Jca

 75 75

 70

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 5

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 18

 9

 54

 52 34

 30

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40 

 20

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 42

 9

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Tb

Tb

Tb Tb

Qac

Qac

Phw Phw

Phw

Jg

Jg

Jg

Jsc Jg

Jsc

Jsr

Jg

Tb

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Tb

Tb

Qac

Jg

Tb

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Tb

Tb

Qac

Phw

Jg

dc

Qls dc

Qls

Jg

dc

hmu

hml

dm

dm Qac

Qac

Je

dm

Qac

dc

dm

Jsr

Jg Jca

dc

Qac

Jm

Je

Je

Jsc

Jsr

Qls

Kcm

Kcm

Jm

Jsr

Jsr

Jsc

Jsc

Qls

Jm

Jsc

Jsr

Je

Jca Jg

Ppc

Ppc

dc

dc

dc

Jg Ppc

Ppc

Qac

dm

dm

dm

dm

Qac

dc

Jsc

Jg

Phw

Qac

Qac

Qac

Phw

Phw

Qac

Jg

Jca

Jsc

Je

Je

Jsr

Jsr

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Jm

Kcm

Kcm

Qls

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Kmf

Kmm

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Kmm

Qac

Qac

Je

Qac Jca

Jsc

Je

Jg

Jsc

Je

Jm

Kcm

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Jg

Kmf

Kmf Kmy

Qac

Jm

Jg

Jg

Ppc

Qac

Qt

Kd

Jsr

Je Je

Kmy

Kmm Jm

Je

Jm

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Jg

dm dm Qac

Kmm

Qac

Jg

dc

dc

dc

Kmf

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Jca

Jca

dc

Kcm

Kcm

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Kmy

Jm

Tb

Kd

Kcm

Jmmg

Kmy

Jsr

Jm

Kd

Jsc

Je

Jca

Ppc

Jsc

dm

dm

Qac

Qls

Qt

Tb

Kc

Kmm

Kmf

Kmy

Kd

Kcm

Jm

Jsr

Jmmg

Jsc

Jg

dc

dm

Ppc

Phw

hmu

hml

Je

Jca Jca

1000 1000 0 2000 3000 4000 5000 6000 7000 FEET

1 .5 0 1 KILOMETER

SCALE 1:24 000

1 1/ 2 0 1 MILE

CONTOUR INTERVAL 40 FEET

DOTTED LINES REPRESENT 20-FOOT CONTOURS

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Base from U.S. Geological Survey, 1962.

Polyconic projection. 1927 North American datum.

10,000-foot grid based on Colorado coordinate

 system, north zone

1,000-meter Universal Transverse Mercator grid

ticks, zone 12

Geology mapped 1988-89

Edited by Diane E. Lane

Color design by Virginia Scott

Digital cartography by R.E. Van Loenen, 

Gary Selner, and Diane E. Lane

Manuscript approved for publication

June 3, 1998

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY GEOLOGIC INVESTIGATIONS SERIES

I–2646

Qac Qls Qt

Tb

Kmm

Kc

Kmf

Kmy

Kd

Kcm

Jmmg Jm

Jsr

Jsc

Je

Jca

Jg

dc

dm

Ppc

Phw

hmu

hml

Holocene and

Pleistocene QUATERNARY

Oligocene TERTIARY

Upper

Cretaceous

CRETACEOUS

Lower

Cretaceous

Upper

Jurassic

Middle

Jurassic

Lower

Jurassic

Upper

Triassic

Middle(?) and

Lower Triassic

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity(?)

Lower

Permian

Upper

Pennsylvanian

Middle

Pennsylvanian

JURASSIC

TRIASSIC

PERMIAN

PENNSYLVANIAN

CORRELATION OF MAP UNITS

DESCRIPTION OF MAP UNITS

Alluvium and colluvium (Holocene and Pleistocene)— 

Unconsolidated, poorly sorted clay, silt, sand, gravel, and rock 

fragments deposited in and along present stream channels and as 

slope-wash deposits at base of slopes and cliffs around Skull Creek 

Dome. Older alluvial deposits of mostly red clay, silt, and sand 

occur in and adjacent to present stream channels, are as thick as 

80 ft, and are dissected by present drainage system. Contact 

transitional with other surficial deposits

Landslide deposits (Holocene and Pleistocene)—Poorly sorted 

debris from unstable shales of Cedar Mountain Formation. 

Deposits accumulated in water gaps cut in hogbacks near Blue 

Mountain, Colo. Landslides dominate slopes of Moose Head 

Mountain. Large slump blocks, some nearly 1 mi across, of the 

hard Cedar Mountain Formation have been rafted down slope 

along glide faults on slick clays of Morrison Formation

Terrace deposits (Holocene and Pleistocene)—Unconsolidated, 

poorly sorted sand, gravel, pebbles, and cobbles of mainly 

quartzite along southern part of quadrangle. Maximum thickness 

about 100 ft

Bishop Conglomerate (Oligocene)—Poorly consolidated, light-gray, 

yellowish-brown, or white, thin-bedded, poorly sorted pebble, 

cobble, and boulder conglomerate. Matrix is locally tuffaceous. 

Clasts consist mostly of red quartzitic sandstone derived from 

Uinta Mountain Group (Middle Proterozoic) and light- to dark-gray 

limestone derived from Paleozoic formations. Soluble coatings of 

calcium salt on boulders make the Bishop terrane look white. 

Thickness varies from a few feet to tens of feet

Castlegate Sandstone (Upper Cretaceous)—Forms hogback couplet 

in sec. 11 at south edge of map. Upper part is yellowish-gray, 

very fine grained sandstone; contains concretions; about 80 ft 

thick. Lower part is gray shale and silty shale grading downward 

into orangish-brown, thin-bedded, fine-grained sandstone; basal 

10 ft is indurated sandstone that forms northern hogback of 

couplet at south edge of quadrangle. Total thickness about 200 ft

Mancos Group (Upper Cretaceous)

Main body—Brownish-gray, mostly noncalcareous, marine shale 

interbedded with minor siltstone, very fine grained sandstone, and 

thin bentonite beds. Lower part is poorly exposed at base of 

hogback formed by Frontier Sandstone and in flats along southern 

part of map area. Maximum thickness is about 4,400 ft in nearby 

Mellen Hill quadrangle (Cullins, 1969)

Frontier Sandstone—Upper part is resistant, light-olive-gray, finegrained, calcareous and fossiliferous sandstone. Lower part is 

brown and pale-blue, fissile shale and siltstone. Frontier is well 

exposed and forms first hogback north of U.S. Highway 40, along 

southern limb of Skull Creek Monocline. Thickness ranges from 

200 to 250 ft

Mowry Shale—Blue-gray to pale-blue, fissile, siliceous shale and 

thin bentonite beds; locally contains gypsum. Weathers to 

distinctive hard chips. Contains fish scales. Thickness ranges 

from 60 to 90 ft

Dakota Sandstone (Lower Cretaceous)—Resistant, yellowish-brown 

to light-gray, medium- to thick-bedded, medium- to coarse-grained 

sandstone interbedded with conglomerate and minor thin shale. 

Weathers reddish-brown and forms hogback along much of 

southern limb of monocline in southern part of quadrangle. 

Thickness ranges from 60 to 75 ft

Cedar Mountain Formation (Lower Cretaceous)—Comprises two 

members: an upper unnamed shale member and lower Buckhorn 

Conglomerate Member. Upper part consists of slope-forming, 

pale-olive and purple shale and mudstone units interbedded with 

thin, fine-grained sandstone and resistant, light-brownish-gray 

limestone containing red jasper near base. Buckhorn Conglomerate Member is ledge-forming, thick-bedded, medium-gray to 

light-gray conglomerate and fine- to coarse-grained sandstone; 

conglomerate is characterized by black chert pebbles. Thickness 

about 175 ft; thickens westward. Unconformable contact with 

Morrison Formation is placed below beds of chert-pebble 

conglomerate or red-jasper limestone

Morrison Formation (Upper Jurassic)—Slope-forming, variegated 

pale-olive, dark-red, and reddish-brown siltstone, claystone, and 

shale interbedded with light-gray to olive-gray, fine- to mediumgrained sandstone, conglomeratic sandstone, minor glauconitic 

sandstone, and argillaceous and nodular limestone. Conglomeratic sandstone about 30 ft thick occurs near middle of the 

Morrison and locally contains fossil dinosaur bones and teeth that 

weather out on dip slopes. Lowermost fine- to medium-grained 

sandstone is strongly crossbedded; basal eolian sandstone is well 

exposed in vicinity of Stinking Water Creek directly north of Blue 

Mountain, Colo. (southwest corner of map area). Elsewhere, 

crossbedded Morrison sandstone uncomformably overlies 

Redwater Member of Stump Formation. Thickness ranges from 

560 to 650 ft

Beds at Martin Gap—Ledge-forming, thick-bedded and crossbedded, medium-gray to light-gray, very coarse grained sandstone 

and pebble conglomerate; lithology is similar to Buckhorn 

Conglomerate Member of Cedar Mountain Formation. Beds 

occur in lens that abruptly pinches out northwestward and 

southeastward within upper part of the Morrison. Interpreted as 

fluvial channel deposit within the Morrison. Thickness 0–50 ft

Stump Formation (Upper and Middle Jurassic)

Redwater Member (Upper Jurassic)—Light-gray and pale-olive 

glauconitic shale interlayered with siltstone, sandy limestone, 

coquina, and thin-bedded sandstone. Weathers to a greenish cast. 

Fossils include brachiopods, pelecypods, cephalopods (belemnites 

very common), and ammonites. Contact with Curtis Member 

distinct; located between soft green beds of the Redwater and 

indurated light-gray beds of the Curtis. Thickness ranges from 

100 to 150 ft; usually well exposed at base of Curtis flatirons

Curtis Member (Middle Jurassic)—Very resistant, ledge-forming, 

light-gray to greenish-gray, fine- to coarse-grained, thin- to 

medium-crossbedded sandstone. Glauconite and fossils are common. “Trash” beds (as much as several feet thick) of petrified 

wood and other plant debris are common at base, locally 

containing copper and uranium minerals. Unconformable contact 

with Entrada Sandstone is sharp. Thickness variable, 0 to 30 ft

Entrada Sandstone (Middle Jurassic)—Resistant, light-gray, fine- to 

medium-grained, thick-bedded, massive sandstone; glauconitic in 

upper part. Where underlying Carmel Formation (unit Jca) is 

absent or very thin (generally east of Red Wash water gap) the 

Entrada–Glen Canyon contact is mapped along a topographic low 

between the two similar sandstone units. Thickness ranges from 

90 to 150 ft

Carmel Formation (Middle Jurassic)—Slope-forming, reddishbrown, fine-grained sandstone, siltstone, and mudstone. Redbeds 

of the Carmel display a striking contrast to eolian sandstone units 

above (Entrada sandstone, unit Je) and below (Glen Canyon 

sandstpme, unit Jg). The Carmel crops out around Moosehead 

Mountain and, in southwestern part of map area, as far east as 

Red Wash water gap; east of the water gap the Carmel is too thin 

(less than 5 ft thick) to map separately; it is located at contact 

between Entrada and Glen Canyon Sandstones. Contact with 

underlying Glen Canyon is mapped along color change from 

reddish-brown Carmel mudstones to light shades of gray of Glen 

Canyon Sandstone. Unit thins to east from about 50 ft in 

southwest to only a few feet east of Red Wash

Glen Canyon Sandstone (Lower Jurassic)—Massive, thick-bedded, 

well-sorted, light-gray to grayish-pink, medium- to fine-grained 

sandstone. Exhibits medium-scale to very large scale sand-dune 

crossbedding. An unconformity lies about 10 ft below the 

Carmel–Glen Canyon contact, within lithologies similar to Glen 

Canyon Sandstone (Pipiringos and O’Sullivan, 1975). The unconformity is marked by a very thin (less than 1 in. thick) layer of 

chert pebbles. Is relatively resistant and weathers to rounded 

buttes. Exposed extensively around Skull Creek Monocline, 

forming the caprock of Skull Creek Rim. Thickness ranges from 

600 to 700 ft

Chinle Formation (Upper Triassic)—Includes main body and Gartra 

Member (not mapped separately) at base. Main body is slopeforming, moderate-red to moderate-pink siltstone interbedded with 

very fine grained sandstone units of similar color. Gartra Member 

is ledge-forming, light-gray, coarse-grained, conglomeratic 

sandstone; contains laminal, angular heavy-mineral clasts as large 

as 1 ft, petrified wood locally; is usually crossbedded. The Gartra 

forms a conspicuous brush-covered bench in otherwise relatively 

soft red cliffs around Skull Creek Monocline and ranges from 10 

to 30 ft thick. Total thickness of Chinle ranges from about 250 to 

300 ft. Unconformable contact with Moenkopi Formation is 

sharp

Moenkopi Formation (Middle? and Lower Triassic)—Moderatereddish-brown, yellowish-gray, and pale-olive micaceous siltstone 

interbedded with minor amounts of mudstone and very fine 

grained sandstone. Gypsum is common. Unconformable contact 

with Park City Formation, covered in most places, was mapped 

below lowermost beds of reddish-brown Moenkopi siltstone; color 

changes subtly from red Moenkopi to orangish Park City. 

Thickness ranges from 500 to 600 ft

Park City Formation (Lower Permian)—Alternating slope-forming, 

pale-orange and pale-olive mudstone and ledge-forming, 

indurated, yellowish-brown siltstone. Contains minor amounts of 

fine-grained, lenticular sandstone (some asphaltic); all lithologies 

are calcareous. The Park City is poorly exposed around Skull 

Creek Monocline, thought to be correlative with Franson Member 

(Hansen and Rowley, 1980). Possible unconformable contact 

with Weber Sandstone is marked locally by a 2-ft-thick 

conglomerate containing coarse quartz pebbles and angular rock 

fragments as large as 1 in. Thickness estimated at 150 ft

Weber Sandstone (Lower Permian and Upper and Middle Pennsylvanian)—Upper part is mainly light-gray, massive, thickbedded, fine-grained sandstone except near top, where the 

sandstone is pale yellowish brown and slightly calcareous; largescale crossbedding is common; several canyons locally expose 

500–600 ft of sandstone at center of Skull Creek Dome. Lower 

part is highly indurated, interbedded light-gray (predominant) to 

pale-yellowish-orange, fine-grained, mostly thin bedded, 

commonly crossbedded, calcareous sandstone and light-gray, finegrained, mostly thin bedded, commonly cherty, somewhat 

crossbedded, fossiliferous, locally sandy limestone; exposed in 

steeply dipping beds north of Wolf Creek Fault. Contact with 

Morgan Formation mapped at top of uppermost Morgan redbed. 

Reported to be about 1,000 ft thick about 6 mi northeast of 

quadrangle (Hansen, Carrara, and Rowley, 1980)

Morgan Formation (Middle Pennsylvanian)

Upper member—Ledge-forming, interbedded light- to moderatered, fine-grained, crossbedded sandstone, gray to pale-lavender, 

cherty, fossiliferous limestone, and purplish-red siltstone. Pink to 

red chert nodules are conspicuous. Beds range from 2 to 10 ft 

thick. Breccia of red siltstone and limestone fragments occurs as 

float in upper part. Contact with lower member placed at break in 

slope at base of ledges formed by relatively hard limestone and 

sandstone units of upper member. Only upper part of member is 

exposed in northeast corner of map area. Hansen, Carrara, and 

Rowley (1980) reported member to be about 690 ft thick a few 

miles north of map area

Lower member—Slope-forming, interbedded varicolored gray, red, 

and lavender shale and siltstone and minor grayish-pink to palelavender limestone and calcareous sandstone. Base not exposed 

in quadrangle; about 280 ft thick nearby (Hansen, Carrara, and 

Rowley, 1980)

Contact—Dashed where inferred

Normal fault—Bar and ball on downthrown side; dashed where 

inferred, dotted where concealed

Thrust fault—Sawteeth on upper plate; dotted where concealed

Glide faults—Open sawteeth on blocks of Cedar Mountain formation 

(unit Kcm)

Monocline—Showing trace of axial surface

Joint—Joints are mainly in Glen Canyon Sandstone

Strike and dip of inclined beds

Rock quarry

INTRODUCTION

The Lazy Y Point quadrangle lies along the southeastern edge of the Uinta 

Mountains about 15 mi north of Wrangle, Colo. The eastern part of Dinosaur 

National Monument is about 5 mi north of the quadrangle. The quadrangle 

contains the hogbacks and picturesque cliffs of the Skull Creek Rim, which can be 

seen from U.S. Highway 40. The southern part of the quadrangle contains large 

tracts of private land; the remainder is administered by the U.S. Bureau of Land 

Management. Access is limited to a single dirt road that runs north-northeast at the 

foot of the Skull Creek Rim and to a county road that runs east-west along the 

northern boundary.

The Lazy Y Point quadrangle contains the eastern one-third of the Willow 

Creek Wilderness Study Area and the western half of the Skull Creek Wilderness 

Study Area. The geology and mineral resources of the wilderness study areas and 

vicinity were mapped and assessed by Van Loenen and others (1990). Color aerial 

photographs, at a scale about 1:24,000, were used in making the map, and the 

geology was transferred from the photographs to the topographic base map using 

a photogrammetric plotter.

GEOLOGIC HISTORY

Rocks in the Lazy Y Point quadrangle range in age from about 300 million 

years old for the Morgan Formation (Middle Pennsylvanian) to about 30 million 

years old for the Bishop Conglomerate (Oligocene). The geologic history of these 

rocks began when the lower member of the Morgan formation was deposited along 

shorelines on older marine sediments (Rowley and Hansen, 1979b). They 

presently crop out only along the northern part of the quadrangle. During Middle 

Pennsylvanian and Early Permian time the Weber Sandstone was deposited over 

the Morgan. The Weber is chiefly shallow marine, intertidal, and eolian sandstone 

that was deposited in a trough in the ancestral Rocky Mountains. The Front Range 

and Uncompahgre Uplifts of the ancestral Rocky Mountains provided sediment to 

this region during late Paleozoic and part of Mesozoic time. This episode was 

marked by repeated rise and fall of sea level in response to ice ages in the Southern 

Hemisphere. The Weber is exposed in the northern part along the Wolf Creek 

Monocline and throughout the core of the Skull Creek Dome. Thick deposits of 

the Lower Permian Park City Formation accumulated to the west of the map area 

in marine and shelf environments, but deposits of the Park City in the Lazy Y Point 

quadrangle accumulated in very shallow water and possibly streams. Only the 

upper part of the Park City is present in this region (Rowley and Hansen, 1979b). 

The clastic redbeds of the Lower and Middle(?) Triassic rocks of the Moenkopi 

Formation were deposited in a desert environment by rivers and shallow marine 

seas. The basal conglomerate of the Upper Triassic Chinle Formation was 

deposited by braided streams on the eroded surface of the Moenkopi. This coarse 

material was later covered by the main body of the Chinle, a clastic redbed 

sequence of silts and sands deposited on alluvial plains. Eolian conditions returned 

to the region during the Early Jurassic, when dune sands of the Glen Canyon 

Sandstone covered the redbeds of the Chinle. The spectacular scenery of the Skull 

Creek Rim results from weathering of the soft Moenkopi and Chinle redbeds, which 

are preserved by the relatively hard overlying Glen Canyon Sandstone. The Glen 

Canyon forms the high plateau around the Skull Creek Dome. During the Middle 

Jurassic, mud and silt of the Carmel Formation were deposited in shallow marine 

conditions over much of the region. The Carmel thins from west to east and is a 

mappable unit only in the western parts of the quadrangle. Dune sands of the 

Entrada Sandstone (Middle Jurassic) covered the region before the sea again 

transgressed the area, depositing the Curtis Member of the Stump Formation. The 

Curtis is a thin but very hard sandstone that forms flatirons along the southern part 

of the map area.

Deep-water marine conditions existed during the Late Jurassic, and these 

deposits are represented by the Redwater Member of the Stump Formation. The 

sea again retreated, exposing a land surface that was covered with continental 

deposits of the Morrison Formation (Upper Jurassic). The Morrison includes fluvial, 

eolian, and possible lacustrine deposits. Following episodes of erosion, the Cedar 

Mountain Formation (Lower Cretaceous) and the overlying Dakota Sandstone 

(Upper Cretaceous), and the Upper Cretaceous Mancos Group were deposited 

along the shorelines and within the Western Interior Cretaceous Seaway. These 

are largely fluvial deposits that were later covered by thick marine deposits. Thin 

sandstone of the Castlegate represent the youngest Cretaceous sedimentary rock 

now present in the quadrangle. 

The Laramide orogeny began near the end of the Cretaceous Period and is 

responsible for the Unita Anticline and other structural features present today. 

During Oligocene time (30 million years ago) fluvial deposits containing very coarse 

material covered parts of the quadrangle. Remnants of these deposits, called the 

Bishop Conglomerate, are preserved in the northern part of the quadrangle. Since 

Oligocene time, the area of the Lazy Y Point quadrangle has remained above sea 

level and exposed to erosion.

STRUCTURE

The predominant structural features in the Lazy Y Point quadrangle, from 

north to south, are the Wolf Creek Monocline, the Wolf Creek Monocline, the Wolf 

Creek Fault, and the Skull Creek Monocline. Asymmetrical folds, including 

monoclines, are common in the eastern Uinta Mountains and are considered to be 

formed above thrust faults (Rowley and Hansen, 1979a).

The Skull Creek Monocline is an east-west-trending structure that extends for 

about 30 mi from near the Utah-Colorado border across the quadrangle and ends 

about 8 mi to the east. The north limb of the monocline dips north at 2o–5o, and 

the south limb dips steeply south 25o–50o. Prominent hogbacks were formed by 

the erosion of steeply dipping beds of contrasting hardness. The Skull Creek 

Monocline forms an ellipsoidal dome, approximately 5 by 10 mi across (referred to 

as the “Skull Creek Dome”), and it extends into the adjoining quadrangle. The 

monocline overlies the Willow Creek Fault, a deep thrust fault that trends east-west 

just south of the map area. The Willow Creek Fault was encountered in a drill hole 

at a depth of 8,000 ft near Dinosaur National Monument headquarters, about 6 mi 

to the west, where Precambrian rock overlies Paleozoic rock (Powers, 1986).

The Wolf Creek Monocline extends east-west across the northern part of the 

Lazy Y Point quadrangle. It dips very gently (less than 5o) to the north and very 

steeply (vertical in places) along its southern limb. The monocline is broken by the 

Wolf Creek Fault, which has, for the most part, juxtaposed Weber and Moenkopi 

rocks at the surface. Unlike the blind Willow Creek Fault, the Wolf Creek is 

exposed at the surface.

In the east-central part of the map area, a system of northeast-trending faults 

cuts the Skull Creek Dome. Down-to-the-east displacement along the faults increases from northeast to southwest. The faults merge near the Red Wash reentrant; from there they probably join a major fault mapped near Blue Mountain by 

Cullins (1969). Cullins (1969) and Powers (1986) suggested that the fault may be a 

surface manifestation of the Willow Creek Thrust.

Northeasterly and easterly trending joints have developed in the Glen Canyon 

Sandstone; some extend into older rock, but none is seen in younger rock. Joints 

are common in massive sandstone deposits such as the Glen Canyon.

MINERAL AND ENERGY RESOURCES

Little, if any, potential exists within the Lazy Y Point quadrangle for mineral 

or energy resources. Traces of metals are fault related in the southern part of the 

quadrangle. Formations within the quadrangle and nearby that contain traces of 

mainly uranium and copper include the Chinle, Stump, and Morrison Formations. 

The Weber Sandstone is a reservoir for oil and gas south of the quadrangle.

During the early uranium “boom” of the 1950’s, small deposits of uranium 

and related minerals were discovered in several nearby localities. A very small 

amount of uranium was mined a few miles to the east (Van Loenen and Bryant, 

1997), but similar deposits are not known in the Lazy Y Point quadrangle. 

Although few metals were available, favorable depositional conditions apparently 

existed in sandstone units where fossil plant remains served to localize 

mineralization. “Trash” beds, composed mainly of carbonized plant remains in 

mudstone and sandstone, served as a reductant for the mineralization.

The two primary targets for uranium exploration were the Gartra Member 

(the coarse basal conglomerate) of the Chinle and the sandstones of the Morrison 

Formation, both known throughout the west for their rich deposits of uranium. 

Petrified wood fragments, fossil dinosaur bones, and some sandstone beds in the 

Morrison Formation are slightly radioactive, as is the conglomerate at the base of 

the Chinle; however, these levels of radioactivity are not considered anomalous for 

either formation. The Curtis Member of the Stump Formation also contains traces 

of uranium, vanadium, and copper in this area. This mineralization is readily 

recognized as a distinctive copper bloom (blue) in the rock; most sites have been 

explored in prospect pits.

Altered rock associated with the large faults that cut the Glen Canyon and 

Entrada Sandstones in the Rock Wall Draw area contain trace amounts of silver, 

arsenic, copper, lead, and zinc (Van Loenen, and others, 1990). Prospect pits in 

this altered rock indicate that the occurrence of metals was already known here.

An oil and gas interest in this region is due to a similarity in geologic setting to 

the nearby Rangley oil field, which lies about 15 mi to the south. The principal 

reservoir rock in the Rangley field is the Middle Pennsylvanian to Lower Permian 

Weber Sandstone, which traps oil in a large monocline very similar to the Skull 

Creek Monocline. Although the Weber is present in a structural setting similar to 

that in the Rangley field, it has very little potential within the Lazy Y Point 

quadrangle because erosion has removed most of the Mesozoic and Cenozoic cap 

rock from the Skull Creek Monocline, thus exposing the Weber and allowing any oil 

and gas accumulations to escape. Several wells have been drilled in the quadrangle 

and nearby to test the Weber and lower Paleozoic rock, but with little success. 

Other reservoirs for oil and gas in this region are foreland subthrust traps. 

The Willow Creek Fault, which lies beneath the southern boundary of the 

quadrangle, has been an exploration target for this kind of trap. Powers (1986) 

analyzed the play from seismic data and from a drill hole located about 6 mi to the 

west of the Lazy Y Point quadrangle. Oil was found, but the amount of closure 

beneath the subthrust is too small and the reservoir rock qualities too poor to 

contain commercial quantities of oil, (Powers, 1986). This play has not been tested 

by drilling within the quadrangle.

Gravel is abundant in terrace and alluvial deposits in the southern part of the 

map area. Conglomerate and limestone from the Cedar Mountain Formation and 

shale from the Mowry Shale have been quarried within the Lazy Y Point 

quadrangle for use as road metal.

REFERENCES CITED

Cullins, H.L., 1969, Geologic map of the Mellen Hill quadrangle, Rio Blanco and 

Moffat Counties, Colorado: U.S. Geological Survey Geologic Quadrangle Map 

GQ–835, scale 1:24,000.

Hansen, W.R., Carrara, P.E., and Rowley, P.D., 1980, Geologic map of the 

Haystack Rock quadrangle, Moffat County, Colorado: U.S. Geological Survey 

Geologic Quadrangle Map GQ–1535, scale 1:24,000.

Hansen, W.R., and Rowley, P.D., 1980, Geologic map of the Hells Canyon 

quadrangle, Moffat County, Colorado: U.S. Geological Survey Geologic 

Quadrangle Map GQ– 1536, scale 1:24,000.

Pipiringos, G.N., and O’Sullivan, R.B., 1975, Chert pebble unconformity at the 

top of the Navajo Sandstone in northeastern Utah: Four Corners Geological 

Society Guidebook, 8th Field Conference, Canyonlands, 1975, p. 149–156.

Powers, R.B., 1986, The Willow Creek fault, eastern Uinta 

Mountains—Geological analysis of a foreland subthrust play, in Stone, D.S., 

ed., New interpretations of northwest Colorado geology: Denver, Colo., Rocky 

Mountain Association of Geologists, p. 183–190.

Rowley, P.D., and Hansen, W.R., 1979a, Geologic map of the Plug Hat Rock 

quadrangle, Moffat County, Colorado: U.S. Geological Survey Geologic 

Quadrangle Map GQ–1514, scale 1:24,000.

———1979b, Geologic map of the Split Mountain quadrangle, Uintah County, 

Utah: U.S. Geological Survey Geologic Quadrangle Map GQ–1515, scale 

1:24,000.

Van Loenen, R.E., and Bryant, W.A., 1999, Geologic map of the Skull Creek 

quadrangle, Moffat County, Colorado: U.S. Geological Survey Geologic 

Investigations Series I–2647, scale 1:24,000.

Van Loenen, R.E., Folger, H.W., Bryant, W.A., and Korzeb, S.L., 1990, Mineral 

resources of the Willow Creek and Skull Creek Wilderness Study Areas, Moffat 

County, Colorado: U.S. Geological Survey Bulletin 1717–D, 20 p.

GEOLOGIC MAP OF THE LAZY Y POINT QUADRANGLE, MOFFAT COUNTY, COLORADO

By

R.E. Van Loenen, Gary Selner, and W. Anthony Bryant

1999

Multiply By To obtain

inches (in.) 2.54 centimeters (cm)

feet (ft) 0.3048 meters (m)

miles (mi) 1.609 kilometers (km)

Any use of trade names in this publication is for

descriptive purposes only and does not imply

endorsement by the U.S. Government.

For sale by U.S. Geological Survey Information Services

Box 25286, Federal Center, Denver, CO 80225

This map was produced on request, directly from 

digital files, on an electronic plotter. It is also available

as a PDF file at http://greenwood.cr.usgs.gov

INDEX MAP SHOWING LOCATION OF THE LAZY Y POINT QUADRANGLE

WOLF C REEK MONOCLI N E

W O L F C R E E K F A U L T

S KUL L C R E E K

M O N O C LIN E

15o

APPROXIMATE MEAN

DECLINATION, 1962

MAGNETIC NORTH

TRUE NORTH

COLORADO

MAP AREA

Creek

Vermillion

River

Green

River

Yampa

River Green

Cub Creek

Creek

Cree

Brush

k

Big

Ashley Creek

Cliff Creek

Little

Brush

Pot Creek

40

40

45

149

45

64

Vernal

Jensen

Dinosaur

Monument

Headquarters

Blue Mountain

Skull

Creek

Elk Springs

Greystone

DINOSAUR

NATIONAL

MONUMENT

UTAH

COLORAD

O

HAYSTACK

ROCK

GQ-1535

INDIAN

WATER

CANYON

GQ-1516

TANKS

PEAK

GQ-1534

HELLS

CANYON

GQ-1536

STUNTZ

RESERVIOR

GQ-1530

SPLIT

MOUNTAIN

GQ-1515

DINOSAUR

QUARRY

GQ-1513

JONES HOLE

GQ-1401

CANYON OF

LODORE

SOUTH

GQ-1403

ZENOBIA

PEAK

GQ-1408

SKULL

CREEK

I-2647

LAZY Y

POINT

I-2646

PLUG HAT

ROCK

GQ-1514

Conway

Draw

Douglas

Draw

DOUGLAS

MOUNTAIN

Jones Hole

Gulch

Diamond

Split Mtn

BLUE MOUNTAIN

40o30'

109o30' 109o 108o30'

FEET

4000

5000

6000

7000

8000

A

4000

5000

6000

7000

8000

A'

FEET

Surficial deposits not shown

A'

A

Ppc

Ppc Jg Jm Kmf

Kmm

Phw

Phw

hml

hml

hmu

hmu

hmu

dc

dc

dc

dm

dm

dm

dm

Ppc

Jg

Kcm

Jsr

Jg

Je

Jca Kmy

Kd

Jsc

hml

Phw

Older Paleozoic and Precambrian rocks

dc

Older Paleozoic and

Precambrian rocks

WOLF CREEK

WOLF CREEK FAULT

MONOCLINE

SKULL CREEK MONOCLINE