A Study of the Cretaceous-Tertiary 

Unconformity in the Piceance Creek 

Basin, Colorado: The underlying Ohio 

Creek Formation (Upper Cretaceous) 

Redefined as a Member of the Hunter 

Canyon or Mesaverde Formation

GEOLOGICAL SURVEY BULLETIN 1482-B

\ Study of the Cretaceous-Tertiary 

Unconformity in the Piceance Creek 

Basin, Colorado: The underlying Ohio 

3reek Formation (Upper Cretaceous) 

Redefined as a Member of the Hunter 

Canyon or Mesaverde Formation

3y RONALD C. JOHNSON and FRED MAY

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1482-B

Palynomorph ages are given for rocks 

ibove and below the unconformity, along 

with a description of the deep paleoweathering 

Profile found below

JNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1980
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. \NDRUS, Secretary

GEOLOGICAL SURVEY 

H. William Menard, Director

Library of Congress Cataloging in Publication Data

Johnson, Ronald C.

A study of the Cretaceous-Tertiary unconformity in the Piceance Creek basin, Colorado.

(Contributions to stratigraphy) (Geological Survey Bulletin 1482-B)

Bibliography: p. 26

Supt.ofDocs.no.: I19.3:1482-B

1. Unconformities (Geology) Colorado Piceance Creek watershed. 2. Geology,

Stratigraphic Cretaceous. 3. Geology, Stratigraphic Tertiary. 4. Geology ColoradoPiceance Creek watershed. 

I. May, Fred E., joint author. II. Title. III. Series. IV. Series: United States Geological

Survey Bulletin 1482-B. 

QE688J63 551.7'? 80-607774

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

Washington, D.C. 20402
CONTENTS

ILLUSTRATIONS

Page

xntr OQuction - . ^

History of Ohio Creek nomenclature -- - - - --- 2

Type locality of the Ohio Creek Member of the Mesaverde Formation 6

Hunter Canyon area stratigraphy 7

Ohio Creek Member principal reference section - 13

DeBeque area stratigraphy 14

ivj.uQ.Q.y v/rcGic section *~~ --- j_ Q

C.E.R. Geonuclear Corporation drill hole 18

Paly nomorph results - ------- --- --- -------------------------------------------------------- 1 9

J-JiiTitGr Csnvon _ . 1 Q

DpRpQiip 31*63. _ ______ ............... _ ........................................ 21

iviuQQy v/reeic section - -- .......... .» ^o

References cited 26

Page

FIGURE 1. Index to mapping and outline of Cretaceous-Tertiary boundary in

the Piceance Creek basin 3

2. Diagrams of type locality of the Ohio Creek Member, Mesaverde

Formation 7

3. Diagrams of upper part of Hunter Canyon section 8 

4-8. Photographs:

4. Cretaceous-Tertiary unconformity in Hunter Canyon area - 10

5. Weathered zone at top of Cretaceous rocks 11

6. Photomicrograph of highly altered Cretaceous sandstone

from Ohio Creek Member of Hunter Canyon Formation ----- 12

7. Root zone at top of Upper Cretaceous rocks 13

8. Cretaceous-Tertiary unconformity near DeBeque ------ -- 15

9. Stratigraphic and facies diagram for the Tertiary rocks from

Hunter Canyon to DeBeque 16

10. Map of locations of measured sections and miscellaneous

sample localities - J. /

11. Photograph of conglomeratic channel at unconformity near

T^oRonno J^t7Ot?qUt7 _____ 1 -LOQ 

12. Diagrams of measured section at Muddy Creek 19

13. Log profile and cored conglomeratic zones, C.E.R. Geonuclear

Hrill Ul 111 Vinlo 11U1C! -- - " - - - ^ily 9O 

14. List of palynomorphs identified from samples collected above the

Cretaceous-Tertiary unconformity 22

15. Diagram showing possible stratigraphic relationships of Ohio

 - -- - ............. ~£*x

in

CONTRIBUTIONS TO STRATIGRAPHY

A STUDY OF THE 

CRETACEOUS-TERTIARY UNCONFORMITY IN

THE PICEANCE CREEK BASIN, COLORADO:

THE UNDERLYING OHIO CREEK FORMATION

(UPPER CRETACEOUS) REDEFINED AS A

MEMBER OF THE HUNTER CANYON OR

MESAVERDE FORMATION

By RONALD C. JOHNSON and FRED MAY

ABSTRACT

Detailed work in the southwest Piceance Creek basin and reconnaissance work 

elsewhere in the basin have shown the presence of a major regional unconformity between rocks of Late Cretaceous and Tertiary age. The time gap represented by this 

unconformity in the southwestern part of the basin, based on palynomorph studies, is 

from late Campanian or early Maestrichtian to late Paleocene time. The Cretaceous 

rocks beneath the unconformity consist of gray-weathering lenticular sandstone units 

as thick as 30 m and more, separated by gray claystone, gray mudstone, and thin coal 

beds. Lenses of small chert pebbles are scattered throughout the upper 410 m of 

Cretaceous strata underlying the unconformity, but they are most abundant in the 

uppermost 150 m.

The uppermost 50 to 150 m of the section beneath the unconformity crop out in a 

distinctive white color. Petrographic and X-ray mineralogy studies at Hunter Canyon 

in the southwestern part of the basin show that the white color is due to a breakdown 

of feldspar and subsequent accumulation of kaolinite, and it probably marks a 

paleoweathering profile developed during the time interval represented by the unconformity. Paleosoils are locally preserved in the upper few meters as well. If the 

kaolinitic zone is a paleoweathering profile as we believe, however, then it is a secondary characteristic superimposed on whatever rocks were being subjected to surface 

weathering at that time. Rates of erosion during this time interval were probably not 

constant throughout the basin and consequently the presently preserved kaolinitic 

zone is probably not everywhere at the same stratigraphic level.

This kaolinitic, sparsely conglomeratic zone has been called the Ohio Creek 

Conglomerate or the Ohio Creek Formation by previous workers. The presence of conglomerate and the white color, the two features used to define the formation, are independent of each other, however, and need not occur together. We recommend, 

therefore, that the Ohio Creek Formation be reduced in stratigraphic rank to member 

and redefined as the white-colored kaolinitic zone, which may or may not contain 

chert-pebble conglomerate, found at the top of the Hunter Canyon or Mesaverde Formation.
2 CONTRIBUTIONS TO STRATIGRAPHY

INTRODUCTION

This report presents evidence of a major regional unconformity in 

the southwestern Piceance Creek basin between rocks of Cretaceous 

and Tertiary age. The Ohio Creek Formation, previously thought to 

be Tertiary in age, is below this unconformity. The mineralogy of the 

Ohio Creek Formation was profoundly altered by weathering during 

the time interval represented by the unconformity, and its distinctive 

white color was developed at this time; therefore, the Ohio Creek Formation is not a formation in the traditional sense at all, but rather a 

weathered zone superimposed on older rocks. At all localities examined, the palynomorph age of the Ohio Creek Formation was found 

to be indistinguishable from that of the underlying rocks. For these 

reasons, we reduce the stratigraphic rank of the Ohio Creek Formation to that of a member of the underlying formation. In the southwest Piceance Creek basin, the underlying formation is called either 

the Hunter Canyon or Mesaverde.

The Ohio Creek Member was studied in detail in the southwestern 

part of the Piceance Creek basin between Hunter Canyon and DeBeque (fig. 1). This detailed study includes measured sections, 

petrographic and X-ray mineralogy studies, and identification of 

palynomorph assemblages that were extracted from a preliminary 

study of the Upper Cretaceous Mesaverde Group and the Tertiary 

Wasatch and Green River Formations in the southwest Piceance 

Creek basin (Johnson and May, 1978b; Johnson and others, 1979). 

The preliminary study was supplemented by a study of a core from 

the C.E.R. Geonuclear Corp. RB-1 drill hole to the north (fig. 1) and 

by the measurement of two sections of the Ohio Creek Member in the 

southern part of the basin (fig. 1), one from the type locality along 

Ohio Creek and the other from along Muddy Creek about 35 km 

northwest of the type locality. The Cretaceous-Tertiary boundary 

was not examined in the northeastern part of the basin.

HISTORY OF OHIO CREEK NOMENCLATURE

First mention of the unusual white unit found beneath the Wasatch 

Formation (then known as the Ruby beds) was by Hills (1890, 

p. 390-391), who described the unit along Ohio Creek at the extreme 

south end of the Piceance Creek basin and along Coal Ridge, about 

90 km to the north (fig. 1). Of the Coal Ridge area he said: "South of 

the Great Hogback at Coalridge there is an abrupt change in the composition of the sediments previously regarded as Laramie. The firm 

gray sandstones of the coal measures are there succeeded by about 

200 feet of soft white sandstones and yellow clays* * *." Hills
PICEANCE CREEK BASIN, COLORADO

FIGURE 1. Index to mapping and outline of Cretaceous-Tertiary boundary (hachured 

line) in the Piceance Creek basin, Colorado. Sections of the Ohio Creek Member 

are delineated. (FromTweto, 1976.)

described the overlying Wasatch Formation or Ruby beds as 

" * * *about 300 feet of tuffaceous strata, more or less conglomeratic 

and loosely aggregated, but resting on a hard coarse basal conglomerate about 40 feet thick, made up wholly of eruptive debris." Of 

the white unit along Ohio Creek, Hills said: "The strata which appear 

between the Ruby beds and the coal measures on Grand River may be 

represented in the Ruby Peak region by certain friable sandstones 

overlying the Laramie on Ohio Creek which differ from the true 

Laramie sandstones in containing an abundance of chert pebbles, 

sometimes fossiliferous, derived from the erosion of Lower Carboniferous beds."

The name Ohio Creek Formation was first applied to the unit by 

Eldridge (1894) in the Anthracite and Crested Butte Quadrangles 

(fig. 1), of which he said: "This formation consists of about 200 feet of
4 CONTRIBUTIONS TO STRATIGRAPHY

sandstones and conglomerates which rest unconformably on the 

Laramie.* * *The sandstones are gray, weathering buff and red, and 

are made up almost wholly of coarse, loosely agglomerated grains of 

quartz."

Lee (1912, p. 48-49) called the unit the Ohio Creek Conglomerate in 

a report on coal resources in the Grand Mesa-West Elk Mountain 

area (fig. 1). According to Lee, the formation is: "* * * white and contrasts sharply with the overlying Wasatch ("Ruby") Formation, 

which is highly colored. In the Grand Mesa Field, it does not differ 

from the formation as described by Eldridge except that it is thinner, 

and the pebbles are smaller than in the type locality." Lee was the 

first to note a similar "white conglomerate sandstone" near Palisade 

in the area studied in detail in this report. Lee thought that the base 

of his Ohio Creek Conglomerate was unconformable with the underlying Hunter Canyon Formation. Lee provisionally assigned the Ohio 

Creek Conglomerate to the Tertiary on the basis of fossil plants 

found by Gale (1910, p. 79-80) in rocks that Lee assumed occupied a 

similar stratigraphic position.

Erdmann (1934, p. 53-55) described what he believed to be the 

equivalent of Lee's Ohio Creek Conglomerate along the Book Cliffs 

north of Palisade. He described the unit as 155 to 370 ft. thick1 , 

composed of about 38 percent sandstone and 50 percent shale with 

pebbles of gray and black chert occurring in strings and stringers. 

Erdmann stated that, "Because of their white and light gray colors 

and cliff-forming habit, the sandstone beds of this unit are especially 

conspicuous." He described the unit as unconformable with the 

underlying Hunter Canyon Formation and gave a detailed description of a basal conglomerate or conglomeratic sandstone that is present in most places.

Gaskill and Godwin (1963) mapped the Ruby-West Elk Mountain 

area in detail and found conglomeratic lenses far below the base of 

Lee's Ohio Creek Conglomerate, in what Lee had mapped as the 

Mesaverde Formation. After examining the type locality along Ohio 

Creek, they redefined the Ohio Creek Formation in the Ruby-West 

Elk Mountain area to include these lower beds, making the formation 380-430 ft thick. Gaskill and Godwin interpreted the lower 

contact of the redefined formation as gradational, and arbitrarily 

placed the lower contact at the base of the lowest pebbly bed. 

Gaskill (1961) collected leaves identified as Paleocene in age from the 

lower part of the redefined formation about 16 km northwest of the 

type locality. This Paleocene age presented many problems, because 

Gaskill considered the unit to be conformable with the underlying

'Measurements cited from an older report are given in the units of that report; 1 ft=0.3048 m.
PICEANCE CREEK BASIN, COLORADO 5

Mesaverde Formation of known Late Cretaceous age. R. H. Tschudy 

(oral commun., 1978) suggested that most of the leaf identifications 

such as those identified for Gaskill need to be reexamined.

Gaskill and Godwin (1963) measured three sections in the DeBeque 

area, and stated (p. C38): "Reconnaissance examination of scattered 

outcrops along the Grand Hogback and in the DeBeque-Mesa, Colo., 

area has convinced the authors that beds present at each of the 

numbered localities* * *are equivalent in part to the redefined Ohio 

Creek Formation." They later cautioned, however, that the beds 

should be traced along outcrop to the Ruby-West Elk Mountain area 

to be certain. Their graphic sections portray the Ohio Creek Formation as a conglomeratic sandstone 20-60 m thick with an indefinite 

top and base.

Donnell (1961, p. 843), in a report on the northern part of the 

Piceance Creek basin between the Colorado and White Rivers, described the Ohio Creek Conglomerate as "composed mostly of pebbles and cobbles of red and black chert and quartzite, ranging from 

the size of a pea to 4 or 5 inches in diameter. At all exposures examined the cobbles and pebbles are associated with poorly indurated 

coarse-grained white sandstone (pi. 56); at places they occur within 

the white sandstone and at other places in a brown sandstone matrix 

either just above or just below the white sandstone." Donnell assigned a Tertiary age to the Ohio Creek.

Donnell (1961, p. 844) also stated: "The observed range in 

thickness of the conglomerate in the area is from 5 feet at a locality in 

T. 9 S., R. 97 W., to about 20 feet on Highway 64, 3 miles west of 

Meeker." The locality Donnell mentioned in T. 9 S., R. 97 W. is in the 

same area where Gaskill measured a thickness of 20 to 60 m for the 

Ohio Creek Formation. The difference in reported thickness is probably due to the fact that these authors were not describing the same 

unit. This discrepancy is dealt with in the section on DeBeque area 

stratigraphy.

A unit tentatively correlated with the Ohio Creek Formation has 

recently been mapped by several workers in the west and northwest 

parts of the Piceance Creek basin. In the Black Cabin Gulch 

Quadrangle, Cashion (1969) described the formation as "light-gray 

very fine grained ledge-forming sandstone, gray and green mudstone 

and shale; a few lenses of conglomerate,* * *thickness (on outcrop) 

80-300 feet." In the Calf Canyon, Razorback Ridge, and Brushy 

Point Quadrangles, Roehler (1972a, 1972b, 1973) described the formation as "gray very fine to fine grained crossbedded sandstone, 

locally coarse grained and containing thin lenses of conglomerate." 

The thickness in the three quadrangles varies from 0 to 230 ft. Farther north the Ohio Creek Formation was found by Hail (1973, 1974) 

to be discontinuous in the Rough Gulch and Smizer Gulch
6 CONTRIBUTIONS TO STRATIGRAPHY

Quadrangles, where he described it as "light brown to white sandstone, massive to crossbedded locally containing very sparse chert or 

quartzite pebbles. Nonpersistent; cannot be recognized with certainty throughout quadrangle. Maximum thickness about 80 feet." 

All these workers tentatively assigned the Ohio Creek(?) Formation 

to the Tertiary.

TYPE LOCALITY OF THE OHIO CREEK MEMBER OF THE 

MESA VERDE FORMATION

An outcrop of white friable sandstone is found on the east side of 

Ohio Creek about 2V* km north of the junction between Ohio Creek 

and Pass Creek and was first mapped as the Ohio Creek Formation 

by Eldridge (1894). The outcrop is the best exposure of the unit along 

Ohio Creek and was designated as the type locality of the then Ohio 

Creek Formation. At the type locality, the Ohio Creek is a member of 

the Mesaverde Formation. The outcrop consists of two resistant, 

friable white sandstone units, each about 15m thick, separated by a 

covered interval about 40 m thick (fig. 2). The sandstone units are 

medium to coarse grained, containing sparse lenses of pebbles with 

pebbles as much as 3 cm in diameter. The pebbles are chert of various 

colors. The units are generally weakly crossbedded with bed sets as 

much as 1 m high. Clay ripups occur just below the top. The base of 

the lower sandstone outcrop is buried in talus and the base of the 

member cannot be well defined. Therefore, a principal reference section has been chosen at Hunter Canyon, an area with better exposures of the Ohio Creek interval.

The Ohio Creek Member is unconformably overlain at the type 

locality by about 20 m of slope-forming mottled maroon and gray, 

medium- to coarse-grained conglomeratic sandstone of the Wasatch 

Formation. Pebbles are as much as 7 cm in diameter, consist of 

various colors of chert, and make up about 5 to 10 percent of the rock. 

This mottled unit is similar to the basal conglomerate of what 

Eldridge (1894) called the Ruby Formation. The basal conglomerate 

according to Eldridge is "* * *from 20 to 30 feet thick and consists 

mainly of chert and quartz pebbles with a few Archean rocks." The 

rest of the Ruby Formation is described as "red, purple, and green 

sandstones and shales with a few beds of conglomerate made up, for 

the most part, of debris of various eruptive rocks." No rocks suitable 

for palynomorph dating are exposed at the type locality of the Ohio 

Creek Member along Ohio Creek.
PICEANCE CREEK BASIN, COLORADO

UNWEATHERED LITHOLOGY 

COLOR Relative resistance 

to weathering "

GRAIN SIZE 

RANGE

SOME INTERNAL 

CHARACTERISTICS

EXPLANATION

-Coarse sand

- Medium sand

-Fine sand

- Very fine sand

- Med to coarse silt

- Clay to fine silt

Calcareous or dolomitic 

Conglomeratic 

jClaystone or clay shale 

Ripup clasts

jium-scale crossbeds 

^ ~ Subhonzontal laminae 

OO Massive 

Cht Chert pebbles

FIGURE 2. Type locality of the Ohio Creek Member of the Mesaverde Formation at 

Ohio Creek. Vertical scale: 1 cm=13.2 m.

HUNTER CANYON AREA STRATIGRAPHY

The Cretaceous-Tertiary boundary was determined in the Hunter 

Canyon area on the basis of palynomorphs. (See section, 

"Palynomorph results.") The uppermost 300 m of Upper Cretaceous 

rocks in the Hunter Canyon area consists of about 75 percent 

medium- to coarse-grained sandstone units interbedded with about 

25 percent gray carbonaceous shale and some nonpersistent coal 

(fig. 3). The sandstone units are as much as 30 m thick, are fairly persistent laterally though irregular in thickness, and generally display 

well-developed later accretion units typical of point bar deposits of 

meandering streams (Bernard and others, 1970). Each accretion unit 

consists internally of alternating zones of ripup clasts, trough 

crossbeds, and even, parallel laminae. Drift ripple laminae, also
CONTRIBUTIONS TO STRATIGRAPHY

Sample Unweathered Grain size Some internal 

No. color Lithology range characteristics

77-101- 

77-100- 

77-99 

FIGURE 3. Upper part of Cretaceous section at Hunter Canyon (from Johnson and 

mineralogy and fossil content: solid circle, major constituent; open circle,
PICEANCE CREEK BASIN, COLORADO

EXPLANATION

Relative resistance

to weathering \ Npnpersistent

Sample 

/number 

RJ-77-109 I

5 BuJlf" 1 ' 

If Light 1 %t Medium 

>. L Dark 

' Small pebbles 

' Coarse sand 

' Medium sand 

 Fine sand 

Very fine sand 

Med. to coarse

silt 

Clay to fine silt

Sandstone

r ~ nSiltstone

j Claystone or clay shale

Coal

I-H1". I Calcareous or dolomitic 

L e0«' e I Conglomeratic 

[ JT ~\ Carbonaceous or woody material 

I »T > I R'Pup clasts 

f\\Vj Lateral accretion in sandstone

Ripups oriented along accretion partings 

fs> Claystone clasts cobble size

Limestone pebbles 

Chert pebbles 

Limestone concretion 

Bedding features shown are cyclic 

A Fossil wood 

A Root casts 

JA! Contorted laminae 

=* Climbing ripples 

~-^ Ripples nonspecific 

M/SS Medium-scale crossbeds (0.3-1 m) 

V\\v-xv Small-scale crossbeds (<0.3 m) 

~ Subhorizontal laminae

 Parallel laminae, nondistinct 

 Parallel laminae 

XX Massive

others, 1979). See figure 10 for location. Mineralogy from bulk X-ray analysis. For 

minor constituent; queried where indefinite. Vertical Scale: 1 cm.= 24m.
10 CONTRIBUTIONS TO STRATIGRAPHY

; c - '

' iS^S^ 'f* ^3K<i*:®^--?

gW**s' .H^.-'.y'V- '^V;Jj|kS^'**?* ''' " ^«^3C-V-

: ^ '* " *^ "

FIGURE 4. View of Cretaceous-Tertiary unconformity in Hunter Canyon area (arrow). 

Brackets show approximate limits of kaolinitic zone.

characteristic of point bar deposits, are present only locally. Some of 

the thicker units, however, have no obvious accretion features and 

consist mostly of crosscutting sets of trough crossbeds. Pebbles of 

dark chert, silicified limestone, and laminated silicified siltstone first 

occur about 115 m below the top. In accretion units, the pebbles are 

in the basal scoured zone. In the sandstone bodies without accretion 

units, the pebbles are in scattered lenses. The pebbles constitute less 

than 5 percent of the sandstone bodies. The contact between the 

nonpebbly part of the Cretaceous section and the overlying pebbly 

part is gradational. The position of the lowest occurrence of pebbles 

varies considerably over short distances and does not constitute a 

mappable contact.

The Cretaceous rocks are separated from the overlying Paleocene 

Atwell Gulch Member of the Wasatch Formation by a major regional 

unconformity. A well-developed paleoweathering profile is found 

beneath the unconformity surface at Hunter Canyon, which gives 

sandstone units in the upper 70 to 90 m of the underlying Upper 

Cretaceous rocks a distinctive white color (fig. 4). Some irregular 

zones of secondary oxidation are also present.

The white color is caused by breakdown of feldspars and the consequent development of abundant kaolinite. Plagioclase is almost 

completely destroyed to a depth of about 60 m below the unconformity and potassium feldspar to a depth of about 6 m. This weathering is
PICEANCE CREEK BASIN, COLORADO 11

FIGURE 5. Closeup of the top of the Ohio Creek Member near Hunter Canyon. 

Massive zone in foreground is thought to be a paleosoil. Note man in upper right 

for scale. View northward in SE1/4SE1/4 sec. 34, T. 8 S., R. 100 W.
12 CONTRIBUTIONS TO STRATIGRAPHY

FIGURE 6. Photomicrograph of highly altered sandstone from Ohio Creek Member of 

Hunter Canyon Formation. Photo is of sample locality 77-134 (fig. 3).

extreme in the upper 6 m (fig. 5), where kaolinite makes up as much as 

60 percent of the rock and all original bedding has been destroyed. A 

thin section of a sample from this zone (fig. 6) revealed only kaolinite, 

coarse-grained quartz, and chert. Vertical root casts extend 

downward from the unconformity for a distance of about 2 m (fig. 7). 

This 6-m-thick, intensely weathered sequence beneath the unconformity is almost certainly a paleosoil zone.

Very little relief on the unconformity surface is evident in the 

Hunter Canyon area; however, the thickness of the white zone and 

paleosoil varies widely, and the paleosoil is locally absent.

Cementing agents typical of the underlying Upper Cretaceous 

rocks are also absent beneath the unconformity and apparently have 

been removed by leaching. Carbonate cement is absent to a depth of 

170 m below the unconformity and analcite cement to a depth of 

120m.

The description of this weathered zone is very similar to the 

description Erdmann (1934) gave for his Tertiary(?) sandstone in the 

Hunter Canyon area, which he correlated with the Ohio Creek Formation. The two units are probably largely the same; however, Erdmann 

described an unconformity at the base of his Tertiary(?) sandstone 

overlain by conglomerates. These features could not be located in our 

study area. The unit is largely fluvial, and many channeled surfaces
PICEANCE CREEK BASIN, COLORADO 13

FIGURE 7. Root zone at top of Upper Cretaceous rocks (sec. 34, T. 8 S., R. 100 W.).

of limited extent occur; it is possible Erdmann was using one or more 

of these surfaces as his base. Also, in the detailed section at Hunter 

Canyon, the lowermost occurrence of conglomerate is about 25 m 

below the lowermost noticeable kaolinite accumulation, and it is 

unclear which criteria Erdmann was using to define his unit.

OHIO CREEK MEMBER PRINCIPAL REFERENCE SECTION

The Hunter Canyon section is designated as the principal reference 

section for the Ohio Creek Member because the unit is much better 

exposed here than at its original type locality along Ohio Creek. The 

top of the member is defined as the unconformity, and the base is 

defined as the base of the lowest white sandstone. At Hunter Canyon, 

the Ohio Creek Member is a member of the Hunter Canyon Formation. Erdmann (1934) excluded the rocks now known as the Ohio 

Creek Member from the original definition of the Hunter Canyon Formation, and we therefore redefine the Hunter Canyon Formation to 

include these rocks.

Overlying the unconformity at Hunter Canyon in the Atwell Gulch 

Member of the Wasatch Formation is a black carbonaceous claystone 

unit about 50 m thick that contains thin coal zones. This unit forms a 

conspicuous dark-gray band on outcrop and can be traced eastward 

from Hunter Canyon into the DeBeque area.
14 CONTRIBUTIONS TO STRATIGRAPHY 

DEBEQUE AREA STRATIGRAPHY

Because of the conspicuous white kaolinitized zone (Ohio Creek 

Member of Hunter Canyon Formation) just beneath it (fig. 8), the unconformity was easily traced by aerial photos and on the ground from 

Hunter Canyon into the DeBeque area where Donnell (1961) and 

Gaskill and Godwin (1963) assigned conglomeratic units to the Ohio 

Creek Formation. The dark-gray carbonaceous claystone zone that 

lies just above the unconformity at Hunter Canyon is 85 m above the 

unconformity at the west end of Horse Thief Mountain (figs. 9, 10), 

just south of DeBeque. Some of this disparity may be due to a lateral 

facies change, but much of it is probably due to onlap on the unconformity surface. Deposition began in the DeBeque area while the 

Hunter Canyon area was still a relative upland subject to some erosion. The 85 m of section below the black claystone sequence at DeBeque but not found at Hunter Canyon consists of variegated 

mudstone and claystone with a few small lenticular sandstone bodies 

and a basal conglomeratic sandstone about 15 m thick. Pebbles compose as much as 40 percent of the basal conglomeratic sandstone and 

consist of varicolored chert and red and gray sandstone. This suite of 

pebbles is more variable in composition than the suite in the pebbly 

part of the underlying Cretaceous section. Some of the clasts attain a 

diameter of 20 cm or more. The upper 60 to 90 m of the Cretaceous 

section contain widely scattered lenses of pebbles at DeBeque and are 

similar in character to the unit at Hunter Canyon.

Thickness of the white kaolinitized Ohio Creek Member in the 

DeBeque area is highly variable but locally is at least 70 m. The upper part of the member is locally oxidized red, but no obvious 

paleosoil is present. Almost no relief has been detected on the unconformity surface except where it is locally channeled. A small channel 

filled with conglomerate is found on the unconformity surface in 

SE J/4 SE '/4 sec. 22, T. 9 S., R. 97 W. (fig. 11). The channel fill is about 

3 m thick, 10 m wide, and of indeterminate length; it is composed of 

as much as 70 percent conglomerate. Pebbles of the conglomerate are 

as much as 4 cm in diameter and are similar in composition to pebbles 

in the overlying basal conglomeratic sandstone of the Atwell Gulch 

Member of the Wasatch Formation. The channel deposit, however, is 

white colored, like the upper part of the underlying Cretaceous section. No concentration of pebbles such as this has been observed 

within the underlying Cretaceous section itself. These pebbles may 

have been deposited by a stream flowing across the unconformity 

surface shortly before basin sedimentation began in the area. Such 

deposits could have been preserved by being rapidly buried beneath 

basin sediments.
PICEANCE CREEK BASIN, COLORADO 15

FIGURE 8. View of Cretaceous-Tertiary unconformity (dashed line) taken along 

DeBeque cutoff road south of DeBeque.

Donnell's description (1961, p. 843) of the Ohio Creek Formation in 

the DeBeque area closely fits the description of the Tertiary basal 

conglomerate of the Atwell Gulch Member of the Wasatch Formation. However, he described the pebbles as being "within the white 

sandstone and at places in a brown sandstone matrix either just 

above or just below the white sandstone." The mention of white sandstone suggests that he may have locally included some of the 

underlying Cretaceous section or conglomeratic channels on the unconformity surface. The unit that Gaskill and Godwin (1963) assigned to the Ohio Creek Formation in the DeBeque area is very 

similar to the white kaolinitized zone or Ohio Creek Member of this 

report at the top of the Cretaceous section. The indefinite base they 

showed for the unit is understandable because both the thickness of 

the white zone and the position of the lowest occurrence of chert pebbles, the other characteristic formerly used to define the Ohio Creek 

Member, vary laterally.

MUDDY CREEK SECTION

The Ohio Creek Formation (Ohio Creek Member of this report) was 

mapped by Godwin (1968) along East Muddy Creek south of McClure
16 CONTRIBUTIONS TO STRATIGRAPHY

'«'Mi

CD
PICEANCE CREEK BASIN, COLORADO

108°30' 108°15'

17

FIGURE 10. Locations of measured sections and palynomorph samples.

Pass (fig. 1). Godwin divided the unit into three parts. The upper and 

lower parts are described briefly as light-gray or white conglomeratic 

sandstone. The middle part is described as interbedded sandstone, 

siltstone, and shale with some thin coal lenses. The total thickness is 

440 ft (135 m). For this study, a section was measured of the upper 48 

m of Ohio Creek Member (of Mesaverde Formation) where it is exposed about 2.9 km north of the junction of East and West Muddy 

Creeks and 3.5 km south of Gaskill and Godwin's (1963) measured 

section 3. The lower 18 m of section consist of very fine to mediumgrained gray sandstone interlayered with olive-green mudstone and 

gray to dark-gray carbonaceous mudstone (fig. 12). Sandstone units 

contain near horizontal and trough crossbeds with crossbed sets as 

thick as 1 m. The upper 33 m of the Ohio Creek Member is cliffforming, light-gray- to white-weathering, medium- to coarse-grained 

sandstone with abundant clay ripups. Sparse lenses of gray and tan 

chert pebbles as much as 3 cm in diameter occur in the upper 10 m. 

Trough crossbeds are abundant, and the sets vary in thickness from 

V3 to 1 m in the lower part of this white zone to almost 3 m in the 

upper part.
18 CONTRIBUTIONS TO STRATIGRAPHY

FIGURE 11. Conglomeratic channel at unconformity near DeBeque. Hammer for

scale.

The overlying Wasatch Formation consists mostly of poorly exposed nonresistant maroon, purple, and olive-green mudstone and 

sandstone. A conglomeratic sandstone unit \Vz m thick is found 9 m 

above the base of the Wasatch and contains as much as 50 percent 

pebbles of gray chert and possibly gray quartzite of at least 10 cm in 

diameter.

C.E.R. GEONUCLEAR CORPORATION DRILL HOLE

The C.E.R. Geonuclear RB-1 drill hole was drilled for project Rio 

Blanco, which was an attempt to stimulate natural gas production by 

fracturing tight reservoirs with nuclear devices. The hole was drilled 

to a depth of 7,800 ft (2,400 m) or approximately 2,200 ft (675 m) into 

the Hunter Canyon Formation. The Cretaceous-Tertiary boundary is 

picked at the abrupt change in electric log character (fig. 13) that corresponds to a lithologic change from predominant thick sandstone 

units of Cretaceous age to predominant mudstones and claystones of 

Tertiary age. This contact is easily traced from surface exposures in 

the DeBeque area to the vicinity of the RB-1 hole (Johnson, 1978) 

through the use of electric log correlations. Five intervals were cored. 

The highest core starts at 5,710 ft (1,750 m) or about 110 ft (34 m) 

below the Cretaceous-Tertiary boundary, and the lowest ends at 

7,752 ft (2,360 m). Because only a few intervals were cored, the base
PICEANCE CREEK BASIN, COLORADO 19

Relative resisUNWEATHERED tance to GRAIN SIZE 

COLOR weathering LITHOLOGY RANGE

EXPLANATION

SOME INTERNAL 

CHARACTERISTICS

VVVVV

vvvvv

Small pebbles 

Coarse sand 

Medium sand 

Fine sand 

Very fine sand 

Med. to coarse silt 

Clay to fine silt

Sandstone

 JGIaystone or clay shale 

jCalcareous or dolomitic

Conglomeratic

] Carbonaceous or 

woody material

|%»""^ iRipupclasts

^ICIaystone ciasts-cobble size

Medium-scale crossbeds 

nail-scale crossbeds 

Contorted laminae 

= Subhonzontal laminae 

XX Massive 

Chf Chert pebbles

FIGURE 12. Measured section at Muddy Creek. Vertical scale: 1 cm=12.4 m.

of the Ohio Creek cannot be determined. Chert and quartzite pebbles 

are found between 5,720 ft and 5,730 ft (1,750 m and 1,753 m), 5,860 

ft and 5,890 ft (1,790 m and 1,800 m), and at about 6,940 ft (2,120 m). 

The lowest pebbles are about 1,340 ft (410 m) below the unconformity. This indicates that chert pebbles can occur much lower in section 

than previously thought.

PALYNOMORPH RESULTS 

HUNTER CANYON

Thirteen samples collected in the upper 300 m of section beneath 

the unconformity at Hunter Canyon yielded pollen (fig. 2). 

Seven samples from the section beneath the lowest white sand-
20 CONTRIBUTIONS TO STRATIGRAPHY

CER GEONUCLEAR

No. RB 01

Sec. 14, T. 3S., R. 98 W. 

KB 6643

DEPTH CORED DEPTH

FEET INTERVAL METERS

520^ SP "ESISTIVITY

h-1600

Tertiary 

/Cretaceous

FIGURE 13. Log profile and cored conglomerate 

zones, C.E.R. Geonuclear drill hole; cored intervals shown by bar on vertical scale. Small 

circles indicate chert-pebble conglomerate. 

Sec. 14, T. 3 S., R. 98 W.
PICEANCE CREEK BASIN, COLORADO 21

stone, or more than 85 m below the top, yielded the following pollen 

diagnostic of Cretaceous age:

Proteacidites Turonian to Maestrichtian

Cranwellia early Campanian to Maestrichtian

Loranthacites sp. (C3RT48 Denver USGS Ident.) early Campanian to probably

early Maestrichtian

Tricolpites reticulatus early Campanian to probably early Maestrichtian 

Kuylisporites scutatus early Campanian to probably early Maestrichtian.

The range for Proteacidites is generally accepted to be Turonian to 

Maestrichtian, and the range of Cranwellia has been determined by 

examining the reference collections of the U.S. Geological Survey, 

Denver, Colo.

These results suggest an early Campanian to early Maestrichtian 

age for the Cretaceous section below the Ohio Creek Member; 

however, a late Campanian baculite was found in the Sego Sandstone 

at Hunter Canyon (Gill and Hail, 1975), which is stratigraphically 

lower than the Hunter Canyon Formation. This would further 

restrict its age to late Campanian to early Maestrichtian.

Two pollen-bearing samples from the white kaolinitic Ohio Creek 

Member at Hunter Canyon indicate the same age as the underlying 

part of the Hunter Canyon Formation. Forms identified include Proteacidites, Cranwellia, Loranthacites (C3RT48), and Tricolpites 

reticulatus. The base of the white kaolinitic zone is about 85 m below 

the unconformity and about 25 m above the lowest pebbly zone 

observed. A late Maestrichtian (Hell Creek) age for this white unit 

reported by the authors in an earlier publication (Johnson and May, 

1978a) was based on incomplete palynomorph studies.

DEBEQUE AREA

One sample (77-34a), collected from beneath a 3-cm-thick bed 

about 30 m below the top of the white kaolinitic zone or Ohio Creek 

Member south of DeBeque (fig. 10), yielded the following palynomorphs: Maceopolipollenites, Proteacidites, Liliacidites, and Loranthacites (C3RT48). Loranthacites (C3RT48) indicates a late Campanian to early Maestrichtian age, the same as the white kaolinitic 

unit at Hunter Canyon.

Eight samples from the Atwell Gulch Member of the Wasatch Formation yielded palynomorphs. Five of these are from the measured 

sections in the stratigraphic diagram shown on figure 9, and their 

positions are shown on the diagram. Samples numbered 76-2a, 76-3, 

and 77-4 were collected from outcrops near the measured sections 

and are projected into the plane of the cross section. The locations of 

the measured sections and of samples 76-2a, 76-3, and 77-4 are 

shown on figure 9. The palynomorph assemblages are listed on figure
22 CONTRIBUTIONS TO STRATIGRAPHY

FIGURE 14. List of palynomorphs identified from samples collected from above the 

Cretaceous-Tertiary unconformity. Samples are listed in approximate 

stratigraphic sequence. All samples carbonaceous shale except No. 77-16, gray, 

silty claystone.

14 in approximate stratigraphic order. Age-diagnostic pollens 

recovered from this interval are:

Maceopolipollenites amplus

Carya

Maceopolipollenites triorbicularis

Pis tillipollenites

Sy mplocoipolleni tes

Tricolpites anguloluminosus

Symplocospollenites

Paraalnipollenites

late Paleocene

late Paleocene to Oligocene

middle Paleocene to middle Eocene(?)

late Paleocene to middle Eocene

late Paleocene(?) to middle Eocene

Paleocene

late Paleocene to middle Eocene

Maestrichtian to Paleocene

The ranges of Symplocospollenites and Symplocoipollenites have 

been determined through examination of reference collections of the 

U.S. Geological Survey, Denver (R. H. Tschudy, oral commun., 

March 1978). The ranges of M. amplus,-M. triorbicularis (with exception of its middle Eocene occurrence; see Green River discussion, 

Johnson and May, 1978b), and T. anguloluminosus are published in 

Leffingwell (1966). The ranges of Carya and Pistillipollenites are 

reported in Leopold and MacGinitie (1972), and the range of 

Paraalnipollenites is reported in Hills and Wallace (1969). Thus, the 

age of the Atwell Gulch Member of the Wasatch Formation is suggested to be late Paleocene.

One sample, No. 77-4, was collected just south of DeBeque from 

the basal conglomerate of the Atwell Gulch Member, about 11 m 

above the unconformity. Only one species, Symplocoipollenites, was 

recovered from this sample. The accepted range for this species is late 

Paleocene to middle Eocene. Inasmuch as late Paleocene pollen was 

collected stratigraphically above the sample, its age must also be late 

Paleocene.
PICEANCE CREEK BASIN, COLORADO 23 

MUDDY CREEK SECTION

Eight samples from the Muddy Creek section were processed and 

examined for palynomorphs; only three yielded pollen and (or) spores. 

Two samples (Nos. RJ78-4a and RJ78-4e) are from the Ohio Creek 

Member of the Mesaverde Formation, and one sample (RJ78-4m) is 

from a partially oxidized zone thought to be Wasatch Formation, 

about 3 m above the top of the highest white sandstone of the Ohio 

Creek.

The two Ohio Creek Member samples appear to be of Cretaceous 

age, yielding Stereisporites (Late Cretaceous to Holocene), 

Araucariacites (Cenomanian through Maestrichtian), and 

Balmeisporites (Campanian through Maestrichtian) (R. H. Tschudy, 

oral cominun., 1979). No pollens indicative of a Tertiary age were 

observed.

The single sample thought to be Wasatch Formation also yielded 

an assemblage of Cretaceous appearance, including Stereisporites 

(Late Cretaceous to Holocene) and Aquilapollenites senonicus 

(Campanian-Maestrichtian) (Tschudy and Leopold, 1970), plus a few 

nondiagnostic pollen and spores. No pollens characteristic of 

Paleocene or younger age were observed. The Cretaceous age for this 

sample suggests that the unconformity is somewhat above the top of 

the highest white sandstone at Muddy Creek.

DISCUSSION

The stratigraphic sequence found near the Cretaceous-Tertiary 

boundary throughout the southwestern part of the Piceance Creek 

basin has certain characteristic features. The gray-weathering largely fluvial sandstones and mudstones of the Hunter Canyon or 

Mesaverde Formation of Late Cretaceous age are overlain by about 

50 to 150 m of Upper Cretaceous fluvial rocks that are white or light 

buff colored on outcrop but are otherwise similar to the underlying 

strata. The white rocks are in turn overlain by Paleocene variegated 

rocks of the Wasatch Formation. Scattered lenses of small chert pebbles are sometimes found in the Cretaceous rocks, whereas large concentrations of pebbles and cobbles are commonly found at the base of 

the overlying Wasatch Formation. Because of the distinctive color 

and the presence of chert pebbles, the white zone (Ohio Creek 

Member of this report) has been considered a separate unit by 

numerous stratigraphers and has been named the Ohio Creek Formation or Ohio Creek Conglomerate. The conglomerates overlying the 

Ohio Creek are usually included in the basal part of the Wasatch Formation; however, some workers have mistakenly called these conglomerates Ohio Creek Formation or Ohio Creek Conglomerate.
24 CONTRIBUTIONS TO STRATIGRAPHY

Basal conglomerate of 

Wasatch Formation

 Unconformity

Kaolinitic unit

(Ohio Creek Member)

Hunter Canyon or 

Mesaverde Formation

FIGURE 15. Possible stratigraphic relationships of the Ohio Creek Member.

Palynomorph studies in the Hunter Canyon, DeBeque, and Muddy 

Creek areas have shown that a major unconformity occurs at the top 

of the Ohio Creek, whereas no detectable time gap occurs at its base. 

This finding is in conflict with the fossil leaf data reported by Gaskill 

and Godwin (1963) from 16 km northwest of the type locality, which 

date the Ohio Creek as Paleocene the same age as the lower part of 

the overlying Wasatch Formation. However, R. H. Tschudy (oral 

commun., 1978) has said that early leaf identifications such as these 

are no longer considered reliable. We will tentatively assume that 

this Paleocene age is in error.

At Hunter Canyon, the white color of the Ohio Creek is due largely 

to a buildup of kaolinite and is only one of several mineralogical 

changes that occur in the rocks beneath the disconformity surface. 

Some of these changes, such as the loss of carbonate cement, extend 

beneath the kaolinitic zone in the underlying rocks as well. The most 

logical explanation for these changes is that they are products of intense weathering that took place during the time represented by the 

unconformity. Locally preserved paleosoils at the top of the white 

zone would also support this hypothesis.
PICEANCE CREEK BASIN, COLORADO 25

If this hypothesis is true, then the white color, a primary 

characteristic used to define the Ohio Creek Formation of former 

usage, was not present when the rock was originally deposited. The 

potential problems that this presents are outlined on figure 15. If the 

kaolinite zone was formed by intense weathering during the time interval represented by the unconformity, then the zone would not 

necessarily be in the same stratigraphic position everywhere. The 

weathered zone would occur stratigraphically lower in areas with 

rapid erosion rates than in areas with slow erosion rates. The only requirement needed to preserve a kaolinite zone would be that the rate 

of formation of the kaolinitic zone at the end of the time interval 

represented by the unconformity was faster than the rate of erosion.

The presence of chert pebbles, the other characteristic most 

workers used to define the Ohio Creek, is problematical as well. 

Chert-pebble lenses occur 25 m below the base of the white zone at 

Hunter Canyon. Core from the C.E.R. Geonuclear drill hole has 

shown that scattered lenses of chert pebbles can occur anywhere in at 

least the upper 410 m of the Upper Cretaceous section. The density of 

chert pebbles is so low that it is possible that people working with 

outcrops have overlooked them. The upper part of the Cretaceous section as a whole is a monotonous sequence of discontinuous sandstones that is generally passed over quickly by workers in the field, 

whereas the white kaolinitic zone has drawn the attention of many 

workers. This may explain why pebble occurrences are better 

documented here. Figure 15 shows that it is possible that the unconformity surface could intersect several different chert-pebble zones in 

the Hunter Canyon Formation.

The Ohio Creek Member cannot be defined everywhere as both 

white in color and chert pebbly, because the two features are 

unrelated and need not occur together. If the presence of a few chert 

pebbles is chosen as the defining characteristic, then, at localities 

such as the C.E.R. Geonuclear drill hole, the member would be at 

least 410 m thick. We feel that this is not the intent of previous 

workers.

It seems, therefore, that if we are to define the unit on the basis of 

one of these two characteristics, we must select its white color. This, 

too, presents problems, for if the Ohio Creek Member is defined as a 

white unit found at the top of the Hunter Canyon or Mesaverde Formation, then it is defined on the basis of a secondary characteristic 

that was overprinted on rocks of varying stratigraphic position after 

deposition. This is somewhat analogous to mapping metamorphic 

facies. A map of the white zone would show variations in thickness of 

the kaolinite accumulation, which may tell something about conditions during the time interval represented by the disconformity. The
26 CONTRIBUTIONS TO STRATIGRAPHY

thickest accumulations of kaolinite may outline areas where the rate 

of erosion was the slowest.

We recommend that the Ohio Creek Formation be reduced in rank 

to Ohio Creek Member of the Hunter Canyon or Mesaverde Formation, and be redefined as the light-gray or white kaolinitic unit of Late 

Cretaceous age found at the top of the Hunter Canyon or Mesaverde 

Formation in the south and southwest parts of the Piceance Creek 

basin. The redefined Ohio Creek may or may not contain sparse zones 

or lenses of chert pebbles, is truncated at the top by a regional unconformity, will usually have a gradational base, and is probably not 

everywhere at the same stratigraphic position.

REFERENCES CITED

Bernard, H. A., Major, C. F., Jr., Parrott, B. S., and LeBlanc, R. J., Jr., 1970, Recent 

sediments of southeast Texas A field guide to the Brazos alluvial and deltaic 

plains and Galveston Barrier Island complex: The University of Texas at Austin, 

Bureau of Economic Geology, Guidebook 11, p. 1-16.

Cashion, W. B., 1969, Geologic map of the Black Cabin Gulch Quadrangle, Rio Blanco 

County, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ-812.

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, p. 835-891.

Eldridge, G. H., 1894, Anthracite-Crested Butte Folio 9: U.S. Geological Survey 

Geologic Atlas of the United States.

Erdmann, C. E., 1934, The Book Cliff coal field in Garfield and Mesa Counties, Colorado: U.S. Geological Survey Bulletin 851,150 p.

Gale, H. S., 1910, Coal fields of northwestern Colorado and northeastern Utah: U.S.

Geological Survey Bulletin 415, 265 p.

Gaskill, D. L., 1961, Age of the Ohio Creek conglomerate, Gunnison County, Colorado, in Short papers in the geologic and hydrologic sciences, Art. 96: U.S. 

Geological Survey Professional Paper 424-B, p. B230-B231.

Gaskill, D. L., and Godwin, L. H., 1963, Redefinition and correlation of the Ohio Creek 

Formation (Paleocene) in west-central Colorado: U.S. Geological Survey Professional Paper 475-C, p. C35-C38.

___1966, Geologic map of the Marcellina Mountain Quadrangle, Gunnison County, 

Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ-511.

Gaskill, D. L., Godwin, L. H., and Mutschler, F. E., 1967, Geologic map of the Oh-BeJoyful Quadrangle, Gunnison County, Colorado: U.S. Geological Survey Geologic 

Quadrangle Map GQ-578.

Gill, J. R., and Hail, W. J., Jr., 1975, Stratigraphic sections across the Upper 

Cretaceous Mancos Shale-Mesaverde Group boundary, eastern Utah and western 

Colorado: U.S. Geological Survey Oil and Gas Investigations Chart OC-68.

Godwin, L. H., 1968, Geologic map of the Chair Mountain Quadrangle, Gunnison and 

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

GQ-704.

Hail, W. J., Jr., 1973, Geologic map of the Smizer Gulch Quadrangle, Rio Blanco and 

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

GQ-1131.

___1974, Geologic map of the Rough Gulch Quadrangle, Rio Blanco and Moffat 

Counties, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ-1195.
PICEANCE CREEK BASIN, COLORADO 27

Hills, L. V., and Wallace, S., 1969, Paraalnipollenites, a new form genus from uppermost Cretaceous and Paleocene rocks of Arctic Canada and Russia: Geological 

Survey of Canada Bulletin 182, p. 139-145.

Hills, R. C., 1890, Orographic and structural features of Rocky Mountain geology: 

Colorado Scientific Society Proceedings, v. 3, p. 362-458.

Johnson, R. C., 1978, Cross section showing depositional environments and 

lithologies of some Upper Cretaceous and Tertiary rocks from DeBeque to the 

north central Piceance Creek basin, Colorado: U.S. Geological Survey Open-File 

Report 78-182.

Johnson, R. C., and May, Fred, 1978a, Maestrichtian conglomerates in the 

southwestern Piceance Creek basin [abs.]: American Association of Petroleum 

Geologists-Society of Economic Paleontologists and Mineralogists Annual 

Meeting, 27th, Rocky Mountain Section, p. 28.

___1978b, Preliminary stratigraphic studies of the Mesaverde Group, the Wasatch 

Formation, and the lower part of the, Green River Formation, DeBeque area, Colorado, including environments of deposition and investigations of palynomorph 

assemblages: U.S. Geological Survey Miscellaneous Field Studies Map MF-1050.

Johnson, R. C., May, Fred, Hansley, Paula, Pitman, J. K., and Fouch, T. D., 1980, 

Detailed measured section of the Mesaverde Group, Hunter Canyon area, 

western Colorado, including petrography, X-ray mineralogy, and palynomorph 

assemblages: U.S. Geological Survey Oil and Gas Chart OC-91.

Leopold, E. B., and MacGinitie, H. D., 1972, Development and affinities of Tertiary 

floras in the Rocky Mountains, in Graham, A., ed., Floristics and paleofloristics 

of Asia and eastern North America: Amsterdam, Elsevier, p. 147-200.

Lee, W. T., 1912, Coal fields of Grand Mesa and the West Elk Mountains, Colorado: 

U.S. Geological Survey Bulletin 510, 237 p.

Leffingwell, H. A., 1966, Palynology of the Lance (Late Cretaceous) and Fort Union 

(Paleocene) Formations of the type Lance area, Wyoming: Geological Society of 

America Special Paper 127, p. 1-64.

Roehler, H. W., 1972a, Geologic map of the Brushy Point Quadrangle, Rio Blanco and 

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

GQ-1018.

___1972b, Geologic map of the Razorback Ridge Quadrangle, Rio Blanco and 

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

GQ-1019. 

_1973, Geologic map of the Calf Canyon Quadrangle, Garfield County, Colorado:

U.S. Geological Survey Geologic Quadrangle Map GQ-1086. 

Tschudy, B. D., and Leopold, E. B., 1970, Aquilapollenites (Rouse) Funkhouserselected Rocky Mountain taxa and their stratigraphic ranges: Geological Society of 

America Special Paper 127, p. 113-167. 

Tweto, O. L., 1976, Preliminary geologic map of Colorado: U.S. Geological Survey

Miscellaneous Field Studies Map MF-788.

IS GOVERNMENT PRINTING OFFICE 198O 577-129/1O