Precambrian to Earliest Mississippian Stratigraphy, 

Geologic History, and Paleogeography of 

Northwestern Colorado and West-Central Colorado

Prepared in cooperation with the 

Colorado Geological Survey

U.S. GEOLOGICAL SURVEY BULLETIN 1 787-U
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Chapter U

Precambrian to Earliest Mississippian 

Stratigraphy, Geologic History, and 

Paleogeography of Northwestern 

Colorado and West-Central Colorado

By JAMES M. SOULE

Prepared in cooperation with the Colorado Geological Survey

A multidisciplinary approach to research studies of sedimentary 

rocks and their constituents and the evolution of sedimentary 

basins, both ancient and modern

U.S. GEOLOGICAL SURVEY BULLETIN 1787

EVOLUTION OF SEDIMENTARY BASINS UINTA AND PICEANCE BASINS
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government

UNITED STATES GOVERNMENT PRINTING OFFICE: 1992

For sale by

Book and Open-File Report Sales 

U.S. Geological Survey 

Federal Center, Box 25286 

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

Soule, James M.

Precambrian to earliest Mississippian stratigraphy, geologic history, and 

paleogeography of northwestern Colorado and west-central Colorado / by 

James M. Soule.

p. cm. (Evolution of sedimentary basins Uinta and Piceance basins ; 

ch. U) (U.S. Geological Survey bulletin ; 1787)

"Prepared in cooperation with the Colorado Geological Survey."

Includes bibliographical references.

1. Geology, Stratigraphic Paleozoic. 2. Paleogeography Paleozoic. 

3. Geology Colorado. I. Colorado Geological Survey. II. Title. 

III. Series. IV. Series: U.S. Geological Survey bulletin ; 1787. 

QE75.B9 no. 1787-U 

[QE654] 

557.3 s dc20

[551.7'2] 91-18607

CIP
CONTENTS

Abstract Ul

Introduction Ul

Early Paleozoic tectonic elements Ul

Uinta aulacogen U2

Gore fracture zone U2

Uncompahgre fracture zone U2

White River uplift and ancestral Axial fault zone U2

Northeast-trending faults U3 

Precambrian sedimentary rocks U4

Red Creek Quartzite U4

Uinta Mountain Group U4 

Lowermost Upper Cambrian to uppermost Cambrian rocks US

Lodore Formation US

Sawatch Quartzite US

Peerless Formation and unnamed overlying rocks U8

Dotsero Formation U9

Glenwood Canyon Member U9 

Clinetop Member U9 

Ordovician rocks U10

Manitou Formation U10

Dead Horse Conglomerate Member U10 

Tie Gulch Dolomite Member U10

Harding Sandstone Ull

Fremont Limestone Ull 

Silurian rocks U13 

Devonian and Mississippian rocks U13

Parting Formation U14

Dyer Dolomite U15

Broken Rib Member U15 

Coffee Pot Member U15

Oilman Sandstone U15

Devonian Lodore(?) Formation U16 

Conclusions U17 

References cited U17 

Appendix 1 Measured sections U22

Appendix 2 Oil and gas wells and test bores that penetrate Devonian and older rocks, 

northwestern Colorado U34

FIGURES

1. Map of western Colorado showing study area U2

2. Chart showing Precambrian and lower Paleozoic sedimentary rocks in 

northwestern Colorado U3

Contents III
3-5. Maps showing:

3. Tectonic elements of study area U4

4. Areas and locations discussed in text U4

5. Paleogeography of northwestern Colorado from about 1,400 Ma to the

Late Cambrian U6 

6-10. Photographs showing:

6. Contact between Sawatch Quartzite and Precambrian rocks U7

7. Crossbedded sandstone interbedded with quartzite near base of Sawatch 

Quartzite U7

8. Massive orthoquartzite immediately below Glenwood Canyon Member of 

the Dotsero Formation U9

9. Silty and sandy dolomite and dolomitic sandstone of Glenwood Canyon 

Member of the Dotsero Formation U9

10. Contact between Manitou and Parting Formations Ull

11. Maps showing paleogeography of northwestern Colorado from the Early 

Ordovician to the Silurian U12

12. Photograph showing Chaffee Group at east end of Glenwood Canyon U14

13. Maps showing paleogeography of northwestern Colorado from the Late 

Devonian to the Early Mississippian U16

14. Photograph showing limestone near base of Broken Rib Member of the Dyer 

Dolomite U17

IV Contents
EVOLUTION OF SEDIMENTARY BASINS UINTA AND PICEANCE BASINS

Late Precambrian to Earliest Mississippian 

Stratigraphy, Geologic History, and Paleogeography of 

Northwestern and West-Central Colorado

By James M. Soule1

Abstract

The early Paleozoic of northwestern and west-central 

Colorado is represented by continental-shelf and continentalshelf-marginal sedimentary rocks of Late Cambrian, Ordovician, and Late Devonian ages. Differentially epeirogenic movements along fracture systems having Precambrian origins 

affected sedimentation patterns and probably mostly account 

for intervening times of erosion or nondeposition; activity 

along these tectonic elements persisted into the Neogene and 

possibly continues. These tectonic elements are west-northwest-, south-southeast-, and northeast-trending fracture systems and an east-trending aulacogen in the approximate area 

of the modern Uinta Mountains. North-central Colorado was 

emergent land throughout most of this time and shed clastic 

sediments at varying rates to the west and southwest. Episodic 

continental motion and the effects of the Antler orogeny to the 

west are probably the direct causes of these epeirogenic 

movements.

INTRODUCTION

During the early Paleozoic, northwestern Colorado 

formed part of the continental shelf in the miogeocline on 

the western flank of North America, near the paleoequator 

(Dietz, 1963; Dietz and Holden, 1974; Cook and Taylor, 

1975; Cook and Egbert, 1981) (figs. 1, 2). This part of the 

shelf was at times emergent and characterized by either 

nondeposition or erosion. As a consequence, sequences 

deposited during the early Paleozoic contain numerous 

unconformities, and only about 25 percent of early PaleoManuscript approved for publication March 29, 1991. 

'Colorado Geological Survey, 1313 Sherman Street, Room 715, 

Denver, Colorado 80203.

zoic time is represented in the rock record of northwestern 

Colorado. Periods of uplift and emergence may have been 

associated with reactivation of Precambrian crustal structures, which probably had significant control on depositional patterns throughout the Phanerozoic. Moreover, 

uplifts of Precambrian rocks are the likely source terranes 

for many of the lower Paleozoic clastic units.

This paper summarizes the early Paleozoic history 

and stratigraphy of northwestern Colorado. Discussions are 

based mostly on extensive literature review, remeasurement 

of one critical reference section of lower Paleozoic rocks 

(appendix 1), and examination of available borehole logs 

from wells that penetrate lower Paleozoic rocks (appendix 

2). Interpretations are illustrated in a series of schematic 

paleogeographic maps that show the inferred locations of 

principal tectonic features and areas of erosion and 

deposition. The periods shown in these maps represent 

intervals during which paleogeography is interpreted as 

relatively constant or changing predictably. Maps for time 

intervals that are not represented in the stratigraphic record 

are highly speculative.

Acknowledgments. This study was supported in part 

by the U.S. Geological Survey Evolution of Sedimentary 

Basins Program. John W. Rold and William P. Rogers of the 

Colorado Geological Survey offered advice throughout the 

course of the work. Drafts of the manuscript were read and 

substantially improved by Wallace R. Hansen, Samuel Y. 

Johnson, and Charles S. Sandberg, and their patience and 

criticism are gratefully appreciated.

EARLY PALEOZOIC TECTONIC ELEMENTS

The early Paleozoic paleogeography of northwestern 

Colorado was strongly influenced by several tectonic 

elements (fig. 3), many of which have remained active well

Precambrian to Earliest Mississippian Stratigraphy, Colorado U1
I /LA

37-LL -J--

50 100 KILOMETERS

25 50 MILES

Figure 1. Map of western Colorado showing study area 

(shaded).

into the late Cenozoic. On a regional scale, Larson and 

others (1985) and Purucker (1988) offered strong evidence 

that a late Precambrian to late Paleozoic west-northwesttrending fault or rift system, characterized by episodic 

tectonic and igneous activity, extended from southeastern 

Oklahoma into southeastern Utah. Warner (1978, 1980) 

postulated a "Colorado Lineament" characterized by a 

system of northeast-trending fractures extending from northwestern Arizona to Lake Superior. Tweto and Sims (1963) 

noted that this feature corresponds to a Precambrianoriginated fault system through the "Colorado Mineral Belt" 

and further stated that, "This fault system corresponds 

approximately in location to a Transcontinental Arch which 

affected lower Paleozoic continental sedimentation on the 

craton and possibly on the continental shelf; these were 

persistent for most of the early Paleozoic in northwestern 

Colorado." The dominant tectonic elements that influenced 

sedimentation during the Precambrian to Mississippian in 

northwestern Colorado are described in the following 

sections.

Uinta Aulacogen

The location of the modern-day Uinta Mountains 

(fig. 4) has been the site of repeated positive and negative 

epeirogenesis and compressional or extensional tectonism.

Hansen (1965, 1986a, b), Stone (1975, 1986, 1989), and 

Sears and others (1982) documented repeated, variously 

directed faulting in the Uinta Mountains since the early 

Precambrian, and Hansen and Stone both suggested that this 

faulting was a major control on regional patterns of sedimentation. Based on interpretation of seismic and drill-hole 

data, Stone (1986) postulated that many of the exposed 

faults in the Uinta Mountains are associated with faults in 

the deep subsurface, that movement on this family of faults 

has been recurrent, and that lower Paleozoic rocks are 

preserved in deep, fault-bounded parts of northwestern 

Colorado basins.

Gore Fracture Zone

Almost as well documented as the Uinta Mountains 

faulting is the persistence through much of geologic time of 

an inferred tectonic highland, the western border of which is 

roughly approximated by the modern-day north-northwesttrending Gore fault. Similarly oriented faults are present to 

the south-southeast of the Gore Range into Chaffee and 

Custer Counties and beyond, and this fault system is herein 

termed the Gore fracture zone. The concept that a "Front 

Range Highland" of tectonic origin contributed clastic 

sediments to many lower Paleozoic rock units is well 

supported (Levering and Johnson, 1933; Tweto, 1977, 

1980a), with the possible exceptions of Canadian time, 

when the Manitou Formation was deposited, Cincinnatian 

time, when the Fremont Limestone was deposited, and 

perhaps other time intervals not represented in the rock 

record.

Uncompahgre Fracture Zone

The area now including the Uncompahgre Plateau 

and the Gunnison uplift, which together form a physiographic and structural zone or barrier between the Piceance 

basin and the Paradox basin (to the southwest of the study 

area in southwestern Colorado and southeastern Utah), 

contains a system of almost west-northwest-trending faults 

that Stone (1977) suggested originated in the Precambrian. 

The parallelism or near parallelism of these faults with 

(1) known subsurface fractures, (2) igneous bodies of westnorthwest strike (Hansen and Peterman, 1968; Hansen, 

1981; Ritzma, 1983; Larson and others, 1985), (3) the salt 

anticlines of the Paradox basin to the southwest of the 

Uncompahgre Plateau, and (4) the Gore fracture zone 

suggests that these faults are related in origin and may have 

had similar effects on regional patterns of sedimentation.

White River Uplift and Ancestral Axial 

Fault Zone

Although the White River Plateau is generally 

considered to be a post-Laramide physiographic feature 

(Tweto, 1975), its structural boundaries may have been

U2 Evolution of Sedimentary Basins Uinta and Piceance Basins
AGE

Early Mississippian

Earliest Mississippian 

or Latest Devonian

Late Devonian

Latest Early Devonian 

(Silurian and most 

of Early and Middle 

Devonian not 

represented by rocks)

Late Ordovician

Latest Middle Ordovician

Earliest Early Ordovician

Latest Late Cambrian

Latest (?) or middle 

Late Cambrian

Middle Late Cambrian

Early Late Cambrian

Late Proterozoic

Early Proterozoic (?) and 

late Archean

SERIES

Osagean and 

Kinderhookian 

^X^XVX^X/X/"V^X

Kinderhookian or 

Famennian

Famennian

Famennian and 

Frasnian

'X^X^X^X/X^X^X 

<a .

0) l

«£ 8 o-E §

E *"= J= 

s- § a) Cincinnatian

a) i 2 ^X^X/X^X/X/X^X

£.2,"= Rocklandian and 

c ro " Black Riveran

Canadian

Trempealeauan 

^Xv ? \^xyx/Xv ? v^V

Trempealeauan or 

Franconian

Franconian 

^Xy ? \^xyx/Xv ? v^X

Dresbachian 

-'XVX^X^X/'X^X^X

925- 1,1 00 Ma 

(Tweto, 1987)

 ^X^XV~V^X/"XVX-/X 

~2£00 Ma 

(Tweto, 1987)

STRATIGRAPHIC UNIT

Leadville Limestone

^X/X^X^X^X^"X-rX_^Xv"X-^X_^XXX^X/X^X^'X^X_x

Oilman Sandstone 

^x^xxxv ' v^x^x^x^xyx^x^x^x^x^x^x^x^x^

^^^ Coffee Pot Member

Dyer Dolomite <C^' 

^^^ Broken Rib Member

Parting Formation

^x^x^x^Xv'^yxv'x^'xxx^x-^xyxyx/xyxyxy^ 

Fremont Limestone

y^x^xyxyx^xv'x^x>'xyxyxvx^xyxyx_^xyxyx_x 

Harding Sandstone

^^^Tie Gulch Dolomite Member

Manitou Formation <C^^ 

^^^Dead Horse Conglomerate Member

^^^-Clinetop Member

Dotsero Formation <C^' 

^^^Glenwood Canyon Member 

^x^X-^xv ' vyx^x^xyxy ' v^xxxyxxx^ ' \^xv~v^x^

Unnamed beds or Deadmans Gulch Formation 

(Glenwood Canyon) (Bush and Bush, 1974)

Peerless Formation

Sawatch Quartzite, Lodore Formation 

/-X/XyxyXy'X/X-/XyX^XyXXX/X-''XyxyX/"X^X^

Uinta Mountains Group

^x^^xyx^xyx^xyx^^x^x.^xv'xyxxx^'^^^xyx^x^ 

Red Creek Quartzite

Figure 2. Precambrian and lower Paleozoic sedimentary rocks in northwestern Colorado.

influenced or controlled by older basement fractures similar 

to those along the Uncompahgre uplift and the Uinta 

aulacogen. The Uinta structural trend, moreover, merges 

southeastward with similar trends in northwestern Colorado, including the "Ancestral Axial Fault Zone" (Stone, 

1986) and faults on the White River Plateau (Hansen, 1965, 

1986a). Dula (1981) considered the present White River 

Plateau fracture system and stress field to be relict from the 

Laramide, but an older stress and fracture system similar to 

those in nearby areas is probably likely because westnorthwest fault trends predominate (Dula, 1981, fig. 2). This 

older fracture system probably influenced at least Late 

Cambrian sedimentation patterns and possibly Mississippian patterns. Stone (1986) did not make a case for 

movement along the ancestral Axial fault zone in the early 

Paleozoic except during the late Middle Proterozoic to Late 

Cambrian, but he did present evidence of Pennsylvanian 

movement. Unfortunately, deep drill-hole data needed to 

test that hypothesis are scanty in the area (appendix 2). 

Recurrent early Paleozoic movement along the ancestral

Axial fault zone might be expected, however, because even 

during the long hiatuses in the lower Paleozoic rock record 

depositional environments were changing as indicated by 

the contrasting lithology of preserved strata. Erosional 

truncation of the Ordovician Harding Sandstone and 

Fremont Limestone and the deepening level of erosion 

down to Precambrian levels during the early Paleozoic in 

the southeastern part of the study area are noteworthy 

because, with further study, they may provide evidence for 

almost continuous tectonic activity in the early Paleozoic of 

northwestern and west-central Colorado.

Northeast-Trending Faults

The northeast-trending system of fractures of Precambrian origin (part of the Colorado lineament) that 

involves basement and overlying sedimentary rocks in 

the southeastern part of the study area and continues 

southeastward into central Colorado probably affected

Precambrian to Earliest Mississippian Stratigraphy, Colorado U3
37°;

J LA i,aPLATA t'u\ m ^ r-rt-n'i: inc AKCHULET A \ CONEJOS ,

100 KILOMETERS 

_I

0 25 50 MILES

Figure 3. Tectonic elements of study area, west-central and 

northwestern Colorado.

sedimentation intermittently throughout the early Paleozoic. 

Movement along these faults probably at least influenced 

depositional facies changes in the Early Ordovician and 

erosional patterns in the Middle and Late Ordovician.

PRECAMBRIAN SEDIMENTARY ROCKS

MQNTEZUMA

LA PLATA

37°

I / LarLftiA v /-nMFint; ! 

j / ARCHULETA\ ^^^^^ , «-l L__ i -^ -'

50 100 KILOMETERS

25 50 MILES

Figure 4. Areas and locations discussed in text: 1, Aspen; 

2, Beaver Creek, Browns Park area; 3, Buffalo Peaks; 4, Canon 

City; 5, Craig; 6, Cross Mountain; 7, Dotsero; 8, Eagle basin; 

9, eastern Uinta Mountains; 10, Fossil Ridge; 11, Glenwood 

Canyon; 12, Gore Range; 13, Gunnison uplift; 14, Jones Hole; 

15, Manitou Springs; 16, Minturn quadrangle; 17, Mosquito 

Range; 18, northern Front Range; 19, Paradox basin; 

20, Piceance basin; 21, Rangely; 22, Redcliff; 23, Royal Gorge; 

24, Sawatch Range; 25, Taylor Park; 26, Trout Creek Pass; 

27, Uncompahgre Plateau; 28, Wellsville; 29, White River 

Plateau.

Red Creek Quartzite

The Red Creek Quartzite of Late Archean and Early 

Proterozoic age , which attains the amphibolite facies of 

regional metamorphism, is the oldest Precambrian sedimentary rock unit in northwestern Colorado (Hansen, 1965, 

p. 36). It crops out in Colorado only near Beaver Creek in 

the Browns Park area, Moffat County (fig. 4). Its stratigraphic thickness is about 3,960-7,000 m (Tweto, 1987). 

Hansen (1965, p. 31) suggested an age of 2,320 Ma for the 

Red Creek, but Tweto (1987) regarded this age as a 

minimum and assigned an age of about 2,500 Ma.

Uinta Mountain Group

The Uinta Mountain Group of Late Proterozoic age 

unconformably overlies the Red Creek Quartzite in the 

eastern Uinta Mountains and is exposed in the extreme

northwestern part of Colorado in Moffat County (Hansen, 

1965; Rowley and others, 1985) (fig. 4). In the Uinta 

Mountains, the Uinta Mountain Group has a total thickness 

of about 7,315 m (Hansen, 1965, p. 33). Tweto (1980b, 

fig. 1) inferred that these strata extend eastward in the 

subsurface to Craig, Colorado. The unit consists predominantly of dark-red, medium- to coarse-grained, massive to 

crossbedded, siliceous sandstone and quartzite and some 

shale and conglomerate (Hansen, 1965, p. 33). On the basis 

of its great thickness, its lithology, and a limited set of 

paleocurrent data, Hansen (1965, p. 37) concluded that the 

Uinta Mountain Group was deposited in an east-trending 

(approximating the trend of the Uinta Mountains), probably 

fault-bounded trough (fig. 5A) (Tweto, 1980b, p. 45; 

Hansen, 1986a; Stone, 1989). Sediments of the Uinta 

Mountain Group have an inferred provenance to the north 

and northeast in south-central Wyoming. Tweto (1987, 

p. 21) provisionally dated the Uinta Mountain Group at

U4 Evolution of Sedimentary Basins Uinta and Piceance Basins
925 Ma near the top and 1,100 Ma at the base and indicated 

that it is correlative with the upper part of the Belt 

Supergroup in Montana and Idaho. It may also be correlative with the Unkar Group of the Grand Canyon Supergroup in Arizona (Elston, 1979, p. 14-16). Assuming these 

dates are correct, the Uinta Mountain Group and its correlatives predate inception of the Cordilleran miogeocline 

(Stewart, 1976) at about 850 Ma.

Speculation about Late Precambrian and Early to 

Middle Cambrian environments in northwestern Colorado 

(post-Uinta Mountain Group) is problematical considering 

the lack of rock record. This time interval may have been 

characterized by a continuation of faulting (Hansen, 1986a, 

p. 12-14), igneous activity, and related tectonic activity. 

Tweto (1980b, p. 44-45) further postulated that during this 

time interval new fracture systems having different geometries developed and erosion was widespread (fig. 5A).

LOWERMOST UPPER CAMBRIAN TO 

UPPERMOST CAMBRIAN ROCKS

Differences in lithology between the at least partly 

correlative Sawatch Quartzite and Lodore Formation 

suggest that the Uinta aulacogen and other basement 

fractures to the southeast in the vicinity of modern White 

River Plateau may have been active during this interval. 

Uplift along these zones may have formed barriers to 

regional sediment transport that affected Dresbachian 

sedimentation (fig. 55).

Lodore Formation

The Cambrian is represented in northwestern 

Colorado north and west of the White River Plateau by the 

Lodore Formation, which is considered by most authors to 

be Dresbachian in age (Unterman and Unterman, 1949; 

Stevens, 1961, p. 9; Hansen, 1965, p. 38; Ross and Tweto, 

1980; Ross, 1986). The uppermost Lodore(?) is possibly 

latest Early Devonian in age as determined by Richard Lund 

of Adelphi University (W.R. Hansen, written commun., 

1969) based on identification of Devonian fish fragments 

collected by Hansen and P.O. Rowley near Jones Hole, 

Dinosaur National Monument, Utah. C.A. Sandberg (U.S. 

Geological Survey, written commun., 1990), however, 

recognized a disconformity between the uppermost (fossilbearing) Lodore (?) and the underlying Cambrian Lodore 

and suggested that the uppermost Lodore(?) be considered 

part of the younger Devonian and Mississippian Chaffee 

Group or the Mississippian Madison (or equivalent Leadville) Limestone.

There are few available data concerning the Lodore 

Formation, and more research is needed to properly 

understand its precise age, depositional environment, and

provenance. The Lodore is well exposed at Cross Mountain 

in the canyon of the Yampa River (Dyni, 1968), in several 

other places in and near Dinosaur National Monument 

(Rowley and others, 1985), and along the southern flanks of 

the Uinta Mountains (fig. 4). At these locations, it unconformably overlies the Uinta Mountain Group and is overlain 

by Mississippian rocks (Hansen, 1965). Thicknesses are 

from 91 to 180 m. The Lodore consists of "white to red, 

coarse poorly sorted, quartzitic and in part arkosic sandstones at top, middle, and base" (Unterman and Unterman, 

1949, p. 689). In the type area (Lodore Canyon, Moffat 

County) and at Jones Hole in Dinosaur National Monument, 

it contains thick sequences of fossiliferous, glauconitic 

shale that elsewhere have been removed elsewhere by 

pre-Mississippian erosion. Hansen (1965, p. 38) believed 

that the Lodore Formation once extended over the area of 

the modern Uinta Mountains and was subsequently 

removed by erosion from a younger Uinta Mountains 

highland area.

The Uinta Mountain Group is a likely source for the 

Lodore, as suggested by Stone (1986, p. 20) and Herr and 

Picard (1981, p. 12), for at least its lower part and also for 

the presumably correlative basal Sawatch Quartzite sandstones in northwestern Colorado (Ross, 1986, p. 100). The 

Uinta Mountain Group was tilted and deeply truncated 

before the Lodore Formation was deposited (Hansen, 

1986a); however, a crystalline source is needed to account 

for the arkosic sandstones in the Lodore Formation. Stone 

(1986, p. 31-32) cited Hansen and Bonilla (1954) and 

Wallace (1972) for originating and subsequently reinforcing 

the concept that the now east trend of the ancestral Uinta 

Mountains structure existed prior to the Middle Cambrian. 

Based on subsurface and geophysical data, Stone extended 

the structural trend of the Uinta Mountains in the subsurface 

about 160 km eastward into the area of the Pennsylvanian 

Eagle basin and named it the "Ancestral Axial Fault Zone" 

(1986, p. 19). South of this trend, Stone (1986, p. 25) 

showed Precambrian crystalline basement and no Uinta 

Mountain Group in the subsurface from Rangely to about 

160 km eastward. Thus, a structurally high area probably 

existed south of the ancestral Axial fault zone, and this area 

could have been a source of the Lodore sediments, including 

the arkoses. Whether this high area exposed Uinta Mountain 

Group rocks, other older Precambrian rocks (possibly 

including the Red Creek Quartzite), or the older Precambrian crystalline basement is unknown.

Sawatch Quartzite

The Sawatch Quartzite (Johnson, 1934; Bass and 

Northrop, 1953, 1963; Campbell, 1972a; Tweto and Lovering, 1977) is present throughout northwestern Colorado 

except on the Uncompahgre uplift, where it presumably was 

deposited but subsequently eroded away during or prior to 

the Pennsylvanian (Stone, 1977), and northwest of the

Precambrian to Earliest Mississippian Stratigraphy, Colorado U5
109° ___ ___ ___ 107 

 ~ Continental Sediments j T

a3 . 

Q'I /

MOFFAT ^?

UINTA AULACOGEN 

Uinta Mountain Group ) \

X

r u

*\\

39'r

POSSIBLE \

. ___ GRAND | 

[ -7\ HIGHLAND /

J i .^>_ } r -*\ ~\A REA >v

-. "'

J (jARRO.1)

I.EACTU """RE__ _ -MrAf

/SAKE

 - " J--T\TMOFFAT

UINTA AULACOGEN 

positive

LODORE

RIO BLANCO 

FORMATION

109°

/ JACKSON \ 

LOW \ 

RELIEF

MOFFAT

UINTA AULACOGEN 

( probably positive

UINTA AULACOGEN 

( probably positive

DOTSEROj 

FORMATION 

GABFIELD SHALLOW 

__QUIET-WATER

MARINTsilfelMENTS

s\ PiTKIN 

/

PEERLESS FORMATION

GARflCLO SHALLOW

QUIET-WATER 

MARINE SEDIMENTS

UNCOMPAHGflE

FRACTfTRF DEl.TA 

UNCOiyiPAHGRE ZO

FRACTJURE

ZONE 

(activJ! ?) r

t""*"% I !

(inactive ? )

MQNTKGSE

EXPLANATION

 Fault zone

 ^ Fault Bar and ball on 

downthrown block

I

25 50 MILES

Figure 5. Paleogeography of northwestern Colorado from about 1,400 Ma to the Late Cambrian. A, About 900 Ma during time 

of deposition of Uinta Mountain Group. B, Dresbachian (Sawatch Quartzite and Lodore Formation). C, Franconian (Peerless 

Formation). D, Trempealeauan (Dotsero Formation).

U6 Evolution of Sedimentary Basins Uinta and Piceance Basins
White River Plateau, where the Lodore Formation is its 

correlative (Ross, 1986, p. 100). The best outcrops are along 

the flanks of the Sawatch and Mosquito Ranges, near 

Redcliff and Minturn, and in the canyons along the southern 

and eastern sides of the White River Plateau (fig. 4).

The predominant lithology in the Sawatch is buff to 

grayish-orange-pink (SYR 7/2), vitreous oithoquartzite in 

beds from 15 cm to 1 m thick. Several other rock types are 

present with lesser frequency in the Sawatch. In Dead Horse 

Gulch, a tributary to the Colorado River in Glenwood 

Canyon (fig. 4), the basal Sawatch consists of 0.1-0.3 m of 

arkosic quartz-pebble conglomerate unconformably overlying weathered Precambrian schist and pegmatite (fig. 6, 

appendix 1). In Glenwood Canyon, this contact has as much 

as 15.2 m of local relief, but it was reported as planar in the 

Minturn area (Tweto and Levering, 1977). Above, but still 

within 15.2 m of the base of the Sawatch in the Dead Horse 

Gulch section, friable, hematite-stained, planar-tabular 

crossbedded sandstone is interbedded with the vitreous 

oithoquartzite (fig. 7, appendix 1). Bass and Northrop 

(1963) reported a thickness of 157.5 m for the Sawatch 

section, which includes an upper dolomite unit and an 

overlying massive oithoquartzite unit. This thickness is 

greater than that reported to the south and east, where Tweto 

and Levering (1977, p. 16-17) reported that the Sawatch is 

67 m thick in the Minturn quadrangle and thins to the south 

(Tweto, 1956, 1974; Tweto and others, 1978).

Chronic (1964, p. 105) reported that the Sawatch is 

30 m thick at Buffalo Peaks and absent at Trout Creek Pass. 

In Taylor Park, Bush and Bush (1974) reported a sequence 

similar to that in Glenwood Canyon. They assigned the 

dolomitic beds to the Peerless Formation, which elsewhere 

overlies the Sawatch, and beds of variable lithology between 

their Peerless and Lower Ordovician rocks to a newly

Figure 7. Typical friable, hematite-stained, planar-tabular 

crossbedded sandstone interbedded with quartzite near base 

of Sawatch Quartzite. Dead Horse Gulch section, Clenwood 

Canyon (fig. 4). Staff is about 1.5 m long.

Figure 6. Contact between basal Sawatch Quartzite and 

Precambrian rocks. Dead Horse Gulch, Glenwood Canyon 

(fig. 4). At this location the contact (arrow) is almost planar, but 

at other locations nearby it has about 15.2 m of relief. A thin 

bed of quartz-pebble conglomerate grades upward to quartzite 

and sandstone. Staff is about 1.5 m long.

named Deadmans Gulch Formation; they assigned 38.7 m 

of section at Taylor Park to the Sawatch.

Paleontological control for the age of the Sawatch is 

poor due to generally barren rock types, but where the age 

has been determined the consensus is that it is Dresbachian 

(Tweto, 1949; Tweto and Levering, 1977). Bass and 

Northrop (1963, p. 5) reported that brachiopods are present 

in the dolomite unit in Glenwood Canyon but made no age 

determinations. The uppermost Sawatch is undated. Tweto 

and Lovering (1977) suggested that the upper dolomite unit 

of the Sawatch probably is equivalent to the Peerless 

Formation, which is variously considered to be of Middle to 

late Late Cambrian age (Behre, 1929, 1953; Johnson, 1934, 

1944), Late Cambrian age (Chronic, 1964; Anderson, 1970; 

Bush and Bush, 1974), or middle Late Cambrian age 

(Franconian) (Tweto and Levering, 1977). If the dolomitic 

unit in my measured section is equivalent to the Peerless, 

then additional quartz sand was deposited over much of 

western Colorado and then partly to almost completely 

eroded before the latest Cambrian, inasmuch as the

Precambrian to Earliest Mississippian Stratigraphy, Colorado U7
overlying Dotsero Formation is latest Cambrian (Trempealeauan) in age (Bass and Northrop, 1953, 1963; Campbell, 

1972a, 1976; Tyler and Campbell, 1975). On a regional 

scale, Palmer (1965, 1981, p. 160) and Sloss (1963, 

p. 96-99) suggested that a regional disconformity separates 

Dresbachian and Franconian rocks. Because of uncertain 

dating, regional correlation of the Upper Cambrian 

formations including the Sawatch and the Peerless is 

problematical (see also the discussion by Bryant, 1979, 

p. 16-17).

If the dolomite unit discussed above is equivalent to 

the Peerless, then my section of the Sawatch in Glenwood 

Canyon is 80.5 m thick, a thickness more consistent with 

surrounding areas than that reported by Bass and Northrop 

(1963). As noted above, however, the Precambrian-Sawatch 

contact is undulatory, and thicknesses vary locally.

The most likely source of Sawatch sediment was an 

eroding highland in the vicinity of the modern Front Range 

(Levering and Johnson, 1933; Tweto and Levering, 1977). 

The lithic composition of this highland is not known, but it 

may have been deeply weathered or quartz rich considering 

the predominantly quartzitic composition of the Sawatch. 

This highland apparently abruptly terminated at the western 

side of the modern Gore Range along an episodically active 

Gore Range fault (Tweto and Levering, 1977), a hypothesis 

generally consistent with that of Campbell and others 

(1976), who believed that the Peerless(?)-equivalent 

dolomites pinch out to the northeast and thicken to the 

southwest (Bryant, 1979, p. 17). Sediment in western 

Colorado in the Late Cambrian was generally moved from 

east to west (Seeland, 1968).

The latest Middle Cambrian to earliest Late Cambrian 

probably was a time of tectonic instability in western 

Colorado, if not most of the western United States (Larson 

and others, 1985). Cambrian disconformities may reflect 

either epeirogenic movements or eustatic sea-level changes, 

or both (Lochman-Balk, 1955, p. 29). Lochman-Balk 

(1970, p. 3197; 1972) presented regional paleogeographic 

reconstructions.

Peerless Formation and Unnamed 

Overlying Rocks

Despite uncertainties concerning the age of the 

Peerless Formation and its problematical relationship with 

the underlying Sawatch Formation and overlying rocks, the 

Peerless Formation is a widely recognized upper Cambrian 

unit in much of central and northwestern Colorado. 

Although variable in thickness, lithology, and sedimentary 

structures, its stratigraphic position and sandy dolomite 

lithology are distinctive, and the formation can be easily 

recognized (Tweto and Levering (1977, p. 19-21). I measured about the same thickness of probably Peerlessequivalent rocks in the Dead Horse Gulch section in

Glenwood Canyon (appendix 1) as Tweto and Levering 

(1977) did in the Minturn quadrangle (20 m). The composition of the Peerless is much more variable in the 

Minturn quadrangle than in the adjacent White River 

Plateau area. In the Minturn quadrangle the Peerless consists of glauconitic sandy dolomite or dolomitic sandstone, 

varicolored mudstone, and minor micaceous shale (Tweto 

and Levering, 1977, p. 19), whereas in Glenwood Canyon it 

consists of cliff-forming, massive, brown, sandy dolomite.

The Peerless Formation is also recognized at Aspen 

(Bryant, 1971, 1979, p. 14-15). Although thicker (30-45 m) 

than at Minturn and at Glenwood Canyon, these outcrops of 

Peerless contain similar rock types. Bryant included remnants of the Deadmans Gulch Formation of Bush and Bush 

(1974) in the Peerless in the Aspen area, but the thickness of 

these beds was not specified and could not be determined 

from Bryant's measured section (1979, section 1, p. 130).

Cambrian beds above the Peerless Formation and 

below the Dotsero Formation or Lower Ordovician rocks 

need additional study. Their age and the nature of their 

contact with the overlying Glenwood Canyon Member of 

the Dotsero Formation (Bass and Northrop, 1953) should be 

determined. The lithology of these beds in Glenwood 

Canyon is essentially the same as that of the Sawatch 

Quartzite, which underlies the Peerless(?)-equivalent dolomite. This similarity is probably why Bass and Northrop 

(1963, p. 5-7) assigned these beds to the Sawatch. The 

lithology of the Deadmans Gulch Formation discussed 

earlier is more variable; the unit consists mainly of quartz 

sandstone and glauconitic sandy dolomite and contains 

sedimentary structures that indicate very shallow water 

deposition (Bush and Bush, 1974, p. 64-68). The panel 

diagram of Bush and Bush (1974, p. 67) shows the 

Deadmans Gulch thinning to nil at Glenwood Canyon and 

suggests either that they believed these uppermost 

Cambrian quartzites should be included with the Peerless 

(making the Peerless anomalously thick) or, alternatively, 

that they ignored these beds. In any case, beds composed of 

predominantly quartzite and lesser dolomite above the 

Peerless(?) and below the Dotsero Formation have been 

reported only from the canyons on the southern and eastern 

sides of the White River Plateau. Their original extent and 

the character of the erosional episode that removed them 

from most of northwestern Colorado are unknown.

Lithdogy and thickness changes suggest that northwestern Colorado was a shallow shelf sea during the 

Franconian and that this sea was subject to mild epeirogenic 

movements (fig. 5C). Minor reactivation of the Gore 

fracture zone and other now-buried fracture zones to the 

west and southwest may have occurred. The DresbachianFranconian interval most likely was a period of erosion or 

nondeposition prior to inundation by this sea. Whether other 

tectonic activity took place is not known.

US Evolution of Sedimentary Basins Uinta and Piceance Basins
Dotsero Formation

As first described by Bassett (1939), the Dotsero 

Formation typically crops out on the eastern and southern 

side of the White River Plateau; its type locality is near 

Dotsero, Colorado. Bass and Northrop (1953, 1963) and 

Campbell (1976) showed that the Dotsero Formation is 

present across much of the White River Plateau, over an 

area of 1,037 km2 (Campbell, 1976, p. 1331). Johnson 

(1945, p. 14-15) first demonstrated the Trempealeauan age 

of these strata. Bass and Northrop (1953) redefined the 

Dotsero Formation and assigned its upper beds to the 

conformably overlying Manitou Formation of earliest 

Ordovician (early Canadian) age. Bass and Northrop (1953) 

revised the Dotsero Formation into two units, a lower 

Glenwood Canyon Member and an upper algal-biostrome 

(stromatolite) limestone that they named the Clinetop Algal 

Limestone Member. The name Clinetop Algal Limestone 

subsequently was shortened to Clinetop Member by Campbell (1976).

As discussed earlier, the lower contact of the Dotsero 

Formation with the underlying unnamed orthoquartzite may 

be disconformable. In the Glenwood Canyon area (appendix 

1), the contact is distinctive and abrupt. Massive orthoquartzite and well-cemented quartz sandstone of the 

unnamed beds above the Peerless form a ledge (fig. 8) and 

are overlain by partly slope forming, predominantly sandy 

dolomite, shaly dolomitic sandstone, and limestone described below. The Clinetop Member and the conformably 

overlying Dead Horse Conglomerate Member of the Manitou Formation are precisely dated (Bass and Northrop, 

1963, p. 10-11), and their contact is regarded as the 

Cambrian-Ordovician boundary.

Figure 8. Highest beds of massive orthoquartzite of unnamed 

unit immediately below Clenwood Canyon Member of the 

Dotsero Formation. Dead Horse Gulch section, Glenwood 

Canyon (fig. 4). Staff and hammer shown for scale.

Figure 9. Typical brown silty and sandy dolomite and 

dolomitic sandstone of Glenwood Canyon Member of the 

Dotsero Formation. Highway roadcut at east end of Glenwood 

Canyon (fig. 4) near Garfield County-Eagle County line. Staff is 

about 1.5 m long.

Glenwood Canyon Member

In the Dead Horse Gulch section (appendix 1), the 

Glenwood Canyon Member of the Dotsero Formation 

consists of 27.1 m of silty and sandy dolomite and dolomitic 

sandstone (fig. 9). Beds are 1.3-7.6 cm thick. Many of these 

beds, especially in the middle third of the member, have 

what may be worm tracks or worm burrows (fucoid marks 

of some authors) on surfaces that otherwise are smooth and 

planar. A few limestone beds, mainly conglomeratic, grade 

to dolomitic sandstone beds. Glauconite is present in 

dolomite beds (Bass and Northrop, 1953, 1963) and locally 

causes a greenish cast. A few beds are capped by minor 

sericite. Some tan to greenish shale is interbedded with the 

sandstone.

Clinetop Member

The most distinctive rock in the Dotsero Formation 

is pinkish-light-gray (SYR 8/1) to very light gray (N8)

Precambrian to Earliest Mississippian Stratigraphy, Colorado U9
biostromal, algal limestone (Bass and Northrop, 1953, 

1963; Campbell, 1976) that weathers white to lavender. In 

the Dead Horse Gulch section, the Clinetop Member is 

about 1.7 m thick (appendix 1) (Bass and Northrop, 1963). 

Campbell (1976, p. 1333) recognized three limestone facies 

in the Clinetop Member on the White River Plateau: a basal 

conglomerate, an algal-head unit, and an upper conglomerate. Consistent with Campbell's (1976, p. 1333) section, 

only the basal conglomerate facies is seen at Dead Horse 

Gulch. This is surprising in that the Clinetop in this area is 

apparently at its thickest (Campbell, 1976). The contour of 

greatest thickness is 1.2 m. The area it encloses passes over 

Glenwood Canyon about 3.2 km west of the Eagle CountyGarfield County boundary. The trend of greatest thickness is 

northwest-southeast.

Except on the White River plateau and its immediate 

vicinity, the Dotsero Formation is missing from the lower 

Paleozoic section in northwestern Colorado, and the 

overlying Manitou Formation rests on older rocks. It is 

therefore difficult to estimate the original extent of Dotsero 

depositional environments (fig. 5£>), but the Dotsero may 

have been much more extensive than is indicated by 

modern-day Dotsero outcrops. According to Campbell 

(1976, p. 1334-1335), carbonate rocks of the Glenwood 

Canyon Member accumulated slowly in a very shallow 

marine environment that became even shallower in Clinetop 

time.

ORDOVICIAN ROCKS

Ordovician rocks in northwestern Colorado consist of 

three formations, in ascending order: the lowest Ordovician 

Manitou Formation (earliest Canadian) (Ross, 1951; Bass 

and Northrop, 1953, 1963; Berg and Ross, 1959; Berg, 

1960; Chronic, 1964; Gerhard, 1972; Ross and Tweto, 

1980; Ross, 1986); the lower Upper Ordovician Harding 

Sandstone (Black Riveran and Rocklandian) (Sweet, 1954, 

1955, 1961; Ross and Tweto, 1980); and the uppermost 

Ordovician Fremont Limestone (Cincinnatian) (Sweet, 

1954, 1961; Ross and Tweto, 1980). In most places in 

northwestern Colorado these three formations are not all 

represented, and outcrops of the Manitou outcrop are the 

most widespread. The Manitou rests on various older rocks 

including Precambrian rocks in the Trout Creek Pass area 

(DeVoto, 1962) and at Wellsville in the canyon of the 

Arkansas River (fig. 4) (Rold, 1961). The Fremont 

Limestone, however, always overlies the Harding Sandstone (Taylor and Scott, 1972; Taylor, Scott, and Wobus, 

1975; Taylor, Scott, Wobus, and Epis, 1975; Ross and 

Tweto, 1980, p. 52). Only the Manitou Formation is present 

in the Glenwood Canyon area.

Ordovician formations vary greatly in thickness 

across northwestern Colorado. Their bounding unconformities apparently represent periods of tectonic instability 

and (or) marine regression from lands formed by uplift

along the northeast-trending Transcontinental arch. During 

the Ordovician, the North American paleocontinent moved 

southward with reference to the paleoequator (McElhinny 

and Opdyke, 1973; Ross, 1976a, b, p. 109-114; Witzke, 

1980; Van der Voo, 1988, p. 314-316).

Manitou Formation

The Manitou Formation in the Glenwood Canyon 

area was divided into two members by Bass and Northrop 

(1953, 1963): the lower Dead Horse Conglomerate Member 

and the upper Tie Gulch Dolomite Member. The French 

Creek measured section of this report (appendix 1) is from 

the same locality as that of Bass and Northrop (1963). 

Although the two sections are similar, I consider some of 

their dolomite beds to be limestone and I measured a 

slightly greater thickness (51 versus 47.5 m). The map of 

Foster^ (1972, p. 80, fig. 4) suggests that the Manitou 

changes from predominantly dolomite to limestone as the 

White River Plateau is approached from the southeast 

(Manitou Springs area).

In Glenwood Canyon the Manitou consists of four 

rock types; limestone and dolomite predominate and 

greenish shale and sandstone are subordinate (appendix 1). 

Other outcrops in northwestern Colorado are similar to 

those in Glenwood Canyon, except at Aspen where the 

Manitou contains more sand and silt (Bryant, 1979, p. 15; 

Ross and Tweto, 1980). Except on the White River Plateau, 

the Clinetop Member of the underlying Dotsero Formation 

is not present. As a result, it is very difficult to determine the 

base of the Manitou, which may, in part, explain the 

variability of reported thicknesses.

Dead Horse Conglomerate Member

The lower 15 m of this member consists of gray- to 

buff-weathering, thin-bedded (5-15 cm), conglomeratic 

limestone; thin-bedded, gray-weathering, sandy limestone; 

and thin-bedded shaly limestone. A calcareous maroon and 

green shale is immediately above the base of the member. 

The upper 15 m contains thick-bedded, gray, crystalline 

limestone that consists partly of conglomeratic, thin-bedded 

sandy limestone and dolomite and includes two beds of 

massive dolomitic orthoquartzite. One of these orthoquartzite beds is at the top of the member.

Tie Gulch Dolomite Member

In Glenwood Canyon the Tie Gulch Dolomite 

Member consists of uniformly bedded (1 m), massive, 

micritic, brown and tan, crystalline limestone and dolomite 

and buff, sandy dolomite near the top. A thin shale that may

U10 Evolution of Sedimentary Basins Uinta and Piceance Basins
Figure 10. Contact between highest bed of Manitou 

Formation (Tie Gulch Dolomite Member) and lowest bed of 

Parting Formation of Late Devonian age. French Creek section, 

Glenwood Canyon (fig. 4). Note thin shale (arrow) at contact, 

which can be interpreted to be the remains of a paleosol. The 

Harding Sandstone and Fremont Limestone are missing from 

this section. Hammer shown for scale.

be a paleosol is at the upper contact (fig. 10) with the 

overlying Upper Devonian Parting Formation.

Gerhard (1972, p. 27-33) studied Early Ordovician 

depositional environments and paleotectonics of central 

Colorado and suggested that the Manitou was deposited 

in two provinces: northwest, typified by the Glenwood 

Canyon section, and southeast, typified by the mostly 

dolomitic type section near Manitou Springs (Brainerd and 

others, 1933). He proposed that an alternate type section 

should be designated for his "northwestern" facies in 

Glenwood Canyon; this French Creek section is the same 

section measured by Bass and Northrop (1953) and by me 

(appendix 1). Gerhard concluded that in both provinces the 

environment of deposition of the Manitou Formation was 

tidal and that very shallow marine water covered Colorado 

during early Canadian time. Gerhard attributed facies 

changes to mild but regional epeirogenic movements and 

resulting shifts of tidal zones. He proposed that five cycles 

of transgression and regression and five intraformational 

unconformities are represented in the Manitou Formation. 

These transgressive and regressive cycles and the variable 

level of the erosion surface on which the Manitou Formation was deposited suggest fault-controlled deposition 

patterns. This faulting may have been localized on the 

northeast-trending Colorado lineament (Warner, 1978, 

1980, p. 16). The end of Manitou time marked the end of 

deposition of the Sauk sequence of Sloss (1963), and a 

continentwide unconformity probably is represented by the 

interval between the Manitou Formation and the overlying 

lower Upper Ordovician Harding Sandstone (Sweet, 1954, 

p. 293) (fig. 1 1 A). Ross and Tweto (1980) indicated that the 

Manitou generally resembles correlative strata in the central 

and southeastern United States (Ross, 1976a, b).

Harding Sandstone

The Harding Sandstone consists of sandstone, quartzite, and shale. The Harding has a latest Middle Ordovician 

(Black Riveran and Rocklandian) age, as determined from 

conodonts (Sweet, 1954, p. 291-292, 1955; Ross and 

Tweto, 1980, p. 51). It is highly variable in thickness and 

crops out only in the southeastern part of northwestern 

Colorado.

Outcrops of the Harding closest to Glenwood Canyon 

are in the Minturn quadrangle (Tweto and Levering, 1977), 

where the formation is about 11.9 m thick. The formation is 

as thick as about 48.5 m in Fremont County (Sweet, 1954, 

p. 290, fig. 2; Scott and Taylor, 1974). It rests unconformably on the Peerless Formation near Minturn (Gilman) in 

Eagle County (Tweto and Levering, 1977, p. 22), on the 

Manitou Formation farther to the south in Lake and Chaffee 

Counties, and on Precambrian rocks at the southern limit 

of its outcrop in Custer, Pueblo, and Saguache Counties 

(Sweet, 1954, p. 290-291).

The origin of the widespread cratonic, shelf-marginal, 

and miogeoclinal Middle Ordovician quartzites and sandstones in the western United States has been the subject of 

some speculation inasmuch as these rocks exhibit compositional and stratigraphic similarities over large areas. 

Chronic and others (1969), Ross (1976b, p. 122, 124, 125, 

figs. 8, 9), Witzke (1980, p. 8), and Sando and Sandberg 

(1987, p. 6) all indicated that correlatives of the Harding, 

having essentially the same lithologic, stratigraphic, and 

faunal characteristics, are present north of the Transcontinental arch and into the cratonic interior of the 

continent to the north and east. Ketner (1968) showed that 

the Canadian Shield was the probable source of these 

sediments. Ross (1976b, p. 122) concluded that this deposition and movement of sand south and southwestward 

continued until early Cincinnatian time when the Canadian 

Shield was inundated. Ordovician rocks are not present in 

Colorado south of the Uncompahgre Plateau and into the 

Grand Canyon region of Arizona. They probably were never 

deposited in the Grand Canyon region, but their original 

extent in west-central, northwestern, and southwestern 

Colorado is unknown. Sando and Sandberg (1987, p. 4-6) 

suggested that uplifted islands in northwestern Colorado 

during Harding time may partly explain the lack of Harding 

correlatives in adjacent areas of Wyoming (fig. 1 IB).

Fremont Limestone

The Fremont Limestone (also called Fremont Dolomite in some areas) (Sweet, 1954, p. 294) of Cincinnatian 

age is perhaps the least studied lower Paleozoic unit in 

northwestern Colorado. It crops out only in the southeastern 

part of northwestern Colorado at the south end of the 

Sawatch Range and farther to the south at Trout Creek

Precambrian to Earliest Mississippian Stratigraphy, Colorado U11
Movement of sand to 

southwest from craton

107°

Facies changesjn pnviN ,

 < - PI 1 KIN /LAKE

MESA causecLhy_dmeijentia

movemefrts along riortheast109° 

41° -

h1-

FREMONT 

IMESTONE

GARHELD

EXPLANATION 

 Fault zone 50 MILES

Figure 11. Paleogeography of northwestern Colorado from the Early Ordovician to the Silurian. A, Canadian (Manitou 

Formation). B, Latest Middle Ordovician (Trentonian?) (Harding Sandstone). C, Cincinnatian (Fremont Limestone). D, Silurian.

U12 Evolution of Sedimentary Basins Uinta and Piceance Basins
Pass. The Fremont is bounded by upper and lower unconformities. The lower unconformity represents a transition 

from clastic shelf to marine carbonate sedimentation, not 

only in Colorado, but throughout much of the western 

United States (Ross, 1976a, b). Strata that correlate wholly 

or partly with the Fremont include the Bighorn Dolomite of 

the northern Rockies, the Fish Haven Dolomite of northern 

Utah, the Viola Limestone of the Midcontinent (Foster, 

1972, p. 82, fig. 6), and the Montoya Group of New Mexico, 

west Texas, and Arizona (Hayes, 1975, 1978). This 

widespread deposition of carbonate can be attributed to the 

inundation of much of North America by shallow epicontinental seas (Ross, 1976b, p. 130).

The extent of these Ordovician seas in Colorado is 

unknown because the limit of the Fremont Limestone is an 

eroded edge wherever it has been observed. The sea(s) must 

have extended at least to the northern end of the Front 

Range where exotic carbonate rocks in diatremes have 

yielded fossils that are the same age as the Fremont 

(Chronic and McCallum, 1969; Chronic, 1972). The abrupt 

end of carbonate deposition accompanied major environmental changes, including a major glaciation, at the end of 

the Ordovician (Sheehan, 1988, p. 408).

The best outcrops of the Fremont Limestone are near 

Canon City in Fremont County. Sweet (1954, p. 295) 

measured a section near Royal Gorge near Canon City that 

consists of a lower massive dolomite member about 63.5 m 

thick and an upper dolomite member about 22.9 m thick that 

has shale at its base. The Fremont is considerably thinner in 

the Sawatch Range where Johnson (1944) measured as little 

as 8.5 m; rocks similar to those at Royal Gorge are 13.5- 

15m thick on Fossil Ridge at the southern end of Taylor 

Park (Zech, 1988). Evidence presented in the reports cited 

above indicates that the Fremont must have been much 

more extensive than its present outcrop distribution suggests. Sweet (1954, p. 303) noted, moreover, that no clastic 

shoreward facies of the Fremont has ever been recognized 

(fig. 11C).

SILURIAN ROCKS

With the exception of fossiliferous carbonate rocks 

preserved as exotic blocks in diatremes in the northern Front 

Range, no Silurian rocks have been recognized in Colorado. 

The time between Late Ordovician (Cincinnatian) and 

possibly earliest Late Devonian (Frasnian), and probably 

latest Late Devonian (Famennian), lacks a rock record. 

There is almost no reference, therefore, to Silurian history in 

the geologic literature of Colorado.

Paleontological data (Chronic and others, 1969, 

p. 154) indicate that most of Silurian time is represented in 

the lone known occurrence of Silurian rocks in Colorado. 

Regionally, the nearest well-dated Silurian rocks are in 

northwestern Utah (Sheehan, 1980), where Lower Silurian 

(Wenlockian) strata are present, and in the Williston basin

of northern Wyoming and northwestern South Dakota, 

where the Interlake Formation is Late Ordovician to latest 

Wenlockian in age (Sandberg and Mapel, 1967; Gibbs, 

1972, p. 87) and the uppermost beds are undated. Sheehan 

(1980) believed that the Silurian environment of northwestern Utah was a shallow marine shelf until at least latest 

Wenlockian and that the slope on the margin of the North 

American miogeocline was probably a short distance to the 

west. Gibbs (1972) concluded that the depositional environment of the Interlake carbonates was a highly oxidized, 

warm-water sea characterized by low energy and restricted 

circulation. Any coexisting landmass was remote and of 

presumably low relief. Witzke (1980, p. 15, fig. 9) showed 

that Colorado was in an arid climatic belt south of the 

paleoequator and ancestral North America was moving 

south. Climatic patterns resembled those for the Late 

Ordovician prior to the latest Ordovician glacial period 

(Ross, 1976a, b; Sheehan, 1980, p. 19; Van der Voo, 1988, 

p. 316).

Tweto (1980a, p. 7) inferred that epeirogenic movements occurred repeatedly in Colorado from earliest Silurian to Middle Devonian, but little or no evidence of such 

movements has been documented. If the fracture systems 

that originated in the late Precambrian influenced sedimentation in the Silurian as they did before and since 

(Tweto, 1980a, p. 5), then Silurian rocks were perhaps 

deposited and subsequently eroded away in western 

Colorado. More likely, however, western Colorado was a 

land area in Silurian time, and a continental shelf and sea 

were to the west. Silurian rocks in the Front Range 

diatremes could be attributed to deposition in a seaway that 

was somehow connected to the Midcontinent sea. The rocks 

are anomalous because the Front Range has been apparently 

structurally high during most of geologic time (fig. 1 ID).

DEVONIAN AND MISSISSIPPIAN ROCKS

In northwestern Colorado the Devonian is represented 

by the Chaffee Group of Famennian (late Late Devonian) 

age and, in the redefined usage of this group name by Tweto 

and Lovering (1977), possibly earliest Mississippian (Kinderhookian) age. C.A. Sandberg (written commun., 1990) 

indicated that conodont age determinations demonstrate a 

late Famennian age for all Devonian rocks in west-central 

and northwestern Colorado. The Chaffee Group includes 

the Parting Formation, Dyer Dolomite, and Gilman Sandstone. The Devonian is probably the best studied lower 

Paleozoic system in northwestern Colorado.

The Upper Devonian sequence in southwestern 

Colorado and southeastern Utah south of the Uncompahgre 

uplift (Beus, 1980) is very similar to the Parting Formation 

of northwestern Colorado. These formations probably were 

continuous before the Uncompahgre uplift was (re-?) 

activated in Pennsylvanian time (Kelley, 1955, p. 76-80; 

Stone, 1977; Larson and others, 1985, p. 1370-1371).

Precambrian to Earliest Mississippian Stratigraphy, Colorado U13
Devonian rocks produce oil from the Aneth Formation of 

the Paradox basin in southeastern Utah. Baars and Campbell 

(1968, p. 35) considered the Aneth to be earliest Frasnian in 

age and suggested that it is correlative with the lowest part 

(Unit A of Campbell, 1970a) of the Parting Formation, the 

oldest rocks in the Chaffee Group. The Aneth Formation is 

known only in the subsurface (Baars, 1972, p. 91; Beus, 

1980, p. 61) and is overlain by the McCracken Sandstone 

Member of the Elbert Formation. C.A. Sandberg (written 

commun., 1990) believed that the Parting is much younger 

than the Aneth. In Glenwood Canyon, Sandberg and Poole 

(1977, p. 168-171) found conodont zones that indicate the 

Parting is Famennian, and they discount prior Frasnian age 

determinations based primarily on Late Devonian fossil-fish 

fragments (Bryant and Johnson, 1936; Poole and others, 

1967; Tweto and Levering, 1977, p. 26). Tweto and 

Levering (1977, p. 23-24) seem to concur with Sandberg 

and Poole. Sando and Sandberg (1987, p. 7) correlated the 

Parting Formation of the Chaffee Group with their newly 

named Fremont Canyon Sandstone in the northern Laramie 

Range of Wyoming, although biostratigraphic control of the 

age of this new formation is lacking. The lower part of the 

Englewood Formation, which conformably overlies the 

Fremont Canyon Sandstone, has produced Famennian conodonts (Sando and Sandberg, 1987, p. 9-11). Other possible 

correlatives are present farther to the north (Sandberg and 

Mapel, 1967).

The predominantly dolomitic Dyer Dolomite of 

Famennian age (Campbell, 1970a, p. 319-324; Sandberg 

and Poole, 1977) overlies the Parting north of the Uncompahgre uplift in northwestern Colorado. Its correlative in 

southwestern Colorado is the Ouray Limestone (Baars and 

See, 1968). The Dyer conformably overlies the Parting, just 

as the Ouray overlies the Elbert. On the White River 

Plateau, Campbell (1970a) divided the Dyer into the Broken 

Rib Member and the overlying Coffee Pot Member. Sandberg and Poole (1977) accidentally transposed the names 

Broken Rib Member and Coffee Pot Member, but their 

samples are in proper stratigraphic order (C.A. Sandberg, 

written commun., 1990). Sandberg and Poole (1977, 

p. 167-174) indicated that correlatives of the Dyer are 

present in adjacent States, but exact age determinations 

based on conodont biostratigraphy are uncertain.

In their revision of the Chaffee Group, Tweto and 

Levering (1977) indicated that the uppermost Dyer may be 

earliest Mississippian in age and the unconformably 

overlying Oilman Sandstone latest Devonian or earliest 

Mississippian. Before this revision, the Oilman Sandstone 

had been regarded as the lowest member of the overlying 

Leadville Limestone. Gutschick and others (1980) assigned 

the lowest Leadville to late Kinderhookian with a regional 

disconformity between it and the underlying uppermost 

Devonian-lowermost Mississippian. As summarized by 

Craig (1972), the entire Leadville had previously been 

assigned to the Osagean.

Parting Formation

On and near the White River Plateau, the Parting 

Formation consists of quartzite, shale, and dolomite. It is 

about 19-30 m thick. Campbell (1970a, p. 315) indicated 

that the Parting is 19 m thick at Grizzly Creek (N!/4 sec. 34, 

T. 5 S., R. 88 W.). Bass and Northrop (1963, p. 19) 

indicated that the Parting is 19.2-29 m thick in 10 measured 

sections (locations unspecified). I remeasured the Parting 

section (fig. 12) that Bass and Northrop (1963, p. 18-19) 

reported in detail, which is located in the cliffs on the north 

side of Interstate Highway 70, directly west of the Eagle 

County-Garfield County line, and obtained a thickness of 

30 m. Sandberg and Poole (1977, p. 169-171) studied this 

same section for conodont faunas. Although Campbell 

(1970a) divided the Parting into three units (A, B, C) that 

he said can be traced over much of the Parting outcrop area 

in northwestern Colorado, I was unable to reconcile these 

units with the section I measured or with the data of Bass 

and Northrop (1963). Campbell used 31 surface and 

subsurface sections on or adjacent to the White River 

Plateau but not the one reported in this study. His lithologic 

descriptions, however, are consistently similar for all 

reported sections.

In the Glenwood Canyon section, the Parting consists 

of quartzite, green shale, and dolomite. The quartzite, which 

consists of well-cemented quartzite grains and minor feldspar and rock fragments, is distinctive and forms minor 

ledges. Quartzite beds are generally 0.15-0.3 m thick., but 

bedding thicknesses of other rock types are highly variable. 

The green shale is commonly interbedded with thin and 

discontinuous quartzite lenses. The dolomite is typically 

fine crystalline micrite (Folk, 1959) and commonly sandy 

and (or) calcareous. Dolomite is gray on fresh fractures and

Figure 12. Section of Chaffee Group measured at east end of 

Glenwood Canyon near Garfield County-Eagle County line 

(fig. 4). The highest ledge is the Leadville Limestone of Early 

Mississippian age. Glenwood Canyon sign is for the westbound lane of Interstate Highway 70.

U14 Evolution of Sedimentary Basins Uinta and Piceance Basins
weathers buff to tan. I could not accurately identify fragmental macrofossils, but Bass and Northrop (1963, p. 20) 

reported fossil-fish fragments at this locality and C.A. 

Sandberg (written commun., 1990) found large fish plates. 

The petrology and origin (fig. 13A) of the sandstones 

(quartzites) of the Parting were studied by Campbell (1967, 

1972b), who concluded that the Parting was deposited in a 

shallow-marine environment (1972b, p. 264). Sediment was 

transported from the east during deposition of the lowest 

part of the Parting and from the northeast to north during 

deposition of the upper part of the Parting (p. 265). 

Campbell postulated that these sediments were derived from 

the Front Range highland located in the same area as the 

possible source of the Cambrian Sawatch Quartzite sediments discussed earlier in this paper and by Tweto and 

Lovering (1977). Subsequently, Thomas (1971) studied this 

same interval to the south in northern Gunnison County and 

concluded that essentially none of the Parting could have 

originated from the Uncompahgre uplift to the southeast, 

which, as noted by Bryant (1979, p. 19), would contradict 

the proposal by Pampe (1970) that the Uncompahgre uplift 

was a sediment source for the Parting (fig. 13A).

Dyer Dolomite

In the White River Plateau, the Dyer Dolomite is 

predominantly limestone in its lower part (Broken Rib 

Member) and dolomite in its upper part (Coffee Pot 

Member). I measured 42 m of Dyer in the Glenwood 

Canyon section; Bass and Northrop (1963, p. 18) reported 

46.3 m at this locality. At another location in Glenwood 

Canyon (SWl/4 sec. 16, T. 5 S., R. 87 W.), Campbell 

(1970b, p. 320, fig. 12) reported a thickness of 18.9 m for 

his predominantly limestone lower Broken Rib Member and 

30.5 m for his predominantly dolomite Coffee Pot Member. 

Minor uplift and erosion terminated Dyer deposition (Campbell, 1970a, p. 97) before the Dyer was overlain disconformably by the Oilman Sandstone.

Broken Rib Member

The Broken Rib Member forms a distinctive ledge 

(fig. 14) of "knobbly" weathering limestone (Bass and 

Northrop, 1963) containing uncommon dolomite lenses and 

stringers. Fossils are common in the Broken Rib, but I made 

no attempt to identify them because Bass and Northrop 

(1963, p. 22, table 1) had already done so. The Broken Rib 

Member is interpreted to have formed in a shallow, sublittoral marine environment (Campbell, 1970b, p. 97).

Coffee Pot Member

The Coffee Pot Member consists of thin to thick beds 

of gray (tan weathering) dolomite, dolomitic limestone, and 

limestone. The fossil faunas of the Coffee Pot have been

described by Bass and Northrop (1963, p. 21-26), Campbell 

(1970a, p. 323-324), and Sandberg and Poole (1977, 

p. 169-171). The most distinctive sedimentary features of 

this sequence are abundant rip-up clasts (some with 

upturned edges suggesting a desiccated mudflat origin), 

stromatolitic algae, intraformational dolomite breccias, thin 

laminations of micrite, and possibly bioturbated bedding. 

Campbell (1970a, p. 94-95) inferred that the Coffee Pot 

Member was deposited in a shallow to subaerially exposed, 

muddy tidal flat on the margins of a regressing latest 

Devonian (and earliest Mississippian?) sea (also see Baars 

and Campbell, 1968). Campbell (1970a, p. 322-323) attributed sedimentary structures in the Coffee Pot Member to 

intertidal channels and burrowing organisms (fig. 13B).

Gilman Sandstone

As previously stated, Tweto and Lovering (1977) 

reassigned the Gilman Sandstone from the Leadville 

Limestone to the uppermost Chaffee Group. Tweto and 

Lovering (1977, p. 24) placed it in the Chaffee Group 

because "of its close relation to the Dyer in character, 

origin, and probably age" and indicated that it is "probably 

of eolian origin although obviously reworked in water." 

Most earlier authors (Rothrock, 1960, p. 19; Nadeau, 1972, 

p. 86) considered this thin sequence of sandstone or 

quartzite, dolomite sandstone, and shale to represent the 

basal transgression of the continental-shelf-margin sea that 

produced the Leadville Limestone and its correlatives 

(Madison Limestone, Escabrosa Group, Redwall Limestone) throughout much of the western United States. This 

concept is now believed to be erroneous because of a 

regional disconformity that intervenes between uppermost 

Famennian-lowest Kinderhookian and uppermost Kinderhookian rocks (Gutschick and others, 1980).

In the two places in Glenwood Canyon where I 

examined the Gilman Sandstone (appendix 1), in the section 

where the rest of the Chaffee Group was measured and in 

the cliffs on the south side of Interstate Highway 70 about 

a third of a kilometer east of the French Creek highway 

crossing, the Gilman is highly variable, consisting of 

dolomite and sandstone. Although it is about 5 m thick at 

the Garfield County-Eagle County boundary, it is much 

thinner at French Creek to the point of being difficult to 

locate beneath the Leadville cliff. At French Creek the loose 

debris is predominantly a ferruginous friable sandstone. I 

did not observe the sedimentary breccias in the Gilman that 

Bryant (1979, p. 21) considered to be distinctive of the 

formation in the Aspen area. The thinness of the Gilman, its 

varied lithology, and its bounding upper disconformity 

suggest that it was deposited in a changing environment of 

very shallow water, probably accompanied by mild epeirogenesis (fig. 13C) that was possibly related to the strengthening Antler orogeny in western Utah and Nevada (Johnson, 

1971).

Precambrian to Earliest Mississippian Stratigraphy, Colorado U15
109'

UINTA

AULACOGEN 

I ( LAND ? ) 

I

FRON

RATSIGE

HIGHLAND

GRAND

DYER 

GARFIELD DOLOMITE

41°,

109°

25

100 KILOMETERS

_J

I 

50 MILES

EXPLANATION 

 Fault zone

Figure 13. Paleogeography of northwestern Colorado from the Late Devonian to the Early Mississippian. A, Frasnian(?) or 

Famennian (Parting Formation). B, Famennian (Dyer Dolomite). C, Famennian or earliest Mississippian (Kinderhookian) (Gilman 

Sandstone).

Devonian Lodore(?) Formation indicate that it may be, in part, Devonian in age. Recent

work by Herr and others (1982, p. 116-119) indicates that

As indicated earlier in this paper, recent pale- an average glauconite age of two samples from the upper 

ontological studies of the top of the Lodore(?) Formation Lodore(?) is Devonian (387±5 Ma), but Herr and others

U16 Evolution of Sedimentary Basins Uinta and Piceance Basins
Figure 14. Distinctive gray nodular limestone near base of 

Broken Rib Member of the Dyer Dolomite. Outcrop is about 

400 m north-northeast of the Interstate Highway 70 bridge 

over French Creek, Glenwood Canyon (fig. 4). Hammer shown 

for scale.

indicated that the dates might be in error because of 

analytical difficulties and would not refute a Cambrian age 

for the Lodore. The ichnofossil determinations of Herr and 

others range over too much time to be conclusive. If the 

Lodore is even partly Devonian, the geologic history of 

extreme northwestern Colorado needs some reinterpretation. Herr and others (1982) offered evidence that the 

Lodore(?) is a relatively thin clastic unit that was deposited 

on the craton in a shallow marine trough and was never 

deeply buried. Because the Lodore(?) was deposited on and 

near the site of the Uinta Mountains and because apparently 

nearly continuous tectonic activity is associated with the 

Uinta Mountains (Hansen, 1986a, b), a thin Lodore(?) 

Formation suggests that subsidence rates in this area were 

minimal well into the early Paleozoic. If these highest 

Lodore(?) rocks are in fact Devonian, a heretofore unrecognized disconformity must separate them from the 

Cambrian rocks, and an additional formation name would 

be warranted, provided the limits of the formation could be 

ascertained. Serious questions remain about the age of the 

Lodore(?), and additional study of its age range, provenance, and sedimentology might be profitable.

CONCLUSIONS

The lower Paleozoic sedimentary sequence in northwestern Colorado and adjacent areas is a result of several 

episodes of shallow-marine transgression and regression 

that accompanied mild epeirogenesis and probably eustatic 

sea-level changes. The patterns and locations of sedimentation and erosion probably were partly controlled by 

regional fault and fracture systems established in the Precambrian and subsequently intermittently reactivated. The 

thinness of all these rock units and their predominantly 

shallow-water carbonate and mature sandstone lithology 

suggest that extensive shallow seas, widely shifting

shorelines, and low-relief land masses were prevalent 

environments from the Late Cambrian to latest Devonian in 

northwestern Colorado. The inception of the latest Devonian to Mississippian Antler orogenic event(s) to the west in 

the area of the modern-day Great Basin probably affected 

sedimentation close to and on the craton.

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Osmond, J.C., 1986, Petroleum geology of the Uinta MountainsWhite River uplift, Colorado and Utah, in Stone, D.S., and 

Johnson, K.S., eds., New interpretations of northwest 

Colorado geology: Rocky Mountain Association of Geologists, p. 213-221.

Palmer, A.R., 1965, Trilobites of the Late Cambrian Pterocephadiid biomere in the Great Basin, United States: U.S. 

Geological Survey Professional Paper 493, 105 p.

____ 1981, Subdivision of the Sauk sequence, in Taylor, M.E., 

ed., Short papers for the Second International Symposium 

on the Cambrian System: U.S. Geological Survey Open-File 

Report 81-743, p. 160-162.

Pampe, W.R., 1970, Stratigraphy of the Devonian rocks of western 

Colorado: Earth Science Bulletin, v. 3, p. 19-43.

Poole, F.G., Baars, D.L., Drewes, H., Hayes, P.T., Ketner, K.B., 

McKee, E.D., Teichert, C, and Williams, J.S., 1967, Devonian of the southwestern United States, in Oswald, D.H., 

ed., International Symposium on the Devonian System: 

Society of Petroleum Geologists, Calgary, Alberta, 

p. 879-912.

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

Mountains Geologic analysis of a foreland subthrust play, 

in Stone, D.S., and Johnson, K.S. eds., New interpretations 

of northwest Colorado geology: Rocky Mountain Association of Geologists, p. 183-190.

Purucker, M., 1988, Petrologic, paleomagnetic, and structural 

evidence of a Paleozoic rift system in Oklahoma, New 

Mexico, Colorado, and Utah, Discussion: Geological 

Society of America Bulletin, v. 100, p. 1846-1847.

Ritzma, H.R., 1983, Igneous dikes of eastern Uinta Mountains, 

Utah and Colorado: Utah Geological and Mineral Survey 

Special Studies 56, 23 p.

Rold, J.W., 1961, The structure and lower and Middle Paleozoic 

stratigraphy of the Wellsville area, Colorado, in Berg, R.R., 

and Rold, J.W., eds., Symposium on Lower and Middle 

Paleozoic Rocks of Colorado: Rocky Mountain Association 

of Geologists Field Conference, 12th, p. 107-117.

Ross, R.J., Jr. 1951, Stratigraphy of the Garden City Formation in 

northeastern Utah, and its trilobite faunas: Yale University, 

Peabody Museum of Natural History Bulletin 6, 161 p.

____ 1976a, Ordovician sedimentation in the western United 

States, in Basset, M.G., ed., The Ordovician System: 

Paleontological Association Symposium, Birmingham, 

Proceedings; Cardiff, Glamorganshire, United Kingdom, 

University of Wales Press, p. 73-205.

____ 1976b, Reprint of 1976a, in Symposium on Geology of the 

Cordilleran Hingeline: Rocky Mountain Association of 

Geologists, p. 109-133.

____ 1986, Lower Paleozoic of northwest Colorado, in Stone 

D.S., and Johnson, K.S., eds., New interpretations of 

northwest Colorado geology: Rocky Mountain Association 

of Geologists, p. 99-102.

Ross, R.J., Jr., and Tweto, Ogden, 1980, Lower Paleozoic 

sediments and tectonics in Colorado, in Kent, H.C., and 

Porter, eds., Colorado geology: Rocky Mountain Association of Geologists, p. 47-56.

Precambrian to Earliest Mississippian Stratigraphy, Colorado U19
Rothrock, D.P., 1960, Devonian and Mississippian Systems in 

Colorado, in Weimer, R.J., and Haun, J.D., eds., Guide to 

the geology of Colorado: Geological Society of America, 

Rocky Mountain Association of Geologists, and Colorado 

Scientific Society, p. 17-22.

Rowley, P.D., Hansen, W.R., Tweto, Ogden, and Carrara, P.E., 

1985, Geologic map of the Vernal I°x2° quadrangle, 

Colorado, Utah, and Wyoming: U.S. Geological Survey 

Map 1-1526, scale 1:250,000.

Sandberg, C.A., and Mapel, W.J., 1967, Devonian of the northern 

Rocky Mountains and Plains, in Oswald, D.H., ed., International Symposium on the Devonian System: Alberta 

Society of Petroleum Geologists, Calgary, Alberta, p. 843- 

877.

Sandberg, C.A., and Poole, F.G., 1977, Conodont biostratigraphy 

and depositional complexes of Upper Devonian cratonicplatform and continental-shelf rocks in the western United 

States, in Murphy, M.S., Berry, W.B.N., and Sandberg, 

C.A., eds., Western North America Devonian: University of California, Riverside, Museum Contribution 4, 

p. 144-182.

Sando, W.J., and Sandberg, C.A., 1987, New interpretations of 

Paleozoic stratigraphy and history in the northern Laramie 

Range and vicinity, southeast Wyoming: U.S. Geological 

Survey Professional Paper 1450, 39 p.

Scott, G.R., and Taylor, R.B., 1974, Reconnaissance geologic map 

of the Rockvale quadrangle, Custer and Fremont Counties, 

Colorado: U.S. Geological Survey Map MF-562.

Sears, J.W., Groff, P.J., and Holden, G.S., 1982, Tectonic 

evolution of lower Proterozoic, Uinta Mountains, Utah and 

Colorado: Geological Society of America Bulletin, v. 93, 

p. 990-997.

Seeland, D.A., 1968, Paleocurrents of the late Precambrian to early 

Ordovician (basal Sauk) transgressive elastics of the 

western and northern United States with a review of the 

stratigraphy: Salt Lake City, University of Utah, Ph.D. 

thesis, 170 p.

Sheehan, P.M., 1980, Paleogeography and marine communities of 

the Silurian carbonate shelf in Utah and Nevada, in Fouch, 

T.D., and Magathan, E., eds., Paleozoic paleogeography of 

the west-central United States: Rocky Mountain Section, 

Society of Economic Paleontologists and Mineralogists 

West-Central United States Paleogeography Symposium 1, 

p. 19-37.

____ 1988, Late Ordovician events and the terminal Ordovician 

extinction, in Wolberg, D.L., compiler, Contributions to 

Paleozoic paleontology and stratigraphy in honor of Rousseau H. Flower: New Mexico Bureau of Mines and Mineral 

Resources Memoir 44, p. 405-415.

Sloss, L.L., 1963, Sequences in the cratonic interior of North 

America: Geological Society of America Bulletin, v. 74, 

p. 93-111.

Stevens, D.N., 1961, Cambrian and Lower Ordovician stratigraphy 

of central Colorado, in Berg, R.R., and Rold, J.W., eds., 

Symposium on Lower and Middle Paleozoic Rocks of 

Colorado: Rocky Mountain Association of Geologists Field 

Conference, 12th, p. 7-15.

Stewart, J.H., 1976, Late Precambrian evolution of North 

America Plate tectonics implication: Geology, v. 4, 

p. 11-15.

Stone, D.S., 1975, A dynamic analysis of subsurface structure in 

northwestern Colorado, in Bolyard, D.W., ed., Symposium 

on Deep Drilling Frontiers in the Central Rocky Mountains: 

Rocky Mountain Association of Geologists, p. 33-40.

____ 1977, Tectonic history of the Uncompahgre Uplift, in 

Veal, H.K., ed., Exploration frontiers of the central and 

southern Rockies: Rocky Mountain Association of 

Geologists, p. 23-30.

____ 1986, Seismic and borehole evidence for important preLaramide faulting along the axial arch in northwest 

Colorado, in Stone, D.S., and Johnson, K.S., eds., New 

interpretations of northwest Colorado geology: Rocky 

Mountain Association of Geologists, p. 19-36.

____ 1989, Uinta Mountains An inverted Proterozoic aulacogen [abs.]: Rocky Mountain Association of Geologists, The

Outcrop. 

Sweet, W.C., 1954, Harding and Fremont Formations, Colorado:

American Association of Petroleum Geologists Bulletin,

v. 38, p. 284-305. 

____ 1955, Conodonts from the Harding Formation (Middle

Ordovician) of Colorado: Journal of Paleontology, v. 29,

p. 226-262. 

____1961, Middle and Upper Ordovician rocks, central

Colorado, in Berg, R.R., and Rold, J.W., eds., Symposium 

on Lower and Middle Paleozoic Rocks of Colorado: Rocky 

Mountain Association of Geologists Field Conference, 12th, 

p. 17-24.

Taylor, R.B., and Scott, G.R., 1972, Reconnaissance geologic map 

of the Wetmore quadrangle, Custer and Pueblo Counties, 

Colorado: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-548.

Taylor, R.B., Scott, G.R., and Wobus, R.A., 1975, Reconnaissance 

geologic map of the Howard quadrangle, central Colorado: 

U.S. Geological Survey Miscellaneous Investigations Map 

1-892.

Taylor, R.B., Scott, G.R., Wobus, R.A., and Epis, R.C., 1975, 

Reconnaissance geologic map of the Cotopaxi 15-minute 

quadrangle, Fremont and Custer Counties, Colorado: U.S. 

Geological Survey Miscellaneous Investigations Map 

1-900.

Thomas, W.A., 1971, Devonian stratigraphy north of the 

Uncompahgre uplift, Colorado: The Mountain Geologist, 

v. 8, p. 85-88.

Tweto, O., 1949, Stratigraphy of the Pando area, Eagle County, 

Colorado: Colorado Scientific Society Proceedings, v. 15, 

p. 149-235.

____ 1956, Geology of the Tennessee Pass area, Eagle and Lake 

Counties, Colorado: U.S. Geological Survey Mineral Investigations Field Studies Map MF-34.

____ 1974, Geologic map and sections of the Holy Cross 

quadrangle, Eagle, Lake, Pitkin, and Summit Counties, 

Colorado: U.S. Geological Survey Miscellaneous Investigations Map 1-830.

____ 1975, Laramide (Late Cretaceous-early Tertiary) orogeny 

in the southern Rocky Mountains, in Curtis, B., ed., Cenozoic history of the southern Rocky Mountains: Geological 

Society of America Memoir 194, p. 1-44.

U20 Evolution of Sedimentary Basins Uinta and Piceance Basins
_ 1977, Tectonic history of west-central Colorado, in Veal, 

H.K., ed., Exploration frontiers of the central and southern 

Rockies: Rocky Mountain Association of Geologists, 

p. 11-22.

_ 1980a, Tectonic history of Colorado, in Kent, H.C., and 

Porter, K., eds., Colorado geology: Rocky Mountain Association of Geologists, p. 5-9.

_ 1980b, Precambrian geology of Colorado, in Kent, H.C., 

and Porter, K., eds., Colorado geology: Rocky Mountain 

Association of Geologists, p. 37-46.

_ 1987, Rock units of the Precambrian basement in Colorado: U.S. Geological Survey Professional Paper 1321-A, 

54 p.

Tweto, O., and Lovering, T.S., 1977, Geology of the Minturn 

15-minute quadrangle, Eagle and Summit Counties, Colorado, and general geology of the Oilman mining district: 

U.S. Geological Survey Professional Paper 956, 96 p.

Tweto, O., Moench, R.H., and Reed, J.C., Jr., 1978, Geologic map 

of the Leadville I°x2° quadrangle, northwestern Colorado: 

U.S. Geological Survey Miscellaneous Geological Investigations Map 1-999.

Tweto, O., and Sims, P.K., 1963, Precambrian ancestry of the 

Colorado mineral belt: Geological Society of America 

Bulletin, v. 74, p. 991-1014.

Tyler, T.F., and Campbell, J.A., 1975, Dotsero Formation, western 

Colorado: The Mountain Geologist, v. 12, p. 113-118.

Unterman, G.E., and Unterman, B.R., 1949, Geology of Green and 

Yampa River Canyons and vicinity, Dinosaur National

Monument, Utah and Colorado: American Association of 

Petroleum Geologists Bulletin, v. 33, p. 683-694.

Van der Voo, R., 1988, Paleozoic paleogeography of North 

America, Gondwana, and intervening displaced terranes 

Comparisons of paleomagnetism with paleoclimatology and 

biogeographical patterns: Geological Society of America 

Bulletin, v. 100, p. 311-324.

Wallace, C.A., 1972, A basin analysis of the Upper Precambrian 

Uinta Mountain Group, Utah: Santa Barbara, University of 

California, Ph.D. thesis, 412 p.

Warner, L.A., 1980, The Colorado lineament, in Kent, H.C., and 

Porter, K., eds., Colorado geology: Rocky Mountain Association of Geologists, p. 11-21.

____ 1978, The Colorado lineament A middle Precambrian 

wrench fault system: Geological Society of America 

Bulletin, v. 89, p. 161-171.

Witzke, B.J., 1980, Middle and upper Ordovician paleogeography 

of the region bordering the transcontinental arch, in Fouch, 

T.D., and Magathan, E., eds., Paleozoic paleogeography of 

the west-central United States: Rocky Mountain Section, 

Society of Economic Paleontologists and Mineralogists 

West-Central United States Paleogeography Symposium 1, 

p. 1-18.

Zech, R.S., 1988, Geologic map of the Fossil Ridge area, Gunnison County, Colorado: U.S. Geological Survey Map 

1-1883.

Precambrian to Earliest Mississippian Stratigraphy, Colorado U21
Appendix 1. Measured sections

LITHOLOGIC TYPES 

(combination of symbols indicates variation in individual units)

Igneous and metamorphic rocks

Orthoquartzite

Dolomite

Sandy dolomite to dolomitic sandstone

HI Dolomitic shale to shaly dolomite

Nodular limestone

Conglomeratic limestone

Stromatolitic limestone

Sandy limestone to calcareous sandstone

Sandstone

Shale

U22 Evolution of Sedimentary Basins Uinta and Piceance Basins
Appendix 1. Measured sections Continued

I

O

o

Q. 

HI

Z

^r CAMBRI/

HI

SERIES/ 

STAGE

z

PEALEAU/

LLJ 

OC

1-

Z

ORMATIO

LL.

OTSERO

Q

MEMBER

i 

o *~

CANYON

Q 

O

i

z

LLJ

O

00 

QC 

LU

150-i

US

130

Section of Dotsero Formation, unnamed Upper Cambrian 

rocks. Peerless Formation(?), and Sawatch Quartzite, Dead 

Horse Gulch area, Glenwood Canyon, Colorado. NW14, 

NW1/4 , SE14, sec. 19, T. 5 S., R. 87 W., Garfield 

County

Manitou Formation

Top of Clinetop Member of the Dotsero Formation.

White- to light-lavender-weathering gray stromatolitic limestone.

(Note: Stromatolites were not seen in the Dead Horse Gulch

section but are present in other places on the White River

Plateau.)

Top of Glenwood Canyon Member of the Dotsero Formation.

Gray sandy and shaly limestone conglomerate in beds 

7.6-15.2 cm thick; minor interbedded calcareous gray-green 

shale. Where elongated, pebbles are mostly flat lying in the 

crystalline limestone matrix. Worm burrows (?) or fucoid markings 

common. Limestone grades to dolomite. It is difficult to 

distinguish dolomitic limestone from calcareous dolomite in most 

of this unit.

125

Calcareous shaly sandstone with glauconite; bottom of bed not 

seen.

Covered interval.

Interbedded conglomeratic tan shaly dolomite and glauconitic 

greenish-tan shale. Worm burrows (?) or fucoid marks common.

Brown silty dolomite in beds 1 5-20 cm thick; few green shale 

interbeds. Uncommon worm burrows (?) or fucoid marks.

Tan dolomitic silty quartz sandstone beds 0.8-2 cm thick.

Gray, tan-weathering crystalline limestone; two beds are 

conglomeratic; thin calcareous sandstone bed at top.

Covered interval

Section offset about 450 m to northwest.

Brown to greenish-brown micaceous sandstone and brown 

sandy dolomite in beds 0.5-3 cm thick; glauconite grains may 

be present. Mudcracks common on some shaly beds. Basal 

contact with underlying quartzite is sharp. Quartzite forms 

distinctive ledge in cliff.

Base of Dotsero Formation. 

Contact probably is conformable.

Precambrian to Earliest Mississippian Stratigraphy, Colorado U23
Appendix 1. Measured sections Continued

c

03

Q.

Z

<

cc

CD

^

6

LU

rf

-1

Z

LU

^f

LU

QLU

1- 

DC

O

Z

z

o

0

1LL.

CO

Q

LU

CO

o

LU

^

Z

z

120-

115-

110

105

Almost white, slightly tan weathering, clean, well-sorted quartzite 

30 and minor tan-weathering light-tan sandy dolomite beds near 

top. Forms sheet cliff at top of Sawatch Quartzite.

U24 Evolution of Sedimentary Basins Uinta and Piceance Basins
Appendix 1. Measured sections Continued

Z

o

CJ

i

100-

95-

90 -

85 

on

-:A'.:j -A:-.

?C-"'.r$':.->s

 w?:$?{ ::: /. :.;:. % : 

'>;£".: : jjfi's

r- ! j?v::. :?/i-'

JL''ffiy.':v'/f; :,

/r ' " '/ ; ' " '* 

' ' j!-i'i-C-jt+S:

^' :^-"V-!v^>

.'. . .-;7-.-V*'"> i

::/. ;. .:':./V:'r.

 . ; >/: , '.; ' ^//

^VvjX'/AV

'flfc'Wfa'':. i:: -.vt-.':V;-ife

^}v:%-i'/ ;.''..;X

vS/'-viv/'Jv'.^vV"^:

vi'/iv'/'/;

'^ i/'f'i' !l. :.

 fc'"\':J: '.' ',*. '

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 ;.^C.v:*.7^

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/ -; .:./ .; . . /:

f:f 'f'y';?j :

V/-../!:^.--.i

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i^^F

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/ :..'/; . ;/.- 

ty';:;:fc ' :. ' 

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<"iv.:X:.:.'.'-v£-;

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'' VJ^V

,

1

/

29

28

27

26

Brown sandy dolomite and minor quartzite pods or stringers(?). 

Possibly an erosional break at top.

Almost white quartz sandstone, slightly dolomitic in beds 0.6 cm 

thick. Abrupt change from dolomite below.

Massive brown sandy dolomite in beds 0.25-0.5 m thick.

Brown sandy dolomite in five distinctive beds 0.2 m thick. Forms 

distinctive notch in ledge. Selected as the contact between 

Sawatch Quartzite and Peerless(?) Formation.

Precambrian to Earliest Mississippian Stratigraphy, Colorado U25
Appendix 1. Measured sections Continued

"^

to

Q. ' '

CAMBRIAN E 

__ _ __

+^

to

Q.

ESBACHIAN (

cc Q

to

Q.

" "

UJ hQUARTZI rCH 

1

75-

70-

65-

60-

55 

'$m&

25

Massive white vitreous orthoquartzite. Sheer cliff in most places 

in Glenwood Canyon and vicinity makes detailed examination 

almost impossible.

24

23

Tan shaly dolomitic sandstone, shaly calcareous sandstone, and 

crenulated mudstone. Mudcracks. Soft-sediment deformation 

may be present in at least one bed. No quartzite. Vegetation 

break at base of unit.

Massive-bedded buff-weathering pink to white quartzite. Similar 

to unit 21 except argillaceous sandstone is mostly missing. 

Sheer cliff.

U26 Evolution of Sedimentary Basins Uinta and Piceance Basins
Appendix 1. Measured sections Continued

(0

CAMBRIAN LATE 

t

to

Q.

DRESBACHIAN

to

.2:

LU

SAWATCH QUARTZI

50-

45-

40-

Purple arenaceous shale 0.1 5 m thick.

'Z3&&&5 \?rx ^ . y'.-.:--

21

20

19

16

15

14

13

Massive-bedded buff-weathering almost white orthoquartzite in 

beds 0.25-1.0 m thick. Some beds have zones of argillaceous 

sandstone, but mostly rock is hard orthoquartzite with no shaly 

interbeds.

Buff-weathering white orthoquartzite and entrained pods or 

stringers of pink to white quartz sandstone that have little 

conformable relationship with bedding of surrounding quartzite. 

Not continuous from place to place.

Quartzite as in unit 18.

Covered vegetation break; interval seen in canyon walls in 

many places.

One massive bed of almost white ferruginous orthoquartzite that 

has purple cast on weathered surface. Rock is marginally a wellindurated ferruginous sandstone; barely breaks across grains. 

Some quartz grains are granule size.

Covered vegetation break.

Interbedded tan-weathering very light gray vitreous glauconitic 

orthoquartzite and purple shale.

Massive-bedded light-tan-weathering white orthoquartzite; minor 

poorly developed crossbedding.

Medium-bedded sandy almost white orthoquartzite and thin 

shale interbeds and massive orthoquartzite as in unit 14.

Medium-bedded sandy almost white orthoquartzite and thin 

shale interbeds; massive white vitreous orthoquartzite at top.

Medium-bedded crossbedded orthoquartzite that has a purplish 

cast on weathered surface.

Precambrian to Earliest Mississippian Stratigraphy, Colorado U27
Appendix 1. Measured sections Continued

-~

to

Q. ' '

CAMBRIAN LATE 

 £ 

(0

Q.

(DRESBACHIAN 

t

to

 

HI 1-

^ WATCH QUARTZI

CO

PRECAMBRIAN

Quartzite with purplish cast and white vitreous orthoquartzite 

interbedded with tan-buff friable arkosic quartz sandstone and 

muddy sandstone. There is distinctive "bedding" between the 

quartzites but not between quartzites and sandstones as shown 

in figure 6. This contrasts with the overlying quartzite unit 1 3, 

which is distinctly bedded. A preliminary interpretation of unit 12 

is that it represents a transition to a higher energy turbulentwater environment from the presumably quieter water 

environment of the massive orthoquartzite above and below.

Massive orthoquartzite as below, but in beds 8-12 cm thick. 

Contains glauconite and minor feldspar grains.

Units 8-10 are massive-bedded vitreous orthoquartzite that 

contains minor glauconite and hematite. Shaly beds are almost 

as resistant as quartzite but have a more pronounced purple 

color and are fine grained. Quartzite is faintly crossbedded in 

places and is well jointed along separation planes. Intervals 

forms a sheer cliff that makes access difficult. Shale forms minor 

notch in cliff.

Massive slightly crossbedded arkosic orthoquartzite, vitreous 

white where freshly fractured; weathers to a purplish cast. 

Thin purple variegated shale. Forms minor notch in cliff.

Massive granular arkosic buff sandstone; crossbedded as unit 2. 

Purple shaly faintly crossbedded sandstone that contains 

distinctive quartz sandstone beds 2-5 cm thick. 

Vitreous white orthoquartzite in one thin bed.

Vitreous white orthoquartzite, crossbedded tabular in beds 

0.1 5-0.3 m thick; minor arkosic sandstone.

Quartz-pebble conglomerate that has 0.5-1.0 cm clasts set in 

reddish-brown to white quartzite matrix.

Base of Sawatch Quartzite

Purple phyllite and weathered "rotted" pegmatite.

U28 Evolution of Sedimentary Basins Uinta and Piceance Basins
LATE DEVONIAN (part)

FAMENNIAN (part)

DYER DOLOMITE (part)

^ARLY MISSISSIPPlAN 

\OR LATE DEVONIAN

( KINDERHOOKIAN 

X OR FAMENNIAN

\ GILMAN 

) SANDSTONE V

COFFEE POT MEMBER (part) X

MISS

KINDE

AND 

LE

LIM

1 - S1 2 « S rt <

3" W <

CD 0) CD

o 

m 

2. fi

0.=- 

C O = o- o "

CT 3 CQ

 < s.- S

Q. CD < 

CD __ Q. 

°" 2? °

(Q O' O M 

. 0>

T °- 

PS

cog

3 *

J

 o 

^eSIO

I .

JT 3

m CQ
Appendix 1. Measured sections Continued

I

z

<

DEVON

LU

^

CO

Q.

Z

1ENNIA

<£

u_

CO

a

LU

t

O

O 

Q

cc

LU

>

t(0a.

H

oa.

LU 

UJ

u_

u_ 

0

CJ

QQ

CC

Z

O

cc

CO

Gray-weathering gray limestone conglomerate in beds about 

0.2 m thick.

Fine-crystalline dolomite similar to that in unit 1 5 except bedding 

is more nearly planar and intraformational conglomerate is 

absent.

Dolomitic gray shale.

Crystalline gray-to-tan weathering gray dolomite in beds 0.2-0.6 m 

thick. Several beds near top contain intraformational conglomerate 

and probable stromatolites.

Covered interval.

Bottom of Coffee Pot Member of Campbell (1 970).

Top of Broken Rib Member of Campbell (1970).

Gray nodular, crystalline, very fossiliferous limestone. Nodular 

character makes bedding virtually impossible to distinguish in 

the field. Evidence of paleokarst and solution cavities. Small 

solution cavities (<1 cm) are commonly filled with white 

crystalline calcite. Forms a distinctive gray ledge.

Calcareous black shale. 

Bottom of Dyer Formation. 

Top of Parting Formation.

U30 Evolution of Sedimentary Basins Uinta and Piceance Basins
Appendix 1. Measured sections Continued

tT

CD

Q.

z

1111

Q

LLJ

§

Z

^j ^ t3

oc> , <0 Q Ul Q 

CC

O

Z

z 

z

111

liCC

0

f^"

z

z

u_

^-* 

F

co

Q.

Z

^

5

z

6

z h-

^1*

->s»X"

to

Q.

^

O

z

^

N.^^ 

5 

Massive-bedded orthoquartzite and minor thin shale beds. Forms 

ledge that is difficult to access.

Gray, tan-weathering fine-crystalline dolomite, calcareous gray 

interbedded shale, and a few beds of very sandy dolomite and 

dolomitic sandstone. Forms rubble-strewn slope. C.A. Sandberg 

(written commun., 1990) indicated that Famennian conodonts 

are at the top of this interval.

Black and green dolomitic shale and thin, gray, tan-weathering 

crystalline dolomite. Forms rubbly slope that is partly covered 

and difficult to access.

Sandstone and sandy gray-green shale in a few thin interbeds. 

Upper beds of sandstone are marginally quartzite.

Sandy gray-green shale.

-Slightly sandy gray, tan- to buff-weathering dolomite in beds 

about 0.2 m thick. 

Fractured, tightly cemented dolomitic gray shale.

Shaly tan-weathering gray dolomite and interbedded greenishgray shale.

Sandy medium-bedded tan-weathering dolomite in beds 

0.2 m thick.

Interbedded dark-gray shale, tan-weathering gray dolomite, and 

dolomitic quartz sandstone.

Three beds of brown crystalline dolomite.

Thin-bedded, brown shaly dolomite and thin shale interbeds. 

Shale is brown to green.

Quartz sandstone and gray-green shale; sandstone contains 

quartz granules, rock fragments, and feldspar. 

Base of Parting Formation. 

Top of Manitou Formation. 

-Buff sandy dolomite.

Precambrian to Earliest Mississippian Stratigraphy, Colorado U31
Appendix 1. Measured sections Continued

X 

CJ

oQ. 

LU

Z

§iLU

Q

« » » 

tfto

Z

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French Creek, Glenwood Canyon, Garfield County, 

Colorado. SE 1/*, sec. 16, T. 5 S., R. 87 W.

Thin-bedded tan fine-crystalline dolomite and some shale and 

sandy streaks.

Thin ledge of light-tan slightly dolomitic orthoquartzite.

Base of Parting Formation of Chaffee Group.

Thin shale or paleosol (?) zone at contact.

Top of Manitou Formation (Tie Gulch Dolomite Member).

Massive beds of buff sandy dolomite.

Massive, uniformly bedded micritic(?) brown-tan crystalline 

dolomitic limestone and dolomite.

Base of the Tie Gulch Dolomite Member of Manitou Formation. 

One bed of gray-green sericitic shale.

U32 Evolution of Sedimentary Basins Uinta and Piceance Basins
Appendix 1. Measured sections Continued

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-Top of Dead Horse Conglomeratic Member of Manitou 

Formation.

One bed of dolomitic quartzite with a "conglomerate" of granulesize quartz grains at top.

Massive thick-bedded gray crystalline limestone; conglomeratic 

in many beds.

Single bed of massive buff-to tan-weathering dolomitic quartzite.

Thin-bedded (about 0.2 m or less) gray-weathering sandy 

limestone; minor calcite crystals fill vugs and a few beds of 

interbedded sandy dolomite.

Massive, buff-weathering dolomitic limestone bed about 0.5 m 

thick and a sandy limestone bed at base.

Thin-bedded gray- to buff-weathering conglomeratic limestone 

similar to unit 6. Interval is partly covered by colluvium.

Thin white calcareous quartz sandstone.

Thin-bedded tan-weathering dark-gray sandy and shaly limestone 

with shale partings between some beds. Some shales show flute 

casts and mudcracks. Limestone is conglomeratic and has 

shallow-water rippling and salt casts in a few places.

One bed of massive buff dolomitic orthoquartzite.

Shaly dolomite conglomerate; internal structure indicating 

turbation, possibly by waves.

-One bed of massive sandy tan-weathering dolomite. 

Gray conglomeratic massive limestone.

Calcareous maroon and green shale. 

Base of Manitou Formation.

-Clinetop Member of Dotsero Formation. (Late Cambrian, 

Trempealeauan).

Precambrian to Earliest Mississippian Stratigraphy, Colorado U33
Appendix 2. Oil and gas wells and test bores that penetrate Devonian and older rocks, northwestern Colorado

The oil and gas test bores listed are in the records of the State of Colorado Oil and Gas Conservation Commission and are the bores 

that I could find that penetrate Devonian and older rocks in northwestern Colorado. Available subsurface geophysical logs for these 

bores were also examined. A few important points about these drill holes are as follows.

1. Very few bores penetrate the Leadville (Madison) Limestone considering the size of the area studied. 

Almost all of those that do terminate in the Mississippian rocks in order to ensure that the entire 

Pennsylvanian section, the presumed exploration objective, has been drilled. The Mississippian limestones 

are easily identified in drill cuttings and geophysical logs.

2. Most of the bores that penetrate Devonian and older rocks were drilled to the Precambrian, which has 

been interpreted in some places to be in fault blocks that have overridden exploration objectives in younger 

rocks in the subthrust. Due to lack of correlations between sample- and geophysical-logs and surface sections 

and a paucity of knowledge about lower Paleozoic rocks in the deep parts of northwestern Colorado basins, I 

did not attempt to interpret further the geophysical logs. Most other interpretations have been aided by deep 

seismic data, most of which are proprietary and unpublished (see Stone, 1986, for recent published data). 

Geophysical log signatures are not distinctive enough to permit reliable interpretations of the lower Paleozoic 

section without additional information.

Oil or gas well or test bore and location Comments

American Metal Climax Unit No. 1 Atchee. Sec. 24, T. 6 

S., R. 104 W., Garfield County.

Arco 1-36 Sheepstead. Near comer of Tps. 8, 9 N., Rs. 99, 

100 W.,Moffat County.

Arco 1-12 Sparks. Sec. 12, T. 8 N., R. 100 W., Moffat 

County.

Benedum-Trees Oil No. 1 Government Dougherty. Sec. 9, 

T. 1 N., R. 88 W., Garfield County.

Champlin Refining No. Black. Sec. 9, T. 5 S., R. 84 W., 

Eagle County.

E. American No. 1 Tulley. Sec. 35, T. 4 N., R. 103 W., 

Moffat County.

Forest Oil No. 1 Government. Sec. 2, T. 7 S., R. 104 W., 

Garfield County.

Louisiana Land and Exploration Axial Federal Unit 11-23. 

Sec. 23, T. 5 N., R. 94 W., Moffat County.

Louisiana Land and Exploration 31-22 Main Elk. Sec. 29, 

T. 4 S., R. 91 W., Garfield County.

Miami Oil Producers, Inc. OBrien 1. Sec. 14, T. 4 N., R. 90 

W., Moffat County.

Natomis North American 1-17 Rangely. Sec. 17, T. 1 N., R. 

100 W., Rio Blanco County.

Phillips Petroleum No. 1 Hells Hole Canyon, Sec. 12, T. 2 

S., R. 104 W., Rio Blanco County.

Vicinity of Uncompahgre uplift. See discussion of Garmesa 

fault zone in Stone (1977).

Entered Uinta Group at 4,354 ft (1,327 m).

Drilled Precambrian from 2,573 ft (784 m) to total depth at 

11,464 ft (3,494 m) in an unsuccessful attempt to drill 

into younger rocks in footwall of fault.

See Campbell (1970a).

See Campbell (1970a). Near Eagle, Colorado.

Total depth 10,231 ft (3,118 m) in Lodore Formation. See 

Powers (1986, p. 184).

Possible total depth in lower Paleozoic rocks.

Drilled 30 ft (9.1 m) of Devonian rock and 20 ft (6.1 m) of 

dolomite that may be Devonian or Ordovician Manitou 

Formation (Ross, 1986).

Proposed as Precambrian test to 14,000 ft (4,267 m). See 

Osmond (1986, p. 217). No data available.

Bottomed in Precambrian Uinta Mountain Group; Beaver 

Creek anticline area.

Total depth 14,013 ft (4,271 m) in Cambrian Sawatch 

Quartzite. See Osmond (1986).

Total depth 12,580 ft (3,834 m) in Devonian(?).

U34 Evolution of Sedimentary Basins Uinta and Piceance Basins
Appendix 2. Oil and gas wells and test bores that penetrate Devonian and older rocks, northwestern Colorado Continued

Oil or gas well or test bore and location Comments

Phillips Petroleum No. 15 Unit. Sec. 14, T. 1 S., R. 102 W., 

Rio Blanco County.

Pure Oil Company No. 1 Blue Mountain Unit. Sec. 35, T. 4 

N., R. 102 W., Moffat County.

Southern Union Pagoda Government 26-35. Sec. 26, T. 4 

N., R. 89 W., Routt County.

Tenneco Oil Company No. 1 Margie Hicks. Sec. 3, T. 3 N., 

R. 103 W., Moffat County.

Texaco Unit 66 (Wilson Creek Field). Sec. 34, T. 3 N., R. 

94 W., Rio Blanco County.

Texas Co. No. 70-30 UPRR (Rangely Field). Sec. 32, T. 2 

N., R. 102 W., Rio Blanco County.

None.

Drilled 2,688 ft (819 m) of Precambrian rocks. See Powers 

(1986, p. 184). Willow Creek anticline area.

Bottomed in Precambrian granite.

Drilled Lodore Formation in Willow Creek thrust feult(?). 

See Powers (1986, p. 184). Willow Creek anticline area.

See composite log in Stone (1975).

Total depth 9,360 ft (2,853 m) in Cambrian(?) rocks.

it U.S. GOVERNMENT PRINTING OFFICE: 1992-673-049/66006 Precambrian to Earliest Mississippian Stratigraphy, Colorado U35

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