Geology and U rani urnVanadium Deposits of 

the La Sal Quadrangle 

San Juan County, Utah, and 

Montrose County, Colorado 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 508 

Prepared on behalf of the 

U.S. Atomic Energy Commission 

Geology and UraniumVanadium Deposits of 

the La Sal Quadrangle 

San Juan County, Utah, and 

Montrose County, Colorado 

By WILLIAM D. CARTER and JAMES L. GUALTIERI 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 508 

Prepared on behalf of the 

U.S. Atomic Energy Commission 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965 
UNITED STATES DEPARTME T OF THE INTERIOR 

STEWART L. UDAL ,. Secretary 

GEOLOGICAL 

William T. Pecora, Director 

Library of Congress cataloll-card No. GS 65-325 

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 
CONTENTS 

Page Abstract __________________________________________ _ 1 Structural geology-Continued Introduction ______________________________________ _ 1 Folds-Continued 

Geologic setting ___________________________________ _ 3 Castle Valley-Paradox Valley anticline _______ _ Stratigraphy ______________________________________ _ 4 Willow Basin syncline ______________________ _ 

General description ____________________________ _ 4 Scorup anticline _______ -- ____ -_------- ___ ---

Pennsylvanian System _____________ ~ ____________ _ 4 Geyser Creek syncline ________ --_----_------- Hermosa Formation ________________________ _ 4 La Sal Creek syncline ________ - __ - ________ - - _ 

Pennsylvanian and Permian Systems _____________ _ 5 Pine Ridge anticline _____________ - ________ --_ 

Rico Formation ___________________________ _ 5 East Coyote Wash syncline ___________ -.- ____ _ 

Permian System _______________________________ _ 5 La Sal Mountains ______________________________ _ 

Cutler Formation __________________________ _ 5 North Mountain ___________________________ _ 

Triassic System ________________________________ _ 6 Middle Mountain ________________________ ---

Lower and Middle(?) Triassic Series __________ _ 6 Stock ________________________________ _ 

Moenkopi Formation ___________________ _ 6 Dikes ________________________________ _ 

Upper Triassic Series _______________________ _ 6 Sills __________________________________ _ 

Chinle Formation ______________________ _ 6 Laccoliths ___________ - - ____ - ___ - _ - - - - - -

Glen Canyon Group (lower part) ________ _ 8 Mount Mellenthin _______________ -- _ 

Wingate Sandstone ________________ _ 8 Bysmalith _________________ -- ____ - __ ---

Upper Triassic(?) Series ____ .. _______________ _ 8 Mount Peale ____________________ ---

Glen Canyon Group (middle part) _______ _ 8 South Mountain ___________________________ _ 

Kayenta Formation ________________ _ 8 Faults _______________________________________ -_ 

Triassic(?) and Jurassic Systems _________________ _ 8 General features _________________________ ---

Glen Canyon Group (upper part) ____________ _ 8 Longitudinal faults _____ -- ______ --_------ Navajo Sandstone _____________________ _ 8 Valley View fault ________________ - - -

Jurassic System _______________________________ _ 9 Dugway fault _____________________ _ 

San Rafael Group __________________________ _ 9 Geyser Creek faults ___________ - __ ---

Entrada Sandstone _____________________ _ 9 Transverse faults __________________ --_------

Contact of the Entrada Sandstone and Paradox Valley ________________________ _ 

Summerville Formation _______________ _ 11 Sharp Canyon fault _________ - --- -------- Summerville Formation _________________ _ 11 Radial faults ________________ - __ ------------

Morrison Formation ___________________ _ 12 Middle Mountain ___________ ------------

Salt Wash Member ________________ _ 12 Structural history ___________________ ------------

Brushy Basin Member ___ ----------_ 13 Uranium deposits ________________________ -----------

Cretaceous System _____________________________ _ 14 History of mining in the La Sal quadrangle _______ _ 

Lower Cretaceous Series ____________________ _ 14 Distribution ________________________ ------------

Burro Canyon Formation _______________ _ 14 Size and shape ________________________________ _ 

Burro Canyon-Dakota contact ______ _ 15 Localization ________________________ - - - - - - - - - - - -

Upper Cretaceous Series ____________________ _ 16 Mineralogy ___________________________________ _ 

Dakota Sandstone _____________________ _ 16 Origin ________________________________________ _ 

Mancos Shale _________________________ _ 18 Mines ________________________________________ _ 

Tertiary(?) System _____________________________ _ 19 Angle mine ____________________ ------------

Geyser Creek Fanglomerate _________________ _ 19 Black Hat mine ___________________________ _ 

Qua ternary System ____________________________ _ 22 Brushy Basin No.1 mine ___________________ _ Igneous RockE _____________________________________ _ 23 Brushy Basin No.3 mine _______ .; ___________ _ Petrography __________________________________ _ 23 Confusion mine _________________ ------------ Inclusions _____________________________________ _ 24 Elray mine __________________ - __ - - - --- - - - - - -

Contact metamorphism _________________________ _ 24 Evening Star mine _______________________ --- Age __________________________________________ _ 25 Firefly-Pigmay mine _________ ----------- ___ _ Structural geology _________________________________ _ 26 Gray Daun mine __________________________ _ Folds _________________________________________ _ 26 Western workings _____________________ -_ 

Sinbad Valley anticline _____________________ _ 26 Eastern workings ____________________ - - _ 

Roc Creek syncline ________________________ _ 27 Hesperus mine ___________________________ -_ 

Taylor Creek syncline ______________________ _ 27 Jackpot mine _________________________ --_---

III 

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IV CONTENTS 

Uranium deposits-Continued Uranium deposits-Continued 

Mines-Continued Page Mines-Continued Page 

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Little Don mine _______ - __ - - - __ - - - - ___ - - _ _ _ _ 62 Wedge mine _______________________________ _ 

Little Peter mine___________________________ 62 Yellow Bird mines _________________________ _ 

Lucky No. 1 mine ______________ -___________ 63 Yip Yip mine _____________________________ _ 

Marjorie Ann mine_________________________ 63 Suggestions for prospecting _____________________ _ 

Maudmine________________________________ 64 Guides to exploration and ore ___________________ _ 

Morning Star mine__________________________ 65 Other resources of possible economic interest __________ _ 

New Yellow Spot mine______________________ 65 Coal _________________________________________ _ 

Sumner mine_______________________________ 66 Copper deposits _______________________________ _ 

Too High mine_____________________________ 66 Iron deposits __________________________________ _ 

Uranium Girl mine__________________________ 67 Oil and gas ___________________________________ _ 

Valley View mine___________________________ 67 Water ________________________________________ _ 

Vanadium Queen mine_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 68 References cited ___________________________________ _ 

Vista Grande mine__________________________ 70 Index ____________________________________________ _ 

ILLUSTRATIONS 

[Plates are in pocket] 

PLA.TE 1. Geologic map and section of the La Sal quadrangle. 

FIGURE 

2. Generalized columnar section of sedimentary rocks exposed in the La Sal quadrangle. 

3. Structural map of the La Sal quadrangle. 

4. Geologic map and sections showing areas of favorable, semifavorable, and unfavorable ground, the location of diamonddrill holes, the position and extent of the ore-bearing sandstone and contained deposits of mineralized material in 

the La Sal Creek area. 

5. Generalized geologic map showing base of the ore-bearing sandstone of the Morrison Formation, the La Sal Creek 

mineral belt, and qistribution of uranium-vanadium deposits, La Sal quadrangle. 

6-13. Maps and geologic sections of the6. Evening Star mine. 

7. Firefly-Pigmay mine. 

8. Gray Daun mine. 

9. Hesperus mine. 

10. Little Don mine. 

11. Marjorie Ann mine. 

12. Vanadium Queen mine. 

13. Yellow Bird group of mines. 

1. Index map of the La Sal quadran.,gle _______________________________________________________________ _ 

2. Photograph of Burro Canyon-Da~ota contact _________________________________ -- ____________________ _ 

3. Photograph of Geyser Creek Fanglomerate __________________________________________________________ _ 

4. Photograph of conglomerate at type section on Deep Creek ___________________________________________ _ 

5. Photograph of a clastic dike _________________ ------"'" _______________________________________________ _ 

6. Isopach map showing thickness of strata from the top of the Entrada Sandstone to the base of the ore-bearing 

sandstone--------------------------------------------------------------------------------------

7. Structure contour map of the base of the ore-bearing sandstone ________________________________________ _ 

8. Composite orientation diagrams showing trends of sedimentary and other structures in mines of the La Sal 

Creek area------------------------------------------------------------------------------------- 9. Photomicrograph of clausthalite bands in sandstone __________________________________________________ _ 

10. Photomicrograph of clausthalite bands in sandstone __________________________________________________ _ 

11. Photomicrographs of uraninite from the Gray Daun mine _____________________________________________ _ 

12. Photograph showing mudstone-pebble conglomerate and breccia in the Vanadium Queen mine _____________ _ 

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CONTENTS v 

TABLES 

Page 

TABLE 1. Minerals identified in ores of the La Sal quadrangle and their vanadium-uranium ratios_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 4 7 

2. Isotopic analyses of clausthalite and unknown lead-vanadium mineral from the Firefly-Pigmay mine and galena from the Cashin mine__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 48 

3. Semiquantitative spectrographic analysis of clausthalite and unknown lead-vanadium mineral from the FireflyPigmaymine______________________________________________________________________________________ 48 

4. Apparent paragenetic sequence of urnaium, vanadium, and accompanying sulfide minerals______________________ 50 

GEOLOGY AND URANIUM-VANADIUM DEPOSITS OF THE LA SAL QUADRANGLE, SAN JUAN 

COUNTY, UTAH, AND MONTROSE COUNTY, COLORADO 

By WILLIAM D. CARTER and JAMES L. GuALTIERI 

ABSTRACT 

. During the period from 1952 through 1956 the U.S. Geological 

Survey conducted exploration by diamond drilling for uraniumvanadium deposits in the Salt Wash Member of the Morrison 

Formation of Jurassic age in the La Sal Creek area, and mapped 

the geology of the surrounding La Sal ( 15 minute) quadrangle, 

Utah-Colorado. 

The La Sal quadrangle, comprising about 240 square miles of 

San Juan County, Utah, and Montrose County, Colo., is in the 

Canyon Lands section of the Colorado Plateau. Upper Paleozoic, Mesozoic, and Cenozoic sedimentary rocks cover most of 

the area. These are gently folded and faulted by uplift, intrusion, and collapse of plastic -evaporite masses on the east and by 

intrusion of laccolithic complexes now composing the La Sal 

Mountains on the west. The folding of the salt anticlines occm·red at different times. The latest folding of the anticlines, 

accompanied by igneous intrusion, took place during the Late 

Cretaceous and early Tertiary periods and may have extended 

through Miocene time. Certain laccolithic bodies may have intruded the sedimentary rocks higher in the stratigraphic column 

prior to emplacement along lower stratigraphic horizons. 

Exploration by the U.S. Geological Survey resulted in the 

discovery of 115,000 tons of uranium-vanadium ore in a mineralrich belt that trends N. 70° E., is approximately 6 miles long, 

and ranges from 500 to 3,000 feet in width. Almost all the ore 

is in the uppermost continuous sandstone of the Salt Wash 

Member of the Morrison Formation. The strata of the orebearing sandstone range in thickness from a few feet to 105 

feet. The strata are medium-to fine-grained quartzose sandstone interbedded with siltstone and mudstone. Near the uranium-vanadium deposits the sandstone is white, light gray, or 

light brown, and the siltstone and mudstone are usually light 

green or gray green. Away from the deposits the sandstone 

and mudstone units are shades of reddish brown. 

In the area of La Sal Creek Canyon the lower beds of the orebearing sandstone fill a northeast-trending paleostream channel containing local scours that are as much as 20 feet deep. 

The scours are filled by sandstone in which cross-stratification, 

current lineation, ripple marks, mud cracks, and slumping and 

compaction structures are common. These structures have 

been recognized in the mines and help to determine the direction of stream flow during deposition of the Salt Wash. The 

main channel in the La Sal Creek area has been defined by 

exploratory drilling and found to coincide with the area that is 

considered ~avorable for the presence of uranium-vanadium 

deposits. 

Uranium and vanadium minerals occur together as bedded or 

roll deposits impregnating sandstone and siltstone and as replacement bodies in accumulations of carbonaceous and mudstone debris. The ore bodies, although extremely irregular in 

size and shape, are elongate, usually have sharp boundaries, 

and are oriented en echelon roughly parallel to the trend of 

sedimentary structures. Individual bodies may contain from a 

few pounds to several thousand tons of ore-grade material. 

These bodies are clustered in such a manner that several thousand tons can be removed from a single mine. 

Uranium minerals in the area include uraninite and uranyl 

silicates, phosphates, arsenates, and vanadates. Vanadium is 

closely associated with the uranium as silicates, vanadates, 

and oxides. Individual deposits are either dominantly unoxidized or oxidized. The unoxidized ores contain minor amounts 

of sulfides, arsenides and selenides. The ratio of v~nadium to 

uranium averages 6:1 and ranges from 4:1 to 14: 1, reflecting 

the gross mineral composition of the deposits. 

The localization of uranium and vanadium minerals in sandstone probably was controlled by (1) the position of the sandstone beds in the channel, (2) the presence of mudstone films, 

seams. and mudstone-pebble conglomerate beds which affects 

the permeability of the sandstone lenses, and ( 3) the presence 

of carbonized wood and plant remains within the beds. Folds, 

faults, and fractures have no apparent relation to the localization of the uranium-vanadium deposits. Secondary ore minerals, however, fill fractures as a result of recent oxidation and 

ground-water movement. 

Exploration guides that have been used successfully in the 

La Sal Creek area to locate uranium-vanadium ore bodies are 

as follows: 

1. White, light-brown, or light-gray, lenticular sandstone, 30 

feet or more in thickness, underlain by, interbedded with, 

and (or) overlain by gray, gray-green or light-green mudstone. 

2. Irregularities at the base of the ore-bearing sandstone: channels, bar and swale topography, and cuspate or noselike 

projections along the channel margins. 

3. Trash pockets : accumulations of mudstone pebbles and carbonaceous debris. 

INTRODUCTION 

The La Sal quadrangle (fig. 1) includes about 240 

square miles along the Utah_;Colorado boundary in the 

Canyon Lands section of the Colorado Plateau (Fenneman, 1931, p. 306-312) between long 109°00' and 

109°15' and lat 38°15' and 38°30'. The area is in the 

northeast corner of San Juan County, Utah, and in the 

1 
2 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORA:DO 

M E S A 

I 

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I L ____ _ I 

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___ j 

S A N J U A N 

0 Monticello --------\ ,__,.,~--./ 

0 10 20 30 40 MILES 

FIGURE 1.-Location of the La Sal quadrangle and major structural features of the esatern part of the 

Colorado Plateau. 

northwest corner of Montrose County, Colo.; more than 

half of the area is in the Manti-La Sal National Forest. 

The area is sparsely populated. The small village of 

La Sal, Utah, near the southwestern margin of the 

area has a general store and post office to accommodate 

the inhabitants of the surrounding countryside. 

Access to the area is by Utah Highway 46, an allweather paved road which connects with U.S. Highway 

160 at La Sal Junction, to the west, and Colorado Highway 90 at the Utah-Colorado line in La 1

Sal Creek 

Canyon. Colorado Highway 90 extends from the 

mapped area eastward through Paradox and Bedrock, 
GEOLOGIC SETTING 3 

Colo., to Naturita where it connects with Colorado 

Highway 140. An intricate network of Forest Service 

roads, drilling access roads, and jeep trails makes most 

of the area accessible during the dry months of the 

year. Three small landing strips for light aircraft are 

available in the southern half of the area. 

Previo·us work.--Many geologists have visited the 

mapped area since A. C. Peale ( 1877 a, b) made a short 

visit in 1875. Geologic work and reports speci·ficaHy 

dealing with the area, however, have been limited to 

early reconnaissance studies of the uranium-vanadium 

deposits made by Coffin (1921) and a preliminary study 

of the igneous rocks of the La Sal Mountains by Gould 

( 1926) . Additional economic studies were made by 

Fischer (1942). Detailed studies of the uranium-vanadium deposits were made by C. W. Livingston (written 

commun., 1945) for the Manhattan Project. In 1952 the 

igneous rocks of the La Sal Mountains were studied in 

detail by Hunt and A. C. Waters (Hunt, 1958). At the 

same time, Richmond ( 1962) studied the glaciology and 

the surficial deposits of the La Sal Mountains area. 

Purpose and scope of report.-This report describes 

the geology and uranium-vanadium deposits of the La 

Sal quadrangle. The fieldwork was undertaken hy the 

U.S. Geological Survey on behalf of the Raw Materials Division of the U.S. Atomic Energy Commission 

as part of a program to stimulate the search for and 

mining of uranium in the Colorado Plateau. The investigations were initiated to help develop known deposits, to explore for new deposits, and to search for 

new areas containing uranium-vanadium deposits. 

They also provided data on the regional geology of the 

area and thereby aided in the evaluation of the uranium 

resources of the Colorado Plateau. 

Fieldwork.-An exploration drilling program was 

started in May 1952 under the direction of George K. 

Brasher and Richard C. Douglas. From April 1953 

to November 1956. the drilling was supervised by the 

authors. During 1953 D. C. Hedlund and R. C. Doman 

acted as geologic assistants. J. C. Warman and W. R. 

Barton joined the party in 1954 and 1955, respectively 

and worked as geologic assistants until the fall of 1955. 

During the drilling program the field party was supplemented by a sampler foreman, Glen Kralicek, and 

severrul samplers who had continual supervision of the 

drill rigs and handled the core samples. 

Diamond drilling on close-spaced centers (holes 

50-100 ft apart) behind mine faces of the Evening Star, 

Gray Daun, and Vanadium Queen mines dis,covered 

new ore bodies and led the Survey to enlarge its program 

to widespread subsurface exploration. A total of 505 

diamond-drill holes totaling 123,371 feet were completed 

in the La Sal Creek area during the seasonable months 

77'7-039 0---65--2 

of 1952, 1953, and 1954. The winter months of 1953 

through 1955 were devoted to subsurface mine studies 

to determine the size, configuration, ore controls, and 

mineralogy of the ore bodies and to discover guides 

which might aid the search for ne~ areas favorable for 

the occurrence of uranium-vanadium deposits. By the 

end of 1954, private industry showed sufficient active 

interest in the search for uranium that the U.S. Geological Survey party withdrew from physical exploration 

and devoted full time to geological investigations. 

These investigations began late in the spring of 1954 

and were carried on concurrently with the final drilling 

program which terminated late in 1954. Field investigations and map compilation continued and consisted 

of rna pping the geology of the La Sal quadrangle and 

detailed studies of the ore-bearing sandstone of the Salt 

Wash Member of the Morrison Formation. The mapping and related studies were completed in November 

1956. 

Most of the mines in the La Sal Creek area were 

mapped by tape and compass methods on a scale of 1 

inch equals 20 feet. Maps of the drilling area were made 

by transit surveys on a scale of 1 inch equals 1,000 feet. 

Areal geologic rna pping was done by plotting the geology on aerial photographs, scale 1 :37,500, and transferring it to topographic maps, scale 1 :24,000, by means 

of photogrammetric plotters. This scale was subsequently reduped to 1 :62,500 (pl. 1). 

Acknowledgments.-The authors wish to express 

their gratitude to the Stocks-Gramlich Corp., The V anadium Queen Mining Corp., U.S. Vanadium Corp., 

Four Corners U rani urn Corp., and Vanadium Corp. of 

America for their cooperation in the exploration and 

mine-mapping phases of the project; to Messrs. H. S. 

Stocks, J. B. Crowley, A. M. Stocks, and W. Hall, 

residents in the La Sal Creek area, Messrs. J. W. Gramlich, Howard Balsley, and Abe Day of Moab, Utah, for 

information on the history and geography of the area, 

and to Mr. J. N. Plake, surveyor, who made the base 

maps of the area explored by diamond drilling. The 

authors wish to express their appreciation also to A. D. 

Weeks, M. E. Thompson, Theodore Botinelly, R. G. 

Coleman, L. R. Stieff, T. W. Stern, and Mona Frank of 

the Geological Survey who contributed information on 

the mineralogy of the deposits. 

GEOLOGIC SETTING 

Exposed within the La Sal quadrangle, Utah-Colorado, is a sequence of Upper Paleozoic, Mesozoic, and 

Cenozoic sedimentary rocks (pl. 1) which have been 

uplifted by movement of plastic evaporite masses to 

form a series of three northwest-trending anticlines. A 

fourth anticline lies outside the mapped area. Between 
4 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORAIDO 

these major anticlinal areas are three major synclinal 

folds. On the west the sedimentary rocks have been uplifted and intruded by three groups of laccolithic masses 

which form the La Sal Mountains. Many minor anticlinal and synclinal folds occur where the crests of the 

major anticlines were breached by erosion and where 

subsequent solution or flowage of salt led to the collapse 

of the overlying strata. Parts of such areas form large 

valleys. 

The sedimentary formations are exposed in these 

valleys and nearby canyons and mesas, and in the hogbacks surrounding the igneous rqcks. Thinning of 

beds, angular unconformities, and wedging out of entire 

formations indicate a history of periodic uplift of the 

evaporite masses. Faults and joints resulting from 

both uplift and collapse of .the salt anticlines and from 

uplift by intrusive igneous bodies are common. 

Most of the economic deposits of uranium and vanadium in sandstone are in the east-central part of the 

area; low-grade deposits of coal, copper, and iron are 

around and within the La Sal Mountains. Vein deposits of argentiferous copper have been exploited east 

of the area. 

STRATIGRAPHY 

GENERAL DESCRIPTION 

Sedimentary rocks exposed within the La Sal quadrangle attain 8,500 feet or more in thickness and range 

in age from Pennsylvanian to Recent. The oldest 

rocks, the Hermos~ Formation of Pennsylvanian age, 

crop out in the floor of Sin bad Valley in the northeast 

corner of the ·area and are probably in .contact with the 

igneous rocks of the North and South Mormtain groups 

of the La Sal Mountains. The next overlying formations, the Rico of Pennsylvanian and Permian age and 

the Cutler of Permian age, are exposed in the walls of 

Sin bad Valley and also around the igneous rocks of the 

North and South Mountain groups. These formations 

are poorly exposed in the mountainous areas and are, 

therefore, together with the Hermosa Formation, considered as a single mapping unit. Triassic and Jurassic formations crop out on the walls of Sinbad Valley 

and Roc Creek canyon and form the sharp hogback 

surrounding the North and South Mountain groups. 

In addition, the Jurassic formations are exposed in La 

Sal Creek Canyon, Sharp Canyon, a.t the northwest end 

of Paradox Valley, near Coyote Wash in the southeastern part of the area, and in the Middle Mountain 

group. High mesas capped by rocks of Early and Late 

Cretaceous age cover almost half of the area. The 

youngest sedimentary rocks, with the e:x;ception of Tertiary ( ? ) fanglomerate and Recent gravel, are those of 

the Mancos Shale of Late Cretaceous age. These rocks 

are restricted -almost entirely to the synclinal structures 

of Taylor Creek, Geyser Pass, and La Sal Pass. Consolidated gravel of Tertiary ( ? ) age crops out along 

Geyser and Deep Creeks. Recent deposits of rmconsolidated stream gravel and glacial and landslide debris 

flank the three uplifted igneous centers of the La Sal 

Mountains; deposits of windblown material and sheet 

wash are widely distributed on the mesas and valley 

floors. The stratigraphy of the area is summarized in 

the columnar section shown on plate 2. 

PENNSYLVANIAN SYSTEM 

HERMOSA FORMATION 

The Hermosa Formation of Pennsylvanian age crops 

out in the floor of Sin bad Valley in the northeast corner 

of the La Sal quadrangle and in the adjacent quadrangles to the north and east which cover Sin bad Valley, 

· Roc Creek, and Paradox Valley. The Hermosa Formation is divided into two members: the lower, the 

Paradox Member, composed predominantly of salt and 

gypsum; the upper, an unnamed member, composed of 

limestone and red beds, including arkose. 

The Paradox Member of the Hermosa Formation 

crops out in the floor of Sinbad Valley as isolated hillocks surrounded by alluvium. Because the beds-composed of gypsum, black shale, micaceous sandstone, 

arkose, limestone, and limestone breccia and conglomerate-are highly contorted, it is impossible to reconstruct the true stratigraphic sequence or to determine 

accurately the thicknesses. Wells drilled in Sin bad and 

Paradox Valleys indicate that, at depth, salt is the 

major constituent of the Paradox Member. One well 

in Paradox Valley, a bout 8 miles east of the La Sal 

quadrangle, was drilled through approximately 11,000 

feet of the Paradox Member and did not penetrate the 

base. This great thickness is attributed to flowage of 

the salt during formation of the salt anticlines. 

The upper member of the Hermosa Forination is 

exposed in an isolated belt along the southwest side of 

Sin bad Valley. The beds, dipping steeply to the southwest, are about 500 feet thick and are composed of gray 

arkose and some fossiliferous limestone. The Ayers 

well 1, located west of Bedrock, Colo., and 5 miles east 

of the La Sal quadrangle, was drilled on the southwest 

flank of the Paradox anticline. It penetrated 1,475 

feet of gray and brown limestone interbedded with 

gray, green, and red arkosic sandstone lenses. The 

sandstone lenses are more abundant in the lower 285 

feet of the well. The well was abandoned before it 

reached the Paradox Member. The upper member in 

the Rico area ranges from 1,800 to 2,000 feet in thickness (Cross, Spencer, and Purington, 1899). Themem-
STRATIGRAPHY 5 

her ranges from 1,500 to 1,800 feet in thickness in the 

Moab area (Baker, 1933, p. 19), is 1,300 feet thick in 

the Green River area (Baker, 1946), and is 600 feet 

thick on the San Rafael Swell (Baker, 1946); general 

thinning in a westerly direction is thus indicated. It 

is quite proba;ble, therefore, that at least 1,800 feet of 

the upper limestone member of the Hermosa Formation underlies the La Sal quadrangle. 

PENNSYLVANIAN AND PERMIAN SYSTEMS 

RICO FORMATION 

The Rico Formation, considered to be of Pennsylvanian and Permian age by the Geological Survey, may 

crop out close to the intrusive rocks of North and South 

Mountains of the La Sals. Doubt of its presence is expressed because much of the interval elsewhere occupied 

by the Rico is covered by landslide debris from the adjacent formations in the mountain area. Isolated exposures of white crystalline, dark-gray, and yellowbrown limestone crop out in a narrow belt surrounding 

the igneous rocks. Springs issuing from the limestone 

are quite salty; this feature was also noted by Baker 

( 1933, p. 24) for the Rico Formation in the Moab dis- · 

trict. No fossils were recognized in the limestone, but 

the dark-gray limestone gives off a petroliferous odor 

when broken. Numerous copper prospects, particularly 

those on the southwest flank of the North Mountain 

group, show that Rico limestone is in close proximity 

to the igneous rock. 

The limestone is notably absent on the northeast 

flank of the Paradox Valley-North Mountain -Castle 

Valley anticline, in areas east and northwest of the 

quadrangle where, if present, it would certainly be exposed. This absence suggests that the limestone has 

been truncated by an unconformity at the base of the 

Cutler, by a post-Cutler unconformity, or by the igneous 

intrusion of North Mountain. The Ayers well 1, east 

of the mapped area near Bedrock, Colo., is on the southwest flank of the structure; it penetrated 630 feet of 

interbedded limestone, limy siltstone, and limy arkosic 

sandstone believed to represent the Rico Formation. 

Baker ( 1933, p. 23) describes the Rico as "a ·bedded 

series of sandstone with some red to lavender shale and 

several thin layers of limestone." He states that the 

upper limit is the top of the highest fossiliferous limestone, locally known as the "Shafer Limestone." Inasmuch as no fossils have yet been found in the limestone 

surrounding the igneous rocks of North and South 

Mountains, the age and formational designation of the 

limestone are uncertain. Conglomeratic sandstone beds 

typical of the overlying Cutler Formation, however, 

are stratigraphically higher than the limestone; therefore the limestone is considered pre-Cutler and, al- ' . though it could be assigned to the Hermosa Formatwn, 

it is herein referred to as Rico but rna pped with the 

Cutler as one unit. 

PERMIAN SYSTEM 

CUTLER FORMATION 

The Cutler Formation of Permian age is poorly exposed in most 10f the La Sal quadrangle. It ~s a sequence 

of white, pink, maroon, and purple conglomerate and 

arkose ·and red -brown sandy mudstone resting conformably on the Rico Formation in the Moab area (Baker, 

1933, p. 29). In the Gateway ·area (Cater 1954b) the 

congl'Omerate and arkose beds contain "grains of fresh 

feldspar, and d·ark minerals, and pebbles and ~boulders 

of granite, gneiss, schist, and quartzite-material derived almost entirely from the Precambrian rocks that 

underlie the Uncompahgre Plateau." 

The Cedar Mesa Sandstone Member of the Cutler 

Formation (Baker, 1933, p. 30) has not been identified 

in the m·apped -area, although it crops out in Castle 

Valley a few miles northwest'where a 300-foot sectiiOn 

is exposed. Boulders of white to pink, quartz pebble 

conglomerate found in Quaternary gravels on the 

flanks of North and South Mountains near exposures 

of limestone beds assigned to the Rico Formation probably were derived from this member. In the Moa;b 

region the Cedar Mesa Sandstone Member is overlain 

by a sequence of red medium-grained sandstone and 

mudstone, 100 feet thick, which Baker (1933, p. 30) 

named the Bogus Tongue and which he (1946, p. 43) 

later changed to Organ Rock Tongue. It is not known 

whether rocks representing this member are present in 

the La Sal quadrangle. 

Cater ( 1954b) and Shloomaker ( 1956a) did not. subdivide the Cutler into members in the .Gateway-Sinbad 

Valley area because there the formation is dominantly 

arkose and conglomerate that thicken from zero along 

the crest of the Uncompahgre Plateau to several thousands of feet a few miles southwest of the uplift. A 

well near ·Gateway, Col!o., that penetrated more than 

7,800 feet of Cutler before reaching the Precambrian 

basement suggested to Cater that this thick sequence 

of beds includes rocks of bdth Permian ( ~) and Pennsy 1-

vanian age that were deposited as a fa~glomerate on 

the flank of the uplift. 

The Cutler Formation varies extremely in thickness 

in the vicinity of the La Sal quadrangle. East of the 

quadrangle boundary the well drilled near Bedrock, 

Oolo., penetrated 2,687 feet of arkose ·and conglomerate 

which were assigned to the Outler. To the west, Baker 

measured 670 feet of Cutler in Lockhart Canyon, 390 . 
6 GEOLOGY, URANIUM-VANADIDM, LA SAL QUADRANGLE, UTAH-COLOR.A!DO 

feet on the crest of the Cane Creek anticline, and 800 

feet south of Indian Creek. Outcrops in Sinbad and 

Paradox Valleys indicate that the CU'tler is, in places, 

truncated by an unconformity at the base of the Moenkopi or, where the Moenklopi is absent, by an unconformity at the base of the Chinle. 

The Cutler Formation is present around N or'th and 

South Mountains, but its thickness and relationship to 

the enclosing beds are uncertain. Therefore, the relationships and thicknesses shown on the aooompanying 

maps and sections (pl. 1) are m'ainly projections based 

on information obtained in surrounding 'areas. Deposition of the Cutler in the areas where igneous rocks 

·were later intruded was undoubtedly controlled by preexisting salt domes in the areas of the Paradox ValleyCastle Valley and Moa.b Valley-Pine Ridge anticlines. 

Salt uplift and erosion during Moenkopi ·and Chinle 

time probably thinned 'the Cutler along the flanks of 

folds. Thicker parts were later obscured by the intrusion of Tertiary igneous rrocks and subsequent formation 

of alluvial and landslide deposits. 

TRIASSIC SYSTEM 

LOWER AND MIDDLE(?) TRIASSIC SERIES 

MOENKOPI FORMATION 

The Moenkopi Formation (Ward, 1901) is the oldest 

formation of Mesozoic ~age in the La Sal quadrangle. 

It is -composed of evenly bedded shale and mudsrtone 

containing numerous ledges of thin-bedded fine-grained 

red-brown and gray sandstone. Gypsiferous sandstone 

beds 'and small seams of gypsum are common. The 

light chocolate-brown color 1of the Moenkopi contrasts 

with the brick red of the overlying Chinle Formation 

and the pale red and maroon of the underlying Cutler. 

Ripple marks are ~the most conspicuous sedimentary 

structures of the Moenkopi, hut fossil mud cracks and 

raindrop imprints are also present. These structures 

in conjunction with even, continuous bedding and a 

great abundance of light-colored mica serve to distinguish the Moenkopi from other forma;tions. 

In west-central Colorado, Shoemaker ( 1956a) and 

Cater ( 1954b) divided the Moenkopi into three members which were referred to as the lower, middle, and 

upper members. Subsequently Shoemaker and Newman (1959) added a fourth member and assigned names 

which, from oldest to youngest, are the Tenderfoot, 

Ali Baba, Sewemup, and Pariott Members. These 

subdivisions of the Moenkopi, however, were not observed within the La Sal quadrangle because, like the 

older formations discussed, the Moenkopi is poorly exposed. Withington (1956) measured a maximum thickness of 450 feet on the northeast side of Paradox Valley. 

Shoemaker and Newman ( 1959) measured a total of 

1,265 feet on the east side of Sinbad Valley. The Ayers 

well 1 near Bedrock, Colo., on the southwest side of 

Paradox Valley, penetrated 867 feet of beds which were 

assigned to the Moenkopi. To the west of the La Sal 

quadrangle, Stewart and Williams (written commun., 

1953) measured 272 feet of Moenkopi in Lockhart 

Canyon, and Stewart and Weir (written commun., 

1953) measured 295 feet on the north side of North 

Sixshooter Peak. On the basis of this evidence, the 

Moenkopi Formation is estimated to reach a maximum 

thickness of about 400 feet in the La Sal quadrangle, 

but it may thin or be absent locally near the igneous and 

salt intrusions. 

UPPER TRIASSIC SERIES 

CHINLE FORMATION 

The Chinle Formation of Late Triassic age crops out 

in isolated patches around North and South Mountains 

of the La Sals and is well exposed in the sides of Sinbad 

and Paradox Valleys. Along the valley walls the Chinle 

forms steep slopes, but around the mountains where it 

is part of the sequence of upturned strata, it is found 

in the valleys between the igneous rock and the prominent hogback formed by the overlying Wingate Sandstone. In general the Chinle Formation is thickest in 

the southwestern corner of the mapped area and thins 

to the northeast. Three miles north of La Sal, Utah, 

the formation may be as much as 600 feet thick, and in 

the northwest end of Paradox Valley it is 375 feet thick. 

In Sin bad Valley, Shoemaker ( 1956a.) measured a maximum of 700 feet of Chinle, but states that in places it 

wedges out and the Wingate rests on the Hermosa Formation. The varied thicknesses of the Chinle Formation obviously are largely the result of movement of salt 

during Tria.ssic time. 

The formation consists of bright-red and red-brown 

mudstone and siltstone and sandstone containing lenses 

of limestone-pebble and mudstone-pebble conglomerate. 

It rests with unconformity on the Rico, Cutler, and 

Moenkopi Formations in and adjoining the map area. 

The Chinle is distinguished from the Moenkopi by a 

color contrast and by differences in bedding. The beds 

of the Chinle are irregular, extremely lenticular and 

discontinuous, in contrast to the uniform bedding in the 

Moenkopi Formation. The upper contact of the Chinle 

with the overlying Wingate Sandstone is, in places, 

gradational, but the formational boundary is usually 

drawn at the base of the massive cliff-forming eolian 

sandstone. 

Because of the sparsity and discontinuity of outcrops 

within the quadrangle boundaries, the Chinle was 

mapped as a single unit. In a few places, however, it 
STRATIGRAPHY 7 

is well-enough exposed to be divided into two members. 

The lower member is dominantly siltstone and contains 

numerous lenses of sandstone and limestone-pebble 

conglomerate. The upper unit consists mainly of siltstone containing lenses of fine-grained sandstone and 

thin-bedded limestone. The following section of the 

Chinle Formation measured in the canyon about half a 

mile south of the Valley View mine demonstrates this 

division and shows that the upper and lower members 

are of nearly equal thickness. 

Section of the Chinle Formation measured in the northeast 

cOr'f'ner of soo. 18, T. 48 N., R. 19 W., Montrose County, Colo. 

Wingate Sandstone. 

Chinle Formation : Thickness 

Upper member: (feet) 

20. Sandstone and siltstone, calcareous, reddishbrown, fine-grained, thin-bedded__________ 5. 0 

19. Sandstone and siltstone, reddish-brown ; 

altered to.light green in places, very fine 

grained, finely laminated, fiat bedded; 

ledge former---------------------------- 6.0 

18. Siltstone, reddish-brown ; altered locally to 

light green______________________________ 2. 0 

17. Sandstone, silty, slightly calcareous; light 

brown grading upward to white near top; 

fine grained ; dominantly quartz containing 

trace of opaque minerals and red and green 

chert; nodular at top; ledge former______ 5. 0 

16. Mudstone and siltstone, reddish-brown, flatbedded--------------------------------- 11.0 

15. Sandstone, calcareous light-brown to light 

reddish-brown, finely laminated ; sparse 

muscovite on bedding planes; pale-green 

glauconitelike grains____________________ 2. 0 

14. Limestxme, silty, light-gray; ledge former____ 2. 0 

13. •Siltstone, calca..re<ms, and silty limestone ; 

light red to fight gray; ledge former____ 2. 2 

12. Quartzite, tlght-gr'ay to ligh!t-green, very fine 

grained; ledge ~er___________________ 2.0 

U. ·Sand•stone, silty, brown to ocange-brown, finegrained, :tla:t-bedded; ledge former________ 16. 5 

10. 1SiltJstone, .reddish-brown, fiat-bedded ________ 121. 0 

':Ddt1al upper member _____________________ 174. 7 

Lower member : 

9. SandStone containing conglome:rta'tic lenses, 

light-gray weatllering ·to yellow-gray ; cong1omer'a:te pebbles af light-gray limestone 

and reddish-bT'own mud'stone as much as 

% in. in dia~er; ma·trtx very fine to nne 

grained, fla1t- :and crossbedded ; ledge 

former--------------------------------- 9.0 

8. !Siltstone, reddi•s'h ... brown ; mdtltled to lightgreen ---------------------------------- 56.0 

7. Sil~ne and conglomerate, calcareous, reddish-brown to light reddish-brown; mudstone pebbles are reddish brown and 

chooola'te brown ·a:s much as 2 inches long ; 

gray limestone pebbles as much as 1 inch 

l<mg; ledge fQl'IDler_______________________ 2. 0 

Section of the Chinle Formation measured in the northeast 

oorner of sec. 18, T. 48 N., R. 19 W., Montrose County, Colo.-

Continued 

Chinle Formation-Continued Thickness 

Lower member-Continued (feet.) 

6. 'Siltstone; conglomeratic at base; reddishbrown; light green in lower 6-12 in.; cong1omera!te pebbles •are reddi•sh brown and 

light green, and 1as much as 1 in. long; base 

of unit is gently undulatory, flat- and 

crossbedded; ledge fOTmer________________ 17. 5 

5. Siltstone, calcareous; ·reddiSh-'b:rown to l.ightgreen along some bed:s and fraetures; bedding poorly formed ______________________ 106.5 

4. Conglomerate, sillty, calcareous; chooolatebvown to gray-green ·Silts1Jone ~bbles as 

much as % in. in diameter; qu:arrtz grains 

very fine'to ~a~se-----------------------

3. 1Sandstone, ligh't-gray to white; weathers ;tJo 

.8 

yellowish brown ; fine to very fine grained__ 5. '5 

2. ·Siltstone, reddish-brown___________________ 1. 0 

1. Conglomerate, silty, calcareous, reddishbrawn; .silltJstone pebble__________________ 2. 5 

Total lower member ___________________ 200.8 

TOtal Ohinle Thrmation ________________ 375. 5 

Outler Form.a'tion ( nodt well exposed) . 

In the La Sal quadrangle the beds of the lower member appear to rest direotly on the Cutler Formation, although the Cutler is very poorly exposed. In sec. 6, 

T. 47 N., R. 19 W., Montrose County, Colo., Chinle 

strata containing conglomerate lenses composed of 

granules, pebbles, and cobbles of siltstone, limestone, 

quartzite, quartz, chert, and silicified wood embedded in 

a reddish-gray fine-grained sandstone matrix are quite 

similar to the Moss Back Mem·ber described by Stewart 

and others ( 1959, p. 512-515). The remainder of the 

Chinle strata in that locality a.re predominantly siltstone and some sandstone. This composition suggests 

a lithofacies change from the dominantly sandstone 

lithology of the unit in Big Indian Wash area to the 

southwest. The change may, in part, 'be responsible for 

the notable absence of uranium deposits in the Chinle 

of the Paradox Valley area, in contrast to the numerous 

deposits in the Chinle of the Lisbon Valley area. 

The upper part of the Chinle Formation reslts conformably on the lower member and consists of reddishbrown and light-brown, horizontally laminated to very 

thick bedded siltstone and sandy siltstone, and in places, 

thin -bedded limestone. These beds are very similar to 

strata in the Monument Valley region of Utah that 

Witkind and Thaden ( 1963, p. 21) named the Chureh 

Rock Member, but the authors have made no definite 

correlation between the two areas. 
8 GEOLOGY, .URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORA:DO 

GLEN CANYON GROUP (LOWER PART) 

The Glen Oanyon Group (Gregory and Moore, 1931) 

comprises, in ascending order, the Wingate Sandstone, 

the Kayenta Fonna'tion, -and othe N a.vajo Sandstone. 

The entire Glen Canyon Group was once considered to 

be Jurassic ( ~) in age. The presence of vertebrate fossils of Late Triassic(~) age in the Moenave and Kayenta 

Formations, which directly overlie the Wingate Sandstone in northern Arizona, and other supporting evidence reported by HarShbarger and others (1957, p. 16, 

19) place the Wingate in the Triassic System. Later 

work by Lewis and others ( 1961) indicate the Kayenta 

Formation to be of Late Triassic ( ~) age, and theN avajo 

Sandstone to be of the Late Triassic ( ~) and Jurassic 

age. 

WINGATE SANDSTONE 

The Wingate Sandstone (Dutton, 1885) is the oldest 

of the three formations of the Glen Canyon Group and 

conformably overlies the Chinle Fonnation. It crops 

out near the eastern edge of the mapped area in the floor 

of Roc Creek canyon, in the northwest end of Paradox 

Valley, and on the southwest edge of Sinbad Valley 

where it fonns a cliff as much as 250 foot high. In the 

western part of the area it fonns the hogbacks which 

surround the igneous rocks of North and South 

Mountains. 

The Wingate Sandstone. is a massive, nearly homogeneous, well-sorted, very fine to fine-grained crosshedded sandstone. On fresh surfaces the sandstone is light 

brown to nearly white, and on weathered surfaces is 

stained red to dark brown and streaked with black 

desert varnish. Where the standstone fonns cliffs, it 

is cut by vertical joints that extend from top to bottom. 

Large blocks spall from the sandstone along the joints 

and form deposits of tal us on the steep slopes of the 

underlying Chin~e Formation. From a distance the 

bedding in the Wingate is obscured by closely spaced· 

joints and the dark color of the weathered surface. In 

detail the formation is composed of many horizontal 

layers of sandstone, ranging thickness from 2 to 50 feet, 

each of which contains sweeping tangential crossbeds 

of eolian origin. These sandstone layers are a favorable 

host for ore minerals derived from ascending hydrothermal solutions, as shown by the presence of the 

Cashin, Cliffdweller, and Sunrise copper deposits and 

other copper prospects in the Wingate Sandstone of the 

Paradox Valley area. 

The Wingate ranges in thickness from 280 feet in the 

northwest part of the map area to 150 feet in the east. 

Shoemaker (1956a) and Withington (1956) found that 

the thickness differs most in the vicinity of the sa'lt anticlines-a feature that indicates minor movements 'of 

salt of the Hermosa Formation before, during, or shortly following deposition of the Wingate Sandstone. 

UPPER TRIASSIC(?) SERIES 

GLEN CANYON GROUP (MIDDLE PART) 

KAYENTA FORMATION 

The Kayenta Formation (Baker, 1933) rests on the 

Wingate Sandstone and is usually recognized by marked 

changes in bedding, color, and resistance to weathering. 

The beds above and below the contact are virtually conformable and, in places, grade into each other. 

The Kayenta Formation crops out in a series of ledges 

and benches formed by the erosion of lenticular sandstone interbedded with minor amounts of siltstone, thinbedded shale, and conglomerate. The sandstone is red, 

buff, gray, or lavender and is composed of fine- to 

coarse-grained rounded to suhrounded quartz grains 

and minor quantities of mica, feldspar, and dark minerals. The sandstone is typically thin bedded and 

flaggy; crosshedded and massive lenses, however, are 

not uncommon. The red siltstone and shale beds, being 

less resistant to erosion, are found in the recesses beneath 

overhanging ledges of sandstone ~nd conglomerate. 

The conglomerate contains angular to rounded pebbles 

of sandstone, shale, and limestone as much as 2 inches 

in diameter. 

The Kayenta Formation is 160 feet thick on the 

south flank of South Mountain and 165 feet thick on the 

south flank of North Mountain. Along Roc Creek and 

in Paradox Valley it ranges in thickness from 140 to 

260 feet. These apparent differences in thickness may 

be due largely to the fact that in some areas the Wingate-Kayenta contact is well marked and easily distinguished hut in other areas, where the two formations 

interfinger, the contact has been located arbitrarily. 

A study of sedimentary structures and feldspar content by Stewart and others ( 1959) and studies of grain 

size and mica content by Dane ( 1935, p. 77, 82) indicate 

that the Kayenta is of fluvial origin. The formation 

probably was derived from the ancestral Uncompahgre 

highland to the northeast and also from an area beyond 

the line of pinchout in southwestern Colorado (Craig 

and Dickey, 1956, p. 95). 

TRIASSIC ( ?) AND JURASSIC SYSTEMS 

GLEN CANYON GROUP (UPPER PART) 

NAVAJO SANDSTONE 

The Navajo Sandstone ('Gregory, 1917, p. 57) of 

Triassic ( ~) and Jurassic age (Lewis and others, 1961) 

is the upper formation of the Glen Canyon Group and 

conformably overlies the Kayenta Formation. It crops 
STRATIGRAPHY 9 

out as steep cliffs and rounded slopes in Coyote Wash 

. and La Sal Creek and their tributary canyons in the 

southern part of the mapped area, at the northwest end 

of Paradox Valley, in Roc Creek, and in Sin bad ·valley. 

It is also exposed in the hogbacks on the flanks of North 

and South Mountains. Rock rubble of Navajo lithology 

in the Middle Mountain area indicates that the formation may have on~ cropped out there as isolated patches. 

The Navajo is light-gray to pale-brown massive, 

medium- to fine-grained sandstone. It is usually distinguished from other formations by its color and largescale tangentia:l crossbeds which are often accentuated 

in relief on weathered surfaces. The sandstone consists of rounded to subrounded grains of quartz and 

minor quantities of feldspar and dark minerals. The 

rock weathers readily to sand because the grains are 

weakly cemented. . 

The character of the crossbedding and the sparmty 

of other sedimentary structures indicating water-laid 

deposits suggest that the Navajo is dominantly of eolian 

origin. Poole and Williams ( 1956) believe that the 

winds transporting this material came from the northwest. Large-scale distortion and crumpling of Navajo 

beds, thought to be of water-laid origin as noted by 

Kiersch (1950, p. "939-942) in the San Rafael Swell, 

Utah were not recognized in the La Sal quadrangle. 

Water-laid ' . d deposits of the Navajo were recognize , 

however, in the hogback on the south flank of North 

Mountain (sec. 36, T. 26 S., R. 24 E., San Juan County, 

Utah) where the sandstone is 22 feet thick. About 17 

feet above the :base is a lenticular unit ranging from 0 to 

2 feet in thickness that is composed of a fine-grained 

limy sandstone and locally contains elongate, irregularly shaped masses of white and yellowish-brown to 

yellowish-gray chert. The masses range in length from 

a fraction of an inch to 1 foot and lie along horizontal, 

minutely crumpled bedding planes of the sandstone. 

Shoemaker ( 1956a) reports similar deposits of chert 

in close proximity to a 6-foot bed of limestone at the 

southwest end of Sewemup Mesa in the Roc Creek 

quadrangle, just east of the La Sal quadrangle. 

The Navajo Sandstone ranges in thickness from 0 in 

the adjacent Paradox quadrangle (Withington, 1956) 

on the east to 240 feet along La Sal Creek near Sharp 

Canyon. To _the north on the south flank of North 

Mountain it is 22 feet thick and has a maximum thickness of 100 feet along Roc Creek. These thickness differences indicate irregular and abrupt thinning and 

pinching out along the Paradox Valley -Castle Valley 

anticlinal structure and reflect areas where salt movement, probably in separate domelike cells, was mo~t 

active prior to or during deposition of the NavaJO 

Sandstone. 

JURASSIC SYSTEM 

SAN RAFAEL GROUP 

The San Rafael Group of Middle and Late Jurassic 

age was first described by Gilluly and Reeside (1928, 

p. 73) as comprising, in ascending order, the Carmel 

Formation, the Entrada Sandstone, and the Summerville Formation. Fieldwork in the La Sal quadrangle 

indicated that, if present, the Carmel Formation is 

different lithologically from typical Carmel in western 

Utah and too thin to be mapped as a separate unit. 

Later regional studies of the San Rafael Group in 

adjacent areas by Wright and others (1962, p. 2057) 

showed that Carmel-like earthy siltstone and sandstone 

beds should actually he considered as facies of the 

Entrada Sandstone. Wright and his coworkers redefined the Entrada by dividing it into three members 

that are, in ascending order, the Dewey Bridge Member, 

the Slick R6ck Member, and the Moab Sandstone Member. Inasmuch as these divisions agree with equivalent 

lithologic units in the La Sal quadrangle, the names 

proposed hy Wright and others (1962, p. 2057) ha':e 

been adopted in this report, although the Entrada IS 

shown on the map as a single unit. The San Rafael 

Group, therefore, includes only the Entrada Sandstone 

and Summerville Formation in the La Sal quadrangle. 

ENTRADA SANDSTONE 

The Entrada Sandstone is a cliff-forming rock unit 

that crops out in Coyote Wash in the southeast corner 

of the quadrangle and to the north in Sharp Canyon, 

La Sal Crook Canyon, at the northwest end of Paradox 

Valley, in Roc Creek Canyon, and in Sin bad Valley. 

On the west it crops out in hogbacks around the N o~h 

and South Mountains, on Mount Peale, and at the 

headwaters of Twomile Creek. 

The base of the Entrada Sandstone is a distinct, even 

erosion surface which, in most places, truncates crossstrata of the underlying Navajo Sandstone. The contact is especially well exposed in the La Sal Creek 

Canyon near the east boundary of the map where the 

Dewey Bridge Member pinches out and the Slick Rock 

Member rests directly on the Navajo Sandstone. There, 

the contact is a sharp, even surface overlain by a thin 

bed of sandstone containing rounded pebbles of black 

chert and subangular fragments of silicified white sandstone -obviously derived from the underlying Navajo 

Sandstone. Wright and others ( 1962, p. 2060-2061) 

mapped a sharp unconformity at the base of the Entrada 

in the Colorado River Valley at the Utah-Colorado 

line. This unconformity continues to the east, and 

Entrada rests on progressively older formations, until 

in the Black Canyon area of the Gunnison River it rests 
10 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

directly on the Precambrian (Craig and Dickey, 1956, 

p. 97). 

The Dewey Bridge Member consists of reddish-brown 

to white and buff, horizontally bedded siltstone, mudstone, and sandstone within the La Sal quadrangle. 

Sandstone is predominant and is composed of layers of 

very fine and fine-grained, fairly well sorted quartz 

grains and abundant interstitial clay and thin red clay 

partings. In places the sandstone is poorly sorted and 

contains grains of medium size. Weak cementation in 

areas of poor sorting results in differential weathering 

of the rock, and the layers form rounded ledges and 

nodules separated by shallow recesses. In places thin 

layers of crossbedded sandstone are interstratified with 

thin flat-bedded units. Locally the basal beds consist 

of black and gray chert pebbles and reworked Navajo 

Sandstone in angular fragments as much as 1 foot in 

length. These sandstone fragments and chert pebbles 

are sufficiently abundant locally to form layers of conglomerate. A notable example of this conglomerate is 

in the canyon of West Paradox Creek at the northwest 

end of Paradox Valley. 

The Dewey Bridge Member ranges in thickness from 

0 to 66 feet, and probably represents subaqueous deposition in a marginal marine environment ( Gilluly 

and Reeside, 1928, p. 75; Baker, 1946, p. 74-75); it may 

b~ equivalent in time of deposition to the Carmel of 

western Utah. No fossils have been found in these beds 

within the rna p area. 

The Slick RJock Member, like the Wing!l!te and N·avajo Formations, is a massive sandstone, but unlike these 

formations, it differs in color from place to place. 

Known locally as the "'Slick Rim," the Slick Rock Member crops out as smoothly rounded orange, buff, and 

whit.e cliffs spotted hy horizontal rows of pits resulting 

from differential weathering. It is well exposed in 

La Sal Creek Canyon and the canyons to the south, at 

the head of Paradox Valley and nea.r Buckeye Reservoir, and in Roc Creek Canyon and Sinbad Valley. It 

is also exposed on the top and sides of Mount Peale. 

The upper and lower pa.rts of the Entrada >Sandstone 

are largely horizontally bedded units suggestive of subaqueous deposition; these two parts are separated by a 

middle unit consisting of tangentially crossbedded sandstone. The middle unit is dominantly of eolian origin 

(Stokes and Holmes, 1954, p. 37). The Entrada Sandstone differs from the somewhat similar Wingate and 

Navajo Formations hy the sort:ing of sand into t'WIO 

distinct grain sizes, :both of which are generally coarser 

than those of the older formations. The hulk of the 

sandgtone is composed 1of subrounded to subangular 

fine grains of quartz, usually less than 0.15 mm in diameter, which are weakly cemented by calcium carbonate. Larger grains, generally distributed along bedding planes in thin layers, range from 0.4 to 0.8 mm in 

diameter, are· frosted, and display excellent sphericity. 

These grains, sometimes referred to as "Entrada berries" are distinctive of the unit and were of considerable 

aid in determining the presence and position of the 

Entrada in the mountai111ous pa.rts of the area. 

The Moab Sandstone Member, within the ma.p area, 

is red to gray and, in places, is white, horizontally 

bedded sandstone that ranges in thickness from 0 to 40 

feet along Roc Creek and from 40 to 100 feet near 

·Geyser Pass. This unit, originally referred to as the 

Moab Tongue (Baker, 1933, 'P· 49), is separated from 

the rest rof the Entrada. Sandstone by a distinctive horizontal bedding plane. The unit is sometimes coarser 

grained ·and more friable than the underlying crossbedded sandstone and differs from the Moab Tongue 

of the type area by the general absence of crosgbedding. 

The following section of ~the Entrada Sandstone measured in La Sal Creek Canyon (sees. 28 and 33, T. 28 S., 

R. 26 E., <San Juan Oounty, Utah) by L. C. Craig and 

others (written commun., 1948) illustrates this relationship. The revised nomenclature of Wright and 

others (1962) is shown in parentheses. 

Summerville Formation. 

Entrada Sandstone : 

Moab tongue ( ? ) (Moab Sandstone Member) : Thickness 

(feet) 

16. Interval covered except upper 1 ft. Sands'tone, white, very fine grained; contains 

rare pink accessory minerals------------- 4. 0 

15. Sandstone, white to pa1le-brawn; weathers 

pale brown ; fine to very fine grained ; 

composed of clear quartz and moderate 

amount of pink accessory minerals; unlaminated, structureless------------------ 5. 7 

14. Claystone, dark-red, 'silty and sandy, very 

poorly ·sorted; grains range from very fine 

to m~dium~fine; weathers shaly to rounded_ 6. 4 

Total Moab Tongue(?) (Moab Member(?))---------------------------- 16.1 

"Slick Rim" Member (Slick Rock Member) : 

13. Sandstone, whi1te to pale-yellow; weathers 

buff to light gray; fine to medium-fine 

grained ; composed of rounded clear quartz 

and rare pink and black accessory minerals; horizontal ridging suggests bedding; unlaminated_______________________ 38. 1 

12. Sandstone, light-buff to white, fine to mediumfine grained; fair sorting; thin-bedded with 

tangential cross lamination______________ 5. 9 

11. Sandstone, buff to white, fine to medium-fine 

grained ; composed of clear quartz and 

minor white chert and colored accessory 

minerals; highly cross laminated; no "Entrada berries"--------------------------- 51. 1 
STRATIGRAPHY 11 

Entrada Sandstone--Continued Thickness 

(feet) 

"Slick Rim" Member (Slick Rock Member)-Con. 

10. Sandstone, brownish-buff, :fine to medium-fine 

grained ; composed of clea·r quartz and 

"Entrada berries" ; long-radius cross lamination; thickly bedded__________________ 41. 6 

9. Sandstone, 'Orange ... buff ; some red 'bands ; 

composition as in unit 8; cross laminated, 

wedge 'bedded___________________________ 8.8 

8. Sandstone, orange-buff, :fine-grained; composed of clear quartz and some white 

chert; "Entrada berries" of medium-coarse 

to medium, rounded and frosted clear 

quartz and white and red chert; cross laminated; wedge bedded ___________________ 41.8 

7. Sandstone, red, very :fine to :fine-grained, 

well sorted ; composed of rounded clear 

quartz and minor subangular white chert; 

some red clay laminae___________________ 5. 4 

6. Sandstone, white below, orange-buff above, 

fine-grained, poorly sorted ; composed of 

clear quartz and disseminated medium to 

medium-coarse frosted clear quartz; white 

and gray chert and some subangular white 

chert; long-radius cross lamination______ 16. 2 

Total "Slick Rim" Member (Slick Rock 

Member) ___________________________ 208.9 

Dewey Bridge Member : 

5. Sandstone, dark-red to buff to white, interbedded ; very :fine and fine-grained, fairly 

well-sorted sand containing abundant thin 

red clay partings and :fine to medium-finegrained, poorly sorted sand______________ 30. 7 

4. Sandstone, brown, very fine to fine-grained, 

poorly sorted; composed of subangular to 

rounded clear quartz and nHmerous large 

granules of angular white chert as much as 

1 inch in diameter______________________ 1.4 

Total Dewey Bridge Member__________ 32.1 

Total Entrada Sandstone ______________ 257, 1 

Navajo Sandstone. 

The average thickness of the Moab Member throughout the area is generally less than 40 feet, and because it 

crops out as part of a steep cliff, making a narrow outcrop in plan, it is undifferentiated from the rest of the 

Entrada on the maps. The total thickness of the 

Entrada Sandstone, including the Moab Tongue, ranges 

from 200 to 310 feet. Differences in thickness depend 

largely on the thickness of the Moab Member. ' 

CONTACT OF THE ENTRADA SANDSTONE AND SUMMERVILLE 

FORMATION 

The top of the Entrada Sandstone within the La Sal 

quadrangle is almost everywhere a distinctive smooth 

surface on which the Summerville Formation conformably lies. In spite of this generally well -defined 

777-039 0-65--3 

contact, deposition of the Entrada and Summerville 

probably was contemporaneous in some places. This 

relation is illustrated near the pinchout of the Moab 

Tongue in Roc Creek Canyon. There, the Moab Tongue 

grades laterally into the Summerville Formation (Shoemaker, 1956a), and locally the contact of the Entrada 

and Summerville is not always on the same surface or 

horizon. In general, however, the contact is uniform 

and readily recognized over most of the area; it was, 

therefore, used as the structure-contour horizon. 

SUMMERVILLE FORMATION 

The Summerville Formation ( Gilluly and Reeside, 

1928, p. 19-80), the uppermost formation of the San 

Rafael Group, is exposed in the same areas described 

for the Entrada Sandstone. The Summerville Formation generally crops out as a steep red earthy or debriscovered slope or a finely banded cliff. It consists predominantly of reddish-brown thin, evenly bedded 

mudstone and shale and some interbedded light-gray 

to light-brown platy to slabby fine-grained sandstone. 

Asyr.unetrical ripple marks are fairly common in the 

sandstone beds. Thin discontinuous beds of dark-gray 

dense limestone occur in the upper part of the formation. 

Locally these beds are fractured and filled with carnelian veinlets. In general, the lower part of the 

formation has more abundant and thicker sandstone 

beds than the upper part .. A tripart division of the 

Summerville Formation is illustrated in the following 

section measured just south of the map area. 

Section of the Summerville Formation half a mile north of Coyote Wash and 1 mile east of the Utah-Colorado line in an 

unsurveyed part ofT. 46 N., R. 20 W., Montrose County, Colo. 

[Measured by J. L. Gualtieri and W. R. Barton] 

Morrison :Formation. Thickness 

Summerville Formation: (feet) 

6. Interval poorly exposed. Dominantly interbedded 

pale-red and reddish-brown mudstone and siltstone. Some thin flat-bedded sandstone composed of wh'ite to light gray to pale red, very 

fine to :fine-grained subrounded to rounded quartz 

and gray and brown accessory minerals, probably chert_ ___________ ·----------------------- 39. 5 

5. Sandstone, pinkish-gray, yellowish-gray, and palered ; weathers to pale reddish brown ; spotted 

with limonitic fine-grained well-sorted subrounded to rounded transparent to translucent 

quartz and gray, black and brown chert grains ; 

flat bedded ; increasingly well cemented toward 

top; surface weathers to concretionlike nodules_ 21. 0 

4. Interval poorly exposed. Interbedded pale redi 

dish-brown :fine- to medium-fine-grained sandstone, siltstone and mudstone ; subrounded 

quartz grains and gray and brown accessory 

minerals------------------------------------ 51.0 

Total thickness of Summerville Formation __ 111. 5 

Entrada Sandstone. 
12 GEOLOGY, URANIUM-VANADIDM, LA SAL QUADRANGLE, UTAH-COLORADO 

The Summerville Formation ranges in thickness from 

65 feet in La Sal Creek Canyon to 140 feet in the upper 

canyon of Roc Creek ( Shoe~aker, 1956a). The greatest local variations in thickness are due to erosion 

marked by sandstone-filled paleostream channels at the 

base of the overlying Morrison Formation. 

MORRISON FORMATION 

The Morrison Formation (Cross, 1894a, p. 2) of Late 

Jurassic age is a;bout 700 feet thick in the La Sal quadrangle. It is composed of two members of ·approximately equal thickness, the older Salt Wash Member 

and the younger Brushy Basin Member. The base of 

the Morrison Formation, according to Craig and others 

( 1955, p. 134), is defined as the base of the fluvial Jurassic deposits overlying beds of the San Rafael Group that 

are of marine or marginal marine origin. In the La 

Sal quadrangle this contact was mapped at the base of 

the lowermost continuous sandstone bed of the Salt 

Wash Member which rests on the eroded surface of the 

Summerville Formation. This surface is mainly flat, 

hut locally may be slightly irregular or show a welldefined channeled scour. In places, a light-gray to 

white limestone bed, a few inches to a few feet thick, 

occurs at the base of the Morrison Formation. In other 

places an orange-red to milky-white chert bed of similar 

thickness is found. The top of the Morrison Formation is placed at the base of the massive conglomeratic 

sandstone of the Burro Canyon 'Formation of Early 

Cretaceous age. The Burro Canyon is easily recognized 

for it crops out as a prominent cliff in the high mesas 

surrounding La Sal Creek Canyon. The contact of the 

Burro Canyon with the Morrison Formation is rarely 

seen, however, b~ause it is generally obscured by landslide deposits and vegetation. Where exposed, the 

sandstone of the Burro Canyon makes a well-defined 

contact with the variegated shale and mudstone of the 

Brush Basin Member. 

SALT WASH MEMBER 

The Salt Wash Member (Lupton, 1914, p. 127; GilJuly and Reeside, 1928, p. 82; Craig and others, 1955, 

p.135) is composed of interstratified lenses of sandstone 

and mudstone. In the mapped area, it ranges in thickness from 250 to 350 feet, and can be roughly divided 

into three lithologic units, each of which has a lenticular 

sandstone at the base, overlain by interbedded siltstone 

and mudstone. The sandstone beds of the basal unit 

form the first continuous ledge above the top of the 

Entrada Formation. The sandstone beds of the middle 

unit, being highly lenticular and discontinuous, form a 

prominent ledge only where· they are thickest. The 

uppermost sandstone strata, although highly lenticular, 

usually crop out as a distinctive ledge that forms a 

prominent bench on many mesas. 

The sandstone strata are reddish- to light-brown, 

very pale orange, grayish-ycllow, and white fine- to 

medium-grained beds composed of clear quartz and 

minor amounts of white, pink, and green chert, clear 

feldspar, black opaque minerals, and interstitial clay 

The.quartz grains are subrounded to rounded ·and generally· well sorted. The chert grains ·are angular to 

subrounded and are generally slightly larger than the 

quartz grains. Calcite is the principal cementing material. Limonite is present in places as specks between 

or coating on the sand grains; limonite diffusion bands 

impregnate sandstone locally. Fossil logs and dinosaur bones are found in places in the sandstone. 

Interstratified siltstone and mudstone separate sandstone strata and also occur within the sandstone as thin 

lenses, films, and fragments ranging in size from pebble 

to cobble. The fact that the fragments are angular to 

rounded probably reflects the distance of transport and 

the amount of abrasion by Salt Wash streams. The 

siltstone and mudstone are dominantly reddish brown 

but in places are gray or greenish gray. The reason for 

this color difference is not well understood, but the occurrence is significant because of its relationship to uranium deposits. In many places near uranium-vanadium 

deposits the red mudstone appears to have been altered 

to greenish gray directly beneath, within, and sometimes 

above mineralized sandstone. A. D. Weeks (written 

commun., 1951) suggests that a chemical reaction took 

place under reducing conditions which decreased the 

total iron content and the ferric-ferrous iron ratio and 

changed the color of the clay from red to greenish gray. 

The ore-bearing sandstone.-Most of the uraniumvanadium deposits in the La Sal Creek area are in the 

uppermost continuous sandstone strata of the Salt 

Wash. This unit is commonly called the ore-bearing 

sandstone or third rim, in reference to its position above 

the Entrada Sandstone. 

The ore-bearing sandstone is, in some places, composed of a single broad lens of cross-laminated sandstone ranging from 0 to 30 feet in thickness. In other 

places it is composed of many overlapping sandstone 

lenses which have a combined total thickness of 30 to 

105 feet. The cross-laminated sandstone appears to 

have been deposited in a flood-plain environment. The 

overlapping lenses are channel deposits in which scourand-fill bedding is common. Scour-and-fill bedding of 

the festoon type consists of crossbedded sandstone lenses 

truncated by and in direct contact with other truncated 

lenses, or separated from them by thin, discontinuous 

mudstone lenses or mudstone conglomerate. Fragments 
STRATIGRAPHY 13 

of fossil wood are abundant in these scour-and-fill beds 

and occur either along the bedding planes or in podlike 

masses called "trash pockets." 

In places, the ore-bearing sandstone was deposited in 

channels cut in the underlying mudstone. These are 

generally broad features which rarely exceed a depth 

of 10 feet but which locally may be as much as 20 feet 

deep where narrow scours are cut into the underlying 

rock. Away from the chann~ls the ore-bearing sandstone may pinch out into interstratified layers of reddish-brown claystone, reddish-gray limestone, and finegrained orthoquartzite. These rocks indicate that a 

lacustrine or flood-plain environment existed along the 

margins of stream channels. Local ponding within the 

channels is indicated by sand-filled dessication cracks 

in mudstone layers that separate the sandstone lenses. 

Such features were observed in the Evening Star and 

Gray Daun mines. 

The trends of sedimentary structures such as crossbedding, current lineation, and ripple marks indicate 

that the streams which deposited the ore-bearing sandstone flowed generally eastward in the La Sal Creek 

area. Fossil logs are generally oriented parallel to the 

trend of paleostream flow. · 

BRUSHY BASIN MEMBER 

The Brushy Basin Member ( Gr~gory, 1938, p. 59) 

is composed of variegated siltstone, mudstone, bentonitic 

clay, and minor amounts of sandstone and conglomerate. It ranges in thickness from 250 to 400 feet and 

crops out as gentle slopes and steep, rounded hills on 

the bench formed by the underlying Salt Wash Member. It is recognized by its contrasting colors of red, 

light greenish gray, and purple. 

A lenticular conglomeratic sandstone containing red, 

green, white, and black chert pebbles usually marks the 

base of the Brushy Basin Member throughout most of 

the mapped area. Be.cause of the variety of color in 

the pebble assemblage, this unit is locally referred to 

as the "Christmas tree conglomerate." It ranges from 

0 to 70 feet in thickness and is usually separated from 

the ore-bearing sandstone of the Salt Wash by layers 

of mudstone and siltstone that increase in thickness 

where the conglomerate thins. In places the conglomerate rests directly on the ore-bearing sandstone. Th~ 

conglomerate is distinguished from the ore-bearing 

sandstone by its assemblage of red and green pebbles, by 

its coarser grain size, and locally by a higher percentage of interstitial clay. Uranium deposits in the Brushy 

Basin are rare, erratically distributed, and generally 

associated with· the basal conglomerate or similar units 

found higher in the member. Typical examples are at 

the Hesperus and Sumner mines on La Sal Creek and 

the Too High mine on the south side of Wray Mesa. 

Petrified dinosaur bones and wood are common in the 

Brushy Basin Member. A fossil tooth, found on Wray 

Mesa by LeRoy Bennett of Grand Junction, Colo., was 

studied by G. Edward Lewis of the U.S. Geological 

Survey. Lewis believes it probably belongs to either the 

genus ApatosauTUS (BrontosauTUS) or Oamarasaurus 

(MorosauTUS), both of which are Archosauria of the 

Order Saurischia and Suborder Sauropoda. Lewis 

stipulates that a definite generic classification cannot 

be made on the basis of a single tooth. The relative 

abundance of saurian fossils, the presence of thin limestone beds, and the marked decrease in the amount of 

sandstone in the Brushy Basin Member suggest that it 

was deposited in a lacustrine environment, possibly 

under a more humid climate than that of the Salt Wash 

Member. 

The following section of the Morrison Formation was 

measured on the north side of La Sal Creek Canyon in 

sees. 28 and 33, T. 28 S., R. 26 E., San Juan County, 

Utah, by L. C. Craig and others (written commun., 

1948). Subsequent sections measured in the La Sal 

quadrangle and cores from drill holes indicate that the 

lithologies described here are representative, although 

the contact between the Brushy Basin and Salt Wash 

Members may differ as much as 50 feet from the contact 

shown here. 

Burro Canyon Formation. 

Morrison Formation: Thickness Brushy Basin Member: (feet) 

47. Claystone, light-green; weathers to coppergreen ; sandy ; contains disseminated fineto medium..,grained rounded clear quartx__ 12. 0 

46. Interval with scattered exposure. Claystone 

is dark red, maroon and chocolate brown, 

silty to sandy; a few thin 2-ft ledges of 

dark-red sil'tstone----------------------- 132. 2 

45. Interval very poorly exposed. Probably gray 

shale and sandstone interbedded. Shale is 

light greenish gray. Sandstone dark green, 

fine grained ; composed of clear quartz, 

siliceous cement ; forms several ledges 1 to 2ft thick _______________________________ 166.0 

44. Interval poorly exposed. Siltstone, clay-

·stone, and sandstone interbedded. Predominantly red and green silty to sandy 

claystone and a few thin interbeds of darkred mottled siltstone and very fine grained 

sandstone ------------------------------ 21.6 

43. Sandstone and shale. Sandstone, white to 

pale-brown, fine grained ; contains abundant orange, red, and green chert as accessory minerals ------------------------ 13. 6 

Total Brushy Basin Member ___________ 345.4 
14 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

Morrison Formation-Continued 

Thickness Salt Wash Member: (feet) 

42. Claystone, dark-red to gray, silty to finegrained, sandy ; contains several thin beds 

of pink to white fine-grained, ripple-laminated to structureless sandstone_________ 8. 5 

41. Sandstone, white and pale-brown, finegrained; faintly cross laminated. (Upper 

ledge of ore-bearing sandstone unit.)------ 10. 3 

40. Interval poorly exposed. Sandstone and 

sandy claystone ; unit is mainly very fine 

to fine-grained sandstone containing grading and variable amounts of clay--------- 19. 8 

39. Sandstone, white to pale-brown ; weathers 

light gray to pale brown; fine to medium 

fine grained ; composed of subrounded clear 

quartz and abundant green, white, and tan 

subangular chert and minor pink, gray, 

and black grains; channeling, cross laminated. (Base of ore-bearing sandstone 

unit.) ---------------------------------- 17.6 

38. Interval poorly exposed. Claystone to sandstone interbedded. Claystone, dark red, 

maroon, and reddish brown, silty. Sandstone pink to white and green, very fine to 

fine-grained, in part ripple laminated______ 52. 0 

37. Sandstone, white; weathers light gray; very 

fine grained; structureless_______________ 2.2 

36. Sandstone and claystone interbedded. Sandstone pink, weathers red brown; very fine 

grained; ripple laminated. Claystone 

dark red, slightly silty; earthy weathering_ 5.1 

35. Sandstone, white; weathers light gray to pale 

brown ; medium-fine to medium-grained ; 

composed of subrounded clear quartz containing minor pink, gray and black, quartz, 

and white to tan angular chert___________ 16. 2 

34. Claystone, dark-red, slightly silty ; friable to 

earthy weathering _______________________ 14.2 

33. Sandstone, white; weathers light gray; very 

fine to fine-grained ; composed of subangular clear quartz and accessory minerals ; 

faintly laminated----------------------- 3. 2 

32. Claystone and sandstone interbedded. Claystone dark red to purple, in part slightly 

silty. Sandstone pinkish, very fine 

grained ; ripple laminated ; in beds as 

much as 6 in. thick______________________ 15. 5 

31. Sandstone, white to pale-brown, very fine to 

medium-fine grained; composed of clear 

quartz and minor accessory minerals ; 

faintly variegated laminations with minor 

channeling ----------------------------- 11.8 

30. Interval covered. Float indicates dark red, 

slightly silty claystone, and interbeds of 

reddish-brown and white, very fine grained 

sandstone------------------------------ 38.2 

29. Sandstone, pink to white; weathers light reddish brown ; very fine to fine-grained ; composed of subangular clear quartz and minor 

pink and black accessory minerals ; indistinct lamination, minor channeling_______ 11. 2 

28. Interval covered. Float indicates claystone, 

dark-red, slightly silty------------------- 27. 8 

Morrison Formation-Continued Thickness 

Salt Wash Member-Continued (feet) 

ZT. Sandstone, white; weathers grayish brown; 

very fine grained ; composed of subangular 

clear quartz and minor pink, black, and 

gray accessory minerals ; evenly bedded, 

not prominently laminated_______________ 1. 3 

26. Interval covered. Float indicates dark-red, 

silty to fine-grained sandy claystone; weathers to chips and earthy fragments______ 19.1 

25. Sandstone, pale-brown, fine- to medium-finegrained ; composed of subangular clear 

quartz and variegated accessory minerals ; 

highly cross laminated, channeled-------- 21. 7 

24. 'Sandstone and claystone. 'Sandstone pink to 

purplish-pink, fine to medium grained, 

poorly sorted; grades to dark-red sandy 

claystone; bedding poorly defined________ 3. 3 

23. Sandstone, slightly conglomeratic, white; 

weathers light gray to pale brown; :fine to 

medium grained; moderate sorting; composed of subangular to rounded clear quartz 

and abundant white to tan angular chert 

and minor variegated accessory minerals ; 

highly cross lamina ted; channelled; conglomerate contains white chert pebbles as much as~ in. in diameter ______________ 11.9 

22. Claystone and sandstone interbedded. Claystone dark-red, very silty to sandy; medium-fine-grained, poorly sorted. Sandstone 

white to reddish brown, very fine to medium 

fine, well sorted ; composed of clear quartz 

and minor variegated accessory minerals_ 15. 0 

21. Sandstone, white to pale-·brown; ·weathers 

reddish brown; medium-fine grained; composed of subangular clear quartz and numerous variegated accessory minerals; 

abundant white chert grains ; highly cross 

laminated; channel-------~-------------- 27.2 

Total Salt Wash Member ______ ..,! _______ 353.1 

Total Morrison Formation _____________ 698. 5 

Summerville Formation. 

CRETACEOUS SYSTEM 

LOWER CRErACEOUS SERIES 

BURRO CANYON FORMATION 

The Burro Canyon Formation, originally described 

as a separate formation hy Coffin (1921) who called it 

Post-McElmo, was defined by Stokes and Phoenix 

(1948) as the beds separating the Morrison Formation 

of Jurassic age from the Dakota Sandstone of Late 

Cretaceous age in southwestern Colorado and southeastern Utah. Stratigraphic position and fossil evidence (Brown, 1950; Katich, 1951; Stokes, 1952; Simmons, 1957) indicate that the Burro Canyon is of Early 

Cretaceous age. 

West of the Colorado River in Utah there are beds 

of somewhat similar lithology and the same age as the 
STRATIGRAPHY 15 

Burro Canyon which Stokes (1944) named thEl Buckhorn Conglomerate a.nd the Cedar Mountain Formation. 

In the mapped area the Burro Canyon Formation 

contains a basal unit, approximately 110 feet thick, 

that is light-gray to light-brown, medium- to coarsegrained crossbedded sandstone containing pebble-conglomerate lenses and sparse silicified logs. This basal 

unit conformably overlies the variegated shale and 

mudstone . units of the Brushy Basin Member of 

the Morrison Formation. The sandstone commonly 

crops out as a prominent cliff and forms mesas. In 

many places the basal sandstone is overlain hy a sequence of light-green mudstone, siltstone, and shale 

containing thin beds of siliceous limestone, limestone 

pebble-conglomerate, limy sandstone, chert and orthoquartzite; the sequence aggregates 150 feet in thickness. ·where present, these stra·ta distinguish the Burro 

Canyon Formation from the overlying Dakota Sandstone. The maximum thickness of the Burro Canyon 

Formation in the mapped area is about 260 feet, as 

shown in the following section measured near Pine 

Ridge in sees. 1 and 12, T. 28 S., R. 25 E., San Juan 

County, Utah. Color designations are after Goddard 

and others (1948). 

Dakota Sandstone. Conglomerate at base rests on erosion 

surface. 

B Thickness urro Canyon Formation: (feet) 

6. MoS't of unit covered by thin veneer of alluvium. 

Light-green tx> gray-green mudstone ; contains 

t hin-bedded sandstone, limestone, and chert as 

much as 1.5 tt thick. Light-gray impure, marly 

and dense limestone; sandy in part ; contains 

fine to medium"fine grains Qlf quartz. Light and 

dark-gray and green thin-bedded dense chert. 

Unit forms very gentle slope that steepens near 

'base of the Dakota Sandstone________________ 99. 0 

5. ·Sandstone, in part C'Onglomeratic and in part contains 'limestone nodules; white (N 9) to very 

light gray (N 8) and very paJe orange (10YR 

8/2) ; weathers to brownish gray (5YR 4/ 1) 

and light olive gray (5Y 5/2) ; fine to medium 

subangular to well-rounded, moderately frosted, 

fair- 1Jo well-sol"ted quartz grains, sparse opaque 

minerals, and limonite spotting. Conglomerate 

pebbles are light-gray, orange-yellow, and darkgray to 'black chert, subrounded, to 8 mm in 

diameter, average 5 mm. Beds are chiefly massive. Forms •ledge on gentle slope____ ________ 11. 0 

4. Covered .interval. PTobably mudstone much like 

t hat deScribed in unit 6----------------------- 2. 5 

3. San'dstx>ne, white (N 9) to very light gray (N 8) ; 

medium-fine- to medium-coarse-grained, subangular to well-rounded, poorly sorted quartz cemented by secondary silica and spotted with limonite; very sparse green mudstone films on 

bedding planes; fiat bedded to massive. Forms 

thin ledges in slope______________________ ____ 6. 5 

Burro Canyon Formation- Continued Thickness 

(feet) 

2. Covered interval. Probably mudstone like that 

described in unit 6. Forms gentle slope ______ _ 

1. Sandstone and conglomeratic sandstone, grayishorange (10YR 7/4), dark yellowish"Orangebrown (lOYR 6/6), and light brown 

(5YR 5/6) ; weathers to dark yellowish brown 

(10YR 4/2) ; medium-fine to coarse, subangular 

to well-rounded quartz grains, sparse white 

opaque minerals, interstitial mudstone, and 

abundant limonite spotting. Chert pebbles occur 

in thin coarse-grained sandstone lenses scattered 

along bedding planes ; range from 1 to 

3 em ·but average 5 mm in diameter. Bedding 

intricRJte; torrential and gen1Jly sweeping crossbeds; in places fiat bedded and massive. Unit 

23.5 

forms prominent cliff ________________________ 110. 0 

Total th-ickness __ _____ ____ _____________ _____ 252. 5 

Basal contact covered. 

Morrison Formation (Brushy Basin Member). 

Although not present in the measured section, a bed 

as much as 8 feet thick of light-gray well-indura-ted 

fine-grained orthoqua1•tzite that is overlain hy the Dakota Sandstone crops out a few hundred feet to the 

west. Here and elsewhere in the mapped area the orthoquartzite bed appears to be the uppermost unit of the 

Burro Canyon Formation. In it are spheroidal structures having concentric crack systems formed around 

irregular nodular cores of light blue-gray chert. Such 

cores, ·according to Pettijohn (1949, p. 149-150), result 

from the local concentration of silica in a sandstone unit 

during epigenetic replacement of carbonate cement. 

Subsequently, after the sandstone has become quartzite, 

dehydration of the silica body causes the host rock to 

shrink and form concentric crack systems known as 

contraction spheroids. This phenomenon is common 

in the orthoquartzite bed, both ·around ohert nodules 

and elsewhere in the unit. 

Silicification of the standstone to form quartzite occurred prior to deposition of the overlying formations, 

as noted in the following discussion of ·the Burro Canyon-Dakota corrtact. Inasmuch as this quartzite is the 

uppermost unit of the Burro Canyon Formation, lithifying processes are presumed to have been active during 

a period of nondeposition under subaerial weat~ering 

conditions. The duration of this hiatus is not yet 

determined. 

BURRO CANYON-DAKOTA CONTACT 

The Burro Canyon-Dakota contact in the La Sal 

quadrangle is extremely undulaJtory (Carter, 1957). 

Where the orthoquartzite bed at the top of the Burro 

Canyon Formation is present, it is conform!l!bly overlain by lenses of conglomerate and sandstone of the 
16 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

basal unit of the Dakota Sandstone. Where the orthoquartzite is absent, the base of the Dakota conglomerate 

is in contact with successively lower beds of the Burro 

Canyon-light-green mudstone, limestone, and chertand defines !broad conglomerate-filled channels. In 

many p}aces the Dakota is in con'tact with ·the thick 

conglomeratic sandstone which is the bll!sal unit of the 

Burro Canyon (fig. 2). 

Previous workers have described the Burro CanyonDakota contact as an angular unconformity between 

the beds above and below the erosion surface, but no 

angular relations or wedging out were observed, except 

locally, in the La Sal quadrangle. Therefore the term 

"disconformity" is used to describe the contact in this 

area. In outcrop, the disconformity is in places obscure 

and, because of its undulatory nature, is difficult to trace. 

Where the basal conglomerate of the Dakota Sandstone 

rests on the basal sandstone unit of the Burro Canyon, 

the contact may be distinguished from a distance by a 

color contrast, that is, the gray sandstone of the Burro 

Canyon is overlain by conglomeratic sandstone beds 

in the Dakota that range from yellow brown to pale 

orange brown. Near the outcrop this color contrast 

is less conspicuous. Where the Burro Canyon is 

bleached immediately below its contact with the Dakota, 

the contact is obvious. Bleached zones range in thickness from a few inches to several feet and are typified 

by rock that is poorly cemented and extremely friable. 

Where the contact is stratigraphically higher- that is, 

on the mudstone and limestone of the upper part of the 

Burro Canyon-it is easily identified, for conglomerate 

of the Dakota forms a ledge 1 to 20 feet thick. 

UPPER CRETACEOUS SERIES 

DAKOTA SANDSTONE 

The Dakota Sandstone in the La Sal quadrangle rests 

on the eroded surface of the Burro Canyon Formation 

and ·is overlain by the Mancos Shale of Late Cretaceous 

age. The strata comprising the Dakota Sandstone can 

generally be divided into three parts: ( 1) a basal unit 

of sandstone and conglomerate, ( 2) a middle unit of 

gray carbonaceous shale containing discontinuous coal 

seams, and (3) an upper unit of sandstone. Where all 

three units are present, the formation has an aggregate 

thickness that ranges from 150 to 200 feet. The contact 

FIGURE 2.- Conglomerate in the Dakota Sandstone containing quartzite and sandstone boulders resting on sandstone which 

is the basal un'it of the Burro Canyon Formation. Locality is on Wray Mesa, north of Coyote Wash, San Juan County, 

Utah. 
STRATIGRAPHY 17 

with the overlying Mancos is generally covered in the 

mapped are·a. 

The basal unit ranges in thickness from a few inches 

to more than 60 feet and crops out as a ledge which 

commonly forms the cap of mesas. It is composed 

of yellow-brown to light orange-brown medium-grained 

sandstone that is characterized in many places by overlapping lentils of sandstone 4 inches to 2 feet thick. 

Many of these lentils contain inclined beds of sandstone 

which dip from 20° to 40°. The basal sandstone unit 

contains sparse to abundant plant debris that is carbonaceous or has been replaced by limonite. These fossils are considered to be of Late Cretaceous age (Brown, 

1950, p. 47) and help to distinguish the Dakota from the 

Burro Canyon Formation. 

In many places sandstone of the basal unit contains 

discontinuous lenses of coarse conglomerate and sandstone. The conglomerate is composed of rounded and 

subrounded pebbles of gray and black chert, milky 

quartz, and gray quartzite ranging in diameter from 

5 mm to 5 em. Local concentrations of angular and 

subangular cobbles and boulders of sandstone, quartzite, 

and chert are found at the base of the sandstone or conglomerate. These fragments are lithologically identical 

to rocks of the Burro Canyon Formation from which 

they were undoubtedly removed and redeposited in 

channels cut by the same streams that deposited the 

basal unit of the Dakota Sandstone. In places the conglomerate is very poorly cemented and extremely friable; elsewhere it contains great quantities of silica 

cement and is well indurated. Where present this conglomerate forms a distinctive base for the sequence of 

beds comprising the Dakota Sandstone. 

In the mapped area these basal conglomerates of the 

Dakota fill broad depressions or channels in the Burro 

Canyon Formation that are more than 100 feet deep, 

several thousand feet wide, and of unknown length. 

Measurements of current lineation, crossbeds, and festoons indieate that the trend of these channels differs 

from place to place, but in general is N. 30° E. Poorly 

preserved fossils in the chert pebbles of the conglomerate have been tentatively identified as of Permian or 

Pennsylvanian age. Some forms are similar to fossils 

found in the Kaiba;b Limestone, and L. C. Craig (oral 

oommun., 1957) suggests a source 'area that lies to the 

southwest. Such a source agrees with measurements of 

sedimentary structures in the conglomerate beds that 

form the base of the Dakota Sandstone. 

The basal unit grades upward into and in places interfingers with the middle unit; a unit composed of 

light-gray ea.rbonaceous shale, siltstone, and mudstone 

which have a total thickness of approximately 100 feet. 

Coal seams, generally less than 3 feet thick, occur at 

various levels throughout the unit. In outcrop the high 

carbon content, which serves to distinguish it from the 

underlying Burro Canyon Formation, imparts a gray 

color to the formation. 

The upper unit is a light-brown medium- to finegrained sandstone which crops out as ledges 10 to 30 

feet high. Both inclined and flat bedding are eommon 

throughout the upper sandstone unit. 

The following detailed section of the Dakota Sandstone is taken from a core obtained in drill hole LC371 

(collar elevation: 7,365.8 ft) in sec. 29, T. 28 S., R. 26 

E., San Juan County, Utah, on Hideout Mesa, north of 

La Sal Creek Canyon. The lithologies are described 

here in much more detail than they are normally seen 

in outcrop and are considered to be typical of the Dakota 

Sandstone in the mapped area. 

Erosion surface. Mancos Shale absent. 

Dakota Sandstone : 

28. Sandstone, light-brown, medium-fine- to medium-grained ; abundant opaque minerals and 

limonite spots; sparse brown mudstone pelThicknesB 

(feet) 

lets, torrential crossbedding separated by 

flat-bedded sandstone. Forms ledge in nearby 

outcrop---------------------------------- 18.4 

27. Mudstone, interbedded brown and gray layers; 

gypsiferous, mostly in fractures____________ . 6 

26. Shale; interbedded black and gray layers, 

ca-rbonaceous ----------------------------- 13. 3 

25. Lignite, black. Abundant gray mudstone 

mixed with coal and in thin seams__________ 2. 8 

24. Shale, black, fissile. Limonite stain along 

bedding planes____________________________ 5.0 

23. Sandstone, light-brown to brown, fine-grained ; 

abundant opaque minerals and limonite 

spots ; sparse carbon. Abundant carbonaceous mudstone along bedding planes. Flat 

bedded ---------------------------------- 2.3 

22. Siltstone, light-gray and black; abundant 

carbon----------------------------------- .3 

21. Sandstone, light-brown, fine-grained ; abundant 

limonite and opaque minerals ; abundant carbon and carbonaceous mudstone as films and 

seams along bedding planes; flat bedded. Interbedded with black carbonaceous mudstone------------------------------~------ 1.7 

20. Sandstone, brown, fine-grained; abundant limonite spots and opaque minerals. Sparse carbon and carbonaceous mudstone as films on 

bedding planes____________________________ .6 

19. Shale, gray_________________________________ .9 

18. Lignite, black_______________________________ 1. 0 

17. Shale, gray; slightly carbonaceous. Gypsum 

fills joints-------------------------------- 2.5 

16. Sandstone, light-gray to white, very fine to 

medium-fine-grained; abundant white opaque 

minerals ; sparse carbon flecks and interstitial gray mudstone________________________ 1. 3 

15. Shale, gray slightly carbonaceous____________ 12. 1 
18 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

Dakota Sandstone--Continued Thickness (feet) 

14. Siltstone; light-gray layers interbedded with 

black layers ; sparse carbon ; abundant carbonaceous mudstone films and seams; contorted and crinkled bedding________________ 14. 8 

13. Sandstone, light-brown, fine-grained; abundant 

limonite spots, sparse carbon, and gray mudstone pellets and films_____________________ 5. 0 

12. Mudstone and siltstone, interbedded, gray; 

sparse carbon_____________________________ 2.4 

11. Shale, dark-gray to black; abundant carbon, 

coaly in part______________________________ . 8 

10. Siltstone, gray to light-gray ; sparse marcasite 

and carbon________________________________ 15. 8 

9. Sandstone, light-br<?wn to gray, medium-fine to 

medium-grained. Sparse gypsum, very 

sparse carbon, and sparse gray mudstone 

filling interstices, also as seams and pellets__ 3. n 

8. Siltstone, dark-gray to brown, sandy; sparse 

carbon----------------------------------- .a 

7. Mudstone, greenish-gray; sparse carbon, fossil 

plants ----------------------------------- .7 

6. Mudstone, gray; thin seams of gypsum________ 4. 8 

5. Mudstone, light-gray; sparse pyrite and bentonite------------------------------------ 1.7 

4. Siltstone, gray, very carbonaceous; sparse marcasite in radiating crystals around a black 

carbonaceous core; 0.3 ft of limonite stain 

at base___________________________________ 1.8 

3. Siltstone, sandy; light-brown to light-gray ; 

sparse carbon and gypsum. Abundant interstitial greenisl},-gray mudstone; also as seams 

and pellets________________________________ 1. 8 

2. Sandstone, light-brown, medium- to mediumcoarse-grained; sparse white opaque minerals, very sparse carbon, sparse whitish 

mudstone pellets ; clean, poorly cemented. 

(Forms ledge in nearby outcrop.) ________ 31. 6 

1. Sandstone, conglomeratic, light-brown to lightgray, coarse-grained; conglomerate pebbles 

of green and white chert; abundant gray 

mudstone pellets. (Forms ledge in nearby 

outcrop)__________________________________ 3.5 

Total Dakota Sandstone _________________ 151. 7 + 

Burro Canyon Formation. 

In the section above, the Dakota Sandstone rests on 

bluish-green mudstone of the upper member of the 

Burro Canyon Formation. Along the west side of Hideout Mesa., not far from the drill hole from which the 

core described in the section was taken the Burro 

Canyon-Dakota contact is well exposed and clearly illustrates the features described in preceding paragraphs. At the southern end of Hideout Mesa the 

sandstone and conglomerate beds of the Dakota rest 

directly on the massive sandstone of the Burro Canyon. 

From there the contact rises stratigraphically to the 

north. 

MANCOS SHALE 

The Mancos Shale (Cross, 1899, p. 4), youngest of 

the Mesozoic sedimentary rocks in the La Sal quadrangle, rests conformably on the · Dakota Sandstone. 

The Mancos is best exposed along Geyser Creek west of 

its confluence with Deep Creek at the head of Roc Creek 

Canyon. The Mancos also crops out in Geyser Pass, 

around Mount Mellen thin, and in a large area extending 

from La Sal Pass southeastward to the head of Pole 

Spring Canyon. Both areas are extensively covered 

by glacial and landslide debris. An isolated exposure 

was found at the top of a downdropped block. of sedimentary rock in the collapsed area at the northwest end 

of Paradox Valley. The Mancos crops out as somber 

gray rounded hillocks and steep slopes, generally barren 

of vegetation. Weathering of the shale surface produces an efllorescent covering of light-gray clay that is 

sometimes several inches thick and extremely sticky and 

slippery when wet. 

The Mancos is composed of dark-gray fissile marine 

shale and thin beds of light-gray siltstone, limy siltstone, petroliferous limestone~, and limestone nodules. 

The limy units contain an abundant faunal ass~blage. 

Thin coquina beds of oyster shell ( Ostrea Oongesta Conrad) are associated with shale zones that contain irregular seams and pods of prismatic aragonite, many of 

which appear to have replaced fossil shells. 

The general homogeneity of the Mancos, possible 

concealed· structural deformation, and the absence of 

:continuous exposures make it difficult to determine 

accurate thicknesses of the formation or to differentiate 

between its members. No complete section·of the Mancos is known to exist in the mapped area; erosion has 

removed most of the beds. Measurable thicknesses of the 

formation differ from a few feet to several hundred 

feet. In places the apparent thickness differences are 

the result of ice action which locally contorted the beds 

during the glacial epoch. The greatest thickness of 

Mancos, an estimated 1,000 to 1,200 feet, is partly exposed along Geyser Creek in the Taylor Creek syn,cline. 

Field identification of the faunal assemblage found here 

suggests that the shales have an age range equivalent to 

that of the Greenhorn, Carlile, and Niobrara Formations of the Western Interior. 

Rocks of an age equivalent to the age of the Tununk 

Shale Member of Gilbert ( 1877, p. 4) are recognized by 

the presence of Gryphaea newberryi which occurs 

throughout the area in the lower 100 feet of the Mancos. 

These strata correlate with the Greenhorn Limestone 

of the western part of the Interior Plains. .Nbout 500 

feet above the base of the Mancos is a thin zone of coquina and limestone beds containing a;bundant fauna, 

among which are Prionocyclus wyomingensu, Scaphites 

warreni, I nocerawus dimidius and Lopha lrugubrius. 

All are of late Carlile age and are in the Ferron Sandstone Member of the Mancos, which is absent here but 
STRATIGRAPHY 19 

present a few miles west of the mapped area (Baker, 

1933, p. 55). This thin zone, less than 10 feet thick, is 

probably equivalent to the Ferron. Inoceramus deformis and Ostrea congesta of Niobrara age are indicative 

of the Blue Gate Shale Member of Gilbert (1877, p. 4), 

with which the remainder of the Mancos in the La Sal 

quadrangle is tentatively correlated. Further, more 

detailed, paleontological studies are needed in this 

locality. 

The base of the Mancos is not exposed throughout 

most of the 'area. Where exposed, the contact is well 

defined by shale resting conformably on the upper sandstone strata of the Dakota or locally on a thin sequence 

of light-gray to !black carbonaceous mudstone beds that 

overlie the upper sandstone of the Dakota. On the 

south side of Mount Mellenthin a conglomerate bed 

about 2 feet thick occurs at the base of the Mancos. 

The matrix is dark gray and is composed of fine- to 

coarse-grained quartz and interstitial carbonaceous clay. 

The pebbles range from 2 mm to 1 em in diameter and 

are composed of rounded light-gray chert and darkgray carbonaceous mudstone galls. Although the geographical distribution of such conglomeratic lenses is 

not known, it appears that the upper part of the Dakota Sandstone was, in places, reworked by the encroaching sea in which the Mancos was deposited. 

TERTIARY(?) SYSTEM 

GEYSER CREEK FANGLOMERATE 

Sedimentary rocks of Tertiary age whtch crop out in 

the Book Cliffs, north of the mapped area, are absent 

in the La Sal quadrangle. Local deposits of Tertiary ( ? ) fanglomerate, however, occur on the flanks of 

the La Sal Mountains. Baker (1933, p. 56) describes 

consolidated gravel resting on folded Mancos Shale on 

the ridge between upper Pack Creek and upper Cane 

Creek on the west flank of South Mountain. Hunt 

( 1956, p. 30) describes a deposit of fanglomerate that 

rests directly on salt of the Hermosa Formation in 

Castle Valley and is downfolded as the result of removal 

of salt. 

A deposit of fanglomerate similar to that described 

by Hunt (1956) was found in the northern part of the 

La Sal quadrangle and the southern part of the Polar 

Mesa quadrangle. It was first recognized on the ridge 

between Geyser Creek and Deep Creek (sec. 36, T. 26 

S., R. 25 E., Grand County, Utah) and has been named 

Geyser Creek Fanglomerate by Carter and Gualtieri 

( 1965). The unit is also well exposed on the north side 

of Deep Creek Canyon in the same general area. 

The Geyser Creek Fanglomerate is a consolidated 

conglomeratic sandstone, cemented with calpium carbonate, that rests with angular unconformity on the 

777-039 0-65-4 

folded Mancos Shale. The Mancos Shale crops out 

along the margins of a narrow northwest-trending 

structural trough known as the Taylor Creek syncline 

which occupies the area between the collapsed anticline 

of Sin bad Valley and North Mountain. The center of 

the trough is filled with the conglomerate which crops 

out as vert~ cal cliffs and steep slopes (figs. 3, 4) . 

The conglomerate may be roughly divided into two 

lithologic units. The lower unit, resting on the Mancos 

Shale, is composed of yellowish-gray to grayish-ora.nge, 

very fine grained thin-bedded silty sandstone, interstratified with sandy siltstone and claystone beds. These 

beds are poorly cemented and very friable, and contain 

abundant fragments of aragonite and fossil shells undoubtedly derived from the underlying Mancos. This 

zone, 4 to 15 feet thick, rests with angular unconformity 

on the Mancos. It is conformably overlain by, and in 

places interfingers with, interstratified layers of sandstone and conglomerate. The sandstone is composed 

of fine-grained quartz and interstitial clay particles 

and cemented with calcium carbonate. The conglomerate beds are lenticular and composed of sandstone and 

igneous pebbles and boulders. The pebbles, generally 

2 inches in diameter or less, comprise the bulk of conglomeratic material. Boulders as much as 2 feet in 

diameter occur in the thicker lenses. Most of the older 

formations exposed in the area are represented by the 

sandstone pebbles and boulders and can be recognized 

by their distinctive lithologic characteristics. In general, they appear to show an inverted age relation, as 

would be expected in the normal cycle of erosion a.nd 

deposition. For example, the sandstone and conglomerate of the Upper Jurassic Morrison Formation and 

Lower Cretaceous Burro Canyon Formation are represented as pebbles and boulders in the lower part of the 

conglomerate. Pebbles and boulders in the upper part 

are derived dominantly from Middle and Lower Jurassic and Triassic rocks. Boulders of sandstone and conglomerate derived from the Kayenta Formation are 

most easily recognized. Igneous boulders in the deposit 

show various degrees of alteration due to weathering. 

Many appear relatively fresh while others a.re highly 

weathered to yellowish brown or bright orange brown 

owing to alteration of the mafic minerals to limonite. 

The igneous boulders also appear to increase in number 

as well as in average size from bottom to top. This va.riation may reflect either the increasing size of the igneous 

source area or a gradual down warping of the synclinal 

basin which increased the gradient and transporting 

capacity of the streams. In the upper unit, fossil fragments derived from the Mancos decrease in abundance 

toward the top. These features are demonstrated in the 

following geologic section. 
20 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

FIGURE 3.-0utcrop of Geyser Creek Fanglomerate. Conglomerate (Tg) resting on Mancos Shale (Km) in SE% sec. 36, 

T. 26 S., R. 25 E., San Juan County, Utah. Both dip westward (left side of picture) and are truncated by an erosion 

surface on which Quaternary terrace gravel (Qg) has been deposited. 

Measured section at type locality of the Geyser Oreek Fa;nglomerate emposed on the north side ot Deep Oreek in NE% sec. 36, 

T. 26 S., R. 25 E., Gra>nd Oounty, Utah 

Qua ternary gravel. Thickness Geyser Creek Fanglomerate: (feet) 

14. Conglomerate, light-brown; diorite porphyry and 

sandstone boulders as much as 1.5 ft long, 0.9 ft 

wide, 0.7 ft thick in fine-grained sandstone matrix cemented with calcium carbonate; layer 

near base contains pebbles as much as 3 in. long, 

encrusted with CaCO,; interiors of pebbles coml)letely weathered to soft powdery limonite. 

Sparse aragonite fragments. Forms ledge____ 7. 5 

13. Sandstone, grayish-orange-pink, very fine to 

coarse-grained, poorly sorted ; 80-90 percent 

rounded quartz grains ; remainder composed of 

black and brown chert grains and angular to 

subangular aragonite fragments______________ 1. 5 

12. Conglomerate, light-brown; diorite porphyry and 

sandstone boulders as much as 1ft in diameter; 

sparse pebbles of limestone ; sandstone boulders 

are composed of fine-grained light-gray quartz 

Thickness Geyser Creek Fanglomerate-Continued (feet) 

sandstone resembling Wingate sandstone. 

Upper 5 ft partly covered. Forms ledge______ 8. 0 

11. Interval covered by talus and loose graveL_____ 16. 5 

10. Conglomerate and interbedded conglomeratic 

sandstone, light-brown, fine- to coarse-grained, 

poorly sorted; cemented with CaCOa; 30 percent 

is diorite porphyry boulders as much as 2 ft in 

diameter, weathered to various degrees. Thirty 

percent is sandstone boulders and pebbles of 

lavender to red-brown sandstone (Kayenta Formation), light-gray to light-brown fine-grained 

sandstone (Wingate Sandstone), and red-brown 

to reddish-orange and brown silty sandstone 

(Chinle Formation). Twenty percent is composed of dark-gray limestone and siltstone 

pebbles as much as 1 in. in diameter (Mancos 

Shale), light-gray fine-grained sandstone and 

light-green and red chert (Morrison Formation), white to light-gray fine-grained quartzite 

(Burro Canyon Formation). Twenty percent 

is unindentified. Forms cliff_______________ _ 24. 0 
STRATIGRAPHY 21 

FIGURE 4.-0utcrop of conglomerate at type section on Deep 

Creek in NEJ4 sec. 36, T. 26 S., R. 25 E., San Juan County, 

Utah, showing zone of reworked fossiliferous Mancos Shale 

in sandstone at base, overlain by well-cemented sandstone 

and conglomerate lenses. Beds dip westward toward their 

mountain source at an angle of about 25°. Outcrop shown is 

about 12 feet high. 

Geyser Creek Fanglomerate--Continued T'1J:e~)88 

9. Conglomerate with pebbles and cobbles of diorite 

porphyry and sandstone; pebbles average 2 

in. in diameter, cobbles as much as 6 in. ; some 

silty sandstone pebbles impregnated with 

limonite. Well cemented. Forms protruding 

ledge -------------------------------------- 2.0 

8. Sandstone, light-brown, flat-bedded to crossbedded, fine- to coarse-grained; poorly sorted 

quartz grains, coarse-grained opaque minerals, 

and angular fragments of feldspar. Scattered 

pebbles of diorite porphyry, sandstone, and siltstone. Differences in cementation of beds 

causes differential weathering to series of 

rounded ledges and recesses__ __ ______________ 9. 0 

7. Conglomerate and sandstone, interbedded lentils. 

Conglomerate lenses composed of pebbles and 

robbles as much as 4 in. in diameter, average 

1-2 in. in diameter; poorly cemented, friable. 

Diorite ·por:phyry ·pebbles, sligh'bly altered by 

weathering, make up 50 ·percent of conglomerate ; sandstone and siltstone ·pebbles form remainder. Sandstone lenses are light brown, 

very fine grained to silty ; rontain scattered 

coarse grains of quartz ; well cemented with 

CaCOa; weather to protruding rounded ledges_ 8. 5 

Geyser Creek Fangl-omerate--Colitinued T~if:e~)88 

6. Conglomerate, light-il>rown, ·poorly sorted ; sandstone matrix is very fine to coarse-grained. 

Pebbles as much as 3 in. in diameter, rounded, 

dominantly sandstone and red siltstone. Some 

impregnated with HmonHe; powdery--------- 1. 0 

5. Conglomerate, light•brown, poorly sorted, weakly 

cemented; crossbedded at 'base, flatcbedded near 

top; •pe!Jbles range from 1 in. in diameter to 

boulders 18 in. across. Sandstone pebbles and 

boulders dominant; diorite porphyry detritus 

less than 10 •percent. .Silty sandstone pebbles 

impregnated with limonite._____________ ____ _ 11. 5 

4. Sandstone, conglomera tic, light-green to yellowtsh-'brown, flat•bedded and crossbedded, finegrained ; contains some coarse lenses ; coarse 

lenses contain scattered pebbles as much as 2 

in. in diameter. Limonitic stain at base______ 4. 5 

3. CongJomerate, light-brown; ·pebbles and cobbles 

av.eraging 2-3 in. in diameter, boulders as much 

as 2 ft long; coarser material in upper 3 ft; 

sandstone boulders dominant. Flat-bedded and 

crossbedded ; 'limonite stain throughout; cementing and induration va·riable_____________ 6. 0 

2. Siltstone, sandy, light-green to ·red-'brown; massive and thin flat-bedded layers extremely friable, weakly cemented. Abundant fossil and 

aragonite fragments deri!ved from Mancos 

Shale -------------------------------------- 6. 0 

1. Conglomerate, light-brown ; pebbles, cobbles and 

boulders. Sands·tone pebbles as much as 14 in. 

in diameter dominant; sandstone boulders as 

much as 18 in. in diameter; a few diorite 

porphyry pebbles; angular fragments of aragonite. Limonite-stained sandstone lens near 

base of unit; basal contact obscured by talus 

composed of shell and aragonite fragments in 

a matrix of light-green powdery clay and finegrained sandstone believed to 'be reworked zone on the Maneos ______________________________ 10.0 

Total thickness of the conglomerate of the 

Unconfonnity. 

Mancos Shale. 

Deep Creek area ________________________ 116. 0 

The Geyser Creek fanglomerate ranges in thickness 

from 0 near the La Sal Mountains to an estimated 600 

feet in the center of the synclinal 'trough and is 50 to 

120 feet thick along its eastern limit. J'he top of the 

formation has been beveled hy erosion and is overlain 

by uncJonsolidated terrace gravel of Quaternary age 

that average ·rubout 40 feet in thickness (.fig. 3). Richmond (1962) has referred the terrace gravels to t.he 

oldest deposits in the Harpole Mesa Formation, glacial 

drift of proba;bly Nebraskan (earliest Pleistocene) age. 

The fanglomerate, therefore, is pre-Quaternary and 

probably of late Pliocene age although no fossils have 

yet been found to substantiate this assumed age. 
22 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORA!DO 

One of the more interesting features of the Geyser 

Creek fanglomerate is its structural relationship with 

the underlying Mancos Shale along the east flank of 

the Taylor Creek syncline. This relationship and its 

implication are discussed in the section describing the 

Taylor Creek syncline (p. 27). 

QUATERNARY SYSTEM 

Quaternary deposits ranging in age from Pleistocene 

to Recent are widespread in the La Sal quadrangle. 

These deposits include •a great variety of unconsolidated d~bris of diverse origin which indicate an interesting history of climatic change, erosion, and deposition 

in and adjacent to the La Sal Mountains. This history 

is the subject of a report :by G. M. Richmond (1962) 

of the U.S. Geological Survey. The oldest of these 

deposits are of glacial and periglacial origin and are 

within and on the flanks of the mountains. Younger 

deposits of alluvium ·and colluvium occur on the canyon and valley floors, eolian deposits and residual soils 

on the mesas and uplands. On the map of the La Sal 

quadrangle these deposits have been classified in six 

groups although, in many placP.s, they grade •into each 

other and are not easily separruble. These g11oups are 

glacial moraines, rock glaciers, rubble, fan gravel, landslides, and loess alluvium. Glacial moraines include 

all deposits which can be directly attributed to a glacial 

origin ; these are discussed in greater detail in succeeding paragraphs. Rock glaciers are few in number, of 

smaller extent, and ruppear to be of postglacial age. 

They are nearly free of vegetation and can ·be distinguished by their lobate plan and a surface cam posed of 

a series of somewhat concentric ridges. Rubble deposits are sheetlike masses mainly composed of blocky 

and sh11bby fragments of igneous rock, and locally of 

resistant sandstone. The contacts of rubble deposits 

with igneous rocks and landslide deposits are indefinite. 

In the areas of Mount Peale and Mount Mellent:hin 

where rubble deposits are contiguous with rock glaciers, 

they were mapped as such. Boulders and coarse gravel 

form fan-shaped or a.pronlike deposits at the mouths 

of the mountain canyons. Landslide deposits include 

talus and talus cones, hummocky deposits of boulders, 

slump blocks, and all other colluvial debris of irregular 

form found in the mountains, around mesas, and in 

the canyons. Loess alluvium includes stream-deposited 

silt, sand, and gravel and wind-hlown silt and sand. 

The most outstanding and readily recognized glacial 

features in the La Sal Mountains are the cirques and 

U-shaped valleys of the Middle Mountain group. 

Within and extending from them are deposits composed 

mostly of unconsolidated igneous rock debris occurring 

as moraines, outwash plains, and erratics. Lateral and 

medial moraines occupy the cirques and U-shaped valleys 

in the higher elevations and, although they have been 

considerably modified by erosion, can be traced to lower 

elevations within a 4-mile radius of the mountains. 

Terminal and recessional moraines are narrow ridges 

extending perpendicular to the direction of ice flow. 

These ridges have steeply inclined slopes on their distal 

side; the proximal side is gentle and marked by 

deep lakes, or in places, coalescent ponds and grassy 

meadows. A notable example of a terminal moraine 

is southwest of Geyser Creek in sec. 9, T. 27 S., R. 25 E., 

San Juan County, Utah. Here recessional moraines 

have created Blue and Dark Canyon lakes as well as 

many other deep pothole lakes that are typical of glaciated terrain. Glacial erratics, some as large as 20 

feet long, 10 feet wide, and 10 feet thick, are common 

throughout the area extending from La Sal Pass to 

Pole Spring Canyon. 

The glacial deposits of pre-Wisconsin, Wisconsin, and 

Recent age have been mapped in detail by Richmond 

(1962) who divided them into four formations representing four major stages of glaciation. These are, from 

oldest to youngest, the Harpole Mesa Formation of preWisconsin age, the Placer Creek Formation of early 

Wisconsin age, the Beaver Basin Formation of late 

Wisconsin age, and the Gold Basin Formation of Recent 

age. Each formation records several episodes of glacial 

advance and recession. Study of the Harpole Mesa 

Formation enabled Richmond to estimate that the ice 

covered a maximum of 85 square miles and that its maximum thickness was 400 feet. During this stage, ice of 

three glacial advances covered most of the mountain 

area. The advances are tentatively correlated with the 

Nebraskan, Kansan, and Illinoian advances of the midcontinent region. Richmond believes that during the 

first recession of the ice there was partial subsidence of 

the Castle Valley anticline and that during the second 

recession Moab and Castle Valleys were partly excavated. The third recession was accompanied by a gradual regional uplift; the subsequent recessions brought 

further subsidence and excavation of the previously 

mentioned areas and also of Sinbad and Paradox 

Valleys. 

Richmond (1962, p. 101-102) states that carbon-14 

age determinations indicate that deposition of the Gold 

Basin Formation of Recent age began about 2,900 years 

ago and came to an end about 1860. During this period 

the receding glaciers partly filled most of the cirques, 
IGNEOUS ROCK:S 23 

and the timberline was about the same as it is today 

(11,000 to 11,500 ft above sea level). In general the 

climate was somewhat cooler and wetter than at the 

present time. 

IGNEOUS ROCKS 

The igneous rocks of the La Sal Mountains have been 

studied by Peale and J. A. Holmes (in Peale, 1877a,b), 

Cross (1894b), Hill (1913), Gould (1926), and more 

recently by Hunt and Waters (Hunt, 1958). Because 

these rocks had been studied in considerable detail, the 

authors made only cursory examinations, mostly in 

areas where the igneous rock affected the surrounding 

sedimentary rocks. Of special interest was the possible 

relationship of igneous rock to uranium-vanadium deposits; consequently a summary of previous petrographic and chemical work and additional information 

the authors believe pertinent is given here. 

The igneous rocks of the La Sal Mountains are intrusive and are constituted almost entirely of diorite porphyry and lesser amounts of monzonite and syenite 

porphyries, intruded in the order listed (Waters, 1955, 

p. 715-716). In the La Sal quadrangle, diorite porphyry is the principal intrusive rock; it crops out in 

three areas along the northern and western margins of 

the map. These three areas are parts of the three intrusive centers that form the mountain groups comprising the La Sal Mountains. Hunt (1958) referred 

to the three groups as North Mountain, Middle Mountain, and South Mountain, and these designations are 

used in this report. Of the North Mountain group only 

the southern part of Mount Tomasaki and the southeastern part of Haystack Mountain lie within the quadrangle. Mount Mellenthin and Mount Peale comprise 

the eastern half of the Middle Mountain group and lie 

near the northwest edge of the map. The southeastern 

part of South Mountain extends into the west-central 

part of the area. 

. PETROGRAPHY 

Gould (1926, p. 80-81) described the megascopic appearance of the diorite porphyry as fine grained, light 

gray to white, and containing dark phenocrysts of ferromagnesian minerals, light-colored phenocrysts of 

feldspar, and sparse phenocrysts of quartz imbedded in 

a light-,gray aphanitic groundmass. The ferromagnesian minerals consist almost wholly of hornblende 

and minor amounts of light-green pyroxene. 

Microscopically, Gould (1926, p. 81-82) determined 

the feldspar phenocrysts to be oligoclase and andesine; 

albite or more calcic pl·agioclase are quite rare. The 

plagioclase forms broad tabular idiomorphic phenocrysts containing albite and showing rare Carlsbad 

twinning. .Zone banding is common. Although rare, 

orthoclase phenocrysts occur in elongate crystals and 

commonly display Carlsbad twinning. Quartz is generally ·associated with feldspar in the groundmass and is 

rarely found as phenocrysts. 

Gould states that hornblende is the most abundant 

ferromagnesian mineral. It occurs most commonly as 

the green pleochroic variety with minor amounts of the 

brown and bluish-green varieties. Hornblende is intimately associated with magnetite, either surrounding 

magnetite grains or crystals or bordered by magnetite. 

Pale-green to colorless augite is less common. Biotite 

is the least a'bundant of the ferromagnesian minerals and 

occurs as the brown, strongly pleochroic variety. 

Magnetite, ·already mentioned in connection with 

hornblende, is the most common accessory mineral. 

Gould recognized two generations of magnetite but did 

not indicate any genetic difference. Sphene occurs as 

widely as magnetite but is less abundant. Apatite is 

present in aU the rocks, whereas zircon is sparsely 

distributed. 

The groundmass of the porphyry is almost entirely 

quartz and feldspar, usually orthoclase. Gould observed that the texture of the diorite porphyry ranges 

from microgranul'ar to coarsely crystalline. Hunt 

( 195'3, p. 152) noted that in the Henry Mountains the 

texture of the diorite porphyry differs from one intrusive body to another, but in any one body he found the 

texture to be uniform. Hunt related this difference to 

conditions within the magma, because the textural differences appeared to be independent of the size or shape 

of the intrusive body or nature of the host rock. 

Alteration of some of the diorite porphyry rocks from 

the La Sal Mountains has been reported by Gould. The 

feldspars are altered to sericite and are associated with 

smaller amounts of calcite. Some of the ferromagnesian minerals are apparently replaced by colorless or 

pale green epidote. Hunt and Waters (Hunt, 1958, p . 

334-339, 345) found varying degrees of alteration, 

especially inN orth Mountain. They recognized that the 

altered rocks range from slightly altered porphyry in 

which less than half the hornblende had been affected, 

the feldspar only incipiently, and the magnetite not at 

all, to recrystallized porphyry in which new minerals 

made up a part of the rock. The alteration occurred 

mainly along joint zones which they attributed to structural adjustments of some laccoliths to later intrusions. 

The alteration minerals they listed are epidote, pyrite, 

calcite, quartz, actinolite, hedenbergite, fluorite, clay 

minerals, sericite, albite, and perthite. The following 

analyses were given by Hunt (1958, p. 321). 
24 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

Ohemioal o;n,alyses of diorite porphyry from the La Sal 

Mountains 

[From Hunt, 1•958, p. 321. Analysts, W. F. Hillebrand (1) and 

Lucille Kebl ( 2) ] 

Mount Mount 

Mount Tom a- Mount Tom a- PeaZe saki Peale saki 

(1) (2) (1) (2) 

Si02---------- 61.21 63.11 CO a ---------- 0 0.36 

AhOs --------- 17.10 16.76 P206---------- .24 .23 

Fe20a --------- 2.72 2.15 SOa ---------- 0 (S).02 

FeO ---------- 1.88 1.85 Cl ----------- .04 0 

MgO --------- 1.47 1.30 F ------------ 0 0 oao __________ 4.83 3.11 MnO --------- .15 .09 

Na20 --------- 5.66 6.23 BaO --------- .13 .06 

K20 ---------- 3.00 3.44 SrO ---------- .07 0 

H20 ---------- .34 .13 Li20 --------- Tr.( ?) 0 ao+ ________ .68 .43 ---- Ti02 --------- . 51 . 43 TotaL ______ 100.05 99.70 

Zr02 --------- .02 0 

These analyses closely agree with the estimated chemical composition of the average intrusive rock in the 

laccolithic mountains of the Colorado Plateau (Hunt, 

1956, p. 43). Hunt reports that the N a20 and K20 contents in the igneous rocks of the La Sal Mountains are, 

in general, higher than in 27 other samples from the 

Henry, La Plata, and other mountains of the Plateau. 

This variation may be due to the intimate association 

of the La Sals with the soda- and potash-rich salt anticlines. Late phases of igneous activity in North Mountain, however, produced soda-rich syenite and rhyolite 

which probably had little or no contact with the salt. 

Hunt and Waters (Hunt, 1958) believe these later intrusions were more fluid and of higher temperature than 

the earlier diorite and monzonite porphyries because 

they contain high-temperature quartz. Hunt (1956, 

p. 43) states that in North Mountain the latest intrusions breached the surface and erupted explosively; 

these eruptive rocks contain potash in great excess of 

soda, in contrast with earlier intrusives. 

INCLUSIONS 

Gould (1926, p. 80-81) recognized hornblendic inclusions in the diorite porphyry which he implied ~ere 

segregations rather than xenoliths. Hunt ( 1953, p. 160, 

164; 1958, p. 349) stated that in the Henry and La 

Sa1 Mountains xenoliths from the sedimentary or basement rocks are relatively rare, whereas hornblendic 

fragments are abundant and comprise 95 percent or 

more of the inclusions. The authors observed that there 

is no gradation between xenoliths and hornblendic inclusions. Xenoliths are relatively unaltered and retain 

their original sedimentary features. They are generally 

near the contacts of intruded rocks, but inclusions are 

widespread throughout the igneous masses. 

Hunt proposed that the inclusions in the Henry 

Mountains are fragments of rock derived from great 

depth, ( 1) from altered wallrock traversed by the magma, ( 2) from segregations formed in the magma reservoir, feeder pipes, or laccoliths, or ( 3) from layers of 

the substratum from which the magma was derived. 

Waters (1955, p. 715-716) preferred the third hypothesis. He pointed out that the order of intrusion in 

the La Sal Mountains was (1) diorite porphyry, (2) 

monzonite porphyry, ( 3) syenite porphyry, and ( 4) 

feldspathoidal syenite. Noting that the hornblendic 

inclusions are much more abundant in the diorite than 

in the other rock types, Waters concluded that the diorite magma was in part a product of partial fusion of 

amphilbolitic rock of which the hornblendic inclusions 

are fragments. The diorite magma became changed 

through time by the solution of the unfused inclusions 

and through filter pressing, produced, in order, the 

other rock types. Shoemaker ( 1956b, .p. 54) made reference to "\Vaters' idea but also proposed an alternative: 

the inclusions are cognate and were derived by crystal 

settling and accumulation of the more basic fraction 

of the magma from which the rocks of the La Sal Mountains were derived. The escaping acid fraction of the 

magma carried some of these hornblendic crystal accumulations in to the stocks and laccolithic chambers of 

the mountains. 

CONTACT METAMORPHISM 

Contact metamorphism has played only a minor role 

in the history of the La Sal Mountains. 

Shale and mudstone in contact with igneous rocks are 

indurated and altered in color. With the exception of 

a small patch of sedimentary rock on the north side of 

the Mount Mellenthin laccolith, beds of the Mancos 

Shale in contact with the igneous rock show little or no 

color change. In contrast are the mudstone beds of 

the Morrison Formation that are· in contact with the 

Mount Peale bysmalith. Beds that are normally red 

have been altered to deep purple and black-a feature 

that indicates that hematite may have changed to magnetite. Elsewhere red mudstone sho.ws only slight color 

change at the igneous contact. 

The small patch of sedimentary rock on the north side 

of Mount Mellen thin contains Upper Cretaceous marine 

fossils and has been mapped as Mancos Shale, but older 

beds may also be present. Metamorphism has been more 

extreme here than at any other place observed in the 

La Sal Mountains. Part of the sedimentary rock has 

been metamorphosed to hornfels. The present beds 

retain only a trace of their forrner bedding and are, of 

course, no longer fissile. In one place the hornfels is 

minutely crenulated. In places it contains 'light-green 

bands and lenses of calcite, quartz, and irregular to 

roughly rounded masses of hematite as large as 1 inch 
IGNEOUS ROCKS 25 

in diameter. Elsewhere within the rock, the light-green 

calcite and quartz masses occur as small nodules as 

much as 1 inch in diameter having centers of disseminated hematite. The hornfels that surrounds these 

bodies displays minute brecciated structures on its margins, possibly the result of shearing stress. 

In the paragraphs ( p. 32) discussing the structure of 

the Middle Mountain group, it is suggested that the 

Mount Mellenthin laccolith is the product of two or 

more coalescing magmas. It is reasonable to assume 

that a small body of sedimentary rock caught between 

and carried upward by these intrusive masses would be 

subjected to considerable compressional stress, enough 

to produce the structures described and to effect a higher 

degree of metamorphism than around the laccoliths. 

Sandstone beds in contact with igneous rocks are 

silicified. On the southwest flank of Mount Peale, 

sandstone beds of the Salt Wash Member of the Morrison Formation are partly silicified but not enough to be 

considered quartzite. On Moore's Ridge in the South 

Mountain area the sandstone beds of the Burro Canyon 

Formation are considerably silicified. Where these 

beds abut the stock, silicification has been intense and 

the rock is a quartzite. Apparently, where permeable 

sandstone units are cut by igneous rock, especially 

around the stqcks, they served as conduits for the escape of silica-bearing solutions. The Wingate, N avajo, and Entrada Sandstones in this same area are 

also silicified, but not to the degree observed in the 

Burro Canyon Formation. 

Epidote, as thin films and small crystals, commonly 

coats the ~racture surfaces of igneous rock. Only 

rarely is epidote found in the sedimentary rocks bordering the igneous rock contact. One place where it is 

found is on the west side of the sedimentary block 

included in the top of the Mount Peale bysmalith. The 

brecciated rock is permeated with epidote that is evenly 

dispersed through the very fine grained matrix. Epidote imparts a pale green ,color that is in sha.rp contrast 

to the white sandstone fragments comprising the bulk 

of the breccia. The epidote probably was derived from 

deuterically altered mafic minerals in the igneous rock. 

AGE 

Age determinations based on the lead-uranium ratios 

of zircons in the three types of porphyry corroborate 

Waters' ( 1955) concept of the order of intrusion. Age 

determinations of zircon from the two types of younger 

porphyry suggest a Paleocene age for the intrusion of 

the monzonite porphyry and a Miocene age for the 

intrusion of the syenite porphyry. Thus the formation 

of the La Sal Mountains probably spanned Late 

Cretaceous to early Miocene time, a period of approximately 40 million years. The major part of intrusion, 

that of the diorite porphyry, probably took place during 

Late Cretaceous and early Tertiary time, approximately 

55 to 65 million years ago. 

These conclusions are based on studies of six samples 

of rocks collected by D. R. Shaw (1957, oral commun.) 

from the Middle and North Mountains of the La. Sal 

Mountains and submitted to H. W. Jaffe of the U.S. 

Geological Survey for age determination of the zircon 

contained. A lead-uranium ratio in zircon method was 

used and the age determinations obtained are believed 

to be accurate to +1 0 percent. The zircon from three 

samp]es of the diorite porphyry indicates ages of 380, 

410, and 470 million years, which approximately correspond to the interval from the Cambrian to the Silurian 

Period. Zircon from the monzonite porphyry upon 

which two determinations were made indicates ages of 

50 and 53 million years, or about middle Eocene. The 

zircon from the syenite porphyry indicate an age of 24 

million years, or approximately early Miocene. 

Hunt and Waters (Hunt, 1958, p. 348-355) have 

suggested that the original diorite magm'a was produced 

by the palingenesis of amphibolite. A continuation 

of this process at increased temperatures together with 

attendant filtration differentiation created the monzonite and syenite differenti·ates. ·This hypothesis is 

supported by the age determinations if it is assumed 

that the older zircon is an unreconstituted fraction of 

the amphibolite that escaped fusion but which did 

undergo internal readjustment, and that the younger 

zircon from the monzonite and syenite porphyries are 

wholly reconstituted, having crystallized from a higher 

temperature magma. In addition to an age difference, 

H. W. Jaffe (written commun., 1957) recognized a 

physical difference between the zircon of the diorite 

porphyry and that of the monzonite and syenite porphyries. Zircon ,crystals in the diorite are elongate, 

prismatic, and doubly terminated, and those in the monzonite and syenite are short and pyramidal. Jaffe also 

noted unusually high alpha activity in the zircon of the 

diorite porphyry. These differences strongly suggest 

that there was some change in the physical-chemical 

conditions under which the magma was being generated. 

Logically this change, as Hunt and Waters indicate, 

may be due to the increased temperature at which the 

palingenetic process was carried out in its later stages. 

If, as assumed, the zircon of the diorite porphyry is 

an unreconstituted fraction of the original amphibolite, 

it poses a serious objection to the Cambrian to Silurian 

age determination. 'The amphibolite must have been 

at great depth if fusion could take place, probably deep 

within the basement complex. That such rocks are 

Precambrian in age would be a fair assumption. About 
26 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

20 miles northeast of the north group of the La Sal 

Mountains, crystalline basement rocks have been uplifted and are exposed on the Uncompahgre Plateau. 

A sample of the youngest or nearly youngest granite occurring there showed variation of ages from 1,050 million years to 1,810+ 160 million years, depending on the 

mineral analyzed and the method used (Davis, 1954, p. 

105). While these differences in ages may be the result 

of errors in certain basic assumptions regarding the 

minerals analyzed, they nevertheless imply a Precambrian age for the Uncompahgre granite. The age discrepancy, however, may not be a real one and can be 

explained in the following way: It is quite probable 

that zircon in the amphibolitic basement rock became 

highly meta.mict before palingenesis. When undergoing the early stages of palingenesis, the zircon was 

refractory enough to remain unfused hut was energized 

enough to reassume in some degree its original crystallinity and to expel radiogenic lead as it did so. As a 

result, the lead-uranium age determination was anomalously low, 'at least 500 million years short of the true 

age. 

Zircon age determinations by Jaffe (written commun., 

1957) of the monzonite porphyry indicate that the rock 

is of Middle Eocene age. The diorite porphyry is intruded by the monzonite porphyry and intrudes the 

Mancos Shales of Late Cretaceous age; younger sedimentary rocks were either not deposited or have been removed by erosion in the mountain area. Presence of the 

Mancos limits the mnplacement of the great bulk of the 

igneous rocks of the La Sal Mountains to some time 

between the Late Cretaceous and middle Eocene. 

STRUCTURAL GEOLOGY 

The stratified rocks of the La Sal quadrangle are 

warped into several gentle folds which, in the northwestern part, have been greatly increased in amplitude 

by intrusion of laccoliths that make up the La Sal 

Mountains. Apart from the laccoliths the most conspicuous structural units in the mapped area are the 

southwestern part of the collapsed Sinbad Valley salt 

anticline, the northwestern end of the collapsed Paradox Valley salt anticline, and the Pine Ridge salt anticline (pl. 3). In a broader regional picture the Sinbad 

Valley, Paradox Valley, and Pine Ridge features are 

but segments of much larger folds: the Sinbad ValleyFisher Valley anticline, the Paradox Valley -Castle Valley anticline, and the Moab Valley-Pine Ridge anticline. These anticlines trend N. 45° W. toN. 70° W., 

and are separated by broad, somewhat sinuous and shallow synclinal troughs which, from north to south, include the Roc Creek-Taylor Creek syncline, the La Sal 

Creek syncline, and the East Coyote Wash syncline. 

Generally these synclinal troughs plunge gently to the 

southeast a way from the domal uplift of the La Sal 

Mountains. 

In contrast to the regional structural trend, the La 

Sal Mountains, the highest structural and topographic 

forms in eastern Utah, form a chain that trends slightly 

east of north. North Mountain, Middle Mountain, and 

South Mountain. each contain several mountain peaks 

separated by deeply dissected basins. Most of the basins 

were formed by glaciation. Structurally, North and 

South Mountains are similar for they lie within and are 

elongated parallel to the structural axis of the Paradox 

Valley-Castle Valley salt anticline and the Moab ValleyPine Ridge salt anticline, respectively. The igneous intrusions forming these two mountain groups uplifted 

the entire sequence of strata from the Rico Formation 

of Pennsylvanian and Permian age to the Mancos Shale 

of Late Cretaceous age. Middle Mountain, in contrast, 

is structurally more complex. It is in the intervening 

syncline and is composed of a stock, dikes, laccoliths, 

and a bysmalith which selectively intrude the strata at 

several horizons. 

The geologic structure of the area is shown on the 

geologic map and its accompanying cross sections (pl. 

1) and in greater detail on the structural map (pl. 3). 

Structure contours are drawn on the top of the Entrada 

Sandstone; Inasmuch as the Entrada. is covered by· 

younger sedimentary rocks in many places, the selection 

of an alternative datum plane was necessary. The base 

of the Burro Canyon Formation was chosen in preference to other contacts because it shows the least relief 

on its surface and is exposed widely. These elevations 

were then projected to the top of the Entrada by subtracting the average thicknesses of the intervening 

formations. 

The cross sections accompanying the geologic map 

represent an interpretation of the structure along the 

lines shown and are constructed at the same vertical 

and horizontal scale. 

FOLDS 

SINBAD VALLEY ANTICLINE 

The Sinbad Valley anticline, part of which is in the 

northeast corner of the mapped area, trends about N. 

45° W. Erosion has removed the crest of the fold and 

left a valley that is about 9 miles long and 4 miles wide. 

The valley walls are cliffs and steep slopes having foothills formed by fault blocks composed of Permian, 

Triassic, and Jurassic sedimentary rocks. Exposed 

within the valley is a large mass of the Paradox Member of the Hermosa Formation which Shoemaker 
STRUCTURAL GEOLOGY · 27 

(1951) believes is a composite of several distinct salt 

cells. These cells are outlined by arcuate zones of intricate :faulting and, in places, are separated by upturned 

beds of limestone of the upper member of the Hermosa 

Formation. Only one of these salt cells is believed to 

be exposed within the quadrangle boundary. 

· The southwest flank of the anticline dips :from 1° to 

8 o for 1 mile, to the axis of the Roc Creek syncline. The 

structural relief between the trough of the Roc Creek 

syncline and the crest of the Sin bad Valley structure, 

prior to collapse, is estimated as more than 2,500 feet. 

Beyond the mapped area the Sin bad Valley feature is 

connected on the northwest to the Fisher Valley collapsed anticline by a gentle anticlinal fold and a complex system of faults. Most of these faults form grabens, 

which are probably the result of loss of salt either by 

flowage or by solution or possibly both. To the northeast the feature is bounded by the Dolores River syncline which separates it from the Uncompahgre uplift. 

ROC CREEK SYNCLINE 

The axis of the Roc Creek syncline is sinuous, trends 

generally N. 55° W., and plunges gently to the southeast. It lies between the Sinbad Valley and Paradox 

Valley anticlines and is separated from the latter by 

a northwest-trending fault complex known as the Valley View fault. It is, for the most' part, an asymmetrical syncline, having st~per dips on the northeast flank. 

As shown in cross section A-A' (pl. 1) the flanks of the 

syncline are inferred to dip more steeply at depth than 

at the surface because unconformities truncate the 

formations near the crests of the adjacent anticlines. 

TAYLOR CREEK SYNCLINE 

The Taylor Creek syncline is a closed synclinal trough 

bounded on the west by the North Mountain dome and 

on the southwest and east by faults. Its northern extremity is at the divide between Beaver Basin and the 

headwaters of Taylor Creek, approximately 6 miles 

north of the quadrangle boundary. The limbs are 

nearly symmetrical and dip 30°-45° on the northeast 

flank and 45° on the southwest flank. 

The estimated structural relief from the axis of the 

Taylor Creek syncline to the crest of the Sinbad Valley 

anticline before its collapse is more than 4,000 feet. The 

south west flank extends to the crest of the North Mountain dome and probably has at least 8,000 feet of structural relief. The presence of the Geyser Creek Fanglomerate, described earlier, within the Taylor Creek 

syncline indicates that the age of final deformation of 

the area m-ay have been as recent as late Pliocene or 

early Pleistocene. 

777-039 0-65-5 

CASTLE V .A,LLEY .pARADOX VALLEY ANTICLINE 

Only a small part of the Castle Valley-Para~o~ Valley anticline is within the mapped area, hut It IS undoubtedly the most interesting and complicated of the 

structural features mapped, apart from the La Sal 

Mountains. The major feature, although mainly anticlinal is within the mapped area, a composite of several minor ' ' l'ft folds which have been formed by the up I 

and in places removal of irregularly shaped salt 

masses. ' ' . b For descriptive purposes the feature IS su -

divided into three provinces: the principal valley, Willow Basin syncline, and Scorup anticline. 

Paradox Valley, which is 35 miles long and about 

5 miles wide, was formed by erosional n:eaching of a 

great salt anticline. It is bounded by chffs an~ steep 

slopes formed by sedimentary rocks of Mesozoic a~e. 

These strata, ranging from maroon to white, provide · 

some of the most colorful scenery in western Colorado. 

Block faulting landslide debris, and alluvium obscure 

most of the int~rnal structure of the anticline which 

Shoemaker (1956a) and Cater (1954a) believe .to be 

composed of clusters of irregularly shaped salt cells 

situated along the structura'l axis. An arcuate set of 

faults in the eastern part of the La Sal quadrangle (pl. 

1) suggests that a collapsed salt cell underlies the valley 

here and near Paradox, Colo. 

WILLOW BASIN S·YNCLINE 

The Willow Basin syncline lies northwest of Paradox 

VaHey where Mesozoic formations extend across the 

valley as a series of steplike cliffs that rise to the nor:thwest. Most of these cliffs were formed by :faulting 

transverse to the synclinal axis. The Willow Basin 

syncline is bounded on the northeast by the Valley View 

fault and on the southwest by the Dugway fault. Both 

are strike faults of considerable local displacement and 

are described in detail in the section on faults (p. 34). 

The Dugway fault dies out about 4 miles west of the east 

boundary of the quadrangle, and beyond it the Willow 

Basin syncline is flanked by the Canopy Gap anticline. 

The Willow Basin syncline is hisected by a transverse 

fault. The synclinal axis plunges gent~y southeastward 

west of the transverse fault, and northwestward east 

of it. The fold is virtually symmetrical. The limbs 

dip as much as 12°, except adjacent to the Valley yiew 

fault where the beds dip 25° to the southwest. Willow 

Basin Creek follows a sinuous course along the synclina'l 

aXIS. 

SCORUP ANTICLINE 

A salt cell probably underlies the Scorup anticline 

which is between the Geyser Creek and Dead Oak syn-
28 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

clines in sees. 11, 12, 13, and 14, T. 27 S., R. 25 E., San 

,Juan County, Utah. The Scorup -anticline is asymmetrical and has dips of 23° to 45° on the northeast 

flank and go to 16° on the southwest flank. The structural relief from the crest of the anticline to the axis 

of the Dead Oak syncline, less than a mile to the northeast, is about 2,000 feet. The southwest Emb, from the 

crest to the axis of the Geyser Creek syncline, has structural relief of slightly less than 1,000 feet. The structural relations along the crest have been dbscured by 

erosion and faulting and covered by alluvium and 

landslide deposits, but the Scorup anticline apparently 

has a structura1 closure of at least 200 feet over an area 

of approximately 150 acres.· Geyser Creek was superimposed on and crosses the anticline at right angles to 

the axis. It has excavated a deep valley and exposed 

the sandstone and shale of the Salt Wash Member of 

the Morrison Formation. The sandstones along the 

crest of the anticline have dropped between two paraHel 

faults which form a narrow graben that is about 11h 

miles long and 500 feet wide._ Vertical displacement 

along the faults ranges from 40 to go feet near ·Geyser 

Creek and is believed to decrease in magnitude to the 

northwest and southeast. 

GEYSER CREEK SYNC'LINE 

On the southwest side of the North Mountain laccolith 

is an asymmetrical syncline named for Geyser Creek 

which originates in Geyser Pass, the divide between 

North and Middle Mountains. The axis of the Geyser 

Creek syncline plunges gently eastward from the pass 

and swings southeastward where it closes in a narrow, 

shallow basin in the SE cor., sec. 10, T. 27 S., R. 25 E., 

San Juan County, Utah. From that point the plunge is 

reversed and the structure extends southeastward for 

about 1 mile where it gradually fades out against a 

minor anticlinal cross fold that separates it from the 

Willow Basin syncline. 

The northeast limb dips from 45 ° to nearly vertical. 

The structura~ relief 'from the trough of the Geyser 

Creek syncline to the crest of the North Mountain anticline, less than 2 miles away, is more than 4,700 feet. 

The southwest limb dips 15° to 25° NE. and has an 

estimated 3,000 feet of structural relief from the trough 

of the syncline to the crest of the Middle Mountain dome, 

more than 4 miles to the south. The relations of the 

Geyser Creek syncline to the adjacent structural features 

are considered in more detail in the discussi'On of Middle 

Mountain (p. 30). 

LA SAL CREEK SYNCLINE 

The La Sal Creek syncline plunges southeastward 

across the central part of the mapped area from La Sal 

Pass, between Middle ·and South Mountains, to the 

Dolores River, southeast of the map boundary. It is 

bounded on the northeast by the Canopy Gap anticline 

and the Dugway fault, both resultant features of the 

collapse of the Paradox Valley anticline. On the southwest it is bounded by the South Mountain dome and the 

Pine Ridge coHa psed anticline. The syncline is named 

for La Sal Creek which pa:rallels and, in places, flows 

along the sinuous trend of the structural axis for 20 

miles. 

The limbs of the syncline are asymmetrical, having 

different inclinations on the northeast and southwest 

depending on the location and magnitude of the adj'acent fdlds. 'For example, near the Paradox V·alley anticline the northeast limb dips go to 10° SW., and the 

southwest limb dips 1° to 3° NE., toward the synclinal 

axis. Along Moore's Ridge of South Mountain, however, the southwest limb dips 40° to 50° NE., and the 

northeast limb dips as much as 10° SW., except where 

disturbed by the intrusive rocks of Middle Mountain. 

The La Sal Creek syncline appears to have been subjected to differential stresses tha;t were both compressional and torsional. The torsional forces were prqba.bly 

quite small in proportion to the large area involved, but 

such forces may explain the diverse joint patterns in 

the La Sal Creek area which are discussed with faults 

and joints (p. 34). 

Structural relief from the axis of the syncline to the 

axis of the Paradox Valley anticline is estimated to be 

at least 1,500 feet, in sharp contrast to the relief of the 

southwest limb which is about 200 feet on Wra.y Mesa. 

Near La Sal Pass the structural relief from the syncline 

axis to the crest of the Middle Mountain dome is 2,900 

feet, whereas the relief of the southern limb, that is, to 

the eroded crest of the South Mountain dome, is 

estimated to be about 5,100 feet. 

PINE RIDGE ANT1:CLINE 

South of the La S'al Creek syncline is a gentle anticlinal arch that is a continuation of the Gypsum 

Valley anticline to the south and the Moab VaHey anticline northwest of the mapped area. The arch has been 

subdivided into the Pine Ridge anticline, which is in 

part collapsed, and the South Mountain dome. The 

South Mountain dome is discussed on page 33. 

The Pine Ridge anticline is a broad, somewhat asymmetrical structure. The northeast limb dips 1° to 2° 

NE. toward the axis of the La Sal Creek syncline 2.5 

miles distant. The southwest limb dips as much as 5° 

and extends from the crest of the anticline to the axis of 

the East Coyote syncline, 4.5 miles to the southwest. 

Mapping and study of the 'Structural features of the 

Pine Ridge anticline suggest that the area is und~rlain 
STRUCTURAL GEOLOGY 29 

by a buried salt mass. The presence of this mass has 

been confirmed by gravity surveys made in 1957 by the 

U.S. Geological Survey. This was further confirmed 

in 1963 (R. J. Rite, oral commun.) when the Tenneco 

well Redd Ranch No.1 in the SE1,4NE%SW0z of sec. 

28, 'T. 28 S., R. 25 E. cut important potash mineralization. in Paradox salt between 3,300 and 3,510 fe~ in 

depth. The gravity survey (Byerly and Joesting, 1959, 

p. 48-49) indicates thalt the center of the broad open valley of Old La Sal extending from the head of La Sal 

Creek Canyon to South Mountain is underlain by an 

elongate salt intrnsion. The strata overlying the plug 

have been downdropped at least 300 feet, probably as a 

result of dissolution of the salt. The collapse area is 

bounded by Pine Ridge on the south, southwest, and 

southeast and by ·another low ridge on the northeast 

that paraTlels La Sal Creek. SurfiCial material obscures the structural features in the north and central 

parts of the valley. Landslide and slump features that 

occurred after collapse border the southern margin of 

the valley. Gravity measurements on W ray Mesa, to 

the southeast of the collapse area, indicaJte that there 

the Pine Ridge ·anticline is underlain by little or no 

salt and owes its existence solely to regional tectonism. 

EAST COYOTE WASH SYNCLINE 

A part of East Coyote Wash syncline lies in the 

southwest corner of the mapped area and separates the 

South Mountain dome and Pine Ridge anticline from 

the Lisbon Valley anticline. In the mapped area the 

limbs strike about N. 70° W. and N. 50° W., are virtually symmetrical, and have dips as high as 5°. The 

whole syncline is an elongate closed trough that is 13 

miles long and about 6 miles wide. The ·amount of 

closure is about 600 feet. The lowest part of the trough 

is at the head of Greasewood Canyon in the northern 

part of the Lisbon Valley quadrangle about 4 miles 

south of the rna pped area. North west of the trough is 

the West Coyote Wash syncline which is separated from 

East Coyote Wash syncline by closure of low relief and 

marked by a gentle drainage divide about 1 mile west 

of the map boundary. The southeastern end of the East 

Coyote Wash structure closes at Island Mesa where a 

gentle arch separates it from Disappointment syncline 

in Montrose County, Colo. 

Tl1e rocks exposed within that part of the East Coyote 

Wash syncline that lies within the 1napped area are 

dominantly the Dakota and Burro Canyon Formations 

of Cretaceous age. Much of the Dakota has been removed by erosion, and near the synclinal axis widespread deposits of alluvium obscure the contacts. 

Fragments of marine fossils and Mancos Shale that 

probably had been moved but a short distance were 

noted in sec. 25, T. 28 S., R. 24 E., northeast of the 

village of La Sal, but no Mancos was found in place in 

the vicinity of East Coyote W a,sh. To the east and north 

of East Coyote Wash, deep canyons have been cut by 

streams draining the southwest flank of the Pine Ridge 

anticline. These streams flow southward into East 

Coyote Wash and in many places have eroded the Cretaceous caprock and exposed the Brushy Basin Member 

of the Morrison Formation. 

LA SAL MOUNTAINS 

The La Sal Mountains comprise three distinct structural units (ltunt, 1958). All are virtually laccolithic 

but the configuration of North Mountain and South 

Mountain contrasts with that of Middle Mountain. The. 

difference is due to the presence of preexisting geologic 

structures that controlled in a large degree the emplacement of the mountain-building magma. A great part 

of the igneous rock forming North and South Mountains was emplaced along an incompetent horizon or 

zone at the top of the salt that forms the cores of the 

salt anticlines. The igneous cores are composed of many 

tonguelike laccoliths that extend from a central stock 

and are emplaced mainly along the trend of the anticlines, where they form elongate domes. The entire 

sedimentary sequence overlying the salt-bearing Hermosa Formation has been uplifted along the margin of 

the intrusive rocks. Middle Mountain, in contrast, is 

in a synclinal area between the anticlines where little if 

any salt remains. Lacking an incompetent zone at 

depth, the magma moved farther upward into younger 

formations where several laccoliths and a bysmalith 

formed at or in at least three different horizons or zones. 

These igneous rocks intrude and are surrounded by sedimentary rocks of Jurassic and Cretaceous age, and are 

connected to a central stock by small dikes and 

apophyses. 

NORTH MOUNTAIN 

North Mountain has been studied in considerable 

detail by Hunt ( 1958). Only a small part of it extends 

into the northern edge of the area included in this report. The igneous core was emplaced directly in the 

trend of the Castle Valley-Paradox Valley anticline and 

is elongate parallel to this trend. All sedimentary formations down to and including part of the Hermosa 

Formation of Pennsylvanian age have been uplifted on 

both sides of the mountain to form a large elongate 

dome which plunges sharply to the southeast within the 

north boundary of the mapped area. The crest of the 

dome has been eroded away exposing an igneous core 

of diorite porphyry which crops out as sharp peaks and 

ridges that form the walls of deeply dissected valleys. 
30 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

Haystack Mountain and Mount Tomasaki at the southern end of North Mountain lie within the La Sal quadrangle. Mount Tomasaki is bounded on the south by 

Porcupine Ridge which consists of sedimentary rocks 

that were upturned by igneous intrusion. 

The limbs of the North Mountain anticline dip from 

45 ° to 90° and in places may be slightly overturned. 

In most places the folding is symmetrical. Vertical 

and overturned bedding appear to be localized near intrusives which lie outside the main igneous mass. This 

bedding was observed on Porcupine Ridge at Haystack 

Mountain and near intrusives in the drainages of Bear 

and Beaver Creeks north of the mapped area. 

Hunt (1958, p. 322) described Haystack Mountain 

as 'a laooolith reSting on Mancos Shale from outcrops 

in Burro Pass immediately north of the La Sal quadrangle boundary. The authors t.raced this CJontact from 

Burro Pass around the southeast margin of the intrusive 

and found it bordered by vertical sandstone and mudstone units of the Morrison, Burro Canyon, 'and Dakota 

Fol'!mations. The rubsence 1of older strata suggests that 

Haystack Mountain may he either a veTtical plug or 

a laccolith emplaced along incompetent beds of the Morrison Formation. 

Nowhere within the quadrangle is ~the base of the 

igneous core of North Mountain or Haystack Mountain 

eX?posed. The authors agree wirth 'Gould ( 1926, p. 91) 

that the horizon of intrusion is prdba:bly directly below 

that represented by the stTatification contacts found 

around them. Rocks al!ong the igneous contact may 

not ~be everywhere of the same formation. Within the 

mapped area, float from the sedimentary rock in contact with igneous rock of Mount Tom·asaki is dominantly 

limestone and m·ay belong to the Hermosa Formation. 

Presence of this horizon along the m'argin of intrusive 

rock would better explain the presence of isolated outcrops of the Hemnosa which Hunt and Waters (Hunt, 

1958) found in Beaver and Miners Basins, well within 

the boundaries of the :ma.in igne1ous mass. 

MIDDLE MOUNTAIN 

The group of peaks comprising the central part of 

the La Sal Mountains were referred to as Midd] e Mountain by Hunt (1958). Although complex in detail, Middle Mountain is, in general, formed hy ,a domal uplift 

within a syncline lying between the Castle ValleyParadox Valley anticline and the Spanish Valley-Pine 

Ridge anticline (pl. 3). The center of the dome is at 

the head of Gold Basin between Mount Peale and the 

west edge of the ~mapped 'area in sees. 14 and 23, T. 27'S., 

R. 24 E., San Juan County, Utah. Sedimentary rocks 

dip away from the crest of the dome at angles from 10° 

to 42°. 

The intrusive rocks of Middle Mountain are composed 

almost entirely of diorite prophyry and crop out as 'a 

stock, as dikes, sills, laccoliths, and as a. bysmalith tha't 

were apparently intruded in that order. 

STOCK 

The stock is an irregularly shaped mass of igneous 

rock near the center of dornal uplift, and is distinguished 

from the other igneous bodies by its smaller size, irregular shape, and crosscutting relat~'Onship with the SliTrounding country rock. The stock exposed in Middle 

Mountain is less than 3,000 feet long and less than 

1,500 feet wide, hut is eonsidera;bly larger than the associated dikes. It may extend under the covering rock 

debris as one continuous igneous mass that ·also forms 

Mount Tukuhnikivwtz, just west of the map !boundary. 

The outer margins of the stock are nearly vertical 

and crosscut the sedimenta.ry formations at sharp angles. 

Where exposed, 'the contact of igneous and sedimentary rocks is well defined. The stock is surrounded for 

the most part by a shat't.er zone in whieh the :adjacent 

sedimentary rocks have hoon indurated and darkened 

by mild metomorphism. Minor deposits of oopper and 

iron occur in the stock and the 'adjacent sedimentary 

rocks. The surrounding laccoliths and related intrusions appear to have been injected radially along feeder 

dikes from the stock. The close association of the stock 

and dikes can best he observed in the glacial cirques in 

sec. 14 and the Slh sec. 11, T. 27 S., R. 26 E. 

DIKES 

Most of the igneous dikes cross the sedimentary contacts at right angles, but some are inclined at steep 

angles to the bedding. Those in sec. 14 and the Slh 

sec. 11, T. 27 S., R. 26 E., tend to crop out in a. radial 

pattern from the parent stock. This characteristic was 

of considerable aid in determining the types of igneous 

bodies that were being mapped in areas where landslide 

and talus obscure the contacts. The dikes range in 

width from a few feet to about 200 feet and are exposed 

for distances of as much as 1,000 foot. Most appear to 

have formed along fault planes where the vertical displacement of the adjacent formations is usually less 

than 100 feet. These dike-filled faults were formed 

during the intrusion of the central stock and initial 

uplift of the Middle Mountain dome. 

Associated with this dike swarm are a clastic dike 

and a clastic pipe which occur near the west boundary 

of the quadrangle, southwest of Mount Mellenthin and 

n;orthwest of Mount Peale, on the ridge separating Gold 

Basin and Dorry Canyon in sec. 14, T. 27 S., R. 24 E., 

San Juan County, Utah (pl. 1) . 

The clastic dike is about 1,300 feet long and bears 

approximately N. 30° E., across the ridge line separa.t-
STRUCTURAL GEOLOGY 31 

ing the two basins. The dike is partly obscured over 

most of its length hy a thin cover of talus, but is well 

exposed at the crest of the ridge where it is about 55 

feet thick. The dike is vertical and emplaced along 

a fault mer most of its length. :rt diverges from the 

fault ·at the southwest end. The dike extends beyond 

the fault •at the northeast end, or at least ·beyond the 

point of any apparent throw. No vertical offset was seen 

in the transected beds on the Dorry Basin side of the 

ridge. 

The dike is dark gray with a greenish cast and is 

composed of bleached fragments of shale, siltstone, sand· 

stone, and limestone (fig. 5). The fragments range 

from sand size to 3 feet in diameter and are angular 

to well rounded. They are highly indurated, much 

more so than either the rocks from which they were 

derived or the beds adjacent to the dike wall. 

The matrix, observed in thin sections, is composed of 

tightly packed, rounded to angular quartz grains and 

minor amounts of calcite which fills the interstices. In 

places, abundant amounts of very fine grained black 

opaque magnetite(?) are embedded in the calcite. A 

very minor amount of plagioclase with albite twinning 

FIGURE 5.-0utcrop of clastic dike exposed in copper prospect 

in the NW'%, sec. 14, T. 27 S., R. 24 E., San Juan County, Utah. 

Photograph shows angular to round boulders of siltstone, 

sandstone, and limestone in a matrix of squeezed and folded 

gray-green shale. All appear to have been derived from the 

Mancos Shale and dropped downward into the Morrison 

Formation which comprises the surrounding wallrock. 

was noted in one section; some of it appears to be highly 

sericitized. 

The fact that most of the quartz grains display undulatory extinction suggests strain. Some of the grains 

are fragmented, although optically they appear as whole 

units; none of the fragmented parts have been displaced 

relative to the others. Haft' (1944, p. 213-214) notes 

this same peculiarity in two clastic dikes near Placerville, Colo., and believes such structure could have been 

formed only in place because a shattered fragment 

would disintegrate when moved. 

At its northeast end the dike cuts through the Dakota 

and Burro Canyon Formations into the upper part of 

the Brushy Basin beds; at its southwest extremity it 

cuts almost to the base of the Brushy Basin. Where 

well exposed at the ridgecrest, the dike contains fragments derived from the Entrada or Navajo Formation 

and younger Jurassic formations. No fragments of the 

Kayenta Formation and older formations were recognized. These fragments are adjacent to undisturbed 

beds of the Dakota Sandstone. Fossiliferous fragments 

of the Mancos Shale that have moved downward in the 

structure were noted adjacent to the Dakota Sandstone. 

At the southwest end of the dike, where it is exposed 

for a width of 10 to 15 feet, the clastics are composed of 

rounded fragments of indurated shale and some limestone derived from the Mancos Shale. The matrix is 

composed of comminuted shale that contains sparse copper minerals, mostly malachite. It appears, therefore, 

that the Mancos Shale fragments have moved downward through the Dakota, Burro Canyon, and most of 

the Brushy Basin, a vertical distance of ahout 500 feet. 

The clastic pipe, too small to be shown at the map 

scale, is in NW!4 sec. 14, T. 27 S., R. 24 E., about 1,000 

:feet northwest of the clastic dike and about 200 feet 

below the ridge top. It is roughly oval in plan and is 

about 40 feet wide and 80 feet long. It crops out 80 

:feet above the base of the Brushy Basin Member of the 

Morrison Formation, but structural relations with the 

surrounding bed rock are mostly obscured by rubble. 

The pipe is composed of angular to subrounded fragments of sandstone and mudstone that range from sand 

size to 4 inches in diameter and are derived from the 

Morrison, Summerville, and Entrada or Navajo Formations. No fragments from other formations were 

recognized. 

The matrix consists predominantly of quartz and 

very sparse amounts of feldspar and calcite. The quartz 

commonly occurs as shattered grains, but in places it is 

found as aggregates of anhedral grains. These grains 

are conspicuous in contrast to the rest of the matrix 

because they are larger and unshattered; they may be 

of hydrothermal origin. The feldspar is oligoclase and 
32 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

is highly sericitized. Calcite fills the interstices of the 

shattered quartz grains of the matrix, but in some places 

it occurs as euhedral rhombs. Both the feldspar and 

calcite may have been introduced by solutions. 

SILLS 

Closely associated with the stock and dikes are several small sills which have been selectively injected into 

less competent beds. The sills are projections of diorite 

porphyry that extend from the stock or dikes along 

incompetent bedding planes and are, therefore, concordant with the country rock. These extensions are 

usually less than 500 feet long and less than 100 feet 

thick. 

One sill, in sec. 23, T. 27 S., R. 24 E., San Juan 

County, Utah, extends from the Middle Mountain stock 

into the mudstone beds of the Salt Wash Member of 

the Morrison Formation near the contact with the 

Brushy Basin Member. A second sill, on the southwest 

side of Mount Mellenthih in the NEl)., sec. 14, T. 27 S., 

R. 24 E., is at the top of a vertical dike and extends 

along the contact between the Dakota Sandstone and 

Mancos Shale approximately 300 feet. A minor fault 

at the distal end of the sill uplifts the beds above the 

igneous body. A third sill was observed near La 'Sa'l 

Cre~k east of La Sal Pass. It is intruded along strata 

in the Mancos Shale and appears to be derived from 

the igneous core of South Mountain. Unfortunately 

much of the intervening area is covered by thick glacial 

deposits and the relationship is not exposed. 

LACCOLITHS 

Like the sills, the laccoliths are generally in concordant contact with the surrounding country rock and 

have been preferentially injected into some of the less 

competent formations or along the 'less coherent horizons. The most common horizons of injection recorded 

in the mapped area are the Mancos Shale, the top of 

the Kayenta Formation, and the top of the Hermosa 

Formation. There may be an inverse relationship between the horizon of intrusion ai1d the order in which 

the igneous bodies were emplaced, that is, the igneous 

bodies found in the Mancos may have been injected 

prior to those found in the Kayenta or Hermosa Formations and similarly those in the Kayenta prior to those 

in the Hermosa. 

MOUNT 111EJLLENTHIN 

The most clearly exposed laccolith of Middle Mountain in the mllipped area is that of Mount Mellenthin 

which rests concordantly on the Mancos Shale about 

400 feet above the contact with the Dakota Sandstone. 

The horizon of intrusion is within a fissile shale that 

rests on a sequence of calcareous siltstone and srlty 

limestone beds. The sedimentary rocks that formerly 

covered the laccolith have been entirely removed by 

erosion. The exposed igneous core is 1,350 feet thick 

and covers a roughly circu'lar area about 4,000 feet in 

diameter. The laccolith appears to have been fed by 

a group of dikes that radiate from the stock which lies 

to the southwest. A thin, dikelike projection of 

Mancos Shale extends from the base of the laccolith to 

the crest of the mountain. The beds have been upturned and compressed by the surrounding igneous rock. 

This deformation may indicate that the Mount Mellenthin laccolith was formed by several smaller but distinct 

lobes which coalesced as intrusion progressed. Such 

a process may explain other such "inclusions" associated 

with the laccoliths. 

An arcuate fault on the south and east flanks of 

Mount Mellenthin separates the laccolith from neighboring intrusive masses. The sedimentary rocks near 

the mountain are downthrown as much as 500 feet. The 

upthrown side of the fault is probably underlain by a 

buried laccolith which extends away from the fault in 

a northeasterly direction and forms the core of the Blue 

Lake anticline. The major part of the igneous core is 

covered. The horizon of injection is believed to have 

been along the contact between theN avajo and Kayenta 

Formations, as in Mount Pea'le to the south. A small 

part of the magma a:ppears to have moved upward 

along the fault and into the Morrison Formation to 

form the diorite porphyry in the center of sec. 12, T. 

27 S., R. 24 E., San Juan County, Utah. 

A similar buried laccolith projects eastward from 

Mount Peale in sees. 19, 20, and 21, T. 27 S., R. 25 E. 

It is overlain by the Entrada Sandstone and younger 

sedimentary rocks exposed in the headwaters of Twomile Creek, and may be connected to the Mount Peale 

intrusive mass. The horizon of intrusion is also thought 

to be along the Navajo-Kayenta contact. The beds 

folded over the laccolith form the Twomile anticline. 

The distal end of the buried laccolith is about 2 miles 

east of Mount Peale, where the anticline plunges 

abruptly. 

BYSMALITH 

MOUNT PEALE 

The Mount Peale bysmalith lies south of Mount Mellenthin and the arcuate fault mentioned in the preceding 

paragraphs. Iddings (1898) suggested the term "bysmalith" for intrusions, the roofs of which have been uplifted by faulting. Hunt (1953, p. 108) noted in the 

Henry Mountains that the linear bulge or anticlinal appearance of the laccolith was in contrast with the bysmalith which he described as a circular 'bulge surrounded 

by quaquaversal dips. Hunt further states that the 
STRUCTURAL GEOLOGY 33 

bysmaliths of the Henry Mountains were distinguished 

from stocks and laccoliths by ( 1) very steep contacts 

which have been ruptured on the side of the bysmalith 

away from the parent stock, and (2) the fact that the 

contacts near the stock are raised by folding; however, 

like that of the laccolith, the roof of the bysmalith is 

less displaced on the side toward the stock than on the 

distal side. 

. Most of these features can be observed on Mount 

Peale, for it is a circular bulge of igneous rock capped 

by an isolated block of sedimentary rocks that is more 

than 600 feet thick. These rocks include the lower part 

of the Brushy Basin Member and the Salt Wash Member of the Morrison Formation, the Summerville Formation, the Entrada Sandstone, and possibly theN avajo 

Sandstone. The Navajo Sandstone is probably present, although most of Mount Peale is covered with a 

thin mantle of rock debris. Fragments of sandstone 

very similar to the Navajo were found on the east face 

in the talus below la~ge blocks of Entrada and above the 

igneous rock debris. Within the sedimentary cap is a 

thin, continuous limestone bed, 1 to 4 feet thick, that 

strikes N. 25° W. and dips 17° SW. and marks the base 

of the Salt Wash ~!ember of the Morrison. This distinctive bed was of considerable aid in determining the formations present in an area that is mostly covered by 

talus. The limestone bed can be traced around the peak 

of Mount Peale on three sides, but on the fourth, the 

southwest side, the beds are truncated by a vertical wall 

of igneous rock which is part of the bysmalith. Similar 

truncation of the Summerville and older formations can 

also be observed on the northeast end of the peak. The 

distribution of rock types represented in the talus covering Mount Peale indicates that the sedimentary rock cap 

is completely underlain by igneous rock. The cap has 

been raised at least 3,000 feet above the corresponding 

stratigraphic contacts of the surrounding sedimentary 

rocks. 

The lack of quaquaversal dips of the beds .surrounding Mount Peale indicates partial nonconformity with 

the criteria established by Hunt (1953, p. 109) which define the bysmaliths of the Henry Mountains. On the 

south and southeast the beds dip away from the mountain at angles as high as 45°. On the north, however, 

they dip eastward ·at more gentle angles of no more 

than 19° and the beds appear to have been ruptured 

by the igneous mass which crops out as a. vertical cliff 

400 feet high. Structural relationships indicate that 

the area included in the Dark Canyon cirque may be 

underlain by a laccolithic lobe connected to the Mount 

Peale intrusive and injected along the Navajo-Kayenta 

contact as far north as the arcuate fault south of Mount 

Mellenthin. The intrusion of this laccolith and that 

underlying the Blue Lake area have raised the overlying strata south and east of the fault. The fault indicates that these intrusive masses may have formed 

contemporaneously but were formed later than the 

Mount Mellenthin laccolith. East of Mount Peale the 

beds have been folded by the Twomile Creek laccolith, 

but in general dip eastward. To the west the beds dip 

southward reflecting more the irregular nature of the 

contact on that side of the bysmalith. 

The structural relations displayed in Middle Mountain suggest that the stock domed and intruded the 

strata, filling the resultant faults and joints with viscous 

magma which moved upward and outward from the 

stock until it reached the Mancos Shale, the least competent formation in the stratigraphic sequence. There 

the magma moved laterally along bedding planes and 

formed a sill. As the sill cooled and crystallized, it was 

domed gently upward by continuous magmatic injection 

until it formed the Mount Mellenthin laccolith. At this 

point there may have been a minor cessation of intrusion 

which allowed the magma to cool and crystallize at 

depths below the Morrison Formation. Such a process 

might explain the paucity of laccoliths in the Morrison 

of the La Sal, in contrast to the relative abundance of 

la~coliths intruding the Morrison of the Henry Mountains. Whatever the cause may have been, the NavajoKayenta contact, rather than the Morrison Formation, 

was intruded at Mount Peale and in Dark Canyon. Injection along this contact probably started as a sill. As 

the body slowly cooled and crystallized, continuous injection expanded, raised, and eventually ruptured the 

overlying beds, which were lifted well above the surrounding area to form the bysmalith of Mount Peale. 

As conduits became clogged or as the weight of the 

igneous rocks and overlying beds became equal to the 

upward force of intrusion, the magma moved laterally 

and formed the adjacent laccolithic lobes under the 

Dark Canyon cirque and at the head of Twomile Creek. 

The Blue Lake laccolith probably formed at this time 

but may have been fed by a separate dike. These laccoliths uplifted the overlying beds and ruptured them 

along the arcuate fault that marks the margin of the 

stable area created by the Mellenthin laccolith. 

SOUTH MOUNTAIN 

Northwest of the Pine Ridge anticline and lying 

within the same structural trend is South Mountain, a 

laccolithic intrusion much like North Mountain. The 

igneous core of the mountain is exposed within the crest 

of an eroded dome. The core is composed of diorite 

porphyry and extends as laccolithic lobes from a large 

central stock that is just west of the mapped area. 
34 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

Flanking the laccoliths of South Mountain is a sequence of sedimentary rocks of late Paleozoic and Mesozoic age. The contact between the igneous and sedimentary rocks is not as well exposed as in North Mountain, owing to mass wasting hy erosion and cover by 

thick deposits of talus. Where exposed, the diorite 

porphyry is in contact with yellowish-brown to darkgray petroliferous limestone thought to be part of the 

Rico or Hermosa Formation. The horizon of m~gmatic 

injection, therefore, is considered to be the sa.me as in 

North Mountain. 

Moores Ridge, a hogback of Jurassic sandstone, flanks 

the northeast side of the igneous mass. Near the base, 

along La Sal Creek, the Burro Canyon and Dakota. Formations crop out as pointed, flatironlike hogbacks. 

These strata trend N. 40°-80° W. and dip 35°-50° NE. 

A thin sill of igneous rock is exposed in the Mancos 

Shale in sees. 35 and 36, T. 27 S., R. 24 E. This sill is 

connected to the central stock of South Mountain, but 

most of it is obscured by glacial and landslide debris. 

Hunt and 'Vaters (Hunt, 1958) mapped the outcrop -as 

a tonguelike sill projecting from a sma.Il laccolith lying 

west of the mapped boundary and north of the stock. 

South of the mountain the sedimentary rocks have 

been beveled by erosion and covered by thick deposits 

of unconsolidated fan gravel. A prominent hogback, 

similar to Moores Ridge, lies along the structural trend 

west of the mapped area. In sec. 23, T. 28 S., R. 24 E., 

south of Coyote spring is a small area where the fan 

gravels have been removed and the more resistant units 

of the formations of Mesozoic age have been exposed. 

The oldest rocks exposed there are thought to be of Permian age. The youngest exposed rocks belong to the 

Burro Canyon Formation of Cretaceous age. The 

younger beds dip to the southwest at an angle of 70°, 

whereas the older beds are known to be inclined only 

about 55° and may be inclined as little as 35°. Measurements of formational thicknesses indicate that a relatively normal stratigraphic sequence is represented. 

Inasmuch as no faults were found to explain them, the 

differences in dip are believed to represent a flexure 

caused by a minor bulge in the wall of the laccolith. 

FAULTS 

GENERAL FEATURES 

Longitudinal, transverse, and radial faults have been 

mapped in the La Sal quadrangle. Most are highangle to vertical faults having normal dip-slip movement resulting from deformation by tensional forces 

involved in the uplift or collapse of salt anticlines or 

the intrusion of the igneous rocks of the La Sal Mountains. Displacements are from a few feet to a few 

thousand feet. The greatest displacement is along 

longitudinal faults that extend along the flanks of 

the collapsed anticlines and can be traced for 5 miles 

or more (pl. 3). The collapsed anticlines are transected by many cross faults that are commonly of lesser 

magnitude and linear extent. A few radial faults are 

associated with the domal uplift of Middle Mountain. 

One of the longer faults, a longitudinal fault that 

parallels the regional trend, may be rotational, that is, 

the beds on the upthrown side at one end of the fault 

are downthrown at the other end. In tracing such a 

fault from one end to the other, it is observed that the 

vertical displacement decreases in magnitude until an 

area is reached where there is virtually no displacement. 

Major deformational stress was mostly tensional, and 

there were two periods of rupture resulting from two 

types of movement. The first and most important was 

the uplift and rupture of the sedimentary rocks by the 

formation of salt anticlines and, later, igneous domes. 

Between some of the centers of uplift, minor torsional 

forces may have been introduced. The second period of 

deformation involved the collapse of the strata, owing 

to removal of the underlying salt masses. This removal 

was by solution of the salt, or by adjustment of the salt 

to the lithostatic load, or by a combination of both 

processes. Much of the original displacement resulting 

from uplift has undoubtedly been masked by later 

collapse. 

LONGITUDINAL FAULTS 

VALLEY VIEW FAULT 

The Valley View fault is a vertical fault which trends 

north west across the northeast corner of the rna pped 

area. It separates the Roc Creek syncline on the northeast from the Willow Basin and Taylor Creek synclines 

on the southwest. It can be traced beyond the east 

boundary of the mapped area for about 1 mile into the 

adjacent Roc Creek quadrangle to where it is obscured 

by the alluvium of Paradox Valley. To the northwest 

it extends 1 mile beyond the mapped area where it 

merges with a monoclinal fold on the southwest flank 

of the Sin bad Valley anticline. Along Carpenter 

Ridge, branch faults extend in a more westerly direction and probably pass under Pine Flat and across 

Geyser Creek before dying out. The branch faults 

separate the Willow Basin and Taylor Creek synclines. 

Along the fault near the Valley View mine, from 

which the fault is named, beds on the southwest side have 

been upthrown an estim·ated 990 feet. Erosion has exposed the Wingate Sandstone, which dips as much as 

42° SW. and crops out as a prominent knifelike ridge 

.at the head of Paradox Valley. At the mine the Wingate is in contact with the middle of the Morrison Formation. The uppermost sandstone of the Salt Wash 

Member of the Morrison has been dragged upward into 
STRUCTURAL GEOLOGY 35 

a nearly vertical position, and it is this upturned block 

that contains the uranium deposits of the Valley View 

mine. 

Near Buckeye Reservoir the main fault is joined on 

the southwest by a group of less conspicious faults that 

form a complex zone which is a horst that has a maximum width of 2,000 feet. Blocks of sedimentary rocks 

within the zone have been uplifted and dip 33°-70° NE. 

North of this area the fault bordering the southwest 

side of the horst may swing westward under the alluvium of Pine Flat and join a subsidiary fault which 

separates the Taylor Creek syncline from the structures 

southwest of it. In the Willow Basin and Taylor Creek 

synclines, thick alluvial deposits cover most of these 

features. 

The Valley View fault may he rotational. At the 

northwest end of ·Carpenter Ridge, sec. 8, T. 27 S., R. 2-6 

E., the structural rel'ations are obscured by landslide 

debris composed entirely of Burro Canyon Sandstone. 

A small outcrop of Burro Oanyon Sandstone southwest 

of the f31ult plane suggests lth3it there has been very 

little if any displacement, ·and that the debris m·ay cover 

the fracture zone near the ·axis of I'lotation. -North west 

of Carpenter Ridge, the direction of throw ·along the 

fault is reversed; downthrow of the beds is on the 

southwest. Maximum displacement along this part of 

the fault is estimated to be 120-170 feet. Faulting is 

·marked by displacement of contacts and op·ptosed attitude of 'beds on either side of the structure at the junction of Geyser and Roc Creeks. Beds within the Roc 

Creek syncline dip from nearly horizontal to 12° NE., 

and across the fault the beds on the flank of the Taylor 

Creek syncline dip 22°-4!5° 8W. 

Apparent T!otaJtion ·along rthe fault, and other evidence, suggests that deformation of the Valley View 

fault took place at different times in different places 

as a result of different causes. Rupture probably began 

near the Valley View mine ~n the final stage of salt uplift 

during formation of the Paradox anticline. Uplift of 

the Sinbad V.alley anticline and initial formation of 

the Taylor Creek and Roc Creek synclines were prrtabably concurrent. Rupture at the northwest end of the 

Valley View fault took place somewhat later -as preglacial erosion of North Mountain deposited thick layers of sand, gravel, and boulders in the basin formed by 

the Taylor ·Orook syncline. These dep1osits increased the 

lithostatic load of the basin and caused it to deepen ·and 

rupture along· its eastern margin. 

DUGWAY FAULT 

The Dugway fault is a longitudinal fault on the 

southwest flank of and parallel to the axis of the Paradox anticline. It trends N. 55° W. and 4 miles within 

777-039 0-65--.6 

the quadrangle boundary, ·and extends southeastward 

almost to Bedrock, Oolo. It is part of an intricate 

system of faults resulting from collapse along the valley 

margin. A1t the northwest end it dies out on the nose 

of •the Canopy ·Gap anticline 'Which formed as the Paradox Valley anticline collapsed and formed the Willow 

Basin syncline. NtQiwhere is there any evidence thwt the 

fault was caused by the uplift of the evaporite intrusives; it is therefore 'thought to he solely the product 

of collapse. Wihere exposed, the beds along the fault 

scarp have boon downthrown toward the valley from 

300 to 460 feet. The displacement of the fault decreases 

along its strike tJo the novthwest. Additional step faulting parallel to the Dugway ·fault immediately east of 

the mapped area indicrutes that some blocks ,along the 

margin of the valley floor m·ay have dropped 1,'500 feet 

or more .. 

GEYSER CREEK FAULTS 

Several minor faults have been mapped in the general 

area of Geyser Creek in the north-central part of the 

quadrangle. Some are longitudinal and !Others ·are 

transverse to the 'Geyser Creek syncline, the Scorup -anticline, and the Dead Oak syncline-minor folds at the 

northwest end of the Willow Basin syncline. These 

folds are thought to have formed over a salt cell from 

which salt was later removed. The faults are thought to 

reflect incipient collapse of the beds overlying the cell. 

The Scon~:p anticline is breached by two parallel normal 

faults of 40 to 80 feet of throw which form the margins 

of a small graben. The faults join to the southeast to 

form a single fault that dies out wbout 1.5 miles to the 

southeast. 

TWio faults cut the Dead Oak and Geyser Creek synclines at oblique -angles to the graben. The fault cutting 

the Dead Oak syncline is best exposed on the southern 

flank of that structure where the contact of the Burro 

Canyon and Dakota Fo:rnnations is displaced about 20 

feet, with the east side down. The fault was not found 

to cross Geyser Creek and is therefore not believed to 

abut the graben faults; 

The fault cutting the ~Geyser Creek syncline is well 

exposed in the NW1,4 sec. 14 where sandstone of the 

Burro Canyon Formation is downthrown 40 foot on the 

south side of the fault. Farther west the fault is -covered with sandstone debris, but a good exposure in the 

NE1,4 sec. 15 shows the Burro Canyon and Dakota 

Formations to be upthrown on the south side of the 

fault. This displacement suggests that rotational movement has •taken place -along the fault plane probably as 

a result of differential subsidence over the salt cell. The 

beds on the south side of the fault at the west end have 

moved down less than those on the north, whereas to 

the east they have moved down more. 
36 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

Two minor normal :faults lie midway between the 

axes of the Geyser Creek syncline and the Canopy Gap 

anticline. They are in the extension of the Willow 

Basin collrupse area and may mark the margin of an 

underlying salt plug. 

An unnamed longitudinal fault lies about hali a mile 

south of :the Buckeye sawmill and may extend northwestward under Pine Flat. The fault cuts the southeast extension of the Scorup anticline and separates it 

from westward -dipping beds northeast of the fault 

that were tilted by movement along the Valley View 

fault. 

TRANSVERSE FAULTS 

PARADOX VALLEY 

The faults at the north end of Paradox Valley, with 

tthe exception of the Valley View fault, are discussed 

here as a group because of their intimate relationship 

and common origin. An arcuate fault zone represented 

by four curved fault traces in sec. 31, T. 48 N., R. 19 W., 

lie just west of the village of Paradox, Colo. (pl. 1). 

The faults bound the northwestern margin of an inferred salt cell, one of many that formed the Paradox 

anticline. The two small mesas just east of the faults 

are capped by the Kayenta Formation. They are separated by two east-trending parallel faults between 

which the Entrada and Navajo Sandstones are exposed. This graben may represent the center of the 

collapsed salt dome. 

Some of the marginal faults extend no~heast from 

the arcuate zone across the northwest end of Paradox 

Valley and 'are represented by a series of step like cliffs, 

· the most prominent of which is marked by outcrops of 

Entrada Sandstone. These faults are nearly at right 

angles to the axis of the Paradox anticline and probably 

are the result of the collapse. A similar fault crosses 

the Willow Basin syncl!ne about one-half mile below 

the confluence of Buckeye and Mellenthin Creeks at 

West Paradox Creek. There the Burro Oanyon and 

Dakota Fornl'ations are downthrown more than 250 

feet on the southeast side. The displacement decreases 

toward both extremities of the fault. The ll!ortheast 

end appears to die out near the Burro Canyon escarpment in sec. 13, T. 48 N., R. 20 W., Montrose County, 

Colo., but it may extend 'tJo the Valley View fault. The 

southwest end may terminate about 1,500 feet short of 

the Dugway fault. 

Two minor longitudinal faults are on the southwest 

flank of the Willow Basin syncline, mainly in sec. 25, 

T. 48 N., R. 20 W., where they abut the 'transverse fault 

that cuts the Willow Basin syncline. Their southeastward extent is not accurately known. They roughly 

parallel the structure of the syncline and are thought 

to be the result of local subsidence in the area between 

the synclinal·axis and the Dugway fault. Their formation may have been concurrent with or later than the 

transverse fault. 

SHARP CANYON FAULT 

A small part of the Sharp Canyon fault is exposed in 

the south fork of Sharp~ Canyon in sees. 19 'and 30, 

T. 47 N., R. 19 W., Montrose County, Colo. The fault 

trace is marked by a zone of silicified veinlets in the 

Entrada and Navajo Formations exposed in the floor 

and walls of the canyon. The fault bears N. 22° E. and 

extends into the adjacent Paradox quadrangle where it 

curves eastward toward the margin of Paradox Valley. 

Near La Sal Creek the beds are downthrown on the 

southeast and have an average throw of 30 feet. This 

displacement continues southwestward to Wray Mesa 

where the fault becomes difficult to trace in the shale 

beds and highly lenticular sandstone of the Salt Wash 

Member of the Morrison Formation. 

The fault is transverse to the regional trend of the 

folds with which it is associated. It is appr~ximately 

parallel to and is similar in displacement and other 

xespects to the Cashin fault to the southeast ~beyond 

the limits of the rna p. The economic possibilities of the 

Sharp Canyon fault are discussed on page 76. 

RADIAL FAULTS 

MIDDLE MOUNTAIN 

The radial faults of the Middle Mountain dome contrast with the longitudinal and transverse faults. The 

majority are associated with and radial to the intrusive 

stock in the west-central part of the mountain group. 

In the structural formation of Middle Mountain there 

appears to have been at least two periods of igneous 

intrusion and major faulting and possibly a thi.rd period 

of minor faulting. The first period accompanied the 

intrusion of the central stock and resulted in the formation of faults that are more or less radial in pattern. 

Most of these faults were later filled with igneous rock 

as dikes which fed the laccoliths in the Mancos Shale. 

The second period of faulting accompanied the formation of those laccoliths intruded along the NavajoKayenta contact and produced the Mount Mellenthin 

fault, the most conspicuous fault in the Middle Mountain area. This fault appears to be the result of uplift 

by the Mount Peale bysmalith and the associated 

laccoliths. The third period of deformation was of 

much less intensity and appears to have produced minor 

faults in both the igneous and sedimentary rocks. 

The Mount Mellenthin fault extends from the stock 

of Middle Mountain eastward through the ridge connecting Mount Mellenthin and Mount Peale, and into 

Dark Canyon. In Dark Canyon the fault curves north-
STRUCTURAL GEOLOGY 37 

ward, along the east border of Mount Mellenthin, and 

separates it from the Blue Lake laccolith. This arcuate 

fault is believed to mark the southern and eastern limits 

of the Mount Mellen thin laccolith prior to erosion. The 

outlier of igneous rock, ·which forms the knoll on the 

ridge between Mount Mellenthin and Mount Peale, just 

north of the fault, supports this hypothesis. Displacement along the fault differs from place to place, but it 

is probably as much as 500 feet on the ridge just described. The beds south and east of the fault are upthrown and are probably underlain, in part, by igneous 

rock that extends from the Mount Peale bysmalith 

northward into the Blue Lake area. It is probable that 

the underlying intrusives formed later than the Mount 

Mellenthin laccolith and that its mass prohibited the 

northward and westward movement of the magma of 

the younger intrusives. The constriction thus formed 

appears to have forced the magma upward and ruptured 

the overlying beds along the margin of the Mount 

Mellenthin laccolith. 

A swarm of minor faults cross the ridge just south 

of Mount Mellenthin and may represent a third and 

final period of deformation in the Middle Mountain 

area. Both the igneous and underlying sedimentary 

rocks have been ruptured by two sets of semiparallel 

faults. One set bears due north, the other due west. 

Both sets lie in the center of the domal uplift which 

elevated the sedimentary and igneous rocks of Mount 

Peale and Mount Mellenthin during the final stage of 

igneous intrusion. 

STRUCTURAL HISTORY 

The history of the structural features within the 

La Sal quadrangle is an integral but very small part 

of the history of the Colorado Plateau about which 

much has already been written. Beginning with the 

work of such pioneers as Powell ( 1875, 1876), Gilbert 

(1877), and Dutton (1880, 1882, 1885), much effort and 

time have been expended by many geologists in studying and piecing together the geologic history of this 

vast area. Much of the work is incorporated and published in reports of the U.S. Geological Survey. Publications that are more directly associated with the 

rna pped area described in this report are the works of 

Baker (1933, 1946), Dane (1935), Gould (1926), Hunt 

( 1953, 1954, 1956, and 1958), Cater ( 1954a), Shoemaker 

( 1954, 1955, 1956a), and Withington ( 1956). 

For a more complete structural history of the Colorado Plateau, the reader is referred to an article by 

Shoemaker (1954). Shoemaker describes the major 

uplifts and basins and attributes their formation to 

large-scale regional warping and strain of the basement complex; the salt cells and anticlines he attributes 

to flowage of plastic masses of evaporites, and the mountain domes, laccoliths, dikes, and diatremes to stress 

transmitted by magmatic pressure within the earth's 

crust. None of the mechanisms inyolved or their resultant structures is entirely separate; on the contrary~ 

within the mapped area they are intimately intermeshed 

and give a revealing story of the structural history of 

this small part of the earth's crust. 

All three types of stress mentioned by Shoemaker 

have affected the rocks within the La Sal quadrangle. 

Field evidence indicates that several periods of major 

deformation were interspersed with many minor periods. The first major period of deformation began either 

late in the Mississippian Period or Early Pennsylvanian 

time with down warping and formation of a large structural basin, the Paradox Basin. The northeast side of 

the structural basin became outlined by the gradual 

emergence of the ancestral Uncompahgre highland. 

The basin began to fill with thick deposits of evaporite, 

limestone, and interbedded arkose (Cater, 1954a) of the 

Hermosa and Rico Formations. A second uplift along 

the Uncompahgre during the Permian Period resulted 

in deposition of the thick arkosic fanglomerates of the 

Cutler Formation. This uplift was accompanied by 

deformation in the basement complex which, in turn, 

caused flowage of salt in the Hermosa Formation. 

Initial growth of the salt cells is marked by pinchouts 

and thinning of the Cutler Formation on the flanks 

of Fisher Valley and Paradox Valley. This growth 

is also marked by the local absence of the Moenkopi on 

Moore's Ridge flanking South Mountain and a thinned 

sequence of Cutler beds on the flanks of both North and 

South Mountains and the west side of Sinbad Valley. 

Through Late Triassic, Jurassic, and Early Cretaceous time, the area was structurally more stable. Thinning of the sedimentary rocks between the Cutler and 

Morrison Formations in the Gypsum Valley area 

(Stokes and Phoenix, 1948) reflects a gradual uplift of 

the salt anticlines. In the La Sal quadrangle this uplift 

is indicated by local thinning or absence of the Cutler, 

Moenkopi, Navajo, and Carmel (?) Formations along 

the flanks of the mountains and salt anticlines. Stokes 

(in Stokes and Phoenix, 1948) suggests that the close 

balance between the rise of salt and sedimentation indicates that growth of the salt masses was governed 

largely by the loading of sediments on their peripheries. 

The salt may have reached the surface in different 

places at different times. A quiescent period began with 

the deposition of the Morrison Formation and lasted 

until near the end of Dakota deposition. Stokes (in 

Stokes and Phoenix, 1948) also suggests that minor uplift of the salt masses may have occurred during deposition of the Burro Canyon Formation and Dakota 
38 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

Sandstone, as indicated by thinning of the two formations. The present writers have found no evidence in 

the La Sal quadrangle to support this theory; they believe that thickness difference of the two formations is 

purely a function of erosional disconformity which 

separates them (Carter, 1957). 

Epeirogenic downwarping of the Colorado Plateau 

during Dakota time allowed encroaclunent of marine 

waters which later deposited the Mancos Shale. Thicknesses of the Mancos Shale and the Mesaverde Group 

which crop out to the north (Fischer, 1936) indicate 

that about 5,500 feet of lTpper Cretaceous sedimentary 

rocks onpe covered.the mapped area. However, Uppe'r 

Cretaceous beds younger than Laramie age are absent 

in the central part of the Plateau and those younger 

than Niobrara age are absent in the La Sal quadrangle. 

It is thus difficult to determine the precise time that 

igneous activity started in the La Sal Mountains, but if 

it is assumed that the laccolithic mountain groups of the 

Plateau, being of similar composition, are contemporaneous, a Late Cretaeeous age is not inconceivable. 

Shoemaker (1954, p. 63) states that the McDermott 

Member of the Animas Formation, which underliPs the 

Ojo Alamo Sandstone of latest Cretaceous age (Laramie or Hell Creek) (Reeside, 1924; Cobban and Reeside, 

1952), near Durango, Colo., contains large boulders of 

diorite porphyry that are lithologically similar to and 

appear to be derived from the igneous ,centers of the La 

Plata Mountains. He concludes that some of the intrusions in the La Plata Mountains are probably of Late 

Cretaceous age. No evidence was found in the mapped 

area to preclude such ·an age for commencement of intrusion that produced the La Sal Mountains. 

Intrusion of the salt anticlines by theN orth and South 

Mountains laccoliths came early in the formation of the 

La Sal Mountains and was apparently started by renewed faulting of the crust along northwest-striking 

zones of weakness. Magma gradually filled and eventually ruptured the crests of the anticlines as plastic 

exaporite beds were pushed outward along the strike 

of the :folds. As eooling and crystallization of the 

magma in North and South Mountains took place, the 

original escape routes probably became clogged and 

intrusion was :forced along seeondary zones of weakness. 

The remarkable north-south alinement of the three 

mountain stocks suggests that secondary :faults in the 

crust may parallel this direction. The emplacement of 

Middle Mountain apparently was somewhat later and 

was restricted by proximity of the other two masses. 

Earliest intrusion in the Middle Mountain area was at 

the central stock a:qd radial dikes and :formed the Mellenthin laccolith. The Mount Peale bysmalith, Twomile Creek laccolith, and Blue L::tke laccolith were intruded at horizons mu,ch lower in the stratigraphic 

column, and :fault displacements suggest that they were 

later than the Mellenthin laccolith. 

The last stage of intrusion in the La Sal Mountains 

is marked by the presence of breccia pipes in the North 

Mountain intrusive. Hunt (1954) suggests that rupture and possibly erosion near the crest of the mountain may have allowed the syenitic intrusion to break 

through the surface explosively. 

Zircon age determinations of syenite and monzonite 

porphyry by H. W. Jaffe indicate that the youngest 

igneous rocks are of middle Eocene age. The diorite 

porphyry is intruded by the monzonite porphyry and 

intrudes rocks no younger than the Mancos Shale of 

Late Cretaceous age; all younger sedimentary rocks 

have been removed by erosion in the mountain area. 

This relation limits the emplacement of the great bulk 

of the igneous rqcks of the La Sal Mountains to some 

time between the Late Cretaceous and middle Eocene 

and indicates that intrusive processes spanned a period 

of at least 20 million years. 

After the igneous uplift of the La Sal Mountains 

came a period of erosion and structural collapse of the 

salt anticlines. Fans of sand and gravel were deposited 

on the flanks of the mountain uplift during Pliocene(~) 

time. Large :fanglomerate deposits crop out in the 

Taylor Creek syncline in the mapped area, in Castle 

Valley to the north, and in Pack Creek to the west. 

Post-:fanglomerate tilting probably resulted from erosion, solution, and settling adjustments of plastic evaporite beds in Castle Valley and in the Taylor Creek 

syncline. 

Recent deformation is believed to be restricted to 

block :faulting along the valley margins; local adjustments in the plastic evaporite cores of the breached anticlines is indicated by small :faults and minor :folds in the 

Quaternary deposits. 

URANIUM DEPOSITS 

HISTORY OF MINING IN THE LA SAL QUADRANGLE 

The early history of discovery and development of 

uranium-vanadium ores of the Colorado Plateau centers 

in areas around Paradox Valley that are both adjacent 

to and within the mapped area. Publications by Burwell ( 1920) and Coffin ( 1921 and 1954) describe most of 

the history of these diseoveries and the growth of the 

uranium-vanadium industry. The following.\ paragraphs summarize the principal historical events in the 

development of the La Sal Creek mining district and 

provide the background which led to the studies eontained in this report. 

Prior to 1880, white settlers knew that local Indians 

obtained a yellow pigment :from the Yellow Bird and 
URANIUM DEPOSITS 39 

other nearby deposits. These deposits were sampled by 

Gordon Kimball, a mining engineer at the Cashin mine. 

The samples and others from deposits in Roc Creek 

were shipped to France for study by Mr. Charles Poulot 

(Kimball, 1904), who _identified the material as uranium ore. Thereafter small tonnages were mined 

periodically for research. 

It was not until 1913, however, when war threatened 

that intensive mining for vanadium began at the La Sal 

Creek Yellow Bird deposits. Mining continued until 

1921 when demand declined, owing to flooding of the 

market by cheaper Belgian Congo ores. Activity was 

renewed in 1936 as, again, war threatened. Vanadium 

was of principal interest during the ]ate thirties, but 

as atomic research and technology progressed, the emphasis gradually changed to interest in uranium. In 

1942, special exploration studies and purchasing programs were started under the Metals Reserve Co., and 

later the Manhattan Proje-ct, to stimulate development 

of uranium-vanadium deposits. Under the Manhattan 

project, C. W. Livingston (1945, unpub. data.) made a 

detailed study of the mines of the La Sal Creek district. 

Exploration and development were left to the mine 

operators. U.S. Vanadium Corp. drilled about 100 

holes with wagon and diamond drills at their properties 

in the northeast part of the district. 

The end of World War II brought another decline 

in the demand for uranium and vanadium and most of 

the mines in the La Sal Creek area closed. In the early 

fifties the Korean conflict ·and threat of world domination by Communism brought renewed search for uranium resources to be used in atomic weapons and as 

energy for peaceful pur:poses. 

In 1952 the lT.S. Geological Survey began a program 

of development drilling in the vicinity of the Evening 

Star and Gray Daun mines to outline new ore bodies 

and extensions of known deposits. This driHing resulted in the discovery of the Marjorie Ann and FireflyPigmay deposits. Mining operations began on these 

properties in 1953. Close-spaced development drilling 

behind the Vanadium Queen mine found new ore bodies 

and discovered favorable ground extending in a northeasterly direction from the mine workings. ·A widespaced drilling pattern (holes spaced 500 to 1,000 ft 

apart) was then employed and resulted in the discovery 

of a favorable belt of ground about 1,000 to 3,000 feet 

wide and about 3 miles long extending from the V anadium Queen mine to the mines along Lion Canyon. Exploratory driHing on a wide-spaced paUern was continned through 1954 both north and south of La Sal 

Creek canyon to further define the favora!ble area and 

to search for other areas which might be favora:ble for 

the localization of uranium deposits. The location of 

the drill holes is shown in plate 4. Private interest in 

exploration and development in the ;~.rea increased during 1954 and the government exploratory drilling program ~as terminated. 

The discovery of extensions of known deposits renewed production in the Gray Daun, Vanadium Queen, 

Hesperus, and Evening Star mines. Of the new deposits discovered and partly outlined by driHing, only 

the Marjorie Ann, Firefly-Pigmay, and Black Hat 

claims had been developed and were being mined by the 

end of 1956. Known production in the area had increased from 18,260 short tons during the period 1940-44 

(Livingston, written commun., 1945), to a total of 42,410 

short tons by the end of 1954. 

The discovery in 1955 of a deposit on Hop Creek, 

about 1~~ miles north of the Gray Daun mine, and another near the east flank of Mount Mellenthin, indicates that other favorable belts and similar deposits may 

be present within the mapped area. In 1957, when this 

study terminated, mining in the La Sal Creek district 

continued at a high rate. 

DISTRIBUTION 

Uranium.:v1tnadium deposits occur in the Brushy 

Basin and Salt Wash Members of the Morrison Formation in the La Sal quadrangle. The vertical distribution 

is narrow, for almost aH of the deposits lie within a 

sequence of sedimentary rock that is about 150 feet 

thick. This sequence includes strata both above and 

below the contact of the two members. The majority 

and largest of these deposits are in the uppermost continuous sandstone of the Salt Wash Member; this unit 

is referred to as the "ore-bearing sandstone." A few 

small deposits have been discovered in a discontinuous 

sandstone lens of the Salt Wash that overlies the orebearing sandstone. Most deposits in the Brushy Basin 

Member are restricted to conglomeratic sandstone lenses 

at the base of the member. A few deposits, however, 

occur in sandstone lenses in the upper part of the Brushy 

Basin Member. 

The areal distribution of the deposits, when considered as a whole, appears wide and erratic (p'l. 5). It 

is best, however, to consider the geographic distribution 

of these deposits according to their stratigraphic position. 

The deposits in the Brushy Basin Member, discovered 

chiefly by surface prospecting, are erratically distributed over a wide area. Most of the deposits are in a 

cherty conglomeratic sandstone, commonly referred to 

as the "Christmas tree conglomerate," which in places 

is the base of the Brushy Basin Member. Mineralized 

material is also associated with carbonaceous material, 

green mudstone, and siltstone strata at various levels 
40 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

throughout the member. The Sunmer mine, near the 

headwaters of Ice Lake Creek (pl. 3), is typical of 

Brushy Basin deposits in that it is small and occurs 

in the basal unit of the member. Similar deposits were 

found by Survey drilling but few were thoroughly explored because they were generally too small and, in 

most places, too deep to be mined profitably. An unusually high concentration of deposits in · the Brushy 

Basin Member is found in the vicinity of Wray Mesa, 

south of La Sal Creek. These deposits are in the lower 

200 feet of the Brushy Basin Member and were mined 

in 1953-55 both by underground and open-pit methods. 

They include the Lucky No.1, Morning Glory, Howling 

Coyote, Too High, and Brushy Basin No. 1 and 3 mines. 

The Morning Glory and Howling Coyote deposits are 

at the east end of Wray Mesa, east of the La Sal quadrangle, and are therefore not shown on the maps. 

A few deposits are in a discontinuoua sandstone bed 

that is less than 25 feet thick and lies about 10 feet above 

the ore-bearing sandstone layer of the Salt Wash Member. The Hesperus, Uranium Girl (formerly Emergency), and the upper workings of the Maud mine, along 

the north and south rims of La Sal Creek canyon, are 

examples of deposits in this sandstone. The deposits 

are small, and have thus far produced a combined total 

of a few hundred tons of ore. The ore minerals are 

generally oxidized, and are mostly carnotite and tyuyamunite associated with and replacing carbonaceous 

material. These deposits are widely spaced and erratic. 

Most of the uranium deposits in the La Sal Creek 

area are in the uppermost continuous sandstone unit 

of the Salt Wash Member which is commonly referred 

to as the "third rim" or the ore-bearing sandstone. This 

unit is in the stratigraphic interval between 250 and 

350 feet above the Entrada Sandstone or 350 to 450 feet 

below the base of the Burro Canyon Formation. The 

deposits in the La Sal Creek area are concentrated in a 

northeast-trending belt of favorable ground which is 

1,000 to 3,000 feet wide and at least 5 miles long. This 

belt is referred to as the "La Sal Creek mineral belt" 

(pl. 5). The western extremity of this belt has not 

been clearly defined. 

Within the belt, individual deposits are elongate and 

their long axes commonly trend east or southeast at a 

slight angle to the overall trend of the favorable area, 

somewhat as do the deposits within favorable parts of 

the Uravan mineral belt as defined by Fischer and 

Hilpert ( 1952). The deposits are generally in the lowermost 20 feet of the sandstone and are separated by 

barren or weakly mineralized lenses of sandstone or 

mudstone. The horizontal distance between deposits 

ranges from 100 to 600 feet. 

The regional relation between the La Sal Creek deposits and the Uravan mineral belt described by Fischer 

and Hilpert (1952) is somewhat obscure. Trends of 

sedimentary structures indicate that prior to uplift, 

erosion, and collapse of the Paradox anticline, the La 

Sal Creek belt probably continued eastward where it 

joined the favorable ground on Carpenter Ridge and 

may have reached as far south as Club Mesa near 

U ra van, Colo. These areas lie on the northeast flank 

of the Paradox anticline east of the map boundary. 

The authors believe that there are other favorable 

areas in the vicinity of the La Sal Creek mining district 

and the La Sal Mountains. This belief is based on field 

observations of the Salt Wash Member and of small, 

scattered uranium-vanadium deposits outside the explored favorable area. These deposits may lie in zones 

that have trends, dimensions, and ore bodies similar to 

those in the La Sal Creek district. The extent, distribution, and nature of such potential areas is not known, 

but their locations and possibilities are discussed on 

page 73. 

SIZE AND SHAPE 

The deposits in the Morrison Formation are of various sizes and shapes. In general, they are layered 

concentrates of uranium-vanadium min~rals occurring 

as isolated ore bodies or as interconnected clusters of 

ore bodies. The bodies are greatly varied in thickness 

and areal extent; they may be flat-lying to gently undulating tabular deposits or may occur as rolls. In places 

the ore deposits occur where ore minerals replace carbonaceous material in "trash pockets" and fossil logs. 

All these types of ore bodies occur in both members of 

the formation, but the largest and most varied in shape 

are the deposits in the Salt Wash Member. 

The flat-lying tabular deposits may occur as single 

layers as much as 3 feet thick, or as several thinner 

superposed layers separated by barren sandstone. Locally several layers join and form a composite layer as 

much as 12 feet thick. These layers generally are 

thicker in some places and thinner in others in conformation with bedding planes inherent in the sandstone lenses or with surfaces of mudstone layers separating sandstone lenses. Drill-hole data and mine 

mapping indicate that the average ore thickness in the 

area is about 3 feet. 

T11e layered deposits are extremely varied in size. 

They range from isolated ore bodies covering a few tens 

of square feet and containing a few tons of ore to clusters of ore bodies that are generally interconnected by 

thin layers of weakly mineralized sandstone or mudstone; these ore bodies cover areas as much as 600 feet 

long and 300 feet wide and contnin as much as 20,000 
URANIUM DEPOSITS 41 

tons of ore. Where these bodies occur in closely spaced 

clusters, from 10,000 to 50,000 tons of ore can be pro1 

duced from a single mine. The orientation and indicated or inferred limits of these deposits are shown on 

the mine maps ( pls. 6-13). In general, they parallel 

the average direction of roll axes and trends of sedimentary structures. Most deposits in the La Sal Creek 

mineral belt trend between N. 70° E. and S. 70° E. A 

few, however, are widely divergent from this trend and 

probably reflect locally divergent directions of Salt 

Wash stream flow. 

The range in trend of sedimentary structures suggests that the ore-bearing sandstone was deposited by 

meandering streams. Widely divergent bearings may 

be due, in part, to the difficulty in obtaining enough accurate measurements from the ore-bearing sandstone. 

According to Raup and Miesch (1957), the number of 

cross-stratification (unidirectional) measurements obtained are approximately half those required for firmly 

based conclusions. This paucity of measurements is explained by the fact that in mining most of the ore-bearing sandstone lens is removed with the ore and only the 

barren lenses which are usually coated by dust and 'mud 

from blasting are left. 

Rolls are layered ore bodies of a great variety of 

forms that curve sharply across the sandstone bedding. 

They most commonly display rough C and S shapes in 

cross seetwn, usually with some irregularity in the 

limbs. Many rolls are C-shaped but the C is turned 

on its side. and the outside roll surface is. either convex 

upward or downward. Less abundant are the more 

complex "socket" and "mirror-image" rolls described by 

Sha we ( 1956). In plan, the r()lls are elongate or linear 

bodies which may be straight but more commonly are 

curved to some degree. 

The roll surfaces that separate mineralized material 

from barren rock have been described as "fractures" 

(D. R. Shawe, oral commun., 1955, Y. W. Isachsen, oral 

commun., 1955). The term "fracture" usually refers to 

a break or separation and is generally associated with 

other results of deformation. Rather than imply a 

deformational process in the formation of roll ore 

bodies, the authors prefer to consider the roll surface as 

a mineral contact along which a zone of weakness or a 

parting surface may form during mining as a result of 

differences in either degree of cementation or in gross 

composition of the ore body and the surrounding wallrock. Differences on either side of the contact allow the 

roll to break away from a smooth surface of barren 

rock when mined. Many of these surfaces are minutely 

undulatory, and a thin scale or crust of mineralized 

material remains on the surface after mining. Such a 

surface is referred to as a "roll scab." 

Log replacement and trash-pocket ore bodies -are considerably smaller but of higher grade than other ore 

bodies. Logs contain very high grade material and are 

as much as 30 feet long and 1 to 2 feet in diameter. 

Many_ of the larger ones are oriented parallel to the dips 

of adjacent cross-stratified beds. The trash pockets 

are podlike accumulations of poorly sorted sandstone, 

fragments of carbonaceous matter, and mudstone or 

clay galls that are partly impregnated with, and in part 

replaced by, uranium and vanadium minerals. These 

pockets are rarely more than a few feet long, are a foot 

or two thick, and are of various shapes. Some pockets 

are circular in plan and appear to represent accumulations deposited by small whirlpools or eddies in Salt 

Wash streams; others are elongate and fill minor channel scours. The direction of elongation of such bodies 

generally agrees with directions determined by crossstratification measurements in subjacent sandstone beds. 

In the Brushy Basin ·Member, mineralized material 

'OCcurs in all four types of ore bodies just described. 

The layered deposits are from 0 to more than 1 focYt 

thick and cover areas as much as a few hundred square 

feet. These bodies oonrt:ain from several pounds to a few 

hundred tons of mineralized .material. The podlike ore 

bodies are small and contain vtolumes of rock from a 

few cubic inches to a few cubic feet. Roll ore bodies 

are uncommon and generally small. An exception to 

this, however, is the ore body at the Lucky No. 1 mine 

at the head of Sharp Canyon on the east end of Wray 

Mesa. The 'Ore body is a C-shaped roll that is approximately 90 feet long, ·about 3 fe~t high, and from 1 tto 3 

feet wide. The trend of the roll axis forms a gentle 

arc that bears from N. 25° E. on the west end toN. 50° 

E. on the east. Ore was concentrated along the convex 

side of the surface along which the trend measurements 

were made. 

LOCALIZATION 

The structural features that probrubly control the 

localization of uranium-vanadium deposits of ·the Colorado Plateau may be divided into two distinct types: 

those of sedimentary origin and those of teci;onic 'Origin. 

Most deposits of the La Sal Creek area are in the lower 

part of the uppermost continuous sandstone stratum of 

the Salt 'Vash. In this host TOCk, ·sedimentary features 

present the m•ost obvious control of position and, usually, of the shape of the ore bodies. 

An isopach map (fig. 6) showingthert:hicknessof sedimentary rocks between the base of the ore-bearing sandstone -and the top of the Entrada Sandstone gives a 

general picture of the surface on which the ore-bearing 

unit was deposited. The most conspicuous feature is 

a roughly circular basin in the central part of the a.rea 
N~=~dJ§£/8:/L~"i~~:_~ 

~~~"---~/ I ~, \ 

I \ 

~ ,, . ~ I ---3oo-r..;...- ...-- / Base of ore-beanng \ 1 --- sandstone \ 1 

----

1

---.... \ I I ) 'A -- _/ / 

) - / 

~'~---)\~'~r N 

).--------

.... 

./1 

y 

/ y/ 

I ~\) j/ 

I \L...-, I 1 1 

I I 1 'l I - / I I - I I r Y I & / / I ~ 

\ 

_l--/ / I .....-- / / 

Base / o fore-bearing/ / 

\ I 

I I ~~~~~ I 

-{ sandstone~ 

p..\.. c ~ \ \ 

, s .• :-~o 1 1 ,,~ "'"' 

\..r CiX''" I ~:: .. · .. ·'<,.>,· .:··.~.'\1<::-." ...., . ''·" ""'" ·, ," ·~:\ I _....("<"< It(>", ··-""'.::<\. ·, "\:; ,~~'~:\' . " :y) 

~~ 

FIGURE 6.-Isopach map of paJ:'It of the La Sal Creek area showing thickness of strata from the top of the Entrada Sandstone to the base of the ore-bearing 

sandstone of the Salt Wash Member. Contours, short dashed where projected, reflect the configuration of the surface upon. which the ore-bearing sandstone was deposited. Contour interval is 10 feet. In 1954, the overlying sandstone contained known uranium-vanadium deposits in the stippled area, 

and potential deposits in the ruled area. 

~ 

~ 

0 

l':l 

0 

~ 

~~ 

c:l 

~ 

~ 

~ I 

~ 

~ I;; 

1-1 

~~ 

~ 

i> 

(Jl 

i> 

~ 

§ 

i> 

I;; 

~ 

i> 

z 

0 

J~ 

s 

~ I 

a 

0 

s 

~ 

~ 0 
URANIUM DEPOSITS 43 

near the Utah-Colorado line. It is in this area, generally outlined hy the '280-foot isopach, that the thickest 

sandstone of the ore-bearing unit in ~the Morrison Formation was penetrated during the drilling progra,m. 

The 'outcrop of the one-bearing sandstone along the 

north side of the La 'Sal Creek canyon is also thickest 

and most prominent in this area. Ore deposits of this 

area are generally in the middle or upper half of the 

sandstone stratum, whereas deposits that oocur outside 

the 280-.foot isopach are nea.r or at the base of the 

sandstone. 

Areas outside the 280-foot isopach represent local 

thickening in the underlying sedimentary stra!ta. These 

areas were probably highs during deposition of the 

ore-bearing unit and locally controlled the course of the 

depositing stream. The greater thickness shown in the 

northeast corner of the figure may also have been a 

topographic high or. it may represent a thickening nea·r 

the margin of the Paradox anticline resulting from 

local subsidence caused by salt movement from this 

area eastward into areas of uplift. Recent erosion of 

the ore-bearing sandstone and underlying strata· east 

of the mapped area make the picture incomplete. 

The general configura;tion of the surface suggests 

tha;t, while the major flow of the Salt Wash stream 

was northeastward through the center of the basin, a 

local channel passed through the southeastern part of 

the basin. Sedimentary structures, logs, and roll directions (see "Yellow Bird mine," p. 71) in this area 

indicate that the southeastern channel turned north and 

probably joined the 'principal channel in the northeast 

corner of the mapped area (fig. 6). The irregular surface seen at the west edge 'Of the area (fig. 6) suggests 

that favorable ground and possibly more deposits may 

be west of the explored area. . 

The ore-bearing sandstone layer overlies impermeable 

mudstone and siltstone beds. Structure contours drawn 

at 10-foot intervals at the base of the ore-bearing sandstone and based on elevations compiled from diamonddrill-hole data show that the surface of deposition was 

irregular. Most of the mineral deposits lie in broad 

shallow depressions or scours near and on the flanks 

and crests of structural noses (fig. 7). These noses 

appear to project into the main channel where the uppermost sandstone beds of the Salt Wash were deposited. This channel is contained in the belt of favorable 

ground in the La Sal Creek area. Within this belt, the 

maximum relief from the lowest depression to the top 

of the highest nose is about 50 feet. 

The deposits also lie in shallow depressions, best seen 

in the Gray Daun mine (pl. 8) and the Vanadium Queen 

mine (pl. 12) ; these depressions appear to be similar to 

local scours in the channel floors of present-day 

meandering braided streams. The structural noses can 

be likened to cuspate projections along the margins of 

streambeds. Such depressions and projections create 

eddies and whirlpools in which a great amount of woody 

debris collects, becomes waterlogged, and sinks. During 

floods, however, debris is rafted onto the higher bars 

and cusps within and along the margins of the channel. 

Such a process may explain the placement of many of 

the trash-pocket accumulations of carbonaceous debris 

associated with the uranium-vanadium ores in the Salt 

Wash Member. 

The ore-bearing sandstone beds fill these depressions 

and are commonly capped by impervious layers of green 

mudstone as shown in section A-A' of the Vanadium 

Queen (pl. 12) and in section A-A' of the Jfirefly-Pigmay mines (pl. 7). The sandstone in the channels is 

highly lenticular and complexly crossbedded. "Festoon 

cross lamination" (Knight, 1930) is common and may 

have controlled localization of the more tabular ore 

bodies in a manner similar to that described by Roach 

and Thompson ( 1959). The festoons are composed of 

finely laminated sandstone that fills secondary stream 

scours or troughs within a channel. These sand-filled 

troughs intersect with, overlap, or are superimposed 

on other festoons. The surfaces separating the festoons 

are commonly thin clay films or seams that are much 

less permeable than the sandstone within the festoons. 

These features along with the mudstone beds, which 

range from thin films to several feet in thickness, separate large sandstone lenses composed of many festoons 

and appear to be the reason, in part, for the highly 

variable transmissivity of Salt Wash sandstones as reported by Jobin (1956). Thus, sedimentary features 

such as channel scours, sandstone lenses, mudstone 

seams, and festoon cross laminations combine as important factors in localizing uranium-vanadium-bearing 

solutions. 

The localization and configuration of roll ore bodies 

have been attributed to both obvious and obscure features. The close association of roll and tabular-type 

ore bodies suggests an interplay of sedimentary features 

and the agent that transported the ore minerals to their 

present site. A variety of transporting agents have 

been postulated for the ore-carrying fluid and are considered in detail on page 52. 

The roll surfaces appear to represent the contact between two immiscible substances which were in either 

a liquid or gaseous state at the time of localization. 

The long axes of the rolls tend to parallel the trends of 

sedimentary structures, that is, the direction of paleostream flow, and reflect the orientation of the most 

permeable units in the sandstone layers (Lowell, 1955; 

Shawe, 1956). Demonstration of this relationship 
0 2000 4000 6000 FEET 

L__·~--L--L--~-----------L----------~ 

\ -.L._~ / 

I \ / 1-i_--..L... \ / 

I ---~--

Base of ore-bearing 

sandstone 

FIGURE 7.-Structure contour map of the base of the ore-bearing sandstone of the Salt Wash Member in part of the La Sal Creek area. Contours, dashed where 

located approximately and short dashed where projected, reflect the configuration of the surface upon which the ore-bearing sandstone was deposited. Contour interval 10 feet; datum is near sea level. In 1954 the overlying sandstones contained known uranium-vanadium deposits in the stippled areas and 

potential deposits in the ruled areas. 

~ 

~ 

0 

t;j 

0 

t"l 

~ c:j 

~ 

~ d 

~ I 

~ 

~ t:::l 

1-1 

d 

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r:n 

> t"l 

§ 

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t"l 

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URANIDM DEPOSITS 45 

WN 

I 

I 

s 

A. Ore roll axes 

(61 measurements) 

N 

I 

00--------.--------- 00 

' I 

goo 

D. Strike (upper diagram) and 

dip (lower diagram) of joints 

(311 measurements) 

wWN 

I 

I 

s 

B. Foreset beds showing 

direction of dip 

(76 measurements) 

N 

I 

I 

s 

-E 

-E 

C. Stream direction according to current lineation, ripple marks, and 

channel scours (70 measurements) 

FIGURE 8.-Composite orientation diagrams showing trends of (A) ore roll axes, (B) unidirectional 

and (C) bidirectional sedimentary structures indicating direction of stream :flow, (D) Sltrike 

and dip of joint surfaces measured in all mines mapped in the La Sal Creek area. 

by use of directional diagrams constructed for each of 

the mines that have been mapped in the La Sal Creek 

area and by a composite of these diagrams (fig. 8) is 

impaired by a lack of sufficient readings. The ore bodies 

and the host sandstone beds appear to be very much 

like the shoestring-sand type of stratigraphic trap 

searched for hy the petroleum industry. Other similarities to stratigraphic traps will be considered on page 49. 

There is no obvious relation of the localization of the 

ore deposits to tectonic structures. La Sal Creek mineral belt crosses the axis of the La. Sal Creek sycline at 

an angle of about 20°. The mineral belt also extends 

between and lies on the flanks of two collapsed folds. 

One is part of the Paradox anticline and the other is 

the Pine Ridge anticline. The belt may extend eastward to the Valley View mine on Carpenter Ridge and 

westward to the Rattlesnake mine west of La Sal. No 

evidence has yet been found to indicate that these structures affected the localization of deposits. The distribution of known deposits outside the belt but within the 

mapped area suggests that other mineral belts may be 

present in different structural environments. To the 
46 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

south, the Uravan 1nineral belt appears to have crossed 

all major structural features prior to deformation and 

collapse. 

Only two major faults were found in the La Swl Creek 

area., the Dugway fault (pl. 3) which delineates a part 

of the southwest flank of the collapsed Paradox anticline, and the Sharp Canyon fault which is approximately perpendicular to the Dugway fault and is in 

Sharp Canyon southeast of the mineral belt. Both 

faults contain copper oxides and sulfides, for which 

they have been prospected, but neither is known to contain uranium-vanadium minerals, nor do they appear 

to he related to the introduction or locaEzation of uranium-vanadium-bearing solutions in the La Sal Creek 

area. 

Only two deposits within the La Sal quadrangle are 

known to be associated with faults; the Valley View 

deposit (sec. 7, T. 48 N., R. 19 W.) adja-cent to the Valley View fault, and the Ja-ckpot deposit (sec. 2, T. 48 

N., R. 20 W.) close to a fault subsidiary ·to the Valley 

View fault. The VaHey View deposit is in strata of the 

ore-bearing sandstone of the Salt Wash Member of the 

Morrison Formation. Part of the deposit lies in beds 

that have been fractured and dragged upward at ·a steep 

angle, but otherwise the deposit displays characteristics 

common to other Salt Wash ore bodies. The association 

of the deposit to the fault is thought to be hruppenstance; the deposit existed prior to faulting and was 

intersected by the fault. The deposit is more fully discussed on page 67. 

The Jackpot deposit is in highly fractured Wingate 

Sandstone adjacent to a fault. The deposit consists 

principaHy of oxidized uranium-vanadium minerals 

coating fracture surfaces. The cmnponents of the ore 

were probably carried there by ground water from one 

or more nearby deposits. The Jackpot is the only 

known deposit in the La Sal quadrangle that is fault 

controlled. This deposit is discussed more fully· on 

page 62. 

Joints are common, as can be seen on the accompanying mine maps. Two dominant joint sets are apparent 

and are related to the folds and faults in the area. 

Joint diagrams for individual mines show that there 

is little relationship between the joints and trends of 

ore bodies. Secondary minerals such as carnotite, tyuyamunite, hewettite, and pascoite are found on joint surfaces in both the oxidized and unoxidized deposits, and 

appear to have been transported by Recent groundwater movements. 

MINERALOGY 

The uranium-vanadium deposits of the La Saf Creek 

area are composed of fine-grained mineral aggregates 

which fill pore spaces in sandstone, and coat and locally, partly replace sandstone. These aggregates are considered ore grade when they occur in rock 1 foot or more 

thick that contains 0.10 percent or more UaOs and (or) 

1.00 percent or more V 20 5. Rock containing less than 

this amount but containing 0.02 percent or more UaOs 

and (or) 0.10 percent or more V205, regardless of thickness, is considered mineralized. In this study, rock 

from drill cores and hand samples containing as little as 

0.02 percent U30 8 or 0.20 percent V205 was recognized 

and chemically ana1yzed. In some places the presence 

of these trace amounts led to discovery of minable ore 

bodies. 

The deposits of the La Sal Creek area are rich in 

vanadium oxide which on the average is approximately 

six times more abundant than uranium oxide. V anadium: uranium ratios differ considerably from deposit 

to deposit and range from 4: 1 to 14 : 1 parts V 205 to 

U 30 8 • Studies of ore samples collected from several of 

the mines have recently been completed by A. D. Weeks, 

M. E. Thompson, and others of the U.S. Geological 

Survey. Weeks (written commun., 1957) indicates that 

this predominance of vanadium over uranium in the 

La Sal Creek area is reflected in the mineralogy, and 

that the vanadium silicates are more abundant than 

other vanadium, uranium, or uranium-vanadium 

minerals. 

Minerals that have been either tentatively or positively identified in the deposits of the La Sal Creek 

area and vicinity and the mines in which they were 

found are listed in table 1. Details of these occurrences 

are given in the discussion of individual mines. The 

assemblages shown for the various mines are probably 

not complete because positive identification of many 

uranium or vanadium minerals by megascopic methods 

is nearly impossible, owing to the close similarities in 

crystal form, color, and mode of occurrence. The time 

alloted to underground mine studies allowed only selective sampling of the various ore bodies by visual inspection. 

As a whole, the suite of minerals comprising the ore 

is large, but in certain mines the assemblage is small. 

Two factors may be responsible for this difference between individual deposits: differences in the original 

chemistry of the deposits, or differences in the degree 

of oxidation to which the ore minerals of the deposits 

have been subjected. 

Details of the original chemistry of the deposits and 

their wallrocks are not thoroughly known, although 

much study has been devoted to the mineralogy and 

trace-element composition and distribution of Colorado 

Plateau ore deposits. The composition of the mineral 

assemblages of certain deposits apparently reflect the 

proportions of metallic constituents present in the orig-
URANIUM DEPOSITS 47 

TABLE 1.-Minerats identified in ores of the La Sa~ quadrang~e, and their vanadium-uranium ratios 

[?, tentative identification) 

Mine and its V10o: U ,o, ratio (in parentheses) 

~ ;:::;- ~ 

~ ~ ;:::;- ~ e ;:::;- ~ 

~ e e ;:::;- e ;:::;- -o ~ 

<=I ;:::;- "' e ; ?i ~ Mineral ;:::;- ~ "' "' ~ :>. ~ ~ ~ "' " e 0 ~ e ::::, " ~ tl. .!'l .!'l " ~ c ::::, <=I ~ Cll ~ 

t:. ~ ~ "' :; 8 ;:::;- ;:::;- ~ a ~ ~ " ~ !i.i § i ... e <=I il: c t:. il: "" ~ "" ~ '" ~ "" e <=I s «: ~ en .9 ~ 8 <=I .!:I 

~ ~ ~ <=I p:; "' "' 0 " "" "" s "' ~ p:) 

~ 0 e .. "' A ~ "' t:. ~ ... .!:I' .a ... "' :>. :>. ·o; .8 :!., A 

~ -o P< ~ .8 gj .a C!:l " :;: il: ~ ,. "" "" .E :>. "' " ~ :>. "" s ~ :>. 

"' "" "" <=I ~ :>. ,. ~ ~ "' <> !l :§ "' gj § ~ ~ ~ "' ,. :;::; <> ·~ "' il: 8 0 <=I "" "' <=I "' 0 "' <> 

~ ~ "' "' 0 z "' 0 

«: ~ ~ ~ 0 i4 Iii ~ ~ ~ "' ...:l ::s ~ ~ Cll 8 p ~ ~ ~ :;: ~ - --- - - - - - - - - - - - - - - - - - - - - - - - - Uranium minerals 

Boltwoodite ___ ______________________ _______ ___ ---- ---- ---- ---- ---- ---- ---- ---- ? ---- -- -- ---- ---- ---- -- -- ---- --- - ---- ---- ---- ---- --- - ---- ---- - --- ---- Carnotite ___ ______ _____ ___________ ____________ X ---- X X X X X X X X X X X X X X X X X X X X X X X X X 

Coffinite _____ ______ ______ __ __________ _________ ---------------- ---- ---- ---- X X ---- ____________ ---- ________ ---- ---- ---- ---- ---- ? X ---- ---- ----

Gummite. ------------------------------------ ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ? ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- --- - Phosphuranylitc ___ _____ _________ ___ ______________ ________ ---- ____ ---- ---- ---- X ___ _ ___ _ ____ ---- ____ ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- Rauvite _____________ ___________________ _______ ____ ---- ---- ---- ---- ---- ---- ---- ---- ____ ---- ---- ? ---- ---- - -- - ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- Schroeckingerite. ----------------------------- ____ ____ ____ ? _____ ___ ___ _______ _______ ___________ ____ ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- Saleeite-novacekite ___________ ____ _____________________________ ____ ___ _________ x __ ________ ________ _________ _______ ___ ___ ______ _________________ ____ _ Torbernite (or meta-) ___ _____ _______ ___ ____ ___ ____ ---- ____ ---- ________________ X __________ __ ---- __ __ ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- Tyuyamunite (or meta-) ______________________ X ---- X X X X X X X X X X X X X X X X X X X X X X X X X Uraninite ____ ______ ___ ___ ________ _______ ___ ___ ---- X ---- ____ ___ __ ___ ___ _ X X ________ ____ __ __ ____ ____________ ---- ---- ____ ____ ? X ---- ____ ----

g~:~~~~~~~~~~~~~~-s: ::::::::::::::::::::: :::: :::: :::: :::: :::: :::: :::: :::: ~ :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: Beta-uranophane ... ---------------------- ___ _ ____ ____ ____ ____ ____ ____ ____ X _______________ _ _____ ___ _________________ __ __ __________ _ ___ _ ____ __ _ _ Uranospathite ____ __ __ _____________________________________________ ---- ---- ____ X ______ ___ ___ __ ______ ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- Metazeunerite __________ __ ___________ ____ ____ _ ____________ ____ ____ ____ ________ X ___________ _ ____ __ __ ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----

Vanadium minerals 

Corvusite.------------------------------------ ---- X ____ ____ ---- ---- 1 X X __ __ ---- ____ ? ---- ___ _ ____ ---- ---- ---- ---- ---- ? X ____ ---- ---- Doloresite____ ____ __ __ _____________ ____________ ____ ? ____ ____ ____ ____ ? ? ? ____ ____ ____ ? ____ __ __ ____ ___ _ ____ ____ ____ ____ ? ? __ _________ _ 

Fervanite _____ ____ ________________ _____ ______ _ ---- ---- ---- ---- ---- ---- ? ? ---- ---- ---- ---- ---- ? ---- ---- ---- ---- ---- ---- ---- ? ---- ---- ---- Hewettite ____ __________ _______ ________________________________________ X X ___ __ ______ _ ____ ________ ____________________________ X ______ __ ___ _ 

Metahewettite_______ __ _____________ ____ __ ____ ____ ____ ____ ___ _ ____ ? ____ X ____________ ___ _ ____ ---- ---- ---- ---- ---- ---- ---- ---- ? ---- ---- ---- Hummerite. ---------------------------------- ____ ____ ____ ____ ____ ____ ____ ____ ___ _ __ __ __ __ __ __ ____ ____ ____ ____ ____ ___ _ ____ ____ ___ _ ____ ___ _ ____ ____ ____ ? Melanovanadite __ ___________________________ __ ________________ ___ _ ____ _____ __ _ __ __ __________ __________________ _______ _ ---- ---- ---- ____ X ____ ---- ___ _ 

Montroseite .... .. ·----------------------------- ____ X ___ _ ___ _ ____ ____ ____ X X ? _______________ _ ___ _ ________ ---- ---- ---- ---- X X ---- ---- ---- X 

Paramontroseite __ ____ _________________ ___ ---- ? ____________ ---- ---- ? ? ? __ __ ____________ ---- - --- ---- ---- ---- ---- ---- ? ? ---- ---- ---- 'I Nolanite ___ ________ ____ ____ _______________ ____ ___ __ ___ ____ _____ ___ _____ ____ ___ ___________________________ _ ______ __ ____ ____ _____ ____ ___ X ___________ _ 

Pascoite ______________ _____ _______ _____ ________ ---- ---- ---- ---- ---- ---- ---- ? ? ? ---- ---- ? ---- ---- ---- ---- ---- ---- ---- ---- ? ? ---- ---- ---- ? Roscoelite __ ______________________ _________ ____ X X ? ? X ? X X X X ? X X X X X X X X X X X X X X X X 

Simplotite. ----------------------------------- ______ _________ _ ____ __________________________ __ _____ ______ _ ____________ ---- __ __ ---- ___ _ X ________ ---- Vanadium hydromica ___________________ __ __ __ X X X X X X X X X X ? · X X X X X X X X X X X X X X X X 

Accessory sulfide minerals 

Chalcocite__ ________________________ __________ ____ ____ ____ ____ ___ _ ____ ___ _ __ ___ X ______ ___________ ______ ____ ________ _ ---- ---- ---- ________ ---- ---- -- --

8f r~~;n~~ :::::::::::::::::::::::::::::::: :::: :::: :::: :::: :::: :::: :::: ·x· :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: Covellite ________ _______________________ ______ ___ ___ _____ ____ __ ________________ X ____________ __ __ ____ ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- Galena_____ ______ _____________________________ ____ ____ ____ ____ ____ ____ ____ X X ___ _ ____ _____ __ _ ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- Pyrite ___ _______________________ ____ ____ ______ _ ____ X ____ ---- __ __ ____ ____ X X ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- X ---- ---- ----

~~~l:~~:i~e:: :::::::::::::::::::::::::::: ::::: :::: :::: :::: :::: :::: :::: :::: ·x· -~- :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: 

inal ore solution or possibly a composite of several solutions which have in one way or another affected the 

deposits. 

Individual deposits can be classified as being either 

oxidized or unoxidized, although each may display 

various degrees of oxidation. The greatest mineral assemblage is in deposits that contain both unoxidized and 

oxidized ore minerals. (See Gray Daun mine, table 1.) 

Oxidation and leaching may be partly responsible for 

the ratio of vanadium to uranium, for those deposits 

having the 'highest ratio generally have the smallest 

mineral assemblage and are, in general, in the eastern 

part of the area wher~ uplift of the Paradox anticline 

and headward erosion of La Sal Creek first exposed the 

ore-bearing sandstone and caused a subsequent fall of 

the water table. Here the beds dip toward La Sal 

Creek canyon, which affords an outlet for ground water. 

In contrast, most of the deposits that have low ratios 

of V2 0 5 to U3 0 8 are either deeply buried or lie near 

the head of La Sal Creek canyon where exposure of the 

ore-bearing sandstone has been limited. 

Oxidized ore consists largely of vanadium hydromica 

and finely disseminated carnotite and limonite. ·where 

carnotite and limonite are sufficiently concentrated to 

impart a speckled or spotted appearance to the rock, it 

is referred to as "rattlesnake ore." Oxidized ore was 

I 

found in the New Yellow Spot, Marjorie Ann, Evening 

Star, Yellow Bird, and adjacent mines at the eastern 

end of the La Sal Creek mining district. 

Examples of deposits little affected by oxidation are 

in the Black Hat, Firefiy-Pigmay, and Vanadium 

Queen mines, where the ore is almost unoxidized, and 

in the Gray Daun mine which contains both unoxidized 

and oxidized ore minerals that represent the entire oxidation sequence. In the first three mines the ore-bearing sandstone lenses are saturated with ground water 
48 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

which appears to have been trapped by impervious 

layers of mudstone that enclose the lenses. The ore is 

bluish black, greenish black, an off shade of black, and, 

in places, brown. The brown material may be partly 

oxidized. The unoxidized ore minerals a.re roscoelite, 

vanadium hydromica, coffinite, and uraninite. Sparse 

amounts of metallic sulfides a.re associa-ted with the 

uranium minerals. The most abundant of these is pyrite, in places closely associated with lesser a-mounts of 

chalcocite, chalcopyrite, galena, covellite, and tennantite. Minor a-mounts of the selenide, clausthalite, have 

also been identified. 

In the Gray Daun mine around unoxidized ore bodies 

there is an ill-defined zone of pa-rtially oxidized vanadium and uranium minerals. The vanadium minerals 

include montroseite, doloresite ( ? ) , paramontroseite, 

corvusite, and traces of simplotite a.nd melanovanadite. 

The uranium minerals include the uranyl phosphates 

torbernite, metatorbernite, and phosphuranylit.e, the 

ura.nyl arsenates meta.zeunerite and saleeite-novacekite, 

and the uranyl silicates uranophane, beta-uranophane, 

and a mineral resembling boltwoodite (A. D. Weeks, 

written commun., 1957). Mrs. Weeks describes a black 

substance, resembling coalified wood, that gives an 

X-ray pattern unlike uraninite and which she believes 

may represent "an amorphous phase in an oxidation 

stage between uraninite and the uranyl minerals." Minerals that represent a more advanced state of oxidation 

occur in the partly saturated parts of the deposits. 

The most highly oxidized deposits, those between 

Lion Creek and Ice Lake canyons and of the Yellow 

Bird groups of mines, are in beds that are covered by 

little or no overburden and that dip gently toward La 

Sal Creek canyon. In these the dominant ore minerals 

are roscoelite, vanadium hydromica, carnotite, and tyuyamunite, and minor amounts of fervanite ( ? ) , hewettite, and metahewettite. Most of the metallic sulfides 

have been oxidized to hematite and limonite which 

form a brown stain on sand grains. In a few places the 

copper sulfides have been oxidized to azurite and malachite which occur as spots within the sandstone and as 

coatings on sand grains. 

A sample of an ore roll surface marked by two parallel bands of clausthalite and an unknown mineral (fig. 

9) was collected from the Firefly mine. An inner band, 

adjacent to the ore, is separated from an outer band by 

5 to 10 mm of mineralized sandstone; both ba.nds cut 

across the bedding. They separate barren to weakly 

minera-lized sandstone from blue-black ore composed 

mainly of finely disseminated coffinite, montroseite, and 

corvusite. The isotopic analyses of the clausthalite 

agree with the ana-lysis of galena in the Cashin mme 

as shown in ta.ble 2. 

FIGURE 9.-Parallel bands of clausthalite and an unknown 

mineral along roll surface separating sandstone oontaining 

ore-grade material (upper right) from barren and sparsely 

mineralized sandstone (lower left). Sample WDC-148 from 

Firefly-Pigrnay mine, San Juan County, Utah, collected by 

J. C. Warman. Letters refer to figure 10. 

TABLE 2.-Isotopic analyses of clausthalite and unknown leadvanadium mineral from the Firefiy-Pigmay mine and galena 

from the Cashin mine 

[Analyses: Firefly mine, by Union Carbide Nuclear Corp. Y-12 Plant, Oak Ridge Tenn. The values are believed to be correct to 0.5 percent. Cashin mine, by L. R. 

Stieff and T . W. Stern, U.S. Geological Survey, Washington, D.C. These values are believed to be correct to 1.0 percent] 

Firefly mine: Pb'" Pb206 Pb"' Pb'" 

Inner band unknown 1. 35 26. 21 21. 03 51. 40 

mineral. 

Outer band clausthalite ____ - 1. 35 25. 21 21. 04 51. 65 

Cashin mine: 

Galena_ _______ _________ __ 1. 32 27. 14 20.84 50.70 

Steiff and Stern (written commun., 1956) state that 

the similarities of enrichment in radiogenic lead (Pb206 , 

Pb207 ) relative to nonradiogenic lead (Pb204 ) and the 

Pb204 : Pb208 ratios with other such samples from the 

Colorado Plateau suggest that all are related in time 

(Tertiary) and possibly in source. 

Spectrographic analyses of the two clausthalite bands 

show significant differences in composition (table 3). 

TABLE 3.-Semiquantitative spectrographic analysis of clausthalite 

(outer band) and unknown lead-vanadium mineral (inner band) 

from the Firefly-Pigmay mine 

[Analyst, Mona Frank] 

Content (percent) Outer band 

>10 ________ __ _ Pb, SL_ __________ _ 

5-10 __________ _ 

1-5-- ---------- Se, AL __ ___ ______ _ 

.5-1 ___ _______ _ v ______ __________ _ 

. 1-. 5- --------- K, Fe, Mg __ ______ _ 

. 05-. L __ _ - _--- Ag, Co, Cu, As ___ _ _ 

. 01-. 05- - -- - - - - Cr, B, Na, Ca, Ti, 

Mo 

. 005-. Ql_ ___ __ _ Ba, Zr _____ ______ _ 

. 001-. 005 _____ _ Mn, Sr ______ ___ __ _ 

. 005-. 001_ - --- -

Inner band. 

Si, Pb 

V, Al 

Fe, K, Mg 

Ag, Cu 

Ti, As 

Ba, Ca, B, Sr, Co, 

Na 

Cr, Zn, Zr 

Mo, Be, Mn 

Sc 
URANIUM DEPOSITS 49 

The most obvious difference in the element composition of the bands is that the outer contains selenium 

and the inner has none. The outer band also contains 

more lead. The inner band, on the other hand, is richer 

in silica, vanadium, iron, potassium, magnesium, silver, 

copper, and minor elements. The substitution of vanadium for selenium suggests that an unnamed leadvanadium-silicate, resembling clausthalite in outward 

appearances, may be present. Comparison of photomicrographs shows that the quartz grains within the 

inner band (fig. lOA) are irregular in shape and widely 

separated and embayed by uranium and vanadium minerals. Traces of quartz grains, almost entirely corroded, are represented by pale shadows in the black 

areas. Outside the outer band (fig. lOB) the quartz 

grains are closely spaced and in shapes typical of ordinary sandstone. Embayments of the quartz grains 

occur along the edge and within the band. These relations indicate that the ore-bearing solution exsolved 

silica from quartz which, in turn, combined with lead, 

uranium, and vanadium to form the inner vanadiumrich lead-silicate band, coffinite, montroseite, and probably other uranium and vanadium silicn,tes. 

The unoxidized minerals, in general, appear to have 

formed at approximately the same time. In detail, 

however, pyrite and possibly son1e galena apparently 

formed first in decaying woody material. The woody 

material was then impregnated by uraninite and coffinite (fig. 11) which also appear to have corroded and 

filled embayments along the edges of the pyrite. Some 

of the pyrite was also replaced by other sulfides (fig. 

llB), such as chalcocite, sphalerite, chalcopyrite, and 

covellite, but it is uncertain whether this replacement 

took place before, during, or after the emplacement of 

uranium. Table 4 summarizes the apparent paragenetic 

sequence of the minerals identified in the ore depm:dts 

of the La Sal Creek area. 

ORIGIN 

The genesis of uraniferous ore deposits in sedimentary 

rocks and especially of those in fluvial sandstone or conglomerate beds of the Colorado Pl'ateau is highly controversial. Both syngenetic and epigenetic sources and 

under these a wide variety of hypotheses have been 

postulated as possible origins for these deposits. None, 

however, have been considered entirely satisfactory or 

unanimously accepted by students in this field. An excellent review of these variQIUs hypotheses and the problems that remain has been presented by McKelvey, 

Everhart, and Garrels (1955, p. 4-64-533; 1956, p. 41-

53). They conclude that the Colorado Plateau and "\iVitwatersrand deposits are epigenetic and were formed 

A 

B 

FIGURE 10. Clausthalite bands in sandstone. Photomicrographs 

in plane light. A, Inner bands (dark area) showing corroded 

quartz grains (light) surrounded by unoxidized uraniumvanadium ore. B, Outer band, in barren to weakly mineralized sandstone: quartz grains (light) are corroded along 

margin of clausthalite band (dark area). See figure 9. 

from deep-seated solutions probably emanating from 

igneous rocks that, ror the most part, did not reach the 

surface. 

Because studies in the La Sal quadrangle were limited 

in area and scope, the following discussion is limited 

to presenting field evidence, results of detailed studies, 

and ideas that have been formula/ted which either support or oppose the syngenetic and epigenetic hypotheses. 

Any hypothesis of the origin of uranium-vanadium 
50 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

TABLE 4.-Apparent paragenetic sequence of uranium, vanadium, 

and accompanying sulfide minerals 

Mineral Sequence 

Unoxidized (primary?) Oxidized (secondary?) 

Uranium minerals 

Boltwoodite(?) ______ ___________ _ Carnotite (U+6) ____ ___ _____ ____ _ Coffinite (U+<) ____________ __ __ _ _ ?--

Gummite ___ -------------------- ?-- Phosphuranyllte ________ __ ___ __ _ Rauvite(?) (U+6) ____ _________ __ _ Schroeckingerite(?) _____________ _ ?- SalMite-novacekite _____________ _ 

Torbernite (or meta-) ___ -------- ?-- Tyuyamunlte (or meta) (U+6) __ _ ?'------ Uraninite (U+<) ______________ __ _ ?-- Uraninite (amorphous) _______ __ _ Uranophane ___________ _________ _ Beta-uranophane ____ ______ _ _ Uranospathite ________ ____ _____ _ _ Metazeunerlte _____ _____________ _ 

Vanadium minerals 

Corvuslte (VH) ________________ _ Doloresite(?) (V+<) _________ ___ _ _ Fervauite ___ ------- ____ ________ _ Hewettlte (V+5) ________________ _ Metahewettlte (V+s) _________ _ Hummerite(?) __________________ _ Melanovauadlte ___ _____ _____ __ _ _ --?-- Montroseite ________________ • ___ _ Paramontroselte _____ ___________ _ N olanlte(?) ________________ _____ _ 

Pascoite (V+•l------------------- Roscoellte (V+3) _______ ___ _______ -- Simplotite (V+<) ___ _____ ______ __ _ --?--

Vanadium hydromlca (V+3) _____ --

Acceuory sulfide and selenide 

minerals 

Chalcocite -------------------- -- Chalcopyrite ___ ______________ __ _ Clausthalite ___ _______ _____ ____ _ _ 

Covelllte ____ ----------- ____ ____ _ Galena: 

Nonradlogenic ____ ---------- Radiogenic ________ ___ ______ _ Pyrite ___ __ ______ ____ ___ _________ -- Sphalerite ___ __ __ __ __ ____ __ _____ _ Tennantite __ ___________ -____ ----

Time---~ 

deposits in the La Sal quadrangle must take into account 

the following geologic evidence : 

1. The areal distribution of uranium-vanadium deposits is restricted largely Ito defineab'le linear 

zones or belts that cross and appear to be independent of major tectonic :features. 

2. Most of the deposits show no obvious relation to 

local igneous rocks or w fissure veins which respectively could have served as source and conduits for hypogene solutions. 

3. Uranium and vanadium minerals have not yet been 

found in veins cutting the igneous and sedimentary rocks of the La Sal Mountains, although 

veins carrying copper and lesser amounts of gold 

and silver have been mined. 

4. Radon, however, has been reported by Hunt ( 1958, 

p. 356, 358) from the Dillon and McCoy ad its of 

Mineral Mountain of the North Mountain group. 

Radioactivity in the igneous rocks is highest 

( abou:t three times background) in the youngest 

B 

FIGURE H.-Photomicrographs of a polished section of ore from 

the Gray Daun mine; specimen contains uranini:te (u), coffinite (c), pyrite (p), and chalcocite (ch) ; galena, chalcopyrite .and covelli:te ore also pres·ent bu't not shown. A, 

Uraninite and coffinite replacing cellular structure of wood 

and surrounding corroded sulfide m~nerals. B, Pyrite replaced 

by chalcocitte, embayed and surrounded by uranini'te and 

coffinite. 

intrusives (soda syenite porphyry) (Hunt, 1958, 

p. 338), but commercial deposits are lacking. 

5. The uranium-vanadium deposits are restricted stratigraphically to certain parts (paleochannels) of 

specific sandstA>ne layers at the top of the Salt 

Wash Member and near the ba:se of the Brushy 

Basin Member of the Morrison Formation. 

6. The ore-bearing sandstone units are believed to have 

been derived from erosion of older rocks along 
URANIUM DEPOSITS 51 

the southwest margin of the Colorado Plateau. 

These older rocks are largely granitic and contain 

hydrothermal veins of uraninite ·(Gruner, 1956). 

7. The deposits consist of clusters of tabular, wedgeshaped, roll, and pod -shaped ore bodies enclosed 

in porous crossbedded sandstone lenses that are 

underlain, overlain, and interbedded by less permeable green mudstone layers, seams, and pellets. 

8. Core sample, mine, and outcrop studies shaw thak 

areas favorable for the occurrence of ore deposits 

are where the sandstone lenses are thickest (30 to 

100 feet) and cleanest (white, light brown to light 

gray) and have litJtle interstitjal clay. Unfa.vorable areas are marked by thinner, finer grained 

sandstone perm8ated with reddish-brown interstitial clay. 

9. Sandstone in favorable areas is permeable. Grain 

size varies locally and ranges from medium coarse 

to very fine. The average grain size is medium 

fine. In unfavorable areas, the sandstone is less 

permeable owing to finer grain size and the 

presence of interstitial clay. 

10. Ore bodies are closely associated with and may eontain carbonaceous material eapahle of creating a 

reducing environment. In places, ore minerals 

replace carbonaceous material; in other places, 

carbonate matrix is replaced. Corrosion of 

quartz grains has been noted. 

11. Both oxidized and unoxidized uranium and vanadium minerals may comprise the deposits, and in 

places these minerals are associated with minor 

amounts of iron, copper, and lead sulfides and 

with traces of lead selenide. 

12. Selenium has been noted in North Mountain by 

Hunt (1958, p. 338) who noted that it was most 

abundant in hydrothermally altered rocks having 

the highest content of copper, lead, and zinc. It 

was also found in the Fire:fly-Pigmay mine as 

cia usthalite. 

13. Age determinations based on ratios of radiogenic 

and nonradiogenic lead as well as Pb206 : U238 

ratios of uraninite indicate that the ore minerals 

formed during Late Cretaceous to early Tert.iary 

time. Strat.igraphic evidence and zircon age 

determinations indicate that the La Sal Mountains 

formed ·a;t the same time. 

Paragraphs 1, 2, 3, and 6 above favor a syngenetic 

origin, whereas 4, 11, 12, and 13 favor an epigenetic 

process. The remaining four paragraphs ( 5, 7, 8, and 

10) are amenable to bath processes. This equal division 

of the evidence presented here suggests to the authors 

tha!t the uraniwn-vanadium deposits were probably 

formed by a ·series of events employing both processes. 

The distribution and localization of uranium deposits 

in the Plateruu, and partieularly those of the La Sal 

Creek mineral be1t, appear to have lbeen independent 

of tectonic structural features. The zonal 'OT halo a.rrangement of deposits around laocolithic intrusives described by Reinhardt (1952) and Shoemaker (1954, 

written commun.) is, in the opinion of the authors, more 

apparent than re·al. 'Recent discoveries (1955) of uranium-vanadium ore in the Salt Wash Member west of 

La Sal Pass and on the east side of Mount Mellenthin 

show that the deposits near igneous rock ·a;re almost 

the same in mineral content, physical cha.racteristics, 

and stratigraphic position as deposits fa:rther away. 

The authors believe that the postulated zonal arrangement merely reflects the fact that, in most places around 

the La Sal Mountains the ore-bearing strata are either 

deeply buried by Cretaceous and younger sedimentary 

rocks or, where they crop out., are poorly exposed; because of this sparsity of exposures, ore deposits appear 

widely separated. Physical conditions making access 

difficult have been a major deterrent to prospecting and 

e~ploration on the mountain :fl·anks. Several exposures 

of the Salt Wash ore-hearing sandstone found in mapping the mountain region indicate that there may be 

several other favorable ·areas simila.r in orientation ~and 

areal extent to that of the La ·Sal Creek mineral belt. 

The almost complete absence of hydrothermally altered material in the sedimentary rocks surrounding the 

dioritic rocks of the La Sal Mountains, which are believed genetically related in time to the uranium and 

copper ores, indicates that most of the magma was 

highly viscous and probably lacked volatiles. The fact 

that contact metamorphism is restricted to narrow zones 

around the igneous rocks indicates that the temperature 

of the magma was low but somewhat greater than that of 

the surrounding rocks. Evidence of hydrothermal alteration around the ore deposits is either lacking or has 

not yet been recognized. Estimates of the geothermal 

gradient based on information compiled by Hodgman 

and others ( 1955, p. 3088) indicate that prior to uplift 

and erosion the ore-bearing sandstone of the Salt Wash 

was covered by about 7,000 feet of rock and probably 

had a minimum temperature of 46°C. The ore zones of 

the Chinle Formation were covered by about 9,000 feet 

of rocks and probably had a temperature of at least 

60°C. McKelvey and others (1956, p. 46) believe that 

host-rock temperatures may have been as high as 120°C, 

and pressures from 200 (hydrostatic load) to 800 atmospheres (lithostat:ic l•oad) at the time the uraniumvanadium deposits were formed. Although these tempera:ture estimates are admittedly crude, they are, according to Bateman (1951, p. 101) and others, within 

the lowest temperature range ( 50°C) of water that is 
52 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

commonly considered to be hydrothermal. It is probable .that igneous intrusion and pressure of tectonic 

forces increased the temperature of the stratified rocks 

and connate ·water into ranges that are considered hydrothennal. Such a process may explain the presence 

of certain sulfide minerals in uranium-vanadium deposits that are believed to have formed at ·temperatures 

as high· as 158°C (R. C. Cqleman, oral commun., 1955). 

The absence of the alterati,on products commonly round 

in low-temperature hydrotherm·al veins, with the exception of kaolinite and chlorite noted in some uranium 

deposits, suggests that the temperatures of the host rock, 

intrastratal solution, and ore-bearing solution (if these 

two solutions were separate) were approximately the 

same. Thus, temp-e.ratures due to the depth of burial 

and perhaps slightly raised by tectonic forces may have 

played an important role in the mineralizing process, 

as indicated by the presence of ·certain metallic sulfides 

in deposits of both the Chinle and Morrison For:m•ations of the Colorado Plateau. The authors belie.ve, 

therefore, that uraniferous deposits of the plateau may 

have been "hydrothermal" only in the sense that, at the 

time the deposits we·re formed, the temperatures of the 

water-saturated sedi·mentary rocks were in the ranges 

a:scrib-e.d as hydrothermal. 

Hypogene solutions may al'Sio have :been active in the 

area at this time. They probahly rose along the earliest 

faults which formed as a result of tensional stresses 

during folding. The minerals believed ·to be derived 

from such solutions appear to be restricted to fault zones 

and associated fracture Zlones that are rarely more than 

30 f~t wide. Several of the major faults in and near 

the marpped area have brecciarted zones containing minruble deposits of argentiferous copper. The most notable 

of these is the Cashin Copper .mine, 3 miles east of the 

La rSal quadrangle, which contains cuprous sulfides in 

the Wingate and native silver in the underlying Chinle 

Fomnation. The ore minerals generally occur as vein 

fillings, but, in places, chalcopyrite has replaced the 

sandstone host rock (Fischer, 1936, p. 572). 

Sa1nples of galena from the Cashin vein were analyzed by L. R. Stieff and T. W. Stern (written commun., 

1956) who stake thart the isotopic compositions ( tha:t is, 

radiogenic and nonradiogenic lead) are present as 

follows: 

Atom 

Isotope percent 

Pb204 ----------------·------------- 1. 32 

Pb200 ----------------------------- 27.14 

P:b207 ----------------------------- 20. 84 

Pb208 ----------------------------- 50.70 

This analysis shows that the sample is su'bst:antially enriched in Ph206 and Pb207 and has a ratio of Pb204 to 

Pb208 similar to that of most of the Colorado Pla:tea,u 

galena sa.mples. On the basis of this evidence Stief£ and 

S'tern reason that the lead in the sample is related in 

origin to that in other samples occurring in the uranium 

ores in the Triassic and Jurassic formations. 

The Pb206 : U238 ratio of a sample of u~anini:te and 

coffini'te from t'he Gray Daun mine collected by Rasor 

(1952, p. 89-90) was ·also analyzed by Stieff and Stern 

(written commun., 1956). They state that "the age 

is 65 million years and is believed to be correct within 

10 percent of the true age of the uraninite. This agrees 

well with dther ages on superior material from the 

plateau." 

These age determinations are not incompatible with 

those derived by H. W. Jaffe 'in rthe study of zircon contained in the porphyry masses of ~the La Sal Mountains 

or with structural and stratigraphic relations. observed 

in the mapped area. It appea.rs, therefore, that the 

dioritic phase 'of the la.ccoHt:hic intrusion, regional folding and faulting, and ~the crystallization of quadrivalent 

uranium in the Morrison Formation ·and of sulfide8 ~n 

nearby vein deposits were contemporaneous and proba;bly took place in Late Cretaceous or early Tertiary 

time. This evidence and the presence of 'Similar accessory minerals in both the uranium and ·copper deposits 

lend greatest support to a hypogene origin but fail to 

exphin, at least locally, the absence of uranium and 

vanadium in the nearby argentiferous copper vein deposit.s. In 1956 the authors and Theodore BdtineHy 

of the U.1S. Geological Survey discovered minor amounts 

of radioaetive material in carbonaceous matter, presumed to ·be a:sphaltite, associated with native silver in 

the lowe·r workings of the Cashin mine. This occurrence 

may eventually shed some light on the p~oblem of 'Origin 

of the uranium. 

Though the approximate time of crystallization of 

the uranium-vanadium and the argentiferous copper 

ores has been established, the source and nature of the 

transporting medium of both types of deposits are still 

obscure. McKelvey and others (1955, p. 505-509) have 

discussed this and other problems involved in considerable detail. They state that at the time of ore emplacement the formations that became mineralized were saturated with water. They also believe that the positions 

of deposits within ore-bearing strata indicate that the 

ore-transporting medium had a density approximately 

the same as that of the pore water. They further suggest that this medium could have been either a liquid or 

a dense gas such as C02 • This reasoning seems to the 

present authors to preclude almost entirely the possibility that petroleum was a transporting agent. Because 

so little is known about the solvent properties of water, 

oil, and dense C02 in elevated temperatures and pressures, McKelvey and others ( 1955, p. 509) prefer to 
URANIUM DEPOSITS 53 

think that the elements concentrated in plateau deposits 

and elsewhere were transported by hydrothermal solutions derived from a hypogene source. 

Although several important aspects of the problem of 

genesis have been ignored here, partly for the sake of 

brevity and partly because of lack of information within 

the mapped area, the authors believe that the following 

conclusions best satisfy the observed field relations. 

The uranium apparently could have been syngenetic 

in the sense that it was derived from the same source 

as the rocks in which it is now contained. Gruner 

(1956, p. 512-513) has indicated the availability of 

uranium in granitic rocks, and the authors believe that 

such a source for plateau ore deposits is feasible. Precambrian granite has been exposed along the margins 

of the plateau at periodic intervals since the late Paleozoic, for several of the formations are derived directly 

from granite and many others are products of reworked 

sediments that had a granitic source area. During 

weathering and erosion of the granitic masses, surface 

waters dissolved uranium, which is extremely . soluble 

and easily leached from such rocks by mildly acidic 

solutions (Hurley, 1950, p. 5; Brown and others, 1953, 

p. 1400). This dissolved uranium was carried in solution as the uranyl ion (U+G0 2 ) +2, or as uranyl sulfate, or 

as carbonate ionic complexes (Garrels and Christ, 1959). 

.Although the pH of the solution may have varied 

slightly from time to time in response to additions of 

materials of different chemical composition, the ionic 

compounds probably remained dispersed within the 

waters. These same waters deposited and saturated the 

sediments that filled the continental basin which occupied the area now referred to as the Colorado Plateau. 

Woody material decays quite rapidly on burial and 

gives oft' H2S (Gruner, 1956). This active decay creates 

a neutral or reducing environment, which appears to be 

reflected by the green mudstone or bleached zone surrounding the deposits. The bleached zone is probably 

the result of removal of Fe20 3 (McKelvey and ·others, 

1955, p. 507). Uranyl ions dispersed throughout the 

static intrastratal solutions in concentrations ranging 

from 0.0002 to 2.0000 ppm (McKelvey and others, 1955, 

p. 467) may have been drawn into the reducing areas by 

electron attraction or differences in pH where they 

formed concentrations of 1,000 ppm and greater. The 

ions nearest the reducing area probably became absorbed 

in and adsorbed by the woody material which acted as 

centers of ion accretion. Those ions traveling greater 

distances were deposited along the margins of such centers. Locally, silica was dissolved from the surface of 

quartz grains composing the sandstone and combined 

with uranium and minor elements to form coffinite and 

other silicates. 

It appears that the concentration process was extremely slow and that these ions may have remained in 

solution until Late Cretaceous time when crustal disturbances initiated folding and igneous intrusion that 

changed the physical and chemical environment of the 

solutions. Such a change may have elevated both temperature and pressure, and precipitated the uranium 

and associated metals. .As folding took place, the connate water began circulating and roll surfaces formed 

at the interface between the mobile water and the water 

containing crystallizing ore minerals. 

MINES 

In 1957 there were 27 mines in the La Sal quadrangle. 

Between 1939 and 1957 these produced a total of about 

75,000 tons of uranium-vanadium ore. Records of production prior to 1939 are incomplete, but estimates and 

records from 1939 to 1944 indicate that a total of about 

12,600 tons had been produced by 1945 (C. W. Livingston, 1945, written commun.) . The ore was mined 

from deposits ranging in size from a few tons to 16,000 

tons and had a combined average grade of 2.02 percent 

V20 5 and 0.32 percent U30s. The grade of the ore 

differs from deposit to deposit. The V205: U30s ratios 

range from 4 : 1 to 14 : 1 and average 6 parts V 205 to 1 

part U30 8 for the total ore produced . 

Most of the mines described are on the benches 

bounding·La Sal Creek canyon (pls. 1, 5) and are included in the La Sal Creek mineral belt. Eight isolated mined deposits lie outside the principal mining 

district but within the mapped area (pl. 5). The ore 

produced from these mines amounts to less than 5 percent of the total production. Most of the deposits are 

contained in the uppermost continuous sandstone layer 

of the Salt Wash Member of the Morrison Formation. 

Three deposits have been mined from a discontinuous 

lens above the ore-bearing sandstone within the Salt 

Wash Member and four deposits are in sandstone lenses 

contained in the Brushy Basin Member of the Morrison 

Formation. The latter deposits range from a few tons 

to 600 tons, have an average production of about 400 

tons, and were the source of less than 2 percent of the 

total ore produced within the mapped area. 

For convenient reference the mines are listed and described in alphabetical order rather than by size, area, 

or stratigraphic position. The geographic location, history of ownership, and production, if known, are included with a description of the workings and stratigraphic and structural relations of the deposits. The 

size, shape, and orientation of the ore bodies are discussed in relation to the features that appear to have 

controlled ore deposition. In some of the mines only 

the more conspicuous minerals are listed. In others, 
54 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

especially those mapped in detail, the minerals and their 

apparent genetic relationship are discussed. These discussions also include the average content and ratio of 

V205: U30s of the ore produced from each mine. 

Eight of the larger mines which were related to or 

resulted from the exploration drilling program conducted by the U.S. Geological Survey were mapped in 

detail on a scale of 1 inch equals 20 feet (pls. 6-13). 

These mines were mapped by two-man teams using a 

modified tape and compass method similar to that described by Forrester (1946, p. 333-340). This method 

is rapid and especially useful in mines where rooms or 

drifts are too small for the use of larger surveying instruments. Vertical sections portraying the geologic 

features were constructed by rna pping the geology of 

the wallrock and projecting it to the line of section. 

ANGLE MINE. 

The Angle mine, shown as the Confusion-Angle mine 

on the map, (pl. 1) is about 2 miles north of Colorado 

Highway 90 along the west rim of Lion Creek canyon 

in sec. 1, T. 47 N., R. 20 W., Montrose County, Colo. 

The claim is one of 26 claims known as the Gramlich 

Group, located on the north side of La Sal Creek canyon 

between Lion Creek and Ice Lake canyons. Most of this 

group of claimso were staked between 1939 and 1941. 

C. W. Livingston (written commun., 1945) states that 

on June 19, 1941., an agreement and deed recorded in 

Book 304, page 36, at the County Recorder's office, 

Montrose County, Montrose, Colo., divides the ownership of the group between Sam V., Irene, and ~John W. 

Gramlich. The Angle claim was one of those deeded 

to Sam V. and Irene Gramlich, who later sold it to the 

U.S. Vanadium Corp. 

The claim lies well within the limits of the· area of 

favorable ground referred to in this report as the La, 

Sal Creek mineral belt. The deposit is within and about 

27 feet above the base of the ore-bearing sandstone of 

the Salt Wash Member of the Morrison Formation. 

It consists of a small ore pod that extends from its exposure on the Lion Creek canyon rim in a westerly to 

northwesterly direction. The workings are an open 

trench and a drift about 100 feet long. The most recent 

working on the claim is an underground drift that extends into the southwest end of the claim from the inclined shaft of the nearby Wedge mine. 

The ore is of the oxidized type and composed dominantly of vanadium hydromica and carnotite which arA 

disseminated as coatings on sand grains and as fillings 

between them. In places these minerals a.ppear to have 

replaced carbonaceous wood fragments. The ore produced thus far averaged 2.60 percent V2 0 5 and 0.70 percent U30s, a ratio of about 4: 1. 

About 100 tons of ore has been mined from the Angle 

claim. A few more tons have apparently been removed 

from the claim through the workings of the Confusion 

and Wedge mines on adjacent claims. 

BLACK HAT MINE 

The Black Hat mine (pl. 1) is 1 mile north of La Sal 

Creek and just west of the Utah-Colorado line in sec. 28, 

T. 28 S., R. 26 E., San Juan County, Utah. The claim 

was staked in1952 by J. B. Crowley of Grand Junction, 

Colo.~ who, in 1954, sold it to the Hardly Able Mining 

Co. of Moab, Utah. In 1956 it was operated by the Blue 

Creek Mining Co. Access to the property is by truck 

road extending from Utah Highway 46; one road turns 

off the highway at the confluence of La Sal and Hop 

Creeks, passes by the Vanadium Queen mine, and winds 

across the north bench of the La Sal Creek canyon to 

the shaft, a distance of 2 miles; the other turns north 

0.2 mile east of the State line and extends to the head 

of Lion Creek Canyon. 

The deposit was discovered in the summer of 1953 

through the diamond -drilling program conducted by 

the U.S. Geological Survey. The deposit was originally 

1nined from a steeply inclined shaft, but in 1957 a drift 

was being driven from the rim. Core samples indicate 

that the ore is contained in the upper part of the orebearing sandstone of the Salt Wash Member. The orebearing sandstone ranges in thickness from 40 to 70 

feet in the vicinity of the deposit. The ore zone occupies 

an interval between 25 and 40 feet above the base of the 

sandstone marked by an underlying layer of green mudstone ranging from 0 to 4 feet in thickness. In places, 

discontinuous green mudstone seams separate the individual sandstone lenses which comprise the ore-bearing sandstone unit. Drilling indicates that the deposit 

is composed of ore bodies that occur as flat tabular layers 

ranging from 0 to 5 feet in thickness. Several of the 

layers of ore locally occur close together and there a 

greater thickness can be mined. 

The ore minerals are closely associated with carbonaceous wood fragments and green mudstone occurring 

as seams and pellets and filling the interstices between 

sand grains. Though the ore minerals have not been 

studied in detail, they appear to be of the unoxidized 

or slightly oxidized type which includes pitchblende, 

coffinite, montroseite, and some melanovanadite and 

corvusite. These minerals occur as disseminations within tlie sandstone and as replacements of carbonaceous 

material. The dark ore minerals and associated carbon 

impart a dark-gray to black color to the sandstone host 

rock. The ore produced through 1956 contained 2.18 

percent V2 0 5 and 0.32 percent U30s, a ratio of about 

7:1. 
URANIUM DEPOSITS 55 

BRUSHY BASIN NO. 1 MINE 

The Brushy Basin No.1 mine (pl. 5) is on the UtahColorado line in parts of sec. 28, T. 29 S., R. 26 E., San 

Juan County, Utah, and in an unsurveyed section in 

T. 6 N~, R. 20 W., Montrose County, Colo. The claim 

was staked in 1952 by W. C. Weaver of Grand Junction, 

Colo. Ore was produced in 1953 by the Great Western 

Uranium Corp. of Moab, Utah. Access to the property 

is by a series of dry-weather truck trails connecting with 

Utah Highway 46 at the Pine Lodge Ranch and extending southeastward across W ray Mesa to the south bench 

where the road turns westward to the claim, a total 

distance of approximately 9.6 miles. 

The workings consist of a single adit that is about 50 

feet long and bears N. 65° W. from the portal whieh is 

on the west side of a dry wash. The deposit is in a thin 

discontinuous sandstone lens about 100 feet above the 

base of the Brushy Basin Member of the Morrison Formation. The lens consists of light-brown fine- to coarsegrained silty sandstone composed of quartz, variegated 

chert, and light-gray mudstone pebbles. Green mudstone layers surround the mineral-rieh part of the lens. 

The ore minerals are oxidized and consist primarily of 

carnotite. The ore is associated with thin carbonaceous 

shale layers that are commonly less than 1 inch thick or 

is contained in a carbonate-rich siltstone layer that 

-ranges from 0 to 2 feet in thickness. The ore layer appears to have had an average thickness of 4 inches, and 

production records indicate that it contained 1.57 percent V20 5 and 0.25 percent U 30 8 , a ratio of 6:1. The 

mine has been abandoned since 1954. 

BRUSHY BASIN NO. 3 MINE 

The Brushy Basin No. 3 mine (pl. 1) lies about 2,000 

feet east of the Utah-Colorado line and the Brushy 

Basin No.1 mine in unsurveyed sec. 10, T. 46 N., R. 20 

W., Montrose County, Colo. It was located by W. C. 

Weaver of Grand Junction, Colo., in 1952. Ore was 

produced in 1953 by the Great Western Uranium Corp. 

of Moab, Utah. Access to the property is by the same 

route that was described for the Brushy Basin No. 1 

mine. 

The workings consist of a shallow open pit that trends 

approximately east and is 300 feet long and 175 feet 

wide. The deposit is in a fine-grained sandstone layer 

that is about 5 feet thick and is about 120 above the 

base of the Brushy Basin Member of the Morrison Formation. The ore layers average 1 foot or less in thickness and cover an area about 200 feet long and 75 feet 

wide. The ore is composed of carnotite, schroeckingerite(? )., and vanadium clay minerals disseminated in 

sandstmie. The average grade is 1.61 percent V205 and 

0.21 percent U 30 8 , a ratio of 6 : 1. The mine was not 

operating in 1957. 

CONFUSION MINE 

The Confusion mine, showi1 as the Confusion-Angle 

mine on the map (pl. 1), in the southwest corner sec. 

1, T. 47 N., R .. 20 W., Montrose County, Colo., was 

originally staked in 1929 by L. J. Gramlich of Paradox, 

Colo., and is part of the group of claims acquired by 

S. V., Irene, and John W. Gramlich in 1941. As of 

1957, it is the property of the lTnion Carbide Nuclear 

Corp., a subsidiary of Union Car•bide and Carbon Covp. 

The mine is on the west rim of Lion Creek Canyon and 

is reached by a truck trail that extends north for -a 

distance of 2 miles from Colorado Highway 90 at the 

Ha;ll Ranch 11;2 miles east of the Utah-Colorado line. 

The workings consist of an open pit and two caved 

inclines connected to a network of underground drifts, 

part of which extend into the Angle claim to the north. 

The open pit, mined between 1942 and 1945, exposes 

ore for a length of 170 feet and a width of 40 to 60 feet 

(C. W. Livingston, written cmnmun., 1945). The ore 

has been mined from two zones in the ore-hearing sandstone unit of the Salt Wash Member of the Morrison. 

The upper zone, in the open pit, lies above a thin bed 

of green mudstone about 30 feet above the base of the 

sandstone. The lower zone is in the lower 10 feet of the 

sandstone. About 2 feet of green mudstone underlies 

this sandstone. The lower zone was mined by the incline and drift method in 1953. 

The ore bodies are tabular, gently rolling deposits 

ranging from 0 to 3 feet in thickness. The roll surfaces 

trend approximately N. 80° W. and were measurable 

a1ong their respective axes for 30 feet or more. The 

ore is of the oxidized type and composed dominantly 

of carnotite and vanadium clay rninerals which fill the 

interstices of the sandstone. The ore contains 2.13 pereent V2 0 5 and 0.47 percent U30s, a ratio of 4: 1. 

The Confusion mine was abandoned at the time this 

study was made. The deposit, however, is well within 

the La Sal Creek mineral belt, and projections of the 

ore deposit may extend westward into the region of the 

Wedge workings (pl. 1) . 

ELRA.Y MINE 

The Elray mine (pis. 1, 5) is in see. 30, T. 47 N., R.19 

W., Montrose County, Colo., on the bench at the east 

end of Wray Mesa which overlooks the south fork of 

Sharp Canyon. Aecess to the mine is by 9.2 miles of 

truck trail which connects with Utah Highway 46 at 

the Pine Lodge Ranch and extends southeastward across 

Wray Mesa. In 1956 the name and ownership were uncertain because the property had changed hands frequently and with each change came a new name. The 
56 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

deposit is believed to have been originally staked as the 

Lucky Strike No. 13 daim. 

The workings are in the upper part of the Salt Wash 

Member of the Morrison Formation at the stratigraphic 

level of the ore-bearing sandstone. Here, however, and 

in the adjacent areas positive correlation is difficult because the ore-bearing sandstone is thin, discontinuous, 

and highly lenticular. The workings consist of a small 

opencut and an underground drift which extends on a 

bearing of S. 65° W. for a distance of 40 feet from the 

edge of the opencut. 

The deposit was mined in an opencut from the edge 

of a lens of thin fine-grained sandstone which trends 

N. 40° E. and pinches out at the portal. The material 

mined in the underground drift consists of carnotite 

in a discontinuous carbonaceous shale seam 4 to 5 inches 

thick, near the top of a lense of green mudstone. The 

green mudstone lens is overlain by reddish-brown mudstone, shale, and siltstone. The mined materia!} contained 1.20 percent Vz05 and 0.19 percent U3 0 8, a ratio 

of 6: 1. 

The deposit is within 1,000 feet of the projection of 

the Sharp Canyon fault, but there is no apparent relation between the two. 

EVENING ST'AR MINE 

The Evening Star mine (pl. 6) is in unsurveyed sec. 

11, NE cor., T. 47 N., R. 20 W., Montrose County, Colo., 

about 1 mile east of the Utah-Colorado 'line. Access 

to the mine is by a steep, winding dirt road that connects with Colorado Highway 90, 1.6 miles to the south. 

The Evening Star deposit was discovered by wagon 

drilling conducted by J. W. Gramlich who began production in 1950. During 1956 and 1957 it was leased 

and operated by the Four Corners Uranium Corp. 

The ore deposit is in the upper part of the Salt Wash 

Member of the Morrison Formation, the relatively continuous sandstone unit previously referred to as the orebearing sandstone (p. 12). The unit is a medium- to 

fine-grained sandstone containing interstratified lenses 

of reddish-brown or green mudstone. At the mine the 

sandstone ranges in thickness from about 60 to 70 feet. 

The mine is divided into two workings (pl. 6). The 

northeast workings (Incline No. 1) consist of an inclined shaft connected to several irregularly trending 

drifts which in places are broadened into rooms as much 

as 40 feet wide. The workings cover an area roughly 

375 feet long and about 340 feet wide. 

The southwest workings ('Incline No. 2), are entered by a short incline and consist of a maze of meandering drifts ai1d rooms that extend over an area 320 

feet long and 240 feet wide. The extreme west end of 

the workings is a single drift that is inclined downward 

20 feet below the main level. This area was being mined 

at the time the mine was mapped. Both workings are 

virtually free of ground water. 

The sandstone in different parts of the mine varies 

from white to gray to brown. The brown sandstone 

contains abundant Emonite. In places the limonite is 

conspicuous as spots or bands against the lighter colored sandstone. In both workings the sandstone is 

dominantly massive, but in a few places it is crossbedded and flat bedded. In places the sandstone grades 

laterally into siltstone. 

Mudstone is abundant in both workings as undulating 

beds, lenses, seams, pebbles, and films. These separate 

the sandstone lenses as illustrated in the mine sections 

(pl. 6). Mudstone conglomerate is also abundant and 

some of it contains angular mudstone fragments arranged in an imbricate fashion that may indicate the 

direction of paleo-stream flow. The mudstone in the 

mine is almost everywhere gray or green, but red mudstone was found as a thin layer within a green mudstone 

layer in the northeast workings. 

The dominant joints in the mine (pl. 6) strike about 

N. 80° E., dip steeply to the southeast, and are roughly 

parallel to the axis of the La Sal Creek syncline. Now here in the mine is there any evidence that ore deposition was affected by the joint system. 

The ore bodies are typical Salt Wash deposits; they 

occur as pods, irregular shaped lenses, and as gently 

roBing, tabular layers. Ore rolls are numerous in both 

workings and have a dominant trend of about N. 40°-

500 E. (pl. 6). In some places two or three layers of 

ore occur in the drift or room walls, but these layers 

generally merge within a short distance. It is thought 

that the deposit is made up of several extensive blanketlike layers, but because of their undulating nature it is 

difficult to ascertain their true extent or to separate 

them, even where they are well exposed in the workings. 

The pods and smali lenses of ore are bodies of quite 

limited extent and are mainly associated with carbonaceous matter. 

The deposit is above the water table and appears to 

be partly oxidized. Nevertheless, the ore is black or 

dark gray, and yellow minerals such as carnotite and 

tyuyamunite are notably sparse. 'The generally dark 

color of the ore is probably due to the greater than normal proportion of vanadium to uranium. ·~e ore has 

a V z05 : U 3 0 8 ratio of 8: 1 which may be due to removal 

of soluble uranium salts by the flushing action of circulating ground water. Vanadium hydromica appears to 

be the dominant ore mineral and occurs as a coating on 

sand grains and filling between them. Corvusite is less 

abundant and occurs in podlike masses surrounding carbonaceous debris. Where these pods are exposed to the 
URANIUM DEPOSITS 57 

air for a short time, pascoite and tyuyamunite form on 

the surface. The ore produced from the Evening Star 

mine between 1950 and 1956 contained 2.00 percent V 205 

and 0.24 percent U a08. 

Carbonaceous woody material is errat~c-ally distributed throughout the workings and most commonly 

occurs as trash pockets or pods, and as thin seams or 

films between sandstone laminae. Fossil logs and log 

impressions are few, but wherever they occ-ur they 

either contain or are surrounded by ore minerals, usually 

both. The logs have an average orientation of N. 55° W. 

FIREFLY·PIGMA Y MINE 

The Firefly-Pigmay mine (pl. 7) is in sec. 30, T. 28 

S., R. 26 E., San Juan County, Utah, about 10 miles 

east of La Sal, Utah. The portal of the mine is at the 

head of La Sal Creek Canyon, about half a mile above 

the confluence of Twomile and La Sal Creeks. The 

mine was, as of 1957, owned and operated by the StocksGramlich Corp. of Moab, Utah. 

The Firefly-Pigmay deposit was discovered in 1952 

through the exploration drilling program conducted by 

the U.S. Geological Survey. It is in the uppermost 

continuous sandstone unit of the Salt Wash Member of 

the Morrison Formation of Jurassic age. This sandstone unit, ; commonly referred to as the ore-bearing 

sandstone, is composed mainly of broad lenses of medium- to fine-grained light-gray and light-brown 

sandstone; it includes lenses of reddish-brown and green 

mudstone. In the vicinity of the mine the sandstone 

ranges in thickness from 30 to 90 feet. The deposit 

trends east and lies at the west end of the explored part 

of the La Sal Creek mineral belt. The deposit is orien ted dbliquely to the axis of the La Sal Creek syncline. 

Contours drawn on the base of the ore-hearing sandstone show a nose, trending slightly west of north, that 

extends about 300 feet before dying out (fig. 7). West 

of the nose is a shallow depression in which the deposit 

is located. This nose is primarily a sedimentary feature that is independent of the tectonic structure, 

probably a cuspate spur projecting from the bank into 

the ancient stream channel. This relationship of the 

deposit to sedimentary and Late Jurassic erosional features is significant in that other deposits in the La Sal 

Creek area are similarly located. 

Access to the deposit is by a 1,200-foot drift bearing 

N. 15°-20° W. (pl. 7). The drift extends into the deposit for about 250 feet on a bearing of N. 50° W. The 

largest workings are west of the main drift, and at the 

time of mapping extended through an area approximately 300 feet long by 200 feet wide. 

For a distance of approximately 600 feet from the 

portal, a continuous massive to crossbedded sandstone 

lens is exposed (pl. 7, section A-A'). It ranges from 

brown and light brown to light gray, white, and light 

green. Some mudstone and mudstone eonglomerate 

beds are interbedded with the sandstone. These mudstone units, some as much as 3 feet thick in some places, 

truncate the sandstone bedding, but in most places eonform with the bedding. The mudstone is red; some is 

partly gray or mottled green. The sandstone unit in 

the drift is completely devoid of carbonaceous woody 

material. Limonite spots are common but not everywhere present in the sandstone. 

Overlying the sandstone and intertonguing with it is 

a red mudstone unit that is exposed at a point 600 feet 

from the portal and extends along the drift for 420 feet 

(pl. 7, section A'-A"). Although predominantly red, 

the mudstone is mottled green in pla;ces and intertongues with gray mudstone. The red mudstone unit 

is overlain by a green mudstone layer, 1 to 2 feet thick, 

which is present at the back of the drift about 980 feet 

from the portal. The green layer dips northward along 

the drift for 140 feet where it enters the floor. About 

1,020 feet from the portal the underlying red mudstone 

unit is sparsely mottled green. The green mottling increases farther inward so that at about 1,080 feet the 

two mudstone units appear to merge and form a si:o.gle 

green layer that is 3 to 4 feet thick. Nodular gray 

limestone masses are all along the walls of the drift in 

this green mudstone unit. 

The sandstone lens containing the Firefly deposit is 

first exposed in the back of the drift about 1,030 feet 

from the portal. It rests on the green mudstone layer 

described rubove. The basal contact of the sandstone 

dips northward and the dip is believed to define the edge 

of a broad channel having characteristics similar to 

those described by McKay (1955, p. 269-270). The 

sandstone is white to gray or light brown where limonite is abundant. The contact between it and the 

underlying mudstone is exposed.for a distance of about 

90 feet, and because the contact is undulatory, a scour I , 

and fill relationship is suggested. This sandstone unit 

is distinctly different and separate from the lens at the 

portal of the mine. 

Beyond 1,120 feet from the portal the drift is in a 

sandstone unit that contains abundant mudstone conglomerate layers and lenses, especially in the back. 

Near the end of the drift a. gray-green mudstone-siltstone unit overlying the ore-bearing sandstone lens extends from the back. About 21h feet of this unit is 

exposed at the end of the drift. The undulatory bedding in the unit is probably the result of differential 

compaction rather than of scour and fill. Drill holes 

show that the total thickness of the sandstone unit is 
58 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

at least 85 feet. Appreciable quantities of carbonaceous woody material are present in the sandstone. 

The channel sandstone lens that constitutes the orebearing unit is continuous from the area of the main 

drift into both of the west workings (pl. 7, section 0-0' 

and D-D'). It is virtually the same in color, lithology, 

and thickness throughout the mine. Drill-hole data 

show that the upper 40 to 50 feet grades westward into 

a finer grained sandstone. Gray and green mudstone 

conglomerate and seams are abundant. Red mudstone 

'is present but not abundant. Carbonaceous wood is 

more abundant in the west working than in the workings along the main drift. -

Fractures are numerous within 200 feet of the portal. 

They strike northeast and dip steeply southeast. The 

strike is parallel to the outcrop of the sandstone along 

the La Sal Creek Canyon and may reflect incipient 

slump due to the deep erosion of the canyon and permeation of the underlying mudstone by ground water. 

Fractures in the main west workings strike N. 20°-30° 

W. (pl. 7) and dip vertical or nearly vertical to both 

northeast and southwest. These fraetures may be the 

result of tensional stresses related to the formation of 

the La Sal Creek syncline. The fractures that cut 

through the ore bodies do not appear to have controlled 

the emplacement of the ore and appear to be later than 

the mineralization. 

The ore bodies in the Firefly-Pigmay deposit are 

tabular or undulating layers as 1nuch as 3 feet thick and 

50 feet long by 40 feet wide. Some of the ore is concentrated in pods or is disseminated in the sandstone as 

irregular concretionlike bodies a few millimeters to a 

few inches in diameter. Ore rolls (pl. 7) are not common along the main drift but are present in the western 

part of the mine. 

All except one of the ore bodies of the Firefly-Pigmay 

deposit are made up of the black, partly oxidized uranium-vanadium minerals. The single exception is in the 

upper workings (pl. 7, section D-D') above the main 

drift. There the ore minerals are in part the oxidized 

types, principally the potassium and calcium uranyl 

vanadates, carnotite and tyuyamunite. Minor amounts 

of corvusite and other less oxidized vanadium minerals 

are present. The presence of both oxidized and unoxidized ore bodies in the Firefly-Pigmany mine is the 

result of ground-water conditions that prevailed in the 

deposit prior to mining operations. The ore bodies in 

the lower level were below the water table and were not 

subjected to oxidation. The upper ore body, which is 

20 to 30 feet higher than the lower ore bodies, is above 

the water table and has been subjected to oxidation. The 

two ore levels are separated by a. thin layer of green 

mudstone-pebble conglomerate. 

The partly oxidized ores of the deposit are dark olive 

green, greenish black, and black. The green color may 

be due to the presence of roscoelite or vanadium hydromica. The black minerals include sooty pitchblende or 

uraninite, coffinite, and montroseite. Corvusite and 

possibly lumsdenite, a low-valent vanadate, are also 

present in the ore. 

Accessory minerals such as pyrite and possibly chalcopyrite are finely disseminated with uranium and vanadium minerals that have replaced carbonized wood but 

are rarely found in the mineralized sandstone of the 

deposits. Clausthalite (fig. 9), a lead selenide, and an 

unknown mineral were found as two parallel bands, 

each no more than 1 mm thick bounding the convex 

edge of an ore roll. On the eoncave side of the bands, 

uraninite, coffinite (?), and montroseite fill the interstices between quartz grains. The quartz grains are extremely irregular in shape and of mueh smaller size 

than those of the opposite side of the band. The quartz 

appears to have been replaced by the uranium-bearing 

medium, and the dissolved silica is apparently atomieally bonded with uranium molecules to form the reeently discovered uranium silicate, eoffinite ( Stieff and 

others, 1955). Ori the convex side of the bands the sandst.one is virtually barren of ore and the quartz grains are 

more rounded and elosely packed. A few fine-grained 

uranium-vanadium minerals fill the interstices but are 

much less abundant than on the other side of the bands. 

Fine-grained carbonate minerals, mostly calcite, cement 

the quartz grains. Overgrowths of authigenic siliea 

were not observed on the quartz grains in the barren 

zone. 

Other samples were collected in 1954 by A. D. Weeks 

and ,J. C. Warman through the courtesy of Mr. Gardner, the mine foreman. Weeks (written commun., 

1957), states that, in one place in the mine, uraninite 

and low-va]ent vanadium minerals eontaining traces 

of tennantite had formed on the surface of a carbonaceous log. She noted saleeite-novacekite had formed 

where uraninite had begun to oxidize. Elsewhere in 

the mine, 'V eeks found pyrite, galena, amber-colored 

sphalerite, and coffinite formed around carbonaceous 

material. She concluded, from the samples studied, 

that the Firefly-Pigmay mine was the least oxidized of 

those in the La Sal Creek area. 

The ore produced from the Firefly-Pigmay mine 

through 1956 continued 2.04 percent V205 and 0.35 percent U aOs in a V: U ratio of approximately 6: 1. 

Localization of ore bodies within such features as 

crossbeds or in festoons as described by Roach and 

Thompson (1959) in the Peanut mine of the Monogram 

Mesa area, Colorado, has not been found in the FireflyPigmay deposit. The ore-bearing sandstone in and 
URANIUM DEPOSITS 59 

around the deposit is flat bedded to gently crossbedded 

and in places steeply crossbedded. Festoon laminae 

are rare and inconspicious. Where the ore bodies are 

in crossbedded sandstone, regardless of their sizes and 

shapes, they transect the cross beds. 

Carbonaceous woody material occurs in appreciable 

amounts in the ore-bearing sandstone at the FireflyPigmay mine. For the most part the carbonaceous 

wood occurs as discontinuous seams in the sandstone or 

with mudstone bodies. One log is replaced by calcite at 

its center and has a carbonaceous rim that is mineralized. It is in the ore-bearing sandstone along the main 

drift about 3 feet above where the sandstone lens occupies a small channel scour in the underlying green 

mudstone (pl. 7, section A-A'). In the western part of 

the mine, carbonaceous ·wood and plants occur in thin 

seams and disseminated in mudstone as well as accumulations or trash pockets. Most of the uranium-vanadium 

minerals associated with carbon are in the west workings. Several logs are mineralized and one that was 

18 feet long and 12 inches in diameter was mined. 

As pointed out in the section on localization (p. 

41), the deposits of the La Sal Creek area appear to 

be localized where sedimentary troughs or lows are 

found. However, the controls of localization of the 

individual ore bodies within the deposits are, in places, 

more subtle. Trites and Chew ( 1955, p. 245-24 7) , in 

discussing the Happy Jack mine in southeastern Utah, 

believe that the localization of ores in the sandstone 

depends upon the permeability of the sandstone and 

the amount of carbonized wood and plants in the sandstone. They consider beds of intermediate permeability, that is, those containing claystone and siltstone 

bodies ·and cement, as more favorable than beds of 

highly permeable sandstone cont,aining little interstitial claystone and siltstone or cement. Although these 

categories of relative permeability were used in describing a Shinarump channel deposit, they are, with modifications, generally applicable to Salt Wash deposits. In 

the Firefly mine, for example, mudstone bodies are generally present throughout the ore-bearing unit (pl. 7, 

sections A-A' and B-B'), as contrasted to the barren 

sandstone unit at the portal. Although a general relation of permeability to ore is believed to exist. the 

position of any single ore body cannot be sho~~ as 

attributable to this factor alone, with perhaps one exception-the oxidized body in the upper workings (pl. 

7, section D-D'). This body is in an upper zone of the 

ore-bearing sandstone 20 to 30 feet above the main deposits; it lies upon or close above a green mudstone lens 

that is 2 feet thick. It is thought that the lens served 

as a shelf above which a solution of uranium-vanadium 

minerals was concentrated and later precipitated to 

form the deposit. 

GRAY DAUN MINE 

The Gray Daun mine, which consists of two separate 

workings, an eastern and a western (pl. 8), is in sec. 

30, T. 28 S., R. 26 E., San Juan County, Utah, about 

10 miles east of La Sal, Utah. The deposit was discovered during the mining on the Little Peter claim 

to the north. The Gray Daun mine was owned and 

operated in 1957 by the Stocks-Gramlich Corp. and 

had been in production since 1949. The portals of the 

mine open on the southwest side of Twomile Creek, 

about half a mile above its confluence with La Sal Creek 

where an access road to the mine leaves Utah Highway 46. 

The mine is in the uppermost continuous sandstone 

unit of the Salt Wash Member of the Morrison Formation of Jurassic age. In the vicinity of the mines 

this unit is composed mainly of broad lenses of mediumto fine-grained light-gray and light-brown sandstone 

containing interbedded lenses of reddish-brown and 

green mudstone. The sandstone ranges from 30 to 105 

feet in thickness. 

WE!STERN WORKINGS 

The western workings of the Gray Daun mine have 

two portals that are 40 feet apart, one roughly west of 

the other. The workings consist mainly of a single 

sinuous drift about 540 feet long extending south from 

the portals (pl. 8) . Just inside the western portal is a 

room that is 20 feet wide and 40 feet long and has two 

short adjoining side drifts. Two other short side drifts 

extend from the main drift at points deeper in the workings. The workings are dry throughout. 

The rocks exposed in the main drift of the workings 

are mostly light-brown to white sandstone that is massive or flat bedded to crossbedded. Mudstone lenses 

are common on the sandstone, mainly at the back or 

high on the walls of the drift. In places the lenses and 

beds of mudstone are contorted about rounded limonite 

sandstone masses as a result of either differential compaction or slump or possibly both. The mudstone units 

in the west workings are green or gray. In one place 

in the drift about 230 feet from the porta!} (pl. 8, section A-A'), the sandstone has been scoured and filled 

by another sandstone unit. The scour boundary is defined by a weakly mineralized mudstone-siltstone bed 

about 6 inches thick. The bed sweeps down from the 

back of the drift at an angle of !'5° to 25°, dips eastward, 

and cuts across the entire exposed section of the original 

sandstone. The scour contact is exposed for a distance 

of 20 feet along the drift. 
60 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

The fractures in the workings trend about N. 30° W. 

and dip steeply to the northeast. There appears to be 

no relationship between the fractures and the mineralized areas. 

Uranium-vanadium minerals are sparse throughout 

the length of the drift and are rarely thick enough to 

be caHed ore. Thin undulating stringers of mineralized 

sandstone occur about 10 feet above the base of the orebearing unit. Where the sandstone unit has been 

scoured and filled, the ore minerals are in the thin mudstone-siltstone unit at the scour boundary and parallel 

to the bedding of the unit. There are two small isolated 

pockets of uranium-vanadium minerals and a mineralized log at the end of the drift. Carbonaceous wood 

fragments are sparse and dispersed as thin seams and 

films throughout the workings. 

The eastern portal of the western workings opens 

into an irregular room about 50 feet long which once 

joined the west portal drift through a narrow opening 

which is now filled with .gob. The sandstone exposed 

in the walls is similar in lithology to that in the rest 

of the workings. The ore occurs as a flat-lying tabular 

layer that terminates in a roll that was about 3 feet 

thick, 30 feet ·long, and 10 feet wide but which has been 

mined out. The roll axis is nearly straight and trends 

approximately 18° north of east. The roll is composed 

of black ore minerals, although they may be of the 

oxidized type. 

EASTERN WORKINGS 

The eastern workings are entered by four portals 

within a distance of 135 feet along the canyon wall. 

These portals join a maze of drifts and rooms. In plan 

the workings trend north-south and cover an area about 

380 feet long and about 180 feet wide. The eastern 

workings are the older part of the mine and many of 

the drifts and stopes are partly filled with gob. The 

workings are entirely dry. 

In ·the east workings the drift, and stope wa.Ils are 

composed of ·white, light-gray, and light-brown sandstone that is both massive and bedded. No mudstone 

units of any substantial thickness are exposed in 

the drifts, ·although thin !beds 'Or lenses are common, 

especially ait the hack of the workings. In one place 

the mudstone has scalloped ripple bedding and contains sand-filled mud cracks that suggest deposition of 

fine-grained material alternating with periods of subaerial drying (pl. 8, section A-A'). 

A few feet south of the mud cracks the mudstone is 

contorted around well-cemented sandstone that occurs 

in rounded boulder-sized masses. This feature may 

have resulted from slumping ·along the edge of a stream 

channel scour. As ~ndica.ted in sections A-A' and 0-0' 

(pl. 8) , from the margin of th'is scour into the eastern 

section of the workings tJhe ore is in progressively lower 

stratigraphic positions in the ore-bearing sandstone. 

This position is ·coincident with an increase in the continuity, thickness, and grade of these bodies. The 

marked difference in the ore bodies probably reflects ·a 

change in t'he nature 'Of the ore-bearing sandstone. Contours drawn on the hase of the sandstone from drilling 

da.ta show a broad depression or channel in the ·area 

immediately behind the portals of the Gray Daun mine. 

Most of .the tonnage produced thus far has been from 

the lower levels which are in this channellike feature. 

The sparse mudsttone and siltstone units exposed in 

the eastern workings are gray or green and occur chiefly 

a:s t:hin lenses or as thin, 'irregular units eom posed of 

mudstone fragments. The mudstone decreases the gross 

permeability of the ore-be·aring sandstone and prohably 

slowed the passage of ore-bearing ·solutions, hut no diroot relationship of mudstone units to ore bodies is 

recognized. 

The dominant fractures are concentrated in the south 

haH of the e31stern workings and trend slightly west 

of north (pl. 8). The fractures -are either vertiea.I or 

dip steeply to the east and west; where they transect 

.the ore bodies, they appear to postdate ore emplacement. 

The ore in the eastern workings lies ·about 15 feet 

above the base of the ore-bearing sandstone in undulating or gently rolling tabular layers that range from 0 

to 4 foot in thiekness (pl. 8, sootion 0-0'). Ore also 

occurs in irregular podlike accumulations as much as 

3 inches in dia.meter that are grouped together ·along 

bedding planes (pl. 8, section 0-0') or occur as isolated 

bodies (pl. 8, section A-A'). In 'a few places the 'Ore 

lies in clearly defined rolls •that cut sharply aeross the 

sandstone bedding. One ore roll is S shaped in cross 

section. Almost all rolls trend a;bout east parallel to 

the scour-a~d-fill structures mapped in the mine. 

The uranium-vanadium minerals in the Gray Daun 

mine are mostly of the oxidized type. H'owever, one 

of the first discoveries of pitchblende from sandstonetype deposits on the Oolorado Plateau came from the 

Gray Daun mine (Rasor, 1952). Associated with pitchblende is earnotite, tyuya.murrite, uranophane, torbernite, ·and p'hosphuranylite. Carnotite is the most abundant uranium ore mineral and is found in high-grade 

concentrations replacing logs and intimately associated 

with black minerals. 

Montroseite, corvusite, hewettite, and metahewettite 

are present in vanadium-rich layers. The deposit appears nearly completely oxidized, probably because it 

is close to the canyon wall and lies 'above the present 

water t;ahle. The water table fell, no doubt, as Twomile Creek cut through the ore-hearing sandgtone. 
URANWM DEPOSITS 61 

Small patches or pods of partially unoxidized minerals 

remain in the lower part of the mine. 

The principal minerals identified from the Gray Daun 

mine include carnotite, tyuyamunite, metatyuyamunite, 

gummite, eorvusi:te, montroseite, a black uranium mineral that is probably coffinite, and vanadium hydromica 

(A. D. Weeks, oral commun., 1954). Also occuring in 

the Gray Daun mine are sparse 'anmunts of pitchblende 

( uraninite) associated with the coffinite(?), and traces 

of selenium minerals (probably eucarite). Minor 

amounts of torbenite ( ? ) and metatorbernite ( ? ) , phosphurany lite, uranophane, hewettite and meta'hewettite, 

and melanovanada.te have been collected (Weeks, oral 

commun., 1954). Traces of the seconda.ry etopper minerals malachite and azurite have also been ·observed. 

The ore produced from the Gray Daunminecontained 

1.79 percent V205 nnd 0.39 percent U3 0 8 , or a ratio of 

5: 1. 

Carbonaceous wood is most abundant in the southern 

end of the eastern workings, and in several places this 

material is impregnated or partially replaced by uranium-vanadium minerals. These fragments of carbonaceous material appear to have served as cente~rs 

about which the ore minerals were deposited. Although 

carbonaceous wood may have been a localizing material, 

not all ore bodies in the Gray Daun mine were localized 

in this way, for many of the ore bodies are devoid of 

such material. Conversely, not all the carbon fragments contain or are associated with nre minerals. I~t 

appears that mineralizing solutions must come in contact with carbon in order to precipitate the contained 

uranium and vanadium. In the south end of the long 

drift of the western workings, ·a carbonaeeous log was 

mineralized, mostly by impregnation, whereas the enclosing sandstone is barren. Possibly such differences 

in mineralization lie in the relative concentrations of 

the mineralizing solutions reaching the different areas. 

The mineralizing process apparently was highly selective and was dependent on many factors. 

HESPERUS MINE 

The Hesperus mine (pl. 9) is in the NE. oor. sec. 32, 

T. 28 S., R. 26 E., ·San Juan County, Utah. It is about 

11 miles east of La Sal, Utah. The mine portals are 

on the north side of La Sal Creek Canyon about 1 mile 

east of the confluence of La Sal and Twomile Creeks. 

Access to the mine is by ·a narrow truck trail which 

passes under the ore hin of the Vanadium Queen mine 

and eontinues in a southeasterly direction along the rim 

formed by the ore-bearing sandstone of the Salt Wash. 

The deposit is in a discontinuous sandstone lens that 

ranges from 0 to 35 feet in thickness. Where exposed 

in t,he canyon wall it ·appears ·uo lie a;hove ·and is separate 

from the uppermost continuous sandstone unit-the 

ore-bearing sandstone of :the Salt Wash-by mudstone 

layers that have a total thickness of 15 feet. This lens 

may extend into the ore-bearing sandstone nor-th of the 

mine workings or it may pinch out. 

The Hesperus mine is divided into two separate workings having eastern and western portals about 100 .feet 

apart. The eastern workings are a single dri:frt a;bout 

120 feet long. The western workings are composed of 

a drift that e:rtends 7·5 fe~ from the portal. A side 

drift ·rubout 60 feet from the portal runs west and has 

branching drifts extending albout 40 feet to the nortJh. 

The drift walls in both workings are in flat-bedded 

light-brown limonitic sandstone or white sandstone. 

Mudstone occurs in beds as much as 2 feet thick and is 

green to gray. 

The fact that the fractures trend east, parallel to the 

canyon face, and dip steeply to the south suggests that 

they are the result of incipient slump of the beds along 

the rim of La Sal Creek Canyon. 

The ore bodies generally are undulating blanketlike 

tabular layers as much as 1 foot thick, and more rarely 

they occur as isolated podlike bodies. They cover areas 

as much as 30 feet long and 10 feet wide and are composed of oxidized uraniun1 and vanadium minerals that 

impregnate the sandstone and replace carbonaceous 

material. The advanced state of oxidation is probably 

due to the proximity of the ore deposit to the canyon 

wall. The principal uranium mineral is carnotite. 

Tyuyamunite occurs with the carnotite. Small amounts 

of corvusite were noted with pods of vanadium hydromica. Schroekingerite(?) is a:lso present. The average 

grade of ore produced thus far is 1.57 percent V205 and 

0.38 percent U30 8, a ratio of about 5: 1. 

FI,'agments of carbonized wood are abundant in the 

mine and occur as carbonaceous seams or are disseminated in mudstone or siltstone beds. One carbonized 

log was found in the workings but it is not mineralized. 

The Hesperus deposit is one of three deposits in the 

La Sal Creek area that are unique in that they are in 

a sandstone lens that lies just above the main ore-bearing 

sandstone. The other two deposits, the Uranium Girl 

and the upper workings of the Maud mine, are on the 

south side of La Sal Creek Canyon within 7,000 feet of 

the Hesperus mine. All three deposits may lie within 

separate tongues of the ore-bearing sandstone, although 

possibly they are in a single narrow shoestringlike 

lens which, prior to erosion, was continuous through the 

area. This sandstone may represent the channel of a 

small distributory stream tha't flowed southeastward 

during the deposition of the uppermost Salt Wash. The 

close areal spacing of these deposits in this unit suggests 

a common origin. 
62 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

JACKPOT MINE 

In 1913 W. W. Chiles and E. J. Reynolds located the 

Jackpot (pl. 5) claim near Buckeye Reservoir in sec. 2, 

T. 48 N., R. 20 W., Montrose County, Colo. It was 

restaked in 1939 and amended in 1953 by J. H. 

Coward. It was most recently operated by the Bee Hive 

Mining Co. which produced a few tons of ore during 

1956. The property is reached from Paradox, Colo., 

by 11.8 miles of Forest Service road and truck trail 

which parallel West Paradox and Buckeye Creeks to 

Buckeye Reservoir. The road turns east at the west end 

of the reservoir crossing Buckeye Creek and continues 

to the mine just north of the lake. 

The workings consist of a small open cut from which 

a drift extends N. 3° W. for 50 feet where it turns west 

along a fault plane which bears N. 60°-65° W. The 

extent of the workings along the fault is. uncertain because the end of the workings has caved. 

The deposit is in the Wingate Sandstone which is part 

of a large fault block within the Valley View fault complex. In the drift from the portal, two joint sets were 

noted, one striking N. 37° E. and dipping 74° NW. and 

the other trending N. 40° W. and dipping 86° SW. 

The ore mineral is principally carnotite· malachite and . ' azunte are in the gangue. These minerals occur as 

spots in the s.andstone along ~he fault and fractures. 

Submicroscopic dark minerals, presumed to be vanadium hydromica, occur in patches as disseminated crystals 

filling the interstices of the fine-grained sandstone. 

The fact that the deposit is in a fault block of Wing~te Sa~dstone and consis.ts entirely of secondary oxidized minerals suggests to the authors that the deposit 

formed by the circulation of ground water that passed 

through nearby uranium-vanadium deposits within the 

Morrison .Formation. The Salt Wash ore-bearing 

sandstone Is not exposed in the immediate area and the 

area has not been explored by subsurface methods 

except for a few shallow drill holes within the fault 

zone. Subsurface exploration in areas either north or 

south of the mine might lead to the discovery of minable 

uranium-vanadium deposits in the ore-bearing sandstone of the Salt Wash. 

The prospect has been worked periodically for many 

years an~ most recently in 1956 as a stripping operation. 

Production has been very -limited. The ore contains 1.25 

percent V205 and 0.14 percent U3 0 8 , a ratio of 9: 1. 

Material of ore grade is obtained by careful hand selection. 

LITTLE DON MINE 

The Little Don mine (pl. 10) is in sec. 30, T. 28 S., 

R .. 26 .E., San Juan County, Utah. The portal of the 

mine Is on the south side of Twomile Creek about half 

a mile above its confluence with La Sal Creek and about 

700 feet southeast of the Gray Daun mine. A truck 

trail paralleling Twomile Creek provides access to the 

mine from Utah Highway 46. The mine was owned 

in 1957 by the Stocks-Gramlich Corp. of Moab, Utah, 

and was in operation during 1953 and 1954. 

The Little Don deposit is in the lower part of the ore· 

bearing sandstone of the Salt Wash Member. This 

unit is ·composed mainly of broad lenses of mediumto fine-grained light-brown flat-bedded to crossbedded 

sandstone containing lenses of predominantly green 

mudstone. The sandstone at the mine ranges in thickness from 30 to 60 feet. 

The mine workings are entered through two closely 

spaced portals, about 20 feet apart. These join and 

form a single sinuous drift hearing roughly S. 60° W. 

for about 200 feet. The mine is dry throughout. 

The ore occurs as thin undulating seams or layers as 

much as 2 feet thick and as irregularly shaped accumulations in the sandstone. The largest body is about 35 

feet long and 25 feet wide. The minerals are predominantly black and mostly are vanadium oxides, as reflected by a high V205: U3 0 8 ratio 12: 1. The chief 

ore mineral, vanadium hydromica, coats sand grains 

and fills the interstices. Tyuyamunite, metatyuyamunite, and sparse amounts of carnotite are also present. 

The high degree of oxidation indicated 'by the yellow 

minerals is probably due to the great number of fractures in ·the country rock and the proximity of the 

canyon wall. Production records show the ore contained 0.14 percent Ua08 and 1.71 percent V20 5. 

Carbonized wood is very abundant throughout the 

mine. It occurs in the sandstone as seams and logs and 

as small fragments in mudstone. Although carbona.-

ceous material and ore minerals occur in close proximity 

to each other, the carbonaceous material in many places 

is barren. In a few places in the mine the carbonaceous 

wood contains calcite, and in one place the wood is 

associated with limestone nodules in sandstone. 

LITTLE PETER MINE 

The Little Peter mine (pl. 1) is on the north side o£ 

Twomile Creek in sec. 30, T. 28 S., R. 26 E., San Juan 

County, Utah. The claim was located on March 1, 1936~ 

by ~Iessrs. B. Stoc-ks, J. Stocks, and M. J. Murphy 

(C. W. Livingston, written commun., 1945), and in 

1956 was owned by the Stocks-GramUch Corp. The 

property is reached by a truck trail that leaves Utah 

Highway 46 near the confluence of Twomile and La 

Sal Creeks and roughly parallels Twomile Creek for a 

distance of 1 mile. 

The workings are in the lower part of the ore-bearing 

sandstone of the Salt Wash Member of the Morrison 

Formation. They consist of about nine drifts that ex-
URANIUM DEPOSITS 63 

tend as much as 100 feet north from portals in the canyon wall. Some of the drifts are connected by cross 

drifts. The ore-bearing sandstone has an aggregate 

thickness o~ about 65 feet, but is divided in two parts by 

a green mudstone bed that ranges from 2 to 10 feet in 

thickness. The base of the mudstone layer is about 20 

feet above the base of the sandstone. 

The ore is in the lower sandstone lens near the mudstone. It occurs as thin discontinuous, gently rolling 

tabular layers and small pods associated with pockets 

of carbonaceous trash in and along bedding planes in 

sandstone. The long axes of two ore rolls and one 

1nineral-replaced ]og trend N. 70° E. This trend is 

roughly parallel to sedimentary structures that indicate the direction of stream flow during deposition of 

the upper part of the Salt Wash. Both oxidized and 

unoxidized uranium and vanadium minerals occur in 

the ore. The layers, rolls, and pods contain finely disseminated uraninite( n, montroseite, and vanadium 

hydromica. Corvusite was noted in several small pods. 

Carnotite occurs in fossil logs in association with minor 

amounts of uraninite and as effioreseent coatings with 

pascoite, tyuyamunite, and fibrous gypsum on the surface of mineralized sandstone in the older workings. 

Operation of the mine by the owners and several lessees has been intermittent, but small tonnages of ore 

have been produced ~nnually since 1940. The average 

grade of the ore produced during the period is 1.31 

percent V205 and 0.30 percent U 30 8 in a ratio of 4: 1. 

LUCKY NO.1 MINE 

The Lucky No. 1 mine (pl. 1) is in sec. 30, T. 47 N., 

R. 19 W., Montrose County, Colo. It is reached by a 

truck trail which leaves Utah Highway 46 at the Pine 

Lodge Ranch and crosses Wray Mesa to the bench at 

the head of Sharp Canyon, a distance of 9.4 miles. During 1953, Mr. H. N. Tidwell operated this mine. 

The deposit is in a thin sandstone lens in the Brushy 

Basin Member of the Morrison Formation. The lens is 

as much as 4 feet thick and is about 70 feet above the, 

ore-bearing sandstone of the Salt Wash Member. The 

beds dip 1° to 2° NE., toward the axis of the La Sal 

Creek syncline. The sandstone is eomposed of lightbrown fine quartz grains spotted with limonite. The 

sandstone is interbedded with silty layers; it overlies 

thinly bedded variegated mudstone and is overlain by a 

partially bleaehed, platy layer of light-green mudstone 

that is 8 to 10 feet thick. 

The workings consist of a single drift along the north 

side of the convex surface of a single ore roll which 

arehes to the northwest and has an overall trend of N. 

25° E. The roll is approximately 90 feet long and appears to have been about 4 feet wide and 3 feet thick 

along much of its length. The roll is displaced about 

3 feet on the southwest end by a fault that trends N. 

55° E. and dips 70° SE. The southeast side is downthrown and the drift inclines downward into the downthrown block a distance of about 20 feet. The exposed 

relations between the fault and ore indicate that the 

faulting oecurred after the ore was in place. A very 

minor roll surfaee trending N. 50° E. was noted near 

the portal. It parallels the east end of the main ore 

roll. 

The ore minerals are earnotite and a very fine grained, 

light greenish-gray to black vanadium mineral presumed to be vanadium hydromica. The gangue minerals 

are dominantly quartz and minor amounts of limonite, 

calcite, and possibly barite. Carbonate cement is 

abundant in the wall which forms the roll surface on 

which the ore rested. Carbonaceous material occurs 

as flakes on bedding planes but is not abundant. 

MARJORIE ANN MINE 

The Marjorie Ann mine (pl. 11) is in unsurveyed 

sec. 11, T. 47 N., R. 20 W., about 11.4 miles east of the 

Utah-Colorado State line. The mine is reached by a 

dry-weath~r truck road that connects with Colorado 

Highway 90 2 miles to the south. The Marjorie Ann 

deposit was found during the course of a close-spaced 

diamond-drilling program conducted in the summer of 

1952, by the lT.S. Geological Survey. 

The claim was staked as part of the Gramlich group 

in the name of Sam V., Irene, and John W. Gramlich. 

John W. Gramlich later acquired the property and in 

1953 leased it to William Hall, Ray Maris, and Paul 

Killion. Their cooperation during the mine mapping 

was greatly appreeiated by the authors. Production 

began early in 1954 and was mainly continuous into 

19;56. The property was purchased in 1956 by the Four 

Corners Uranium Corp. 

The Marjorie Ann deposit is in the ore-bearing sandstone of the Salt Wash Member of the Morrison Formation. The ore-bearing sandstone in the vicinity of 

the deposit is more than 100 feet thiek. The deposit occurs in the interval between 20 and 40 feet above the 

base of the sandstone. 

The workings of the mine are reached by an incline 

having a 25 percent grade. It is about 170 feet long 

and bears S. 75° E. at the portal. The mine workings 

consist of a single large room supported by several 

pillars. The room is oriented north-south and is about 

190 feet long and about 50 feet wide at the widest point. 

The mine is above the water table and usually dry except 

during the winter months. 
64 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

The sandstone in which the deposit occurs is dominantly light brown but, in places, it is white or variom~ 

shades of gray. The brown sandstone is permeated with 

limonite which occurs locally as small concretionary 

bodies or as spots called freckles. Cross beds and ripple marks in sandstone lenses that overlie the ore 

indicate that the stream depositing the sandstone 

flowed southeastward. Scour features at the base of 

these lenses have a similar trend. In the ore layer, however, the bedding is obscure and the sandstone usually 

has a massive appearance. The direction of paleostream 

flow in this particular lens was, therefore, not positively 

established but appears to have been eastward. 

The only large lens of mudstone in the workings is a 

thick red mudstone unit near the portal. The mudstone 

near the ore occurs as pellets and films or very fine 

f r a g m e n t s disseminated through the sandstone. 

Layers of mudstone conglomerate are rare. The mudstone near the ore bodies is green or gray, except for 

minor amounts of yellow and yellowish-brown mudstone. Grayish-black mudstop.e pellets found in one 

place are thought to be mineralized. 

In the Marjorie Ann mine, uranium-vanadium minerals occur in undulating blanketlike layers (pl. 11, 

section A -A') that are commonly too thin to be classed 

as ore. Most of the production has been from ore rolls, 

nine of which were discovered during mining. Most 

of the roll axes are straight, but one is curved and another splits into two divergent axes. In the latter, the 

roll formed a compound curved surface where the axis 

separates. The average direction of the axes of the rolls 

is about N. 85° E. (pl. 11). 

Some of the ore is in a very friable limonitic sandstone unit that it 3 to 4 feet thick and contains abundant 

carbonaceous material. On casual inspection the sandstone unit does not appear mineralized, but close scrutiny reveals that very finely disseminated carnotite occurs in the interstices. This deposit is probably the result of oxidation and subsequent migration of uraniumvanadium minerals from nearby ore layers and rolls, 

possibly through the action of downward-percolating 

surface waters. The ore produced in the Marjorie Ann 

mine averaged 0.26 percent U30s and 1.37 percent V205 

in a ratio of 5 : 1. 

Carbonaceous woody material is abundant in the host 

sandstone and occurs as disseminated fragments and as 

trash seams or pockets. It is commonly associated with 

or close to mineralized material but is not everywhere 

mineralized. Only one small fossil log or branch was 

found in the mine. 

Fractur:es are so sparse in the Marjorie Ann mine that 

no truly representative trend was noted. 

MAUD MINE 

The Maud mine (pl. 1), in the center of sec. 14, T. 

47 N., R. 20 W., Montrose County, Colo., has for many 

years been the property of the Vanadium Corp. of 

America. It is reached by leaving Utah Highway 46 

at the head of La Sal Creek Canyon and traveling 3.8 

miles along the truck trail, then turning north and 

traveling one-fourth mile to the Canyon rim. 

The claim has been mined at three different levels, 

and the workings consist of several opencuts on the top 

of two sandstone lenses in the upper part of the Salt 

Wash Member of the Morrison Formation. The sandstone lenses form the surface of the bench overlooking 

La Sal Creek Canyon. Underground drifts at the base 

of the o~e-bearing sandstone are reached by a portal in 

the reentrant east of the surface cuts. 

The upper workings are in a thin sandstone lens that 

may be the same as the one containing the deposits a.t 

the Uranium Girl and Hesperus mines to the west. 

Erosion and cover make positive correlation of this lens 

uncertain. The deposit occurs in a light-green to white 

fine-grained silty sandstone that ranges from 0 to 35 

feet in thickness. The ore is in thin tabular layers and 

small rolls, one of which trends N. 40° W. Although 

most of the mineralized material has been removed, the 

ore apparently consisted mainly of carnotite and 

vanadium hydromica disseminated in the sandstone. 

The middle workings are in the top of the ore-bearing 

sandstone of the Salt Wash Member. They consist of 

a shallow open pit about 50 feet in diameter and two 

short exploratory drifts; one of the drifts bears N. 55° 

W. and the other S. 50° E. from the rear of the pit. 

Each drift is about 50 feet long and contains the most 

promising mineralized material in the mine. The mineralized material occurs as thin tabular, slightly undulating layers which range from 0 to 1 foot in thickness. In the northwest drift the ore lies between joints 

that parallel the walls. These joints may have, in part, 

controlled the localization of the ore. The principal 

ore minerals are carnotite, corvusite, montroseite, and 

vanadium hydromica. 

The lower workings are 45 feet below the middle 

workings and at the base of the ore-bearing sandstone. 

They consist of several drifts and small gob-filled stopes 

extending westward from the portal. An inclined track 

on a wooden trestle was used to raise the ore from the 

portal of the lower workings up the cliff to the middle 

workings. The principal ore minerals are vanadium 

hydromica and carnotite which occur disseminated in 

sandstone layers 4 to 6 inches thick. Carbonaceous 

material is closely associated with the ore minerals. 

Limonite is abundant and occurs as spots staining the 

sand grains. 
URANIDM DEPOSITS 65 

The mine appears to be out of ore; however, the seams 

and pellets of green mudstone within the thick sandstone back of the portal together with carbonaceous 

trash give a favorable picture of the surrounding area. 

Drilling indicates that the ore-bearing sandstone thins 

to the south, but favorable ground may extend to the 

west. 

Complete records of production are not available for 

the Maud mine. Ore produced in 1953 contained 3.60 

percent V20s and 0.50 percent U30 8 in a ratio of 7: 1. 

This ore is presumed to have been mined from the upper 

and middle levels. 

MORNING S.TAR MINE 

The Morning Star mine (pl. 1) is on the west rim of 

Lion Creek Canyon in sec. 12, T. 47 N., R. 20 W., 

Montrose County, Colo. The claim was originally located in 1913 by L. F. Gramlich of Paradox, Colo. In 

1939 it was owned and operated by J. W. Gramlich who, 

by 1945, had mined nearly 5,000 tons of ore. From 1945 

through 1953, only small tonnages were removed. In 

1954 it was acquired and operated by the Four Corners 

Uranium Corp. of Grand Junction, Colo. The mine 

is reached by a truck trail that leaves Colorado Highway 90 at the Hall Ranch about 1.6 miles east of the 

Utah-Colorado line. 

The workings consist of a large open pit bounded on 

the west by a series of underground drifts which, combined, cover an area 640 feet long and 140 feet wide. 

The deposit is in the upper part of the ore-bearing sandstone of the Salt Wash Member of the Morrison Formation. Here the beds dip about 2112 ° S. toward the axis 

of the La Sal Creek syncline. 

The ore occurs in elongate, gently rolling tabular 

bodies and in isolated pods in crossbedded sandstone in 

a zone about 40 to 50 feet above the base of the sandstone. In places, films, galls, and seams of green mudstone mark the crossbedding planes which bound the 

ore bodies. A continuous green mudstone layer ranging 

in thickness from 1 to 5 feet is 5 to 10 feet above the ore 

layer. The individual ore bodies are as much as 4 feet 

thick and the average thickness of ore is about 1 foot. 

The orientation of the long axes of the ore rolls is dominantly S. 60°-70° E. and parallel to the direction of 

paleostream flow, as determined by sedimentary structures which are well exposed in the floor of the open pit. 

The ore is yellow and greenish gray to dark gray and 

is mainly vanadium hydromica and sparse amounts of 

carnotite. These minerals occur in layers of platy sandstone and as "rattlesnake ore" where bedding planes are 

farther apart. "Rattlesnake ore" has a spotty appearance because the ore minerals are irregularly disseminated through the interstices and coat the sand grains. 

Carbonaceous material occurs as films and small fragments along bedding planes and in trash pockets. The 

thickest ore is in close proximity to the carbonaceous 

trash pockets; this association appears to be a reflection 

of the texture of the sandstone, for here the sand grains 

are somewhat coarser, more poorly sorted, and less well 

bedded than elsewhere. 

The Morning Star deposit is within the southern 

boundary of the La Sal Creek mineral belt. Drill-hole 

data indicate that the ore-bearing sandstone thins on a 

structural nose that separates the Morning Star deposit 

from the deposit on the Evening Star claim. The 

structural nose· is presumed to represent a cusp which 

formed along the paleochannel margin; it projects 

northward into the Salt Wash stream channel under the 

Big Bug claim at the west end of the Morning Star 

claim. Favorable sandstone and ore of the Morning 

Star deposit may e.xtend into the Moonlight and Birthday claims to the northwest. 

Records of production show the ore has an average 

grade of 1.80 percent V20 5 and 0.13 percent of U30s in 

a ratio of 14: 1. 

NEW YELLOW SPOT MINE 

The New Yellow Spot mine (pl. 1) is in the southwest corner of sec. 6, T. 47 N., R. 19 W., Montrose 

County, Colo. It is reached by traveling 8.6 miles from 

Paradox, Colo., by way of the Buckeye Reservoir-Dugway road which climbs the northwest end of Paradox 

Valley and extends southeastward along the southwest 

rim to the mine. The deposits were discovered and located as the New Yellow Spot claim by John W. 

Gramlich. They are on the east side of Lion Creek 

Canyon opposite the Gramlich Group. In 1940 the 

claim was relocated as the New Yellow S;?ot No. 1 claim 

by John, Richard, Leonard, and A. M. Stocks (C. W. 

Livingston, written commun., 1945) ; the following year 

the Stocks added the New Yellow Spot No. 2 and 3 

claims. Shortly afterward they sold the group of claims 

to the U.S. Vanadium Corp. (now the Union Carbide 

Nuclear Corp.), the present (1956) owner. Ore was 

produced between 1940 and 1944, and the mine has been 

idle since that time. Production records for that period indicate that the ore had an average content of 1.70 

percent V20 5 • The uranium /content was not given 

(Livingston, written commun., 1945) but is estimated to 

have been about equal to that of the nearby Morning 

Star mine or about 0.13 percent U30s, a ratio of 14: 1. 

The workings are a series of opencuts in an erosional 

remnant of the ore-bearing sandstone of the Salt Wash 

Member of the Morrison Formation. Lower sandstone 

and shale beds of the Salt Wash form the surface of the 

surrounding area which is on the southwest flank of the 
66 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

Paradox Valley anticline. The beds dip 2° to 3·o SW. 

toward the axis of the La Sal Creek syncline. The 

dominant joint pattern trends N. 55° W., roughly parallel to the strike of the beds. A less conspicuous set of 

joints trends N. 65° E. -All the joints dip at high 

angles. 

The deposits occur in a thin-bedded platy and crossbedded limonitic sandstone lens resting on a massive 

crossbedded sandstone that is 25 feet thick and forms 

the base of the ore-bearing unit. The ore bodies are 

tabular blanketlike masses, and rolls and pods as muph 

as 4 feet thick; they cover areas from 30 to 160 feet 

long and 1 to 20 feet wide. The size and configuration 

of the workings suggest that the major production came 

from roll-type ore bodies which trend approximately 

N. 80° E. 

The ore minerals are carnotite and vanadium hydromica, which occur ·along bedding planes and are disseminated in the host sandstone. The "rattlesnake ore" 

typical of oxidized deposits is common. The ore appears to have been localized largely by bedding structures such as platy sandstone referred to as festoons 

(Knight, 1930). Seams of green mudstone occur near 

the ore and in ·a few places may have limited the migration of the mineral-bearing solutions. 

SUMNER MINE 

The Sumner mine (pl. 1) is in unsurveyed sec. 2, T. 

47 N., R. 20 W., Montrose County, Colo. The property 

was located in 1941 as part of the Gramlich group under 

the ownership of Sam V., Irene, and John W. Gramlich, who later sold it to the U.S. Vanadium Corp. The 

property is reached by 3 miles of truck trail that turns 

north from Colorado Highway 90 at the William Hall 

ranch, which is 1.6 miles east of the Utah-Colorado line. 

The workings consist of a group of opencuts in the 

eroded surface of a light-gray medium-grained conglomeratic sandsto:iJ.e. The sandstone is composed 

largely of quartz grains. Pebbles of black, rod, ~and 

green chert are scattered throughout or are in thin 

lenses 1 to 2 feet thick near the base of the sandstone. 

The unit is frequently referred to locally as the "Christmas tree conglomerate," and it marks the base of the 

Brushy Basin Member of the Morrison Formation. The 

conglomeratic sandstone is separated from the orehearing sandstone of the Salt Wash Member by mudstone and siltstone beds which have an aggregate thickness of 70 feet. 

The deposit, a cluster of ore rolls, covers an area about 

200 feet long and 100 feet wide. The rolls appear to 

have been less than 50 feet long and -about 3 to 6 feet 

wide, and to have had an average ore thickness of 'a:bout 

1 foot. The long axes of the rolls trend roughly N.75° 

E. As erosion and surface stripping have removed 

most of the ore, the relationship between the rolls is 

uncertain, but they appear to have been interconnected 

by thin tabular layers of ore minerals that impregnated 

the sandstone. 

The ore minerals are vanadium rich, averaging 1.79 

percent V20 5 (Livingston, written commun., 1945), and 

include vanadium hydromica, tyuyamunite, and metatyuyamunite. Uranium is sparse, averaging about 0.07 

percent U30 8 , and occurs as carnotite intermixed with 

the tyuyamunite which imparts a greenish cast to the 

ore. The ratio of V 20 5 to U aOs in the deposit is about 

12:1. 

l-"00 HIGH MINE 

The Too High mine (pl. 3) is on the southeast side of 

Wray Mesa in sec. 36, T. 47 N., R. '20 W., Montrose 

County, Colo. The mine is reached from Utah Highway 46 by a dry-weather truck trail that turns southeast at the Pine Lodge ranch and crosses W ray Mesa to 

the mine on the south bench, a distance of about 9 miles. 

The deposit was discovered in 1952 by William C. 

Weaver of Grand Junction, Colo. It was mined during 

1953 and 1954 by-the Great Western Uranium Corp. of 

Moab, Utah. 

The deposit is near the crest of a low anticlinal structure, an extension of the Pine Ridge anticline. The 

beds dip 1 o to 2° SE. toward Greasewood Canyon and 

the axis of the East Coyote syncline. The workings 

consist of an open pit about 350 feet long and 150 feet 

wide. 

The deposit is in a light-green fine- to coarse-grained 

conglomeratic sandstone lens that is about 200 feet 

above the base of the Brushy Basin Member of the 

Morrison Formation. The sandstone lens ranges from 

0 to 30 feet in thickness and is com posed dominantly of 

quartz grains and abundant varicolored chert, lightgreen clay minerals, and carbonaceous trash. The 

chert is black, red, or green and ranges from sand size 

to pebbles 1 em in diameter. The sm~ller chert grains 

are scattered throughout the quartz sand and the pebbles are generally concentrated in lenticular pods. 

Green mudstone is 'a:bundant and occurs as films, seams, 

and pebbles and also fills the interstices between sand 

grains. 

The ore bodies occur as pods in the coarser lenses near 

the base of the sandstone. In places, the pods appear to 

be connected by thin layers of ore that impregnate the 

sandstone. The ore minerals are carnotite, tyuyamunite 

or metatyuyamunite, and vanadium hydromica associated with the carbonaceous wood fragments, carbonaceous mudstone, and green mudstone. The average 

ore contains 2.23 percent V205 and 0.34 percent UaOs in 

a ratio of 1: 1. 
URANIDM DEPOSITS 67 

URANIUM GIRL MINE 

The Uranium Girl mine is near the west side of sec. 14, 

T. 47 N., R. 20 W., Montrose County, Colo. (pl. 1), on 

the south rim of La Sal Creek Canyon. It is reached 

by the Yellow Bird truck trail which leaves Utah Highway 46 at the head of La Sal Creek Canyon and extends 

eastward for 3.2 miles to where a road turns north to the 

property. The Uranium Girl mine was first called the 

Emergency claim and was originally located in 1949. 

It was relocated in 1951 by Robert B., Shirley V., James, 

and H. W. Lammert. It wa.S again relocated in 1953 by 

E. B. Swanson who renamed it the Uranium Girl and 

acquired quit claim deeds from previous owners. 

The workings consist of a single opencut that covers 

an area approximaJtely 75 feet long and 30 feet wide. 

The deposit is in a light-brown medium- to fine-grained 

sandstone lens that ranges from 0 to 30 feet in thickness 

and may be equivalent to the unit that contains the 

Hesperus mine and the uppermost workings of the 

Maud mine. This lens overlies about 35 feet of interbedded mudstone and sandstone which separate it from 

the ore-bearing sandstone of the Salt Wash Member. 

Recent ( 1954) drilling on the claim indicates that the 

ore-bearing sandstone is about 40 feet thick, is overlain 

and underlain by green mudstone layers, and contains 

green mudstone seams and pellets. 

The ore minerals consist of carnotite and vanadium 

hydromica which are disseminated in thin layers of 

sandstone that range in thickness from 2 to 6 inches. In 

one place the mineralized material may have been 1 

:foot thick. Small pods containing carbonaceous :trash 

and ore minerals are also present. The grade of the 

ore produced averages 1.95 percent V20 5 and 0.24 

percent U 308 in a ratio of 8 : 1. 

VALLEY VIEW MINE. 

The Valley View mine (pl. 1) is in sec. 7, T. 48 N., 

R. 19 W., Montrose County, Colo. The property includes a group of five claims, the Valley View, Valley 

View No. 2, Lucky Lode, Inspiration, and Inspiration 

No. 1, which were staked by Messrs. J. B. and R. J. 

Columbo and Robert Proctor of Paradox, Colo., between November 16, 1936, and June 10, 1940. The 

property was leased with option to purchase by U.S. 

Vanadium Corp. during 1941 and 1942, but after an 

unsuccessful program of exploration the property was 

returned to the original owners (Livingston, writ.ten 

oommun., 1945). The claim was amended by Columbo 

on November 20, 1953. It has since been operated by 

the owners or on a lease basis by many different miners. 

In 1956 it was owned by the Price Exploraltion C<:>. of 

Grand Junction, Colo. The property is reached by the 

Carpenter Ridge Truck Trail from Paradox, Colo., a 

distance of 8 miles. 

The mine workings are on the northeast flank of the 

Paradox anticline, just east of the Valley View fault. 

Here the brittle sandstones such as the Entrada have 

been sheared into thin blocks along the fault. The 

intercalated beds of sandstone and mudstone of formations such as the Morrison, however, have been abruptly 

upturned at a point of flexure that lies about 100 feet 

northeast of the fault trace. The more plastic shale 

layers separating the sandstone beds have been thinned 

by squeezing. The Morrison Formation is in contact 

with the Wingate, Kayenta, and Navajo Formations, 

which crop out on the southwest side of the fault. 

The workings consist of seven ad its, three of which lie 

northeast of the fault zone in an undisturbed, almost 

flat lying part of the ore-bearing sandstone unit of the 

Salt Wash Member. A few feet to the southwest of 

these workings the beds turn abruptly upward; dips 

range frmn 77° NE. to slightly overturned. In the 

upturned beds, ore has been mined from four different 

levels which are connected by winzes and raises. It is 

from these workings that the major part of the ore has 

been produced. The drifts bear N. 50° W., paralleling 

the strike of the upturned beds and the fault. The longest drift extends 580 feet, and along it are several over-

, head stopes. The vertical distance between the 

· uppermost and lowermost workings is 140 feet. 

The ore-bearing sandstone is about 30 feet thick and 

is composed largely of medium to fine quartz grains and 

minor amounts of chert and black opaque minerals. 

The upturned sandstone is well cemented by silica., iron 

oxides, and carbonates. 

The ore bodies occur in the upper half of the sandstone and, aside from the fact that-the beds are vertical, 

are typical of Salt Wash deposits. They occur as tabular sheets, pods, and rolls that range from 0 to 2 feet in 

thiekness. The principal ore layers are localized behveen or near two seams of green mudstone which 

separate the sandstone lenses that compose the orebearing sandstone. 

The ore minerals are carnotite, eorvusite, montroseite, metatyuyamunite, and minor a.mounts of uraninite 

associated with carbonaceous logs, trash, and green 

mudstone. Carnotite and other oxidation products 

occur along slippage planes of minor faults and on 

fradture surfa.ees. The ore averages 1.34 percent V205 

and 0.38 peroont U 308, a ratio of 4: 1. 

The similarities of the ore bodies in the Valley View 

deposit to other Salt Wash.deposits, the high degree of 

cementation in the upturned part of the ore zone, and 

the absenee of radioactive minerals along the prineipal 

fault plane in the vicinity of the Valley View mine indicate that the ore was present prior to movement along 

the Valley View fault. As diseussed on page 34, the 
68 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

Valley View fault may have formed during Late 

Cretaceous or early Tertiary time, possibly as the result 

of adjustment of the salt to compressional forces of the 

Laramide revolution. During this period of uplift, the 

formations on the southwest side of the fault were raised. 

The mass on the northeast side of the fault was left 

mainly intact, hut the more plastic Morrison Formation was upturned as a result of drag along the fault. 

Later collapse of the salt mass initiated some downward 

movement of the beds on the southwest side of the fault, 

as shown by their present attitude, but it is doubtful 

that the formations lying to the northeast were disturbed 

to any great degree. 

VANADIUM QUEEN MINE 

The Vanadium Queen mine (pl. 12) is in sec. 29, T. 

28 S., R. 26 E., about 11 miles east of La Sal, Utah. 

The portals, on La Sal Creek Canyon about a third of a 

mile northeast of the confluence of La Sal and Twomile 

Creeks, are reached by a half mile of truck trail that 

connects with Utah State Highway 46 at the stream 

junction. 

The Vanadium Queen claim was originally ~taked on 

July 16, 1931, by Messrs. L. H. Couchman and H. W. 

Balsley of Moab, Utah. The property was later acquired by Mr. Abe Day of Moab, Utah, who relocated 

the Vanadium Queen claim and staked 11 additional 

claims from a block 3,000 feet wide and 3,600 feet long. 

The Vanadium Queen Nos. 1-12 claims were drilled in 

the summer of 1953 by the U.S. Geological Survey. 

The mine workings, at that time, were those nearest the 

outcrop on the Vanadium Queen No.1 claim. Mining 

activity had stopped because an exploratory drift bearing northeast penetrated .a thick layer of dark-green 

mudstone that marked the edge of the ore-bearing 

sandstone lens. 

Mining was resumed after the discovery of ore by 

drilling beyond the mudstone layer. In 1954 the property was sold to Mr. Don Danvers of San Antonio, Tex., 

and in 1955 it became the property of the Vanadium 

Queen Mining Corp., for whom Mr. Joe Pitts of Grand 

Junction, Colo.,was mine supervisor. 

The Vanadium Queen deposit is in the uppermost continuous Salt Wash sandstone, commonly referred to as 

the ore-bearing sandstone (see p. 12). Drill-hole data 

from around the mine show that the ore-bearing.sandstone ranges in thickness from 20 to 87 feet. In plan 

the group of deposits trend northeast and lie close to 

the axis of the La Sal Creek syncline but are oriented 

obliquely to it. The deposits extend along a. low depression at the base of the ore-bearing sandstone. This 

depression is a sedimentary feature independent of tectonic structures and represents a local channel scoured 

by a Salt Wash stream into the underlying mudstone 

prior to deposition of the ore-bearing sandstone. 

All three workings of the mine are connected by a 

single haulage drift. The main drift is about 550 

feet long and varies in trend from N. 50° E. at the portal 

to about due north at the innermost workings. 

The outer workings are the largest and oldest of the 

mine and are in the area around mine portals 1, 2, and 

3. These workings comprise a maze of drifts and rooms 

that extend northwest and southeast of. the main drift. 

Part of the workings are caved and were not rna pped. 

The workings 'cover an area a:bout 510 feet long and 

about 160 feet wide at its widest point and have an 

arcuate trend from northwest-southeast to northeastsouthwest. The arcuate shape of the deposit and the 

trends. of sedimentary features suggest that the deposit 

may be contained in a lenticular sandstone that was deposited in a channel meander. 

The sandstone in the outer workings is light brown 

to light gray and consists of medium- to fine-grained 

quartz and minor accessory minerals. With the exception of the red and green mudstone at the portal and 

the dark-gray mudstone unit in the main drift (pl. 12, 

section A-A') and in the east end of the working (pl. 

12, section B-B'), mudstone is sparse and is limited 

chiefly to thin seams and films. 

The dark-gray mudstone lens exposed in the main 

drift is considered important in reconstructing the 

order of sedimentation in the Vanadium Queen mine 

area and may be a factor affecting ore emplacement. 

Section A-A' (pl. 12), measured along the main haulageway, shows that the mudstone fills a scour cut in 

sandstone. This mudstone is also e.xposed farther east 

in the back of the middle workings where it overlies 

the same sandstone unit, but at a higher stratigraphic 

level. In the main haulageway the base of the mudstone swings downward toward the portrul at an angle 

of 17°. The sandstone lens disappears in the floor of 

the drift and mudstone is exposed along the wall for 

a distance of 70 feet. The mudstone unit, in turn, is 

truncated on the west by another sandstone body. The 

mudstone lens may have been cut or scoured hy a locally degrading stream, probably a stream at flood 

stage. This stream is marked by a small terrace that 

has been cut in the mudstone at the contact. These 

exposures indicate that at least five distinct episodes of 

sedimentation and scouring are recorded within this 

part of the mine: ( 1) deposition of the inner (middle 

workings) sandstone, (2) scour by stream action, (3) 

deposition of mudstone, ('4) scour by stream action, 

and ( 5) deposition of outer (outer workings) sandstone. 

The dark-gray mudstone exposed in the main drift 

also occurs near the back in the eastern end of the outer 
URANIUM DEPOSITS 69 

workings (pl. 12, section B'-B") and in the middle 

workings. The basal contact of the mudstone is stratigraphically higher than in the main drift. The mudstone rests on a sandstone lens that is continuous with 

the deeply scoured sandstone of the middle workings. 

Both the sandstone unit and the gray mudstone overlying it have been 8coured and are in contact with the 

same sandstone lens that truncates the gray mudstone 

in the main haulageway. The trend of the contact of 

this scour is indicated by the location of the edge of 

the gray mudstone -(pl. 12). 

Sedimentary features, such as crossbedding, ripple 

marks, and stream lineation (pl. 12), indicate that 

although the general channel direction was N. 70°- 80° 

E., local meanders were widely divergent from the 

major trend. This same general channel direction was 

determined in the Firefly-Pigmay and Gray Daun mines 

and is confirmed by information from drill holes northeast of the Vanadium Queen mine. 

The dark-gray mudstone may have been an impermeable barrier to mineral-rich solutions. If so, the 

solutions moving through the ore-bearing sandstone 

were deflected around the flanks or trapped by the mudstone lens. The elongate ore bodies and long axes of 

the ore rolls (pl. 12) generally parallel the margin of 

the mudstone lens and also the scour-and-fill features 

observed in the adjacent sandstone. Similar associations of mudstone lenses and ore bodies can be observed 

elsewhere in the mine. 

The ore bodies of the outer workings occur as tabular 

blanketlike bodies and as pods and rolls. The blanket 

ore bodies are as much as 180 feet long and 80 feet wide. 

Some of the rolls are as much as 30 feet long. The ore 

in the outer workings is considerably oxidized and rich 

in disseminated carnotite, which with roscoelite and 

vanadium hydromica impart a greenish color to the ore. 

Roscoelite and vanadium hydromica are the principal 

vanadium minerals. The proximity of the deposits to 

the outcrop and their location above the water table 

explain the high degree of oxidation. Very sparse 

amounts of malachite and azurite occur as spots or 

"buttons" in one place on the drift walls. Carbonaceous 

wood is sparse in the outer workings where it occurs 

in barren mudstone. In a few places it occurs with 

mineralized material. 

Most of the middle workings are east of the main drift 

and cover an area 130 feet long and 125 feet wide. It 

is almost entirely made up of rooms, pillars, and connecting drifts which join the main drift in two places. 

The middle workings are wet and require pumping. 

The deposit mined in the middle workings is in a 

light gray to light brown massive to crossbedded sandstone lens containing minor amounts of mudstone. The 

mudstJone occurs mostly ·as thin seams or lenses and is 

usually green or gray. In ·a few places, however, it is 

red. In the hack over much of the working the darkgray mudstone lens, described earlier, is exposed. 

The ore in the middle workings occurs chiefly in undulaiting, trubular, or hlanketlike ibodies. The ore in 

some tabular bodies rea0hes a thickness of 6 feet or 

more. There are three shart ~re rolls, all 10 feet or 

less in length, in the workings. The ore is composed 

principally of black unoxidized and partially oxidized 

minerals. Apparently most of the ore bodies lay partly 

beneath the water table in a sandstone lens that was 

nearly enclosed by mudstone and partly saturated prior 

to mining. Sparse amounts of yellow minerals indicate 

that parts of the ore bodies were above the water table 

and partially oxidized. 

In 1954 the ore body nearest the haulageway was 

sampled, shortly after it was first exposed, by A. D. 

Weeks and the authors. The ore below the track level 

was completely water saturated. Weeks (written commun.,.1957) identified carnotite, tyuyamunite, metatyuyamunite, melanovanadite, simplotite, and vanadium 

silicates. She found that the water standing in the 

workings had a pH greater than 7.6. She believes the 

alkaline environment explains the presence of melanovanadite and simplotite, which form under such a 

condition. Weeks also noted the presence of a vanadium-iron mineral 1that gives an X-ray paltJtern similar 

to nolanite, which 'is a low-valent vanadium-ircm 

mineral. 

Carbonaceous wood is sparse in tJhe middle workings, 

but where it is found ore minerals replace or ·impregnate 

it. 

The innermost workings lie at the northeast end of 

the main drift, which is composed of roorrrs and connecting dri:fits covering an area ahout 100 feet long and 

80 feet wide. Like the middle workings, the inner 

workings are wet, and places mined ibelow the level of 

the main drift must·be pumped. 

The sandstone in •the inner working is light brown to 

ligh1t gray, massive to crossbedded and, in places, is 

tightly cemented. A mudstcme conghl'lnerate layer 2 

feet t hick at ltJhe back just above t'he ore is exposed ~n 

the north and east walls of the working. A gray mudstone breccia lies near the margin of the ore body ·and 

below the conglomerate. The breccia apparently represents collapse of mudstone al>cmg the stream ma.rgin 

(fig. 12) during depositionofttheore-bearing sandstone. 

In places the angular mudstone fragments rest in ·an 

imbricate fashion within a broad shallow scour. In 

cross section, the degree of overlap shown by the fragments appears to indicate where individual fragments 

are with respect to the channel margin. Near ~the chan-
70 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

FIGURE 12.-Greenish-gray mudstone-,pebble conglomerate (top) 

and mudstone breccia (middle) resting on ore-bearing sandstone lens in the Vanadium Queen mine. 

nel a xis, for example, overlap of ·the fragments is complete, and a line drawn along their edges will be almost 

vel'tical. On either side of the axis the fragments display overlap which increases laterally toward the channel margin, and the result is a shingling effect. A line 

drawn along the edges of overlapping fragments will 

be inclined toward the axis of the channel. Near the 

channel margins, overlap is slight, a.nd lines drawn 

along t he edges of overlapping fragments are only 

slightly inclined toward the channel axis. In the V anadium Queen mine the local channel marked by mudstone fragments rests on a sandstone lens that contains 

ore. It is conceivwble, therefore, tha.t <the study of imbricate mudgtone 'brecci•as may be used locally as a. guide 

to thicker sandstone lenses and, subsequently, to new 

ore bodies. 

The ore of the inner workings occurs in undulating 

tabular or blanketlike bodies as much as '60 feet long, 

50 feet wide, and 5 feet thick. Several small pods as 

much as 3 feet long occur in the workings. The ore is 

predominantly the bl[\jck type but in places blue-black 

and yeUow ore is found. The yellow carnoti•tetype ore 

is on or in close proximity to open fractures. The presence of blue-black minerals in the ore of the inner workings suggests that the ore bodies are in an in:itial stage 

of oxidation. As in the ore bodies of the middle workings, t:he oxidation state of these ore bodies is prohwbly 

related to a relatively recent drop in the water table. 

Carbonaceous wood is very sparse in the inner 'WOrkings and is found as macerated debris on the bedding 

planes of the barren sandstone. 

The principal vanadium minerals in the Vanadium 

Queen mine are montroseite, corvusi·te, vanadium hydromica, hewettite, tyuyamun:ite •and simplotite. The principal uranium minerals are uranini.te, coffinite(?), and 

carnotite. Most of the ore minerals coat the quartz 

grains, fill the interstices hetrween them, and, in places, 

replace fossil wood. Montroseit e, corvusite, pitchblende, and coffinite(?.) are intima-tely intermixed in the 

ore bodies that are virtually unoxidized. The oxidized 

parts of the deposits contain the remainder of the mineral suite. The ore produced contains 2.79 percent V20 5 

and 0.35 percent U 3 0 8 in a ratio of 8: 1. 

There are two sets of fractures in the V•anadium 

Queen mine: a dominant set that trends N. 70° W. to 

due west, and a minor set that trends slightly west of 

north. The dominant set is bes-t exposed in the main 

drift near t he portal. This set roughly parallels the 

axis of the La Sal Creek syncline and is thought to 

be accentuated by incipient slumping of the beds near 

the canyon wall. The second set is nearly perpendicular to the axis and is thought to be the result of tensional 

stress. The fractures ·appear to have in no way cont;rolled the deposition of the •are; however, where the 

fractures are open and penetrate the ore bodies, they 

have facilit•ated the circulation of ground water and 

the oxidation of the ore. Carnotite and tyuyamunite 

commonly coat the fracture surfaces. 

VISTA GRANDE MINE 

The Vista Grande mine (pl. 1), in unsurveyed sec. 

2, T. 4 7 N., R. 20 ·w., Montrose Coun•ty, Colo., is reached 

by 2 miles of truck trail which turns north from Colorado Highway 90 at the William Hall ranch, llh miles 

east of the Utah-Colorado line. The claim was staked 

a;s part of the Gramlich Group by Sam V. and Irene 

Gramlich and has since been acquired by the U.S. Vanadium Corp. (now Union Carbide Nuclear Corp.). 

The workings consist of a small opencut in the upper 

part of the ore~ bearing sandstone of the Salt W·ash Member of the Morrison Formation. The beds strike N. 65° 

W. and dip about 4° 18. toward the axis of the La Sal 

Creek syncline. 

Drill-hole data from the Vista Grande claim indicate 

that the ore-bearing sandstone ranges in thickness from 

27 to 36 feet and is underlain by a layer of green mudstone that is 1 foot thick or less. The ground lies within 

the limi·ts of the La Sal Creek mineral belt. 
URANIDM DEPOSITS 71 

The ore bodies have been obscured by recent bulldozer operations, but they are assumed to be similar to 

those of ,the Confusion and Angle deposits nearby. In 

1953 the mine produced ore that averaged 2.57 percent 

V20s and 0.44 percent U30s, a ratio of 6: 1. 

WEDGE MINE 

The Wedge mine (pl. 1) is in the southeast corner 

of unsurveyed sec. 2, T. 47 N., R. 20 W., Montrose 

County, Colo. The Wedge daim ·was located in 1941 

as part of the Gramlich group of 26 possessory claims 

which were staked by Sam V., Irene, and J'ohn W. 

Gramlich. On June 14, 1941, the group was divided 

and the Wedge claim became the property of Sam V. 

and Irene ·Gramlich, who later sold it to the U.S. Vanadium Corp., of Uravan, Colo. Company exploration 

by diamond drilling during 1951 and 1952 resulted in 

the discovery of ore under the Wedge and the Independence claim to the north. The mine was active 

during 1952 and 1953 when ore was produced from both 

claims. 

The ·wedge mine workings consist of an inclined 

shaft which bears N. 22° E. from the portal for about 

150 feet where it is joined by a drift. This drift, bearing N. 35° E., extends for a distance of approximately 

180 feet along the base of the ore-bearing sandstone of 

the Salt Wash. About 30 feet from the end a side drift, 

bearing N. 80° E., extends for a distance of 380 feet. 

There are small rooms adjoining the drifts. 

The deposits are in the lower part of the ore-bearing 

sandstone, which within the claim ranges in thickness 

from 37 to 56 feet. The sandstone is underlain by a 

green mudstone layer that ranges from 0 to 3 feet in 

thickness. Mining has removed most of the ore, but it 

appears that the ore bodies were discontinuous podshruped masses rather than tabular layers and rolls. 

Abundant carbonized fragments of wood indicate that 

the pods were small trash pockets. The ore minerals are 

of the oxidized type and include carnotite, metatyuyamunite, and vanadium hydromica. These occur as 

coatings on quartz grains and as replacements of woody 

material. The carbon occurs as minute flakes in gray 

mudstone and as seams of shiny, black vitrainous material containing a minor amount of very ·fine grained 

marcasite. A few fragments of fossilized dinosaur 

bone were noted that are replaced largely by calcite and 

possibly by some barite. The ore produced had an 

average grade of 1.68 percent V20 5 and 0.38 percent 

U 30s, in a ratio of 4: 1. 

YELLOW BIRD· MINES 

The Yellow Bird mines (pl. 13) are in sees. 13 and 14, 

T. 47 N., R. 20 W., Montrose County, Colo., approximately 1112 miles east of the Utah-Colorado line on the 

south side of La Sal Creek Canyon. 

The mines are included in a group of claims owned 

and operated by the Vanadium Corp. of America, 

Durango, Colo. The four mine workings of the Yellow 

Bird group that have been mapped are on the Butterfly claim. Additional unmapped mine workings on the 

Eva and the Three Jacks claims, which lie east and 

west, respectively, of the Butterfly claim, are part of 

the Yellow Bird group. All the ore mined from these 

claims is listed under Yellow Bird. The claims are 

reached by a truck trail which leaves Utah Highway 46 

near the top of the hill at the head of La Sal Creek 

Canyon and extends eastward along the north bench 

of W ray Mesa for a distance of 41h miles. 

The Yellow Bird mines have long been famous for 

their rich carnotite ore which was first mined in 1899 

and used in concentration experiments at the Cashin 

~{ill by Messrs. Poulot and V oillique. Ore from the 

Yellow Bird mines and the Rajah mine, of the Roc 

Creek area, was shipped to France ·where Madame 

Curie extracted radium. The remnants of a burro trail 

which traversed the canyon waH below the Yell ow Bird 

mines serve as a reminder"of those early days of uranium 

mining. 

The Yell ow Bird deposits are in the uppermost continuous sandstone of the Salt Wash Member of the Morrison Formation. The ore-bearing sandstone is about 

50 to 110 feet thick in the vicinity of the mines and is 

composed of fine- to medium-grained light-brown to 

light-gray sandstone. 

The mapped workings are along the canyon rim in a 

roughly east-west line extending a distance of about 

700 feet. The westernmost consist of a single drift 110 

feet long and 10 to 15 feet wide, trending S. 75° W. from 

the portal. The drift has one short adjoining side drift. 

The west middle workings, the smallest of the mines, 

consist of a wide drift that extends about 80 feet from 

the canyon rimS. 35° W. from the portal. In places the 

drift is as much as 20 feet wide. A short side drift 

adjoins the main drift near the portal. 

The east middle working is a single room supported 

by several pillars. It is about 200 feet long and 95 feet 

wide at its widest point. In plan the workings have 

a "dog-leg" outline that trends S. 20° E. in the vicinity 

of the portal and S. 55° W. in the innermost part. 

The easternmost workings are the largest and consist 

of several straight drifts that trend south from the 

canyon face and are connected by a sinuous cross drift. 

In places the drifts widen into rooms. The mine has 

two portals on the canyon rim that are about 50 feert 

apart. ·The mine workings cover an area 340 feet wide 

and 400 feet long. All the workings are virtually dry. 
72 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

The sandstone is generally of the same character 

throughout the mine workings. It is mainly light brown 

to light gray, hut locally where the sandstone is silty or 

contains abundant small mudstone lenses it is light 

green. The sandstone is crossbedded in places and, in 

other places, is nearly flat bedded or massive. Mudstone and siltstone are abundant in the ore-bearing 

sandstone and occur as thin seams or in layers as much 

as 4 feet thick and more rarely as thin conglomerate 

units. Some of the mudstone units display a ",pinchand-swell" structure. In section G-G' (pl. 13) where 

the lithology has been projected between the mapped 

sections, the mudstone cuts across the sandstone at an 

angle of 20°, a feature that suggests a scour-and-fill 

structure. In a few places the mudstone is contorted 

as a result of the slump of the immediately overlying 

sandstone beds. Nearly all mudstone and siltstone in 

the workings are gray or green. 

The ore bodies of the Yell ow Bird deposit are similar 

to those throughout the La 'Sal Creek area. They occur 

as gently rolling ta:bular layers as much as 170 feet long 

and 170 feet wide, and they range from 0 to 5 feet in 

thickness. Locally the ore occurs as discontinuous podlike bodies that are a few feet in length and less than a 

foot in thickness." Rolls are sparse in the mine workings. Only seven rolls were mapped; five of these bear 

northward between N ... 30° W. and N. 30° E. (pl. 13). 

They range in length from 8 to 18 feet. 

The ore of the Y eHow Bird mine is generally dark 

gray to light greenish gray. The dominant ore minerals 

are vanadium hydromica, tyuyamunite, and carnotite 

which are most conspicuous near the east portal In 

places, montroseite, corvusite, and pitchblende ( ~) are 

in small pods and thin layers that are generally dark 

gray, black, or bluish black jn contrast with the other 

ores. The darker, less oxidized ores are in the rooms in 

the southern part of the east workings. ·The location 

of the light and dark minerals suggests that oxidation 

is greatest near the outcrop and progressively decreases 

a way from it. The ore produced from the Y eHow Bird 

mine contained 1.80 percent V2 0 5 and 0.34 percent 

U30 8 , a ratio of 5 : 1. 

Carbonaceous wood fragments and plant debris are 

sparse throughout the mine and only very few carbonaceous films occur in mineralized material. Two 

carbonaceous logs were found, a small barren log near 

ore and a larger mineralized log 30 feet long and as 

much as 1 foot in diameter. A few nonmineralized 

silica-replaced saurian bone fragments occur in the mine 

within ore layers. 

Fractures in the mine workings trend generally N. 

60°-80° W. (pl. 13) and have vertical or steep dips to 

the northeast. The fractures transect the ore bodies 

and nowhere appear to have had control over ore emplacement. In general, the fractures parallel the 

canyon rim and the axis of the La Sal Creek syncline. 

They appear to be accentuated by incipient slump 

along the canyon escarpment. 

It is noteworthy that the Yellow Bird mines represent 

the only large accumulation of deposits on the south 

rim of La Sal Creek Canyon. The relation of the Yellow 

Bird deposits to the deposits on the north side of the 

canyon is obscured by erosion of the ore-bearing sandstone in the 4,000 feet of intervening canyon area that 

separates the Yellow Bh·d and Gramlich groups of 

mines. Data gained through mapping the Yell ow Bird 

mines (pl. 13) and the mines north of the canyon (pis. 6, 

12) indicate that the trends of the paleostream channels 

in the two areas are nearly normal to each other. The 

ore deposits north of the canyon are in a channel that 

trends generally east, whereas the Yell ow Bird deposit 

is in what appears to be a north-trending channel. In 

the area west of the Yell ow Bird mines, trends of sedimentary structures observed in rim exposures and in the 

lower workings of the Maud mine combined with drillhole information from around the lT ranium Girl mine 

indicate that a paleostream flowed along what is now 

the south edge of La Sal Creek Canyon. South of the 

Yellow Bird group, drilling showed that the ore-bearing sandstone consists of several relatively thin lenses 

separated by greater thicknesses of red mudstone. This 

suggests an "off-channel" or flood-plain area where 

streams depositing the Salt Wash flowed intermittently. 

By relating these areas to one another, it is postulated 

that a southern subsidiary channel branched from the 

main Salt Wash channel in the general area of the Firefly-Pigmay, Gray Daun, and Vanadium Queen ~ines 

and followed a more easterly course. This channel 

passed through an area that has since been eroded and 

is now the location of the present canyon. Only in the 

areas of the Uranium Girl, Maud, and Yellow Bird 

mines are vestiges of the paleochannel preserved. 

Trends of sedimentary structures in the Yell ow Bird 

mine indicate that this subsidiary channel swung abruptly north in the area of the mine and perhaps rejoined the main channel in the vicinity of the Evening 

Star or Morning Star mines. 

The ore rolls in the Yellow Bird mines display conspicuo~s parallelism to sedimentary structures (pl. 13) 

-such. as current lineation, the dip of the cross beds, and 

local stream scours. If the ore rolls were formed parallel to the movement of the mineralizing solutions as 

suggested by Shawe (1956, p. 239-241), then certainly 

the ore-bearing solutions followed the channels. This 

evidence and supporting evidence from other mines of 

the La Sal Creek area strongly indicate that the paleo-
GUIDES TO EXPLORATION AND ORE, 73 

stream channels were the primary conduits through 

which the ore-bearing solutions moved and are the main 

sites in which ore is deposited. 

YIP YIP MINE 

The Yip Yip mine (pl. 1) is on the south bench of 

Wray Mesa in unsurveyed sec. 1, T. 46 N., R. 20 W., 

Montrose County, Colo. The property was staked in 

1951 by William C. Weaver. Access to the Yip Yip 

claims is gained by turning southeast from Utah Highway 46 at the Pine Lodge Ranch and crossing Wray 

Mesa on a dry-weather truck trail, for a distance of 8 

miles. The mine was operated in 1952 and 1953 by the 

Don Danvers Uranium Co. of Moab, Utah. 

The workings consist of an opencut along the ledge 

formed by the ore-bearing sandstone of the Salt Wash 

Member. An adit enters the base of the sandstone on 

the north side of the cut and extends 50 feet on a bearing 

N. 37° W. Near the end a second drift bearing N. 20° 

E. extends 60 feet, and along its northwest side are several small rooms. The portal is cut in a thin lens of 

light-brown thin-bedded silty sandstone that ranges 

from 0 to 5 feet in thickness. The sandstone is overlain 

by a green mudstone layer which separates the lens 

from other .sandstone beds of the ore-bearing sandstone. 

The lens is composed of thin laminae of fine- to very 

fine grained well-sorted quartz grains. Limonite stain 

is abundant. The sandstone grades upward into platy 

carbonaceous siltstone which in turn grades upward into 

green mudstone. The carbonaceous siltstone contains 

the ore minerals; it ranges from 0 to 6 inches in thickness. Above the green mudstone layer is another silty 

carbonaceous unit similar to the one beneath the mudstone. Above this upper silty unit is highly crossbedded 

sandstone that is coarser grained than that at the base of 

the ore-bearing unit. 

The deposit covers an area about 40 feet wide and 

100 feet long. It consists of a single tabular ore body 

in the platy carbonaceous siltstone described earlier. 

Carnotite and vanadium hydromica appear to be the 

only ore minerals and are disseminated throughout the 

siltstone. The average grade of the material produced 

was 1.46 percent V 205 and 0.34 percent U 30 8 in a ratio 

of 4: 1. 

SUGGESTIONS FOR PROSPECTING 

The authors believe that several undiscovered deposits 

of uranium-vanadium exist in the La Sal quadrangle. 

The most favorable areas for these deposits will be discussed in the following paragraphs, in an order based 

on the amount of information available at the present 

time. 

The area along La Sal Creek considered favorable 

(pl. 4) probably contains several deposits in addition 

to those now known. These may be found in the process 

of further defining the known deposits and the limits 

of the La Sal Creek mineral belt. Subsurface explora-

. tion between the Firefly and the Rattlesnake mine, west 

of La Sal, Utah, beyond the mapped area may disclose 

that the La Sal Creek mineral belt is virtually continuous to the west and contains deposits similar to those 

along La Sal Creek. 

Other such belts may be present in the area and exploration around such deposits as those recently discovered on Hop Creek and the east flank of Mount 

Mellen thin may find favorable areas containing 

uranium-vanadium deposits. The area on Carpenter 

Ridge between the Valley View mine and the Lone Pine 

mine on Roc Creek, east of the rna pped area is also con- · 

sidered to be worthy of drill exploration for uraniumvanadium deposits. The recent development of a deposit west of La Sal Pass, which is just west of the 

mapped area, and observed favorable thicknesses of 

the ore-bearing strata on Moore's Ridge and to the north 

suggest that the La Sal Pass area may contain deposits 

of uranium-vanadium ore. The :fact that thick sandstone containing seams and pebble conglomerates of 

green mudstone crops out in the graben of the Scorup 

anticline along Geyser Creek suggests that this area 

may be :fa.vorable for uranium-vanadium deposits. 

West of the Valley View mine and Valley View fault 

are several prospects containing uranium-vanadium 

minerals. Where the ore-bearing sandstone is exposed 

it is more than 30 feet thick. Such thickness suggests 

that the area along the ridge east of West Paradox 

Creek and north of the National Forest boundary to 

Buckeye Reservoir may be underlain by ground favorable for uranium deposits. 

In most of the areas discussed, surface prospecting 

will be extremely limited, for the ore-bearing sandstone 

is either poorly exposed or covered by younger sedimentary rocks or by rock debris and soil. . In many 

places, the cover is many hundreds of feet thick. Much 

of the western part of the area is covered by debris from 

the igneous rock of the La Sal Mountains. Drilling will 

be difficult in fractured and faulted rock and in areas 

underlain by gravels composed of boulders of igneous 

rocks. 

GUIDES TO EXPLORATION AND ORE 

Thickness of sandstone, its color and grain size, carbon and mudstone content, and sedimentary features 

such as scour-and-fill bedding, festoon bedding, and 

trash pockets (described on p. 43) were used in the 

process of searching for uranium-vanadium deposits by 

drilling and surface exploration. Various combinations of these features were used as criteria to determine 

whether the ground was favorable, semi:favorable, or 
74 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

unfavorable for the presence of ore. For example, 

ground considered favorable is underlain by sandstone 

strata that are 30 feet or more thick; are light brown 

to light gray and of medium and fine grain size; contain sparse to abundant carbonaceous material and gray 

or grayish-green interstitial mudstone or mudstone as 

films, pebbles, or seams; and are underlain and (or) 

overlain by gray, greenish-gray, or green mudstone 

that is 0.1 foot or more thick. In contrast unfavorable 

ground is characterized by sandstone less than 30 feet 

thick or by complete absence of sandstone; if present, 

the sandstone is usually reddish brown, is composed of 

fine to very fine grains of sand and silt, contains no carbonaceous material, and is enclosed by reddish-brown 

mudstone above and below. Ground designated as 

semifavorable has a combination of favorable and unfavorable criteria as seen in a drill hole or vertical section of outcrop. These criteria were listed, and a scoring system similar to that described by Weir (1952, 

p. 23) was devised for ground classification. This system was revised as drilling progressed and more information was .gained. A map showing the location of 

drill holes and ground classification was used concurrently with the drilling to determine the location of 

future drill holes (pl. 4). Supplemental maps such as 

contour maps of the base of the ore-bearing sandstone, 

isopachous maps showing thickness of the sandstone, 

isolithic maps showing ratio of sub-sand-size particles 

to sand-size particles in the sandstone, and maps showing areas underlain by green mudstone were also constructed from drill-hole data. 

Geologic cross sections were constructed through completed drill holes to determine the most favorable coring 

interval for future drilling in unexplored groun!l. In 

explored ground, cross sections were used to show the relation to the ore-bearing sandstone to overlying and underlying strata and to correlate mineralized layers within the sandstone. 

In .general, these studies show that the ground designated as favorable (pl. 4) includes an irregular elongate belt bearing about N. 70° E. This belt roughly 

parallels the direction indicated by sedimentary structures. In this belt the ore-bearing sandstone is generally 

thickest, owing to scour-and-fill channels at the base of 

the sandstone and also to thickening at the top. North 

and south the sandstone lenses are thinner and interfinger with mudstone lenses. 

The ~ollowing summary of geologic features considered favorable for the presence of uranium-vanadium deposits is given to assist the search for additional 

deposits within the mapped area. 

1. The host rock is composed of lenticular channel-type 

sandstone that is 30 feet thick or more. It is the 

uppermost continuous sandstone layer of the Salt 

Wash Member of the Morrison Formation. 

2. The sandstone is light brown, white, or light .gray. 

3. The sand grains range from medium to fine (Wentworth scale) in size. 

4. Green or gray mudstone is above or below the sandstone and within the sandstone as seams or pebbles, 

or it fills the interstices between sand grains. 

5. Carbonaceous material is present as flakes or In 

trash pockets. 

In addition to the basic features above, the following 

features may be helpful to the prospector at the outcrop or to the miner underground in determining t_he 

best direction in which to mine. Many of the ore bodies 

are known to parallel the direction of ancient Salt Wash 

stream flow. The measurement of the dip direction of 

bedding -contacts and foreset bedding, the direction of 

current lineation on bedding surfaces, and local scour 

features may aid in determining this direction. Once 

determined, driHing along lines perpendicular to this 

direction or mining parallel to it with systematic crosscutting are accepted methods of exploration. 

OTHER RESOURCES OF POSSIBLE ECONOMIC INTEREST 

COAL 

Deposits of low-rank bituminous coal in the La Sal 

quadrangle are mentioned here mainly because similar 

deposits in the Nucla-Naturita area to the east have 

been of local value to the uranium-vanadium industry 

and surrounding community. Thin ~earns, ranging 

from a few inches to three feet in thickness, are erratica1ly distributed throughout the area in the middle 

member of the Dakota Sandstone of Late Cretaceous 

age. In much of the area, however, the middle and 

upper members of the Dakota have been removed by 

erosion, and only the lower conglomeratic _sandstone 

member is left, especially in the southern third of the 

mapped area. To the north the Dakota has been preserved in entirety mainly in structural basins or in fault. 

blocks associated with collapse. 

The most notable occurrence of coal in the mapped 

area is at an abandoned mine in sec. 25, T. 48 N., R. 20 

W., Montrose County, Colo., that is shown on Coffin's 

(1921) map as Mitchell's Coal mine (pl. 1). The deposit is at the head of Paradox Valley between the road 

from Paradox to Buckeye Reservoir and West Paradox 

Creek. The coal bed, as much as 2 feet thick, is in the 

upper part of the middle shale member of the Dakota, 

about 88 feet above the Burro Canyon-Dakota contact. 

The coal bed is in a sequence of .gray carbonaceous mudstone and shale layers that total110 feet in thickness. 

This sequence is -capped by a yellowish-brown sand-
OTHER RESOURCES OF POSSIBLE E.CONOMIC INTEREST 75 

stone ledge 20 feet thick. The total thickness of the 

Dakota in this area is 14 7 feet. 

The coal is generally dull black and has a brownish 

to black streak. Seamlets of a shiny black vitrainous 

material are very common. On weathered surfaces the 

bed disintegrates to small fragments and fine powder, 

but below the surface it forms shaly blocks which appear to be firm enough to withstand shipping. The 

ash content is high. Fusain or mineral charcoal is common. Specks of resin, common in other Cretaceous 

coals, are scattered through most of the unit. Minute 

flakes of marcasite and crystals of pyrite are present 

at many places. 

One peculiar feature of the coal of the abandoned 

mine, which may be of academic interest only, is the 

abundant ellipsoidal cavities which resemble the casts 

of small pine cones. These cavities are of variable size 

but most are approximately 16 mm in length and 10 

mm in diameter. The cavities are partly filled with a 

brown powdery fusainous substance which disintegrates 

to the touch and is therefore unidentifiable except that 

it is woody material of coniferous origin (R. W. Brown, 

written commun., 1956) . Samples collected by ,J. C. 

Warman were studied by J. M. Schopf, U.S. Geological 

Survey, who states that, "the surface of the cast shows 

the cockscomb structure of marcasite which apparently 

crystallized during the peat stage of coalifaction, that 

is prior to compaction and consolidation. This time of 

crystallization prevented compaction of the organic matter encased by the marcasite. As crystallization progressed, the enclosed material became crushed and disorganized. After coalifaction the marcasite was, for 

the most part, leached out * * * and disorganized 

conical shapes which fit rather loosely in their casts 

were left. The cuticular material on the surface of 

the casts * * * has not suffered from vertical compression." 

Other areas where coal beds of possible economic interest were noted were in sees. 14 and 17, T. 27 S., R. 

. 25 E., and sees. 4 and 15, 'T. 28 S., R. 25 E., of San 

Juan County, Utah. 

COPPER DEPOSITS 

Within the mapped area, copper minerals are in disseminated replacement deposits near the sedimentaryigneous contact and in fissures in sedimentary rock both 

near to and far from contacts with igneous rocks. None 

of the deposits is known to be of sufficient size or tenor 

to be classed as ore. 

Minor concentrations of copper minerals were noted 

in rock dug from three caved prospect pits in sec. 31, T. 

26 S., R. 25 E. (pl. 1), between Porcupine Ridge and 

North Mountain. The prospect pits are in beds belonging to either the Cutler o~, more likely, the Rico Formation and lie within 300 to 800 feet of the igneous 

contact. The copper minerals are chalcopyrite and 

malac}:lite that occur with more abundant amounts of 

pyrite. As far · as determinable, the copper occurs in 

veinlets, probably filling fissurM and replacing carbonate wallrock. Landslide material obscures much of the 

deposit and judgment was made on the basis of material 

in the prospect dump. However, a well-exposed deposit 

on the north side of North Mountain, outside the 

mapped area, is believed to be in a comparable geologic 

setting. This deposit is within 200 to 300 feet of the 

igneous contact and is composed of disseminated chalcopyrite and pyrite in minute veinlets in a gray limestone bed. 

In sec. 14, T. 27 S., R. 24 E. (pl. 1), there is a. copper 

deposit at the southwest end of a clastic dike. The 

clastic dike, described on page 30, is emplaced along a 

fault over most of its length, but is divergent from the 

fault near the deposit. A short exploratory drift that 

once gave access to the deposit is now caved, and talus 

covers much of the area. The copper occurs as chalcopyrite and malachite which are sparsely disseminated 

in the finely -oomminuted matrix material. No other 

metallic minerals were found associated with the copper. 

The source of the copper in the limestone and clastic 

dike deposits is probably the same as the source of copper in the deposits in the igneous rock of North Mountain. Deep-seated hydrothermal solutions of late 

magmatic origin moved through the igneous rocks and 

precipitated copper minerals on contacting the carbonate beds of the enclosing sediments. Butler and others 

(1920, p.161-162, 198) considered the La Sal and Henry 

Mountain copper deposits similar to those of the Beaver 

Lake district of Utah and considered them to be derived 

from solutions that were produced by differentiation in 

the magma reservoir. 

North and northwest of Buckeye Reservoir, along the 

escarpment of the Valley View fault and its subsidiary 

faults, copper minerals, especially copper carbonates, 

are"'extensive but are not concentrated enough to be 

classed as ore. Several prospect pits and drifts reveal 

that chalcopyrite, azurite, and malachite are disseminated along fault planes and related fractures. In many 

places the copper carbonates occur as coatings and crystalline growths on the fracture surfaces, apparently 

independent of the copper sulfide minerals. Samples 

collected from a prospect near the Utah-Colorado State 

line west of Buckeye Reservoir contain a mineral that 

has been identified as crystalline malachite. It is a 

light-green acicular mineral commonly clustered in 

radial aggregates on fracture surfaces. Qualitative 

spectrographic analyses show that in addition to copper 

the mineral contains an unusual amount of vanadium. 
76 GEOLOGY, URANIUM-VANADIUM, LA SAL QUADRANGLE, UTAH-COLORADO 

It may include, therefore, some volborthite, a hydrous 

copper vanadate. Copper and uranium minerals are 

found in the Jackpot mine in sec. 2, T. 48 N., R. 20 W. 

(pl. 1). Both oxidized copper and uranium minerals 

are intermixed as coatings on fractures in the Wingate 

Sandstone. 

The copper deposits along the Valley View fault are, 

in many respects, like the copper-bearing veins that 

Fischer (1936) described and thought to be of hypogene origin. The Valley View copper deposits have 

been modified by later oxidation processes. Evidence 

indicating the origin of these deposits is inconclusive. 

The fact that the deposits occur in part as sulfides and 

are emplaced in structures of tectonic origin suggests 

that they may be of hydrothermal origin. No other 

metallic sulfides have been found with the copper in the 

deposits of the Valley View fault complex within the 

rna pped area. 

Copper carbonate coats fault and joint. surfaces at 

places that are a considerable distance from any known 

copper sulfide mineral; this relation suggests that recent oxidation and ground-water movement carried the 

copper from the places of original deposition and redeposited it at the present sites. This sequence of 

events appears to apply also to the associated uranium 

where it occurs only as the yellow oxidized minerals 

carnotite and tyuyamunite ( ? ) . These minerals are 

mostly in the form of incrustations or crystals on fracture surfaces of sandstone, in contrast to the more 

common occurrence as mineral grains and masses impregnating sandstone. 

Where the Sharp Canyon fault passes through the 

northeast wall of La Sal Creek Canyon, east of the 

mapped area, several prospects in the Entrada Sandstone expose thin (less than ¥2 in. thick) veinlets of copper and iron sulfides, mostly chalcopyrite containing 

traces of bornite. If similarities with the Cashin, Sunrise, and other 0opper-bearing faults (Fischer, 1936) are 

consistent and continue at depth it is ~ot improbable that 

deposits of argentiferous-copper ores occur near the 

base of the Wingate Sandstone, the zone in which such 

deposits were found in the other veins. The estimated 

depth to such deposits is about 420 feet where the 

Sharp Canyon fault crosses La Sal Creek in the adjacent 

Paradox quadrangle; however, at this location both 

surface and subsurface waters could create a major 

mining problem. Near the west wall of Spring Creek 

Canyon to the east, the depth to the base of the Wingate 

is estimated to be about 320 feet. These estimates are 

made on the assumption that normal thicknesses of the 

Kayenta and Wingate Formations are present in the 

area. 

IRON DEPOSITS 

Deposits of iron-rich minerals are widely distributed 

within and around the margins of the igneous rock of 

the La Sal Mountains. Many of the deposits have been 

prospected, but none were being exploite~ in 1956 .. 

Iron minerals mainly as specular hematite occur In at 

least six types of deposits: (1) as disseminated mas~es 

coating the joint surfaces in igneous rock, (2) as veins 

containing quartz and filling fractures in igneous rock, 

( 3) as veinlets transecting sandstone, ( 4) as .layers of 

disseminated minerals and in veinlets paralleling sandstone beds, ( 5) as minute botryoidal bodies and fin~ly 

granular masses in the openings of sandston? breccia, 

and ( 6) as disseminations in lenses and as ovmd masses 

in metamorphosed shale. Hunt (1958, p. 335-336, 339) 

in his discussion of North Mountain notes the occu.rence 

of hematite in several environments and suggests that 

it was derived from the alteration of hornblende and 

other mafic minerals. 

OIL AND GAS 

Numerous oil seeps and outcrops of bituminous sandstone have been known for many years in southwestern 

Colorado and southeastern Utah. Drilling in the Paradox Basin began in 1891 near Green River, Utah 

(Baker, 1933, p. 80), and has continued sporadically. 

Most of the exploratory wells were drilled on top or on 

the flanks of the salt anticlines and domes. A few holes 

were drilled in synclinal structures on the theory that, 

inasmuch as they are underlain by a thinner sequence of 

salt the surface is much closer to the pre-Hermosa ' . . sedimentary rocks which may stand structurally higher 

there than under the adjacent anticlines. 

The La Sal Mountain area lies within the Paradox 

Basin oil province, and all the formations containing 

producing horizons are represented in the stratigraph~c 

section of the La Sal Mountain region. Although oil 

and gas associated with igneous and ~etamorphic ~ks 

generally occur in quantities too small for commercial 

production it might be well to consider the favorable 

aspects of 'the area.. The La Sal Mountains .can be 

considered as three separate domes, two of whiCh are 

superimposed on elongate major anticlines. Small~r 

subsidiary structures are also superimposed on the.anticlines near the mountains. These structures are higher 

in altitude than ·any of the structures producing oil or 

gas in the surrounding a~eas, nnd therefore, offer ideal 

conditions for the migration and accumulation of petroleum. As Hunt ( 1942, p. 197-203) points out, it is 

the doming of the sedimentary strata about the stocks 

of the laccolithic mountains that produces strupture favorable for the entrapment of petroleum. Therefore, 

in spite of the fact that the Mesozoic and younger Pale-
REFERENCE'S CITE.D 77 

ozoic rocks have been breached where they arch over 

the laccoliths, there may be traps at depth in the older 

Paleozoic rocks. 

WATER 

Water is of considerable importance within the La 

Sal quadrangle, for drinking, for the watering of stock 

and crops, and as a drilling medium in the exploration 

and mining of uranium-vanadium deposits. 

The perennial streams include Taylor, Deep, Geyser, 

Twomile, Buckeye, West Paradox, and La Sal Creeks. 

Irrigation canals that connect Deep Creek to Geyser 

Creek and Geyser Creek to Buckeye Creek divert most 

of those drainages into Buckeye Reservoir which serves 

the farmlands in the north west end of Paradox Valley. 

La Sal Creek is partly diverted by a canal which carries 

water to the village of La Sal and the surrounding 

farmland. 

Numerous springs issue from the Burro Canyon Formation throughout most of the area. In La Sal Creek 

Canyon subsurface waters emerge from sandstone lenses 

in the Brushy Basin and Salt Wash Members of the 

Morrison Formation and the Entrada and Navajo 

Formations. 

Artesian water supplied by large recharge areas in 

the La Sal Mountains and on the crests or flanks of the 

anticlines can be found in each of the above formations 

in certain areas. In exploring for uranium deposits by 

diamond drilling, several holes penetrated sandstone of 

the Morrison Formation which produced artesian 

water at depths ranging from 150 to 400 feet. A few 

of these wells have had an average output of 5 gallons 

per minute for more than 21}2 years, have served as an 

excellent source of drinking water, and have provided a 

local water source for drilling projects. 

REFERENCES CITED 

Baker, A.A., 1933, Geology and oil possi!blities of the Moab district, Grand and San Juan Counties, Utah: U.S. Geol. 

Survey Bull. 841, 95 p. 

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A 

Page 

Acknowledgments ____________ :_______________ 3 

Ali Baba Member, Moenkopi Formation _____ _ 

Analyses, diorite porphyrY-----~-------------- 24 

galena .. ------------------________________ 52 

Angle mine __________________________ :_________ 54 

Apatite _____ -------------_____________________ 23 

Apatosaurus.------------_____________________ 13 

Ayers well L __ ------------------------------- 4, 5, 6 

Aznrite __ --------- ___ ___ ___ ___ ___ _ __ _ _ _ __ _ _ _ _ _ 61 

B Baker, A. A., quoted _________________________ _ 

Beaver Basin Formation______________________ 22 

Beta-nranophane_______ _ ___ ___ ____ ___ ______ __ 48 

Biotite ___ ------------------------------------ 23 

Black Hat mine·--------------------------·___ 54 

Bogus Tongue________________________________ 5 

Boltwoodite ______________________ ------ _ ___ __ 48 

Brontosaurus __ ------------------------------- 13 

Brushy Basin Member, Morrison Formation __ 12,13 

Brushy Basin No.1 mine______________________ 55 

Brushy Basin No.3 mine. ___ ----------------- 55 

Burro Canyon Formation_____________________ 14 

Bysmalith____________________________________ 32 

c 

Camarasaurus ___ ------- ___ ··-- _ _ _ _ __ _ ___ ___ _ _ _ 13 

Carmel Formation____________________________ 9 

Carnotite_____________________________________ 47, 

54, 55, 56, 58, 60, 61, 62, 63, 64, 66, 67, 

70, 71, 72, 73, 76. 

Cashin copper deposit ___ --------------------- 8 

Castle Valley-Paradox Valley anticline________ 27 

Cedar Mesa Sandstone Member, Cutler 

Formation________________________ 5 

Chalcopyrite __ ------------------------------- 75 

Chinle Formation._-------------------------- 6 

Christmas tree conglomerate __________________ 13,39 

Chnrch Rock Member, Chinle Formation_____ 7 

Clausthalite __________________________________ 48, 58 

Cliffdweller copper deposit ____ ·-------------,_ 8 

CoaL _______________________________________ ·- 74 

Coffinite ________________________________ 48, ~~. 61,70 

Confusion mine _____________________________ ·- 55 

Contact relations, Bnrro Canyon-Dakota ___ . _ 15 

Entrada Sandstone and SummerviUe 

Formation ______________________ ·- 11 

Copper deposits __ --------------------------·- 75 

Corvusite ___ --------- 48, 54, 56, 58, 60, 61, 63, 1~4, 67,70 

CretaCeous System ____ ---------------------·- 14 

Cutler Formation_____________________________ 5 

D 

Dakota Sandstone __________________________ ·- 16 

Dewey Bridge Member, Entrada Sandstone___ 9, 10 

Diamond drilling_____________________________ 3 

Dikes ____ --------------------- ___ ----------__ 30 

Dinosanr bones _______________________________ 13,71 

Diorite porphyry---------------------------·- 23 

Distribution, nranium-vanadium deposits____ 39 

Doloresite_ ---------------------------------·- 48 

Dugway fault_ __ ---------------------------·- 35 

INDEX 

[Italic page numbers indicate major references] 

E 

East Coyote Wash syncline ___________ ,. ______ _ Elray mine __________________________________ _ 

Entrada Sandstone __________________________ _ 

Epidote _____ --------------------------------- Eucarite _____________________________________ _ 

Evening Star mine ______ --------------------- Exploration, guides __________________________ _ 

history ____ -------------------------------

F 

Page 

29 

55 

9 

25 

61 

56 

73 

3 

Faults, description___________________________ 34 

mineralization ______ -------_______________ 46 

Fervanite. __ --------------------------------- 48 

Festoon cross lamination._------------------- 43 

Fieldwork. _____ -------_______________________ 3 

Firefl.y-Pigmay mine.------------------------ 57 

Folds __________ ----------_____________________ 26 

Fossils, Mancos Shale_________________________ 18 

Morrison Formation______________________ 13 

G 

Galena, analysis______________________________ 52 

Gas. __ --------------------------------------- 76 

Geologic setting __ ---------------------------- 3 

Geyser Creek Fanglomerate__________________ 19 

Geyser Creek faults. __ ----------------------- 35 

Geyser Creek syncline________________________ 28 

Glacial features_______________________________ 22 

Glen Canyon Group_________________________ 8 

Gold Basin Formation_______________________ 22 

Gray Daun mine_____________________________ 59 

Gryphaea newberryi___________________________ 18 

Gummite ___ --------------------------------- 61 

H 

Harpole Mesa Formation_____________________ 22 

Hermosa Formation__________________________ 4 

Hesperus mine ___ ---------------------------- 61 

Hewettite ______________________________ 48, 60, 61,70 

Hillebrand, W. F., analyst____________________ 24 

Hornblende ___ ------------------------------- 23 

Hornfels______________________________________ 24 

Hydrothermal alteration ____ ----------------- 51 

Hypogene solutions___________________________ 52 

I 

Igneous rocks_________________________________ 23 

Inclusions____________________________________ 24 

Inoceramus deforrnis___________________________ 19 

dimidius_ --------------------------------- 18 

Iron deposits __ ------------------------------- 76 

J 

Jackpot mine_________________________________ 62 

Joints ___ ------------------------------------- 46 

Jurassic System______________________________ 9 

K 

Kayenta Formation__________________________ 8 

Kehl, Lucille, analyst_ __ --------------------- 24 

L 

Page 

La Sal Creek mineral belt.------------------- 40 

La Sal Creek syncline________________________ 28 

La Sal Mountains---------------------------- 29 

Laccoliths __________________ ----------________ 32 

Lead-uranium ratios, zircons_________________ 25 

Limonite ___ ------ ___ ------------------------- 47 

Little Don mine______________________________ 62 

Little Peter mine_____________________________ 62 

Log replacement ore bodies___________________ 41 

Longitudinal faults--------------------------- 34 

Lopha lugubrius ___ --------------------------- 18 

Lower and Middle Triassic Series_____________ 6 

Lower Cretaceous Series______________________ 14 

Lucky No. 1 mine____________________________ 63 

M 

Magnetite __________ ------ ____ ------_---- __ -___ 23 

Malachite·------------------------------------ 61,75 

Mancos Shale.-------------------------------- 18 

Mapping, methods---------------------------- 3 

Marjorie Ann mine___________________________ 63 

Maud mine.---------------------------------- 64 

Melanovanadite. -------------------------- 48, 54,61 

Metahewettite.---------------------------- 48, 60,61 

Metamorphism, contact_ ___ ------------------ 24 

Metatorbernite. __ ---------------------------- 48, 61 

Metatyuyamunite ___________________ 61, 62, 66, 67,71 

Metazeunerite. ___ ---------------- ________ ---- 48 

Middle Mountain, structnre __________________ 30,36 

Mineralogy, nranium-vanadium deposits_____ 46 

Mines. __ ------------------------------------- 63 

See also individual mine. 

Mining, history------------------------------- 38 

Mitchell's Coal mine__________________________ 74 

Moab Sandstone Member, Entrada Sandstone. 9, 10 

Moenkopi Formation_________________________ 6 

Montroseite _________________ 48, 54, 60, 61, 63, 64, 67,70 

Monzonite porphyry-------------------------- 23 

Moraines._----------------------------------. 22 

Morning Star mine._------------------------- 65 

Morosaurus _____ ____ ------------- ______ ------- 13 

Morrison Formation, description______________ 1S 

uranium-vanadium deposits______________ 39 

Moss Back Member, Chinle Formation_______ 7 

Mount Mellenthin fault_______________________ 36 

Mount Mellenthin laccolith___________________ 32 

Mount Peale bysmalith_______________________ 32 

N 

Navajo Sandstone____________________________ 8. 

New Yellow Spot mine_______________________ 65 

North Mountain______________________________ 29 

0 

OiL_----------------------------------------- 76 

Ore-bearing sandstone________________________ 12 

Ore production. See individual mine. 

Organ Rock Tongue__________________________ 5 

Ostrea congesta •. ------------------------------ 19 

gongesta ____ ------------------------------ 18 

81 
82 INDEX 

p Page 

Page Section, Burro Canyon Formation____________ 15 

Paradox Member, Hermosa Formation_______ 4 Chinle Formation________________________ 7 

Paradox Valley, faults________________________ 36 Dakota Sandstone________________________ 17 

Paramontroseite_____________ ___ ___ ___ ___ ____ _ 48 Geyser Creek Fanglomerate______________ 20 

Pflriott Member, Moenkopi Formation_______ 6 Morrison Formation______________________ 13 

Pascoite _____ --------- __________ -------------- 63 Summerville Formation __________________ 10,11 

Pennsylvanian System_______________________ ~. 5 Sedimentary rocks _____ ---------------------- 51 

Permian System______________________________ 5 Sewemup Member, Moenkopi Formation_____ 6 

Petrography, igneous rocks___________________ 23 Sharp Canyon fault, description______________ 36 

Phosphuranylite ___ ----------------------- 48, 60,61 

Pine Ridge anticline__________________________ 28 copper depositsy------------------------- 76 

Sills __ ----- __ --_----_------------------------- 32 

Pipe, clastiC---------------------------------- 31 Simplotite _____ ------------------------------- 48, 70 

Pitchblende------------------------------- 54, 61,70 Sinbad Valley anticline_______________________ 26 

Placer Creek Formation______________________ 22 Slick Rock Member, Entrada Sandstone _____ 9,10 

Previous work________________________________ 3 South Mountain, structure___________________ 33 

Prionocyclus wyominqemis____________________ 18 Sphene _______________________ ------- ____ ----- 23 

Prospecting, suggestions______________________ 73 Springs •• ________________ -----________________ 77 

Purpose and scope____________________________ 3 Stock·--------------------------------·------- 30 Pyrite ________________________________________ 48, 75 Stratigraphy ____ ----------------------------- ~ 

Streams. _____ -------------------------------- 77 

Q Structural geology____________________________ 26 

Quaternary System___________________________ 22 Structural history_--------------------------- 37 

Sulfides ____ ---------------------------------- 49 

R Summerville Formation______________________ 11 

Radial faults ___ ------------------------------ 36 Sumner mine_________________________________ 66 

Rattlesnake ore_______________________________ 65 Sunrise copper deposit________________________ 8 

Rico Formation __ ---------------------------- 5 Syenite porphyry_____________________________ 23 

Roads ________ ---------- _____________ -------__ 2 

Roc Creek syncline___________________________ 27 T 

Rock glaciers __________________ --------------- 22 Taylor Creek syncline________________________ 27 

Rolls_------ ______ ------- _____ ----- ___ ------__ 41 Tenderfoot Member, Moenkopi Formation___ 6 

Roscoelite_ ----------------------------------- 48, 69 Tennantite __________________ --- ___ ----------'" 58 

Tertiary System______________________________ 19 

s 

Sateeite-novacekite __ ------------------------- 48 

Salt Wash Member___________________________ 12 

San Rafael Group____________________________ 9 

Scaphites warrenL _ --------------------------- 18 

Too High mine_______________________________ 66 

Torbernite. ___ ---------------------------- 48, 60, 61 

Transverse faults_____________________________ 36 

Trash pockets.------------------------------- 13,41 

Schopf, J. M ., quoted ___ --------------------- 75 Triassic and Jurassic Systems. __ ------------- 8 

Schroeckingerite____ ___ ____ ___ ___ _ ___ ___ __ _ ___ 55 Triassic System ___ --------------------------- 6 

Scorup anticline______________________________ 27 Tyuyamunite. _ --------- 58, 60, 61, 62, 63, 66, 70, 72,76 

u 

Page 

Upper Cretaceous Series______________________ 16 

Upper Triassic Series.------------------------ 6, 8 

Uraniferous ore deposits, origin_______________ 49 

Uraninite _______________________________ 48, 63, 67,70 

Uranium deposits __ -------------------------- 38 Uranium Girl mine___________________________ 67 

Uranium-vanadium deposits, distribution____ 39 

fault controL____________________________ 46 

localization. _______ ------- ___ ------------- 41 

size and shape____________________________ 40 

Uranophane •• ----------------------------- 48, 60,61 Uravan mineral belt__________________________ 40 

v Valley View fault_____________________________ 34 

copper deposits--------------------------- 76 

Valley View mine_--------------------------- 67 

Vanadium claY------------------------------- 55 

Vanadium hydromica_ ----------------------- 47, 48, 

54, 56, 61, 62, 63, 64, 66, 67, 69, 70, 71, 72, 73 

Vanadium oxide______________________________ 46 

Vanadium Queen mine_______________________ 68 

Vista Grande mine___________________________ 70 

Volborthite __________ ------- _ _ ___ _ __ _ ___ ____ __ 76 

w 

Water __ -----------_------------------------__ 77 

Wedge mine .. -------------------------------- 71 

Willow Basin syncline________________________ 27 

Wingate Sandstone___________________________ 8 

y 

Yellow Bird mines __ ------------------------- 71 

Yip Yip mine._------------------------------ 73 

z 

.lircon. ---------- ____________________ --- _ _ __ __ 23 

Zircon age determination, porphyries_________ 25 

U.S. GOVERNMENT PRINTING OFFICE: 1965 0-777-G39