Bishop conglomerate grades eastward from very coarse-grained quartzitic conglomerate to mediumgrained tuffaceous sandstone with lenses and thin beds of boulders. 

At intermediate positions, and near the base of the formation, beds of 

chalky-white tuffaceous sandstone are found interbedded with conglomerate, thus suggesting an interfingering of facies. The tuffaceous 

sandstone superficially resembles the, Browns Park formation of 

northwestern Colorado. The Bishop conglomerate of the south flank 

of the Uinta Mountains rests on an erosion surface, here identified 

as the Gilbert Peak surface of Bradley, which underlies the type 

Bishop conglomerate on the north flank of the mountains. 

The correlation of exposures of poorly consolidated boulders on 

the crest of the Buckskin Hills is questionable because the altitude of 

the exposures is too low to correspond with the base of the Bishop. 

Although the boulder deposit may represent only the remnant of a 

high-level terrace deposit of Brush Creek, it is correlated with the 

Bishop conglomerate on the grounds of lithologic similarity. 

STRUCTURE 

METHODS OF REPRESENTING STRUCTURE 

The geologic structure of the area shown on plate 1 gives the location and direction of throw of the faults and the attitude of the strata 

by dip and strike symbols and by structural contour lines drawn 

through points of equal altitude above sea level on the top of the 

Navajo sandstone. The structure is also shown, graphically and without distortion, by means of cross sections drawn to scale which show 

the inferred folding and faulting of beds at depth, based on surface 

observations and well information. 

The structure contours are based on (1) altitudes of key beds obtained at many places by angles determined with the telescopic alidade 

from stations established by three-point intersection from control 

stations, and by distances measured on the photo-mosaics, (2) observed dips, and (3) stratigraphic interval above or below the top of 

the Navajo sandstone interpolated from the correlation chart (pl. 2). 

In contouring, the assumption is made that the folding has been of 

the concentric type in which the stratigraphic thickness of the beds 

remain unchanged in the folds. The vertical depth to the top of the 

Navajo sandstone (Jurassicn has been computed by dividing the 

stratigraphic thickness by the cosine of the observed dip angle, The 

structure-contour lines are accurate for the purpose of recording the 

surface structure only along the line of outcrop of the top of the 

Navajo sandstone. In areas where younger rocks are exposed, the 
STRUCTURE 117 

lines represent the inferred altitude of the top of the Navajo sandstone; the information is based upon deformation of the overlying 

younger beds and, where older rocks are exposed, of the inferred altitude of the top of the Navajo before erosion removed it. Of the three 

controlling factors used in the computation of the altitudes of the 

points controlling the location of structural contour lines, the observed 

dips are the source of the greatest inaccuracy. 

Strike and dip of beds cannot be determined with a high degree of 

accuracy by means of Brunton compass and clinometer, and a Ineasurmnent of strike and dip, which may be accurate for the particular 

locality, may not have regional significance. For these reasons, contour lines based on horizons some distance stratigraphically above 

or below the top of the Navajo sandstone only approximate the position of the Navajo prior to erosion. The field sheets, on which the 

published structural contour lines are based, were compiled at 200-

foot intervals but only even-numbered thousand-foot contour lines 

are shown because of the limited distribution of control elevations in 

the area underlain by the thick Mancos shale and in the area overlain by Bishop conglomerate. The location of contours is primarily 

based on the method of equal spacing between points of different altitude; thus, the greater detail of the original compilation is reflected 

in the published 1na p. 

Surface altitudes for the profile of the different cross sections were 

taken from the topographic maps of the Marsh Peak and Ashley 

quadrangles of the U. S. Geological Survey and were supplemented 

by altitudes established by triangulation, three-point intersection, or 

angles determined with the telescopic alidade 'and by distances measured on the photo mosaics. The geologic cross sections were based on 

observed surface dips, the altitudes of formations in wells, the predicted altitudes of the top of the Navajo sandstone from the structurecontour lines, and the measured thicknesses of the formations. 

GENERAL FEATURES 

The Uinta Mountains are formed by a large anticlinal arch, 150 

1niles long and 20 to 40 miles wide, trending generally east-west. The 

axis of the fold is arcuate to the south, and the fold is asymmetrical 

with the steep flank on the north side. The structure of the broad 

anticlinal arch is complicated by a steeply dipping reverse fault on 

the north flank and by steeply dipping normal faults, arranged in 

echelon on the south flank. 

The area studied lies on the south flank of thhe Uinta Mountain 

arch near the central and east-central part of the range. The principal structure of the area is a south-dipping homocline with superposed small, sharp, south-southeast plunging anticlinal noses and subsidiary and parallel anticlinal folds. 
118 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

The area shown on plate 1 is divided, by Dry Fork of Ashley Creek 

and by a line trending S. 60° E. across Ashley Valley, into two parts 

that show different structural characteristics. East and northeast of 

this line, open folding predominates and faulting has only minor significance. South of Dry Fork and as far west as Uinta River, faulting 

is dominant and sharp folds are also present. 

Eastward and northward frmn Dry Fork, the strata dip to the 

southeast, then to the south, and finally to the south,vest at angles of 

H1° to 15°. The swing in strike of the bed along the homoclinal 

southern dip of the Uinta Mountains east of Dry Fork is a reflection 

of the Island Park syncline, which separates the Uinta Mountain 

arch frmn the parallel folds of the Split Mountain and Section Ridge 

anticlines to the south. The Split Mountain and Section Ridge 

anticlines are separated by the shallow Daniels Draw syncline, and 

they join in northwestern Colorado to form the Blue Mountain 

anticline. The Split Mountain and Section Ridge anticlines plunge 

steeply westward into Ashley Valley. 

West of Dry Fork, the wide zone of faulting most prominently displayed in the valley of Deep Creek merges with the zone of echelon 

faulting known as the South Flank fault, which in general bounds the 

pre-Cambrian core of the Uinta Mountains. The faulting in Deep 

Creek probably extends southeastward to join with the faulting on 

the south flank of the Section Ridge anticline. The South Flank fault 

displacement becomes smaller to the northeast and it disappears east 

of Ashley Creek. Dips in the faulted area are moderate to steep and 

they vary in direction. 

FOLDS 

ISLAND PARK SYNCLINE 

The steep-flanked and gently arched Split Mountain anticline is 

separated frmn the homoclinal dips on the south flank of the Uinta 

Mountain arch by the Island Park syncline, named for Island Park 

on the Green River to the east of the mapped area. The axis of the 

syncline trends east-west through the southern part ofT. 3 S., R. 23 

E., and the SEl~ T. 3 S., R. 22 E., but it is deflected to the southwest 

into the Nlh T. 4 S., R. 22 E., by a saddle between the southeastern 

extension of the Ashley Creek anticlinal nose and the Split Mountain 

anticline. The syncline is asy1nmetrical; because dips of 20° to 25° 

to the south on the ridge of Cretaceous strata through the northern 

sections ofT. 3 S., Rs. 22 and 23 E., rapidly diminish to a few degrees 

or a fraction of a degree for a distance of 2 miles north of the axis and 

then change abruptly to 50° to 70° toward the north as the axis is 

passed. This change in attitude is so rapid that the presence of faulting is suggested. Faulting cannot be proved, however, because of 

the lack of competent beds, the development of a masking soil cover, 

and the prevalence of slumping in the upper shale mmnber of Mancos 
STRUCTURE 119 

shale, which occupies the central part of the syncline. Faulting of 

the Frontier sandstone 1nember of the Mancos shale is evident along 

the axis of the syncline a few miles east of the boundary of the map, 

and some northwest-trending faults cut the hogback of Cretaceous 

strata on the north flank of Split Mountain and enter the upper shale 

member where they no longer can be detected. The change in strike 

of the Mississippian and Pennsylvanian rocks in the northern part of 

Diamond Mountain from northeast to northwest is a reflection of 

the folding that formed the Island Park syncline. The westward 

plunging Ashley Creek anticlinal nose and Neal dome fonn a shallow 

closed basin in the Mancos shale area north of Split Mountain. 

SPLIT MOUNTAIN ANTICLINE 

Only the north and south flanks and the westward plunging strata 

of Mesozoic age of Split Mountain anticline are shown on plate 1, 

because much of the anticline is within the Dinosaur National Monument or east of longitude 109° 15'. The crest of the anticline is broad 

and gently arched, but the fold has steeply dipping northern and 

southern flanks. Two minor anticlinal axes are developed on the 

main fold: one extends from sec. 7, T. 4 S., R. 23 E., slightly south of 

west for 5 miles to sec. 17, T. 4 S., R. 22 E., and lies along the extreme 

north flank of the main anticlinal fold; the second, located along the 

south flank of the main arch, extends from sec. 20, T. 4 S., R. 23 E., 

westward for at least 8 miles to see. 31, T. 4 S., R. 22 E. The intervening syncline is sharply folded near Brush Creek, but it becomes 

more gentle as it plunges westward. The upper shale member of the 

Mancos shale underlies most of the plunging Split Mountain anticline west of Brush Creek, and the structure-contour lines in the 

NW1;4 T. 4 S., R. 22 E., are based, in part, on a detailed map of the 

area prepared in 1925 for the Humphrys Phosphate Co. by L. H. 

Williams and R. H. Ratliff. Weber sandstone (Pennsylvanian) forms 

the topographic crest of the anticline within the Monument area and 

the limestone unit of Mississippian age is exposed along the axis of 

the fold in Split Mountain Canyon. The fold dies out in the western 

part ofT. 4 S., R. 22 E., in the area south of the Buckskin Hills and 

east of Ashley Creek. 

SECTION RIDGE ANTICLINE 

The axis of the Section Ridge anticline extends westward from 

sec. 31, T. 5 S., R. 24 E., to the western part ofT. 5 S., R. 22 E. Faulting, with downthrow on the south, is common along the steep south 

flank of the fold; it probably is connected with the reported thrust 

fault on the south side of the anticline to the east. A saddle in sec. 

19, T. 5 S., R. 23 E., and sec. 2±, T. 5 S., R. 22 E., and probably some 

faulting that is the northwestward continuation of the faults (noted 
120 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

above) on t4e south flank o£ the £old, separate the closed anticlinal 

high (the Ashley Creek oilfield) £rom the main part o£ the anticline 

to the east. The saddle area is covered with alluvial deposits and a 

heavy soil cover, thus making it impossible to obtain dip Ineasurements in critical areas o£ the upper shale member o£ the Mancos shale. 

The Utah-Vernal Oil Co.'s Caldwell welll in the SW~SW1;4SW~ 

o£ sec. 20, T. 5 S., R. 23 E., is structurally only 350 feet above the 

crest o£ the Ashley Creek field; the oil and gas accumulation in the 

field clearly indicates structural closure. Details o£ the Ashley Creek 

oilfield structure are discussed under Oil and Gas in the section on 

Economic Geology. 

DANIELS DRAW SYNCLINE 

Split Mountain anticline is separated £rom the Section Ridge anticline to the south by a syncline here named the "Daniels Draw syncline," £or the intermittent stream that enters the Green River in see. 

32, T. 4 S., R 24 E., and generally follows the axis eastward. The syncline enters the area shown on plate 1 a short distance south o£ Split 

Mountain Gorge and west o£ the Green River in sec. 31, T. 4 S., R. 

24 E. The axis o£ the Daniels Draw syncline plunges gently westward and trends slightly south o£ true west into the broad Ashley 

Valley. It is asymmetrical, with the steep north flank formed by 

the Split Mountain anticline and the south flank rising gently to the 

southeast toward the axis o£ the broad Section Ridge anticline. A 

northeast dip in the Wlh see. 6, T. 5 S., R. 23 E., suggests a saddle, or 

shallowing o£ the syncline, near the boundary between Rs. 22 and 

23 E., but this dip may be a result o£ undetected faulting near the axis. 

NEAL DOME 

Neal dome, named £or Charles Neal, o£ Vernal, who has held the 

leases £or oil and gas in this area £or many years, lies in the southwestern part o£ T. 3 S., R. 21 E., on the boundary between the highly 

faulted area west o£ D:r;y Fork and the folded area to the east. The 

structural high point o£ the £old lies in the Slh of sec. 30 at the intersection o£ Ashley Creek and Dry Fork o£ Ashley Creek. The Chinle 

£or1nation, overlain by the lower massive sandstone of the Navajo, 

is exposed in the canyon walls, and Navajo sandstone underlies the 

surface in the remaining parts o£ the area. True dips are difficult 

to find in the highly crossbedded Navajo sandstone, but a calcareouscemented, brown-weathering sandstone bed in the Elh sec. 29 and 

the Wlh sec. 28 is believed to follow a single stratigraphic horizon and 

to reflect the true structure o£ the area. 

The southwestern side of the dmne is formed by a fault, downdropped on the southwest, which extends from sec. 28, T. 3 S., R. 20 

E., in a southeasterly direction to sec. 6, T. 4 S., R. 21 E. A parallel 
STRUCTURE 121 

fault, 1 mile to the northeast, extends southeastward as far as sec. 

26, T. 3 S., R. 20 E., and may possibly extend into sec. 31, T. 3 S., R. 

21 E. However, this southeasterly continuation is difficult to prove 

because Navajo sandstone lies on both sides of the break; nevertheless, topography and stream alinement suggest such a projection. 

The southeast flank of the dome is formed by the regularly dipping 

strata of Mesozoic age along Steinaker Draw. The northeast flank 

is formed by a syncline, complicated by faulting, which extends fron1 

sec. 19, T. 3 S., R. 21 E., into sec. 28, T. 3 S., R. 21 E. A thin remnant 

of the Carmel formation is preserved in the axis of the syncline in 

the Nlh sec. 19, T. 3 S., R. 21 E., east of Ashley Creek. The northwest 

flank of the dome is formed by a shallow synclinal saddle whose axis 

lies near the township boundary between R. 20 E. and R. 21 E.· on 

Dry Fork of Ashley Creek. 

A structural closure of about 150 feet is indicated by surface dips 

and formation boundaries, but the fold does not have sufficient closure 

at depth to provide an oil trap. 

LITTLE MOUNTAIN SYNCLINES 

Two small sharp synclines, separated by a fault downthrown on 

the northeast, are present on the northwest side of Little Mountain. 

The first syncline lies high on Little Mountain in sec. 30, T. 3 S., R. 20 

E., and in the Wlh sec. 25, T. 3 S., R. 19 E., and the second syncline 

is located at a lower altitude in sees. 18 and 19, T. 3 S., R. 20 E. The 

flrst syncline involves the ~forrison formation, the Dakota sandstone, 

and the Mancos shale. It strikes east-west and is exposed for only 

a mile before it is covered by the Bishop conglomerate (Miocene~). 

Its projection beneath the Bishop is unknown, but it may be cut 

off to the east by the fault that trends N. 65° W. across the Slh sec. 

25, T. 3 S., R. 19 E., and intercepts the axis of the syncline to the west. 

The second syncline involves the same formations but it is smaller 

and less clearly defined. 

COAL MINE SYNCLINE 

The Coal Mine syncline lies in sees. 19 and 20, T. 3 S., R. 19 E., 

directly north of a small reverse fault and 2 miles west of the juncture of Mosby Creek and Deep Creek. The northern dips are all recorded in heavy sandstone beds in the upper part of the Frontier 

sandstone member of the Mancos shale. The syncline is about 2 miles 

long and is cut off both to the east and to the west by the reverse fault. 

Only a portion of the south flank of the syncline remains north of 

the fault. 

MOSBY MOUNTAIN SYNCLINE OR FAULT 

The structural conditions beneath the Bishop conglomerate on 

Mosby Mountain are unknown. The northeast strike on the strata 

111 Whiterocks Canyon and the general northwest strike of the 
122 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

faulted Mesozoic strata in the Mosby Creek area suggest a trough or 

southward-plunging synclinal axis beneath Mosby l\1:ountain. The 

proximity of the 12,000-foot contour (controlled by the Park City 

formation and Weber sandstone boundary on Lake Mountain) and 

the 17,000-foot contour (controlled by the limestone unit of Mississippian age and Uinta Mountain group boundary on the northeast side 

of Mosby Mountain) are not explained by the 20°-35° dips observed 

in the field. It is possible that the Weber sandstone and limestone 

unit of Mississipian age on the east side of :Mosby Mountain are separated by a fault, clowndropped on the southeast, that extends southward beneath Mosby Mountain and separates the area of steep clips 

in Whiterocks Canyon frmn the n1ore gently dipping, but faulted, 

strata in the Deep Creek fault zone. 

WHITEROCKS ANTICLINAL NOSE 

A bowing of strata across a southward plunging nose between 

'Vhiterocks River and Fann Creek is indicated by structure contours, 

which trend N. 30° E. across Whiterocks River, swing to east-west between Whiterocks River and Fann Creek, and trend northwesterly 

in sec. 3, T. 2 N., R. 1 W. Ho-wever, westward dips, measured in the 

lower part of the upper member of the Morgan formation in sec. 3, 

T. 2 N., R. 1 W., may be due to the slumping of great blocks of strata, 

because landslide topography is prevalent at the horizon of the black 

shale unit of Mississippian age on the west side of Far1n Creek. 

DRY FORK ANTICLINAL NOSE 

The axis of the Dry Fork nose follows, for the n1ost part, the canyon of Dry Fork of Ashley Creek. It trends about S. 30° E. and is cut 

by theN. 60° W. trending Deep Creek fault zone. That part of the 

nose extending south of Dry Fork Canyon into sees. 7 and 8, T. 3 S.~ 

R. 20 E., and sees. 1 and 12, T. 3 S., R. 19 E., is known as the Pine 

Ridge structure from the Tidewater Associated and Mohawk Oil Companies Government well 1-58-7 drilled in the SW1f4SWJ4SE~ sec. 

7, T. 3 S., R. 20 E. Weber sandstone and the Morgan formation are 

exposed in the walls of Dry Fork Canyon, and the Park City, 

Moenkopi, and Shinarump formations form the surface of the structure to the south. The surface expression of the nose in the younger 

rocks can best be seen in the SE:l;! sec. 12, T. 3 S., R. 19 E., where the 

thin, resistant Shinarump conglomerate has been breached and the 

red Moenkopi formation is exposed beneath the ledge. 

ASHLEY CREEK ANTICLINAL NOSE 

The Ashley Creek anticlinal nose extends frmn sec. 1, T. 3 S., R. 20 

E., southeastward to sec. 21, T. 3 S., R. 21 E. The fold is well defined 
STRUCTURE 123 

near the mouth of Ashley Creek where dips and strikes, together with 

elevations on the Park City and Weber formations, have controlled 

the structure contours. The southeastward extension of the fold is 

well marked by the basal boundary of the Navajo sandstone, but its 

eontinuation to the east is poorly defined in the highly crossbedded 

Navajo. It is believed, however, that the Ashley Creek nose is continuous to the east with the sharp asymmetric. fold that is revealed in 

sees. 24 and 25, T. 3 S., R. 21 E., by the trend of the ridge of Cretaceous 

strata. The Ashley Creek nose is bounded on the southwest by the 

faulted syncline which forms the northeast flank of Neal dome and 

on the northeast by a gentle trough which becomes more sharply 

defined as the synclinal axis crosses Steinaker Draw and the ridge of 

Cretaceous strata. Eastward, beyond the ridge, the fold dies out in 

the upper shale member of the Mancos shale. The fold may continue 

to the northwest beneath the Bishop conglomerate on Dry Fork Mountain, but data are lacking. 

DAVIS SPRING ANTICLINAL NOSE 

The Davis Spring anticlinal nose is situated in sees. 1 and 12, T. 2 S., 

R. 20 E. (unsectionized), and sees. 6 and 7, T. 2 S., R. 21 E., 1 mile 

cast of Ashley Creek. Southwest dips in an area of northeast regional 

E:trike are well exposed in the limestone and interbedded limestone 

and sandstone of the Morgan fonnation. The axis of the fold strikes 

south to south-southeast and dies out beneath the unconformably 

overlying Bishop conglomerate. The nose does not extend northward 

to the dip slopes and north-facing escarpment formed by the lim.estone 

unit of Mississippian age. The segments of the South Flank fault, 

which die out in sec. 1, T. 2 S., R. 20 E., may be related to the anticlinal 

nose. 

BRUSH CREEK ANTICLINAL NOSE 

The Brush Creek nose lies in the Elh of T. 2 S., R. 21 E., and the 

SW:J4 T. 2 S., R. 22 E.; it extends for a distance of 6 miles, or more, 

in a south-southeasterly direction. The fold is best exposed in the 

canyon of Brush Creek, where the strike of the strata swings abruptly 

from N. 25°-35° E. toN. 45°-50° W. and then, within a mile, it returns 

to its former trend. The fold appears to die out to the southeast where 

the flexure enters less competent beds of the Moenkopi formation. To 

the north, the flexure dies out beneath the unconformably overlying 

late Tertiary strata. The change in strike is so abrupt, and the southwest dips are so steep, that the fold has been 1nappecl as a fault down~ 

thrown to the southwest (Schultz, 1919, pl. 5). Some faulting may be 

present in the area of steep dips but it would be difficult to detect in 

the massive Weber sandstone, especially as the fault, if such exists, 

must follow Brush Creek canyon. 

2,95163-55-9 
124 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

BARKER SPRING ANTICLINAL NOSE 

Three miles northeast of the Brush Creek nose, the Barker Spring 

anticlinal nose extends frmn the E¥2 ofT. 1 S., R. 21 E., south-southeast for a distance of 9 miles to the W1;2 ofT. 2 S., R. 22 E. All rocks 

from the li1nestone unit of Mississippian age in see. 24, T. 1 S., R. 

21 E., to the ~ioenkopi formation in see. 27. T. 2 S., R. 22 E., are 

affected by the flexure. The folding in the older, n1ore competent 

rocks is 1nore gentle, and the greatest intensity of folding is in the 

upper part of the Weber sandstone and the overlying Park City forIllation in sees. 7, 17, and 18, where the beds dip as much as 25° to 

the southwest. The Barker Spring anticlinal nose dies out in the 

~ioenkopi fonnation towards the southeast. In many particulars, the 

parallel Brush Creek and Barker Spring anticlinal noses have much 

In common. 

FAULTS 

SOUTH FLANK FAULT ZONE 

A series of faults, clownthrown on the south and arrranged in echelon, bound the pre-Cambrian quartzite core of the Uinta Mountains 

from Dry Gulch eastward to Ashley Creek. The faults, although 

not a continuous break, have many similar eharacteristies whieh suggested their earlier identification as a single fault by Forrester (1937, 

p. 644), who supplied the name "South Flank" fault. The dip on the 

faults is nearly vertical although actual fault planes are not exposed. 

Some faults separate pre-Cambrian quartzite from the shale sequence 

at the top of the Uinta Mountain group and others separate pre-Cambrian quartzite from Mississippian or Pennsylvanian strata. 

The trends on the faults range frmn N. 70° E. in the headwaters of 

Dry Gulch in T. 3 N., R. 3 W., to E. near Uinta River in T. 3 N., R. 

3 W., and to N. 65°-70° vV. in Whiterocks Canyon. In Whiterocks 

Canyon, the strike of the South Flank faults conforms closely with 

the strike on the wide Deep Creek fault zone (about N. 60° W.) ; it is 

possible that the two fault systems merge in the area between Whiterocks River and Dry Fork of Ashley Creek. The agreement of trends 

in these fault systen1s 1nay be coincidental or related to a third stnh>-

tural feature, the suggested south- or southwest-trending fault beneath the Bishop eonglon1erate on Mosby Mountain. East of Whiterocks River, the strike on the fault, or faults, bounding the pre-Cambrian core of the range swings to N. 70° E., and the displacement deereases gradually and dies out a short distance east of Ashley Creek. 

DEEP CREEK FAULT ZONE 

The Deep Creek fault zone, named for the area between Little 

Mountain and Mosby Mountain in T. 3 S., R. 19 E., trends S. 60° E. 

from the canyon of Whiterocks River through Little Mountain into 
STRUCTURE 125 

the alluvial- and terrace-covered Ashley Valley. Southeastward, the 

zone is believed to connect with the faults mapped on the south side 

of the Sec.tion Ridge anticline in T. 3 S., R. 23 E., but the lack of outcrops in Ashley Valley makes this connection uncertain. The zone 

represents an area of considerable structural readjustment, because 

14 faults with displacmnents ranging frmn a few feet to several hundred feet occur in section C-C' drawn perpendicular to the strike of 

the zone. The net vertical displacement across the zone, however, is 

not great because faults downthrown to the south ahnost balance (in 

total displacmnent) faults downthrown to the north. Horizontal 

movement along a fault zone is difficult to prove, but it seems probable 

that a horizontal nwvement, the southwest side shifting towards the 

northwest, was the principal1novement along the zone and that tilted 

grabens and horsts were developed in adjustment to this horizontal 

movement. 

AGE OF DEFORMATION 

The earliest deformation in the area it: faulting of the Uinta Mountain group on the east side of the canyon of Whiterocks River. The 

faulting was followed by erosion that beveled the area and left unequal thicknesses of the upper shale or the Uinta Mountain group in 

the different fault blocks beneath the limestone unit of Mississippian 

age. TheN. 65°-70° W. trend of these faults, which are clearly preMississippian in age, and the general trend on the Deep Cre.ek fault 

zone, which affects rocks as young as the Mancos shale of Late Cretaceous age, suggest that the Deep Creek zone of faulting is the result 

of a rejuvenation of a very old line of weakness in the earth's crust. 

No sedimentary strata on the south flank of the Uinta Mountains 

represent the long period of time between the deposition of the Upper ( ? ) Cambrian Lodore fonnation and the lin1estone unit of Mississippian age. If strata were deposited in the area during this period, 

they were removed by subaerial erosion prior to the deposition of the 

limestone unit. It is not known whether the faulting in Whiterocks 

Canyon came early, or late, in the period represented by the missing 

strata. 

A second period of deformation, a gentle tilting of the area toward 

the "\Vest, took place prior to the depm:ition of the Shinarump eonglomerate. The Moenkopi formation thins from 1,120 feet along 

"\V"hiterocks River to 745 feet on the flanks of Split Mountain anticline. At least some of this thinning is due to erosion of the top of the 

Moenkopi which was exposed by regional tilting of the area. 

The principal deformation of the strata in the area followed the 

deposition of the youngest Cretaceous rocks, the Mesaverde formation, and during the deposition of the earliest Tertiary rocks. Deformation did not come as a single spasm, but as a series of Inovements, 
126 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

because no pronounced angular unconformity is present at the base 

of the Tertiary. There is very little discrepancy in dip between the 

Upper Cretaceous and the lowest Tertiary sedimentary rocks ; however, a pronounced angular unconformity is present at places where 

the Cretaceous rocks are overlain by late Tertiary rocks (the Bishop 

conglomerate of possible Miocene age) . This observation suggests 

that there was continued uplift through Paleocene, Eocene, and Oligocene time into the Miocene, when uplift had ahnost ceased. This 

movement may have been caused by continued uplift of the block underlying the Uinta Mountains, by down warping of the Uinta Basin, or 

by isostatic adjustment of the mountain and basin blocks as eroded 

sediments were transported from the 1nountains and deposited in the 

basin. The faulting and folding involved in the relative rise of the 

Uinta Mountain arch were not uniformly distributed but were concentrated in an elongate zone paralleling the axis of the uplift. This 

zone now corresponds with the area of outcrop of the strata of 

Mesozoic age. Dips in the area underlain by pre-Cambrian rocks in 

the central mass of the Uinta Mountains are gentle, and the Tertiary 

rocks of the Uinta Basin are almost flat lying. 

GEOMORPHOLOGY 

GENERAL FEATURES 

The geomorphology and late Cenozoic history of the eastern Uinta 

Mountains have been the subject of 1nany papers and much speculation since the exploration of the area by geologists and geographers 

of early Territorial Surveys. The interest in the area has centered 

on the anomalous position of the Green River, which crosses the axis 

of the Uinta Mountain uplift in a deep canyon cut in resistant rock, 

whereas an alternate course to the east would have avoided the uplift; on the relationship of the Browns Park formation to the Bishop 

conglomerate; and on the late Cenozoic history of the area, including 

the glaciation. With the exception of the glaciation, the investigators 

have given only cursory attention to the geomorphic evidence present 

on the south flank of the range, and they quote the observations of 

J. W. Powell in their discussions. 

GILBERT PEAK SURF ACE 

The Gilbert Peak surface, upon which the Bishop conglomerate 

was deposited, is a surface of very low relief that usually slopes radially from the higher peaks and northward and southward from 

the crest of the range. The Gilbert Peak surface, now exposed, was 

cut on the quartzite of the Uinta Mountain group; it is due to the resistance of this formation that exposed portions of the erosion surface have been preserved. This surface is shown on plate 3 between 

Whiterocks River and Paradise Creek, northwest of the East Fork 
GEOMORPHOLOGY 127 

of Dry Fork of Ashley Creek, and on the north side of Taylor Mountain. On the younger rocks of Paleozoic and Mesozoic age, the Gilbert Peak surface is preserved only where it is protected by the overlying Bishop conglomerate; it appears as a line marking the lower 

boundary of the Bishop. The surface has been warped into a shallow 

syncline whose axis is parallel to, and approximately 3 miles south 

of, the South Flank fault zone. The altitude of the surface (lower 

boundary of the bishop) decreases gradually from Uinta River eastward to Diamond Mountain. The surface probably is continued eastward in the for1n of the flat-topped crest of Split Mountain and Blue 

Mountain. 

Coarse-grained sediments derived frmn glacial erosion are classified as "glacial moraine" or as "glacial outwash material." These 

subdivisions are further divided on their relative time of formation 

into moraines of earliest glaciation, moraines of maxi1num glaciation, 

moraines of latest glaciation, and their respective outwash plains. 

The moraines were deposited directly by ice and still retain much of 

their original form. The glacial outwash material has been deposited 

by streams flowing frmn the glaciers. In the field, and during subsequent stereoscopic study of the contact aerial photographs, end 

moraines, ground moraines, and lateral moraines have been recognized, but due to the difficulty of drawing boundaries between the 

different types of moraines, all morainal material deposited by the 

same glacial advance is grouped together. Deposits of proglacial 

streams are classified as glacial outwash material when the source of 

the deposit is sufficiently close to warrant correlation, and they are 

termed erosion surfaces (see Vernal and Thornburg erosion surfaces 

above) when the gravel and boulder cover is thin and so far removed 

from its source that correlation with glacial deposits is problematic. 

South of the Uinta Mountain front, erosion of rocks of Mesozoic 

and Tertiary age has formed an area of lower relief. Three gravelveneered erosion surfaces of probable Quaternary age have been differentiated in the mapping. The older terrace, here named the "Jensen surface" (Qj), is subdivided into an upper surface (Qj 1 ) and a 

lower surface (Qj 2 ). Remnants of the Jensen surface flank the 

higher mountains or cap interstream divides. The lower surfaces, the 

"Vernal" ( Qtv) and the "Thornburg" ( Qtt) strath terraces, parallel 

the present stream channels. The Vernal surface, as mapped along 

Ashley Creek, includes two closely related strath terraces (Qtv1 ) 

and (Qtvz). 

The basic data bearing on the late Cenozoic history of the area 

have been assembled from plate 1, and the photomosaics and are consolidated on plate 3 which shows the erosion surfaces and deposits 

of late Cenozoic age in the Uinta River-Brush Creek area. The main 

mass of the Uinta Mountains, as shown on plates 1 and 3, extends fron1 
128 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Jefferson Park on the west, eastward to Diamond Mountain and forms 

a high, rolling, dissected plateau that slopes southward from the crest 

of the range and decreases in elevation toward the east. The similarity of the summit elevations of the higher portions of this plateau 

are a striking feature of the gemnorphology of the mountains. This 

high-level surface, herein named the "Lake Mountain" surface, is cut 

on the Bishop conglmnerate which, in turn, rests on the "Gilbert 

Peak" surface, which was named by Bradley (1936, p. 169) from the 

north flank of the Uinta Mountains. The Gilbert Peak and Lake 

Mountain surfaces are believed to be late Tertiary in age. 

LAKE MOUNTAIN SURFACE 

The upper surface of Jefferson Park, Pole Mountain, Mosby Mountain, Lake Mountain, Dry Fork Mountain, Little Mountain, the area 

between Ashley Creek and Brush Creek, the area between Brush 

Creek and Little Brush Creek, and Dia1nond Mountain are remnants 

of a once extensive erosional surface cut on the Bishop conglmnerate. 

The surface slopes southward frmn the crest of the Uinta Mountains 

at a rate of 65 to 100 feet per mile. It also slopes, or has been tilted 

eastward, at a rate of 30 to 35 feet per n1.ile, or from an elevation of 

10,300 feet at Jefferson Park to 7,800 feet on a few isolated flat-topped 

buttes on Dianwnd Mountain. The surface is here named the "Lake 

Mountain erosion surface" for the flat-topped mountain in T. 2 S., R. 

19 E. The Bishop conglmnerate presumably spread southward and 

eastward from the crest of the Uinta Mountains sometime during late 

Tertiary ti1ne, and the Lake Mountain surface was developed as a 

final stage of deposition or by later erosion. The surface apparently 

extended northward from Diamond Mountain into the area now occupied by the tributaries of Pot Creek. It was on this surface that the 

antecedents of the present Green River 1nust have eroded headwarcl 

or have been superposed from uneonformable cover aeross the axis 

of the Uinta Mountain arch and Split Mountain anticline. With the 

inauguration of exterior drainage through the aneestral Green River 

to the Colorado River, erosion of the Tertiary sediments of the Uinta 

Basin and dissection of the Lake Mountain surface began. The Lake 

Mountain surface is n1.ore fully preserved west of Ashley Creek than on 

Diamond Mountain. 

JENSEN SURF ACE 

The erosion of the early Tertiary sedimentary rocks in the central 

part of the Uinta Basin and the removal of the Bishop conglmnerate 

from the area to the south of the present exposures required vigorous 

erosion and a long period of time. The erosion was not continuous, 

and pauses in the late erosional history of the area are recorded by 

two, or more, gravel-covered erosion surfaces. These surfaces are best 
GEOMORPHOLOGY 129 

preserved on the upper shale 1nember of the Mancos shale between 

Ashley Creek and Brush Creek and are here named the "Jensen surfaces," for the community of Jensen on the Green River between the 

mouths of Brush Creek and Ashley Creek. The higher of the surfaces ( Qh) is 50 to 7 5 feet above another surface ( Qj 2 ) , which in 

turn, is 250 to 300 feet above the present stream level. A veneer of 

caliche-coated gravel and boulders, ranging from 5 to 10 feet in thickness, caps these surfaces and contains representative rock types from 

the Bishop conglomerate. The pebbles and boulders on the surface 

are well-rounded. The surface slopes away from the higher hills at 

a rate of 100 to 200 feet per mile. 

Those surfaces designated Qh are correlated because they have 

similar characteristics and are adjacent to surfaces 50 or 1nore feet 

lower; they may be remnants of one continuous surface. The gradient 

of the surfaces, the thickness of the gravel co-ver, and the geographical 

location of the Jensen surface abutting higher hills are characteristic 

of pediments cut under arid conditions. The lower Jensen surface 

( C~j z) is well exposed on Sunshine Bench in Ts. 4 and 5 S., R. 22 E., 

between Ashley Creek and Brush Creek. The higher surface on Sunshine Bench is represented by a cluster of small buttes in sec. 18, T. 5 

S., R. 22 E. Surfaces correlated with Qj 1 and Qj 2, along Brush Creek 

and north of Split Mountain, are n1ore abundant and, except for a 

difference in elevation, they 1naintain a close relationship to each 

other. 

The Jensen surface has also been recognized on the east and south 

sides of Little Mountain, the west side of Ashley Creek, east and west 

of Whiterocks River, and betweenlTinta River and Dry Gulch. These 

surfaces probably truncated the hogback formed by the Frontier sandstone member of the Mancos shale, from Little Mountain eastward to 

Dia1nond Mountain, at about the altitude of the present crest of the 

escarpment. The surfaces were formed during periods of crustal 

stability, uniform climate, and constant base level of the 1naster stream 

in the area. Lateral planation and slope wash were the dominant 

agencies during formation. 

YOUNGER EROSION SURFACES 

One hundred and fifty to 180 feet below the Jensen surface ancl100 

to 125. feet above the present stream level of Ashley Creek there is a 

second and lower erosion surface, here na1ned the "Vernal strath terrace" ( Qtv1 ), for its develop1nent along Ashley Creek, east of Vernal, 

Utah. A second and slightly lower terrace (Qtv2 ), grouped with the 

Vernal surface, is present along the west side of Ashley Creek from 

sec. 9 to sec. 36, T. 5 S., R. 22 E., and along the Green River from 

sec. 24, T. 5 S., R 22 E., northeastward to Brush Creek. Terraces along 
130 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

the east side of the Green River and a rolling upland surface extending 

eastward from the river are correlated with the lower Vernal surface. The soil and debris that is mapped with the lower Vernal surface east of the Green River may be, in part, wind-transported material 

that was deposited during the time that the lower Vernal surfa.ce was 

being cut in the Ashley Valley. 

The main Vernal terrace ( Qtv or Qtv 1 ) is cut on the soft clay shale 

of the upper shale member of the Mancos shale; it is covered with 5 

to 10 feet of boulders and coarse gravel. Most of the boulders are 

well-rounded, red quartzite of the Uinta Mountain group. Springs 

and seeps mark the base of the gravel cover on the west side of Ashley 

Creek. The main Vernal surface probably had its origin in the lateral planation of Ashley Creek during the interglacial stage that followed maximum glaciation in the Uinta Mountains; it tentatively is 

correlated with the glacial outwash from that glaciation. 

Located 50 feet below the Vernal surface and 55 feet above the 

present low water level of Ashley Creek, there is a younger erosion 

surface called the "Thornburg strath terrace," which was named for 

Fort Thornburg (an early Army post located in the Ashley Valley 

north of Vernal). The Thornburg surface is also cut in soft Mancos 

shale and veneered with 5 to 10 feet of red quartzite boulders. It 

had the smallest extent of any of the erosion surfaces, and the present 

flood plain of Ashley Creek has largely destroyed its original development. In all probability, it dates from the closing phase of the 

latest glaciation in the mountains. 

GLACIAL DEPOS.ITS 

Distribution.-Atwood (1909, p. 12 and pl. 4) has shown that the 

the largest and longest glaciers in the Uinta Mountains had their 

source in the high peaks near the central part of the range and that 

they rapidly diminished in size and length towards the east and the 

west. For the most part, the size of the glaciers was directly proportional to their drainage areas. The eastward decrease in size and 

maximum extent of the glaciers is shown by the areal extent of the 

glacial deposits on the map (pl. 3). 

The most extensive glacial deposits in the area are found either in 

the canyon of Uinta Riv_er, or adjacent to it. Massive moraines also 

are present in the valley of Dry Gulch to the west of lJinta River. 

l\1orainal deposits on Whiterocks River and on Dry Gulch of Ashley 

Creek are much less prominent than those on Uinta River. The broad 

flat area of glacial terrain in the headwaters of Ashley Creek probably was occupied by a neve field. The ice formed at that place must. 

have been thin; thus it performed less erosion and failed to move 

down the valley of Ashley Creek. 
GEOMORPHOLOGY 131 

Lithology and dating of glacial advances. -The rock fragments 

making up the morainal deposits and glacial outwash plains are almost exclusively of red, tan, and white quartzite and quartzitic sandstone derived :from the Uinta Mountain group. The lack of coarsegrained igneous rocks, limestone and other rocks in the central part 

of the range, which would yield a soil profile that would vary in depth 

with the time of exposure to natural weathering processes, makes it 

difficult to determine the relative ages of the separate ice advances in 

the Uinta Mountains. In the absence of soil profiles, the dating of 

successive ice advances is based upon: (1) relative :freshness of 

geomorphic and topographic :features (steepness of end moraines, dissection by later outwash waters, abundance of small lakes, etc.), (2) 

relationship of surfaces underlying different moraines, ( 3) relationship of lateral moraines to the end moraines of other ice advances, 

and ( 4) correlation of terrace deposits related to certain glacial 

n1oraines and outwash plains. Although the use of these criteria does 

not give the relative time between successive ice advances, a very satisfactory chronological succession and correlation of moraines, outwash plains, and terrace deposits is possible within the area. 

Earliest glaciation.-!The moraine of earliest glaciation rests on a 

remnant of the Jensen erosion surface in the Slh T. 2 N., R. 2 W., 

located 1 to 3 miles west of Uinta River. This earlier moraine has 

been considerably eroded by outwash waters, but it still includes shallow closed depressions, one of which has been converted and enlarged 

to serve as an Indian Service reservoir by building a dam on the lower 

side. The end moraine is 100 to 150 feet high, but it presents gently 

rounded contours and a fairly gentle front. Boulders and blocks of 

massive red quartzite are prominent constituents of the morainal 

material. The end moraine is cut off on a line from the NE~ sec. 

21 to the center of sec. 8, T. 2 N., R. 2 W., by the lateral moraine formed 

by the most recent ice advance in Uinta Canyon. Probably because 

the Jensen erosion surface has been largely destroyed adjacent to 

canyons down which the glaciers moved, this earliest moraine is not 

present elsewhere in the area. Glacial outwash from earlier glaciation formed an outwash plain that must have stretched southward 

for many miles. The surface of the outwash is only 10 to 15 feet 

below the level of the Jensen surface adjacent to the corresponding 

end moraine; however, a difference in elevation of 300 to 500 feet 

separates the surfaces in the NE~ T. 1 N., R. 3 W. Although no 

morainal material of this earliest glaciation is located along Whiterocks River, isolated remnants of an erosion surface, 300 to 400 feet 

below the Jensen surface and similar to the outwash plain of the 

earliest glaciation west of Uinta Canyon, is present in sees. 23, 26, 

and 35, T. 2 N., R. 1 W. The surface is continued to the southwest 
132 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

by channels in sec. 34, and by outwash debris in sees. 20, 21, 27, 28, 

29, 33, and 34, T. 2 N., R. 1 W., and sees. 3 and 4 of T. 1 N., R. 1 W. 

M aximu1n glaciation.-The moraine of maximum glaciation in 

Uinta Canyon reaches an altitude of 7,000 feet on the southern border 

ofT. 2 N. The end n1oraine, composed of angular pieces of quartzite, 

forms a ridge, 75 to 100 feet high, which swings eastward aeross the 

southern border of sees. 35 and 36 towards the Uinta River. More 

recent proglacial strea1ns have removed much of this end moraine, 

which at one tin1e must have joined the massive lateral1noraine that 

is now terminated by the lTinta River in sec. 25, T. 2 N., R. 2 W., 

on the east side of Uinta Canyon. The lateral moraines of the 

1naxin1mn glaeiation throughout most of the length of Uinta Canyon 

were altered by the latest glaciation. This later glaciation carried 

very little roek debris, and Inost of the Inassive lateral moraine on 

both the east and west sides of Uinta Canyon probably was deposited 

by the Inaximum glaciation. The ridge, which separates the channel 

of Pole Creek frmn Uinta Canyon in the Elh T. 2 N., R. 2 W., and 

which therefore causes the two strea1ns to flow parallel for a distanee 

of 4 n1iles, is probably underlain by lateral Inoraine with a core of 

rocks of Paleozoic, Mesozoic, and Tertiary age. The present channel 

of Uinta River has been incised into the end Inoraine blocking the 

canyon Inouth to forn1 a narrow noteh 100 to 200 feet deep. 

A sn1all iee lobe diverged frmn the main glaeier flowing in Uinta 

Canyon in sec. 3, T. 2 N., R. 2 vV., and deposited an end n1oraine in 

sees. 11 and 12 in the Pole Creek: drainage. The 1noraine still shows 

a few closed depressions, but the eontonrs are gently rounded, thus 

indicating that considerable time for erosion has elapsed since deposition. Two glaeial moraines showing a similar stage of dissection 

are found in Pole Creek tributaries. One Inoraine, located in the 

main ehannel of Pole Creek, terminates in the Nlh sec. 26, T. 3 N.~ 

R. 2 W., and the other moraine, located in the southeastern continuation of Clover Creek, reaches into sec. 34, T. 3 N., R. 2 W. Clover 

Creek, during Pleistoeene time, was a tributary of Pole Creek; reeently, it has breaehed the lateral moraine of Uinta Canyon and has 

entered Uinta River in sec. 32, T. 3 N., R. 2 vV. 

In Dry Gulch, the Inoraine that is eorrelated with the maximum 

glaciation in Uinta River reaehes to an approximate altitude of 8,200 

feet in sees. 20 and 21, T. 2 N., R. 3 vV. The morainal front is steep 

and well defined, and sn1all lakes and closed depressions dot the area 

behind the. front. The glacier that deposited this end moraine probably had its souree in the headwaters of Dry Guleh and in the West 

Fork of Dry Gulch. Glacial outwash material from this glaciation 

formed a plain now preserved in sees. 20, 21, an9- 28, T. 2 N., R. 3 W., 

and in the NW. part of T.1 N., ·R. 3 W. . 
GEOMORPHOLOGY 133 

The end moraine on \Vhiterocks River, correlated with the Inaximum glaciation in Uinta Canyon, descended to an altitude of 7,200 

feet in sec. 18, T. 2 N., R. 1 E. This moraine has been greatly altered 

by pro glacial streams, and the topographic expression has been largely 

destroyed. Large quartzite blocks dot the surface of the moraine. 

Most of the lateral moraines on canyon walls have been destroyed by 

the slumping of the shale in the upper member of the Uinta Mountain 

group. 

Glacial stages in Dry Fork of Ashley Creek cannot be differentiated" 

By means of comparison with Uinta Canyon, most of the morainal 

material that clogs the canyon of Dry Fork north of Lake Mountain 

and east of Mosby Mountain is found to belong to the stage of maximum glacial advance. The glacier that flowed down the valley of 

Dry Fork stayed well within the mountain front, reaching no lower 

than an altitude of 8,000 feet. It was broader than the glaciers in 

the canyons of Uinta River and Whiterocks River, and it left a wide 

belt of poorly drained bogs and small lakes on ·the eastern side of 

l\Iosby Creek and on the divide between the North Fork of Dry Fork 

and Dry Fork. At places, as in the area east of Mosby Mountain, 

it flowed around islands of hard quartzite of the Uinta Mountain 

group. During its farthest advance, it extended into the drainage 

of the North Fork of Dry Fork and in the 1nain channel of Dry Fork, 

to a point directly north of Lake Mountain. The end moraine marking this maximum advance is very massive, and the only breach that 

has been 1nade by the present stream in Dry Fork is a narrow 

V -shaped notch. At its maxim tun extent, the glacial ice formed a 

short lobe that extended into the headwaters of the present Mosby 

Creek, where it deposited a rocky 1norainal ridge. The failure of the 

glacier to extend farther down the main canyon in Dry Fork is probably due to the inability of the ice advance to negotiate the sharp 

bend in the original stream channel. 

No definite correlation is possible between the nev~e field (which 

led to the development of the wide, poorly drained area of lakes, 

swan1ps, and forest in the headwaters of Ashley Creek) and the glacial 

stages recognized in Uinta Canyon. However, it is probable that 

the neve field was in existence at the ti1ne of maximum glacial development in the canyons to the west. 

Late8t glaciation.-The most recent glacier to occupy the canyon of 

Uinta River failed (by more than a mile) to reach as far south as the 

previous ice advance. Although it was not heavily laden with glacial 

rl_ebris, it deposited a small end moraine and prominent latera] 

moraines, which extended along both the western and eastern sides 

of the canyon to a height of more than 800 feet above the present valley floor in T. 3 N., R. 2 W. On the west side of Uinta River, the 
134 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

lateral moraine is 150 to 200 feet high, and it dams the streams entering from the west to form small lakes or marshes. On the east side 

of the canyon, the lateral moraine is not distinct in T. 2 N. where it 

forms a part of the ridge dividing Pole Creek from Uinta River. 

Northward, in T. 3 N., the lateral n1oraine forms a ridge and trench 

that have been breached at several places by streams entering from the 

east. A series of ice-contact features (areas of slump and ridges 

parallel to the edge of the glacier ice) mark the ground moraine on 

the east side of Uinta River near the middle of T. 2 N., R. 2 W., and 

provide abundant evidence that ice occupied the canyon very recently. 

End moraines in tributaries of Pole Creek correlated with tlw 

1nost recent glacial advance in Uinta Canyon are marked by an extremely youthful appearance, steep fronts, and a poorly drained, hummocky topography covered by dense undergrowth. The moraine in 

the southeastern extension of Clover Creek reached to the SE14 sec. 28~ 

T. 3 N., R. 2 vV. It has the most youthful appearance of any moraine 

in the area because the melt water, which would have pa.rtly destroyed 

the ice-deposited rock, is diverted to the Uinta River upstream from 

the massive end moraine. 

Two moraines in the Dry Gulch area are correlated with the most 

recent glacial advance. The first 1noraine lies in sees. 5, 8, and 17~ 

T. 2 N., R. 3 W. It is dotted with small lakes and has a steep foot 

that rises above the overridden moraine of n1axi1num glaciation. It 

came from the West Fork of Dry Gulch, west of the mapped aren. 

The second moraine lies in sec. 4, T. 2 N., R. 3 W., and sec. 33, T. 3 N., 

R. 3 W., across the main channel of Dry Fork. The moraine has 

dammed the main strean1 to fonn Heller Lake in sec. 33, and the overflow from the lake is slowly cutting a deeper channel through the 

moraine. 

The end moraine of the latest glaciation in Whiterocks Canyon 

reaches to an altitude of 7,300 feet and extends to the center of sec. 

7, T. 2 N., R. 1 E. Most of the 1norainal material is on the east side 

of the canyon because the stream hugs the west bank and has removed 

all but a small quantity of glacial debris from that side. The thickest 

part of the moraine occurs in1mediately south of the narrowing of the 

canyon (which was caused by the resistant walls of the limestone 

unit of Mississippian age). Whiterocks River exposes excellent cross 

sections of the n1orainal material along its banks. The thickness of 

the ice-deposited 1naterial decreases abruptly in the northern part of 

sec. 7, and a poorly draif1ed ground moraine occupies the canyon to the 

north. Definite lateral moraines related to this ice advance are not 

as prominent as in Uinta Canyon but the height of the ice deposits can 

be easily traced in the field. 
GEOMORPHOLOGY 135 

The canyon of Dry Fork of Ashley Creek and the neve field in the 

headwaters of Ashley Creek probably were occupied by ice during the 

latest glaciation period. However, the deposits of this stage cannot 

be differentiated from the deposits of maximum glaciation, and therefore they have been discussed in that section of this report. 

Quartzite debris in the upper tributaries of Brush Creek and Little 

Brush Creek suggests the occurrence of ice transport but the area lacks 

any typical glacial depositional features. The valleys are wide and 

fiat. 

Correlation with glacial stages in adjacent areas.-lt is difficult to 

correlate glacial advances in the Uinta River-Brush Creek area with 

the stages recognized by Bradley (1936, p.194-195) on the north flank 

of the Uinta Mountains. The earliest glacial stage that moved outward on the Jensen surface probably corresponds to Bradley's Little 

Dry glacial stage, which advanced upon the Bear Mountain erosion 

surface. Bradley (1936, p. 196) by analogy correlates his Little Dry 

glacial stage with the Buffalo stage in the Wind River Range which 

Blackwelder (1932, p. 918) has suggested may be the equivalent of 

the l{ansan stage of the standard section. The Little Dry glacial 

~age 1nay be correlative with the stage that elsewhere in the Rocky 

Mountains is correlated with Atwood and Mather's (1932, p. 82-83) 

Cerro stage of glaciation in the San Juan Mountains. The maximum 

and latest glacial stages probably correspond to Bradley's Black Fork 

and Smith Fork stages; the latter is definitely of Wisconsin age. 

CANYON DEVELOPMENT 

The 1nost rugged and picturesque scenery on the south flank oi tl..:~ 

Uinta Mountains is in the deep canyons that were cut by glacial ice 

and strean1s flowing from the higher portions of the mountains. Uinta. 

Canyon and Whiterocks Canyon are steep-walled, flat-bottomed, or 

U-shaped valleys carved by g,lacier ice. The melt water from the 

glacier in Dry Fork of Ashley Creek and the melt water from the 

glacier in the headwater of the West Fork of Ashley Creek are responsible for cutting the steep V-shaped lower canyons of Dry Fork 

and Ashley Creek. Melt waters from the glacier in the headwaters 

of Ashley Creek also flowed southward to cut Black Canyon, and the 

stream to the west, known as East Fork of Dry Fork of Ashley Creek. 

Melt waters from the glacier in Dry Fork also cut the channel of 

Paradise Creek, a tributary of Whiterocks River. To a certain extent, 

the deep canyons of Brush Creek and Little Brush Creek, which cross 

the Weber sandstone, have been carved by streams swollen by the high 

precipitation of Pleistocene time; perhaps the melting of small glaciers or nev~e fields in their headwaters aided in the development of 

the canyons. 
· 136 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

ECONOMIC GEOLOGY 

COAL 

I ntrodttwt-ion.-Coal beds of variable thickness occur in the upper 

part of the Frontier sandstone member of the J\{ancos shale. Coal has 

been recognized in the western part of T. 3 S., R. 19 E., in the Deep 

Creek area, eastward for a distance of 25 1niles to the northwestern 

corner ofT. 2 S., R. 23 E. and east of Little Brush Creek. It is also 

present south of the Island Park syncline on the westward extension 

of the Split Mountain anticline into T. 4 S., R. 22 E. Workable coal 

is not continuous, the individual heels occur as discontinuous lenses 

in brown shale. They are broken by faulting, concealed by unconformably overlying younger deposits, and may have been rmnoved by 

erosion prior to the deposition of the overlying Frontier deposits. 

The coalbearing series is believed to be continuous across the area but 

the coal is not necessarily contemporaneous in deposition. 

Coal is also reported to be present in the black shale unit of Mississippian age on Farm Creek and low-grade lignite is found in the 

Mesaverde for1nation along The Hi1n Rock (the extension of Asphalt 

Ridge ·east of the Green River). However, these occurrences are of 

minor importance. 

The areas that have been n1ined for coal in the Frontier sandstone 

mmnber of the Mancos shale are : ( 1) west of Deep Creek, ( 2) in 

Coal Mine Draw northwest of Vernal, (3) east and south of Steinaker 

Draw, and ( 4) along Brush Creek on the westward extension of the 

Split Mountain anticline. The areas of maximun1 development are 

largely controlled by the thickness of the coal, which locally thickens 

frmn an average of about 2 feet to 4 or 5 feet. Of secondary importance in regard to utilization is the distance of these local areas of 

thicker coal to the towns of Vernal, Fort Duchesne, and Roosevelt, 

Utah. 

Maximum development of coal deposits in the Frontier sandstone 

1nember of the Mancos shale occurred frmn 1899 to 1929, when the 

isolated geographic position of the Uinta Basin, the lack of transportation facilities, and the high cost of freight into the basin made it necessary for the area to be almost self -sufficient. During this period, smne 

individuals dug coal for their own use in small mines, and the larger 

mines in Coal Mine Draw, in Deep Creek, and along Brush Creek 

were developed. The decline in coal mining in the area was not 

prompted by a lack of coal or by poor quality of the mined product; 

it was caused by economic factors, including: (1) establishment of 

an oil refinery on the east bank of the Green Hiver at Jensen making 

available a cheaper and 1nore convenient fuel, (2) the development 

of the Ashley Creek gas field and t11e pi ping of the gas to the town 
ECONOMIC GEOLOGY 137 

of Vernal for heating and cooking, ( 3) the manufacture of hydroelectric power on Ashley Creek, ( 4) the improvement of roads and 

truck transportation and the cutting of mine props in the Uinta 

Mountains for the mines in Carbon County to the southwest (trucks 

taking props to the mine return with coal), and ( 5) the development 

in 1948-49 of the old Ashley Creek gas field as an oilfield. During the 

fall of 1947, only the Wardle mine (previously known as the Joe Rich 

mine) in SW1MSW1M sec. 2, T. 4 S., R. 20 E., was in operation, although others 1night have been worked for short periods by individuals to supply their own needs. Probably not more than six mines 

in the entire area were operated during the period 1927-47. 

Previous geologic investigations of the coal deposits.-Although 

coal deposits in the lower part of the Mancos shale had been noted by 

Hayden and Powell, the first survey devoted primarily to coal resources was by Hoyt S. Gale and party in 1907, and the report was 

published as U. S. Geological Survey Bulletin 415 (1910, p. 204-219). 

Gale's work extended westward to Coal Mine Draw on the east side 

of Little Mountain and 7 miles west of Vernal, Utah. The Deep 

Creek area of the Vernal coal district to the west of Little Mountain 

was studied by C. T. Lupton and partly in 1910 and was published 

as part of Geological Survey Bulletin 471 (1912, p. 579-594). While 

surveying the Deep Creek area, Lupton and his party also visited 

the mines on Brush Creek and north of Vernal (which had been 

studied by Gale) and measured many detailed coal sections in that 

area. In 1920, C. A. Allen, of the U. S. Bureau of Mines, sampled 

a coal section at the Rasm'ussen mine in the Deep Creek area; J. J. 

Bourquin and W. F. Murray, of the Conservation Division, U. S. 

Geological Survey, Ineasured and sampled five detailed coal sections 

at active mines in the area in 1926. Since that time, other members 

of the Conservation Division have measured coal sections in mines 

operated on Government land. 

To give as complete a picture as possible of coal occurring in the 

Frontier sandstone member of the Mancos shale in the Vernal area, 

selected coal sections at intervals across the area are given in plate 4. 

These include a few sections given in Bulletins 415 and 471, and many 

other coal sections measured by other geologists whose work has not 

been published. Where 1nore than one section was available for a 

mine, a single representative section is given. All sections for which 

analyses have been made are included in plate 4, in order to give a 

complete picture of the chemical and physical composition of the 

coal. Earlier work is also included because exposed coal sections 

rapidly deteriorate, and coal sections frmn mines or prospects that 

were active 20 to 40 years ago (and measured at that time) are far 

superior to sections that can be measured at the present time. 
138 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Detailed stratigraphy of coal occurrences.-The· detailed stratigraphy of the coal-producing beds as given on plate 4 is obtained 

from 52 n1easured sections, extending frmn the Warburton n1ine in 

the western part of the Deep Creek area, eastward to the 1nines and 

prospects on Brush Creek. The sections are correlated by alining the 

top of the coal horizon. The position of the coal in respect to the 

sandstone beds of the Frontier member of the Mancos shale changes 

progressively eastward across the area from a position lying above 

the sandstone along Deep Creek to 65 feet below the top of the sandstone at Coal Mine Draw east of Little Brush Creek, and then to 90 

feet below the top of the sandstone at the Collier mine, as is shown 

in the following hand -leveled sections : 

Coal Mine D1·aw section 

[Measured by D. M. Kinney] 

Mancos shale : 

Upper shale member: 

Frontier sandstone member: Feet 

Sandstone, tan to white, in part crossbedded, :fine- to mediumgrained ____________________________________________________ 60.0 

Gray shale, with sandstone pebbles____________________________ . 25 

Shal~ sandy, gray, carbonaceous______________________________ .25 

Sandstone, white, poorly bedded_______________________________ 5. 5 

Coal-------------------------------------------------------- .9 

Shale, black, carbonaceous____________________________________ . 1 

'Coal-------------------------------------------------------- .25 

Shale, gray, with conchoidal fracture__________________________ 2. 5 

Shale, black, carbonaceaus, with streaks of coaly materiaL.:.______ 2.1 

Sandstone, thick (base of measured section). 

Collier Mine section 

[Measured by D. M. Kinney] 

Feet 

Sandstone, light-gray, tan-weathering, massive, :fine-grained____ 19. 0 

Covered, sandstone, light-gray, thin-bedded with shale partings__ 18. 8 

Sandstone, light-gray, tan-weathering, fine-grained, ledge forming_ 3. 0 

Covered; sandstone, light-gray, thin-bedded and shale__________ 6. 0 

Sandstone, light-gray, :fine-grained, hard, massive_______________ 3. 5 

Covered, probably light-gray, shale and interbedded fine-grained sandstone _________________________________________________ 27.0 

Sandstone, light-gray, tan-weathering, :fine-grained, hard________ 1. 5 

Sandstone, thin-bedded, light-gray, and sandy, light-gray shale__ 8. 0 

Sandstone, light-gray, thin-bedded, :fine- to medium-grained_____ 4. 3 

Coal, with shaly streaks______________________________________ 3. 5 

Covered; shale and thin-bedded, medium-grained, carbonaceous 

gray sandstone------------~-------------------------------- 20.0 

Sandstone, light-gray, massive, medium-grained, crossbedded____ 8. 0 
ECONOMIC GEOLOGY 139 

The continuity of the coal beds cannot be proved because of the 

nature of the outcrops and because of interruptions of exposures by 

unconformably overlying deposits, particularly on Little Mountain, 

in Ashley Valley, and on Diamond Mountain. The coal sections in T. 

4 S., R. 22 E., along Brush Creek, are separated from exposures to the 

west and north by the upper member of the Mancos shale in the Island 

Park syncline. 

In coal section No. 33, a thin upper coal, located 8 feet above what 

has been interpreted as the main coal horizon, was measured. Gale 

(1910, p. 217) mentions, "Another small coal bed about 8 or 10 inches 

thick crops in the hillside above the main entry [of the Joseph Rich 

mine]." The measured section at the Joseph Rich mine (coal section 

No. 14) shows a coal bed at the same general stratigraphic position as 

the thin upper coal of coal section No. 33. Careful search of this 

horizon in the intervening area may result in identification of the 

upper bed elsewhere. However, it probably is not of economic importance because it would have been opened by prospects between 

Ashley Creek and Brush Creek. 

Oharaoter of the ooal.-Fresh surfaces of the coal are black and 

vitreous, but weathered surfaces are dull. The coal is hard and 

brittle, and its fracture ranges from uneven to regular. The structure 

of the coal is prominently bedded only on weathered surfaces. 

As can be noted from the plotted sections on plate 4, the coal is 

interbedded with bone, dirty coal, and shale, thus making physical 

separation of waste difficult. 

Oherr~.Jioal oharaoteristios.-All coal analyses in the Vernal district 

(including 16 analyses frmn 12 1nines) are given in the table below. 

Analyses are listed by number and 1nine name to correspond to the 

numbers of the graphic sections given on plate 4. In addition to the 

proxilnate, sulfur, air-drying loss, and calorific values, the sampler, 

the analyst, alternate mine na1nes, laboratory number, ultimate analysis, and softening temperature are given where such information is 

available. 

Analyses Nos. 5,511, 5,753, 5,754, 5,755, 5,515, 5,517, and 5,518 (bearing laboratory numbers in the 5,000 series) were made at Pittsburgh, 

where it was later discovered that the natural gas burners gave high 

results for fixed carbon. These analyses cannot be used in the classification of coal (American Society for Testing Materials, 1938, p. 6) 

but all acceptable analyses indicate that the coal in the Frontier sandstone member of the Mancos shale in the Vernal district should be 

classed as high volatile C bituminous, in accordance with the classification of the American Society for Testing Materials ( 1938, p. ~). 

295163-55-10 
Goal analyses f'rotn 12 rnines in the Vernal distr·,ict 1-' 

~ 

[Coal sections numbered to correspond with plate 4. Condition of sample: 1, as received; 2, dry coal; 3, moisture and ash-free] 0 

Sample Proximate (percent) Ultimate (percent) Air- Calorific value Soften- 0 

Coal I 

I Laboca-1 Condtdrying ing t_:>:j 

section Mine (locality) 

Ash I Sulfur I H:ec;ro-1 Carbon 

loss 

Calories I B. t. u. 

temper- 0 No. Mois- lvolatilel Fixed Nitro- I Oxygen (per- ature t"l 

tory No. tion 0 ture matter carbon gen cent) (oF.) 0 

,_. ,_. r= ~~~~~~~J~~~~~~~ ------ ~ 

3 I """'""'""" ncoe., lll-'t off •lope 300 foot I ' 83, 2281 1 9.6 37.0 46.4 4.0 6, 485 11, 674 2, 510 0 

from surface, cover 50 feet. 2 40.9 51.4 7.6 1. 0 -------- ------- 7,174 12,915 ":1 

3 44.3 55.6 1.1 -------- -------- -------- -------- 7, 766 13,980 q 2 I F. A. Gross mine ______________________ 2 A23388 1 8.8 36.8 44.3 10.1 2.4 5. 5 63.0 1.1 17.9 2.1 6,189 11, 140 H -------- z 2 40.3 48.6 11.1 2.6 4. 9 69.1 1.2 11.1 -------- 6, 783 12,210 -------- 1-3 3 45.3 54.7 2. 9 5. 5 77.7 1.3 12.6 -------- 7, 628 13,730 -------- > 4 I Reynolds mine------------------------1 310,812 I 1 11.3 35.6 46.4 6. 7 . 95 -------- -------- -------- -------- 4. 5 6, 322 11,380 2, 740 ::d 2 -------- 40.1 52.3 7. 6 1. 07 -------- -------- -------- -------- -------- 7,128 12,830 -------- H 

< 3 43.3 56.6 1.16 -------- -------- -------- -------- -------- 7, 710 13,880 t_:>:j 

13 I Gray mine, 46!Hnch cut ______________ I 4 5, 511 1 1 8. 5 34.3 47.1 10.1 1.6 5. 3 62.8 1.0 19.2 2. 9 6, 250 11,250 ::d 

2 37.5 51.5 I 11.0 1.7 4.8 68.6 1.1 12.8 -------- 6,828 12, 290 -------- tl:l 3 -------- 42.1 57.9 -------· 1.9 5.4 77.1 1.2 14.4 -------- 7, 672 13,810 ::d 13 I Gray mine, 42-inch cut_ ______________ J 4 5, 753 1 1 8. 6 36.4 47.7 7.3 1.3 5. 6 65.6 1.1 19.1 2.6 6, 600 11,880 -------- q 

UJ. 2 -------- 39.9 52.1 8.0 1.4 5.1 71.8 1.2 12.5 7, 222 13,000 -------- P:1 3 -------- 43.3 56.7 -------- 1.5 5. 5 78.0 1.3 13.7 7, 856 14, 140 -------- J' I Joseph Rich mine (now known as thP 2 A23384 1 8. 8 38.2 44.9 8.1 1.5 5.6 65.7 1.1 18.0 6,467 11,640 -------- 0 

Wardle mine). ::d 2 41.9 49.3 8. 8 1.7 5.1 72.1 1.2 11.1 7,094 12,770 -------- t_:>:j 

3 46.0 54.0 -------- 1.8 5. 6 79.1 1.4 12.1 -------- 7, 783 14,010 t_:>:j 

15 I Timothy mine, 2 lower benches, 17Y2- 4 5, 754 1 8. 2 35.7 45.8 10.3 1.3 5. 5 63.5 1.0 18.4 2.3 6, 344 11,420 -------- ~ 

inch cut. 2 38.9 49.9 11.2 1.4 5. 0 69.2 1.1 12.1 -------- 6, 917 12, 450 > 3 -------- 43.8 56.2 -------- 1.5 5.6 78.0 1.2 13.7 -------- 7, 790 14,020 -------- ::d 15 I Timothy mine, 2 upper benches, 33~2- I 4 5, 7551 1 8.6 36.7 46.7 8.0 2.1 5.8 65.7 1.0 17.4 2. 5 6, 539 11,770 t_:>:j -------- inch cut. ? 2 -------- 40.2 51.1 8. 7 2.3 5. 2 71.9 1.1 10.8 7,156 12,880 -------- 3 -------- 44.0 56.0 -------- 2. 5 5. 7 78.7 1.2 11.9 7, 839 14,110 -------- q 16 I Pack Allan Coal Co. mine (known 2A23378 1 8. 6 38.6 42.9 9. 9 1.8 5.6 63.2 i.1 18.4 2.5 6,306 11,350 -------- 1-3 earlier as the C. C. Rich mine). 2 -------- 42.2 47.0 10.8 2.0 5.0 69.2 1.2 11.8 -------- 6, 906 12,430 --------

3 -------- 47.3 52.7 2. 2 5.6 77.6 1.4 13.2 -------- 7, 739 13,930 ~ 2r I Gibson mine, lower 14 inches of 22-inch 4 5, 515 1 9.4 32.8 44.9 12.9 1.9 5.1 57.8 .9 21.4 3. 0 5, 761 10,370 

top bench. 2 -------- 36.2 49.6 14.2 2.1 4. 5 63.8 1.0 14.4 -------- 6, 361 11,450 

3 -------- 42.2 57.8 -------- 2. 5 5. 2 74.4 1.2 16.7 7,411 13,340 
20 I Gibson mine, middle bench, 4272-ineh 4 5, 517 1 11.7 34.4 44.5 9.4 1.9 5. 6 59.2 0. 9 23.0 4.4 5,878 10,580 

cut, 2 -------- 38.9 50.4 10.7 2. 2 4. 9 67.0 1.0 14.2 -------- 6,650 11,970 

3 -------- 43.6 56.4 -------- 2.4 5. 5 75.0 1.2 15.9 -------- 7,444 13,400 

20 I Gibson mine, lower bench, 21-inch cut. 4 5, 518 1 10.2 32.7 44.8 12.3 .8 5.3 60.0 1.0 20.6 3. 3 5,939 10,690 

2 36.4 50.0 13.6 . 9 4.6 66.9 1.1 12.9 -------- 6,611 11,900 

3 42.2 57.8 -------- 1.0 5. 4 77.4 1.2 15.0 -------- 7,656 13,780 

28 I Blue Bell (Massey) mine, 225 feet on 5 10,712 1 9.8 37.2 43.5 9. 5 1.5 -------- -------- -------- -------- 1.8 -------- -------- 2, 520 

main entry. 2 -------- 41.2 48.2 10.6 1.7 -------- -------- -------- -------- -------- -------- -------- -------- 3 -------- -------- -------- -------- -------- -------- -------- -------- -------- -------- -------- -------- -------- 43 I Green mine ___________________________ 4 10,713 1 8.8 38.8 44.2 8. 2 2.4 -------- -------- -------- -------- 1.1 -------- -------- 2,370 

2 -------- 42.6 48.4 9.0 2. 6 -------- -------- -------- -------- -------- -------- -------- -------- 3 -------- -------- -------- -------- -------- -------- ---- --- ·------- -------- ·---........ -------- -------·· , ................... 

45 I Joseph Dudley mine-------------------1 2 A23386 I 1 8. 4 38.3 43.8 9. 5 1.5 5. 5 64.7 1.1 17.7 1.8 6,289 11,320 2,830 

2 -------- 41.8 47.8 10.4 1.6 4. 9 70.6 1.1 11.4 -------- 6,867 12,360 

3 46.6 53.4 1.8 5. 5 78.8 1.3 12.6 -------- 7,667 13,800 

48 I Collier mine ___________________________ I 2 A23390 I 1 7. 9 39.6 43.8 8. 7 2. 4 5. 6 64.8 1.2 17.3 1.9 6, 417 11,550 I 2,390 

2 -------- 43.0 47.6 9.4 2. 6 5. 1 70.4 1.3 11.2 6, 967 12,540 

3 47.51 52.5 -------- 2. 9 5. 7 77.7 1.4 12.3 7,694 13,850 

1 Sampler, C. A. Allen; analyst, H. M. Cooper, U.S. Bureau of Mines. s Sampler, C. T. Lupton and W. L. Mielke, U. S. Geological Survey; analyst, A. C. 

2 Sampler, J. J. Bourquin and W. F. Murray, U.S. Geological Survey; analyst, H. M. Fieldner, U. S. Bureau of Mines. 

Cooper, U. S. Bureau of Mines. 4 Sampler and analyst are unknown. 

• Sampler, C. T. Lupton, U. S. Geological Survey; analyst is unknown, 

t;l 

8 

z 

0 

H 

~ 

a 

0 

t;l 

0 

~ 

0 

0 

1-<j 

1--L 

~ 

1--L 
142 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Ooal in the black shale unit of Mississippian age.-Coal is reported 

to have been obtained frbm the upper part of the black shale unit of 

Mississippian age on Farm Creek in sec. 11, T. 2 N., R. 1 W., Uinta 

Special Ineridian. Coal prospects were located on the west side of 

Farm Creek, but landslides, which are prevalent in the black shale, 

have covered all traces of developm,ental work. Original claims filed 

on these prospects covered the SW1;4 sec. 2, the Elj2 sec. 3, and the Elj2 

of sec. 10, T. 2 N., R. 1 W. The SW:lJ.t, sec. 2 and the E 1h sec. 3 are not 

underlain by the black shale, therefore it is possible that the prospects 

were located in ground that has been subjected to a landslide. Some 

lignitic material was noted in the soil underlain by the black shale 

unit on the trail near the crest of the divide between Farm Creek and 

Whiterocks River in the NWlJ.t, sec. 12, T. 2 N., R. 1 W., and highly 

carbonaceous fissile shale is present at water level on Fann Creek. No 

record of the thickness of the coal beds in the rocks of Mississippian 

age is available. 

Although showing higher fixed carbon, lower volatile matter and 

higher B. t. u. content than the coal in the Mancos shale, this coal is 

still high volatile C bituminous in rank. The abundance of pyrite 

( Fe2S) in the black shale unit is probably responsible for the high 

sulfur content. 

Percentage analyses of coal from two beds in the black shale unit of Mississippian 

age on Farm Creek, sec. 11, T. 2 N., R. 1 W., Uinta Special meridian 

[Samples collected by J. C. Mulville, analyses by H. M. Cooper] 

Labo- M . Vola- F" d ratory OIS- tile Ixe Ash No. ture matter carbon Sulf Air dry- Cal- I or ing loss ories B. t. u. 

--------1:------------------

Outcrop, upper vein I _______ 83,561 22 34.9 Do.2____________________ ________ ________ 35.7 

Outcrop, lower vein I _______ 83,562 7. 4 34.2 Do.2____________________ ________ ________ 36.9 

1 As received. 2 Dry coal. 

50.6 12.3 51.7 12.6 48.0 10.4 51.8 11.3 1.8 

1.8 

2.4 

2.6 

0.4 7,117 12,810 

7, 278 13, 100 4. 9 6, 733 12,120 

7, 272 13,090 

Ooal production.-The following table shows the production of 

coal from Uintah County. The information was obtained from publications of the U. S. Geological Survey; the U. S. Bureau of Mines; 

the Coal Mine Inspector, State of Utah; and the Industrial Commission, State of Utah. Where the published coal production from 

the area has been combined with the production from other counties 

to conceal the output of individual Inines, the production from the 

Uinta River-Brush Creek area has been estimated. Because some 

of the small producers may have been omitted from the compilations, 

the larger published figure has been used in each case. In addition, 

the total yearly production probably can be increased by 10 percent 

to offset the omission of the small operations. S1nall producers prob-
ECONOMIC GEOLOGY 143 

ably were operating for a few years prior to 1896, but the correction 

figure is probably less than 1,000 short tons. 

The noticeable drop in output from 1920 to 1921 and from 1929 to 

1930 can be traced to a lower farm income during times of business 

recession. When farm and livestock prices are high, coal is purchased for domestic heating, but when prices are low, scrub cedar on 

the foothills is utilized. 

Year Short 

tons 

1896 300 

1897 1,000 

1898 5,000 1899 6,450 1900 6,500 1901 7, 750 1902 3,540 1903 10,300 1904 12,200 1905 12,945 

1906 3,887 1907 4,000 1908 5,150 1909 4,480 1910 8,590 1911 4, 700 1912 6,800 1913 5, 595 1914 4,879 1915 4,341 1916 3, 785 1917 3,500 

1918 6,100 1919 9,929 1920 9,228 1921 3,814 1922 3,015 1923 3, 500 

1924 4,184 1925 5, 214 1926 5, 510 1927 6,000 

1928 7,484 1929 5,860 1930 3,544 1931 2,500 

1932 2, 581 1933 2,422 1934 2,500 1935 2,500 1936 2,500 1937 2,500 1938 2,500 1939 2,500 1940 2,500 1941 2,500 1942 2,880 1943 2,000 1944 1,140 1945 1,000 1946 599 1947 2,496 1948 2,950 

Total 239,642 

Goal production of Uintah Gmtnty, Utah, 1896-19.1-8 

Sources of information 

Estimated from combined statistics of Utah and~Uintafi.Countie('by U.S. Geological Survey. 

Estimated from combined statistics of Iron, Sanpete, and Uintah Counties by U. S. 

Geological Survey. Utah State Coal Mine Inspectors report. 

Do. 

Do. 

Do. 

U. S. Geological Survey. Utah State Coal Mine Inspectors report. 

Do. 

Estimated from groduction of Summit and Uintah Counties (U.S. Geological Survey) and Summit County (Utah State Coal Mine Inspectors report). 

Do. 

Estimated. 

U.S. Geological Survey. 

Do. 

Do. 

Utah State Coal Mine Inspectors report. U. S. Geological Survey. Utah State Coal Mine Inspectors report. U.S. Geological Survey. Utah State Coal Mine Inspectors report. 

Do. 

Estimated from combined production statistics of Summit and Uintah Counties by U. S. Geological Survey. 

Do. 

U.S. Geological Survey. 

Do. 

Do. 

Do. 

Estimated from combined statistics of Grand, Iron, San Juan, and Uintah Counties by U.S. Geological Survey. U. S. Geological Survey. 

Do. 

Do. 

Estimated from combined statistics of Grand, Iron, Summit, and Uintah Counties by U.S. BureauofMines. 

U.S. Bureau of Mines. 

Do. 

Do. 

Estimated from combined statistics of Grand, Iron, Kane, Sevier, Summit, and Uin· 

tah Counties. 

U. S. Bureau of Mines. 

Do. 

Estimated. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

U.S. Bureau of Mines. 

Estimated. 

U.S. Bureau of Mines. 

Estimated. 

State of Utah, Biennial report of the Industrial Commission. 

Do. 

Do, 

0 oalreserves.-The following rules, definitions, and basic assumptions that have been used in calculating the original coal reserves in-
144 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

sure that reserve estimates frmn widely separated localities have comparable basic data and that these estimates can be integrated on a 

regional or national scope : 

(1) R(J;nk of coal.-Where coal of more than one rank is covered by 

a report, the reserve data shall be reported separately for the coal of 

each rank, aceording to specifications of the An1erican Society for 

Testing Materials (D 38S-38). 

(2) Overbu,rden.-Reserve data shall be reported according to the 

amount of overburden on the eoal as follows : A, 0-1,000 feet; B, 1,000-

2,000 feet; C, 2,000-3,000 feet. 

(3) Glasses of reserves.-On the basis of the relative reliability of 

data on whieh calculations are based, eoal reserves shall be reported 

in three separate classes as follows : 

A. Measured coaL-Measured eoal is that tonnage computed 

from di1nensions revealed in outerops, trenches, mine workings, 

and drill holes. The points of observation and measurement are 

so closely spaeed, and the thickness and extent of the coal is so 

well defined that computed tonnage is judged to be accurate within 20 percent or less of the true tonnage. The points of observation are approximately half a mile apart. 

B. Indicated coaL-Indicated coal is that tonnage computed 

partly frmn specific measurements, and partly frmn projection of 

visible data for a reasonable distance on geologic evidence. In 

general, the points of observation are 1 mile apart. 

C. Inferred coaL-Inferred coal is the quantitative estimate 

based largely on broad know ledge of the geologic character of a 

bed, or region, for which there are few, if any, measurements. 

The estimates are based on an assumed continuity. 

( 4) Size of u~nU area.-Coal reserves shall be calculated and reported for small geographic areas. 

(5) Reserves in individ~wl beds.-)Vithin the selected geographic 

area, reserves shall be reported for each individual bed, and all assumptions in regard to average thickness and areal extent shall be 

shown. 

(6) Thickness 'l'ange.-In all reports of coal reserves, subtotals shall 

be prepared to show the reserves contained in beds falling within the 

following thickness ranges : 

A. For anthracite, semi anthracite, and bituminous coal: (a) 

More than 42 inches, (b) 28 to 42 inches, (c) 14 to 28 inches. 

B. For sub bituminous coal and lignite: (a) More than 10 feet, 

(b) 5 to 10 feet, (c) 21j2 to 5 feet. 

(7) Original 'reserves.-For each bed, or part of a bed, within a 

prescribed thickness range, the original reserve prior to mining shall 

be calculated first, and reported separately; net, or short tons of 2,000 

pounds shall be used in the reports. 
ECONOMIC GEOLOGY 145 

A. Average thickness.-The use of isopach lines is the most 

effective way to evaluate the thickness of a bed. Generally, however, the data are insufficient for this purpose, and average figures 

1nust be used. When this is clone, the averages 1nust be weighted 

according to the approximate area of bed represented by each 

observation. . . . Partings of more than three-eighth inch thickness shall be mnitted in determining the thickness of individual 

beds. 

B. Areal extent.-The total area of coal of all classes may be 

determined in several ways. When the continuity of the bed is 

well established by n1aps, the entire area of known occurrence 

1nay be taken. Persistent beds that have traced around a basin 

or spur 1nay be considered to underlie the area enclosed by the 

outcrop. Otherwise, the length of outcrop (within the thickness limits listed above) is considered to establish the presence 

of coal of all classes in a semicircular area having a diameter 

equal to the length of the outcrop. 

C. Weight of coal.-When other precise data are not available, 

the following values shall be assigned as the weight of coal : 

Anthracite and smni anthracite, 2,000 short tons per acre-foot. 

Bitmninous coal, 1,800 short tons per acre-foot. 

All coal in the lower part of the Mancos shale is of high volatile 

U bituminous rank. Although enough measured sections are available over much of the area to classify the coal as "1neasured," it is 

considered "indicated" coal because rapid changes between coal and 

bone along the strike make it impossible to estimate tonnages within 

20 percent. Two areas are classified "inferred" coal because, in spite 

of the fact that the coal outcrop is covered by unconformably overlying rocks, there is geologic evidence to believe that the coal bed is 

continuous beneath each area. 

Calculation of reserve tonnage is based on the assumption that coal 

in the ground weighs 1,800 short tons per acre-foot; tonnage figures 

are given in thousands of short tons and are rounded off to the nearest 10,000 tons. In calculating the reserves remaining in the ground, 

the assmnption is 1nade that losses incident to mining activities are 

equal to the total production to date. ]\fining losses have been apportioned to different townships according to the mining activity and 

the total production estimated to have come from each area. Seventy 

percent of the district's production is assigned to the Coal Mine Draw 

area, and 15 percent is assigned to the Steinaker Draw-Brush Creek 

area and to the Deep Creek area. For the sake of uniformity with 

other reports on coal reserves, 50 percent is assumed for estimating 

future recovery. 

The following table gives the coal-reserve estimates for the entire 

Vernal coalfield, as shown on plate 4. 
Reserves of coal in the Vernal district, Uintah County, Utah 

[Inferred reserves marked by an asterisk (*); all others classed as indicated reserves] 

I Overburden 

(feet) 

I 

0-LOOO 

1,00G-2,000. _____________________________________________________ _ 

0-1 000 

1,00G-2,000.- ___ . ________________________________________________ _ 

2,00G-3,000.- ---------------------------------------.-------------

Q-1,000 __ ---------------------------------------------------------I 

Estimated Mined or Remaining Recoverable 

Range in Total reserves lost in min- reserves, reserves, Area (acres) Thickness of original re- thickness (thousands ing (thou- January 1950 January 1950 (inches) coal (feet) serves (thou- of tons) sands of (thousands (thousands 

I 

Salt Lake meridian 

T. 3 S., R. 21 E. 

sands of tons) tons) of tons) of tons) 

1, 350 1,390 

28j~ I 1, 001.61 3. 3 I 5, 950 ~--------------~------------~--------------~-------------­ ::1~ -------- ~~~~ ~- ---------~~~-- --------- -~~~- --------~~~~~- --------- ~~- --------~~~~~- --------- ~~ ~~~ 14-28 233.6 3. 3 

-------------- ,_- ------------ '--------------I--------------I------------I--------------

--2;74o_l __________ o_l ________ 2;74ii_l _________ i;37o 

42 28-42 

14-28 42 28-42 

14-28 42 28-42 

14-28 

14-28 42 28-42 

14-28 

T. 3 S., R. 22 E. 

1, 080.0 

217.6 

100.0 6.4 

107.2 

372.8 

784.0 

1, 579.2 

219.2 

73.6 

140. 81" 1, 688.0 1,190.4 

T. 3 S., R. 23 E. 

14-281 83. 21 

4. 85 9,430 3. 3 1, 290 1. 8 320 3. 6 40 

t ~ 1, g~g 1-------i3;o4o T--------iii T------i3;o3iiT--------6; 5i5 4. 85 6, 840 3. 3 9, 380 

t t 1j~g ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 3. 3 10,020 -------------- ------------ -------------- -------------- 1. 8 3, 870 15, 120 0 15, 120 7, 560 

1. 9 1 280 1 280 1 o 1 280 1 140 

1--l 

~ 

0 

tz:j 

0 

t'i 

0 

~ 

0 

"'J 

0 

z 

8 

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t;t:l 

H 

<: 

tz:j 

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~ 

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0 

t;t:l 

tz:j 

tz:j 

!;1 

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~ 
T. 4 S., R. 20 E. 

()-1,000 __ ---------------------------------------------------------I 

~:888=~:888~ ~ ~~~~~~ ~ ~ ~~~ ~ ~~~ ~ ~~ ~= ~~~~~~~ = ~~ ~ ~ ~~ ~ ~ ~~~==~~ ~ ~~ ~ ~ ~~~~~ 1 

421 

499.2 28-42 1, 289.6 28-42 1, 609.6 28-42 460.8 

I 

3.81 2.85 i: ~ ~----- i~:~-~----- ---,z-1·----- -i:~-~---- --n~ 2.85 

2. 85 2, 360 2, 360 0 2, 360 1, 180 

T. 4 S., R. 21 E. 

0-LOOO 28-42 78.4 2.85 400 -------------- ------------ -------------- -------------- 14-28 788.8 1.8 2,550 2,950 5 2,945 1,471 1,00o-2,000 ______________________________________________________ _ 

2,000-3,000_- ----------------------------------------------------- {)-1,000 __________________________________________________________ _ 

1,00o-2,000 __ --- _________________________________________________ _ 

2,00o-3,000_- -----------------------------------------------------

28-42 12.0 14-28 1,060. 8 14-28 1, 289.6 14-28 803.2 14-28 1,022.4 14-28 1, 104.0 

I 

2.85 60 -------------- ------------ -------------- -------------- 1.8 3,440 3,500 0 3,500 1, 750 

1.8 4,180 4,180 0 4,180 2,090 

1.8 *2, 600 *2, 600 0 *2, 600 *1, 300 t?J 

1.8 *3, 310 *3, 310 0 *3, 310 *1, 655 C":l 

1.8 *3, 580 *3, 580 0 *3, 580 *1, 790 0 

z 

0 

T. 4 S., R. 22 E. H 

~ 

C":l 

42 17.6 28-42 120.0 14-28 3, 057.6 

4.6 150 -------------- ------------ -------------- -------------- Q 2.8 600 -------------- ------------ -------------- -------------- tz:j 

2. 2 12,200 12,950 15 12,935 6,465 0 

()-LOOO 

42 52.8 4.1 390 -------------- ------------ -------------- -------------- tot 28-42 113.6 14-28 2, 379.2 14-28 169.6 

I 

3. 0 610 1,000 35 965 482 0 2.2 9,420 9,420 0 9,420 4, 710 

2. 2 670 670 0 670 335 ~ 1,00o-2,000 ______________________________________________________ _ 

2,00o-3,000_- -----------------------------------------------------

T. 3 S., R. 19 E. 

421 48.0 28-42 16.0 14-28 68.8 14-28 8.8 

I 

0-LOOO 

1,000-2,000_- -----------------------------------------------------

•• I 380 3.0 

2.0 2~g ~-- --- -----7~g -~----- ----ig -~----- -----7ig -~-- ---------agg 2.0 

T. 3 S., R. 20 E. 

28-421 39.21 2.851 200 1 200 1 101 190 1 95 

~ "'"""" 

---1 
Reserves of coal in the Vm·nal district, Uintah Ootmty, Utah-Continued 

[Inferred reserves marked by an asterisk (*); all others classed as indicated reserves] 

Overburden Range in Estimated Total reserves Mined or Remaining Recoverable 

(feet) thickness Area (acres) Thickness of original re- lost in min- reserves, reserves, 

(inches) coal (feet) serves (thou- (thousands ing (thou- January 1950 January 1950 

sands of tons) of tons) sands of (thousands (thousands 

tons) of tons) of tons) 

--

Uinta Special meridian 

T.2 N., R.1 E. 

0-1000 42 171.2 4.4 1, 360 28-42 88.0 3. 0 480 -------------- ------------ -------------- -------------- 14-28 150.4 2.0 540 2,380 15 2,365 1,187 1,000-2_000 42 128.0 4.4 1, 010 -------------- ------------ -------------- -------------- 28-42 116.8 3.0 630 -------------- ------------ -------------- -------------- 14-28 235.2 2.0 850 2,490 0 2, 490 1, 245 2.0oo-3.000 14-28 14.4 2.0 50 50 0 50 25 

T.2 N., R.2E. 

421 752.0 4.4 ,,,@I _ __

1 

____ 28-42 57.6 3.0 14-28 54.4 2.0 '·~ ---- -::ll:: --~r --- H~r-------.;lll 42 179.2 4.4 

0-1.000 

1,000-2,000.- -----------------------------------------------------

T.lN.,R.lE. 

42 12.0 4.4 100 28-42 54.4 3.0 ,~ 

1

------- 430

1

- ---- •

1

14-28 12.0 2.0 ----------"·r- ------,i, 28-42 27.2 3.0 150 -------------- ------------ -------------- -------------- 14-28 316.8 2. 0 1, 120 1, 270 0 1, 270 635 

1,000-2,000.------------------------------------------------------

2,000-3.000. --

1--' 

~ 

00 

0 

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T.1N.,R.2E. 

il-1.000_ 42 28.8 4.4 28-42 42.4 3.0 14-28 76.8 2.0 1.00Q-2,000. 42 377.6 4.4 28-42 240.0 3.0 14-28 302.4 2. 0 

2,00Q-3,000.- ------ ~- --------------------------------------------- 28-42 66.4 3.0 14-28 394.4 2. 0 

Total tonnage 

tl\~~gte""<ii_-~ = =:== = == = = == = = == = = == = = == = = == = = == = = == = = == = = =========I--------------

~~=~~~g ~~~~= == =============================================== 1-------------:-[----------1 : ••••••••••• Beds with Q-1,000-foot overburden _______________________________ _ Beds with l,OOD-2,000-foot overburden. __________________ ------ __ _ -- Beds with 2,00D-3,000-foot overburden ___________________________ _ 

230 1--------------1------------1--------------I------------- 230 

280 740 0 740 370 

2, 990 1----------- __ c 1------------1--------------I-------------- 1,300 

1,090 

360 

1,420 

60,160 

54,170 

5,380 0 5, 380 1 2, 690 --------------~-----------

--------i;7so- ----------o -1--------i;7so_l_----------siio 

143,340 460 142,880 71,440 

34,940 

51,620 --1--------------1-------------- 47,290 1------------1--------------1--------------

*9, 490 1------------1-

:: !============== 

29, 010 1--------------I------------I--------------I--------------

t':l 

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150 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

OIL AND GAS 

Surface indications.-Sandstone, impregnated with viscous or dry 

petroleum residue, crops out at a number of places on the north side 

of the Uinta Basin and at a few localities within the area shown on 

plate 1. The petroleum residue is found in rocks of Mesozoic and 

Tertiary age. The largest exposure of dry oil sand is found 1 to 2 

miles south of the southern border of the map, along the north-facin!; 

escarp1nent of Asphalt Ridge. At that point, it impregnates both 

the Wasatch fonnation, which represents the basal Tertiary strata 

of the area, and sandstones of the underlying Mesaverde formation 

of Late Cretaceous age. The oil accumulation probably is related to 

the unconformity at the base of the Tertiary because saturation occurs 

in rocks both above and below the unconformable contact. Spieker 

( 1931, p. 96-97) has estimated that between 1112 and 3 billion barrels 

of oil were present in the deposit before loss by erosion and escape 

of volatile constituents. 

A second, but less extensive exposure of petroleum residue, is in the 

Navajo sandstone east and west of Whiterocks River. The impregnated sandstone is especially well exposed west of the river, where an 

adit has been driven 20 to 30 feet into the upper part of the steeply 

dipping Navajo. Heavy oil mixed with water seeps from the roof 

of the adit and accumulates on the floor. 

Small, dry oil-impregnated sandstone localities are found in the 

basal Tertiary beds between Deep Creek and Whiterocks River, and 

n dry oil sand is exposed in the NW%,NE:L4 sec. 24, T. 2 N., R. 3 W., 

between Uinta River and Dry pulch. 

Small particles of a shiny gilsonite-like hydrocarbon are found in 

u. sandstone bed in the Park City formation in the NE:L4NE:L4 of 

sec. 34, T. 2 S., R. 21 E., north of Red Mountain. 

Chemical con~position and physical properties.-Spieker (1931, 

p. 94), quoting from a report by E. Theodore Erickson, of the Geologjcal Survey, on a chmnical analysis of the petroleum residue from 

Asphalt Ridge, states, 

The sulphur content is unusually low. Native asphalt contains from 1.7 to 10 

percent of sulphur. . . . The bitumen appears to consist of residual material 

derived from a paraffin base petroleum. 

A sample of heavy oil collected from the adit in the Navajo sandstone on Whiterocks was submitted to the Bureau of Mines Petroleum 

Experiment Station, Bartlesville, Okla. Harold M. Smith, petroleum chemist, reports (letter dated Sept. 15, 1949), 

... an unsuccessful attempt was made to analyze the oil by the Routine 

method. The oil is virtually a natural asphalt, and also contains some water and 

sediment, a distillation by normal means was almost impossible . . . The specific 

gravity of the sample at 60° F. was 1.011. We have also determined the sulfur 
ECONOMIC GEOLOGY 151 

content, which surprisingly enough is only 0.41 percent. To my knowledge this 

is the lowest sulfur content for an asphaltic material that I have ever run across. 

Additional analyses of the material for the presence of sulfur and 

nitrogen, by the Petroleum and Oil Shale Experin1ent Station of the 

Bureau of Mines at Laramie, Wyo., are given in the following table 

supplied by John S. Ball, refinery engineer. The analyses of oil and 

bitumen from other localities in the Uinta Basin are included for the 

purpose of comparison. 

S~tlfur and nitrogen contents of m·ude oils and bitumens from Uinta Basin 

Oil-producing areas Formation 

Oil, Rangley field, Colorado______________________ Weber ___________________ - __ _ Oil, Uintah Co., Utah ____________________________ Green River_ ______________ _ Oil, Rangely field, Colorado ______________________ Mancos _____________________ _ Oil, Rangely field, Colorado_______________________ Shinarump _________________ _ Bitumen, Vernal deposit_ _________________________ Wasatch and Mesaverde ____ _ Bitumen, Sunnyside deposit_ _____________________ Wasatch ____________________ _ Bitumen, Whiterocks _____________________________ Navajo _____________________ _ 

Sulfur 

(percent) 

0.67 

.31 

.10 

.36 

• 50 

. 51 

.47 

Nitrogen 

(percent) 

0.04 

.49 

.016 

.018 

1.18 

. 96 

1. 28 

Mr. Ball states, "This material exhibited a positive spot when tested 

with Oliensis solvent and also with 100 percent xylene. A positive 

spot test is indicative of heterogeneous material." 

Some physical properties of the asphaltic material from Whiterocks also were determined and are given in the following table: 

Some properties of asphaltic material (sample PA-49-1) from Uintah County, 

Utah 

Bitumen __________________________________________________________________________ (percent) __ 

Bitumen soluble in carbon tetrachloride ___________________________________________ (percent) __ Ash ____________________________ --------- __________________________________________ (percent) __ 

Penetration: At 60° F., 100 gm. wt., 5 sec ____________________________________________ (decimillimeter) __ At 77° F., 100 gm. wt., 5 sec ____________________________________________ (decimillimeter) __ Softening point ______________________________________________________________________ (° F.) __ Specific gravity at 77/77 F ___________________________________________________________________ _ 

Spot tests: 

Oliensis: InitiaL _____________________________________________________________ ---- _______ ------- After 24 hours ___________________________________________ -- _________ ------------------

suir~~~-t~~~~~~~~~~-~~~!~~!~~:-~-----~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ci>ercelit):: Nitrogen __________________________________________________________________________ (percent) __ 

1 Solvent used was 100 percent xylene. 

99.8. 

99.9. 

0.00. 

84. 

240. 

99. 

0.986. 

Positive. 

Do. 

Do. 

0.47. 

1.28. 

From these analyses it is concluded that: (1) the sulfur and nitrogen 

content of the Whiterocks bitmnen is similar to other bitumen occurrences in the Uinta Basin and might have been derived from oil from 

Tertiary rocks (as found in the Roosevelt discovery well), and ( 2) the 

high sulfur content of the crude oil from the Weber sandstone at 

Ashley Creek and at Rangely, and the lower sulfur content of the 

bitumen at Whiterocks, makes the Weber an unlikely source of the 

bitumen in the Navajo sandstone at Whiterocks. 
152 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Oil and gas exploration.-Oil and gas exploration in the area by 

drilling is summarized in the table, "Summary of oil and gas wells 

in the Vernal area, Uintah County, Utah," which has been compiled 

from many sources. This summary is arranged according to Township and Range for ease of location, with subheadings indicating the 

location on known structural features. The stratigraphic data, given 

in the summary, are based upon examination of well cuttings and 

drillers' logs in wells drilled before 1940, and upon electric logs and 

well cuttings in wells drilled after that date. All depths are given 

as the number of feet below the well collar. The altitude above or 

below sea level at any stratigraphic point can be calculated by subtracting the depth in the well from the surface altitude of the \veil. 

Asphalt Ridge monocline.-The first drilling for petroleum in the 

Vernal area was by the Uintah Development Co. ; four shallow wells 

were drilled south of Asphalt Ridge frmn 1911 to 1913. These wells 

were drilled because of the expectation that the dry oil cropping out 

along the Asphalt Ridge escarp1nent had sealed the bed and that 

liquid petroleum was present down the dip. Traces of oil and s1nall 

amounts of gas are reported in the drillers' logs. The Carter Oil Co. 

drilled a deep test well in the same area in 1947, but although the 

well cored oil sand, it did not achieve commercial production. 

Neal dome.-Neal dome, between Steinaker Draw and Ashley Creek, 

and north of Vernal, was drilled in 1925 by the Maude Ellen Oil Co. in 

the NE14NW14SE1,4 sec. 28, T. 3 S., R. 21 E. This well, drilled to 

2,552 feet, surfaces in the Navajo sandstone and entered the Weber 

sandstone at a depth of 1,575 feet; water was flowing over the top of 

the casing in 1946. This test well was not located at the highest 

strutural location on the anticline and in 19±7 the Vernal Oil and 

Gas Company drilled Hullinger well 1, located in the N"\V:t;!SW14-

SEl4 see. 30, T. 3 S., R. '21 E. This well surfaced alluvium at 

the bottmn of the Ashley Creek valley (which is lower than the top of 

the Chinle formation) and entered the Shinarump conglomerate at 

97 feet, the Moenkopi fonnation at 150 feet, and the Weber sandstone 

at approximately 1,190 feet. Although structurally located about 

400 feet higher than the ~laude Ellen well, Hullinger well 1 also 

flowed fresh water frmn the vV eber sandstone. 

Ashley Creek gas field.-The Ashley Creek gas field, located in 

see. 2~3, T. 5 S., R. 22 E., southeast of Vernal, Utah~ was discovered 

when the Utah Oil Refining Co. completed the drilling of well 1, in 

the SW14SW1,4_NW14 sec. 23, on April 18, 1925. The well was located on the basis of surface dips in soft Mancos shale, which indicated a structural high point on the westward-plunging Section Ridge 

anticline. The wells produced from a 10-foot interval of coarsegrained sandstone in the lower one-third of the Morrison formation 

of Jurassic age. Of the five wells drilled on the structure between 
ECONOMIC GEOLOGY 153 

1925 and 1934, only the discovery well and Midwest Exploration Co. 

well 3 were commercial producers. Utah Oil Refining Co. well 1 

logged two gas sands, the first frmn 1,431 to 1,475 feet, and the second 

from 1,673 to 1,680 feet. The upper zone was rated at 15 million 

cubic feet of gas, and the lower zone was rated at 60 million cubic 

feet. Midwest Exploration Co. well 3, completed iri 1928, was rated 

as a 29-million-cubic-foot producer and had an initial gas pressure of 

580 pounds per square inch. The latter well reported production of 

8 barrels of oil per day frmn a depth of 1,790 feet in the lower part 

of the Morrison formation. 

Although it was discovered in 1925, with a second gas well completed in 1928, the Ashley Creek field was not produced commercially 

until September 1929, when a pipe line to Vernal was completed. 

Yearly production of the field, accumulated production, and the gas 

pressure at the end of the year, as compiled from the records of the 

Conservation Division, U. S. Geological Survey, Casper, Wyo., by 

Raymond M. Larsen, a.re shown below. 

Statist,ics of yearly production of the Ashley Creek gas field 

Gas Gas 

Million Total pressure Million Total pressure 

Year cubic (end (pounds Year cubic (end (pounds 

feet of per feet of per year) square year square inch) inch) 

1929 ________________ 17,267 17,267 580 1936 ________________ 51,476 344,131 200 

1930 __ -------------- 50,395 67,662 1937 _______________ 49,038 393,169 200 1931 ________________ 43,859 111,521 1938 _________ ------- 43,995 437,164 180 1932 ________________ 53,927 165,448 1939 ____ ----------- 47, 109 484,273 195 1933 ________________ 44,103 209,551 320 1940 ___ ------------ 35,639 519,912 1934 ________________ 37,441 246,992 270 1941 (Jan.l to Aug. 1935 ________________ 45,663 292,655 230 30) _______________ 16,424 536,336 100 

A total production of 536,336 1nillion cubic feet of gas is recorded 

from the sandstone of Jurassic age until the field was abandoned in 

1941. During this time, the gas pressure had decreased frmn an 

initial 580 pounds per square inch to 100. It is reported in Vernal 

that the principal reasons for abandonment of the field were the deterioration and leaks developed in the transporting pipe and the high 

resale value of the reclaimed pipe. However, the drop in gas pressure indicates the depletion of the original producing sandstone. 

The following analysis of the gas frmn the Ashley Creek field 

(Shaw, E. S., 1934, p. 347) shows it to be essentially methane: 0.20 

percent carbon dioxide, 0.13 percent oxygen, 99.42 percent methane, 

0.24 percent nitrogen, and 0.01 percent heliun1. 

Ashley Creek oil field.-The Ashley Creek gas field, which had 

known structural closure, was especially prmnising as a potential oilproducing structure from deeper horizons following the development 

of Rangely oil field in Rio Blanco County, northwestern Colorado, in 

1942. It was drilled in August and September of 1948; after the 
Sumnwry of wells drilled for oil and gas in the Uinta River-Brush Creek a1·ea, Uintal~ County, Utah 

[Structure and surface formation: F, faulted no~e; S, Shinarump conglomerate; A, anticline; Jn, Navaho sandstone; Qc, Quaternary alluvium on Chinle formation; M, monocline; 

Qm, Quaternary alluvium on Mancos shale; N, nose; T, terrace gravel on Mancos shale] 

Top of Frontier Top of Structure sandstone and Spud Completion Initial production Alti- Total member Navajo Driller Lease and well No. Location Surface date date (barrels per day) tude depth of the sandformation (feet) (feet) Mancos stone 

shale (feet) 

(feet) 

------- -------

Tidewater Associated- Pine Ridge 58-7 _______ SWSWSE sec. 7, T. 3 S., F,S 7/27/49 Abandoned ---------------------- 7, 504 3,508 ---------- --------

Mohawk. R. 20 E. 9/17/49__ ___ Maude Ellen Oil Co ___ Neal!_ ________________ NENWSE sec. 28, T. 3 S., A,Jn 7/10/25 Abandoned ---------------------- 5, 750 2,386 ---------- -------- R. 21 E. 11/32. Vernal Oil and GasCo_ Hullinger L ___________ SWSESE sec. 30, T. 3 S., A,Qc 7/14/47 Abandoned ---------------------- 5, 780 -------- ---------- -------- (l 

R.21E. /48. Mayo-Utah Oil Co _____ Asher-Merkley L ______ SWNW sec. 22, T. 4 S., R. M,Qm. 8/10/45 Abandoned ---------------------- -------- 6, 773 4, 210 6,103 . 21E. 1/46. Equity Oil Co _________ Powell!1. _____________ SWNWNW sec. 34, T. 4 S., N,T 8/20/45 Abandoned ---------------------- -------- 1, 763 883 -------- . R.22E 1/8/46. Do _________________ Kendall!. ____________ SWNESW sec. 33, T. 4 S., N,T 7/22/49 Abandoned ---------------------- 4, 987 4,922 1, 225 3,060 R. 22E. 9/49. Sun Oil Co ____________ Neal-Government L __ NESWSE sec. 26, T. 4 S., T 10/21/49 12/10/49__ __ -- ---------------------- 5, 274 4,302 576 2,348 9 R. 22E. California-Utah Oil Co_ Slaugh) ___ ----------- C. ofNESE sec.12, T. 5 S., T 9/28/49 Abandoned ---------------------- 5,339 6,133 4,275 6,110 R. 21E. 11/16/49. Baird and Robbins ____ _____ do __________ ------- C. of SESW sec. 4, T. 5 S., T 2/12/49 Abandoned ---------------------- 5,308 5, 900 2,100 4.585 R. 22E. 8/49. H. D. Moore ___________ Government L _______ SWSENW sec. 18, T. 5 S., T 6/17/49 Abandoned_ ---------------------- 4,901 4,439 923 -------- . 

0 

R. 23E. Utah-Vernal Oil Co __ Caldwell L ___________ SWSWSW sec. 20, T. 5 S., N,T 5/17/49 Abandoned ---------------------- 4, 750 4,447 381 2,085 

R. 23 E. 6/29/49. 

Utah Oil Refining Co __ Valley Fuel Supply L. SWSWNW sec. 23, T. 5 S., A,Qm 11/20/24 4/13/25 ____ --- (Gas, 15millioncubic 4,910 1, 685 676 -------- R.22E. feet) 2 .. NENW sec. 23 ____________ A,Qm 9/27 Abandoned --------------------... 4,892 709 708 -------- 9/27. 

Midwest Exploration 3 __ SESWNW sec. 23 __________ A,Qm 10/11/27 2/23/28 _______ (Gas. 29 million cubic 4,904 2, 720 695 2, 327 

Co. feet) 

Ashley Valley Oil Co __ 4 __ NWSENE sec. 22 _________ A,Qm 8/ 7/28 Abandoned 

12/20/28_--- ---------------------- 4,923 2,165 890 --------

Uintah Gas Co ________ 5 __ C. of NESW sec. 23 _______ A,Qm 10/23/34 Abandoned t2t4m4 ___ ---------------------- 4,836 1, 730 785 --------

~ 

01 

~ 

0 

t".J 

0 

~ 

0 

0 

~ 

0 

"::1 

0 

z 

8 

> 

~ H 

< t".J 

~ ~ 

0 

ffi 

c 

~ 

t".J 

t".J 

p:j 

Ed 

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~ 
Equity Oil Co.--------1 Ashley Valley Oil CoL N. of NWSW sec. 23 _______ A,Qm 8/14/48 9(14/48 _______ 300_----------------- 2_ SWNESW sec. 23 __________ A,Qm 2/ 3/49 3/13/49 _______ 430_----------------- 3_ SWNWSE sec. 23 __________ A,Qm 3/18/49 4/18/49 _______ 480 ___ --------------- ~ 4_ SENWSW sec. 23 __________ A,Qm 4/19/49 5/15/49 _______ 295 (3.B-inch choke) __ <:o 5_ SENESE sec. 22 __________ A,Qm 5/24/49 6/16/49 _______ 261i__ ---------------- 01 

..... 6_ SESENE sec. 22 __________ A,Qm 6/24/49 7/16/49 _______ 432 (H-inch choke) __ g; 7. SWSENW sec. 23 __________ A,Qm 9/ 9/49 10.'1/49 _______ 960 ()4-inch choke) __ 

I 8_ SWSWNE sec. 23 __________ A,Qm 3/11/50 4/16/50 _______ 100_----------------- 01 9 0. of SWNW sec. 23 _______ A,Qm 4/19/50 5/20/50 _______ 99 ___________________ i Stanolind Oil and Gas Government L _______ NESWSW sec. 23. _________ A,Qm 2/28/49 4/11/49 __ ----- 288 (1~1)4-inch choke) Co. 2 __ ------ NWNWNE sec. 26 ________ A,Qm 4/19/49 5/23/49------- 375_----------------- 3 ________ NWNENW sec. 2:6 ________ A,Qm 4/17/49 5/16/49_------ 1008 ___________ ------ ..... 4 ________ NESESE sec. 22 __________ A,Qm 5/21/49 6/20/49 _______ 95 ___________________ ..... 5 ________ NWNENE sec. 26 _________ A,Qm 5/29/49 7/3/49 ________ 174 (1~1\4-inch choke) 6 ________ N~:2NWNW sec. 26 ________ A,Qm 6/22/49 7/26/49._ _____ 240_----------------- 7-------- NWNWNW sec. 25 ________ A,Qm 8/2/49 9/8/49 ________ 792_----------------- 8_ g ________ ------- NENWSE sec. 22 _________ A,Qm 8/22/49 9/18/49..----- 257------------------ NENENE sec. 27 _________ A,Qm 11/1/49 12/9/49 _______ 55 (~il.-inch choke) __ 10 __ ------ NESWSE sec. 22 __________ A,Qm 1/24/50 2/19/50 _______ 100 (Park City pro- duction). Crane and Griffith I Hall L ________________ NWSESW sec. 23 __________ A,Qm 10/31/48 12/11/48__ ____ Drilling Co. 502_----------------- 3 _________________ NWSESE sec. 23 __________ A,Qm 3/22/49 4/26/49 _______ 4 _________________ 600_-- --------------- SESESE sec. 23 ___________ A,Qm 9/18/49 10/21/49._ ____ 480 _______ ----------- Rennie L _____________ NESWNE sec. 26 _________ A,Qm 1/23/49 -------------- 720_ ----------------- Government L _______ NESENW sec~ 26 _________ A,Qm 5/3/49 5/29/49 _______ 10L _____ ----------- _ Uintah Basin 3 ________ NWSWNW sec. 25 _________ A,Qm 6/20/49 7/23/49._ _____ 142 (wet) ____________ Hillman L ____________ SESWNW sec. 15 __________ A,Qm 8/2/49 Abandoned ---------------------- Hollandawo,th and I Govocnmont lA ______ NWSENE ""- 26._ _______ 3/28/49 

9/49. 

A,Qm 4/21/49 _______ 864_----------------- Travis. 

R. Lacy Production Government 1B_______ NESWNW sec. 26 _________ A,Qm 4/28/49 Abandoned ---------------------- Co. 5/23/49. Tested (4, 

372-4, 393) 

3_ ------- NWSWNW sec. 25._ _______ A,Qm 6/20/49 7/23/49 142_----------------- 1_------- NWSWSE sec. 23 __________ A,Qm 1/23/49 3/3/49 ________ 734 __________________ California Company ___ j Wyman L _____________ SWNESW sec. 23 __________ A,Qm 4/25/49 6/22/49._----- 132 (10% cut) ________ Gentry L _____________ SESWNE sec. 22 __________ A,Qm 10/9/49 11/15/49 __ --- 137 (%4-inch choke, 

Robert Six-Carter I Nelson!_ _____________ 10% cut). SWSWSW sec. 24 __________ A,Qm 8/13/49 9/49_- ------- 130 (%4-inch choke)_ Oil Co. Massey L _____________ SWSESW sec. 24 __________ A,Qm 10/31/49 Abandoned ---------------------- Stewart-Sixandothers _ _l Hullinger!_ ___________ SWNENW sec. 23 _________ A,Qm 12/5/49 

11/28/49. 

1/50_-------- ----------------------

4, 904 4,152 690 

4,895 4, 218 625 4,894 4,268 700 4,904 4,271 605 4, 912 4, 290 804 4, 923 4, 293 770 4,897 4, 230 701 4,875 4, 239 786 

--4;9o2- 4,260 729 

4,327 610 4,889 4,310 720 4,912 4,287 700 4, 933 4,308 774 4,868 4, 243 720 4, 916 4,301 769 4,856 4,216 757 4, 946 4,306 920 

4, 922 4, 290 918 

4, 962 4, 331 995 

4,890 4,122 628 4,858 4, 208 713 4, 860 4, 200 738 4,878 4, 255 ---------- 4, 926 4,307 878 4, 823 4, 205 810 4, 995 4,378 ----------

4, 881 4, 235 796 

4, 954 4, 393 1,079 

4,823 4, 205 810 4, 878 4, 255 812 4,844 4, 235 752 4, 931 4,301 916 

4,856 4,190 774 

4, 776 4, 255 788 

4,887 4, 534 1,000 

2,408 

2,340 

2,421\ 

2,339 

2,430 

2, 451 2,414 

2,440 

2,460 

2,375 

2,380 

2,424 

2,458 

2,408 

2,473 

2,478 

2, 585 2, 630 2, 642 

2,350 

2, 427 2, 424 

-------- 2, 523 2, 475 _______ .,. 

2,486 

2, 677 

2, 475 2, 510 2,448 

2,605 

2, 463 

2, 509 

2, 705 

4,138 

4,065 

4,105 

4,076 

4,147 

4,185 

4,152 

4, 220 4, 214 4,088 

4,107 

4,146 

4,188 

4,093 

4, 205 4,168 

4, 280 4, 268 4,328 

4,080 

4,135 

4,132 

4, 202 4, 294 

4,193 ___ ,.. ____ 

4,184 

4,372 

4,193 

4,227 

4, 204 4, 277 

4,163 

4,249 

4, 526 

t:::j 

Q 

0 

z 

0 

~ 1-t 

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0 

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0 

~ 

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Cl 
156 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

mineral ownership of the land had been clarified in court. The first 

well, Equity Oil Co.'s Ashley Valley 1, topped saturated Weber sandstone at 4,136 feet, and when cmnpleted, it flowed 260 barrels per day 

of 31 to 34 degree gravity oil frmn the interval 4,136 to 4,152 feet. 

Subsequent drilling of 27 wells on the structure in 1949 established a 

reported potential of more than 10,000 barrels per day and actual 

production of about 2,700 barrels per clay. The producing area of 

the field will be approximately 800 acres. At first, the oil was hauled 

to Salt Lake City, but later it was trucked to Rangely, Colo., for 

transport via pipeline to refining facilities in Salt Lake City. By 

January 1, 1950, the field 'vas approxi1nately one-third drilled out. 

An analysis by IC P. Moore, of the Geological Survey, of an oil 

sa1nple frmn the Stanolind Oil and Gas Co.'s Government well 1, located near the crest of the Ashley Creek oilfield, showed a gravity 

(API) of 31.7, pour point of 45 F. and a sulfur content of 0.75 percent. 

The oil is brown and has an intennediate base. The approximate 

summary of the distillation by the Hmnpel method is as follows: 

Percent 

Total gasoline and naphtha____________________________________ 23.7 

Kerosene distillate_____________________________________________ 10.8 

Gas oiL______________________________________________________ 14.3 

Nonviscous lubricating distillate_________________________________ 11.2 

Medium-lubricating distillate___________________________________ 5.5 

Viscous-lubricating distillate---------------------------------""'-- 2.6 

Residuum ----------------------------------------------------- 31.8 

Distillation loss________________________________________________ 0.1 

A structure-contour 1nap of the field, drawn on the top of theW eber 

sandstone, by J. S. Adair, Conservation Division, U. S. Geological 

Survey, and based for the most part on electric logs, is given in figure 12. Edgewater elevation on the southwest side of the field was 

established by the Stanolind Oil and'Gas Co.'s Government well1 and 

well 2, when both drilled cmnpletely through the saturated Weber 

sandstone. Edgewater elevations are 623 and 599 feet above sea level, 

respectively. Hollandsworth Drilling Co.'s well1B, on the southwest 

flank, topped Weber at 4,372 feet depth ( 573 feet above sea level) and 

was abandoned. Robert Six-Carter Oil Co.'s Massey well 1 topped 

Weber at 527 feet above sea level on the southeast end of the field and 

Robert Six-Carter Oil Co.'s Hullinger well 1 topped vVeber at 361 

feet above sea level on the north flank of the field; both wells were 

abandoned. 

Stanolind Oil and Gas Co.'s Government well10 (fig. 12, No. 33), 

an edge well on the southwest flank of the anticline, was completed as 

a 60-barrel-per-day producer through a %4 -inch choke from the Park 

City for1nation. Equity Oil Co. well 2-A, near the crest of the structure, was drilled in 1950 to test oil saturation in the Entrada sandstone. It pu1nped 12 barrels of oil per day from the Entrada sand-
5 + 

s 

15 

ECONOMIC GEOLOGY 157 

R. 22 E. ----- ----~-+ 

EXPLANATION 

Structure contour on top of the 

Weber sandstone. Contour 

onterval is 50 feet, dashed 

where approximately located 

Datum is mean sea level 

lt)OO 

~ 

0 

WELL SYMBOLS 

Well data as of November I, 1950 

~~E Dry hole that penetrates th& Chinle shale 

but dod not lost the Weber sandstone 

-¢- Dry hole that tested the Weber sandstone 

. Oil well, producing from the Weber sandstone 

@ 

Oil well, producing from the Pork 

City formation 

By J S. Ado1r, 1950 

FIGURE 12.-Subsurface structure-contour map of the Ashley Creek oilfield. 

stone, was plugged back to 1,872 feet in the basal part of the Morrison 

formation, and was completed as a 5:1;2-nlillion-cubic-foot gas well. 

S pUt 111 ountain anticline.-The rapid development of the Rangely 

oilfield frmn 1943 to 1945 led to increased exploration for oil in adjacent Uintah County, Utah. In addition to the Vernal Oil and Gas 

Co.'s Hullinger well 1, on Neal dome, and the Mayo-Utah Oil Co.'s 

Asher-Merkley well1, drilled to 6,150 feet in the SWlUNWlU sec. 22, 

T. 4 S., R. 21 E., the Equity Oil Co. tested the westward plunging nose 

of the Split Mountain anticline, east of the eon1munity of Naples, with 

the Powell well 1 located in the SW1h NW1MNW1_4 sec. 34, T. 4 S., 

R. 22 E. This well, drilled to 1, 763 .feet, topped the Morrison formation at 1,295 feet, but it did not enter the underlying Curtis formation. 

The well was abandoned in January 1946. The nose was further 

tested in 1949 by the Equity Oil Co.'s l(endall well 1, located in the 

SW1MNE1_4SW1_4 sec. 33, half a mile to the southwest of the Powell 

well, and by the Sun Oil Co.'s Neal-Government well 1, in the NE%,-
158 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

SW1;4SE%, sec. 26, T. 4 S., R. 22 E. Equity Oil Co.'s l{endall welll 

was drilled to 4,992 feet and entered the Weber sandstone at a depth 

of 4,907 feet; the Sun Oil Co.'s Neal-Govern1nent well 1 topped the 

Weber at 4,279 feet and was drilled to a total depth of 4,296 feet. 

Both wells were abandoned as dry holes. 

Section Ridge anticline.-The successful completion of the Ashley 

Creek field as a petroleum producer resulted in the drilling of anumber of wildcat wells to the north and east of the field. The UtahVernal Oil Co. drilled Caldwell well1 in the SW1;4SW%,SW1;4 sec. 

20, T. 5 S., R. 23 E., 3 miles east of the field, to a depth of 4,44 7 feet on 

the westward plunging axis of the Section Ridge anticline. This well 

was structurally higher than the Ashley Creek field, but the anticline 

had no closure at that point. H. D. Moore drilled Governn1ent well1 

in the SW1;4NE%,NW%, sec. 18, T. 5 S., R. 23 E., 2 miles northeast 

of the field, to a depth of 4,439 feet on the northwest flank of the Section Ridge anticline. Caldwell well1 topped the Weber sandstone at 

3,757 feet and Government well1 topped the Park City formation at 

4,569 feet (more than 500 feet structurally lower than the Ashley 

Creek field). Baird and Robins drilled Slough well1, in the center of 

SE1;4SW1;4 sec. 4, T. 5 S., R. 22 E., to a depth of 5,787 feet and probably tested the Park City and Weber formations in the bottom of the 

hole. Slough well1 is located almost 3 miles northwest of the Ashley 

Creek field, and structurally, it is 1,500 to 1,700 feet lower (on the top 

of the Weber standstone). 

Dry Fork anticlinal nose.-In 1949, the Tidewater Associated-Mohawk Petroleum Co. Pine Ridge well 58-7 tested the highly faulted 

anticlinal nose, 1 mile west of Dry Fork. The well surfaced on the 

Shinarmnp conglomerate, topped the Park City formation at 730 feet 

depth, the Weber sandstone at 876 feet, the black shale unit of Mississippian age at 2,588 feet and the limestone unit of Mississippian age 

at 2,735 feet. It was abandoned at 3,508 feet total depth, after testing 

most of the Mississippian section. 

Oil and gas possibilities.-The most obvious oil and gas structures 

in the rocks of Mesozoic and Paleozoic age of the Vernal area, the 

Ashley Creek field, the Neal dome and the Pine Ridge anticlinal nose 

have already been tested by wells. The better remaining possibilities 

are at localities where Tertiary rocks overlap on rocks of Mesozoic and 

Paleozoic age. At these points, the structure of older rocks is hidden, 

and the true attitude of the covered beds can only be inferred by geophysical exploration. One area offering such possibilities is the glacial outwash plain south of Whiterocks Canyon. The saturated sandstone in the Navajo sandstone along Whiterocks River appears to be 

localized on a slight anticlinal nose, which plunges southward. The 

Dakota sandstone, Frontier sandstone member of Mancos shale, and 

Mesaverde formation 1nay have offered suitable reservoir conditions 
ECONOMIC GEOLOGY 159 

for oil accmnulation under sufficient cover. The great overlap of 

Tertiary rocks over rocks of Mesozoic and Paleozoic age west of 

Whiterocks River covers an area offering both reservoir rocks and 

complex structural conditions, especially faulting. The area should 

also be closely examined for conditions favorable to oil accumulation. 

A considerable amount of seismic geophysical prospecting already 

has been done by major oil con1panies in the area south of Uinta Canyon, but no information is available in regard to their success in the 

recording of seismic reflections frmn beneath the glacial outwash. 

METALLIC MINERAL DEPOSITS 

Introduction.-The Uinta Mountains have not been intruded by 

igneous rock, and because rich metalliferous deposits generally are 

associated with intrusive rocks, the area is only slightly mineralized. 

A few copper, lead, and iron prospects have been developed in the 

lower part of the limestone unit of Mississippian age in the Carbonate 

district, T. 1 S., R. 21 E., and small iron deposits are scattered across 

the area adjacent to the South Flank fault. The high terraces along 

the Green River have been prospected for· placer gold, and a gold 

dredge has worked the sands of the Green River above, and below, 

Split Mountain and on Horseshoe Bend on the southern boundary of 

the mapped area. 

COPPER 

Dyer mine.-The principal copper production from the Carbonate 

district has been from the Dyer mine, an open cut 50 to 75 feet in diameter, lying along the crest of an east-trending ridge that descends 

from the high peak lying between Brush Creek and Little Brush 

Creek. The Dyer mine is located in the NW~ sec. 16, T. 1 S., R. 21 E., 

and can be reached by a truck trail that leaves the Iron Springs road 

at Iron Springs camp ground and winds northward 3.5 miles through 

scattered pine and aspen to the mine. In addition to the open cut, 

the area is pitted with numerous prospect holes 3 to 6 feet deep. Most 

of these pits were sunk in the soil cover until limestone was encountered. Other pits are located on the red sandy shale of the Uinta Mountain group, which underlies the thin Lodore formation at this locality. 

The open cut has been prospected by shafts sunk in the bottom of the 

pit and by tunnels driven southward into the north-facing limestone 

escarpment. 

The maximum yearly production from the Carbonate district was 

reached between 1898 and 1901, when, for a 2-year period beginning 

in October 1899, a blast furnace was operated in the SE¥4 sec. 7, T. 

1 S., R. 21 E., to treat ore from the Dyer mine. Several unsuccessful 

attempts to find additional ore bodies in the vicinity of the 1nine have 

been made. 
160 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Ore.-The ore, so far as it can be observed from dumps in the vicinity of the open cut, consisted of the carbonate of copper, malachite, and 

a small amount of azurite. It is reported that the sulphide (chalcocite) 

was present only as incompletely oxidized cores of large ore masses and 

that these cores were filled with 1ninute veinlets of carbonate (Butler, 

Laughlin, Heikes, and others, 1920, p. 604). The ore formed irregular 

bodies in limestone, and two such bodies, one directly beneath the 

other, were mined in the open pit. The upper of these bodies extended 

1 o the surface, and float was present below the outcrop. It seems probable that the pri1nary ore body was chalcocite (formed by replacement of lilnestone), and that subsequently the chalcocite was partly 

altered to copper carbonate. 

The metal content of the original ore body can best be estimated 

frmn assay reports of carload ship1nents. Butler (Butler, Laughlin, 

Heikes, and others (1920, p. 602) reports one shipment of 400 tons of 

copper glance (sulfides) assayed 49.47 percent of copper, 26 ounces of 

silver, and $6 of gold per ton. Another shipment assayed 51.5 per cent 

copper. The ore treated at the blast furnace is reported to have averaged 33.5 percent copper. Earlier shipments of hand-sorted ore, 

which were shipped by wagon to the railroad at Carter, Wyo., averaged between 49 and 51 percent of copper. 

The output of the Carbonate district, as reconstructed from published sources for the period 1891 to the present time, is given in the 

following table. 

JJ1 etals produced in the Carbonate district 

[Years 1891-1917, from Butler, B. S., and others, 1920, p. 601] 

Quantity 

of ore (short tons) 

Gold (fine 

ounces) 

Silver 

(fine 

ounces) 

Copper 

(pounds) Value 

189L _ _ __ ________ ___ ____ __ ____ _______ _ __ _ __ 18. 5. 22 468 17, 784 $2,865 

1892_______________________________________ 73 21.19 1, 898 71,136 10,341 

1893_-- ------------------------------------ 93 26.99 2, 418 90, 896 12, 261 1894_- ------------------------------------- 73 21. 19 1, 898 71, 136 8, 392 

1895_- ------------------------------------- 36 10.45 936 35, 568 4, 630 1896_- ------------------------------------- 111 32. 22 2, 886 108,680 14, 365 

1897--------------------------------------- 30 8. 71 780 30,900 4, 356 1898_- ------------------------------------- 500 96. 75 10,000 300,000 45, 100 1899_______________________________________ 906 175.31 18,120 558,800 110,051 

1900_______________________________________ 1, 7.51 350.00 35,020 1, 156,100 220,859 

1901_- ------------------------------------ 270 39. 18 20, 250 108,000 30,996 

1904_- ------------------------------------- 500 125.00 8, 000 25,000 10, 289 

1915_- ------------------------------------- 6 ------------ 27 5, 724 1, 016 1916_______________________________________ 5 ------------ 26 5, 423 1, 351 

1917--------------------------------------- 5 ------------ 20 4, 098 1, 250 1918_______________________________________ 1 ------------ 6 372 ------------ 192.5 _____________________ c ____ _______ ____ __ 1 __ ___ _______ 4 743 109 

19191 ______________________________________ ------------ ------------ ------------ ------------ ------------ 1931_______________________________________ 4 ------------ 5 1, 276 ------------

1935 _______________________________________ ------------------------ ------------ 5,831 502 

1936_- ------------------------------------- ------------ ------------ ------------ 3, 804 357 

1937--------------------------------------- ------------ 3 31 3, 000 492 1938_- ------------------------------------- ------------ ------------ ------------ 1, 235 179 1939 _______________________________________ ------------ ------------ ------------ 596 101 

1940_- ------------------------------------- 8 ------------ 14 1, 000 123 

1941_- ------------------------------------- 2 ------------ ------------ 100 12 

tOne truckload of ore shipped. No statistics available. 
ECONOMIC GEOLOGY 161 

LEAD 

Four patented mineral clai1ns, filed on occurrences of high-grade 

lead carbonate in the soil overlying the limestone unit of Mississippian 

age and a few showings of galena (PbS) in limestone ledges, are 

located a 1nile and a quarter south of the Dyer mine, near the center of 

sec. 21, T. 1 S., R. 21 E. The galena, 1nostly altered to the carbonate 

of lead (cerussite), occurs as thin lenses lying parallel to the bedding 

of the gently dipping limestone. The lenses appear to have been 

formed by replacement of certain limestone beds. The high-grade lead 

carbonate (found at the surface) has been concentrated from these 

lenses by solution of the surrounding limestone. From the limited exposures noted in the area, no structural control of the replacement 

bodies is evident. 

The carbonate ore on the surface or in the upper few feet of the soil 

is cheap to 1nine and load for shipment, but most of the readily available ore has been removed. The replacement-type sulphide bodies are 

small and would be expensive to 1nine. In conjunction with developInent work on these prospects in 1947, churn drilling and geophysical 

prospecting of adjacent areas was carried on; the results of this prospecting are unknown. 

In the summer of 1948, a road was built from a point on the Iron 

Springs road and 1 mile east of the bridge over Brush Creek to a small 

galena-lead carbonate prospect a short distance upstream from Brush 

Ureek Cave near the quarter-section corner between sees. 20 and 32, T. 

1 S., R. 21 E. This prospect, developed in fractured dark gray cherty 

limestone in the lower part of the limestone unit of Mississippian age, 

is an enlargen1ent of a natural cave fonned along a joint plane. At 

the time of this investigation, a small quantity of galena was stockpiled at the end of the automobile road; reserves are very limited. 

Other mineral claims are located on the south side of Little Brush 

Creek Mountain in the Slj2 sec. 13 and the Nlh sec. 24, T. 1 S., R. 21 E. 

These prospects are similar to those to the west, but some structural 

control for their localization is evident. They lie near the crest of the 

southeast plunging anticlinal nose developed in the limestone unit of 

Mississippian age. 

IRON 

Iron prospects in the Uinta River-Brush Creek area occur in the 

brown-weathering sandy shale of the upper part of the Uinta Mountain group, in the lower part of the limestone unit of Mississippian 

age, and as cement in breccias for1ned of the limestone unit of Mississippian age or of Uinta Mountain group shale along the South Flank 

fault zone. A small deposit of brown iron ore, cementing a fault 

breccia of sandy shale, was noted in a prospect shaft in sec. 10, T. 2 

S., R. 19 E. ( unsectionized). An occurrence of similar appearance, 
162 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

part of the Pope deposit mentioned by Butler (Butler, and others, 

1920, p. 603), is present below the peak of limestone that lies to the 

northwest of the Dyer mine. 

The Pope deposit yields high-grade red hematite in very limited 

quantities from pits sunk in soil covering the shale in the upper part 

of the Uinta Mountain group. This hematite probably comes from the 

underlying red sandy shale, although Butler reports that iron oxide 

replaces certain limestone beds in the Pope area. Gradations from 

high-grade ore, to partly replaced ore, to little-altered limstone is said 

to be present in the Pope area. Some of the ore was used as a flux for 

the Dyer blast furnace. It is reported to be low in both sulfur and 

phosphorus. 

Brown oxide of iron cements a limestone breccia on the east side of 

Black Canyon in sec. 8, T. 2 S., R. 20 S. (unsectionized). This occurrence was described as the Woodside deposit by Butler and lies along 

a branch of the South Flank fault zone. An additional gosson-like, 

brown iron ore deposit, located along a fault zone in the limestone unit 

of Mississippian age in the NW%, sec. 33, T. 3 N., R. 1 W., on the west 

side of Farm Creek, is being developed for its reported gold content. 

It can be reached by a timber road and trail, which branches from the 

road up Pole Mountain in the east half of sec. 4, T. 2 N., R. 1 W. A 

short adit trends generally west into the brecciated iron-stained limestone unit of Mississippian age a short distance above the Uinta Mountain group boundary. 

GOLD 

The high terraces of the Green River south of the Dinosaur N ationa! Monument are pockmarked with prospect holes sunk to test 

the gold content of the gravels. No development has been clone for 

many years, and the prospects are presumed not to be of economic 

importance. A gold dredge has been operated on the Green River 

above Split Mountain, south of Split Mountain, and on the great 

Horseshoe Bend of the river (on the southern boundary of pl. 1). 

The source of the auriferous gravels is unknown, but some goldbearing gravel may have been derived from the pre-Cambrian rocks 

of the Red Creek quartzite in Browns Park, northwestern Colorado 

and the pre-Cambrian Uinta Mountain group. 

:PHOSPHATE 

The phosphate deposits of the Phosphoria formation underlie a 

large area centering in southeastern Idaho and extending into central Montana, western Wyoming, and northern Utah. Although included in the Park City formation in northeastern Utah, the phosphate-bearing beds along the flanks of the Uinta Mountains are 

markedly similar and continuous with the beds in the Phosphoria 

formation. 
ECONOMIC GEOLOGY 163 

Lithology and occurrence.-Phosphate rock, interbedded with phosphatic mudstone and argillaceous and phosphatic limestone, occurs 

in the basal member of the Park City formation. The lower mmnber 

of the Park City formation rests on the thick, massive to crossbedded 

Weber sandstone and is overlain by an upper 1nember of interbedded 

light-gray, sandy and cherty dolomitic limestone, light-tan to red, 

fine- to coarse-grained sandstone, and light-gray shale. The lower 

member of the Park City, 20 to 30 feet thick, is soft, and easily eroded; 

it forms a gentle slope or bench above the rugged, almost vertical 

cliffs of the Weber. The upper mmnber weathers into two ledges 

separated by soft, easily eroded beds. These ledges were mapped by 

L. E. Smith, of the Mineral Deposits Branch of the Geological Survey, so that phosphate reserves under different thicknesses of overburden might be calculated. The top of the lower ledge is 39 to 43 

feet above the phosphatic 1nember of the Park City formation, and 

the base of the upper ledge is 66 to 78 feet above the phosphatic member. The lithology, thickness of beds, and graphic portrayal of three 

detailed sections, together with the chmnical analyses and graph of 

the phosphate content of the individual beds, is given on plate 5. 

The phosphatic member crops out on Whiterocks River, in limited 

areas in the complexly faulted zone between Mosby Mountain and 

Dry Fork Mountain, in the banks of dry creek gulches from Ashley 

Creek to Brush Creek, and along dip slopes and in dry gulches tributary to Brush Creek between Brush Creek and Little Brush Creek. 

Beds at the same stratigraphic position as the phosphatic mmnber 

on the flanks of Split Mountain within the Dinosaur National Monument contain only a few very thin beds of low-grade phosphate rock. 

West of Ashley Creek the phosphatic member is broken, intermittent 

in outcrop, of lower grade, and not of econmnic importance. The 

extent of the phosphate rock beneath Diamond Mountain is unknown. 

The phosphate rock in T. 2 S., Rs. 21 and 22 E., and T. 3 S., R. 21 

E., dips at angles ranging from 6° to 23° to the south and southeast. 

The resistant ledges of the upper member have protected the underlying phosphate from erosion. This protection has resulted in broad 

exposures of the phosphatic member, under relatively thin cover, in 

an area where the phosphatic member reaches its maximum thickness 

and grade. 

Physical appearance.-The phosphate rock is soft, pale-olive to light 

olive-gray, and is thin-bedded to massive. It contains abundant ovules 

and pellets, or angular fragments, of phosphate. The ovules range 

in size from very fine- to very coarse-grained. Small ovules having 

very poorly defined outlines, as well as some fully rounded ovules 

are present in parts of the phosphatic mudstone and limestone beds. 

The P 20s content of the rock is roughly proportional to the abundance of the ovules, the more abundant the ovules, the higher the 
164 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

grade. The higher grade rock is granular in texture and is formed 

ahnost entirely of phosphate ovules cemented by calcite, dolmnite, or 

silt-sized particles. The leaching of the cementing 1naterial in surface outcrop results in a soft, friable rock that readily disintegrates 

upon handling. At least some of the phosphate fragments are mechanically worn shell fragn1ents that have been replaced by phosphate. S1nall bivalves, a few Ostracoda, and small i1nmature gastropods (completely replaced by phosphate) are present in some beds 

and readily -vveather from the 1natrix. 

The color of the phosphatic mmnber, pale-olive to light olive-gray, 

usually reflects the color of the individual phosphate ovules and fragments. The phosphate rock approaches specific gravity 2.8. It reacts with 1noderate-to-strong efl'ervescenee to concentrated hydrochloric acid. Smne of the released carbon dioxide is frmn the carbonate that cmnents the ovules, but at least a part of it is from the 

carbonate radical included in the cmnplex collophane molecule. The 

phosphate.rock gives a strong fetid odor when freshly broken or when 

dissolved in acid. The rough quantitative test for phosphate, the 

formation of a white coating after application of concentrated hydrochloric acid, (Gardner, 1947, p. 16-17) does not give good results because the rock rapidly absorbs the acid, partly by reaction with the 

carbonate present as cement and partly in pore spaces between the 

ovules before reaction with the phosphate is possible. 

The phosphate rock in the Vernal area differs in some characteristics frmn roc.k typical of the Phosphoria and Park City formations 

to the west. The n1ost noticeable difference is the lighter color of 

the higher grade phosphate beds in the Vernal area. In southeastern 

Idaho, western 'Vymning, the 1Vasatch Mountains, and even in the 

Duchesne River area of the western Uinta Mountains, the unit is a 

black to clark-gray, highly organic shale that frequently has been 

prospected for coal. Organic matter is relatively rare in the Vernal 

area; thin streaks of carbonaeeous material were noted in petographic 

thin sections frmn Brush Creek Gorge. Similar light-colored phosphate rock has been noted near the eastern boundary of the Phosphoria fonnation in the Wind River Mountains of west central 'Vymning (King, R. H., 194 7, p. 42). Thin sections of chips fron1 six 

representative beds from the Brush Creek Gorge section (pl. 5), chosen 

on the basis of physical characteristics and chmnical analysis, have 

been exa1nined. They show a great variation in 1nicroscopic characters of the beds and especially in the phosphate ovules and fragments. 

In contrast to many of the thin sections studied from the southeastern Idaho area and reported by Mansfield (1927, pl. 63, 65, 66), 

true oolites of phosphate mineral are extremely rare in the Park 

City formation of the Vernal area. The thin sections from beds 3 
ECONOMIC GEOLOGY 165 

and 5 of the Brush Creek section (pl. 5) include a few large complex 

ovules which enclose as many as five smaller ovules or nuclei of collophane cemented by collophane. Under polarized light, these included 

nuclei are of two types-brown collophane cen1ented by clear Inaterial, 

and clear collophane surrounded by brown collophane. The variation in these nuclei suggests sources in previously consolidated beds, 

mechanical disintegration, and concentration of the large complex 

oolites in a single bed. Under crossed Nicols, the included nuclei 

show faint rims of a weakly birefringent fibrous mineral, probably 

francolite. All simple ovules in thin section, exa1nined under a binocular 1nicroscope or with a hand lens, fail to show oolitic structure. 

Clear rodlike crystals (perhaps francolite), rounded to sub angular 

crystals of quartz, and rhmnbic crystals or irregular particles of carbonate are included in the ovules. The inclusions closely resmnble, 

in size and relative proportion, the particles in the adjacent groundmass. In a carbonate-cen1ented rock, the inclusions in the collophane 

ovules are carbonate, and, when sand grains are common, some have 

been included in the ovules. Small particles of collophane were noted 

in the groundmass of bed 20. Detrital sand grains and silt-sized particles are relatively common in 1nost of the beds. The abundance 

of detrital n1aterial probably reflects proximity to a land area and 

the edge of the basin of deposition of the phosphate mmnber. 

Bedding in the phosphate unit usually depends upon the quantity 

of argillaceous material in the individual bed. The higher grade 

phosphate is 1nassive to ·thick bedded, and the argillaceous phosphate 

beds are thinner bedded. The bedding in thin section was observed 

only in bed 10, where phosphate ovules, calcite particles in the groundmass, and the organic .material, are concentrated in parallel bands 

that give the rock a schistose appearance. The same thin section 

shows a flattening of ovules in contact; in other sections, the ovules 

maintain their spheroidal shape when in contact. 

Terminology.-The amount of phosphate in a rock is usually reported in percentage of phosphorus pentoxide (P2 0 5 ) or tricalcium 

phosphate Ca3 (P04) 2· The latter is called "bone phosphate of lime" 

or B. P. L., and equals 2.18 times the a1nount of P 20 5 • The term 

"phosphate rock" is limited to rocks containing over 50 percent collophane (19.6 percent P205 or 42.7 percent B. P. L) just as "limestone" is limited to rocks containing over 50 percent calcite ( CaCo3). 

The 1nodifying adjective, "phosphatic," is used where collophane 

amounts to more than 20 percent of the rock ( 7.85 percent P 205 or 

17.1 per cent B. P. L.). This usage is a modification of previous Geological Survey practice which divided phosphate-bearing rock into 

three groups: high-grade rock that has 70 percent or more B. P. L. 

(32.1 percent P205), medium-grade rock that has 50 to 70 percent 

B. P. L. (22.9 to 32.1 percent P 20 5 ), and low-grade rock that has 30 
166 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

to 50 percent B. P. L. (13.7 to 22.9 percent P 20 5); the adjectival 

modifier "phosphatic" was reserved £or rocks containing less than 30 

percent B. P. L. and was prefixed to other lithologic types, such as 

phosphatic mudstone or phosphatic limestone. 

0 omposition.-Splits o£ samples £rom the three detailed sections 

were submitted to the Bureau o£ Mines' Northwest Electrodevelopment Laboratory, at Albany, Oreg., where all samples £rom the Brush 

Creek Gorge section were analyzed £or Pz05, Alz03, Fez03, Vz05, 

Acid Insoluble, and Loss on Ignition. All samples £rom the Rock 

Canyon and Little Brush Creek sections were analyzed £or P 2 05 and 

Acid Insoluble, and in addition, those samples containing more than 

13.8 percent P 2 05 were analyzed £or Al203, Fez03, Vz05, and Acid 

Insoluble. These analyses are given in the right-hand columns o£ 

plate 5, and are correlated with the proper beds, columnar section, 

thickness, and graphic representation o£ phosphate content. Radiometric analyses o£ the Brush Creek Gorge section are given in the 

extreme right-hand column. Additional splits o£ the Brush Creek 

Gorge section (except £or sample DMK-5) were analyzed by spectrograph, and these determinations are given in the £allowing table. A 

detailed chemical analysis o£ sample DMK-5 £rom the Brush Creek 

Gorge section is also given below. 

Analysis of sample DMK-5, B1·ush G1·eek Gorge section, Uintah County, Utah 

Elements [Analyst: Harry Levine] 

Percent 

Pz05------------------------------------------------------- 27.88. CaO _______________________________________________________ 39.44. 

11g0 _______________________________________________________ 0.27. 

SiOz-----------------------------~-------------------------- 15.16. F __________________________________________________________ 2.92. 

Organic matter______________________________________________ 0.40. 

CrzOa------------------------------------------------------ 0.11. 

TiOz------------------------------------------------------- 0.04. 

Vz05------------------------------------------------------- 0.03. 

11003------------------------------------------------------ 0.003. 

11n 0 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 0. 007. 

Co------------------------------------------------~-------- 0.002. Li _________________________________________________________ 0.001. 

vv ________________________________________________________ _ Ag ________________________________________________________ _ 

Cu _________________________________________________________ 0.001. 

Pb _________________________________________________________ 0.001. 

Zn _________________________________________________________ 0.0008. 

Bao _______________________________________________________ (~. 

LhO_------- ----------------------------------------------- (1). SrO_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ (1). 

l'ra20 _______________________________________________________ 0.48. 

]{20-------------------------------------------------------- 0.64. 

C02

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Present. 

8---------------------------------------------------------- Present. 

1 Not detectable with flame photometer. Examination was made on solution without prior chemical 

separation and therefore does not imply absence of these elements. 
Spectrograph-ic analyses in weight percent/ of samples from the Brush Or·eek Gorge sect,ion, U'intah County, Utah 

[Analyses by trace elements laboratory, U. S. Geol. Survey] 

Samples Si AI Ca Mg p Fe Na Pb Or Ba Mn Sr Ni T"i v y La Zr Cu 

------------------------------------

DMK 25 _____ a b b b b b c d d d d d d d d e e e e DMK 24 _____ a c b b c b c d d d d d d d d e e e e DMK 23 _____ a b b b b b c d d d d d d d d e e e e DMK 22 _____ a a b b b b c d d d d d d d d e e d e DMK 21_ ____ a c b b b b c d d d d d d e d e e ------ e DMK 20 _____ b b a b b c c d d d d d d d d e e e e DMK 19 _____ b c a b a c c d d d d d d d d e e e e DMK 18 _____ a b b b b c c ------ d d d d d d d e e e e DMK 17 _____ b c b a b b c c d d d d d d d e e e e DMK 16 _____ a b b b b b c e d d d d d d d e e e e DMK Hi _____ b c a b a c c ------ d d d d d d d d e e e DMK 14 _____ a b b b b b c ------ d d d d d d d e e e e DMK 13 _____ b c a c b c c ------ d d e d e d d e d e e DMK 12 _____ a b b b b b c ------ c d d d d d d e e e e DMK 11 _____ a c b b b c c ------ d d d e d d d e e e e DMK 10 _____ a c b b b c c ------ d d d d d --d-- d e e e e DMK 9 ______ a b b c b b c ------ c d d d d d e e e e DMK 8 ______ b c a c b b c e d d e d d d d d d e e DMK 7 ______ b c a c b c c ------ d d e d d d d d d e e DMK 6 ______ a a b b b b c e c d e d d d d e e e e DMK 52 _____ DMK ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ ------ 4 ______ b c b a c c c e d c c e d d d e e e e DMK 3 ______ a a b b b b c d c c e d e d d e e e e DMK 2 ______ b a b b b b c d c d e d e d d e e e e DMKL _____ a c b c b b c d d c d d d d d d d e e 

t a = more than 10 percent, b = 1.0-10.0 percent, c = 0.1-1.0 percent, d = 0.01-0.1 percent, e = 0.001-0.01 pp,rcent, f = 0.0001-o 001 percent. 2 No spectrographic analysis. 

Ga Mo B Zn 

--------

e e e e e e e ------ e e e ------

e e e ------ ------ e e e e e e ------

e e f ------ e e e ------ e e e ------ e e e ------

e e f ------ e e e e e ------ f ------ e ------ e ------ e ------ f ------ e e f ------ e ------ e ------ c e f ------ e ------ f ------ e ------ e ------ ------ ------ e ------ f ------ e ------ e ------ e e e ------ e e f ------

Yb 

--

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

------ f 

f 

f 

e 

Be 

---

f 

---{--

f 

------

------

------

------

f 

f 

f 

---{--

---{--

f 

------

---{ --

------

--Tf 

------

l?:l 

0 

0 

z 

0 

H 

~ 

0 

0 

l?:l 

0 

t-t 

0 

~ 

1-L 

0":> 

-1 
168 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Phosphate content.-Analyses of individual beds range from 3.1 to 

28.5 percent P 20 5 in the Brush Creek Gorge section, from 4.6 to 25.5 

percent P 205 in the Rock Creek Canyon section, and from 4.6 to 28.2 

percent P205 in the Little Brush Creek section. The total thickness, 

weighted average grade of the individual sections, and the weighted 

average thickness and grade of the three sections, is given in the following table : 

Sections Thickness Weighted average grade P20s Average thickness and 

(feet) (percent) weighted average grade 

Rock Creek Canyon ___________ _ Brush Creek Gorge ____________ _ Little Brush Creek _____________ _ 

16. 85 16.4 (35.8 B. P · L.)_ ---------- }17.8 feet, averaging 20 percent 19.70 20,5 (44.8 B. P. L.)___________ p 0 (43 6B p L) 16.90 23.0 (50.1 B. P. L.)___________ 2 5 • • • • 

All phosphate in the Vernal area is medimn- to low-grade rock, 

and the average grade falls within the limits of "low grade" according 

to earlier Geological Survey practice. In the three detailed sections, 

28.6 percent of the beds contain less than the 1ninimmn for low-grade 

rock, 31.5 percent of the beds are low grade, and 39.9 percent of the 

beds are medium-grade rock. No high-grade rock is present. 

Iron oxide and alu!lnina.-Acid soluble Fe20s and Al20s are 

undesirable in phosphate rock that is to be treated with sulfuric acid 

to for1n superphosphate. An upper li1nit of between 3 and 4.5 percent of Fe20s and Al20 3 is generally provided in foreign standards, 

and, although not acceptable from the standpoint of phosphate con·· 

tent, most of the 1nedium -grade rock in the Vernal area ranges between these stated limits. However, if the rock is to be used as charge 

for an electric furnace, the iron and alumina of the rock combined with 

the high Acid Insolubles should fonn a self-fluxing charge. 

Vanadium.-Content of V20 5 in the sa1nples ranged frmn less than 

0.005 percent to a maximum of 0.066 percent. Of the eight samples 

containing more than 0.025 percent V205, all had phosphate contents 

ranging between 10 and 13 percent, but the acid insoluble content 

ranged from 37.0 to 60.0 percent, and the combined Al20a plus Fe20s 

ranged between 9 and 20 percent. As has been observed in southeastern Idaho and western Wymning (Gardner, 1947, p. 19), the 

vanadium is 1nore abundant in the phosphatic mudstone and is less 

prevalent in the highly phosphatic beds; the most vanadiferous beds 

contain approximately 1 to 2 percent P 205 (V. E. Mcl{elvey, personal communication, July 1951). It has been suggested that the 

amount of vanadium in phosphate rock may vary with the amount 

of organic matter. However, in the Brush Creek area, the scarcity 

a.nd the s1nall variation of the organic content between the different 

beds precludes such an association. Other factors that might pos-
ECONOMIC GEOLOGY 169 

sibly control the abundance o£ V20 5 are the Fe20 3 plus Al20 3 content 

or the silt-sized particles o£ the mudstone. It is noteworthy that the 

beds containing the higher quantities o£ V20 5 are generally less than 

0.5 £oot thick. The vanadium content o£ the mudstones in the 

\7' ernal area is very low, and it is not economically comparable to 

beds in the Phosphoria £ormation o£ Wyoming and Idaho, where 

concentrations o£ more than 1.0 percent are recorded. 

Hydrocarbons.-In soutlnvestern Montana, phosphatic shales of 

Penni an age yield (on distillation) 25 to 30 gallons o£ oil per ton. 

The position o£ the phosphatic member o£ the Park City £onnation 

above the petrolemn producing Weber sandstone, the frequent oil 

staining and oil production £ron1 one well in the £ormation in the 

Ashley Creek field, and the presence o£ dry gilsonitic hydrocarbon 

in a sandstone be.d o£ the Park City £ormation at Red Mountain, 

suggest the possibility that the unit 1night be a source rock £or 

petroleum. 

Sample splits £rmn the Brush Creek Gorge section were combined 

into six composite samples representing groups based on general 

lithology and P 20 5 content, and weighed amounts o£ the individual 

samples were analyzed at the Petroleum and Oil Shale Experiment 

Station o£ the Bureau o£ Mines at Laramie, Wyo. The phosphatic 

unit at Brush Creek carries no detectable hydrocarbons. The distillation analyses by the modified Fischer retort method are given in 

the following table. 

OU shale assays of Bru8h Creek Gorge section 

[Determined by the modified Fischer retort method by Petroleum and Oil-Shale Experiment Station U. S. Bureau of Mines, Laramie, Wyo. Shale disclosed no oil and no tende.ncy to coke] 

Yield Properties of spent shale (per- cent of original 

Composite samples Percent by weight shale) Lithology Gallons 

per ton 

Water Spent Gas of water Ignition Ash shale loss loss 

------ Group!_ ___________________ 1.9 98.1 0.0 4. 6 14.2 83.9 Group!_ ___________________ 1.9 98.1 .0 4.6 13.7 84.4 Average ____________ -- 1.9 98.1 . 0 4.6 13.9 84.2 Mudstone . Group 2 ____________________ 1.3 97.8 . 9 3.1 4.4 93.2 Group 2 ____________________ 1.3 97.9 .8 3.1 5.1 92.8 Average ___________ --- 1.3 97.9 .8 3.1 4.8 93.0 Phosphatic mudstone. Group 3 ____________________ 1.4 98.6 .0 3.2 25.3 73.3 Group 3-------------------- 1.4 98.6 .0 3.2 24.8 73.8 Average _______ ------- 1.4 98.6 .0 3.2 25.0 73.6 Limestone. Group 4 ____________________ 1.0 98.6 .4 2.4 21.3 77.3 Group 4 ____________________ 1.0 98.7 .3 2.4 21.3 77.4 Average ___________ --- 1.0 98.6 .4 2.4 21.3 77.3 Phosphatic limestone. 

G'oup ·'--------------- _ ----~ 1.7 98.0 .3 4.0 4. 9 93.1 Group 5 ____________________ 1.7 97.8 . 5 4.1 5.2 92.6 

Average _______ ------- 1.7 97.9 .4 4. 0 5.0 92.9 Phosphate rock. Group 6 ____________________ .8 98.8 .4 1.8 2.0 96.8 Group 6 ____________________ .8 98.6 . 6 1.8 1.9 96.7 Average _____________ -[ . 8 98.7 . 5 1.8 1.9 96.8 Phosphatic sandstone . 
170 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

D'evelopment of the phosphate deposits.- The continuity of the 

phosphate rock along the south flank of the Uinta Mountains was first 

den1onstrated by A. R. Schultz, of the Geological Survey, whose findings during a reconnaissance in the summer of 1914 resulted in the 

removal of parts df Tps. 18-25 E., Rs. 2-4 S. as Phosphate Withdrawal 

No. 24, Utah No.3, and the publication of Geological Survey Bulletin 

690-C. Placer claims, now held by the Humphreys Phosphate Co. in 

T. 2 S., Rs. 21 and 22 E., were filed prior to Phosphate Withdrawal 

No. 24. The outlines of Phosphate Withdrawal No. 24, Utah No. 3, 

and its relationship to the patented claims, are shown in figure 13. 

Development work required of the Humphreys Phosphate Co. to 

patent its claims has exposed the phosphate-bearing beds at a hundred 

or more prospects distributed over the patented area and has resulted 

in the cutting and chemical analyses of thousands of channel samples. 

The results have been made available by Mr. Harry Ratliffe, resident 

manager of the Humphreys Phosphate Co., Vernal, Utah, to many 

geologists interested in the area, but they are not available to the general public. Since publication of Geological Survey Bulletin 690, the 

only published studies of phosphate in the Uinta Mountains has been 

by Williams (1939) and Willia1ns and Hanson (1942). 

Reserve estimates.-:Reserve estimates of phosphate rock in the 

Ashley Creek-Brush Creek area are presented in the following table. 

In these estimates, the thickness of overburden and of phosphatic section is based on detailed 1neasurements of the Park City formation by 

l{inney and Rominger. The grade of the phosphate is dependent upon 

the analyses of the Bureau of Mines, and the extent of the different 

depths of overburden is based upon a detailed n1ap of the Park City 

formation in the Ashley Creek-Brush Creek area prepared by L. E. 

Smith, of the Mineral Deposits Branch of the Geological Survey. It 

is assumed that the phosphate unit maintains uniform thickness over 

the area and that 11.8 cubic feet of rock weigh 1 ton, or 1 acre-foot 

weighs 3,700 tons. 

Undoubtedly, reserves exist beneath the unconformably overlying 

Bishop conglomerate, but because the phosphatic member may be channeled and inaccessible, they have not been considered. Phosphate rock 

of a grade similar to that found along Brush Creek may extend to the 

east beneath Diamond Mountain, but because the eastern li1nits are 

unknown, no tonnage is alloted for that area. Faulting and lower 

grade rock 1nake it i1npracticable to calculate the reserves and mining 

potentialities of phosphate rock west of the divide between Ashley 

Creek and Dry Fork. 
t-.:l 

~ 

~ 

1-' 

~ 

I 

<:11 

r 

1-' 

l'-' 

T. 

T, 

N. 

EXPLANATION 

Phosphate Wlthdrawl 

~ No. 24, Utah No.3 

R.l E. ij.2E. 

IJ2IT] Patented phosphate claims of Humphreys 

Phosphate Co. 

R.21 E. R. 22 E. 

FIGURE 13.-0utline map showing Phosphate Withdrawal No. 24, Utah No.3, and patented claims of the Humphreys Phospate Co. 

T. 

2 

s. 

·I 

il 

I T. 

4 

s. 

t.=l 

0 

0 

z 

0 

H 

~ 

0 

0 

t.=l 

0 

~ 

0 

0 

~ 

~ 

-1 

~ 
172 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

Estimates of reserves of phosphate rock in the Ashley Creek-Brush Creek area 

Township Dip 

I 

Area along I Thickness I (a~~~s) (feet) 

43 feet or less of overburden 

T. 2 S., R. 22 E---------------------------------------- T. 2 S., R. 23 E _______________________________________ _ T. 2 S., R. 21 E _______________________________________ _ T. 3 S., R. 21 E _______________________________________ _ T. 3 S., R. 20 E _______________________________________ _ 

5°-25° 

50-100 

50-100 

50-100 

10°-20° 

2,022 62 1,357 

315 

274 

18.3 

16.9 

18.3 

16.9 

16.9 

TotaL _______ ------ ____ -- ___ ----------------------

1

------------ ------------ ------------

43 to 78 feet of overburden 

T. 2 S., R. 22 E ___________________________________________________ _ 

T. 2 S., R. 23 E ___________________________________________________ _ T. 2 S., R. 21 E ___________________________________________________ _ 

~: ~ ~:: ~: ~ ~======================================== ============ 

3,267 131 2,080 

346 

270 

18.3 

16.9 

18.3 

16.9 

16.9 

TotaL---~--------- ______ ------------------------- ----------- -~------ ------ ------------

78 to 100 feet of overburden 

T. 2 S., R. 22 E ____________________________________________________ _ 

T. 2 S., R. 23 E _________________________________________ ------------ T. 2 S., R. 21 E ________________________________________ ------------ T. 3 S., R. 21 E ___________________________________________________ _ 

T. 3 S., R. 20 E ________________________________________ ·------------

5,392 

339 

4, 523 1, 234 

349 

18.3 

16.9 

18.3 

16.9 

16.9 

Reserves 

(millions 

of tons) 

136.7 

3. 9 91.8 

19.8 

17.2 

269.4 

220.0 

8. 2 

140.7 

21.7 

16.9 

407.5 

366.0 

21.2 

307.0 

77.0 

21.8 

TotaL ____________________________________________________________________ ------------ 793. 0 

More than 100 feet of overburden to top of water level in streams 

T. 3 S., R. 20 E ___________________________________________________ _ T. 3 S., R. 21 E ___________________________________________________ _ 

T. 2 S., R. 21 E ________________________________________ ------------ T. 2 S., R. 22 E ___________________________________________________ _ T. 2 S., R. 23 E ____________________________________________________ _ 

343 1, 803 1,255 

830 

1,280 

16.9 

16.9 

18.3 

18.3 

16.9 

21.4 

112.5 

85.0 

56.2 

80.0 

TotaL____________________________________________ _ _ _ __ __ __ __ _ _ _ ___ _ ___ __ _ __ _ ___ _ ___ __ 355. 1 

From stream level to 1,000 feet below stream level 

T. 3 S., R. 20 E ________________________________________ ------------ T. 3 S., R. 21 E ___________________________________________________ _ 

T. 2 S., R. 21 E ________________________________________ ------------ T. 2 S., R. 22 E ___________________________________________________ _ 

T. 3 S., R. 22 E ________________________________________ ------------ T. 2 S., R. 23 E ________________________________________ ------------

1,220 

2,930 

144 

3,930 580 

1,338 

16.9 

16.9 

18.3 

18.3 

16.9 

16.9 

76.3 

183.2 

9. 7 266.0 

36.2 

83.5 

TotaL ______________________________________________________________ ------ ______ _ _____ 654. 9 

Summary of phosphate rock reserves in millions of tons 

43 feet or less 

43feet to 78 feet 

Amount of overburden 

78feet to 100 feet 

100 feet to top of water 

level in streams 

Stream 

level to 1,000 feet below 

stream 

level 

Total 

---------------1----1----·1---------------- T. 3 S., R. 20 E___________________________ 17.2 16.9 21.8 21.4 T. 2 S., R. 21 E___________________________ 91.8 140.7 307.0 85.0 T. 3 S., R. 21 E___________________________ 19.8 21.7 77.0 112.5 T. 2 S., R. 22 E___________________________ 136.7 220.0 366.0 56.2 

T. 3 S., R. 22 E ___________________________ ---------- ---------- ---------- ---------- T. 2 S., R. 23 E___________________________ 3.9 8.2 21.2 80.0 

TotaL _____ ------------------------- 269.4 407.5 793.0 355.1 

76.3 

9. 7 183.2 

266.0 

36.2 

83.5 

654.9 

153.6 

634.2 

414.2 

1,044. 9 36.2 

196.8 

2, 479.9 
ECONOMIC GEOLOGY 173 

Utilization.-The phosphate reserves of the Ashley Creek-Brush 

Creek area are undeveloped for two important reasons. In the first 

place, no railroad enters the Uinta Basin, and a long expensive truck 

haul of more than 100 miles is required to reach a railhead, and in 

the second place, the average grade of individual beds (maximum: 

28.5 percent P 20 5 ) that might be recovered by selective mining is below 

standards required in the present process for manufacturing superphosphate by treatment of the rock with sulfuric acid. If rail transportation could be made available, a process for separating the phosphate from the gangue minerals by using flotation, or by some other 

method relying upon the greater specific gravity of the phosphate 

1ninerals, probably could be devised. Such a process would not only 

raise the grade of the phosphate, but it would also remove objectionable 

Fe203 and Alz03 impurities. 

The entire phosphatic member could be mined at a relatively low 

cost by stripping the overlying slabby limestone, dolomite, and shale 

of the upper part of the Park City formation and removing the phosphate rock by the use of power shovels; the ease of mining may prove 

to be an important factor in influencing the ultimate utilization of the 

deposit. 

SAND AND GRAVEL 

The increased use of concrete in the building industry and in construction of hard-surface roads has made it increasingly important to 

have large supplies of sand and gravel. Not only must the quantity of 

sand and gravel be adequate, but only limited percentages of deleterious minerals (especially chert) may be present. John M. Cattermole, 

of the Engineering Geology Branch of the Geological Survey, examined a number of deposits with the writer in October 1947 to assist in 

their evaluation and description; he also made a mechanical size analysis of finer grained constituents of the samples collected from the 

gravel pits. 

Occurrence.-Sand and gravel occur in terrace deposits above the 

present levels of Green River, Ashley Creek, Brush Creek, Whiterock~ 

River, and Uinta River. They also occur as the sedimentary cover on 

an old pediment (the Jensen erosion surface) 300 feet or more above 

the present level of the streams, and as the principal constituents of the 

Bishop conglomerate, which underlies the high and almost flat surface 

rhat forms the summits of Little Mountain, Dry Fork Mountain, Mosby 

]\fountain, Pole Mountain, and Jefferson Park. The terrace deposits 

are the most accessible and most easily mined gravels in the area and 

have been the source of most of the material used in the area. 

The gravel deposits of the terraces range in thickness from 6 to 15 

feet and average about 8 feet; the gravel cover on the pediment is some-
17 4 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

what thinner, averaging about 5 feet; and the Bishop conglomerate is 

as much as 800 feet thick west of Uinta Canyon. The largest boulders 

commonly found in the terraces are 6 to 8 inches in dia1neter; occasionally, some pieces as large as 18 to 24 inches are present. Gravel that is 

more than three-fourths inch in diameter is round or subround. The 

coarse sand is subangular to angular, but the fraction that passes the 

30-mesh screen contains many rounded to subrounded frosted grains. 

Most of the finer fractions (even below 200-mesh) consist of fragmental 

unweathered material. 

Counts of pebbles ranging from lj~, to llh inches in diameter from 

deposits at different elevations above the level of the Green River show 

the following percentage ranges : . 

Rock types (1) (2) (3) (4) Rock types (1) (2) (3) (4) 

------ Quartzite ___________ ---- 43 26 48 49 Quartz __________________ 7 1 4 9 

Limestone __ ------------ 28 49 27 21 Chert_ ______ ------------ 2 8 4 4 Granite _________________ 16 10 15 14 Sandstone _______________ 4 6 2 3 

(1) Vernal Sand and Gravel Co., 20 feet above level of Green River SEUNWUSWU sec. 21, T. 5 S., R. 23 E. 

(2) Stewart Gravel Co., 40 feet above level of Green River NEUSWU sec. 19, T. 5 S., R. 23. 

(3) Utah State Highway Commission, 200 feet above level of Green River NEUSWU sec. 22, T. 5 S., R. 23 E. 

(4) Utah State Highway Commission, 300 feet above level of Green River SEUSWU sec. 33, T. 4 S., R. 23 E. 

The quartzite is brick-red, mottled red and white, or tan, and is undoubtedly derived either directly from the Uinta Mountain group or 

from boulders of the Uinta Mountain group in the coarse-grained 

Bishop conglomerate. The limestone is from the Madison or Morgan formations and the different sources frequently can be determined 

by the characteristic red chert associated with the limestone of the 

Morgan formation. The granite, quartz, and occasional large euhedral crystals of pink :feldspar (which have been counted as granite) 

are :from outcrops of peg1natitic intrusives into the pre-Cambrian 

Red Creek quartzite, which underlies the Uinta Mountain group in 

Browns Park on the north side of the Uinta }\fountains. The chert 

could be from a number o:f sources, the Madison, the Morgan, or the 

Park City formations. 

The gravel may be coated with a white caliche-like material, and 

streaks o:f gravel have been slightly cemented by soluble salts. Caliche 

cementation is con1mon in the gravel that veneers the pediment surface. Most of the terrace deposits are cut on the upper part of the 

Mancos shale, and fragments of shale are included in the gravel near 

the contact. 

Deposits.-Sand and gravel deposits in the Vernal area are operated :for only short periods; a deposit is opened to :fulfill a specific 

demand, and the equipment is moved and the pit is abandoned when 

that demand is satisfied. The principal use for sand and gravel is 
ECONOMIC GEOLOGY 175 

as a base for hard -surfaced or gravel roads in areas underlain by the 

sticky Morrison or Mancos formations. Generally, the material is 

used without crushing or other processing except for the removal 

of the larger boulders. Gravel for the surface-chip coat on improved 

highways is processed according to specifications of the Utah Highway Cmnmission engineers. Deposits used for road base provide 

poorly sorted material that has sufficient "fines" to bind the gravel. 

Any of the terrace deposits along Ashley Creek or Green River 

appears to be suitable for use as road material, and because these 

'deposits are thicker and closer to areas of demand, they will be used 

before the thin but cleaner gravel covering the Jensen surface is utilized. In 1947, a deposit in the NW!4NW%,NWlJ4 sec. 19, T. 4 S., R. 

23 E. was used to surface part of the road from Vernal northward 

to the hogback of the Frontier sandstone member of the Mancos shale 

on Utah State Highway 44. 

The demand for sized sand and gravel for use in concrete has been 

met frmn deposits west of Jensen and 20 to 40 feet above the Green 

River. The sand and gravel is clean and, after crushing and sizing, 

the 1naterial in excess of current demand is stockpiled for future use. 

Some of this concrete aggregate is trucked as far as the Rangely oilfield in northwestern Colorado. 

The following deposits represent most of the sand and gravel pits 

that have been operated in the area shown on plate 1: 

Location 

Name of owner or operator: 

Vernal Sand and Gravel Co _________ SENWSW sec. 21, T. 5 S., R. 23 E: 

Stewart Gravel Co __________________ NESW sec. 19, T. 5 S., R. 23 E.1 

Name unknown _____________________ SWNE sec. 19, T. 5 S., R. 23 E.1 

Utah State Highway Commission ____ NESW sec. 22, T. 5 S., R. 23 E.2 

U. S. Park Service __________________ SESW sec. 33, T. 4 S., R. 23 E.2 

Utah State Highway Commission ____ NWNW SW sec. 27, T. 5 S., R. 23 E. 2 

Do---------------------------- NWNW NW sec. 19, T. 4 S., R. 23 E.~ 

Do ____________________________ NESE sec. 35, T. 3 S., R. 21 E. 2 

U. S. Forest Service _________________ NWSE sec. 22, T. 2 N., R. 2 W. 2 

1 Concrete aggregate. 2 Highway base and surface. 

Reserves.-Adequate reserves of sand and gravel for road building 

are located in the general area, although many of the naturally occurring deposits are not suitable for concrete aggregate. These unsuitable 

deposits contain too high a percentage of fine-grained sand and silt, 

and the included chert might cause concrete failure if used with highalkali cement. In the event that large quantities of aggregate should 

be required for concrete construction, local supplies would soon be 

exhausted, and some other source, such as crushed quartzitic sandstone 

of the Uinta Mountain group, must be utilized. 
176 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

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178 GEOLOGY OF UINTA RIVER-BRUSH CREEK AREA, UTAH 

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INDEX 

A Page 

Accessibility to area _______________ 17-18 

Acknowledgments _________________ 7 

Anticlinal nose, Ashley Creek ___ 122-123, 

152,153 

Barker Spring________________ 124 

Brush Creek_________________ 123 

Davis Spring_________________ 123 

Dry Fork __________________ 122,158 

Whiterocks___________________ 122 

Anticlines, Section Ridge _____ 119-120, 158 

Split Mountain _____________ 119, 157 

Apatite-------------------------- 85 

Ashley Creek_____________________ 9, 10 

Ashley Creek oil and gas field _____ 152-157 

B 

Bishop conglomerate______________ 114 

See also under Formations. 

Black shale ______________________ 24, 33 

See also under Mississippian series. 

Brush Creek_____________________ 9, 10 

c 

Cambrian system ________________ _ 22 

Copper _________________________ _ 

Cretaceous system _______________ _ 

See also Lower(?) and Upper Cretaceous series, and Upper Cretaceous series 

under Formations. 

Curtis formation _________________ _ 

See also Middle and Upper Jurassic series, San Rafael 

group under Formations. 

D 

Page 

3 

95 

85 

Dakota sandstone _________________ 95-97 

See also Lower(?) and Upper Cretaceous series under 

Formations. 

Deep Creek fault zone ___________ 124-125 

Deep Fork_______________________ 9 

Deformation, age oL ____________ 125-126 

Drainage_________________________ 9 

Duchesne, precipitation ____________ 11, 13 

temperature__________________ 15 

E See also Lodore formation under 

Formations. 

Canyon development_ _____________ _ 

Carboniferous system _____________ _ 135 

Elkhorn, precipitation _____________ 10-1

1

3

temperature------------------ 5 

See also Mississippian series, ancl 

24 Entrada sandstone________________ 81 

Pennsylvanian series 

under Formations. 

Carmel formation ________________ _ 

See also Middle and Upper Jurassic 

series, San Rafael 

group under Formations. 

77 

Chert ---------------- 64, 91, 95, 111, 115 

Chinle formation__________________ 67 

See also Upper Triassic series 

undet· Formations. 

Climate __________________________ 10--16 

Coal_____________________________ 136 

character -------------------- 139 

chemical characteristics _____ 139-141 

in black shale unit of Misissippian age_____________ 142 

introduction________________ 136-137 

previous investigations________ 137 

production---------- 17, 103, 142-143 reserves ____________________ 143-149 

stratigraphy of occurrences____ 138 

Coal Mine Draw section___ 138 

Collier Mine Draw section- 138 

See also Middle and Upper Jurassic 

series, San Rafael group 

under Formations. 

F 

Faults, Deep Creek zone _________ 124-125 

South Flank zone_____________ 124 

Feldspar_________________________ 64 

Field work_______________________ 5-7 

Folds, Ashley Creek anticlinal nose_ 122-123 

Barker Spring anticlinal nose___ 124 

Brush Creek anticlinal nose____ 123 

Daniels Draw syncline________ 120 

Davis Spring anticlinal nose____ 123 

Dry Fork anticlinal nose_______ 122. 

Island Park syncline ________ 118-119 

Little Mountain synclines______ 121 

Mosby Mountain syncline or fault ______________ 121-122 

Neal Dome _____________ 120-121, 152 

Section Ridge anticline ______ 119-120 

Split Mountain anticline_______ 119 

Whiterocks anticlinal nose_____ 122 

181 
182 INDEX 

Formations, Bishop conglomerate __ _ 

definition ---------------- distribution and topographic 

Page 

114 

114 

expression--------- 114-115 

fossils and age _________ 115-116 

lithology and thickness____ 115 

stratigraphic relations and 

correlations _________ _ 

Green River _________________ _ 

,Lodore ______________________ _ 

conditions of deposition ___ _ 

definition ---------------- distribution nad character __ 

fossils and age __________ _ 

lithology and thickness ___ _ 

stratigraphic relations and 

correlations ----------

Lower(?) and Upper Cretaceous 

series, Dakota sandstone ----------------

definition----------------

distribution and topographic expression ___________ _ 

fossils and age ___________ _ 

lithology and thickness ___ _ 

stratigraphic relations and 

correlations _________ _ 

116 

5 

22 

24 

22 

22 

23 

23 

23-24 

95 

95 

96-97 

97 

95-96 

97 

Lower Triassic series, Moenkopi 

formation____________ 56 

conditions of deposition____ 61-62 

definition ________________ 56-57 

distribution and topographic 

expression ___________ _ 

fossils and age ___________ _ 

lithology and thickness ___ _ 

stratigraphic relations1 and 

correlations _________ _ 

Middle and Upper Jurassic series, 

San Rafael group, Carmel formation _______ _ 

conditions of deposition ___ _ 

distribution and topographic 

57-58 

59-60 

58-59 

60-61 

77 

80-81 

expression ____________ 78-80 

fossils ------------------- 80 

lithology and thickness ____ 77-79 name____________________ 77 

stratigraphic relations and 

correlations___________ 80 

Middle and Upper Jurassic series, 

San Rafael g r o u p, 

Curtis formation______ 85 

conditions of deposition____ 89 

distribution and topographic 

expression____________ 87 

fossils and age ____________ 87-88 

lithology and thickness____ 85-87 name____________________ 85 

stratigraphic relations and 

col'l'elation ___________ 88-89 

Middle and Upper Jurassic series, 

San Rafael group, Entrada sandstone formation_______________ 81 

conditions of deposition ___ 84-85 

Formations, etc.-Continued 

Middle and Upper Jurassic 

series-Continued 

distribution and topographic expression ___________ _ 

fossils and age ___________ _ 

lithology and thickness ___ _ name ___________________ _ 

stratigraphic relations and 

correlations _________ _ 

Mississippian series, black shale 

unit ________________ _ 

conditions of deposition __ _ 

definition ----------------

distribution and topographic expression ___________ _ 

fossils and age ___________ _ 

lithology and thickness ___ _ 

stratigraphic relations and 

correlations _________ _ 

Mississippian series, limestone unit ________________ _ 

conditions of deposition ___ _ 

definition ---------------- distribution and topographic expression ___________ _ 

fossils and age ___________ _ 

lithology and thickness ___ _ 

stratigraphic relations and 

correlations __________ _ 

Navajo sandstone ____________ _ 

conditions of deposition ___ _ 

correlation ---------------

distribution and topographic 

Page 

83 

83-84 

81-82 

81 

84 

33 

38 

33 

33-34 

35-37 

34-35 

37-38 

25 

33 

25 

25-26 

30-31 

26-30 

32-33 

73 

76 

76 

expression ____________ 7 4-75 

lithology and thickness____ 73-7 4 

name and definition_______ 73 

stratigraphic relations and 

age__________________ 75-76 

Park CitY-------------------- 48 

conditions of deposition ____ 54-55 

definition---------------- 48 

distribution and topographic expresdon ____________ 48-49 

fossils and age ____________ 51-53 

lithology and thickness---- 49-51 

stratigraphic relations and 

correlations __________ 53-54 

Pennsylvanian series, Morgan 

formation____________ 38 

conditions of deposition and 

origin________________ 44 

definition ---------------- 38 

distribution and topographic 

expression ____________ 38-40 

fossils and age ____________ 42-44 

lithology and thickness ____ 40-42 

stratigraphic relations and 

correlations ---------- 44 

Pennsylvanian series, Weber 

sandstone____________ 45 

conditions of deposition and 

origin ________________ 47-48 
INDEX 183 

Page Page 

Formations, etc.-Continued 

Upper Jurassic series-Continued 

Formations, etc.-Continued 

!Pennsylvanian series-Continued 

definition ---------------- distribution and topographic 

45 lithology and topographic 

expression ___________ _ 

fossils and age ___________ _ 

lithology and thickness ___ _ 

stratigraphic relations and 

correlations __________ _ 

Uinta ~ountain group ________ _ 

conditions of deposition ___ _ 

definition ----------------

46 

46-47 

46 

47 

20 

22 

20 

distribution and character __ 20-21 

lithology and thickness____ 21 

stratigraphic relations and 

age __________________ 21-22 

Upper Cretaceous series, ~ancos 

shale ________________ 97-98 

Upper Cretaceous series, ~ancos 

shale, li'rontier sandstone member________ 102 

conditions of deposition __ 106-107 

correlation--------------- 106 

definition -------------- 102-103 

distribution _______ ------- 105 

fossils, age, and stratigraphic relations ___ 105-106 

lithology and thickness __ 103-105 

Upper Cretaceous series, Mancos 

shale, ~owry shale 

member-------------- 98 

conditions of deposition___ 102 

correlation --------------- 102 

distribution -------------- 101 

fossils, age, and stratigraphic relations ___ 101-102 

lithology and thickness ___ 99-101 

name and definition _______ 98-99 

Upper Cretaceous series, Mancos 

shale, upper shale mem- ber__________________ 107 

conditions of deposition __ 109-110 

definition ---------------- 107 

distribution and topographic 

expression ----------- 108 

fossils and age____________ 109 

lithology and thickness __ 107-108 

stratigraphic relations' and 

correlations----------

Upper Cretaceous series, Mesaverde formation ______ _ 

conditions of deposition ___ _ 

definition ----------------

distribution and topographic 

109 

110 

113 

110 

expression____________ 112 

fossils and age _________ 112-113 

lithology and thickness __ 110--112 

stratigraphic relations and 

expression----------- 91-93 name____________________ !:10 

stratigraphic relations and 

correlations ---------- 94 

Upper Triassic series, Chinle 

formation____________ 67 

conditions of deposition ___ 72~73 

distribution and thickness_ 69-70 

fossils and age___________ 71 

lithology and topographic expression ------------- 68-6!) name and definition _______ 67-68 

stratigraphic relations and 

correlations __________ 71-72 

Upper Triassic series, Shinarump 

conglomerate_________ 67 

conditions of deposition or 

origin --------------- 67 

definition---------------- 63 

fossils ------------------- 65 

lithology and thickness ____ 64-65 

stratigraphic relations, age, 

and correlations ______ 65-67 

topographic expression and' 

distribution___________ 63 

Fort Duchesne, precipitation ____ 11, 13, 14 

temperature__________________ 15 

Frontier sandstone member, Mancos 

shale ---------------- 102 

See also Upper Cretaceous series, 

~ancos shale under 

Formatioos. 

G 

Geology, previous investigations ___ _ 

Geomorphology, canyon development_ 

general ---------------------- glacial deposits ______________ _ 

correlation with adjacent areas _______________ _ 

distribution --------------

earliest ------------------ latest ___________________ _ 

lithology and dating of ad- vances ______________ _ 

18-20 

135 

126 

130 

135 

130 

131 

133 

131 

maximum________________ 132 

surfaces, Gilbert Peak _______ 126-128 

Jensen _________________ 12~129 

Lake Mountain___________ 128 

younger erosion _________ 129-130 

.Gilbert Peak surface. See surfaces 

under Geomorphology. 

Glacial deposits _____________ 127, 130-135 

Gold_____________________________ 162 

Green River______________________ 9 

correlations ---------- 113 GypsUnl__________________________ 77 

Upper Jurassic series, Morrison 

formation ------------ 90 

conditions of deposition___ 94 Iron_____________________________ 3 

distribution-------------- 90 Island Park syncline. See under 

fossils and age____________ 93-94 Folds. 
184 INDEX 

Page Page 

J Mosby Mountain syncline or fault. 

Jensen, precipitation______________ 11 

temperature------------------ 15, 16 

Jensen surface. See surfaces under 

Geomorphology. 

Jurassic(?) system. See Navajo 

sandstone under Fprmations. 

Jurassic system. See Middle and Upper Jurassic series, and 

Upper Jurassic series 

under Formations. 

L 

Ladore formation ________________ _ 

See also under Formations. 

Lake Mountain surface. See surfaces under Geomorphology. 

Lead----------------------------

Lignite--------------------------

Limestone unit_ _________________ _ 

See also Mississippian unit under 

Formations. 

Little Brush Creek _______________ _ 

Little Mountain synclines. See under 

Folds. 

Location ________________________ _ 

Lower and Upper Cretaceous series. 

See undet· Formations. 

Lower Triassic series. See under 

Formations. 

M 

22 

3 

103 

25 

9 

4-5 

See under Folds. 

Moury shale member______________ 98 

See also Upper Cretaceous series, 

Mancos shale under Formations. 

Mudstone _____________________ 68, 77, 91 

Myton, precipitation ___________ 11, 13, 14 

temperature__________________ 15, 16 

N 

Navajo sandstone_________________ 73 

See also under Formations. 

Neal dome. See under Folds. 

Oil 

0 

and gas _________________ 3,5, 17,150 

Ashley Creek gas field _______ 152-153 

Ashley Creek oil field ________ 153-157 

Asphalt Ridge monocline______ 152 

chemical composition and physical properties ______ 150-151 

Dry Fork anticlinal nose_______ 158 

explQration___________________ 152 

Neal dome___________________ 152 

possibilities---------------- 158-159 

Section Ridge anticline________ 158 

Split Mountain anticline ____ 157-158 

surface indications___________ 150 

p 

Park City formation ______________ _ 48 

See also under Formations. 

Pennsylvanian series. See under ForMancos shale ____________________ _ 97 mations. 

See also Upper Cretaceous series 

under Formations. 

Mesaverde formation _____________ _ 

See also Upper Cretaceous series 

under Formations. 

Metallic mineral deposits _________ _ 

110 

159 

copper_______________________ 159 

Dyer mine_______________ 159 

ore______________________ 160 

gold_________________________ 162 

iron ----------------------- 161-162 

lead_________________________ 161 

Middle and Upper Jurassic series. See 

under Formations. 

Mississippian series. See under Formations. 

Moenkopi formation ______________ _ 

See also Lower Triassic series under 

Formations. 

56 

Moon Lake, precipitation __________ 11, 12 

Permian system ___________________ 48-55 

Phosphate _______________________ 48,162 

composition ________________ 166-167 

content of beds_______________ 168 

development Qf deposits_______ 170 

hydrocarbons__________________ 169 

iron oxide and alumina________ 168 

lithQlogy and occurrence_______ 163 

physical appearance _________ 163-165 

reserves ____________________ 170-172 

terminology---------------- 165-166 

utilization------------------- 173 

vanadium__________________ 168-16!) 

Pine Ridge structure______________ 122 

Population and occupation_________ 16-17 

Pre-Cambrian -------------------- 20 

See also Uinta Mountain group 

tf,nder Formations. 

Purpose and scope of report_ ______ _ 

Q 

5 

temperature__________________ 15 

Morgan formation_________________ 38 Quartzitic sandstone ___________ 64, 68, 82 

See also Pennsylvanian series under 

Formations. 

Morrison formation ______________ _ 

See also Upper Jurassic series under 

Formations. 

R 

90 References and publications_______ 18-20, 

176-180 

Rim Rock------------------------ 9 
s 

San Rafael ~roup ________________ _ 

See also Middle and Upper Jurassic 

series under Formations. 

INDEX 

Page Tourmaline _______________________ _ 

Triassic system __________________ _ 

77 ,<gee also Lower Triassic series, a,nd 

Upper Triassic series 

under Formations. 

Sand and gravcl ______________ 4, 115, 173 u 

185 

Page 

85 

55 

deposits-------------------- 174-175 occurrence----------------- 173-174 Uinta Basin_____________________ 5, 8 

reserves______________________ 175 Uinta Mountain group____________ 20 

Sandstone----------------------- 20, See a-lso under Formations. 

22, 24, 38, 45, 48, 56, 64, Uinta Mountain range______________ 7, 8 

68, 73, 77, 81, 85, 91, 9 5, Uinta River _______________________ 9, 10 

98, 102, 107, 110, 115. Upper Cretaceous series. See under 

Section Ridge anticline. See under Formations. 

Folds. Upper Jurassic series. See under 

Shale____________________________ 20, Formations. 

22, 38, 48, 56, 65, 68, 77, Upper shale member______________ 107 

81, 85, 91, 95, 97, 98, 104, See also Upper Cretaceous series, 

107, 110. Mancos shale under ForShinarump conglomerate __________ _ mations. 

See also Upper Triassic series under 

Formations. 

63 

Siltstone ___________ 57, 68, 79, 81, 103, 107 

Upper Triassic series. See under Formations. 

v South Flank fault zone. See under 

Faults. Vegetation----------------------- 16 

Split Mountain anticline. See under Vernal, precipitation ______________ 11, 13 

Folds. temperature __________________ 15, 16 

Spring __________________________ _ 10 Vernal strath terrace. See younger 

Stratigraphy, generaL ____________ _ 

See also under particular Period or 

System. 

2.0 erosion surfaces under 

Geomorphology. 

Structure, general features_________ 117 

methods of representing_______ 116 

Synclines ______________ 118-119, 121-122 

T 

Tertiary system ________________ 114-116 

w 

Weber sandstone _________________ _ 

See also Pennsylvanian series under 

Formations. 

Whiterocks anticlinal nose. 

under Folds. 

See 

45 

Tetrataxis -----------------------

Thornburg strath terrace. See 

43 Whiterocks !liver_ _________________ 9, 10 

younger erosion surfaces under Geomorphology. 

y 

Yampa Plateau __________________ _ 

Topography, drainage, and water z 

8 

supply_______________ 7-10 Zircon___________________________ 85 

0