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Revision of Nomenclature of the 

Upper Part of the Green River Formation, 

Piceance Creek Basin, Colorado, and 

Eastern Uinta Basin, Utah

GEOLOGICAL SURVEY BULLETIN 1394-G

Revision of Nomenclature of the 

Upper Part of the Green River Formation, 

Piceance Creek Basin, Colorado, and 

Eastern Uinta Basin, Utah

By W. B. CASHION and JOHN R. DONNELL

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1394-G

Nomenclature changes involving the 

Evacuation Creek and Parachute Creek 

Members of the Green River Formation 

and the Uinta and Bridger Formations

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1974
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 74-600018

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

Washington, D. C. 20402 - Price 25 cents (paper cover)

Stock Number 2401-02473
CONTENTS

Page

Abstract __________________________________________ Gl

Introduction ________________________________________ 1

Parachute Creek Member ________________________________ 2

Evacuation Creek Member _______________________________ 3

Uinta Formation _____________________________________ 3

Correlations ________________________________________ 7

Nomenclature changes __________________________________ 8

References _________________________________________ 8

ILLUSTRATIONS

Page

FIGURE 1. Map showing locations of core holes and measured sections ________ G2

2. Stratigraphic sections of the upper part of the Green River Formation _ _ 4

3. Diagram showing Stratigraphic nomenclature of Bradley (1931) and of this

paper ___________________________________ 9

TABLE

Page

TABLE 1. Locations of core holes and sections shown in figure !___________ G7

in

CONTRIBUTIONS TO STRATIGRAPHY

REVISION OF NOMENCLATURE OF THE

UPPER PART OF THE

GREEN RIVER FORMATION,

PICEANCE CREEK BASIN, COLORADO,

AND EASTERN UINTA BASIN, UTAH

By W. B. CASHION and JOHN R. DONNELL

ABSTRACT

Stratigraphic study of the upper part of the Green River Formation and overlying beds in 

northwestern Colorado and northeastern Utah shows that the upper part of the Parachute 

Creek Member at the type locality in the Piceance Creek basin, Colorado, is the same 

lithologic and stratigraphic unit as the Evacuation Creek Member at its type locality in the 

Uinta Basin. The Evacuation Creek Member as used by most workers in the Piceance Creek 

basin is equivalent to the lower part of the Unita Formation in the Uinta Basin. The name 

Evacuation Creek Member is abandoned and is replaced by the Parachute Creek Member in 

the eastern Uinta Basin and by the Uinta Formation in the Piceance Creek basin.

INTRODUCTION

The Green River Formation (Eocene) in Colorado and Utah has been 

studied by numerous workers investigating the geology and resources of oil 

shale and saline minerals of the formation. Although much has been learned 

in recent years of the stratigraphy of the formation, little has been done to 

update the stratigraphic nomenclature in Colorado and Utah since a classic 

paper by Bradley (1931) established member names in the Piceance Creek 

basin and in the eastern Uinta Basin more than 40 years ago. Changes in 

nomenclature are needed for the best presentation of the results of current 

studies and for facilitating future studies. Many workers have become very 

comfortable with the old names and have made mental adjustments for the 

awkward nomenclature, but such adjustments are not an acceptable permanent solution.

Bradley (1931) first divided the Green River Formation of the Piceance 

Creek basin and eastern Uinta Basin (fig. 1) into four members, named, in 

ascending order, the Douglas Creek, Garden Gulch, Parachute Creek, and 

Evacuation Creek Members. Changes adopted in this paper involve the 

Parachute Creek and Evacuation Creek Members (fig. 2).

Gl
G2 CONTRIBUTIONS TO STRATIGRAPHY

41'

40'

39'

111 1'WYOMING j 10^ 

' UTAH r

109' .____107

100 MILES

50

I 

100 KILOMETERS

FIGURE 1. Locations of core holes (dots) and measured sections (X). Green River

Formation is patterned.

PARACHUTE CREEK MEMBER

The type locality of the Parachute Creek Member is along Parachute 

Creek in Garfield County, Colo. The member was named by Bradley (1931, 

p. 11), who stated that it is distinguished from other parts of the Green 

River Formation by its content of oil-shale beds, including all the large 

groups of rich beds, most of the individual rich beds, and a very large 

proportion of the low-grade oil shale. In this member the richest and 

thickest sequence of oil-shale beds exposed in the Piceance Creek and Uinta 

Basins is extremely persistent and is called the Mahogany ledge on the outcrop and the Mahogany zone in the subsurface. That part of the member 

that includes the Mahogany ledge and the section above it consists mostly of 

oil shale with some marlstone and is more than 730 feet thick along 

Parachute Creek. That part of the member below the Mahogany ledge consists dominantly of barren marlstone with minor amounts of rich oil shale 

and is 560 feet thick. About 15 miles northwest of the type locality, near the 

depositional center of the Piceance Creek basin, the Mahogany zone is 

thicker and richer than at the type locality, and the upper part of the 

member thins to 500 feet. In contrast, that part below the Mahogany zone 

thickens to about 1,000 feet and consists dominantly of rich oil shale and 

large amounts of nahcolite (NaHCO3). In the Piceance Creek basin and the 

eastern part of the Uinta Basin numerous thin tuff beds are interspersed 

through the upper part of the Parachute Creek Member.
NOMENCLATURE, GREEN RIVER FORMATION, COLORADO, UTAH G3

EVACUATION CREEK MEMBER

The Evacuation Creek Member is named for exposures along Evacuation 

Creek in Uintah County, Utah, but the type locality was actually measured 

4 miles northeast of Evacuation Creek along the canyon of the White River 

in sec. 27, T. 9 S., R. 25 E., Uintah County (Bradley, 1931, p. 14-15). At 

the type locality the member is about 530 feet thick and consists chiefly of 

platy and chippy marlstone, which is lean in organic matter, and scattered 

beds of rich oil shale and a few thin beds of altered tuff (Bradley, 1931, 

pi. 8).

In the Piceance Creek basin at the type locality of the Parachute Creek 

Member, Bradley (1931, pi. 7) placed the lower boundary of an incompletely measured section of the Evacuation Creek Member at the base 

of a massive sandstone, about 20 feet thick, which is about 350 feet above 

the Mahogany ledge. On the north side of the basin in the vicinity of 

Piceance Creek, Bradley (1931, p. 14), noting the increased sandy character 

of the member, found a sequence of sandy marlstone and alternating beds of 

brown sandstone and marlstone more than 840 feet thick that he assigned to 

the Evacuation Creek. These rocks are overlain by 400 feet of "sandy beds" 

that Bradley provisionally asigned to the Bridger Formation. Donnell 

(1961, p. 857 858), finding no mappable base for these sandy beds, included them in the Evacuation Creek Member. Donnell (1961, p. 857) 

placed the base of the member at the first occurrence of intertonguing 

sandstone or siltstone more than 10 feet thick, which is generally found 

about 200 to 500 feet above the Mahogany ledge. As thus redefined, the 

Evacuation Creek Member in the Piceance Creek basin has a total 

thickness of more than 1,500 feet and includes a transitional sequence of 

sandstones and marlstones which grade upward into predominantly massive 

brown medium- to coarse-grained sandstone and some thin beds of 

marlstone and siltstone. Most workers have subsequently followed 

Donnell's redefinition of the member in the Piceance Creek basin.

UINTA FORMATION

A review of early, somewhat confusing, applications of the name Uinta to 

rock units in the Uinta Basin is presented by Wood (1934, p. 242-244), who 

concluded that the first use of Uinta should be credited to Comstock (1875). 

The Uinta Formation of the eastern Uinta Basin, as used by most authors, 

is composed of brown sandstone and gray siltstone and marlstone and 

overlies the Green River Formation (Abbott, 1957; Cashion, 1967; 

Douglass, 1914; Osborn, 1929; Riggs, 1912). A few hundred feet of strata in 

the lower part of the sequence, assigned to the Uinta Formation in this 

report, was placed in the Bridger Formation by a few early workers, but 

Bridger has not been used for these rocks in recent reports describing the 

Uinta Basin. The Uinta Formation is divided into parts A, B, and C from 

lower to upper, based on vertebrate fossil studies. This usage evolved from
£

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OX03

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NOMENCLATURE, GREEN RIVER FORMATION, COLORADO, UTAH G5

Shale-oil yield,

columns 3,4and 5

(gallons per ton)

30 45

I

VERTICAL SCALE 

FEET METERS 

0 -i- 0

50

Evacuation Creek and Parachute Creek Members of Bradley (1931). Column numbers are 

is the Mahogany marker. Explanation of lithologic symbols is on the following page.
G6 CONTRIBUTIONS TO STRATIGRAPHY

EXPLANATION FOR LITHOLOGIC SYMBOLS

IN FIGURE 2 

COLUMNS 1 AND 6 COLUMNS 2 AND 4

Marlstone and oil shale

Carbonaceous claystone

FIGURE 2. Continued.

the division made by Peterson (Osborn, 1895, p. 72-74), in which the rocks 

above the Green River Formation were separated into "horizons" A, B, and 

C.

The upper boundary of Uinta A, as originally selected, was later changed 

to a lower stratigraphic position. (Compare Osborn, 1895, p. 75, and 

Osborn, 1929, fig. 63.) The lower boundary of Uinta A in the easternmost 

Uinta Basin is placed at the top of the Green River Formation as designated 

by Bradley (1931, pi. 12A). As thus defined, Uinta A is approximately 740 

feet thick near the confluence of Evacuation Creek and White River and, 

according to Osborn (1929, p. 92), is unfossiliferous. Uinta A interfingers 

with the upper part of the Green River Formation and pinches out westward 

in the area between Evacuation Creek and Willow Creek.

Uinta A is chiefly very fine-grained to medium-grained sandstones interbedded with thin marlstone in the lower part and siltstones in the upper
NOMENCLATURE, GREEN RIVER FORMATION, COLORADO, UTAH G7 

TABLE 1. Locations of core holes and sections shown in figure 1

Location no. Description County and State

1 Surface section of type Evacuation Creek Uintah County, Utah 

Member of Bradley (1931, pi. 8), in sec. 

27, T. 9 S., R. 25 E.

2 Surface section measured by W. B. Cashion Do. 

and R. W. Blair, Jr., near mouth of 

Evacuation Creek.

3 Shell Oil Company core hole 1, in sec. 2, T. Do. 

10 S., R. 24 E.

4 Composite of U.S. Bureau of Land Manage- Garfield County, Colo. 

ment, Triangulation Station Shale core 

hole 1, in sec. 13, T. 7 S., R. 97 W., and 

core hole 2, in sec. 24, T. 7 S., R. 97 W.

5 Union Oil Company, Jann core hole, in sec. Do. 

33, T. 5 S., R. 96 W.

6 Surface section of type Parachute Creek Do. 

Member measured by Bradley (1931, pi. 

7) on Parachute Creek in Tps. 5 and 6 S., 

R. 96 W.

part. Bedding is thin to massive, and many thin sequences are crossbedded. 

Sandstones in the lowermost 250 feet are contorted by differential compaction or plastic flowage prior to lithification. Uinta A weathers to yellowbrown cliffs and ledges with some steep gray and yellow-brown slopes. The 

appearance and lithology of Uinta A are similar to those of rocks that have 

been called the Evacuation Creek Member in the Piceance Creek basin.

CORRELATIONS

Stratigraphic and lithologic equivalency of the upper part of type 

Parachute Creek Member and the lower part of type Evacuation Creek 

Member is shown by Curry (1964). The correlation between thin rich oilshale beds in the Uinta Basin and thicker richer beds in the Piceance Creek 

basin is not easily perceived in outcrops, due to the differences in weathering 

characteristics, but is easily recognized when comparing oil-yield 

histograms or geophysical logs. Several rich oil-shale zones and thin tuff 

beds are identifiable over large areas and have been given informal names 

(fig- 2).

Curry (1964, p. 171) also pointed out that the lower part of the Uinta Formation is equivalent to a part of the Evacuation Creek Member, as it is 

commonly mapped in the Piceance Creek basin. The lithology of the 

Evacuation Creek Member of the Piceance Creek basin is essentially the 

same as that of the lower part of the Uinta Formation of the Uinta Basin. 

During some period of geologic history, both units were probably one 

laterally continuous body of interfingering fluvial and lacustrine sediments 

containing clastic material that was derived from a northerly or 

northeasterly source.
G8 CONTRIBUTIONS TO STRATIGRAPHY

NOMENCLATURE CHANGES

On the basis of the stratigraphic relations described above and shown in 

figure 2, the following changes are made in the nomenclature of the Green 

River, Uinta, and Bridger Formations of the Piceance Creek and Uinta 

Basins (fig. 3): 

1. The name Evacuation Creek Member is abandoned.

EASTERN UINTA 

BASIN

PICEANCE CREEK 

BASIN

Bradley (1931) This paper

u

Bradley (1931) This paper

Mahogany marker

co .2 

S 2

U

FIGURE 3. Stratigraphic nomenclature of Bradley (1931) and of this paper.
NOMENCLATURE, GREEN RIVER FORMATION, COLORADO, UTAH G9

2. The upper boundary of the Parachute Creek Member is placed at the 

base of the Uinta Formation and thus the Parachute Creek Member 

includes all rocks previously assigned to the Evacuation Creek 

Member in the Uinta Basin.

3. The name Uinta Formation is extended to the Piceance Creek basin for 

the stratigraphic sequence previously assigned to the Evacuation 

Creek Member by Donnell and other recent workers.

4. The name Bridger Formation is restricted from the Uinta and Piceance 

Creek basins.

REFERENCES

Abbott, Ward, 1957, Tertiary of the Uinta Basin, in Intermountain Assoc. Petroleum

Geologists Guidebook, 8th Ann. Field Conf., Geology of the Uinta Basin: p. 102-109. 

Bradley, W. H., 1931, Origin and microfossils of the oil shale of the Green River Formation of

Colorado and Utah: U.S. Geol. Survey Prof. Paper 168, 58 p. 

Cashion, W. B., 1967, Geology and fuel resources of the Green River Formation, southeastern

Uinta Basin, Utah and Colorado: U.S. Geol. Survey Prof. Paper 548, 48 p. 

Comstock, T. B., 1875, Geological report, in Jones, W. A., Report upon the reconnaissance of

northwestern Wyoming, including Yellowstone National Park, for 1873 [2d ed.]:U.S.

Cong., 43d, 1st sess., House Representatives Executive Doc. 285, p. 85-292 (1st ed., p.

85-184, 1874). 

Curry, H. D., 1964, Oil-content correlations of Green River oil shales, Uinta and Piceance

Creek Basins, in Intermountain Assoc. Petroleum Geologists Guidebook, 13th Ann. Field

Conf., Uinta Basin, 1964: p. 169-171. 

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. Geol. Survey Bull.

1082-L, p. 835-891. 

Douglass, Earl, 1914, Geology of the Uinta Formation: Geol. Soc. America Bull., v. 25, p.

417-420. 

Osborn, H. F., 1895, Fossil mammals of the Uinta beds: Am. Mus. Nat. History, Bull., v. 7, p.

71-106. 

 1929, The titanotheres of ancient Wyoming, Dakota and Nebraska: U.S. Geol. Survey

Mon. 55, v. 1, p. 1-701. 

Riggs, E. S., 1912, New or little known titanotheres from the lower Uintah formations: Field

Mus. of Nat. History Pub. 159, geol. ser., v. 4, no. 2, p. 17-41. 

Wood, H. E., 1934, Revision of the Hyrachyidae: Am. Mus. Nat. History Bull., v. 67, p.

181-295.

* U.S. GOVERNMENT PRINTING OFFICE: 1974 543 5S3'/79