Petroleum Potential of 

Wilderness Lands in 

Utah 

By Cornelius M. Molenaar and Charles A. Sandberg 

PETROLEUM POTENTIAL OF WILDERNESS LANDS IN THE 

WESTERN UNITED STATES 

GEOLOGICAL SURVEY CIRCULAR 902-K 

This chapter on the petroleum 

geology and resource potential of 

Wilderness Lands in Utah is also 

provided as an accompanying 

pamphlet for Miscellaneous lnvestiga tions Series Map 1-1545 
j 
CONTENTS 

Page 

Abstract---------------------------------------------------------------------- K1 

Introduction-------------------------------------------------------------------

Major sedimentary basins--------------------------------------------------------

Major structural features--------------------------------------------------------

Regional stratigraphy and associated petroleum accumulations-------------------------

Cambrian through Middle Devonian rocks ---------------------------------------

Upper Devonian and Mississippian rocks ----------------------------------------

Pennsylvanian rocks---------------------------------------------------------

Permian rocks--------------------------------------------------------------

Triassic and Jurassic rocks----------------------------------------------------

1 

1 

4 

4 

4 

7 

7 

8 

8 

Cretaceousrocks------------------------------------------------------------ 9 

Tertiary rocks -------------------------------------------------------------- 9 

Petroleum-potential ranking of Wilderness Lands ------------------------------------ 9 

Areas of Utah east of the Eastern Basin and Range province ----------------------- 10 

Eastern Basin and Range province --------------------------------------------- 11 

Summary--------------------------------------------------------------------- 12 

Referencescited---------------------------------------------------------------- 13 

ILLUSTRATIONS 

Page 

FIGURE 1. Map of Utah showing Wilderness Lands, present structural features, and medium and larger sized oil and gas 

fields ------------------------------------------------------------------------------------ K2 

2. Map of Utah showing Wilderness Lands and tract clusters, USGS petroleum provinces, and medium and larger 

sized oil and gas fields----------------------------------------------------------------------- 3 

3. Map of Utah showing Wilderness Lands, selected ancestral uplifts, leading edge of Sevier thrust system, distribution of important Upper Devonian and Mississippian hydrocarbon source rocks, and an area in western Utah 

with favorable thermal history for hydrocarbon generation----------------------------------------- 5 

TABLE 

Page 

TABLE 1. Medium and larger sized oil and gas fields of Utah--------------------------------------------------- K6 

III 

PETROLEUM POTENTIAL OF WILDERNESS LANDS IN THE WESTERN UNITED STATES 

Petroleum Potential of Wilderness Lands in Utah 

By Cornelius M. Molenaar and Charles A. Sandberg 

ABSTRACT 

Utah contains parts of several sedimentary basins ranging in 

age from early Paleozoic to early Tertiary. Structural events 

that occurred during or after deposition have divided the State 

into separate basins or provinces having different hydrocarbon 

potentials. The provinces containing most of the larger oil and 

gas fields and also having the greatest petroleum potentials are 

the Paradox basin of southeastern Utah, the Uinta basin of 

northeastern Utah, and the thrust belt of north-central Utah. 

Wilderness Lands throughout the State are grouped for convenience into clusters having similar resource attributes. Petroleum potential of these clusters is qualitatively evaluated as 

zero, low, medium, or high with respect to the province in 

which they are located. These evaluations are based on (1) 

stratigraphic setting or exploration objectives, (2) structural 

setting, (3) petroleum source rocks and thermal history, and 

(4) results of previous exploration in the area. Most of the Wilderness Lands are classified as having low and medium potentials. 

INTRODUCTION 

Lands classified as Wilderness Lands are scattered throughout the State of Utah (fig. 1). These 

lands include BLM Further Planning or Study 

Areas and BLM Lands under Appeal, USFS Designated Wilderness, USFS Administratively Endorsed as Suitable, USFS Further Planning or 

Study Areas and NPS Administratively Endorsed 

as Suitable. The purpose of this report is to qualitatively assess the petroleum potential of these 

Wilderness Lands by relating the tracts to their 

overall stratigraphic and structural setting and 

comparing them with areas of known oil and gas 

fields of Utah. 

Much of the State has been explored for oil and 

gas, including some areas now classified as Wilderness Lands. Many areas of the State, however, 

have been only lightly or never explored because 

of low potential or lack of exploration techniques 

necessary to resolve the subsurface geology. 

Large hydrocarbon accumulations have been discovered in several different basins or parts of basins. The three areas of significant production are 

Kl 

(1) the Paradox basin of southeastern Utah, (2) 

the Uinta Basin of northeastern Utah, and (3) the 

thrust belt of north-central Utah (figs. 1 and 2). In 

addition, a few small- and medium-size fields have 

been found outside of these three major producing 

areas. 

The discussion of the geology is very brief and 

generalized and much of the discussion is based on 

Hintze (1973) or the many papers in Mallory 

(1972a). However, there are many reports, too 

numerous to list here, that cover the geology of 

different parts of Utah. A geological highway map 

by Hintze (1975) at a scale of 1:1,000,000 is useful 

in relating the Wilderness Lands to the local geology. Because of the impact of recent exploration 

in the thrust belt, which includes part of Utah, 

the thrust belt will be covered in more detail by 

R. B. Powers in chapter N in this circular. 

MAJOR SEDIMENTARY BASINS 

Utah has been the site of all or parts of several 

large sedimentary basins of diverse character and 

age throughout Phanerozoic (Cambrian and later) 

time. Many of the basins have subsequently been 

uplifted, deformed or disrupted, at least in part, 

by later tectonic events, primarily during latest 

Cretaceous and early Tertiary time and later during late Tertiary time, especially in the western 

third of the State (Eastern Basin and Range province). Some of the younger basins are superposed 

on parts of older basins. The major sedimentary 

basins that include parts of Utah are, in 

chronological order, (1) the Paleozoic Great Basin, 

a large shelf basin that traversed western Utah 

and bordered the North American cratonic shelf 

to the east, (2) the Pennsylvanian-Permian 

Paradox basin of southeastern Utah, (3) the 

Pennsylvanian-Permian Oquirrh basin of centralnorthwestern Utah, ( 4) the Western Interior seaway, a north-south trending Cretaceous basin that 

extended throughout the Western Interior of the 
BASIN AND RANGE 

~ 

~\J 

\ 

\ THRUST BELT 

\ 

\ 

) 

0 

I 

0 

75 MILES 

I 

I 

75 KILOMETERS 

PARADOX 

FIGURE 1.-Map of Utah showing Wilderness Lands (outlined), present structural features, and medium and larger sized oil 

(black pattern) and gas (gray pattern) fields, whose numbers are in circles. (See table 1 for names of fields and pertinent 

field data). 

K2 
42 1140 

(L) 

WYO.-UTAH-IDAHO 

24 (M) 

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_____ __... / I I 

{J 23 (L;,/ 

{1 n / ----~ --- L) ~--:: (M) _!!J 21 (H) trr __ 

I. -t-1 a? /--

l dtt I EASTERN 

,:_ I 

I I BASIN A.ND 

\ ~0 (M) 

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0 

I 

0 

I 

75 MILES 

I 

75 KILOMETERS 

SW WYOMING 

BASINS ,.-

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FIGURE 2.-Map of Utah showing Wilderness Lands (outlined) and numbered tract clusters (dashed lines and numbers), USGS 

petroleum provinces (heavy black lines), and medium and larger sized oil (black pattern) and gas (gray pattern) fields, whose 

numbers are in circles. (See table 1 for names of fields and pertinent field data). Petroleum potential of tract clusters is 

ranked zero (diagonal hatched), low (L), medium (M), and high (H) with respect to the provinces in which they are located. 

K3 
United States and Canada and includes the eastern two-thirds of Utah, and (5) the Uinta Basin, 

an early Tertiary basin in northeastern Utah. In 

addition, the narrow belt of sedimentary rocks 

north of the Uinta Mountains is the southernmost 

part of the early Tertiary Green River basin of 

Wyoming. There are several other early Tertiary 

basins in Utah, but late Tertiary epeirogenic uplift 

of the Colorado Plateau, which includes areas in 

Utah south of the Uinta Mountains and east of the 

Wasatch Mountains, has resulted in dissection or 

removal by erosion of much of the Tertiary section 

in most Tertiary basins except the Uinta basin. 

MAJOR STRUCTURAL FEATURES 

Several major structural elements in Utah are 

recognized from surface structures. Generally 

from west to east, these are the Eastern Basin 

and Range province in western Utah, the thrust 

belt in central and northern Utah, the Kaibab uplift and Circle Cliffs uplift in south-central U tab, 

the San Rafael uplift in east-central Utah, the 

Uinta uplift in northern Utah, the Monument uplift in southeastern Utah, and the Uncompahgre 

uplift, which extends into central-eastern Utah 

from Colorado (fig. 1). The Eastern Basin and 

. Range province is a series of late Tertiary to 

Quaternary horsts and grabens. The thrust belt is 

a Late Jurassic to earliest Tertiary compressional 

fold and thrust-fault belt that extended across 

Utah from the northern part to the southwest 

corner of the State. The later Basin and Range 

structure (essentially the area west of the 

Wasatch Mountain front) marks the present west 

boundary of the thrust- belt province in northern 

Utah. The areas of thrust faulting do continue 

farther west, but those areas are superposed by 

later Basin and Range structure, which is presently the dominant surface feature. In places, the 

boundary between the two structural provinces is 

arbitrary because of this overlap, and in southern 

Utah, the Basin and Range structure overlaps the 

entire thrust belt. 

The uplifts east of the thrust belt or east of the 

Basin and Range in southern Utah are latest Cretaceous to early Tertiary in age. Many of these 

uplifts had earlier movements, or overlapped 

parts of earlier uplifts. The Basin and Range province probably contained older PennsylvanianPermian uplifts and certainly was involved in Late 

Jurassic to Cretaceous orogenic movements. Parts 

of the Kaibab, Circle Cliffs and San Rafael uplifts 

K4 

were part of the larger Piute platform, a Pennsylvanian feature (Mallory, 1972b).·The Uncompahgre 

uplift was primarily active during the Pennsylvanian and Permian; its Laramide or later movement was relatively minor, at least in Utah. Figure 3 shows selected ancestral uplifts that are discussed. 

REGIONAL STRATIGRAPHY AND 

ASSOCIATED PETROLEUM 

ACCUMULATIONS 

For purposes of discussion of major stratigraphic units and their contained petroleum accumulations, the Phanerozoic sedimentary section 

is here divided into seven packages, each one having somewhat common characteristics relating to 

its depositional history or petroleum potential. In 

ascending order, the ages of the rocks comprising 

these packages are (1) Cambrian through Middle 

Devonian, (2) Upper Devonian and Mississil:)pian, 

(3) Pennsylvanian, (4) Permian, (5) Triassic and 

Jurassic, (6) Cretaceous, and (7) Tertiary. 

In the discussion of oil and gas fields associated 

with the various rock units, small-size fields are 

those with ultimate recoveries of less than 10 million barrels (MMB) of oil or 60 billion cubic feet 

(BCF) of gas, medium-size fields are those between 10 and 50 MMB oil or 60 and 300 BCF gas, 

large-size fields are those between 50 and 100 

MMB oil or 300 and 600 BCF gas, and giant-size 

fields are those larger than 100 MMB oil and 3,000 

BCF gas. Table 1 lists some pertinent data on the 

medium- and larger-size oil and gas fields of Utah. 

CAMBRIAN THROUGH MIDDLE DEVONIAN 

ROCKS 

Rocks included in the Cambrian through Middle 

Devonian package, although not necessarily an unbroken sequence, are present, at least in part, 

throughout Utah except in areas where they have 

been removed by erosion on ancestral uplifts, such 

as the Uncompahgre, Sevier, anfl parts of the 

Uinta uplifts (fig. 3), and on late Mesozoic and 

later uplifts. These rocks were deposited in mostly 

shallow-marine environments in a cratonic setting 

(thin shelf deposition on stable continental crust) 

in eastern Utah and in a shelf-basin setting where 

they aggregate in excess of 20,000 feet (6, 100 m) 

in thickness in the area west of the Sevier thrust 

system (Hintze, 1973). This western area is part 

of the Great Basin. 
j Leading edge of Sevier thrust system 

y (Shelf basin rocks to west) 

I Area in western Utah with favorable 

thermal history for hydrocarbon 

generation 

0 

I 

0 

EXPLANATION 

I 

75 MILES 

I 

75 KILOMETERS 

.J Area of rich source rocks of Mississippian 

/ starved basin 

.J Area of rich source rocks of Late Devonian 

/ age 

FIGURE 3.-Map of Utah showing Wilderness Lands (outlined), selected ancestral uplifts, leading edge of Sevier 

thrust system (Late Jurassic), distribution of important Upper Devonian and Mississippian hydrocarbon 

source rocks (from Sandberg and Gutschick, 1983; and Sandberg and Poole, 1975), and an area in western 

Utah that has a favorable thermal history for hydrocarbon generation ("cold spot" of Sandberg and Gutschick, 

1977). 

K5 
TABLE 1.-Medium and larger sized oil and gas fields of Utah 

[Production data from Smith and Brown, 1981; NA, data not available) 

Cumulative prod. Estimated 

No. on Primary 1980 Production through 1980 ultimate prod. 

figures Field Basin or Year reservoir 

province discovered age Oil Gas Oil Gas Oil Gas 

MB MMCF MMB BCF MMB BCF 

1 Aneth (Greater) Paradox 1956 Pennsylvanian 6,741 7,315 306 294 1

378 NA 

2 Lisbon do 1960 Mississippian 718 17,078 43 358 NA NA 

3 Ismay do 1956 Pennsylvanian 79 91 10 17 112 21.5 

4 Altamont-Bluebell Uinta 1955-72 Eocene 8,446 12,351 132 168 2

250+ NA 

~ 5 Red Wash do 1951 do 2,935 4,368 115 316 8135 NA 

6 Natural Buttes do 1952 do 140 13,093 0.3 59 NA NA 

7 Ashley Valley do 1948 Perm.-Penn. 296 0 19 0 422 0 

8 San Arroyo do 1955 Cret. & Jur. 3 1,851 125 74 NA NA 

9 Clay Basin Green River 1927 Cretaceous 5 1,836 318 139 NA NA 

10 Bridger Lake do 1966 do 160 2,988 10 31 NA NA 

11 Pineview Thrust Belt 1975 Jurassic 2,948 3,436 16 17 NA NA 

12 Anschutz Ranch do 1978 do 147 7,129 0.1 7 NA NA 

13 Anschutz Ranch E do 1979 do 278 1,245 0.3 1 NA NA 

14 Clear Creek Wasatch Plat. 1951 Cretaceous 0 103 0 135 0 4 168 

15 Upper Valley Kaiparowits 1964 Permian 674 0 19 0 121 0 

'From Fassett, 1978 

•From Lucas and Drexler, 1976 

•From Oil and Gas Journal, 1970 

•From Preston, 1961 
Rocks of this lower Paleozoic package consist 

generally of a basal sandstone and shale unit overlain predominantly by thick carbonate units 

(limestone and dolomite) with thinner interbeds of 

shale and sandstone. All the units of the cratonic 

sequence are thinner than equivalent units to the 

west and there are many disconformities or diastems within the section. For instance, Ordovician 

through Middle Devonian rocks are missing in 

eastern U tab. The shelf-basin sequence on the 

west contains much thicker units and a more complete section, although there are areas where uplifts such as the ancestral Sevier uplift (Sandberg 

and Poole, 1977) within the shelf basin resulted in 

removal of strata. In addition, because of the 

mobile nature of the shelf basin, there are more 

variations in depositional thicknesses. 

There is no production in U tab from rocks of 

this package. However, in western Utah, recent 

drilling suggests that hydrocarbon source rocks 

are present in some of the Cambrian and possibly 

Lower Ordovician shales. In addition, oil shows in 

Cambrian dolomites have been reported from drill 

holes in that area. 

UPPER DEVONIAN AND MISSISSIPPIAN ROCKS 

The Antler orogeny in central Nevada profoundly affected depositional patterns of Upper 

Devonian and Mississippian rocks. Although great 

differences in their lithologic character and 

paleotectonic setting would require that rocks of 

these two systems should be treated separately, 

for ease of assessment of hydrocarbon potential, 

they are grouped herein. For some of the profound paleotectonic and source-rock differences 

between these systems, the reader is referred to 

Sandberg and Poole (1977), Gutschick, Sandberg, 

and Sando (1980), and Sandberg and others (1983). 

Deposition of these rocks in the Eastern Great 

Basin was complicated by intrabasinal uplifts (ancestral Sevier and Stansbury uplifts) shedding 

clastics into surrounding areas in part of Late Devonian time concurrent with foreland trough development that continued into Mississippian time 

(Gutschick and Sandberg. 1983). In the Eastern 

Great Basin, Upper Devonian rocks consist of 

thick sections of carbonate, shale, sandstone, and 

locally, conglomerate. Overlying Mississippian 

rocks consist of thin starved-basin shale and argillaceous limestone with some sandstone tongues 

extending into the basin from deltas in the Uinta 

uplift to the east and the Antler orogenic highlands to the west (Sandberg and others, 1983). To 

the southeast, Devonian and Mississippian rocks 

grade landward into a more stable cratonic-shelf 

facies. There the Upper Devonian consists of a 

basal organic black shale (locally) and sandstone 

unit overlain by dolomite with interbedded shale, 

all aggregating only a few hundred feet in thickness. The Mississippian consists of widespread 

shelf limestone and dolomite ranging from a few 

hundred to more than a thousand feet thick. 

The only petroleum production from Upper Devonian and Mississippian rocks in Utah is in the 

Paradox basin (fig. 1). Mississippian carbonate 

rocks are the primary producing formation at Lisbon field, a structurally trapped oil and gas accumulation of large size (Parker, 1981; Smith 

and Prather, 1981). Upper Devonian carbonate 

rocks directly beneath the Mississippian, and 

sandstones at the base of the Upper Devonian are 

minor producing reservoirs in this field. The 

source rocks for the hydrocarbons in this field are 

thought to be Pennsylvanian organic-rich shale interbeds in the Paradox salt section (Murphy and 

Claypool, oral commun.), which is in fault contact 

with the Mississippian and Devonian reservoirs on 

the northeast flank of the structure. Mississippian 

carbonate rocks also are the producing formation 

at four small oil or gas fields in the Utah part of 

the Paradox basin. 

Mississippian carbonate rocks generally have 

good reservoir properties, but good petroleum 

source rocks are not common in the Upper Devonian and Mississippian cratonic sequence, except 

for lowermost Upper Devonian shales (Aneth Formation) that are present in the southern Paradox 

basin (Spencer, 1975). In addition, shale and argillaceous limestone units of Mississippian age in 

north-central Utah and the Great Basin to the 

west are probably good source rocks. 

K7 

PENNSYLVANIAN ROCKS 

Rocks of the Pennsylvanian System are present 

in much of U tab but were stripped off or never 

deposited over the Pennsylvanian-Permian Uncompahgre and Piute platform uplifts. In addition, 

they are absent on the late Mesozoic-early Tertiary uplifts. The thickest sections of these rocks 

are in the Oquirrh basin of central-northwest 

Utah, where 13,000 ft (3,962 m)has been reported 

(Hintze, 1973), and in the Paradox basin of southeastern Utah, where as much as 8,000 ft (2,438 m) 
has been penetrated by drill holes. Elsewhere, 

Pennsylvanian strata thin rapidly toward adjacent 

platforms or shelves. 

Pennsylvanian rocks were deposited in a wide 

range of depositional environments ranging from 

nonmarine eolian and fluvial to locally deep-marine 

environments. However, most of these rocks were 

deposited in a shallow-marine environment and 

characteristically consist of alternating layers of 

limestone, shale, and sandstone. The cyclic nature of deposition is caused by eustatic sea-level 

changes common to the Pennsylvanian Period. 

Thick deposits of evaporites, primarily halite, 

(Paradox Formation of industry usage) are present in the Paradox basin, and a thick eolian 

sandstone unit (Weber Formation) is present in 

northeastern U tab. 

The major production in the Paradox basin 

comes from Pennsylvanian rocks. One giant-size 

field (Aneth), one medium-size field (Ismay), and 

many small-size fields produce from Middle 

Pennsylvanian (Desmoinesian) carbonate mounds 

along the southern flank of the basin (Peterson, 

1966) (fig. 1 and table 1). The location of the porous mound development is stratigraphically controlled, but low-relief structures within the field 

area controls the oil-water contact. This type of 

stratigraphic trap is very difficult to identify or 

delineate by methods other than drilling. Interbedded or laterally adjacent organic-rich dolomitic 

shales are the source rocks for hydrocarbons in 

the southern Paradox basin. 

In addition to the many fields in the southern 

Paradox basin, a few small one-well fields have 

produced oil from fractured siltstone and shale interbeds within the Paradox salt section in the 

northern Paradox basin. 

Elsewhere, the only significant production from 

Pennsylvanian (and overlying Permian) rocks is at 

Ashley Valley field, a medium-size structurally 

trapped oil accumulation on the northeast flank of 

the Uinta Basin (fig. 1). The production comes 

from an eolian sandstone of Pennsylvanian-Permian age (Weber Sandstone). 

PERMIAN ROCKS 

Rocks of Permian age are present in most of 

Utah except on the Uncompahgre uplift, where 

they were never deposited, and on the late 

Mesozoic-Tertiary uplifts, where they have been 

removed by erosion. Like the Pennsylvanian, the 

thickest sections of Permian rocks are in the 

K8 

Oquirrh and Paradox basins. Permian rocks conformably overlie Pennsylvanian rocks in basinal 

areas but unconformably overlie Pennsylvanian to 

Mississippian rocks on the Piute platform of central Utah. 

Permian rocks consist of nonmarine and marginal-marine red beds and eolian sandstone on the 

east that grade to shallow-marine sandstones and 

limestones to the west. Like the Pennsylvanian 

sequence, deposition of marine rocks of the Permian is cyclic, consisting of alternating layers of 

limestone, sandstone, and shale. Rich hydrocarbon 

source rocks are present in northern Utah and 

were probably the origin of the oil occurring in 

several oil fields in northern Utah and Wyoming. 

For details of these source rocks and other Permian rocks of northern U tab, refer to Maughan 

(1979). 

Two medium-size oil fields produce from Permian reservoirs; the previously mentioned Ashley 

Valley field in northeastern Utah, and the Upper 

Valley field in south-central Utah (fig. 1). The 

major, if not all, production at Ashley Valley 

probably is from the Permian part of the thick 

sandstone (Weber) reservoir. The Upper Valley 

field produces primarily from carbonate reservoirs 

in the Lower Permian Kaibab Limestone 

(Campbell, 1969). The trap is a south-southeast 

plunging anticline in which a hydrodynamic gradient of the formation water has caused an inclined oil-water contact (Sharp, 1978). 

Permian sandstones and carbonate rocks also 

are secondary reservoirs in some of the fields in 

the thrust belt of northern Utah. In addition, 

large heavy-oil (tar) deposits occur at or near the 

surface in the Permian White Rim Sandstone in 

central-southeastern Utah. This accumulation occurs near the eastern pinch-out of the sandstone 

unit, and is an exhumed super-giant-size oil field. 

TRIASSIC AND JURASSIC ROCKS 

Triassic and Jurassic rocks are at or near the 

surface over much of the Paradox 'basin of southeastern Utah and are present in the deeper subsurface in the Uinta basin, the Wasatch Mountains and Plateau, and the thrust belt. They are 

missing largely by erosion and parts of the sequence were never deposited over most of the 

Great Basin part of U tab. 

During deposition of the Triassic through Middle Jurassic part, which contains several colorful 
red-bed units, the seaway was to the west, northwest, and north. On the west and northwest, the 

sequence consists of three shallow-marine 

sandstone, shale, and limestone units separated 

by nonmarine fluvial or eolian deposits. To the 

east, all the units become thinner and the marine 

units pinch out. 

Latest Jurassic rocks, which consist of fluvial 

sandstone and variegated shale (Morrison Formation), were derived from an orogenic belt in western Utah and farther south. These rocks were deposited in and beyond eastern Utah, which was 

part of the developing Western Interior 

geosyncline. 

Because of the lack of petroleum source rocks in 

much of the section and because much of the section is at or near the surface in southeastern 

Utah, most of the Triassic and Jurassic rocks in 

southeastern Utah have little hydrocarbon potential. However, parts of the Lower Triassic limestones to the west are petroliferous and several 

small oil and gas fields produce from reservoirs in 

or near these limestones. Small oil and gas fields 

also are present in Jurassic sandstone reservoirs 

in faulted structural traps in the southeastern 

Uinta basin and northern Paradox basin. 

In addition, large or giant oil and gas fields 

occur in the thrust belt of north-central Utah, 

where Jurassic sandstone reservoirs are in thrustfault contact with Cretaceous source rocks. The 

thrust-belt area is discussed by R. B. Powers in 

chapter N in this circular. 

CRETACEOUS ROCKS 

As much as 14,000 ft (4,267 m) of Cretaceous 

rocks were deposited in the Utah part of the 

Western Interior seaway. Most of these rocks 

have been eroded in Tertiary time and the more 

complete sections are preserved only in the Tertiary basins such as the Uinta basin, the Green 

River basin (a small part of which is in Utah on 

the north side of the Uinta Mountains), the 

Kaiparowits basin, and other areas such as under 

the Wasatch Plateau and in synclinal areas in the 

thrust belt. Cretaceous strata consist of thick sections of marine shale and siltstone that intertongue to the west with eastward-prograding wedges 

of thinner shallow-marine sandstone units and 

thicker nonmarine units of sandstone, shale, minor 

conglomerate, and coal. Organic-rich shale is present in parts of the thick marine shale section. 

K9 

These shales are the probable source rocks for oil 

at the Bridger Lake field and gas at the Clay 

Basin field north of the Uinta Mountains and for 

the hydrocarbons in some of the Jurassic reservoirs in the thrust belt. In addition, one mediumsize gas field (San Arroyo, fig. 1) and several small 

oil and gas fields that produce from Jurassic and 

Lower Cretaceous sandstone reservoirs in the 

southeastern part of the Uinta basin were probably charged by Cretaceous source rocks. On the 

Wasatch Plateau of central Utah, carbonaceous 

shales and coals were probably the source rocks 

for the gas in the Clear Creek field, a medium-size 

accumulation in a structural trap. 

TERTIARY ROCKS 

Beginning in latest Cretaceous time and continuing into the lower Tertiary, Laramide structural movements developed separate internal 

drainage basins flanked by uplifts. The most 

prominent of these Tertiary basins in Utah is the 

Uinta basin in northeastern Utah. As much as 

15,000 ft (4570 m) of Paleocene and Eocene shale, 

limestone, sandstone, and conglomerate were deposited in this intermontane basin. Much of this 

deposition, especially in the basin center, occurred 

in a lacustrine environment in which large 

amounts of organic matter were incorporated in 

the muds and marls. These organic-rich sediments, which intertongue with or are overlain by 

sand layers, have subsequently been buried 

deeply enough in the deeper parts of the basin 

to thermally generate hydrocarbons (Lucas 

and Drexler, 1976). As a result, two giant-size 

oil fields (Altamont-Bluebell and Red Wash) and 

one medium-size gas field (Natural Buttes) as 

well as many small gas or oil fields produce 

from early Tertiary sandstone reservoirs in 

stratigraphic traps in the deeper parts of the 

Uinta basin. 

PETROLEUM-POTENTIAL RANKING 

OF WILDERNESS LANDS 

The petroleum potential of the Wilderness 

Lands of Utah, most of which are in southeastern 

and southern Utah, were qualitatively ranked in 

respect to the petroleum province in which they 

are located (fig. 2). The petroleum provinces were 
used by the USGS for convenience in making resource appraisals of the entire United States (Dolton and others, 1981). Because of differences in 

age and overlapping of geologic basins, the province boundaries may or may not coincide with 

present geologic basin outlines. U tab includes 

parts of five provinces, which are (1) the Eastern 

Basin and Range, (2) the Paradox Basin (expanded), (3) the Uinta-Piceance- Eagle Basins, (4) 

the Wyoming-Utah-Idaho Overthrust belt, and (5) 

the Southwestern Wyoming Basins province. 

The rankings of the Wilderness Lands range 

from zero through low, medium, and high potential. Zero potential areas are those in which basement or nonprospective rocks are at or near the 

surface. However, consideration is given to areas 

in which nonprospective rocks may be thrust over 

prospective rocks, such as along the north flank of 

the Uinta Mountains. Higher potential areas are 

those areas near oil and gas fields or areas having 

attributes that make them more favorable for petroleum than other areas of the particular province. A map of Utah has been prepared at a scale 

of 1:1,000,000 which shows the petroleum potential of Utah's Wilderness Lands (Miscellaneous Investigations Series Map I-1545, in press). 

The factors by which the various lands are 

ranked include (!)stratigraphic setting or exploration objectives, (2) structural setting, (3) petroleum source rocks and thermal history, and(4) results of previous exploration in the area. Many 

Wilderness Lands have been explored for petroleum during the past 30 years, and some areas 

have been tested by drilling. A dry hole, however, 

doesn't necessarily condemn the entire tract or 

group of tracts and, indeed, some wells did not 

test deeper objectives .. For convenience in describing the factors that went into assessing the 

various Wilderness Lands, the tracts are grouped 

into clusters of tracts in which the geologic attributes are similar. Twenty-five clusters of·various 

sizes covering the five petroleum provinces are 

differentiated in figure 2. 

AREAS OF UTAH EAST OF THE 

EASTERN BASIN AND RANGE PROVINCE 

The area east of the Eastern Basin and Range 

province has been tested by drilling to a much 

greater extent than areas to the west, and the petroleum geology is better known. In addition, several oil and (or) gas fields are scattered throughKlO 

out the area. These fields and the many dry drill 

holes provide much data with which to compare or 

rank the petroleum potential of the Wilderness 

Lands. The evaluation and the geologic attributes 

that affected the ranking of these clusters are as 

follows: 

Cluster 1.-High potential. This area is not far 

from oil and gas fields producing from Pennsylvanian carbonate-mound reservoirs. It has the potential for a small field, although there are many 

dry holes surrounding the area. 

Cluster 2.-Medium potential. This area is on 

the Monument uplift and many dry holes have 

been drilled throughout the area. Isolated 

Pennsylvanian carbonate-mound reservoirs may 

be present. 

Cluster 3.-Low potential. This area is on the 

north plunge of the Monument uplift. Deep canyons dissect the area and Pennsylvanian strata 

are exposed at the north end. 

Cluster 4.-Medium potential. This area includes or is adjacent to a huge heavy-oil (tar) deposit in the Permian White Rim Sandstone. Several dry Mississippian tests have been drilled on 

or adjacent to this cluster. The area is deeply dissected by the Colorado and Green Rivers and seismic resolution of subsurface structure is difficult. 

Mississippian prospects may still exist. In addition, Pennsylvanian stratigraphic traps are a possibility. 

Cluster 5._:_Medium potential. Differential salt 

flowage has occurred in this area and seismic resolution of presalt structure is difficult. Mississippian structures may be present in the area. 

Cluster 6.-Medium potential. This area is on 

the San Rafael uplift-mostly on the flanks. Permian rocks are exposed on the crest of the uplift 

and heavy oil is present in some sandstone outcrops. The objectives in this area would be older 

rocks, most likely Mississippian carbonate rocks. 

Several dry holes are scattered throughout this 

area. 

Cluster 7.-Medium potential. This area is 

covered by Tertiary volcanic rocks, thereby masking the structure of prospective Mississippian, 

Permian, Triassic, and Cretaceous rocks, all of 

which are in a favorable facies belt. 

Cluster 8.-Low potential. This area falls along 

the Circle Cliffs monocline on the northeast side of 

the Circle Cliffs uplift and in the Henry basin, a 

structurally low area to the northeast. Much of 
the Wilderness Land in the Henry basin includes 

the Henry Mountains, which are Tertiary laccolithic intrusive rocks-a poor place to explore 

for petroleum. 

Cluster 9.-Medium potential. This large area 

surrounds the Upper Valley field, a 21-MMB oil 

field that produces from Permian carbonate reservoirs. Oil shows were reported from other Permian formations in this field and a small amount of 

oil was produced from Mississippian carbonate 

rocks. Many dry holes have been drilled throughout the area, but possibilities still exist for oil accumulations in Permian or Mississippian reservoirs. 

Cluster 10.-Low potential. This area lies 

mostly on the north plunge of the Kaibab uplift. 

This is a sparsely explored area, but several dry 

holes have been drilled. The Permian carbonate 

rocks that produce oil at Upper Valley field to the 

northeast are exposed at the surface of the uplift. 

Mississippian rocks would be the primary objective in this area. 

Cluster 11.-Medium potential. This area includes Cedar Breaks National Monument, Zion 

National Park, and areas to the south and southeast. The Virgin oil field, a very small, shallowdepth subcommercial oil field that produced or is 

producing from a Lower Triassic sandy limestone 

reservoir, is located a few miles southwest of Zion 

Park. Oil shows were reported from Permian, 

Pennsylvanian, and Mississippian rocks penetrated by deeper tests (Driscoll, 1978). The Triassic and Jurassic strata at the surface in this cluster are very low dipping. 

Cluster 12.-Medium potential. This small cluster borders the Hurricane fault zone and is on the 

upthrown block. A noncommercial field (Anderson 

Junction field) produced a small amount of oil from 

a Pennsylvanian carbonate reservoir on this block 

a few miles south of the cluster. Fault-bounded 

structures may provide traps for oil in Mississippian through Permian reservoirs. 

Cluster 13.-Medium potential. This area is on 

the south flank of the Uinta basin, which overlaps 

with the northern extent of the Paradox basin. In 

addition, the southwest-bounding fault of the 

Pennsylvanian-Permian Uncompahgre uplift cuts 

across the area. A few dry holes have been drilled 

on or adjacent to the cluster. Rugged topography 

of the Book Cliffs makes seismic definition of deep 

structure difficult. 

Cluster 14.-Medium potential. Attributes of 

K11 

this cluster are the same as cluster 13. The two 

clusters are separated because they are in two different petroleum provinces. Cluster 14 is probably 

all, or mostly, on the Uncompahgre block, although there are no deep tests to verify this. 

Cluster 15.-High potential. This area is on the 

south and southeast flank of the Uinta basin and 

is adjacent to and includes several small gas fields. 

The medium-size San Arroyo gas field lies to the 

northeast of the southeastern tract. Almost all 

these fields produce from small structural traps in 

basal Cretaceous and Jurassic sandstone reservoirs. One small oil field (Peters Point) located 

west of the northern tract produces a small 

amount of oil from a Tertiary reservoir. 

Cluster 16.-Low potential. This area encompasses the western end of Dinosaur National 

Monument, which structurally is the steep-flanked 

Split Mountain anticline. Erosion by the Green 

River has exposed Mississippian and locally 

Cambrian rocks on the crest of the structure. The 

area has very low potential for hydrocarbons. 

Cluster 17.-Low potential. This area lies along 

the north flank of the Uinta Mountains. Rocks at 

the surface are Precambrian in age, but because 

the fault that bounds the Uinta uplift dips to the 

south at an unknown angle, prospective Cretaceous rocks may be encountered at depth (Gries, 

1983). 

Cluster 18.-Low potential. Attributes of this 

cluster are the same as cluster 17. The two clusters are separated because they are in two different petroleum provinces. This cluster falls within 

the southernmost edge of the Wyoming-UtahIdaho Overthrust Belt province. 

EASTERN BASIN AND RANGE PROVINCE 

The resource evaluation of frontier petroleum 

provinces, such as the Eastern Basin and Range 

province, presents problems quite distinct from 

those of the other four Utah provinces, which are 

in various stages of economic development. In developing provinces such as the Paradox basin, producing oil and gas fields provide analogs for predicting where and how similar accumulations 

might be found under matching sedimentary and 

structural conditions. In the Eastern Basin and 

Range province, however, subsurface control is so 

sparse that analogs are unavailable. Moreover, 

the geology is so complex, as described by C. A. 

Sandberg in chapter L of this circular that treats 
the part of this province lying in eastern Nevada, 

that reservoir rocks and traps can be presumed to 

be broadly distributed. Faults and fractures that 

might have leaked hydrocarbons to the surface as 

a result of Basin and Range block faulting are presumed to have been at least partly sealed before 

the cycle of generation thought to be presently in 

progress. Consequently, the prime parameters for 

resource evaluation are the presence of source 

rocks and their degree of maturation. Because 

source rocks in this province are of Paleozoic age, 

one method of determining their maturation is by 

examination of a unique group of microfossils 

called conodonts. Conodonts provide virtual geothermometers that readily tell by their temperature-induced color changes or conodont color-alteration index (CAl) values the maximum temperature to which containing rocks have been subiected. The CAl scale was developed by Epstein, 

Epstein, and Harris (1977). The utility of conodonts to petroleum exploration in this province and 

adjacent areas has been described by Sandberg 

and Poole (1977), Sandberg and Clark (1979), 

Sandberg (1980), and Sweet and others (1981). Papers by Sandberg and Poole (1975), Sandberg and 

Gutschick (1977, 1979), Sandberg, Grogan, and 

Clisham (1979), Sandberg, Poole, and Gutschick 

(1980), Sandberg and Gutschick (1980a, 1980b), 

and Harris and others (1980) provide CAl values 

and source-rock evaluations that were used in 

making the following resource evaluations. 

Cluster 19.-Low potential. Tracts in this cluster lie either east of the Sevier thrust system (fig. 

3), where Mississippian source rocks are thin or 

absent, or within the ancestral Sevier uplift, 

where source rocks were eroded. A low potential 

exists because of possible long-distance eastward 

petroleum migration that also may be responsible 

for the nearby Virgin oil field. 

Cluster 20.-Medium potential. Tracts in this 

cluster have mainly Cambrian and Lower Ordovician rocks at the surface because they lie mostly 

within the ancestral Sevier uplift (fig. 3), from 

which younger rocks were eroded. Some source 

rocks are present in this sequence, as indicated by 

exploratory wells just to the west in the Confusion 

Range. Moreover, one or more complete sequences of Paleozoic and (or) Mesozoic rocks 

might be expected in lower thrust plates at depth. 

As indicated by a deep exploratory test that was 

drilled within this cluster, near Delta, Utah 

(Mitchell, 1979), thermal maturation of hydrocarK12 

bons would be optimum for oil and gas generation. 

Cluster 21.-High potential. This single-tract 

cluster is located on Conger Mountain on a synclinal axis, but anticlinal structures could be expected at depth in lower thrust plates. Because 

this tract lies within the "cold spot" of Sandberg 

and Gutschick (1977) and within areas of rich 

source rocks of the Devonian Pilot Shale and Mississippian Chainman Shale (Sandberg, 1975; 

Sandberg and Poole, 1975; Sandberg, Poole, and 

Gutschick, 1980) and of the Mississippian Deseret 

starved basin (Sandberg and Gutschick, 1980a, 

1980b), it has the greatest potential of any tract in 

the province. Oil is present in a spring just south 

of the tract and live oil is found in fossil 

cephalopods just east of the tract. 

Cluster 22.-Low potential. Tracts of this cluster lie in the vicinity of Mount Nebo in the 

Wasatch Mountains. Conodont CAl values in the 

vicinity indicate that hydrocarbons are at the high 

range of maturity or are overmatured. 

Cluster 23.-Low potential. Tracts in this cluster are situated in the Deep Creek and Fish Creek 

Ranges and Stansbury Mountains. Conodont CAl 

values of 3 to 6 indicate that hydrocarbons range 

from highly mature to overmatured. 

Cluster 24.-Medium potential. This singletract cluster occupies the Cedar Mountains, which 

are formed mainly by Pennsylvanian and Permian 

rocks. The one conodont value reported from this 

area by Harris and others (1980) has a CAl value 

of only 1, which would indicate very low thermal 

maturation of hydrocarbons. This value may be 

anomalously low, however, and optimum maturation could be expected at other localities in the 

tract and at depth. 

Cluster 25.-Low potential. The eastern tract 

of this cluster occupies a major syncline along the 

crest of the Bear River Range. The western tract 

occupies Wells ville Mountain, the western prong 

of the Wasatch Mountains. The average conodont 

CAl values are 3.5, a number which indicates that 

hydrocarbons are within the gas-generation window but at the upper end of the oil-generation 

window. 

SUMMARY 

Of the 4,482, 727 acres involved in this study for 

the assessment of the petroleum potential of the 

Wilderness Lands in Utah, the potential acreage 

can be summarized as follows: high potential, 
- I I Oil. 

208.9 thousand acres; medium potential, 2,638.3 

thousand acres; low potential, 1,010.4 thousand 

acres; and zero potential, 625.2 thousand acres. 

The petroleum potential by acreage of all Wilderness Land categories in the Western United 

States is shown in this circular by B. M. Miller 

in table 1 , chapter P. 

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K13 

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K14 

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