U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2012–5076

Isopach and Isoresource Maps for Oil Shale Deposits in the 

Eocene Green River Formation for the Combined Uinta and 

Piceance Basins, Utah and Colorado
Cover. Aerial image of Uinta and Piceance Basins, northeast Utah and northwest Colorado. 

I3_Imagery_Prime_World ArcGIS Globe Service, courtesy of Esri, Inc. Copyright: © 2009 i-cubed.
Isopach and Isoresource Maps for Oil 

Shale Deposits in the Eocene Green River 

Formation for the Combined Uinta and 

Piceance Basins, Utah and Colorado

By Tracey J. Mercier and Ronald C. Johnson

Scientific Investigations Report 2012–5076

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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Suggested citation:

Mercier, T.J., and Johnson, R.C., 2012, Isopach and isoresource maps for oil shale deposits in the Eocene Green River 

Formation for the combined Uinta and Piceance Basins, Utah and Colorado: U.S. Geological Survey Scientific Investigations Report 2012–5076, 85 p., 1 pl.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Stratigraphy of the Green River Formation and Definition of Rich and Lean Zones of 

the Oil Shale Section .......................................................................................................................4

Detailed Description and Assessment Results of Oil Shale Zones .......................................................8

R-0 Zone..................................................................................................................................................8

L-0 Zone..................................................................................................................................................9

R-1 Zone..................................................................................................................................................9

L-1 Zone..................................................................................................................................................9

R-2 through L-3 Zones........................................................................................................................23

R-2 Zone.......................................................................................................................................23

L-2 Zone.......................................................................................................................................23

R-3 Zone.......................................................................................................................................23

L-3 Zone.......................................................................................................................................35

R-4 Zone................................................................................................................................................35

L-4 Zone................................................................................................................................................35

R-5 Zone................................................................................................................................................52

L-5 Zone................................................................................................................................................52

R-6 Zone................................................................................................................................................52

B-Groove ..............................................................................................................................................65

Mahogany Zone ..................................................................................................................................65

A-Groove ..............................................................................................................................................73

The Interval above A-Groove............................................................................................................73

Discussion.....................................................................................................................................................83

References Cited..........................................................................................................................................83

Figures

1. Generalized geologic map of the Uinta and Piceance Basins, northeastern Utah 

and northwestern Colorado, showing Upper Cretaceous and lower Tertiary 

stratigraphic units.........................................................................................................................2

2. Map showing extent of Uinta and Piceance Basins and Greater Green River 

Basin and approximate extent of oil shale in the Eocene Green River Formation ............3

3. Cross section showing members of the Eocene Green River Formation, 

 stages in the evolution of Lake Uinta, correlation of rich (R) and lean (L) oil 

shale zones of Cashion and Donnell (1972), and oil-yield histograms .................................5

4. Paleogeographic map of the Uinta and Piceance Basins showing uplifts, 

depositional environments, and types of sediments being deposited during the 

period when vast amounts of halite and nahcolite (sodium bicarbonate) were 

being deposited along with rich oil shale in the north-central part of the 

Piceance Basin .............................................................................................................................6

5. Isopach map of R-0 zone in Uinta and Piceance Basins using Radial Basis 

Function method for contouring...............................................................................................10
iv

6–8. Isoresource maps of:

 6. R-0 zone in Uinta and Piceance Basins showing oil yield in gallons per ton............11

 7. R-0 zone in Uinta and Piceance Basins showing oil yield in weight percent ...........12

 8. R-0 zone in the Uinta and Piceance Basins showing oil yield in barrels per acre...13

9. Isopach map of L-0 zone in Uinta and Piceance Basins using the Radial Basis 

Function method for contouring...............................................................................................14

10–12. Isoresource maps of:

 10. L-0 zone in Uinta and Piceance Basins showing oil yield in gallons per ton ............15

 11. L-0 zone in Uinta and Piceance Basins showing oil yield in weight percent............16

 12. L-0 zone in Uinta and Piceance Basins showing oil yield in barrels per acre ..........17

13. Isopach map of R-1 zone in the Uinta and Piceance Basins using the Radial 

Basis Function method for contouring...................................................................................18

14–16. Isoresource maps of:

 14. R-1 zone in the Uinta and Piceance Basins showing oil yield in gallons per ton.....19

 15. R-1 zone in Uinta and Piceance Basins showing oil yield in weight percent ...........20

 16. R-1 zone in the Uinta and Piceance Basins showing oil yield in barrels per acre...21

17. Isopach map of L-1 zone in Uinta and Piceance Basins using the Radial Basis 

Function method of contouring ................................................................................................22

18–20. Isoresource maps of:

 18. L-1 zone in Uinta and Piceance Basins showing oil yield in gallons per ton ............24

 19. L-1 zone in Uinta and Piceance Basins showing oil yield in weight percent............25

 20. L-1 zone in Uinta and Piceance Basins showing oil yield in barrels per acre ..........26

21. Isopach map of R-2 zone in Uinta and Piceance Basins using the Radial Basis 

Function method of contouring ................................................................................................27

22–24. Isoresource maps of:

 22. R-2 zone in Uinta and Piceance Basins showing oil yield in gallons per ton............28

 23. R-2 zone in the Uinta and Piceance Basins showing oil yield in weight percent.....29

 24. R-2 zone in Uinta and Piceance Basins showing oil yield in barrels per acre..........30

25. Isopach map of L-2 zone in Uinta and Piceance Basins using the Radial Basis 

Function method of contouring ................................................................................................31

26–28. Isoresource maps of:

 26. L-2 zone in the Uinta and Piceance Basins showing oil yield in gallons per ton......32

 27. L-2 zone in Uinta and Piceance Basins showing oil yield in weight percent............33

 28. L-2 zone in Uinta and Piceance Basins showing oil yield in barrels per acre ..........34

29. Isopach map of R-3 zone in Uinta and Piceance Basins using the Radial Basis 

Function method of contouring ................................................................................................36

30–32. Isoresource maps of:

 30. R-3 zone in Uinta and Piceance Basins showing oil yield in gallons per ton............37

 31. R-3 zone in Uinta and Piceance Basins showing oil yield in weight percent ...........38

 32. R-3 zone in Uinta and Piceance Basins showing oil yield in barrels per acre..........39

33. Isopach map of L-3 zone in Uinta and Piceance Basins using the Radial Basis 

Function method of contouring ................................................................................................40

34–36. Isoresource maps of:

 34. L-3 zone in Uinta and Piceance Basins showing oil yield in gallons per ton ............41

 35. L-3 zone in Uinta and Piceance Basins showing oil yield in weight percent............42

 36. L-3 zone in Uinta and Piceance Basins showing oil yield in barrels per acre ..........43
v

37. Isopach map of R-4 zone in Uinta and Piceance Basins using the Radial Basis 

Function method of contouring ................................................................................................44

38–40. Isoresource maps of:

 38. R-4 zone in Uinta and Piceance Basins showing oil yield in gallons per ton............45

 39. R-4 zone in Uinta and Piceance Basins showing oil yield in weight percent ...........46

 40. R-4 zone in Uinta and Piceance Basins showing oil yield in barrels per acre..........47

41. Isopach map of L-4 zone in Uinta and Piceance Basins using the Radial Basis 

Function method of contouring ................................................................................................48

42–44. Isoresource maps of:

 42. L-4 zone in Uinta and Piceance Basins showing oil yield in gallons per ton ............49

 43. L-4 zone in Uinta and Piceance Basins showing oil yield in weight percent............50

 44. L-4 zone in Uinta and Piceance Basins showing oil yield in barrels per acre ..........51

45. Isopach map of R-5 zone in Uinta and Piceance Basins using the Radial Basis 

Function method of contouring ................................................................................................53

46–48. Isoresource maps of:

 46. R-5 zone in Uinta and Piceance Basins showing oil yield in gallons per ton............54

 47. R-5 zone in Uinta and Piceance Basins showing oil yield in weight percent ...........55

 48. R-5 zone in Uinta and Piceance Basins showing oil yield in barrels per acre..........56

49. Isopach map of L-5 zone in Uinta and Piceance Basins using the Radial Basis 

Function method of contouring ................................................................................................57

50–52. Isoresource maps of:

 50. L-5 zone in Uinta and Piceance Basins showing oil yield in gallons per ton ............58

 51. L-5 zone in Uinta and Piceance Basins showing oil yield in weight percent............59

 52. L-5 zone in Uinta and Piceance Basins showing oil yield in barrels per acre ..........60

53. Isopach map of R-6 zone in Uinta and Piceance Basins using the Radial Basis 

Function method of contouring ................................................................................................61

54–56. Isoresource maps of:

 54. R-6 zone in Uinta and Piceance Basins showing oil yield in gallons per ton............62

 55. R-6 zone in Uinta and Piceance Basins showing oil yield in weight percent ...........63

 56. R-6 zone in Uinta and Piceance Basins showing oil yield in barrels per acre..........64

57. Isopach map of B-groove in Uinta and Piceance Basins ....................................................66

58–60. Isoresource maps of:

 58. B-groove in Uinta and Piceance Basins showing oil yield in gallons per ton...........67

 59. B-groove in Uinta and Piceance Basins showing oil yield in weight percent..........68

 60. B-groove in Uinta and Piceance Basins showing oil yield in barrels per acre ........69

61. Isopach map of Mahogany oil shale zone in Uinta and Piceance Basins ........................70

62–64. Isoresource maps of:

 62. Mahogany oil shale zone in Uinta and Piceance Basins showing oil yield in 

gallons per ton .....................................................................................................................71

 63. Mahogany oil shale zone in Uinta and Piceance Basins showing oil yield in 

weight percent.....................................................................................................................72

 64. Mahogany oil shale zone in Uinta and Piceance Basins showing oil yield 

in barrels per acre...............................................................................................................74

65. Isopach map of A-groove in Uinta and Piceance Basins ....................................................75
vi

66–68. Isoresource maps of:

 66. A-groove in Uinta and Piceance Basins showing oil yield in gallons per ton...........76

 67. A-groove in the Uinta and Piceance Basins showing oil yield in weight percent ...77

 68. A-groove in Uinta and Piceance Basins showing oil yield in barrels per acre ........78

69. Isopach map of bed 44 to A-groove in Uinta and Piceance Basins...................................79

70–72. Isoresource maps of:

 70. Bed 44 to A-groove in Uinta and Piceance Basins showing oil yield in gallons 

per ton ...................................................................................................................................80

 71. Bed 44 to A-groove in Uinta and Piceance Basins showing oil yield in weight 

percent ..................................................................................................................................81

 72. Bed 44 to A-groove in Uinta and Piceance Basins showing oil yield in barrels 

per acre.................................................................................................................................82

Plate

1. Stratigraphic cross section showing correlation of Cretaceous and lower Tertiary 

rocks, Uinta and Piceance Basins, Utah and Colorado
Abstract

The in-place oil shale resources in the Eocene Green 

River Formation of the Piceance Basin of western Colorado 

and the Uinta Basin of western Colorado and eastern Utah are 

estimated at 1.53 trillion barrels and 1.32 trillion barrels, respectively. The oil shale strata were deposited in a single large 

saline lake, Lake Uinta, that covered both basins and the intervening Douglas Creek arch, an area of comparatively low rates 

of subsidence throughout the history of Lake Uinta. Although 

the Green River Formation is largely eroded for about a 

20-mile area along the crest of the arch, the oil shale interval 

is similar in both basins, and 17 out of 18 of the assessed oil 

shale zones are common to both basins. Assessment maps for 

these 17 zones are combined so that the overall distribution of 

oil shale over the entire extent of Lake Uinta can be studied. 

The combined maps show that throughout most of the history of Lake Uinta, the richest oil shale was deposited in the 

depocenter in the north-central part of the Piceance Basin and 

in the northeast corner of the Uinta Basin where it is closest to the Piceance Basin, which is the only area of the Uinta 

Basin where all of the rich and lean oil shale zones, originally 

defined in the Piceance Basin, can be identified. Both the oil 

shale and saline mineral depocenter in the Piceance Basin and 

the richest oil shale area in the Uinta Basin were in areas with 

comparatively low rates of subsidence during Lake Uinta time, 

but both areas had low rates of clastic influx. Limiting clastic 

influx rather than maximizing subsidence appears to have been 

the most important factor in producing rich oil shale.

Introduction

The in-place oil shale resources in the Eocene Green 

River Formation of the Piceance Basin of western Colorado 

and the Uinta Basin of western Colorado and eastern Utah 

are estimated at 1.53 trillion barrels and 1.32 trillion barrels, 

respectively (Johnson, Mercier, Brownfield, and others, 2010; 

Johnson, Mercier, Brownfield, and Self, 2010). The oil shale 

strata were deposited in a single large saline lake, Lake Uinta, 

that covered both basins and the intervening Douglas Creek 

arch (figs. 1 and 2). Although the Green River Formation is 

largely eroded for about a 20-mile area along the crest of the 

arch, the oil shale interval is similar in both basins, and 17 of 

the 18 assessed oil shale zones are common to both basins. 

The Greater Green River Basin of Wyoming, Utah, and Colorado also contains significant oil shale resources in the Green 

River Formation, recently estimated at 1.44 trillion barrels 

of oil in place (Johnson and others, 2011); however, these 

oil shale resources were deposited in a separate Eocene lake, 

Lake Gosiute, that underwent a different depositional history 

from that of Lake Uinta. There has been little success thus far 

correlating the oil shale deposits of Lake Gosiute to those of 

Lake Uinta; therefore, the oil shale deposits of Lake Gosiute 

are excluded from this report. 

The oil shale interval in the Uinta and Piceance Basins 

is divided into 18 rich and lean zones (fig. 3), 17 of which are 

recognized in both basins, and one zone, bed 76, is unique 

to the Uinta Basin. Four maps are presented here for each 

assessed zone: (1) isopach, (2) variations in gallons per ton 

(GPT), (3) variations in barrels per acre (BPA) oil yield, and 

(4) total in-place oil in each 6-mi by 6-mi township. Gallons 

per ton maps depict variations in the richness of oil shale 

deposited in a particular oil shale zone, whereas BPA maps 

depict variations in the total amount of oil. In this report, 

the individual assessment results for the Uinta and Piceance 

Basins are combined into a single set of maps for the 17 oil 

shale zones common to both basins. The maps are identical to 

those published by Johnson, Mercier, Brownfield, and others 

(2010) and Johnson, Mercier, Brownfield, and Self (2010), 

except the contoured intervals are changed so that both basins 

use the same intervals for each map. Some detail on a few of 

the Uinta Basin maps originally published by Johnson, Mercier, Brownfield, and Self (2010) is lost due to the new contour 

intervals. Combined maps depicting total oil in each township 

were considered of limited usefulness and are not presented 

here.

Maps showing variations in weight-percent oil for each 

zone are presented for the first time. This step was taken 

because weight-percent oil is used instead of GPT to measure 

variations in oil shale richness by most countries; thus, these 

Isopach and Isoresource Maps for Oil Shale Deposits 

in the Eocene Green River Formation for the Combined 

Uinta and Piceance Basins, Utah and Colorado

By Tracey J. Mercier and Ronald C. Johnson
Figure 1. Generalized geologic map of the Uinta and Piceance Basins, northeastern Utah and northwestern Colorado, showCretaceous and lower Tertiary stratigraphic units. 

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Oil shale bearing rocks deposited in Eocene Lake Gosiute

Oil shale bearing rocks deposited in Eocene Lake Uinta

U.S. Geological Survey Uinta-Piceance province boundary

U.S. Geological Survey Southwest Wyoming Province boundary

Line of section (see figure 3) 

EXPLANATION

River

(Greater Green River Basin)
4 Maps for Oil Shale Deposits in Uinta and Piceance Basins, Utah and Colorado

maps will make our assessments more readily understandable 

to workers worldwide. These maps were created by applying 

a hillshade function to the Esri GeoStatistical models instead 

of the Esri GRIDs to visually enhance the displayed contours 

creating the illusion that the maps are three-dimensional. 

Weight-percent oil is measured with the standard Fischer assay 

analysis used to determine the oil content of oil shale, and the 

maps were generated by substituting weight-percent oil for 

gallons per ton oil using the assessment methodology outlined 

in Mercier and others (2010).

The Fischer assay method is a standardized laboratory 

test for determining oil yield from oil shale and has been 

almost universally used to determine oil yields for Green 

River Formation oil shales (Stanfield and Frost, 1949; American Society for Testing Materials, 1984). The Fischer assay 

standard method consists of heating a crushed and screened 

(–8 mesh (2.38-mm mesh)) 100-g sample in a small aluminum 

retort to 500°C at a rate of 12°C/min and then held at that temperature for 40 min. The volatile vapors of shale oil, gas, and 

water pass through a condenser cooled with ice water (about 

5°C) and are collected in a graduated centrifuge tube. The 

oil and water are then separated by centrifuge and weighed. 

The quantities reported in the original sample are the weight 

percentages of shale oil, water, shale residue (containing 

carbon char), and “gas plus loss” (noncondensable gas yield). 

The specific gravity of the shale oil is measured and used to 

calculate the oil yield in gallons per ton (GPT). 

The Fischer assay method does not determine the total 

amount of hydrocarbons in an oil shale sample nor does it 

measure the amount or composition of the gases released 

during the heating of the sample. These gases—chiefly light 

hydrocarbons, hydrogen, and carbon dioxide—are reported as 

“gas plus loss.” 

Fischer assay does not measure the maximum amount 

of oil that an oil shale can produce; there are retorting methods that yield more oil than Fischer assay (see Dyni, 2003, p. 

195–196, for a discussion of methods to determine oil yields). 

However, the oil yields achieved by other technologies are 

typically reported as a percentage of the Fischer assay oil 

yield; thus, Fischer assay is still considered the standard by 

which other methods are compared.

Stratigraphy of the Green River 

Formation and Definition of Rich and 

Lean Zones of the Oil Shale Section

The Uinta and Piceance Basins are structural and sedimentary basins formed during the Laramide orogeny, a major 

tectonic event that affected the central Rocky Mountain region 

from Late Cretaceous through Eocene time. The Green River 

Formation in the Uinta and Piceance Basins was deposited in 

Lake Uinta, a large saline lake that formed in early Eocene 

time when two much smaller freshwater lakes, one in each 

basin, coalesced across the Douglas Creek arch to form one 

large lake during a major transgression called the Long Point 

transgression (pl. 1) (Johnson, 1985). The Douglas Creek arch 

was an area with relatively low subsidence rates throughout 

the Paleocene and Eocene, and pre-Long Point Paleocene and 

lower Eocene rocks thin and largely wedge out on both flanks 

of the arch (pl. 1). Lake Uinta sediments, in contrast, appear 

to have extended unbroken across the arch (pl. 1) (Johnson, 

1985, 1989; Johnson and Roberts, 2003, their pl. 1), although 

there is significant thinning of these sediments toward the 

crest of the arch (pl. 1) (Johnson and Finn, 1986, their fig. 12). 

Johnson (1985) hypothesized that a relatively deep-water connection existed between the Uinta Basin and Piceance Basin 

parts of the lake along the northern part of the arch adjacent 

to this rich oil shale area in the Uinta Basin (fig. 4). However, 

this remains problematic because the Green River Formation 

has been largely eroded for an east-west distance of about 20 

mi in this hypothesized connecting area (fig. 1).

The salinity of Lake Uinta increased through time (Johnson, 1985), ultimately leading to deposition of vast quantities 

of halite and the potentially valuable sodium bicarbonate mineral nahcolite (NaHCO3

) along with many other minerals such 

Figure 2. Extent of Uinta and Piceance Basins and Greater Green River Basin and approximate extent of oil shale in the Eocene Green 

River Formation. Extent of the Uinta and Piceance Basins is the same as the Uinta-Piceance Province boundary (USGS Uinta-Piceance 

Assessment Team, 2003). Extent of the Greater Green River Basin (which includes the Hoback, Great Divide, Green River, Washakie, 

and Sand Wash Basins) is the same as the Southwest Wyoming Province boundary (U.S. Geological Survey Southwestern Wyoming 

Province Assessment Team, 2005). For the extent of oil shale in the Piceance Basin, the base of the Parachute Creek Member of the 

Green River Formation as mapped by Tweto (1979) was used for all but the northwest part of the basin where the base of the lower 

member of the Green River Formation is used. For the extent of oil shale in the eastern part of the Uinta Basin, the base of the Parachute 

Creek Member as mapped by Cashion (1973) and Rowley and others (1985) was used. In the western part of the Uinta Basin, the top of 

the Mahogany oil shale bed as mapped by Witkind (1995) was used. In the northern part of the Uinta Basin, only those areas where oil 

shale is at a depth of 6,000 ft or less are shown, based on a structure contour map of the top of the Mahogany oil shale bed compiled by 

Johnson and Roberts (2003a). For the Sand Wash, Washakie, and Great Divide Basins and southeastern part of the Green River Basin, 

the base of the Tipton Shale Member of the Green River Formation as mapped by Tweto (1979) and Love and Christiansen (1985) was 

used as the extent of oil shale. For the western part of the Green River Basin, the base of the Wilkins Peak Member of the Green River 

Formation, and for the northern part of the Green River Basin, the base of the Laney Shale Member of the Green River Formation as 

mapped by Love and Christiansen (1985) was used. Location of cross section in figure 3 shown in black.
Figure 3. Cross section showing members of the Eocene Green River Formation, stages in the evolution of Lake Uinta, correlation of rich (R) azones of Cashion and Donnell (1972), and oil-yield histograms. Core hole U-53 is in the northeast corner of the Uinta Basin, core holes CO-172 asoutheastern and central parts of the Piceance Basin respectively, and CO-158 is in the central part of the Piceance Basin. Location shown on 

0 20 40 60 80 100

C0-195

Arco-Mobil-Equity,

Figure Four 31-1 

Sec. 31, T. 3 S., R. 98 W. 

500

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500

0

0 20 40 60 80 100

0 20 40 60 80 100

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Sec. 10, T. 7 S., R. 97 W.

0 20 40 60 80 100

100

0 20 40 60 80 100

0 20 40 60 80

500

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0

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Shell Oil Co.

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top A-groove

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R-6 zone

L-5 zone

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L-4 zone

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L-0 zone

R-0 zone

Stratigraphic nomenclature for oil shale zones from Donnell and Blair (1970), Cashion and Donnell (1972), Donnell (2008); stages from Johnson (1985)

Garden Gulch Member

Green River Formation

Parachute Creek Member

Oil yield (gallons per ton)

Oil yield (gallons per ton)

Oil yield (gallons per ton)

Oil yield (gallons per ton)

 U-53

Skyline Oil Co., Watson 1A

 Sec. 5, T. 11 S., R. 25 E.

Base Porcupine

tuff–top bed 44

Porcupine tuff

Top bed 76–top

Porcupine tuff

Stage 1 Stage 2 Stage 3 Stage 4 Stage 5 

1,000 1,000 1,500 1,500
Figure 4. Paleogeographic map of the Uinta and Piceance Basins showing uplifts, depositional environments, and types of sediments during the period when vast amounts of halite and nahcolite (sodium bicarbonate) were being deposited along with rich oil shale in the part of the Piceance Basin. Modified from Johnson (1985, his fig. 11). In central part of figure, isopachs show thickness from base of LoGreen River Formation to top of Mahogany oil shale zone (from Johnson and Finn,1986, their fig. 12; contour interval is 100 ft).

UTAH COLORADO

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Uinta

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3,000

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EXPLANATION

0 2

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CARBON

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GUNNISON

HINSDALE

JAC

JUAB

L

MESA

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MONTROSE

OURAY

PITKIN

RIO BLANCO

ROUTT

SAG

SAN JUAN

SAN MIGUEL

SANPETE

SEVIER

SUMMIT

UINTAH

UTAH

WASATCH

WAYNE

PIUTE

Glenwood

Springs

Craig

Montrose

Nephi Price

Provo

Vernal

Salt Lake

City

Gunnison

Salina

Grand 

Junction

SAN

RAFAEL

SWELL

Uplands with moderate relief

Uplands with high reliefVariegated mudstone, sandstone, 

and siltstone

Carbonate-rich marginal saline lacustrine

Sandy marginal lacustrineLow-grade carbonate-rich oil shaleHigh-grade carbonate-rich oil shale 

with nahcolite and halite

DOUGLAS CREEK ARCH

UINTA UPLIFT

WHITE

RIVER 

UPLIFT

UNCOMPAHGRE UPLIFT

SEVIER OROGENIC BELT

Hypothetical river
Stratigraphy of the Green River Formation and Definition of Rich and Lean Zones of the Oil Shale Section 7

as dawsonite (NaAl (OH2CO3)), eitelite (Na2CO3·MgCO3), 

and shortite (Na2Ca2 (CO3) 3) (for a summary, see Dyni, 1996). 

Saline mineral deposition was confined to the depocenter in 

the north-central part of the Piceance Basin (pl. 1) throughout much of the history of Lake Uinta and only shifted to 

the Uinta Basin late in the lake’s history after the Piceance 

depocenter had been filled with volcaniclastic sediments from 

the north (Brownfield, Johnson, and Dyni, 2010). Dyni (1996) 

believed that there was a net flow of water from the Uinta 

Basin across the Douglas Creek arch and into the Piceance 

Basin, thus confining saline mineral deposition to the Piceance 

Basin prior to infilling. 

The Green River Formation has been divided variously 

into (1) members based on lithology, (2) stages based on the 

evolution of the lake, and (3) rich and lean oil shale zones 

representing approximately time-stratigraphic intervals of 

alternating high-organic productivity and low-organic productivity (fig. 3 and pl. 1). Each of these divisions will be 

discussed briefly. 

Four of the members of the Green River Formation—

Parachute Creek, Douglas Creek, Garden Gulch, and Evacuation Creek—were originally defined by Bradley (1931) 

who recognized them in both the Uinta and Piceance Basins, 

thereby reinforcing the concept that Lake Uinta was a single, 

unbroken lake spanning the two basins and the intervening 

Douglas Creek arch throughout much of its history (pl. 1). 

The name Evacuation Creek was later abandoned (Cashion 

and Donnell, 1974) because it was determined to be lithologically and stratigraphically equivalent to the upper part of the 

Parachute Creek Member. In the oil shale section deposited 

in the offshore areas of the lake, the name Garden Gulch is 

applied to the illitic oil shale deposited early in the history of 

Lake Uinta, and the name Parachute Creek is applied to the 

dolomitic oil shales deposited later. The name Douglas Creek 

Member is applied to marginal lacustrine rocks along the east 

and south margins of the Uinta Basin and the west and south 

margins of the Piceance Basin (Bradley, 1931; Cashion, 1967). 

The name Uinta Formation is applied to a sequence of sandstones and siltstones containing abundant volcanic debris that 

interfingers with the upper part of the Green River Formation 

(Dane, 1954; Cashion and Donnell, 1974). Although Bradley 

(1931, his pl. 8) applied the name Garden Gulch Member to 

strata in the easternmost part of the Uinta Basin, subsequent 

mapping in the Uinta Basin did not use the name (for example, 

see Cashion, 1977, 1978, 1986; Pipiringos, 1978), and usage 

of Garden Gulch Member is now confined to the Piceance 

Basin.

Johnson (1985) subdivided the history of Lake Uinta 

into five roughly time-stratigraphic periods or stages with the 

change from one stage to the next corresponding to a significant change in conditions in the lake (fig. 3 and pl. 1). The 

first two stages are equivalent to the illitic oil shales of the 

Garden Gulch Member, and the last three stages are generally 

equivalent to the dolomitic oil shales of the Parachute Creek 

Member (fig. 3 and pl. 1). The beginning of stage 1 is marked 

by the initial transgression of Lake Uinta, the Long Point 

transgression, that caused two comparatively small freshwater 

lakes—one in the Piceance Basin and one in the Uinta Basin—

to form one large lake that spanned the intervening Douglas 

Creek arch (pl. 1). The illitic-rich oil shales from this stage 

that were deposited in the offshore areas of the lake generally 

average less than 15 GPT, and because of their great depth 

and low grade, they have received little economic interest. 

These shales, however, form one of the most widespread units 

recognized in both the Uinta and Piceance Basins. The unit is 

approximately equivalent to the “second lacustrine phase” in 

Bradley’s (1931) Indian Canyon section in the western part of 

the Uinta Basin. In the subsurface, stage 1 strata extend from 

the base of the Long Point Bed and its equivalent rocks to 

the top of the carbonate marker in the Uinta Basin and to the 

top of the orange marker in the Piceance Basin. Distinctive 

electric log markers representing a slight increase in carbonate content can be traced throughout much of the offshore 

lacustrine areas of both basins (Fouch, 1975; Ryder and others, 

1976; Johnson, 1985).

Average oil yields increased at the beginning of stage 2 

in the Piceance Basin from less than 15 GPT to a maximum 

of about 27 GPT with some thin beds averaging nearly 60 

GPT. This increase is more difficult to detect in the Uinta 

Basin because wedges of sandstone, siltstone, and mudstone 

are common in the interval deposited at that time (fig. 3) and 

because they are rarely cored and assayed. Stage 2 strata can 

be detected in a few of the deeper oil shale core holes in the 

eastern part of the basin (fig. 3). 

A gradual shift from illitic-rich to carbonate-rich oil 

shales occurred at the beginning of stage 3 (fig. 3), and for 

the first time nahcolite was deposited in the central part of the 

Piceance Basin to the east. As noted above, nahcolite was not 

deposited in the Uinta Basin part of Lake Uinta until much 

later. Nahcolite is disseminated in oil shale as aggregates and 

as beds (Dyni, 1974, 1981; Brownfield, Johnson, and Dyni, 

2010). Bedded nahcolite grades laterally into halite beds 

toward the middle of the saline depocenter. All oil shales 

deposited after the beginning of stage 3 are carbonate rich with 

dolomite the dominant carbonate (Robb and Smith, 1974). 

Stage 4 began with a relatively minor transgression, 

represented by an increase in oil yield at the base of the R-4 

zone (fig. 3 and pl. 1) that may have been caused by increased 

outflow from Lake Gosiute in the Greater Green River Basin 

into Lake Uinta (Johnson, 1985, 2007). The transgression at 

the start of stage 5 is represented by the base of the Mahogany 

oil shale zone (also referred to as Mahogany zone in this 

report and Mahogany ledge where exposed in outcrop) (fig. 3 

and pl. 1). The Mahogany zone (ledge) is the most widely distributed and easily recognized oil shale zone in both the Uinta 

and Piceance Basins (pl. 1). This transgression was almost 

certainly related to increased outflow from Lake Gosuite 

because volcaniclastic sediments thought to be derived from 

the Absaroka volcanic field in northwestern Wyoming reached 

the north margin of Lake Uinta in the northern part of the 

Piceance Basin shortly after maximum transgression (Surdam 

and Stanley, 1980). These volcaniclastic sediments could only 
8 Maps for Oil Shale Deposits in Uinta and Piceance Basins, Utah and Colorado

have reached Lake Uinta once Lake Gosiute was largely filled 

because prior to its infilling Lake Gosiute would have acted as 

a sediment sink. The volcaniclastic sediments gradually filled 

the Piceance Basin part of Lake Uinta, thus ending oil shale 

deposition there and shifting saline mineral deposition to the 

Uinta Basin (Johnson, 1985). A saline zone as much as 900 ft 

thick, where saline minerals have been leached, was deposited 

in the Uinta Basin after the saline depocenter in the Piceance 

Basin was filled (Dane, 1955; Brownfield, Johnson, and Dyni, 

2010).

Trudell and others (1970) correlated individual oil 

shale beds throughout the central part of the Piceance Basin. 

Cashion and Donnell (1972) recognized that the entire 

Parachute Creek and Garden Gulch Members in the Piceance 

Basin could be subdivided into a sequence of oil-rich zones 

(R-0 through R-6 zones) and oil-lean zones (L-0 through L-5 

zones) (fig. 3). The lower zones, from L-0 zone through L-1 

zone, are clay-rich and contain little carbonate; they form the 

Garden Gulch Member. All zones above L-1 zone are dolomitic and form the Parachute Creek Member. Units above R-6 

zone are (in ascending order) B-groove, which is a lean zone; 

Mahogany zone, the richest oil shale zone in the basin; and 

A-groove, another lean zone (fig. 3). On a finer scale, many 

individual rich and lean beds within each rich and lean zone 

can be traced for considerable distances as well. All of these 

oil shale zones grade into marginal lacustrine rocks toward the 

margins of the Piceance Basin, and their marginal equivalents 

are difficult to identify. Johnson and others (1988) were able 

to trace some of the rich and lean zones into their marginal 

lacustrine equivalents along the eastern margin of the Uinta 

Basin and western margin of the Piceance Basin.

Cashion and Donnell (1972) also traced R-4 and younger 

oil shale zones into the eastern part of the Uinta Basin (fig. 3), 

and Johnson (1985, 1989) subsequently traced them into the 

western part (pl. 1). The interval above A-groove is one of the 

easiest intervals to correlate in the two basins, and Donnell 

(2008) correlated many individual beds over wide areas. All 

of these oil shale beds and oil shale zones appear to closely 

represent time-stratigraphic units representing changing rates 

of organic matter production and preservation that occurred 

simultaneously throughout Lake Uinta. 

Oil shale zones below R-4 zone are difficult to trace in the 

Uinta Basin because they are leaner than in the Piceance Basin, 

and many are thin (fig. 3). Johnson (1989) traced R-0, R-1, and 

L-0 zones throughout much of the eastern two-thirds of the 

Uinta Basin, but correlations were problematic in the western 

one-third of the basin. The R-2 through L-3 zones were traced 

into a 150- to 250-ft-thick interval, but Johnson (1989) did not 

distinguish the individual zones in that interval. These individual zones are traced here in a limited area of the easternmost 

part of the Uinta Basin where the zones could be identified in 

core drill holes and traced into nearby rotary drill holes. 

The entire Green River Formation below the Mahogany 

zone becomes interbedded with clastic wedges of sandstone, 

siltstone, and mudstone toward the southern part of the Uinta 

Basin dividing the oil shale interval into thin, discrete oil shale 

intervals separated by intervals of barren rock that thicken 

toward the south (fig. 3). Many of these clastic wedges can be 

traced into the southwestern part of the Piceance Basin as well 

(fig. 3). Ultimately, these discrete oil shale intervals grade into 

marginal lacustrine and fluvial rocks toward the south margin 

of the Uinta Basin where the individual oil shale zones can no 

longer be identified. The R-0 zone, a part of stage 1 of Lake 

Uinta discussed earlier (fig. 3), can be identified much farther 

to the south than any other oil shale zone below the Mahogany 

zone. The Mahogany zone becomes split by clastic wedges 

toward the south margin of the basin with only the Mahogany 

oil shale bed (also referred to as Mahogany bed in this report), 

the richest bed in the zone, still present there. 

Detailed Description and Assessment 

Results of Oil Shale Zones

R-0 Zone

The R-0 and L-0 zones compose the first stage of Lake 

Uinta as defined by Johnson (1985) (pl. 1 and fig. 3). The 

R-0 oil shale zone is the first oil shale zone deposited after 

the Long Point transgression when two much smaller freshwater lakes in the Piceance and Uinta Basins expanded and 

connected across the Douglas Creek arch to form one large 

lake, Lake Uinta (pl. 1) (Johnson, 1985). It is one of the most 

widespread oil shale zones in both basins. A transgressive, 

mollusk-rich bed named the Long Point Bed of the Douglas 

Creek, Anvil Points, or Garden Gulch Members of the Green 

River Formation (Johnson, 1984) commonly marks the base of 

the R-0 zone in marginal areas of both basins where it overlies variegated mudstones of the fluvial Wasatch Formation 

(Johnson, 1989). The base of the R-0 zone can be identified 

throughout much of the deeper parts of the Piceance Basin as a 

distinctive resistivity “kick” on electric logs (for example, see 

Johnson, 1989). Along the northwest margin of the Piceance 

Basin, the R-0 zone overlies freshwater lacustrine rocks of 

the Cow Ridge Member of the Green River Formation, and 

in this area the base of the R-0 zone is marked by a change 

from mollusk-bearing freshwater lacustrine rocks below to 

low-grade oil shale above (Johnson, 1985; Johnson and others, 

1988). The R-0 zone grades into sandstones toward the eastern 

margin of the Piceance Basin.

The upper 30 to 75 ft of the R-0 zone is marked in the 

central part of both basins by a distinctive increase in resistivity on electric logs known informally in the Piceance Basin as 

the orange marker, named for the color of a pen used to mark 

it on geophysical logs (Chancellor and others, 1974; Ziemba, 

1974), and in the Uinta Basin it is referred to as the carbonate 

marker (Fouch, 1975; Ryder and others, 1976; Johnson, 1989). 

The increase in resistivity is caused by a slight increase in 

carbonate in the illitic strata. 
Detailed Description and Assessment Results of Oil Shale Zones 9

In the Piceance Basin, the R-0 zone is thinnest in the 

westernmost part of the basin along the Douglas Creek arch 

(fig. 2) where it is about 75 ft thick (fig. 5). It thickens and 

becomes sandy to the southeast, east, and northeast, reaching a 

maximum thickness of about 585 ft thick at Anvil Points, just 

west of Rifle, Colo. (fig. 2), in the southeast part of the basin 

where it is predominantly fluvial and consists of variegated 

mudstone and lenticular sandstone. The R-0 zone is included 

in the Anvil Points Member of the Green River Formation in 

the eastern part of the Piceance Basin where it is sandy. The 

R-0 zone generally thickens to the north and west across the 

Uinta Basin from a minimum of 89 ft in one well near the 

crest of the Douglas Creek arch to 340 ft near the west margin 

of the study area (fig. 5).

Oil yields for the R-0 zone in the Piceance Basin range 

from 10 to 20 GPT throughout a broad area of the central part 

of the basin with yields decreasing in a regular fashion toward 

the basin margins (fig. 6). Oil yields are low along the east 

margins of the basin where the zone is predominantly sandstone. In the Uinta Basin, oil yields are greatest in the northeastern part of the basin where they are as much as 9.8 GPT 

(fig. 6). Maximum oil yield in weight percent is 9.2 percent 

in the central part of the Piceance Basin decreasing to less 

than 4.0 percent around the basin margins. Maximum weightpercent oil in the Uinta Basin is 4.0 in the northeast part of the 

basin (fig. 7). Barrels of oil per acre in the central part of the 

Piceance Basin range from 150,000 to 250,000 and decrease in 

a regular fashion outward (fig. 8). Barrels of oil per acre in the 

Uinta Basin range from 27,000 to 95,000 throughout much of 

the basin; two rotary drill holes in the central part of the Uinta 

Basin indicated yields of 130,000 and 140,000 BPA (fig. 8). 

Values approach 0 BPA toward the south margin (fig. 8). 

L-0 Zone

The L-0 zone is a thin, lean zone with a thickness range 

of 13 to 35 ft throughout most of the Piceance Basin (fig. 9). 

It thickens in an irregular fashion toward the east margin of 

the basin where it grades into sandstone. In the Uinta Basin, 

the L-0 zone thickens from 30 to 43.3 ft along the west flank 

of the Douglas Creek arch to a maximum of about 120 ft in 

the western part of the assessed area (fig. 9). Oil yields for the 

L-0 zone in the Piceance Basin range from 5.0 to 14.3 GPT in 

the central part of the basin and decrease in a regular fashion 

toward the basin margins (fig. 10). In the Uinta Basin, maximum oil yields range from 3–4 GPT in the northeast corner of 

the basin (fig. 10). Weight-percent oil reaches a maximum of 

14.6 percent in limited areas in the central part of the Piceance 

Basin. Maximum values for the Uinta Basin are about 4 

weight-percent oil in the northeast part of the basin (fig. 11). In 

the Piceance Basin, maximum in-place resources range from 

7,500 to 32,000 BPA in the central part of the Piceance Basin 

and decrease outward toward the basin margins (fig. 12). Maximum in-place resources in the Uinta Basin are about 12,000 

BPA in the northeast part of that basin.

R-1 Zone

The R-1 zone consists of illite-rich oil shale similar to 

the underlying R-0 zone but is much richer. In the Piceance 

Basin, the R-1 zone ranges in thickness from about 100 to 

125 ft in the central part of the basin to more than 350 ft along 

much of the eastern, southeastern, and southwestern margins 

(fig. 13). Much of the thickening toward the southwest is 

due to the presence of discrete, southwestward-thickening, 

kerogen-poor, mudstones and sandstones wedging into the 

oil shale interval (fig. 3) (Johnson, 1985, 1989; Johnson and 

others, 1988; Pitman and others, 1989). The wedges appear 

to be predominantly lacustrine consisting of nonlaminated to 

laminated carbonate-rich mudstone in the center of the basin 

grading to the southwest into sandstone and mudstone that is, 

in part, highly contorted and then grading into carbonate-rich 

mudstone and ripple-laminated sandstone with stromatolitic, 

ostracodal, and oolitic limestone (Johnson, 1985; Johnson and 

others, 1988). These wedges can be traced into the Uinta Basin 

where they thicken and coalesce toward the south margin 

of the basin replacing much of the oil shale in the R-1 zone, 

ultimately grading into fluvial rocks of the Renegade Tongue 

of the Wasatch Formation (Cashion, 1967). In the Uinta Basin, 

the R-1 interval thickens from about 400 ft on the west flank 

of the Douglas Creek arch to 910 ft in the eastern part of the 

assessed area (fig. 13). 

In the Piceance Basin, estimated oil yield for the R-1 

zone ranges from about 20 to 29 GPT in the central part of the 

basin with oil yields decreasing markedly toward the margins 

of the basin (fig. 14). In the limited area in the Uinta Basin 

where the R-1 zone was assessed, oil yield ranges from a 

maximum of 4.3 GPT in the northeast corner of the basin to 

a minimum 1.9 GPT in the northwest corner of the assessed 

area (fig. 14). Weight-percent oil reaches a maximum of 11.8 

percent in the central part of the Piceance Basin (fig. 15). 

Maximum weight-percent oil for the R-1 zone in the Uinta 

Basin is about 4 percent in the northeast part of that basin (fig. 

15). In the Piceance Basin, estimated in-place oil ranges from 

300,000 to 435,000 BPA through a broad crescent-shaped depocenter (fig. 16) that is somewhat south of the depocenter for 

the underlying R-0 and L-0 zones. Oil yields are lower in this 

depocenter than farther to the north, but this is due largely to 

the presence of clastic wedges into the R-1 interval discussed 

earlier. In the Uinta Basin, estimated BPA ranges from 87,000 

to 160,000 in the limited area that was assessed (fig. 16). 

L-1 Zone

The L-1 zone is lithologically similar to the clastic wedges 

that split the underlying R-1 zone and is essentially the highest 

of these clastic wedges. In the Piceance Basin, it generally 

thickens toward the south and west from 60 to 270 ft, and in the 

Uinta Basin, in the limited area where the L-1 zone is assessed, 

it generally thickens toward the south and west from 60 to 270 

ft (fig. 17). Maximum oil yields in the Piceance Basin are from 
Figure 5. Isopach map of R-0 zone in Uinta and Piceance Basins using Radial Basis Function method for contouring. Contour interval in 

RIO BLANCO

GARFIELD

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EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-0 zone—Thickness in feet

≤100101 to 150151 to 200201 to 250251 to 300301 to 350351 to 400401 to 450451 to 500501 to 550551 to 600

MAP LO

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Figure 6. Isoresource map of R-0 zone in Uinta and Piceance Basins showing oil yield in gallons per ton. 

RIO BLANCO

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EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-0 zone—Average oil yield in  gallons per ton

≤22.1 to 44.1 to 66.1 to 88.1 to 1010.1 to 1212.1 to 1414.1 to 16
Figure 7. Isoresource map of R-0 zone in Uinta and Piceance Basins showing oil yield in weight percent.

RIO BLANCO

GARFIELD

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EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-0 zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 8>8

0 10 20 MILES 5

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Figure 8. Isoresource map of R-0 zone in the Uinta and Piceance Basins showing oil yield in barrels per acre. The Radial Basis Function used for contouring.

RIO BLANCO

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EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-0 zone—Barrels per acre

≤25,00025,001 to 50,00050,001 to 75,00075,001 to 100,000100,001 to 125,000125,001 to 150,000150,001 to 175,000175,001 to 200,000200,001 to 225,000225,001 to 250,000

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

15

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Figure 9. Isopach map of L-0 zone in Uinta and Piceance Basins using the Radial Basis Function method for contouring. Contour interval in 

RIO BLANCO

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WASATCH

DUCHESNE

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Grand Junction

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111° 110° 109° 

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EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-0 zone—Thickness in feet

≤1011 to 2021 to 3031 to 4041 to 5051 to 6061 to 7071 to 8081 to 9091 to 100101 to 110

111 to 120121 to 130
Figure l0. Isoresource map of L-0 zone in Uinta and Piceance Basins showing oil yield in gallons per ton.

RIO BLANCO

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CARBON

WASATCH

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D

MONTROS

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Price

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Grand Junction

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Moab

111° 110° 109° 

40°39°

MAP LOC

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EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-0 zone—Average oil yield in  gallons per ton

≤22.1 to 44.1 to 66.1 to 88.1 to 1010.1 to 1212.1 to 1414.1 to 16
Figure 11. Isoresource map of L-0 zone in Uinta and Piceance Basins showing oil yield in weight percent. 

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MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

£¤6

£¤40

¤£50

¤£191

£¤40 £¤87

£¤6

£¤191

Grand Junction

Fruita

Del

Battlem

Vernal

Roosevelt

Price

Moab

Grand Junction

Fruita

Del

Battlem

Vernal

Roosevelt

Price

Moab

111° 110° 109° 

40°39°

MAP LO

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-0 zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 88.1 to 1010.1 to 12>12
Figure 12. Isoresource map of L-0 zone in Uinta and Piceance Basins showing oil yield in barrels per acre. The Radial Basis Function mefor contouring.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

¤£6

£¤40

£¤50

£¤191

¤£40 ¤£87

£¤6

¤£191

Grand Junction

Fruita

Battleme

Vernal

Roosevelt

Price

Moab

Grand Junction

Fruita

Delt

Battleme

Vernal

Roosevelt

Price

Moab

111° 110° 109° 

40°39°

MAP LOC

UTAH CO

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-0 zone—Barrels per acre

≤5,0005,001 to 10,00010,001 to 15,00015,001 to 20,00020,001 to 25,00025,001 to 30,00030,001 to 35,000
Figure 13. Isopach map of R-1 zone in the Uinta and Piceance Basins using the Radial Basis Function method for contouring. Contour in

is variable.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

£¤40

£¤50

£¤191

¤£40 £¤87

£¤6

¤£191

Grand Junction

Fruita

De

Battlem

Vernal

Roosevelt

Price

Moab

Grand Junction

Fruita

De

Battlem

Vernal

Roosevelt

Price

Moab

111° 110° 109° 

40°39°

MAP LO

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-1 zone—Thickness in feet

≤100101 to 200201 to 300301 to 400401 to 500501 to 600601 to 700701 to 800801 to 900901 to 1,000
Figure 14. Isoresource map of R-1 zone in the Uinta and Piceance Basins showing oil yield in gallons per ton. 

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

¤£6

¤£40

¤£50

£¤191

£¤40 £¤87

£¤6

£¤191

Grand Junction

Fruita

De

Vernal

Roosevelt

Price

Moab

Grand Junction

Fruita

De

Battlem

attlem

Vernal

Roosevelt

Price

Moab

111° 110° 109° 

40°39°

MAP L

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-1 zone—Average oil yield  in gallons per ton

≤33.1 to 66.1 to 99.1 to 1212.1 to 1515.1 to 1818.1 to 2121.1 to 2424.1 to 2727.1 to 30
Figure 15. Isoresource map of R-1 zone in Uinta and Piceance Basins showing oil yield in weight percent. 

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

¤£6

¤£40

¤£50

¤£191

£¤40 £¤87

¤£6

£¤191

Grand Junction

Fruita

Del

Battlem

Vernal

Roosevelt

Price

Moab

Grand Junction

Fruita

Del

Battlem

Vernal

Roosevelt

Price

Moab

111° 110° 109° 

40°39°

MAP LO

UTAH C

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-1 zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 88.1 to 10>10

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

15

15
Figure 16. Isoresource map of R-1 zone in the Uinta and Piceance Basins showing oil yield in barrels per acre. 

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

¤£40

£¤50

¤£191

£¤40 £¤87

£¤6

£¤191

Grand Junction

Fruita

Del

Battlem

Vernal

Roosevelt

Price

Moab

Grand Junction

Fruita

Del

Battlem

Vernal

Roosevelt

Price

Moab

111° 110° 109° 

40°39°

MAP LOC

UTAH CO

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-1 zone—Barrels per acre

≤50,00050,001 to 100,000100,001 to 150,000150,001 to 200,000200,001 to 250,000250,001 to 300,000300,001 to 350,000350,001 to 400,000400,001 to 450,000
Figure 17. Isopach map of L-1 zone in Uinta and Piceance Basins using the Radial Basis Function method of contouring.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

£¤6

£¤40

¤£50

£¤191

¤£40 £¤87

£¤6

¤£191

111° 110° 109° 

40°39°

Grand Junction

Fruita

Del

Vernal

Roosevelt

Price

Moab

Grand Junction

Fruita

Del

Vernal

Roosevelt

Price

Moab

MAP LOC

UTAH CO

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-1 zone—Thickness in feet

≤2526 to 5051 to 7576 to 100101 to 125126 to 150151 to 175176 to 200201 to 225226 to 250
Detailed Description and Assessment Results of Oil Shale Zones 23

about 5 to 25 GPT in the north-central part of the basin 

(fig. 18). In the limited area of the Uinta Basin where the L-1 

zone is assessed, estimated oil yields range from 0.8 to 2.5 

GPT (fig. 18). Maximum weight-percent oil for the L-1 zone 

in the Piceance Basin is 12.2 percent, whereas weight-percent 

oil in the Uinta Basin is less than 4 (fig. 19). The BPA map (fig. 

20) shows a depocenter with from 20,000 to 80,000 BPA in 

the south-central part of the Piceance Basin, the same area as 

the depocenter during the previous R-1 zone, but several much 

smaller areas with high in-place oil are scattered throughout the 

northern part of the basin. Estimated BPA in the Uinta Basin 

range from 7,000 to 39,000 (fig. 20), but control is sparse in the 

limited area assessed. 

R-2 through L-3 Zones

The R-2, L-2, R-3, and L-3 zones compose the third stage 

of Lake Uinta as defined by Johnson (1985). In the Piceance 

Basin, the R-2 zone marks a transition from illitic-rich oil 

shales to carbonate-rich oil shales. On electric logs, this shift 

is represented by a distinctive increase in resistivity informally 

known as the blue marker (Ziemba, 1974). The first occurrence of disseminated nahcolite, a sodium bicarbonate mineral 

(NaHCO3

), is in the upper part of the L-2 zone in the northcentral part of the Piceance Basin (Dyni, 1974, 1981). Dawsonite, a hydrated aluminum carbonate mineral (NaAl(OH)2

CO3), 

appears for the first time in the lower part of the R-2 zone, 

about 65–75 ft below the first occurrence of nahcolite in that 

same area (Dyni, 1981) and increases in abundance upward. 

Illite correspondingly decreases in abundance upward though 

the R-2 zone (Dyni, 1974, 1981; Robb and Smith, 1974). 

Dyni (1981) suggested that the alkaline lake waters destroyed 

much of the fine-grained detritus in the sediments, including 

the clays, replacing them with a suite of authigenic minerals 

including feldspars, quartz, and dawsonite. 

The R-2 through L-3 interval is poorly correlated and 

poorly understood in the Uinta Basin. Johnson and others 

(1988) traced these zones from the central part of the Piceance 

Basin into a comparatively thin interval of stromatolites, sandstones, and mudstones ranging from about 110 to 150 ft thick 

in outcrops along the east margin of the Uinta Basin but could 

not distinguish them individually. Johnson (1989) then traced 

this combined interval from outcrops at the east margin of the 

Uinta Basin westward along the trough of the basin where it 

gradually thickens to a maximum of about 400 ft in the western 

part of the basin. The interval consists mainly of mudstone with 

varying amounts of carbonate. Dyni (2008) published a cross 

section along the trough of the Uinta Basin that included some 

of the same wells used by Johnson (1989) but included Fischer 

assay results from cuttings. The R-2 through L-3 interval along 

Dyni’s line of section contains little kerogen. In their recent 

assessment of oil shale in the Uinta Basin, Johnson, Mercier, 

Brownfield, and Self (2010) could identify only the individual 

R-2, L-2, R-3, and L-3 zones in a limited area of the northeastern part of the basin. 

R-2 Zone

The R-2 zone in the Piceance Basin is thickest along an 

east- to northeast-trending belt across the south-central and 

northeastern parts of the basin where it ranges from about 90 

to 155 ft thick (fig. 21). The interval thins generally toward the 

southwest in the direction that the previous R-1 and L-1 zones 

had thickened markedly. Along the south and west margins 

of the Piceance Basin, the R-2 zone cannot be separated from 

the overlying L-2, R-3, and L-3 zones, and all four zones are 

generally lumped together (Johnson and others, 1988), have 

a combined thickness of about 75 to 155 ft, and consist of marlstone oil shale beds and stromatolites. In the Uinta Basin, the 

R-2 zone ranges from 95 to 150 ft thick in the limited area that 

was assessed (fig. 21). 

The oil shale depocenter during deposition of the R-2 zone 

is in the north-central part of the Piceance Basin and north of 

the area where the zone is thickest (figs. 22 to 24). Maximum 

oil yield there reaches 45 GPT and decreases in a radial pattern 

outward. Oil yields reach near zero along the southeastern and 

southwestern margins and about 10–15 GPT along the northern 

and northwestern margins (fig. 22). Weight-percent oil reaches 

a maximum of 17 percent in this depocenter (fig. 23). Estimated in-place oil reaches a maximum of 240,000 BPA in this 

depocenter and decreases outward (fig. 24). In the Uinta Basin, 

estimated oil yield ranges from 1.1 to 5.0 GPT (fig. 21) or a 

maximum of about 4.0 weight percent (fig. 23), and estimated 

oil in place ranges from about 15,000 to 5,000 BPA (fig. 24). 

L-2 Zone

In the Piceance Basin, thickness and oil shale richness 

patterns for the L-2 zone are similar to those for the R-2 zone 

with the area of maximum thickness rimming the south end 

of the oil shale depocenter (fig. 25). The L-2 zone reaches a 

maximum thickness of 115 ft in this area. Maximum oil yield 

for the L-2 zone is about 34 GPT in the oil shale depocenter, 

with oil yields decreasing in a radial pattern outward (fig. 26). 

Maximum weight-percent oil reaches 12.7 in the depocenter 

(fig. 27). Maximum BPA in the L-2 zone is 112,000 (fig. 28). 

In the limited area of the Uinta Basin where the L-2 zone is 

recognized, the L-2 zone ranges in thickness from 10 to 50 ft 

(fig. 25), with estimated oil yield ranges from 0.5 to 8.9 GPT 

(fig. 26), 2 to 4 weight-percent oil (fig. 27), and estimated inplace oil ranges from 1,000 to 22,000 BPA (fig. 28).

R-3 Zone

The saline depocenter in the north-central part of the 

Piceance Basin became well established during deposition of 

the R-3 zone, and several thick beds consisting of predominantly nahcolite are dispersed throughout the zone in this area 

(Dyni, 1974, 1981; Brownfield, Mercier, and others, 2010). 

Unlike the underlying R-2 and L-2 zones in which maximum 

thicknesses were south and east of the oil shale and saline 
Figure 18. Isoresource map of L-1 zone in Uinta and Piceance Basins showing oil yield in gallons per ton. 

RIO BLANCO

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MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

£¤40

¤£50

¤£191

£¤40 £¤87

£¤6

¤£191

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

MAP LO

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-1 zone—Average oil yield  in gallons per ton

≤33.1 to 66.1 to 99.1 to 1212.1 to 1515.1 to 1818.1 to 2121.1 to 2424.1 to 27
Figure 19. Isoresource map of L-1 zone in Uinta and Piceance Basins showing oil yield in weight percent. 

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

¤£6

£¤40

¤£50

£¤191

£¤40 £¤87

¤£6

¤£191

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

MAP L

UTAH 

UTAH COLORADO

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-1 zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 88.1 to 10>10
Figure 20. Isoresource map of L-1 zone in Uinta and Piceance Basins showing oil yield in barrels per acre. 

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

£¤40

£¤50

£¤191

£¤40 £¤87

¤£6

¤£191

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

MAP LO

UTAH C

UTAH COLORADO

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-1 zone—Barrels per acre

≤10,00010,001 to 20,00020,001 to 30,00030,001 to 40,00040,001 to 50,00050,001 to 60,00060,001 to 70,00070,001 to 80,000
Figure 21. Isopach map of R-2 zone in Uinta and Piceance Basins using the Radial Basis Function method of contouring.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

¤£6

£¤40

£¤50

£¤191

¤£40 ¤£87

£¤6

¤£191

Moab Moab

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

MAP LO

UTAH C

UTAH COLORADO

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-2 zone—Thickness in feet

≤2526 to 5051 to 7576 to 100101 to 125126 to 150151 to 175
Figure 22. Isoresource map of R-2 zone in Uinta and Piceance Basins showing oil yield in gallons per ton.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

¤£6

¤£40

£¤50

¤£191

¤£40 ¤£87

¤£6

¤£191

MAP L

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battle

attle

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-2 zone—Average oil yield  in gallons per ton

≤55.1 to 1010.1 to 1515.1 to 2020.1 to 2525.1 to 3030.1 to 3535.1 to 4040.1 to 4545.1 to 50

15
Figure 23. Isoresource map of R-2 zone in the Uinta and Piceance Basins showing oil yield in weight percent.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

£¤40

¤£50

¤£191

¤£40 £¤87

£¤6

£¤191

MAP LO

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-2 zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 88.1 to 1010.1 to 1212.1 to 14>14
Figure 24. Isoresource map of R-2 zone in Uinta and Piceance Basins showing oil yield in barrels per acre.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

¤£6

£¤40

¤£50

£¤191

¤£40 £¤87

£¤6

£¤191

MAP L

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battle

attle

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-2 zone—Barrels per acre

≤25,00025,001 to 50,00050,001 to 75,00075,001 to 100,000100,001 to 125,000125,001 to 150,000150,001 to 175,000175,001 to 200,000200,001 to 225,000225,001 to 250,000
Figure 25. Isopach map of L-2 zone in Uinta and Piceance Basins using the Radial Basis Function method of contouring.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

£¤6

£¤40

£¤50

£¤191

¤£40 £¤87

£¤6

¤£191

MAP LOC

UTAH CO

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battleme

attleme

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-2 zone—Thickness in feet

≤2021 to 4041 to 6061 to 8081 to 100101 to 120
Figure 26. Isoresource map of L-2 zone in the Uinta and Piceance Basins showing oil yield in gallons per ton.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

£¤6

£¤40

£¤50

£¤191

£¤40 ¤£87

£¤6

¤£191

MAP LO

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-2 zone—Average oil yield  in gallons per ton

≤55.1 to 1010.1 to 1515.1 to 2020.1 to 2525.1 to 3030.1 to 35
Figure 27. Isoresource map of L-2 zone in Uinta and Piceance Basins showing oil yield in weight percent. 

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

D

MONTROSE

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

£¤6

£¤40

¤£50

¤£191

¤£40 £¤87

£¤6

£¤191

Price Price

MAP LOCA

UTAH COL

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlemen

attlemen

Price

111° 110° 109° 1

40°39°

Grand Junction

Fruita

Delta

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Delta

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-2 zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 88.1 to 10>10
Figure 28. Isoresource map of L-2 zone in Uinta and Piceance Basins showing oil yield in barrels per acre.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

£¤6

¤£40

¤£50

¤£191

¤£40 £¤87

¤£6

¤£191

Grand Junction

MAP L

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battle

attle

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-2 zone—Barrels per acre

≤10,00010,001 to 20,00020,001 to 30,00030,001 to 40,00040,001 to 50,00050,001 to 60,00060,001 to 70,00070,001 to 80,00080,001 to 90,00090,001 to 100,000100,001 to 110,000110,001 to 120,000
Detailed Description and Assessment Results of Oil Shale Zones 35

depocenter, the R-3 zone is thickest in the depocenter itself 

where it is over 150 ft thick and thins in a radial pattern outward (fig. 29). The presence of several thick nahcolite beds in 

the R-3 zone is at least in part responsible for this thickening 

trend. The R-3 zone reaches a maximum of over 43 GPT, 16.4 

weight-percent oil, and 381,000 BPA in this depocenter (figs. 

30 to 32). In the limited area of the Uinta Basin where the R-3 

zone is recognized, the zone ranges in thickness from 10 to 40 

ft (fig. 29), with estimated oil yields ranging from 1.3 to 20.4 

GPT (fig. 30), estimated weight-percent oil ranging from less 

than 2 to nearly 8 (fig. 31), and in-place oil ranging from 8,000 

to 46,000 BPA (fig. 32). 

L-3 Zone

The L-3 zone is a comparatively thin oil shale zone in the 

Piceance Basin that represents a near cessation of nahcolite 

deposition. Interestingly, the zone is thickest along the south 

margin of the oil shale depocenter in the Piceance Basin, 

similar to the R-2 and L-2 zones. There, the L-3 zone reaches 

a maximum thickness of 68 ft (fig. 33). The oil shale depocenter during deposition of the L-3 zone occupies the same area 

in the north-central part of the basin as the previous R-3 zone 

(figs. 34 to 36). Maximum oil yields in this depocenter are 

about 35 GPT (fig. 34), maximum weight-percent oil is 13.1 

(fig. 35), and maximum in-place oil is about 94,000 BPA (fig. 

36). In the limited area of the Uinta Basin where the L-3 zone 

is recognized, the zone ranges in thickness from 7 to 20 ft (fig. 

33). Estimated oil yield in this limited area ranges from 0.6 to 

12.9 GPT (fig. 34), estimated weight-percent oil ranges from 

less than 2 to about 6 (fig. 35), and in-place oil ranges from 0 

to 15,000 BPA (fig. 36). 

R-4 Zone 

The base of the R-4 zone through the base of the Mahogany zone represents the fourth stage of Lake Uinta of Johnson 

(1985). The R-4 zone is recognized throughout most of the 

Piceance Basin and is the first oil shale zone above the R-0 

zone to be recognized throughout much of the Uinta Basin as 

well (Johnson, 1989). A comparatively minor transgression 

marks the beginning of this stage, extending oil shale deposition into areas of the lake where deposition of a marginal 

lacustrine facies previously predominated (Johnson, 1985; 

Johnson and others, 1988). In some areas along the south and 

west margins of the Piceance Basin and the east margin of 

the Uinta Basin, the transgression is marked by a shift from 

a marginal lacustrine sequence containing abundant thick 

stromatolite units to oil shale interbedded with marlstone and 

thin stromatolites. In other places the transgression is marked 

by a shift from interbedded oil shale and marlstone to predominantly oil shale (Johnson and others, 1988). At Renegade 

Canyon along the extreme southern exposure of the Green 

River Formation in the Uinta Basin, all but the uppermost part 

of the interval from the base of the R-4 zone to the base of 

the Mahogany zone grades into fluvial rocks of the Renegade 

Tongue of the Wasatch Formation (Cashion, 1967, his pl. 3, 

Renegade Canyon measured section). 

The presence of stromatolites both above and below 

the base of the R-4 zone in some sections indicates that 

the increase in average water depth after this transgression 

may not have been great. It should be noted that water level 

probably fluctuated constantly throughout the history of this 

closed saline lake, but average water levels appear to have 

been somewhat higher beginning with the deposition of the 

R-4 zone than previously. Nahcolite is mostly absent from 

the lower part of the R-4 zone in the saline depocenter in the 

north-central part of the Piceance Basin, and only a few comparatively thin, persistent beds high in nahcolite content are 

in the R-4 zone (Dyni, 1974, 1981) suggesting that lake water 

was less saline after the transgression than before.

In the Piceance Basin, the R-4 zone is thickest along a 

southeast-trending belt extending from the oil shale depocenter in the north-central part to the east margin of the basin, 

reaching a maximum thickness of about 165 ft along this trend 

(fig. 37). In the Uinta Basin, the R-4 zone ranges from about 

35 to 50 ft thick in the northeast part, adjacent to the crest of 

the Douglas Creek arch, and thickens to the north and west to 

a maximum of about 200 ft (fig. 37). In the Piceance Basin, oil 

yield reaches a maximum of about 43 GPT and 16.3 weight 

percent in the saline depocenter (figs. 38 and 39). The area 

containing at least 20 GPT extends farther toward the margins 

of the basin during R-4 deposition than any of the previous 

oil shale zones except the R-1 zone. Maximum BPA is about 

424,000 in the middle part of the saline and oil shale depocenter in the north-central part of the basin (fig. 40). In the Uinta 

Basin, estimated oil yields are as much as 24 GPT (fig. 38) or 

10 weight percent (fig. 39), and in-place oil ranges from about 

50,000 to 104,000 BPA (fig. 40). 

L-4 Zone

In the Piceance Basin, the L-4 zone is thickest in about 

the same southeast-trending belt as the underlying R-4 zone, 

reaching a maximum thickness of 184 ft in the saline depocenter (fig. 41). The L-4 zone contains large amounts of 

nahcolite in the saline depocenter, and several persistent 

nahcolite beds have been traced throughout the depocenter 

(Dyni 1974, 1981). Oil yields are significantly lower overall in 

the L-4 zone than in the underlying R-4 zone with a maximum of about 34 GPT or 12.7 weight percent in the saline 

depocenter and lower values throughout the marginal areas of 

the basin (figs. 42 and 43). Maximum BPA is about 426,000 

in the saline depocenter (fig. 44). In the Uinta Basin, the L-4 

zone thickens from about 24 to 43 ft along the west flank of 

the Douglas Creek arch to a maximum of about 130 ft in the 

central part of the basin (fig. 41). Estimated oil yields are as 

much as 8.2 GPT (fig. 42) or about 4 weight percent (fig. 43), 

and estimated in-place oil varies from about 12,000 to 35,000 

BPA (fig. 44).
Figure 29. Isopach map of R-3 zone in Uinta and Piceance Basins using the Radial Basis Function method of contouring.

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0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battleme

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Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-3 zone—Thickness in feet

≤2526 to 5051 to 7576 to 100101 to 125126 to 150151 to 175
Figure 30. Isoresource map of R-3 zone in Uinta and Piceance Basins showing oil yield in gallons per ton. 

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Battleme

attleme

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Delta

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Delta

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-3 zone—Average oil yield  in gallons per ton

≤55.1 to 1010.1 to 1515.1 to 2020.1 to 2525.1 to 3030.1 to 3535.1 to 4040.1 to 45
Figure 31. Isoresource map of R-3 zone in Uinta and Piceance Basins showing oil yield in weight percent. 

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UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-3 zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 88.1 to 1010.1 to 12>12
Figure 32. Isoresource map of R-3 zone in Uinta and Piceance Basins showing oil yield in barrels per acre.

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¤£191

MAP LOC

UTAH CO

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battleme

attleme

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-3 zone—Barrels per acre

≤50,00050,001 to 100,000100,001 to 150,000150,001 to 200,000200,001 to 250,000250,001 to 300,000300,001 to 350,000350,001 to 400,000
Figure 33. Isopach map of L-3 zone in Uinta and Piceance Basins using the Radial Basis Function method of contouring.

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¤£6

¤£191

MAP L

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battle

attle

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-3 zone—Thickness in feet

≤1011 to 2021 to 3031 to 4041 to 5051 to 6061 to 7071 to 80
Figure 34. Isoresource map of L-3 zone in Uinta and Piceance Basins showing oil yield in gallons per ton. 

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MAP 

UTAH 

UTAH COLORADO

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0 10 20 KILOMETERS 5

Battle

attle

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-3 zone—Average oil yield  in gallons per ton

≤55.1 to 1010.1 to 1515.1 to 2020.1 to 2525.1 to 3030.1 to 35
Figure 35. Isoresource map of L-3 zone in Uinta and Piceance Basins showing oil yield in weight percent. 

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¤£6

£¤191

MAP LO

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-3 zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 88.1 to 10>10
Figure 36. Isoresource map of L-3 zone in Uinta and Piceance Basins showing oil yield in barrels per acre.

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¤£40 £¤87

£¤6

¤£191

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UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-3 zone—Barrels per acre

≤10,00010,001 to 20,00020,001 to 30,00030,001 to 40,00040,001 to 50,00050,001 to 60,00060,001 to 70,00070,001 to 80,00080,001 to 90,00090,001 to 100,000
Figure 37. Isopach map of R-4 zone in Uinta and Piceance Basins using the Radial Basis Function method of contouring. 

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£¤6

£¤191

MAP LOC

UTAH CO

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battleme

attleme

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-4 zone—Thickness in feet

≤50

51 to 7576 to 100101 to 125126 to 150151 to 175

176 to 200
Figure 38. Isoresource map of R-4 zone in Uinta and Piceance Basins showing oil yield in gallons per ton. 

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£¤191

¤£40 £¤87

¤£6

¤£191

Moab Moab

MAP LOC

UTAH CO

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battleme

attleme

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-4 zone—Average oil yield  in gallons per ton

≤55.1 to 1010.1 to 1515.1 to 2020.1 to 2525.1 to 3030.1 to 3535.1 to 4040.1 to 45
Figure 39. Isoresource map of R-4 zone in Uinta and Piceance Basins showing oil yield in weight percent.

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§ ̈¦70

£¤191

£¤6

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¤£50

¤£191

¤£40 £¤87

£¤6

£¤191

MAP L

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-4 zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 88.1 to 1010.1 to 1212.1 to 14>14
Figure 40. Isoresource map of R-4 zone in Uinta and Piceance Basins showing oil yield in barrels per acre. 

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£¤191

¤£40 £¤87

£¤6

£¤191

MAP LO

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-4 zone—Barrels per acre

≤50,00050,001 to 100,000100,001 to 150,000150,001 to 200,000200,001 to 250,000250,001 to 300,000300,001 to 350,000350,001 to 400,000400,001 to 450,000
Figure 41. Isopach map of L-4 zone in Uinta and Piceance Basins using the Radial Basis Function method of contouring.

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¤£191

MAP LO

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-4 zone—Thickness in feet

≤2526 to 5051 to 7576 to 100101 to 125126 to 150

176 to 200

151 to 175
Figure 42. Isoresource map of L-4 zone in Uinta and Piceance Basins showing oil yield in gallons per ton. 

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MAP 

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battl

attl

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-4 zone—Average oil yield  in gallons per ton

≤55.1 to 1010.1 to 1515.1 to 2020.1 to 2525.1 to 3030.1 to 35
Figure 43. Isoresource map of L-4 zone in Uinta and Piceance Basins showing oil yield in weight percent. 

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¤£6

¤£191

MAP L

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-4 zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 88.1 to 1010.1 to 12>12
Figure 44. Isoresource map of L-4 zone in Uinta and Piceance Basins showing oil yield in barrels per acre.

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Roosevelt Roosevelt

MAP LOC

UTAH CO

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battleme

attleme

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-4 zone—Barrels per acre

≤50,00050,001 to 100,000100,001 to 150,000150,001 to 200,000200,001 to 250,000250,001 to 300,000300,001 to 350,000350,001 to 400,000400,001 to 450,000
52 Maps for Oil Shale Deposits in Uinta and Piceance Basins, Utah and Colorado

R-5 Zone

A significant increase in oil yield marks the base of the 

R-5 zone (fig. 3). In the Piceance Basin, the basal bed of the 

R-5 zone contains abundant nahcolite in the oil shale depocenter, and thick beds of halite and nahcolite exist throughout the 

lower part of the R-5 zone starting about 15–20 ft above the 

base (Dyni 1974, 1981). Thinner beds of halite and nahcolite 

exist in the upper part of the R-5 zone, and nahcolite levels, in 

general, are comparatively high in the R-5 zone when compared to older oil shale zones. In the Piceance Basin, the R-5 

zone is thickest through a broad band that extends from the oil 

shale depocenter southeastward to near the basin margin (fig. 

45). Maximum thickness for the zone is in the oil shale and 

saline-mineral depocenter where thickness ranges from 225 to 

380 ft. In the Uinta Basin, the R-5 zone thickens from about 

58 to 120 ft along the west flank of the Douglas Creek arch 

to a maximum of about 220 ft in the western part of the Uinta 

Basin (fig. 45). 

The R-5 zone contains as much as 41.4 GPT or 15.5 

weight-percent oil in the oil shale and saline depocenter in the 

north-central part of the Piceance Basin with oil yields generally decreasing in a radial pattern outward (figs. 46 and 47). 

Maximum BPA varies from about 400,000 to 870,000 in the 

oil shale and saline depocenter (fig. 48). In the Uinta Basin, 

estimated oil yields range to as much as 16.8 GPT (fig. 46) or 

to about 10 weight percent (fig. 47), and estimated in-place oil 

ranges to as much as 155,000 BPA (fig. 48). 

L-5 Zone

In the Piceance Basin, the lower part of the L-5 zone 

contains large deposits of halite and nahcolite in two beds 

about 20 ft apart with each bed reaching a maximum thickness 

of 60–65 ft (Dyni 1974, 1981). These two beds are the highest 

preserved saline beds in the section, but there is a persistent 

collapse breccia near the top of the L-5 zone indicating that 

an additional thick saline bed was probably once present. The 

two thick nahcolite and halite beds have been leached out over 

much of their original extent and were replaced by collapse 

breccias. The isopach map for the L-5 zone in the Piceance 

Basin (fig. 49) shows complex thickening trends that are 

significantly different from underlying oil shale zones because 

the L-5 zone has been highly modified by relatively recent 

leaching of the thick nahcolite and halite beds. Throughout 

much of the Piceance Basin, the L-5 zone thickens in a fairly 

regular pattern to the east-northeast. In the depocenter, however, the L-5 zone thickens from about 80 to 100 ft where the 

two saline beds have been leached, to nearly 230 ft where they 

are still preserved. In addition, the L-5 zone thickens markedly 

toward the northern part of the basin (fig. 49). This thickening is due to an influx of clastics from the north that Johnson 

(1985, 2007) suggested was related to outflow from Lake 

Gosiute to the north. In the Uinta Basin, the L-5 zone thickens 

from about 60 to 100 ft along the west flank of the Douglas 

Creek arch to a maximum of about 230 ft in the northeast 

corner of the basin (fig. 49). 

In the Piceance Basin, estimated oil yield for the L-5 

zone ranges to more than 22 GPT or 8.1 weight percent in the 

oil shale and saline depocenter in the north-central part with 

values decreasing outward in a general radial pattern (figs. 

50 and 51). In-place oil ranges to as much as 274,000 BPA in 

the Piceance Basin depocenter with values decreasing rapidly 

toward the southwest and northeast and more slowly toward 

the southeast (fig. 52). In the Uinta Basin, estimated oil yields 

for the L-5 zone range to as much as 10.8 GPT or as much as 6 

weight percent (figs. 50 and 51) with estimated in-place oil as 

much as 88,000 BPA (fig. 52).

R-6 Zone

The R-6 zone contains no preserved nahcolite or halite 

in the Piceance Basin depocenter, but some solution cavities 

that may once have been filled with nahcolite were described 

in the upper part of the R-6 zone in outcrop near the mouth 

of Piceance Creek in the north-central part of the basin by 

Pipiringos and Johnson (1976). There are no breccia zones in 

the R-6 zone (Dyni, 1974); thus, it is doubtful that thick beds 

of halite and nahcolite, like those in the underlying L-5 zone, 

ever existed in the R-6 zone. According to Dyni (1974, p. 

119), the highest solution breccia is in the middle of his zone 

12 (the L-5 zone) and “No unleached saline beds equivalent to 

this breccia, or younger solution breccias, are known to exist 

in the Piceance Creek basin.” 

In the Piceance Basin, the R-6 zone thickens generally 

toward the east-northeast across the basin to a maximum of 

about 250 ft in the eastern part of the basin, then thins abruptly 

to 106 ft along the northeast margin (fig. 53). There is no 

thickening toward the saline depocenter in the north-central 

part of the basin as in previous oil shale zones that contain 

abundant saline minerals. There is a pronounced thickening to 

537 ft toward the north-central part of the basin, in the vicinity 

of where the underlying L-5 zone thickened, suggesting again 

a source of sediment from the north. In the Uinta Basin, the 

R-6 zone thickens from about 166 to 200 ft along the west 

flank of the Douglas Creek arch to a maximum of more than 

450 ft in the western part of the Uinta Basin (fig. 53). 

Maximum oil yields for the R-6 zone in the Piceance 

Basin range from about 21 to 33 GPT or 11.9 weight percent 

through an elongated south- to southeast-trending area that 

extends for a considerable distance to the southeast from the 

former oil shale and saline mineral depocenter (figs. 54 and 

55). This expansion of the oil shale depocenter toward the 

southeast, which was apparent but less pronounced in the 

underlying L-5 zone, is especially conspicuous on the map 

showing estimated BPA for the R-6 zone (fig. 56). The area of 

maximum in-place oil, from about 300,000 to 425,000 BPA, 

extends to the upper reaches of the Parachute Creek drainage north of the Colorado River. In the Uinta Basin, the R-6 

zone thickens from about 166 to 200 ft along the west flank 
Figure 45. Isopach map of R-5 zone in Uinta and Piceance Basins using the Radial Basis Function method of contouring. 

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EMERY

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§ ̈¦70

§ ̈¦70

£¤191

¤£6

¤£40

£¤50

£¤191

¤£40 ¤£87

£¤6

¤£191

MAP LO

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-5 zone—Thickness in feet

≤5051 to 100101 to 150151 to 200201 to 250251 to 300301 to 350351 to 400
Fgure 46. Isoresource map of R-5 zone in Uinta and Piceance Basins showing oil yield in gallons per ton. 

RIO BLANCO

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UINTAH

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CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

£¤6

¤£40

¤£50

£¤191

¤£40 £¤87

¤£6

£¤191

Roosevelt Roosevelt

MAP L

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-5 zone—Average oil yield  in gallons per ton

≤55.1 to 1010.1 to 1515.1 to 2020.1 to 2525.1 to 3030.1 to 3535.1 to 4040.1 to 45
Figure 47. Isoresource map of R-5 zone in Uinta and Piceance Basins showing oil yield in weight percent. 

RIO BLANCO

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UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

£¤6

¤£40

¤£50

£¤191

£¤40 £¤87

£¤6

£¤191

MAP LO

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-5 zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 88.1 to 1010.1 to 1212.1 to 14>14
Figure 48. Isoresource map of R-5 zone in Uinta and Piceance Basins showing oil yield in barrels per acre. 

RIO BLANCO

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UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

¤£6

¤£40

£¤50

£¤191

£¤40 ¤£87

¤£6

£¤191

MAP LO

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-5 zone—Barrels per acre

≤100,000100,001 to 200,000200,001 to 300,000300,001 to 400,000400,001 to 500,000500,001 to 600,000600,001 to 700,000700,001 to 800,000800,001 to 900,000
Figure 49. Isopach map of L-5 zone in Uinta and Piceance Basins using the Radial Basis Function method of contouring.

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MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

¤£6

¤£40

£¤50

£¤191

£¤40 ¤£87

¤£6

¤£191

MAP LO

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-5 zone—Thickness in feet

≤5051 to 7576 to 100101 to 125126 to 150151 to 175176 to 200201 to 225226 to 250251 to 275
Figure 50. Isoresource map of L-5 zone in Uinta and Piceance Basins showing oil yield in gallons per ton. 

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UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

£¤6

£¤40

¤£50

£¤191

£¤40 £¤87

¤£6

¤£191

MAP L

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-5 zone—Average oil yield in gallons per ton

≤33.1 to 66.1 to 99.1 to 1212.1 to 1515.1 to 1818.1 to 2121.1 to 24
Figure 51. Isoresource map of L-5 zone in Uinta and Piceance Basins showing oil yield in weight percent.

RIO BLANCO

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UINTAH

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CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

¤£6

£¤40

£¤50

£¤191

£¤40 £¤87

¤£6

¤£191

MAP LO

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-5 zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 8>8
Figure 52. Isoresource map of L-5 zone in Uinta and Piceance Basins showing oil yield in barrels per acre. 

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CARBON

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DUCHESNE

MESA

MONTR

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

¤£6

£¤40

¤£50

£¤191

£¤40 ¤£87

£¤6

¤£191

MAP 

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battle

attle

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

L-5 zone—Barrels per acre

≤25,00025,001 to 50,00050,001 to 75,00075,001 to 100,000100,001 to 125,000125,001 to 150,000150,001 to 175,000175,001 to 200,000200,001 to 225,000225,001 to 250,000250,001 to 275,000
Figure 53. Isopach map of R-6 zone in Uinta and Piceance Basins using the Radial Basis Function method of contouring.

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CARBON

WASATCH

DUCHESNE

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MONTR

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

£¤6

£¤40

£¤50

£¤191

¤£40 ¤£87

¤£6

¤£191

MAP 

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battl

attl

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-6 zone—Thickness in feet

≤100101 to 150151 to 200201 to 250251 to 300301 to 350351 to 400401 to 450451 to 500
Figure 54. Isoresource map of R-6 zone in Uinta and Piceance Basins showing oil yield in gallons per ton. 

RIO BLANCO

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UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

£¤6

£¤40

£¤50

£¤191

¤£40 £¤87

£¤6

¤£191

Price Price

MAP L

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battle

attle

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-6 zone—Average oil yield  in gallons per ton

≤33.1 to 66.1 to 99.1 to 1212.1 to 1515.1 to 1818.1 to 2121.1 to 2424.1 to 2727.1 to 3030.1 to 3333.1 to 36
Figure 55. Isoresource map of R-6 zone in Uinta and Piceance Basins showing oil yield in weight percent. 

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CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

£¤191

£¤6

¤£40

£¤50

£¤191

¤£40 £¤87

¤£6

£¤191

MAP L

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-6 zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 8>108.1 to 10
Figure 56. Isoresource map of R-6 zone in Uinta and Piceance Basins showing oil yield in barrels per acre. 

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MONTRO

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GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

£¤40

¤£50

£¤191

£¤40 £¤87

£¤6

£¤191

Grand Junction

Fruita Fruita

MAP LO

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°

39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

R-6 zone—Barrels per acre

≤50,00050,001 to 100,000100,001 to 150,000150,001 to 200,000200,001 to 250,000250,001 to 300,000300,001 to 350,000350,001 to 400,000400,001 to 450,000
Detailed Description and Assessment Results of Oil Shale Zones 65

of the Douglas Creek arch to a maximum of over 450 ft in the 

western part of the basin (fig. 53). Estimated oil yields are as 

high as 13.9 GPT (fig. 54) or 8 weight percent (fig. 55), and 

estimated in-place oil ranges to as much as 195,000 BPA 

(fig. 56). 

B-Groove

B-groove is a comparatively thin interval that represents 

a major decrease in oil yields that is evident throughout the oil 

shale areas of the Piceance and Uinta Basins. It is one of the 

most distinctive and easily recognizable units on geophysical 

logs and oil-yield histograms in the entire oil shale interval 

(fig. 3). In the Piceance Basin, B-groove ranges from 5 to 40 

ft thick throughout most of the basin (fig. 57) but thickens 

markedly toward both the north, where it reaches a thickness of almost 100 ft, and toward the east, where it reaches 

a maximum thickness of 90 ft (fig. 57). B-groove is very 

sandy in these marginal areas of the Piceance Basin where it 

is thickest (R.C. Johnson, unpub. sections; Donnell, 1961, his 

plate 49). In the Uinta Basin, B-groove thickens from about 

5 to 50 ft along the west flank of the Douglas Creek arch to a 

maximum of about 160 ft in the north-central part of the basin 

just south of the Uinta Mountains (fig. 57). B-groove appears 

to represent a major contraction of the lake that brought sandy 

sediments much farther into the lake than during the previous R-6 interval or the Mahogany interval that followed. It is 

unclear why organic productivity was so much lower during 

this contraction of the lake than during previous contractions.

B-groove is organically poor overall with oil yields generally less than 10 GPT (4 weight percent) throughout most of 

the Piceance Basin, but oil yields are locally as much as 

25 GPT (12.6 weight percent) in the central part of the basin 

(figs. 58 and 59). The overall pattern is a general increase in 

oil yield toward about the same southeast-trending oil shale 

depocenter as for the underlying R-6 zone but with a high 

degree of scatter. In-place oil is also higher in this depocenter 

(fig. 60) with values ranging to more than 40,000 BPA, but 

again, there is a high degree of scatter. Estimated oil yields in 

the Uinta Basin are as high as 14.5 GPT, but most values are 

less than 5 GPT (fig. 58). Estimated weight-percent oil is generally less than 4 (fig. 59). Estimated in-place oil in the Uinta 

Basin ranges to as much as 70,000 BPA (fig. 60). 

Mahogany Zone 

The Mahogany zone and the strata above it compose the 

fifth stage of Lake Uinta as defined by Johnson (1985). The 

Mahogany zone has been the target of most oil shale extraction projects in both basins thus far because of its richness and 

because it crops out around the margins of the basins where 

it can be easily reached by underground mining. The base 

of the Mahogany zone is marked by a significant increase in 

oil yields (fig. 3). Oil yields generally increase upward in the 

Mahogany zone to a maximum in the Mahogany bed, one of 

the richest and probably the most widespread oil shale beds 

in both the Piceance and Uinta Basins (fig. 3). The Mahogany 

bed is the only significant oil shale bed remaining in the Green 

River Formation throughout much of the southern part of the 

Uinta Basin where most of the Green River Formation has 

graded into marginal lacustrine and fluvial rocks (Cashion, 

1967, his pl. 3). It represents the culmination of a major transgression of Lake Uinta that began at the base of the Mahogany 

zone. 

The Mahogany bed can be recognized throughout most, 

if not all, of the area where the Green River Formation is preserved in both the Uinta and Piceance Basins. However, near 

the mouth of Yellow Creek (fig. 1) in the north-central part of 

the Piceance Basin, it grades into organically lean marlstone, 

siltstone, and sandstone. Johnson (1985, 2007) believed that 

(1) the Mahogany zone graded into clastics in this area due to 

outflow from Lake Gosiute to the north, and (2) the expansion 

of the lake during deposition of the Mahogany was caused 

by the increase in water supplied to Lake Uinta due to this 

outflow. The Mahogany bed represents the maximum extent of 

Lake Uinta when oil shale was deposited across nearly all the 

areas that had previously been marginal lacustrine. Oil yields 

gradually decline in the Mahogany zone above the Mahogany 

bed. In the Piceance Basin, the expansion of the oil shale 

depocenter toward the southeast that began during deposition 

of the L-5 zone continued with deposition of the rich oil shale 

of the Mahogany zone across much of the southeastern part of 

the basin. 

The Mahogany zone in the Piceance Basin ranges from 

150 to 250 ft thick through a broad northwest-trending belt in 

the middle of the Piceance Basin (fig. 61). It thins toward the 

west, south, and east but thickens and grades into marlstone, 

siltstone, and sandstone near the mouth of Yellow Creek. In 

the Uinta Basin, thickness of the Mahogany zone is variable 

and complex (fig. 61). In about the northeastern one-third of 

the Uinta Basin, the Mahogany zone generally increases in 

thickness to the north-northeast from about 65 to 160 ft (fig. 

61). In the western one-third of the basin, it generally thickens to the north from 106 to more than 300 ft. In the southern 

part of the basin, where the Mahogany zone is only partially 

preserved, the remaining unit varies widely ranging from 9 ft 

thick to as much as 185 ft thick, depending on the thickness of 

clastic wedges within it (fig. 61). The insertion of these clastic 

wedges toward the south is marked by a distinct thickening 

of the Mahogany zone just north of the area where it is only 

partially preserved (fig. 61). 

Oil yield for the Mahogany zone in the Piceance Basin 

ranges from about 21 to 33 GPT (8 to 12.7 weight percent) 

throughout the oil shale depocenter (figs. 62 and 63). In-place 

oil ranges from 200,000 to 427,000 BPA in the richest part 

of the depocenter with values decreasing in a regular fashion outward (fig. 64). In the Uinta Basin, oil yield reaches a 

maximum of about 25 GPT (12 weight percent) in the eastern 

one-third of the basin (figs. 62 and 63). Oil yields gradually 

decrease to the west-northwest, away from this area, to as little 

as 3 to 5 GPT (less than 2 weight percent) in the westernmost 
Figure 57. Isopach map of B-groove in Uinta and Piceance Basins.

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GRAND

§ ̈¦70

§ ̈¦70

£¤191

¤£6

¤£40

¤£50

¤£191

¤£40 £¤87

¤£6

¤£191

MAP LOCA

UTAH COL

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battleme

attleme

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Delta

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Delta

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

B-groove—Thickness in feet

≤2526 to 5051 to 7576 to 100101 to 125126 to 150151 to 175
Figure 58. Isoresource map of B-groove in Uinta and Piceance Basins showing oil yield in gallons per ton. 

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MONTROS

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GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

¤£40

¤£50

¤£191

¤£40 ¤£87

£¤6

¤£191

MAP LO

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

B-groove—Average oil yield  in gallons per ton

≤33.1 to 66.1 to 99.1 to 1212.1 to 1515.1 to 1818.1 to 2121.1 to 2424.1 to 27
Figure 59. Isoresource map of B-groove in Uinta and Piceance Basins showing oil yield in weight percent. 

RIO BLANCO

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WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

¤£40

¤£50

¤£191

¤£40 ¤£87

¤£6

¤£191

Roosevelt Roosevelt

MAP LO

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

B-groove—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 88.1 to 1010.1 to 12>12
Figure 60. Isoresource map of B-groove in Uinta and Piceance Basins showing oil yield in barrels per acre.

RIO BLANCO

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UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

£¤40

¤£50

¤£191

¤£40 ¤£87

¤£6

¤£191

MAP LOC

UTAH CO

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

B-groove—Barrels per acre

≤10,00010,001 to 20,00020,001 to 30,00030,001 to 40,00040,001 to 50,00050,001 to 60,00060,001 to 70,000
Figure 61. Isopach map of Mahogany oil shale zone in Uinta and Piceance Basins. 

RIO BLANCO

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UINTAH

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CARBON

WASATCH

DUCHESNE

MESA

M

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

¤£40

¤£

¤£191

¤£40 ¤£87

¤£6

¤£191

Price Price

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

Mahogany zone—Thickness in feet

≤2526 to 5051 to 7576 to 100101 to 125126 to 150151 to 175176 to 200201 to 225226 to 250
Figure 62. Isoresource map of Mahogany oil shale zone in Uinta and Piceance Basins showing oil yield in gallons per ton. 

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONT

EMERY

GRAND

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§ ̈¦70

¤£191

¤£6

¤£40

¤£50

¤£191

¤£40 ¤£87

¤£6

¤£191

M

UTA

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Ba

a

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

Mahogany zone—Average oil yield  in gallons per ton

≤33.1 to 66.1 to 99.1 to 1212.1 to 1515.1 to 1818.1 to 2121.1 to 2424.1 to 2727.1 to 3030.1 to 3333.1 to 36
Figure 63. Isoresource map of Mahogany oil shale zone in Uinta and Piceance Basins showing oil yield in weight percent.

33.1 to 3633.1 to 36

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

¤£40

¤£50

¤£191

¤£40 ¤£87

¤£6

¤£191

Price Price

MAP L

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battle

attle

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

Grand Junction

Fruita

D

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

Mahogany zone—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 88.1 to 1010.1 to 12>12
Detailed Description and Assessment Results of Oil Shale Zones 73

part of the basin. In the southern part of the Uinta Basin, 

where the Mahogany zone is split by clastic wedges and only 

partially preserved, average oil yields vary markedly with 

lower GPT values in areas where thick clastic wedges are 

present in the zone. In-place oil ranges from about 120,000 to 

230,000 BPA in the depocenter to minimum values of about 

25,000 BPA in some areas in the western part of the basin and 

3,000 BPA along the south margin (fig. 64). 

A-Groove

A-groove represents another comparatively thin interval, 

similar to B-groove, that contains low oil yields. A-grove 

ranges in thickness from 5 to 25 ft throughout most of the 

Piceance Basin (fig. 65). In the Uinta Basin, A-groove is thickest in a north- to south-trending area in the central part of the 

basin where it reaches a maximum of 100 ft thick (fig. 65). Oil 

yields for A-groove in the Piceance Basin range from less than 

1 GPT to about 22 GPT (less than 1 to 13.1 weight percent) 

in a highly irregular fashion (figs. 66 and 67). Total in-place 

oil also shows a high degree of irregularity, but in general, inplace oil is greatest along approximately the same southeasttrending area where in-place oil was highest for the underlying 

Mahogany zone (fig. 68). In the Uinta Basin, estimated oil 

yields range to as much as 14.3 GPT (6 weight percent) in 

the northeast part of the basin (figs. 66 and 67). In-place oil 

is as much as 200,000 BPA in the northeast part of the basin 

(fig. 68).

The Interval above A-Groove

The interval above A-groove represents the infilling stage 

of Lake Uinta when the Piceance Basin part of the lake was 

largely, if not completely, filled in. Thick wedges of volcaniclastic sediments derived from the Absaroka volcanic field 

in northwestern Wyoming prograded from north to south 

across the Piceance Basin starting from a point source near the 

mouth of Yellow Creek in the north-central part of the basin 

(Johnson, 1981, 1985). The southward progradation of these 

volcaniclastics occurred over a significant period of time with 

intervals of oil shale deposited during periods when the rate of 

volcaniclastics supplied to the basin from the north diminished 

or ceased entirely. These oil shale intervals coalesce toward 

the south end of the Piceance Basin as the intervening clastic 

wedges pinch out resulting in a nearly continuous interval of 

oil shale several hundred feet thick in the southern part of the 

basin. 

Only the interval from the top of A-groove to the top of 

bed 44 of Donnell (2008) is presented here because it is the 

highest oil shale zone assessed by Johnson, Mercier, Brownfield, and others (2010) and Johnson, Mercier, Brownfield, 

and Self (2010) in both the Uinta and Piceance Basins. A 

higher interval from the top of bed 44 to the top of bed 76 was 

assessed in the Uinta Basin but not in the Piceance, because 

it is present in only a limited area in the southern part of 

that basin. In the Piceance Basin, the interval from the top 

of A-groove to the top of bed 44 thickens from about 150 ft 

along the southwest margin of the basin to over 1,500 ft in 

the north-central part of the basin (fig. 69) where it consists of 

predominantly volcaniclastic sandstone with a few thin zones 

of marlstone. In the Uinta Basin, the interval from the top of 

A-groove to top of bed 44 thickens to the west-northwest from 

about 135 to 170 ft along the west flank of the Douglas Creek 

arch, to 270 ft thick in the northeastern part of the basin, and 

to 500 ft in the northwestern part (fig. 69). 

Estimated oil yield for the interval from the top of 

A-groove to the top of bed 44 in the Piceance Basin ranges 

from about 16 GPT to 22 GPT (4 to 6.9 weight percent) 

throughout much of the south-central part of the basin. Oil 

yields drop off rapidly to the north as the interval becomes 

intertongued with the Uinta Formation but more gradually 

to the east, south, and west, due to an overall decrease in oil 

yields (figs. 70 and 71). In-place oil in the Piceance Basin 

ranges from 375,000 to 475,000 BPA in this area and diminishes in a more or less radial pattern outward (fig. 72). In the 

Uinta Basin, estimated oil yield throughout much of the northeastern part of the basin ranges from about 10 to 14.3 GPT (4 

to 6 weight-percent oil) and decreases to the northeast, south, 

and west (figs. 70 and 71). In the Uinta Basin, in-place oil 

for the interval from the top of A-groove to the top of bed 44 

ranges from about 120,000 to 200,000 BPA in the depocenter 

with values decreasing markedly away from that area (fig. 72).
Figure 64. Isoresource map of Mahogany oil shale zone in Uinta and Piceance Basins showing oil yield in barrels per acre.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

¤£40

¤£50

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¤£40 ¤£87

¤£6

¤£191

350,001 to 400,000

MAP LOC

UTAH CO

UTAH COLORADO

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Battleme

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111° 110° 109° 

40°39°

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

Mahogany zone—Barrels per acre

≤50,00050,001 to 100,000100,001 to 150,000150,001 to 200,000200,001 to 250,000250,001 to 300,000300,001 to 350,000400,001 to 450,000
Figure 65. Isopach map of A-groove in Uinta and Piceance Basins.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTRO

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

¤£40

¤£50

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¤£40 ¤£87

¤£6

¤£191

MAP LO

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

A-groove—Thickness in feet

≤1011 to 2021 to 3031 to 4041 to 5051 to 6061 to 7071 to 8081 to 9091 to 100
Figure 66. Isoresource map of A-groove in Uinta and Piceance Basins showing oil yield in gallons per ton. 

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

¤£40

¤£50

¤£191

¤£40 ¤£87

¤£6

¤£191

MAP LO

UTAH 

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

A-groove—Average oil yield  in gallons per ton

≤22.1 to 44.1 to 66.1 to 88.1 to 1010.1 to 1212.1 to 1414.1 to 1616.1 to 1818.1 to 20

20.1 to 22
Figure 67. Isoresource map of A-groove in the Uinta and Piceance Basins showing oil yield in weight percent.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

D

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

¤£40

¤£50

¤£191

¤£40 ¤£87

¤£6

¤£191

MAP LOC

UTAH CO

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battleme

attleme

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

A-groove—Weight-percent oil

≤22.1 to 44.1 to 66.1 to 88.1 to 1010.1 to 12>12
Figure 68. Isoresource map of A-groove in Uinta and Piceance Basins showing oil yield in barrels per acre.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

D

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

¤£40

¤£50

¤£191

¤£40 ¤£87

¤£6

¤£191

MAP LOC

UTAH CO

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battleme

attleme

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Delt

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

A-groove—Barrels per acre

≤5,0005,001 to 10,00010,001 to 15,00015,001 to 20,00020,001 to 25,00025,001 to 30,00030,001 to 35,000
Figure 69. Isopach map of bed 44 to A-groove in Uinta and Piceance Basins.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

¤£40

¤£50

¤£191

¤£40 ¤£87

¤£6

¤£191

Roosevelt Roosevelt

MAP LOC

UTAH CO

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

Bed 44—Thickness in feet

≤200201 to 400401 to 600601 to 800801 to 1,0001,001 to 1,2001,201 to 1,400

1,201 to 1,400
Figure 70. Isoresource map of bed 44 to A-groove in Uinta and Piceance Basins showing oil yield in gallons per ton.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

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§ ̈¦70

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¤£6

¤£40

¤£50

¤£191

¤£40 ¤£87

¤£6

¤£191

MAP LO

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

Grand Junction

Fruita

De

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

Bed 44—Average oil yield  in gallons per ton

≤22.1 to 44.1 to 66.1 to 88.1 to 1010.1 to 1212.1 to 1414.1 to 1616.1 to 1818.1 to 20

20.1 to 22
Figure 71. Isoresource map of bed 44 to A-groove in Uinta and Piceance Basins showing oil yield in weight percent. 

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

¤£6

¤£40

¤£50

£¤191

¤£40 ¤£87

£¤6

¤£191

Roosevelt Roosevelt

MAP LOC

UTAH CO

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

Bed 44—Weight-percent oil

≤22.1 to 44.1 to 6>6
Figure 72. Isoresource map of bed 44 to A-groove in Uinta and Piceance Basins showing oil yield in barrels per acre.

RIO BLANCO

GARFIELD

MOFFAT

SUMMIT

UINTAH

UTAH

CARBON

WASATCH

DUCHESNE

MESA

MONTROS

EMERY

GRAND

§ ̈¦70

§ ̈¦70

¤£191

£¤6

£¤40

¤£50

¤£191

¤£40 ¤£87

¤£6

¤£191

MAP LOC

UTAH C

UTAH COLORADO

0 10 20 MILES 5

0 10 20 KILOMETERS 5

Battlem

attlem

Price

111° 110° 109° 

40°39°

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

Grand Junction

Fruita

Del

Vernal

Roosevelt

Moab

15

15

EXPLANATION

Mahogany ledge outcropBase of Parachute Creek Member

Bed 44—Barrels per acre

≤100,000100,001 to 150,000150,001 to 200,000200,001 to 250,000250,001 to 300,000300,001 to 350,000350,001 to 400,000400,001 to 450,000450,001 to 500,000
Discussion 83

Discussion

The total in-place resource for the Uinta Basin of 1.32 

trillion barrels of oil is only slightly lower than the total of 

1.53 trillion barrels of in-place resource for the Piceance 

Basin, which is thought to contain the richest oil shale deposit 

in the world. However, the area underlain by oil shale in the 

Uinta Basin is much larger than that of the Piceance Basin, 

with the Mahogany zone underlying 3,834 mi2

 of the Uinta 

Basin as compared to 1,335 mi2

 in the Piceance Basin. Average GPT and BPA values for each oil shale zone assessed are 

significantly lower in the Uinta Basin than in the Piceance 

Basin. 

The oil shale and saline mineral depocenter throughout 

much of the history of Lake Uinta was in the north-central part 

of the Piceance Basin, and this depocenter is clearly defined 

on all GPT, weight percent, and BPA maps, including the R-0 

zone, the first zone deposited after Lake Uinta formed (figs. 6 

to 8). The depocenter is considerably west of the rapidly subsiding trough of the basin (pl. 1), and Johnson (1985) hypothesized that sediment eroded off the rising White River uplift 

east of the basin pushed the lake west of the basin trough. 

The area of richest oil shale in the Uinta Basin, as measured 

by GPT, weight percent, and BPA, is generally in the northeast part adjacent to the crest of the Douglas Creek arch, in a 

west- to northwest-trending area that is nearly perpendicular to 

subsidence trends at that time (fig. 4). This is the only area of 

the Uinta Basin where all of the rich and lean oil shale zones, 

originally defined in the Piceance Basin, can be identified. 

This area is also distant from sources of clastic influx, such as 

the Uinta Mountains to the north, the Sevier orogenic belt to 

the west, and a major river system that entered the lake from 

the south (fig. 4). 

References Cited

American Society for Testing Materials, 1984, Designation 

D 388-80, Standard test method for oil from oil shale: 

American Society for Testing Materials Annual Book of 

ASTM Standards, 1984, p. 513–525.

Bradley, W.H., 1931, Origin and microfossils of the oil shale 

of the Green River Formation of Colorado and Utah: 

U.S. Geological Survey Professional Paper 168, 58 p.

Brownfield, M.E., Mercier, T.J., Johnson, R.C., and Self, 

J.G., 2010, Nahcolite resources in the Green River Formation, Piceance Basin, Colorado, chap. 2 of U.S. Geological 

Survey Oil Shale Assessment Team, Oil shale and nahcolite 

resources of the Piceance Basin, Colorado: U.S. Geological 

Survey Digital Data Series DDS–69–Y, 51 p.

Brownfield, M.E., Johnson, R.C., and Dyni, J.R., 2010, 

Sodium carbonate resources of the Eocene Green River 

Formation, Uinta Basin, Utah and Colorado, chap. 2 of

U.S. Geological Survey Oil Shale Assessment Team, Oil 

shale resources of the Uinta Basin, Utah and Colorado: 

U.S. Geological Survey Digital Data Series DDS–69–BB, 

13 p.

Cashion, W.B., 1967, Geology and fuel resources of the Green 

River Formation, southeastern Uinta Basin, Utah and Colorado: U.S. Geological Survey Professional Paper 548, 48 p.

Cashion, W.B., 1973, Geologic and structure map of the Grand 

Junction quadrangle, Colorado and Utah: U.S. Geological 

Survey Miscellaneous Investigations Series Map I–736, 

scale 1:250,000.

Cashion, W.B., 1977, Geologic map of the Weaver Ridge 

quadrangle, Utah and Colorado: U.S. Geological Survey 

Miscellaneous Field Investigations Map MF–824, scale 

1:24,000.

Cashion, W.B., 1978, Geologic map of the Wash Knolls 

quadrangle, Uintah County, Utah, and Rio Blanco County, 

Colorado: U.S. Geological Survey Miscellaneous Field 

Investigations Map MF–1013, scale 1:24,000.

Cashion, W.B., 1986, Geologic map of the Bonanza quadrangle, Uintah County, Utah: U.S. Geological Survey Miscellaneous Field Investigations Map MF–1865, scale 1:24,000. 

Cashion, W.B., and Donnell, J.R., 1972, Chart showing correlation of selected key units in the organic-rich sequence of 

the Green River Formation, Piceance Creek Basin, Colorado, and Uinta Basin, Utah: U.S. Geological Survey Oil 

and Gas Investigations Chart OC–65.

Cashion, W.B., and Donnell, J.R., 1974, Revision of nomenclature of the upper part of the Green River Formation, 

Piceance Creek Basin, Colorado, and Eastern Uinta Basin, 

Utah: U.S. Geological Survey Bulletin 1394–G, 9 p.

Chancellor, R.E., Barksdale, W.L., and Dolezal, George, Jr., 

1974, Occurrence of oil and gas in the Tertiary System, Rio 

Blanco unit, Rio Blanco County, Colorado, in Murray, D.K., 

ed., Guidebook to the energy resources of the Piceance 

Creek Basin, Colorado: Rocky Mountain Association of 

Geologists, 25th Field Conference, p. 225–233.

Dane, C.H., 1954, Stratigraphic and facies relationships of 

upper part of Green River Formation and lower part of 

Uinta Formation in Duchesne, Uintah, and Wasatch Counties, Utah: American Association of Petroleum Geologists 

Bulletin v. 38, no. 3, p. 405–425.

Dane, C.H., 1955, Stratigraphic and facies relationships of 

upper part of Green River Formation and lower part of 

Uinta Formation in Duchesne, Uinta, and Wasatch Counties, 

Utah: U.S. Geological Survey Oil and Gas Chart OC–52.
84 Maps for Oil Shale Deposits in Uinta and Piceance Basins, Utah and Colorado References Cited 84

Donnell, J.R., 1961, Tertiary geology and oil-shale resources 

of the Piceance Creek Basin between the Colorado and 

White Rivers, northwestern Colorado: U.S. Geological 

Survey Bulletin 1082–L, 56 p.

Donnell, J.R., 2008, Intertonguing of the lower part of the 

Uinta Formation with the upper part of the Green River Formation in the Piceance Creek Basin during the late stages of 

Lake Uinta: U.S. Geological Survey Scientific Investigation 

Report 2008–5237, 25 p.

Dyni, J.R., 1974, Stratigraphy and nahcolite resources of the 

saline facies of the Green River Formation in northwest 

Colorado, in Murray, D.K., ed., Guidebook to the energy 

resources of the Piceance Creek Basin, Colorado: Rocky 

Mountain Association of Geologists 25th Field Conference, 

p. 111–122.

Dyni, J.R., 1981, Geology of the nahcolite deposits and associated oil shales of the Green River Formation in the Piceance 

Creek Basin, Colorado: Boulder, University of Colorado, 

Ph.D. dissertation, 144 p.

Dyni, J.R., 1996, Sodium carbonate resources of the Green 

River Formation: U.S. Geological Survey Open-File Report 

96–729, 39 p.

Dyni, J.R., 2003, Geology and resources of some world oilshale deposits: Oil Shale, v. 20, no. 3, p. 193–252.

Fouch, T.D., 1975, Lithofacies and related hydrocarbon accumulations in Tertiary strata of the western and central Uinta 

Basin, Utah, in Bolyard, D.W., ed., Deep drilling frontiers 

of the central Rocky Mountains: Rocky Mountain Association of Geologists 1975 Symposium, p. 163–173.

Johnson, R.C., 1981, Stratigraphic evidence for a deep Eocene 

Lake Uinta, Piceance Creek Basin, Colorado: Geology, 

v. 9, p. 55–62.

Johnson, R.C., 1984, New names for units in the lower part of 

the Green River Formation, Piceance Creek Basin, Colorado: U.S. Geological Survey Bulletin 1529–I, p. I1–I20.

Johnson, R.C., 1985, Early Cenozoic history of the Uinta and 

Piceance Creek Basins, Utah and Colorado, with special 

reference to the development of Eocene Lake Uinta, in

Flores, R.M., and Kaplan, S.S., eds., Cenozoic paleogeography of the west-central United States: The Rocky Mountain 

Section, Society of Economic Paleontologists and Mineralogists, Rocky Mountain Paleogeography Symposium 3, 

p. 247–276.

Johnson, R.C., 1989, Detailed cross section correlating the 

Upper Cretaceous and lower Tertiary rocks between the 

Uinta Basin of eastern Utah and western Colorado and the 

Piceance Basin of western Colorado: U.S. Geological 

Survey Miscellaneous Investigations Map I–1974, 2 sheets.

Johnson, R.C., 2007, The outflow of Eocene Lake Gosiute into 

Lake Uinta and its effects on sedimentation in Lake Uinta 

in the Piceance Basin of western Colorado [abs.]: American 

Association of Petroleum Geologists Rocky Mountain 

Section Meeting, Snowbird, Utah, Oct. 7–9, 2007, Program, 

p. 43.

Johnson, R.C., and Finn, T.M., 1986, Cretaceous through 

Holocene history of the Douglas Creek arch, Colorado and 

Utah, in Stone, D.S., ed., New interpretations of northwest 

Colorado geology: Rocky Mountain Association of Geologists Guidebook, p. 77–95. 

Johnson, R.C., Mercier, T.J., Brownfield, M.E., and Self, J.G., 

2011, Assessment of in-place oil shale resources of the 

Eocene Green River Formation, Greater Green River Basin, 

Wyoming, Colorado, and Utah, chap. 1 of U.S. Geological 

Survey Oil Shale Assessment Team, Oil Shale Resources 

of the Eocene Green River Formation, Greater Green River 

Basin, Wyoming, Colorado, and Utah: U.S. Geological 

Survey Digital Data Series DDS–69–DD, 63 p. 

Johnson, R.C., Mercier, T.J., Brownfield, M.E., Pantea, M.P., 

and Self, J.G., 2010, Assessment of oil shale resources 

of the Green River Formation, Piceance Basin, western 

Colorado, chap. 1 of U.S. Geological Survey Oil Shale 

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Publishing support provided by: 

Denver Publishing Service Center

For more information concerning this publication, contact: 

Center Director, USGS Central Energy Resources Science Center 

Box 25046, Mail Stop 939 

Denver, CO 80225 

(303) 236-1647 

Or visit the Central Energy Resources Science Center Web site at: 

http://energy.usgs.gov/
Mercier and Johnson—Maps for Oil Shale Deposits in Uinta and Piceance Basins, Utah and Colorado—Scientific Investigations Report 2012–5076