* The Chinle (Upper Triassic) and 

Sundance (Upper Jurassic)

* Formations in

->

' North-Central Colorado

/* By G. N. PIPIRINGOS, W. J. HAIL, JR., and G. A. IZETT

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1274-N

H A description of hitherto unreported 

or little-understood stratigraphic and 

~ paleontologic details of marine 

 Jurassic and Upper Triassic rocks of 

4 a scantily studied area

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

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

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

Abstract__ ___-____---____--_---____ 

Introduction..___-___________----__-_

Chinle Formation___-____-____-_.___ 

Sundance Formation.____-_____--_-_-_

Canyon Springs Sandstone Member. 

Lak(?) Member__-__-___--------_

Pine Butte Member_____________

Windy Hill Sandstone Member_ __ 

Stratigraphic sections_____-___--_.__-_

References cited_____________________

Page

Nl

1

5

9

10

12

13

15

16

34

ILLUSTRATIONS

FIGURE 1. Map of north-central Colorado showing location of stratigraphic sections.__--_-__-___--__-__-___--_----______

2. Map showing some geographic features of northwestern 

Colorado and adjacent parts of Utah and Wyoming _____

3. Restored section showing correlation and facies changes of 

Triassic and Jurassic rocks in north-central Colorado.___

Page

N3

SECTION A 

B 

C 

D

STRATIGRAPHIC SECTIONS

Page 

Elk Creek..____________.__._____...____._______....___ N16

Radium SW.__________

Radium SE______________.

Kremmling. _______________

E. Lazy Bear___._._______.

F. Snowshoe Ranch._._______.

G. Tyler Mountain___._____.

H. McMahon Reservoir_____. 

I. McMahon Reservoir, north.

J. Frantz Creek.____________

K. Barber Basin.____________

18

20

21

23

24

25

27

30

31

33

TABLE

TABLE 1. Late Jurassic fossils collected from the Sundance Formation 

in north-central Colorado._________-_________-_--__---

Page

N4

in

CONTRIBUTIONS TO STRATIGRAPHY

> THE CHINLE (UPPER TRIASSIC) AND

SUNDANCE (UPPER JURASSIC) FORMATIONS 

IN NORTH-CENTRAL COLORADO

By G. N. PIPIRINGOS, W. J. HAIL, Jr., and G. A. IZETT

ABSTRACT

The Chinle Formation (Upper Triassic) and Sundance Formation (Upper 

Jurassic) have been studied in 11 stratigraphic sections along the flanks of the 

Park Range near Kremmling, north-central Colorado. The Chinle at Elk Oreek 

on the west side of the Park Range is about 127 feet thick and is divided into a 

lower conglomerate to sandy siltstone member, a middle silty claystone member, 

and an upper sandstone and siltstone member. To the east the Chinle is truncated 

beneath an unconformity at the 'base of the Canyon Springs Sandstone Member 

of the 'Sundance Formation, and the Chinle is absent a few miles west of 

Kremmling on the east flank of the Park Range. The lower and middle members 

of the Chinle reappear north of Kremmling between the Lazy Bear Ranch and 

McMahon Reservoir. North of McMahon Reservoir the Chinle is truncated by the 

Canyon Springs Sandstone Member.

The Chinle rests on Triassic and Permian red 'beds on the east side of the Park 

Range and on rocks lithologically similar to the red beds on the west side of 

the range.

The Sundance Formation is about 260 feet thick at Elk Creek on the west 

flank of the Park Range. It thins eastward to about 55 feet at Tyler Mountain 

and thickens northward to about 230 feet at Frantz 'Greek. The Sundance is 

divided in ascending order into the Canyon Springs Sandstone, Lak(?), Pine 

Butte, and Windy Hill Sandstone Members. The Canyon Springs is equivalent 

to the Entrada Sandstone, and the Pine Butte Member is equivalent to the lower 

part of the Gurtis Formation of northwest Colorado.

INTRODUCTION

Marine Jurassic rocks and Triassic red beds that lie below the Morrison Formation of Late Jurassic age are exposed discontinuously along 

both the east and west sides of the Park Range near Kremmling in 

north-central Colorado (figs. 1, 2). (For convenience of discussion, the 

area shown in fig. 1 will be referred to in this report as the Kremmling

Nl
N2 CONTRIBUTIONS TO STRATIGRAPHY

area.) The upper part of this sequence is here divided into four thin 

but widespread units that correspond in lithology, fossil content, and 

stratigraphic position to named members of the Upper Jurassic 

Sundance Formation of south-central Wyoming. Underlying red 'beds 

comprise the Triassic Chinle Formation and older rocks. This paper 

describes the Upper Triassic and marine Jurassic rocks exposed in the 

Kremmling area and gives the reasons for their correlation with named 

units in southern Wyoming or western Colorado. Upper Triassic and 

Upper Jurassic rocks described in this report have received scant 

attention from previous workers; references to these rocks have been 

of a general nature, or incidental to investigations of areas marginal 

to north-central Colorado, or incidental to the study of overlying or 

underlying stratigraphic units. Consequently, the principal contributions of this report are (1) detailed descriptions of the lithologies and 

fossil content of 11 stratigraphic sections, (2) the calling of attention to surprisingly rapid facies and thickness changes, particularly 

in the Sundance Formation, and (3) the correlation of the various 

stratigraphic units within the study area and with similar stratigraphic 

units in southeastern Wyoming and in the southwesternmost part of 

the Kremmling area.

The Jurassic and Triassic rocks in Colorado, mainly west of the 

Park Range, have been studied by Heaton (1933, fig. 4, p. 115), Lovering and Johnson (1933, p. 357), Baker, Dane, and Reeside (1936, p. 18, 

28, figs. 3, 6), Donner (1949, p. 1229-1230), Poole and Stewart (1964), 

and others. The rocks in North Park have been studied by Beekly 

(1915) and those in Middle Park by Jenkins (1957).

Work reported here was done mostly in 1963. Information was gathered by studying 11 stratigraphic sections, which are described on 

pages N16 to N34 and are located in figure 1. Correlation and 

facies changes of stratigraphic units are shown in figure 3. W. B. 

Cashion, A. A. Bookstrom, and C. S. V. Barclay helped measure the 

sections. Regional correlations reported here are supported by geologic 

mapping in Middle Park, Cqlo., by Izett (1968) and in North Park, 

Colo., by W. J. Hail, Jr. (1965), and by regional stratigraphic studies 

in southern Wyoming and northern Colorado by Pipiringos (1968).

Fossils collected during the studjr are listed in table 1 according to 

age. I. G. Sohn identified the ostracodes, R. A. Scott identified the plant 

microfossils, and R. W. Imlay identified the pelecypods.
107°

CHINLE AND SUNDANCE FORMATIONS, COLORADO

R.85W. 84 83 82 81

N3

R. 80 W.

10 15 MILES

COLORADO

FIGURE 1. Map of north-central Colorado showing location of stratigraphlc 

sections: A, Elk Creek; B, Radium SW; C, Radium SE; D, Kremmling- E 

Lazy Bear; F, Snowshoe Ranch; G, Tyler Mountain; H, McMahon Reservoir- 

/, McMahon Reservoir, north; J, Frantz Creek; and K, Barber Basin Light 

stipple, pre-Triassic rocks; dark stipple, Triassic and Jurassic rocks; unpatterned, post-Jurassic rocks. Geology and base from "Geologic Map of Colorado" 

(Burbank and others, 1935), modified by W. J. Hail, Jr., 1964
N4

110°

CONTRIBUTIONS TO STRATIGRAPHY

109° 108° 107° 106" 105°

:

VVJ[ UlYliiiVJ _ «:«:;, ,«:>... \ asjsgsjjjf pgf-gpsgiig

COLORADO .aSMSSW:-:.- TSWSM*1 ' 1 0\ S¥:S:S5:^fSSS!Wi^:4SiSS:K;s-:S

F |S<«f|SliKiJtE» ?Sts;S S

ilsfll*. M!i|ill!!ils. ^illiilii

^: ^:.:.:-:.: ^:::v:::1 :^::;Lv:::^::::;:::v:::::::^;- / .:-:-:.Ji:^^ 'i-:-:.L

 iP^botseraiii 

"^"^ Glen wood Jk:,":»!il

"S: ,.. ..... .-:::;::«SK:SSS!::15:«;s;s

11 ..

'iliWPiMWr^

ll, ipp-» %«:: SSiiiisli

100 200 MILES 

_I

FIGURE 2. Map showing some geographic features of northwestern Colorado 

and adjacent parts of Utah and Wyoming. Heavy line indicates area of figure 1.

TABLE 1. Late Jurassic fossils collected from the Sundance Formation in northcentral Colorado

Collection Stratigraphic section 

(in fig. 1)

Stratigraphic

position above

base of member

(feet)

Fossil identification

Windy Hill Sandstone Member

[Ostracodes, identified by I. Q. Sohn]

FC-1. B. Radium SW.............. 7-8.5 Darwinulaf sp. 

BisulcocypTis-Theriosynoecum group sp.

Pine Butte Member

[Pelecypods, identified by R. W. Imlay]

FC-2.

3.

4.

A. Elk Creek................ 6-13

.....do ...._............ 4-5

B. Radium SW.............. 8

J1 .SnowshoeRanch......... 6-8.5

G.Tyler Mountain.... __-... 0-5

Lopha sp.

Grammatodonf sp.. Tancrediat sp. 

Vaugonia conradi (Meek and Hayden). 

Quenstedtia cf. Q. planulata (Whitfield and

Hovey). 

Tancredia sp.

Pleuromyaf sp., Pronoellaf sp. 

Vaugonia cf. V. conradi (Meek and Hayden). 

Vaugonia conradi (Meek and Hayden).
CHINLE AND SUNDANCE FORMATIONS, COLORADO N5

TABLE 1. Late Jurassic fossils collected from the Sundance Formation in northcentral CoZorado-Continued

Stratigraphic

Collection Stratigraphic section position above Fossil identification 

(In flg. ]) base of member 

(feet)

Pine Butte Member

[Ostracodes, identified by I. G. Sohn]

FC-7--------- /. McMahon Eeservoir N- 10-11 Virtually same assemblage as FC-8 but

much more poorly preserved.

8---.--.-......do__.................. 5-6 Drawinulasp.

Bisulcocypris-Theriosynoecum group spp.

with 1 and 2 sulci.

Genus or genera indeterminate, large 

smooth.

9-....---- J. Frantz Creek_......... 0-10 Same assemblage as FC-8; many of the

specimens are squashed.

Lak(?) Member

[Plant microfossils, identified by R. A. Scott]

FC-10........ J. Frantz Creek............. 23-28 CaytonipollenUes sp., ClassopoUis sp.

EucommiidUes sp., Tsugaepollenites sp. 

Monosulcites sp., Klukisporites sp.

Canyon Springs Sandstone Member

[Pelecypods, Identified by R. W. Imlay]

FC-11........ F. Snowshoe Ranch........ 20-25 (estimated) Vaugonia conradi (Meek and Hayden).

CHINLE FORMATION

The Chinle Formation, which is exposed on both sides of the Park 

Range in the Kremmling area, ranges in thickness from 0 to 127 feet 

and is divisible into a lower conglomeratic sandstone and sandy siltstone member, a middle silty claystone land clayey siltstone member, 

and an upper sandy siltstone member. On the east side of the Park 

Range, the Chinle Formation rests with erosional unconformity on red 

sandstone and siltstone of Triassic and Permian age (sees. E and /), 

and on the west side of the range, it rests on a sequence of red beds 

whose age has been considered Permian by some geologists and Permian 

and Triassic by others. The Chinle is overlain with a slight angular 

unconformity by Jurassic rocks. Previously the Chinle has been generally lumped with the Chugwater on the east side of the Park Range.

The lower part of the lower member consists principally of lightgray sandstone and conglomeratic sandstone. The upper part consists 

principally of sandy siltstone, generally banded or mottled gray and 

pale red to grayish purple. Black iron oxide nodules mostly less than 1 

inch in diameter are characteristic of the lower member. The two major 

lithologies locally are interbedded and grade into each other laterally 

and vertically. In most places the lower member forms small cliffs and 

slopes interrupted by rounded strong to weak ledges.

326-840 O 69 2
Canyon Springs Sands
> «,.

^ X.

Canyon Springs Sandstone 'Me
N8 CONTRIBUTIONS TO STRATIGRAPHY

The lower member is thickest on the east side of the Park Range, in 

the Lazy Bear-Tyler Mountain area (sees. E and G, fig. 1), but is 

absent in sections less than 10 miles to the south (sec. D) and to the 

north in the Frantz Creek-Barber Basin area (sees. / and K). On the 

west side of the Park Range, the lower member is about 35 feet thick 

at Elk Creek (sec. A) and 21 feet thick in the vicinity of Radium, 

Colo. (sec. B). It is thinner at section C, also near Radium, but there 

it is thinned by faulting.

Fossils were not found in the lower member of the Chinle along the 

Park Range, but inasmuch as the lower member is lithologically similar to the basal Gartra Member and overlying mottled member of the 

Chinle Formation in the Uinta Mountains, Utah (Poole and Stewart, 

1964), and to the Brynt Draw Member of the Popo Agie Formation 

in Wyoming, (Pipiringos, 1968, p. D15) its age is assumed to be Late 

Triassic. The two units in the lower member in the Park Range represent one continuous period of deposition of alternating conglomerate, 

conglomeratic sandstone, sandstone, and sandy siltstone beds that do 

not warrant subdivision.

The middle member consists of claystone that is somewhat sandy 

or silty in the lower part. It is mostly grayish to purplish red but contains some yellowish-orange bands. The middle member characteristically weathers to a slope that separates ledgy beds in both the upper 

and lower members. At Tyler Mountain (sec. G) it is 23 feet thick, 

but is unconforma'bly overlain by Jurassic rocks. At the Lazy Bear 

section (#), faults prevent measurement of the total thickness, but 

it is at least 10 feet. At Elk Creek (units 5 and 6, sec. A) rocks equivalent to the member almost certainly are present but they are not shown 

separately from the upper member because at this locality the contact 

between the members is not obvious. At Snowshoe Ranch (sec. F) the 

middle member is presumed to be present below the base of the measured section, and at the McMahon Reservoir sections (77, 7) it is 

concealed if present. It is absent at all the other sections, probably because it has been eroded away. The middle member grades into the 

underlying lower member through an interval of 1-2 feet.

Fossils were not found in the middle member, but its stratigraphic 

position and lithology are similar to those of the ocher siltstone member of the Chinle of the Uinta Mountains in Utah (Poole and Stewart, 

1964) and the Lyons Valley Member of the Popp Agie Formation in 

Wyoming (Pipiringos, 1968, p. D15-D16). Therefore, it is assumed 

to be of Late Triassic age.

The upper member of the Chinle Formation consists of reddishbrown slope-forming siltstone beds alternating with ripple-laminated 

tightly lime-cemented ledge-forming siltstone beds. It occurs only at
CHINLE AND SUNDANCE FORMATIONS, COLORADO N9

the Elk Creek section (A, beds 7-11), where it is about 33 feet thick, 

but is not readily separated from the middle member; consequently, 

at this locality the upper and middle members of the Chinle are undivided. The upper part, however, is correlated by lithologic features 

and stratigraphic position with the upper member of the Chinle 

Formation as mapped by Kinney (1955, p. 69) in the Uinta Mountains 

and with the Bell Springs Member of the Nugget Sandstone in Wyoming (Pipiringos, 1968, p. D16-D17) and it is considered on this basis 

to be of Late Triassic age.

The presence of the lower and middle members of the Chinle on the 

east side of the Park Range (fig. 3) suggests that an embayment of 

the formation extended from southern Wyoming or northern Utah 

southeastward or eastward into north-central Colorado. The shape of 

this embayment, however, cannot be outlined on the basis of present 

information.

SUNDANCE FORMATION

The Sundance Formation in south-central Wyoming consists of, in 

ascending order, the Canyon Springs Sandstone, Stockade Beaver 

Shale, Hulett Sandstone, Lak, Pine Butte, Redwater Shale, and Windy 

Hill Sandstone Members (Pipiringos, 1968, p. D18-D25).

The Sundance has been traced from Wyoming into the northern 

part of north-central Colorado to a point about 9 miles north of Steamboat Springs on the west side of the Park Range, and to a point on the 

east side of Sheep Mountain, about 11 miles northwest of Walden on 

the east side of the Park Range. In both areas, the Sundance comprises, in ascending order, the Canyon Springs Sandstone, the Pine 

Butte, the Redwater Shale, and the Windy Hill Sandstone Members. 

Mapping by W. J. Hail, Jr. (1965), indicates that, because of poor 

exposure, the Redwater Shale and the Pine Butte Members cannot 

be traced from the northwestern corner of North Park southward 

along the east side of the Park Range into the study area. Furthermore, 

reconnaissance along the west side of the range suggests that it is 

equally unfeasible to trace these members from the vicinity of Steamboat Springs southward into the western part of the study area (G. L. 

Snyder, oral commun., 1967). Fortunately, the Sundance in the 

Kremmling area is fossiliferous; correlations based partly on the 

fossils and partly on lithology, stratigraphic position, and regional 

stratigraphic relations suggest that the Redwater pinches out at some 

point north of the Kremmling area, but that the Pine Butte persists 

southward.

The Sundance Formation in the Kremmling area (fig. 1) is exposed 

on both sides of the Park Range. It ranges in thickness from 54 feet 

at Tyler Mountain (sec. G) to 259 feet at Elk Creek (sec. A) and is
N10 CONTRIBUTIONS TO STRATIGRAPHY

divisible into four members. The basal member is the Canyon Springs 

and the uppermost member is the Windy Hill, but the correlation of 

the two medial members is less certain. Detailed stratigraphic studies 

of the lower part of the Sundance Formation in areas north of the 

Kremmling area show that the Stockade Beaver and the Hulett of 

southern Wyoming change facies southward and do not extend into 

north-central Colorado. The two medial members, therefore, are correlated with the overlying Lak and Pine Butte Members of the 

Sundance Formation of southeastern Wyoming.

Kocks exposed on the west side of the Park Range near Burns (sec. 

A, fig. 1) and here assigned to the Canyon Springs Sandstone and the 

Pine Butte Members of the Sundance Formation correlate with the 

Entrada Sandstone and Curtis Formation, respectively, of Baker, 

Dane, and Reeside (1936, p. 28, fig. 6, loc. 16).

CANYON SPRINGS SANDSTONE MEMBER

The Canyon Springs is 166 feet thick at Frantz Creek and 60 feet 

thick in a partial exposure at Barber Basin (sees. / and K, fig. 1). At 

these places it consists of massive to obscurely crossbedded very fine 

grained yellowish-white or pink sandstone that forms rounded cliffs 

and ledges. This lithology, color, and topographic expression are normal for this member throughout most of southeastern Wyoming and 

northwestern Colorado. At the Frantz Creek section (/) the member 

rests unconformably on the Triassic and Permian red beds. At the 

Barber Basin section (K) the uppermost few feet of the Canyon 

Springs contains borings made by organisms that probably were introduced with the advent of the sea in which the overlying rocks were 

deposited.

Along the east side of the Park Range south of Frantz Creek, the 

Canyon Springs is completely exposed at Tyler Mountain and Kremmling (sees. G and Z>), partly exposed at localities H and F, and 

completely concealed at localities / and E. The member is only 33 feet 

thick in the complete section at Tyler Mountain (sec. G] , but is 79 feet 

thick in the partial section at McMahon Reservoir (sec. H).

At McMahon Reservoir only the basal few feet and the upper 30 

feet are typical of the Canyon Springs in some nearby areas; the 

intervening part (beds 6-10, sec. H) consists principally of reddishorange ledgy sandstone containing thin beds of greenish-gray, gray, 

and dark-gray clay shale and a thin bed of greenish-gray bentonite. 

Farther south, at Tyler Mountain (sec. #), the Canyon Springs consists almost entirely of reddish-orange silty clayey sandstone that 

greatly resembles bed 9 of the McMahon Reservoir section. At Snowshoe Ranch less than 2 miles south of Tyler Mountain, the upper part
CHINLE AND SUNDANCE FORMATIONS, COLORADO Nil

of the red sandstone sequence is replaced laterally by shale and sandstone containing marine pelecypods (sec. F, beds 2 and 3). Near 

Kremmling (sec. D} the lateral change from red beds to normal marine 

^ shale and sandstone is complete, and the Canyon Springs consists entirely of shaly sandstone and siltstone interbedded with green clay

 ) shale. A bed of bentonite 12 feet below the top of the sequence is identical in appearance, and in its association with greenish-gray clay shale, 

with the bentonite in the McMahon Reservoir section (H). Bentonitic

' clay shale was found at only one other locality Frantz Creek (sec. /,

^ bed3).

The facies change just described is duplicated in reverse (fig. 3) on

^ the west side of the Park Range. Only the lower part of the Canyon 

Springs has the faint crossbedding to massive bedding normal for the 

member at section C, but 1.5 miles farther west the lower half of the 

upper part also has this normal appearance and lithology (sec. B) . At

_) the farthest west section (A) considered here, the Canyon Springs is 

entirely a massive to obscurely crossbedded sandstone except for a

"* thin shaly bed in the upper part.

' Although the Canyon Springs east of the Park Range varies greatly 

from section to section, two key beds are persistent enough to tie the 

sections together. The bentonite and bentonitic clay shale beds already 

described help correlate the Frantz Creek, McMahon Reservoir, and 

Kremmling sections («7, H, and D). Similarly, a light-gray to light-

 yellowish-brown sandstone at the top of the Canyon Springs serves

 \ to tie together the Radium, Kremmling, and Snowshoe Ranch sections 

(B,C,D,a,ndF).

The base of the Canyon Springs everywhere examined rests unconformably on the underlying rocks. At Elk Creek (sec. A) and at the 

sections near Radium and Kremmling (sees. /?, (7, and Z>), chert 

pebbles clearly mark the base. At Frantz Creek (sec. /) the chert 

pebbles are small and inconspicuous, but the basal inch of the member 

is notably gritty (bed 2, sec. /). At Tyler Mountain (sec. G}, the only 

other section where the basal contact of the Canyon Springs is exposed, the contact is an abrupt change from the bentonitic grayish-red 

claystone in the Chinle Formation to the pale-reddish-brown very fine 

grained sandstone in the Canyon Springs Member of the Sundance.

At a locality about 3 miles southwest of Burns, Colo. (fig. 1), the 

Entrada Sandstone (Baker and others, 1936, p. 28, fig 6, loc. 16) contains chert pebbles at the base, unconformably overlies the Chinle, 

and grades up into the Curtis. Its lithology and its stratigraphic and 

structural relations to the overlying and underlying rocks are identical 

with those of the Canyon Springs at Elk Creek (sec. J., fig. 1) with 

which it is here correlated.
N12 CONTRIBUTIONS TO STRATIGRAPHY

Imlay (1947, table 1) considers both the Canyon Springs of Wyoming and the Entrada Sandstone of Utah and Colorado to be of 

Callovian Age. At the Snowshoe Ranch (sec. F) bed 2 contains 

Vaugonia conradi (Meek and Hay den). This pelecypod has not been 

reported from beds younger than the Pine Butte Member which is 

probably middle or late Callovian in age (member B of Pipiringos, 

1953, p. 34; 1957, p. 22-23).

LAK(?) MEMBER

In the northern part of the area, at sections H, /, /, and K, there 

occurs a sequence of rocks consisting of light- to yellowish-gray limy 

silty clayey sandstone and gray to yellowish-gray clay, shale, claystone, 

and siltstone which is tentatively interpreted to be a f acies of the Lak 

Member of the Sundance Formation of Wyoming and is here referred 

to as the Lak(?) Member. The Lak at its type section (Black Hills, 

Wyo.), and throughout much of eastern, central, and south-central 

Wyoming, consists principally of red siltstone and sandstone, although 

locally it is yellowish gray. The red f acies has been traced southward as 

far as Big Sandstone Creek on the west flank of the Sierre Madre 

(northern extension of the Park Range of Colorado) about 7 miles 

north of the Wyoming-Colorado State line. The Lak (?) is absent from 

outcrops along the Park Range between this point and the northern 

part of the Kremmling area (fig. 1), and the Lak (?') of the Kremmling 

area, therefore, has not been traced into the main body of the member 

to the north in Wyoming. Correlation with the Lak is based almost 

entirely on its stratigraphic position above the Canyon Springs and 

beneath the Pine Butte Members of the Sundance.

The Lak( ?) ranges in thickness from 37 feet at McMahon Reservoir 

(sec. H) to 47 feet at Frantz Creek (sec. J). At the three northernmost 

sections (/, /, and K] it is predominantly gray, and, although it is 

sandier and more yellowish gray at McMahon Reservoir (sec. /7), its 

position in all four sections beneath the Pine Butte and above the 

Canyon Springs leaves little doubt about its correlation among these 

localities. It is not present at Tyler Mountain (sec. G-} ; presumably 

it thins and pinches out in the area between sections H and G.

At Barber Basin, Frantz Creek, and McMahon Reservoir (sees. K, 

e7, and H} the Lak(?) grades downward into the Canyon Springs 

Sandstone Member. The contact is marked by only a slight change in 

lithology, by a change from soft slopes characteristic of the Lak (?) 

to more resistant slopes and rounded ledges in the Canyon Springs, and 

by the presence of bottom-dweller borings (beds 4 and 1, sees. / and 

K, respectively) in the upper few feet of the Canyon Springs.

The Lak( ?) grades both upward into the Pine Butte Member and
CHINLE AND SUNDANCE FORMATIONS, COLORADO N13

downward into the Canyon Springs Member, both of which are of 

Callovian Age.

Pollen and spores of vascular land plants were collected from bed 

7 of the Frantz Creek section (table 1, FC-10). None of the forms is 

specifically identifiable and all were easily carried by wind; thus they 

are diagnostic neither of age nor of environment of deposition.

PINE BUTTE MEMBER

The Pine Butte Member of the Sundance Formation in the Kremmling area is present in all the sections examined and consists of interbedded sandstone, siltstone, clay shale, and limestone. The member is 

only 13 feet thick at Kremmling (sec. Z?), but thickens northward 

to 48 feet at the McMahon Keservoir (sec. H). It is about 62 feet thick 

at Elk Creek (sec. A ). The member grades downward into the Lak( ?) 

but is unconformably overlain by the Windy Hill Sandstone Member.

The Pine Butte in the Kremmling area contains abundant glauconite, 

oolitic limestone, and oolitic sandstone. Such sedimentary features in 

southern Wyoming are common in the Redwater Shale, less common 

in the Windy Hill Sandstone, a,nd least common in the Pine Butte 

Members of the Sundance Formation (Pipiringos, 1953, p. 34; 1957, p. 

11; 1968, p. D23). The Pine Butte does not contain thin platy rippleimbricate limy sandstone beds marked with furrowed bottom-dweller 

trails that are characteristic of the Pine Butte of Wyoming. These 

comparisons suggest possible correlation of the Pine Butte in the 

Kremmling area with the Redwater Shale Member in Wyoming.

The following stratigraphic and paleontologic features, however, 

strongly suggest that the Pine Butte of north-central Colorado more 

likely correlates with the Pine Butte of Wyoming:

1. The Redwater Shale Member in south-central Wyoming consists of 

four distinct and persistent lithologic units. In ascending order, 

these are a lower siltstone, a lower shale, an upper siltstone, and 

an upper shale (Pipiringos, 1968, p. D23, fig. 3). By contrast, the 

Pine Butte of the Kremmling area does not show orderly superposition of lithologic units nor does any one lithologic sequence 

within the member persist laterally for any great distance.

2. The basal contact of the Redwater is unconformable, whereas the 

basal contact of the Pine Butte in the Kremmling area is 

gradational.

3. In southeastern Wyoming, progressively older units of the Redwater are truncated southeastward, and the vanishing edge of 

the lower siltstone unit trends south westward across the southern 

part of the Laramie Basin, Wyo., into and across the northern 

part of North Park, Colo. Extrapolation of this trend suggests

326-840 O 69 3
N14 CONTRIBUTIONS TO STRATIGRAPHY

that the zero line passes a few miles north of Steamboat Springs, 

Colo. Consequently, although it is not impossible that the Redwater extends southward into the Kremmling area, it seems improbable ; more likely the Redwater has been truncated and it is 

the Pine Butte that extends into the study area.

4. Absence of the furrowed bottom-dweller trails from the Pine Butte 

of the study area is fortuitous inasmuch as they are abundant in 

equivalent rocks near Burns, Colo., about 7.5 miles southwest of 

stratigraphic section A.

5. Absence from the Pine Butte in the Kremmling area of belemnites, 

certain ammonites, the pelecypods Camptonectes bellistriatus and 

Astarte packardi, and other fossils such as are abundant in the 

Redwater is significant, inasmuch as these forms are likewise absent from the Pine Butte of Wyoming (Imlay, 1947, p. 259-263; 

Pipiringos, 1957, p. 22-24).

6. Identification of the Pine Butte Member in the Kremmling area is 

based mainly on the presence of Vaugonia conradi (Meek and 

Hay den), which is the only species of Vaugonia recognized to 

date in the Pine Butte of Wyoming; it is unknown from the Redwater. A form previously identified as Trigonia sturgisensisl 

(Whitfield and Hovey, 1906) in Wyoming (Pipiringos, 1953, p. 

34; 1957, p. 22, 23) has since been determined by R. W. Imlay 

to be Vaugonia conradi (Meek and Hay den).

This species occurs in beds as old as Bajocian (early Middle Jurassic) 

(Imlay, 1964, p. C30) and as young as middle or late Oallovian, but 

has not ;been found in rocks of Oxfordian Age in Wyoming or adjacent 

States (Imlay, 1964; written commun., 1966). Whereas ammonites 

are scarce in the Callovian rocks of Wyoming and adjacent States, 

Vaugonia, conradi is common. Consequently, tlhe latter, in many areas, 

may prove to be very useful in differentiating beds of Callovian Age 

from beds of Oxfordian Age.

Specifically unidentifiable ostracodes from beds 3 and 5 of the 

McMahon Reservoir north section (/) and from bed 10 of the Frantz 

Creek section (/) were referred by I. G. Sohn (written commun., 1964) 

to the genus Darwinula, to genera in the Bisulcocypris-Theriosynoecum group, and to an indeterminate large smooth genus or genera 

(table 1, FC-7, 8, 9). These fossils could not be used for dating the 

rocks, but Sohn (written commun., 1964) remarked, "The only element 

lacking to make this a typical Morrison assemblage is Theriosynoecum 

Wyoming ense (Branson)." Sohn further stated, "No Foraminifera 

were found. The ostracodes are all of the fresh-water type; some of 

the genera can tolerate brackish-water, but none is found in marine 

sediments except ne^r shore where specimens can be washed in from
CH3NLE AND SUNDANCE FORMATIONS, COLORADO N15

a fresh-water habitat. The abundance of individuals would rule out 

transport to a marine environment. It is noteworthy that no ohara 

were observed; these are normally present in Morrison sediments * * *."

The ostracodes occur in unit 5, section /, which contains marine 

pelecypods and is overlain by glauconitic oolitic beds, one of which 

(bed 12, sec. 7) contains echinoid spines. .This indicates marine deposits are intercalated with fresh-water deposits of Callovian Age. 

Apparently the ostraoodes persisted with but little change into Morrison time (probably Kimmeridgian).

The Curtis Formation (Baker and others, 1936, p. 28, fig. 6, loc. 16) 

contains marine Jurassic fossils including the furrowed bottomdweller trails that are characteristic of the Pine Butte of Wyoming. 

The formation grades down into the Entrada (Baker and others, 1936, 

pi. 2(L4) and is sharply overlain by 'beds equivalent to the Windy Hill 

Sandstone Member. The lithology and faunal content (except the furrowed trails of the Curtis) and its stratigraphic and structural relations to the underlying and overlying rocks of this locality are nearly 

identical with those of the Pine Butte at Elk Creek (sec. A, fig. 1) with 

which it is here correlated.

WINDY HILL SANDSTONE MEMBER

The Windy Hill Sandstone Member of the Sundance is presentthroughout the area. It consists of light-greenish-gray amorphouslime- and crystalline-calcite-cemented ripple-marked sandstone beds, 

which weather to slabby grayish-yellow ledges, and locally interbedded 

grayish-green clayey siltstone beds, which weather to form reentrants 

and slopes. Locally the member is sparsely oolitic and glauconitic, and 

at section 7 (-bed 14) it contains salt crystal casts. Its thickness ranges 

from 1 foot at the McMahon Reservoir north (sec. 7) to 10 feet at 

Radium (sec. B). Throughout the area the Windy Hill rests sharply 

and apparently unconformably on the Pine Butte, and it grades upward into the Morrison Formation.

In most sections the lithology and weathering characteristics of the 

member are closely similar to those of the Windy Hill of southeastern 

Wyoming (Pipiringos, 1968, p. D23-D24). Locally, as at the Radium 

SW section (5), the member is atypical and correlation with the 

Windy Hill at adjacent localities is based principally on stratigraplhic 

position. Except for ripple marks it lacks most of the lithologic and 

weathering characteristics, and in addition it contains ostracodes, 

wihich have not been reported form this member elsewhere.

Bed 13 of section B contains ostracodes (table 1, FC-1) that appear 

to be similar to those found in the Pine Butte (I. G. Sohn, written 

commun., 1964).
N16 CONTRIBUTIONS TO STRATIGRAPHY

The age of the Windy Hill in Wyoming is probably Kimmeridgian. 

Eegionally, the member truncates underlying units of Oxfordian Age 

and grades up into the Morrison (Pipiringos, 1953, p. 34; 1957; p. 24; 

1968, p. D23-D25, fig. 3).

STRATIGRAPHIC SECTIONS

Locations of stratigraphic sections are shown in figure 1. Fossil collections are identified by the numbers FC-1, FC-2, and so forth; fossils identified in each collection are listed in table 1.

In the descriptions that follow, the term "unit" is applied to an 

interval that contains more than one rock type.

SECTION A. Elk Creek

[In Leadville quadrangle, Army Map Service (A.M.S.), near Elk Creek about 4.5 miles west of McCoy, 

Colo., In the SWK sec. 33, T. 1 S., R. 84 W., and In the NWJ4 sec. 4, T. 2 S., R. 84 W.; beds strike N. 30" 

W., dip 5° SW. Measured by Q. N. Pipiringos and A. A. Bookstrom, July 1963]

Morrison Formation (in part): Feet 

23. Mostly siltstone, gray-green, clayey, limy; makes slope capped 

by thin ledge of greenish-gray and reddish-brown silty 

clayey limy sandstone______________________________ 3

Sundance Formation:

Windy Hill Sandstone Member:

22. Sandstone, light-gray, light-yellowish-brown-weathering, finegrained, well-sorted, tightly lime-cemented; bedding surfaces show trails of crawling organisms; ripple marked; 

forms slabby ledge___________________________________ 2

21. Siltstone, grayish-green, clayey; makes slope_____________ 3

20. Sandstone, like bed 22; contains scattered medium grains of

quartz; ripple marked, makes ledge___________________ 4

Thickness of Windy Hill Sandstone MemberUnconformity.

Pine Butte Member:

19. Sandstone, greenish-gray, very fine grained, fairly well sorted, 

silty and .clayey, slightly limy; contains a few scattered 

glauconite grains and marine pelecypod fragments; a ledge 

0.4 ft thick, 7 ft below top, contains obscure tubular 

scaphopod? casts; forms ledgy slope.___________________ 18

18. Sandstone, like bed 19; no fossils; weathers to thin plates;

makes ledgy cliff_______________________-___--_---_--- 31

17. Sandstone, like bed 19; contains a few limy nodular concretions, carbonaceous debris; has contorted bedding; contains 

pelecypods (FC-2), especially abundant in top 3 ft; forms 

slope.______________________________________________ 8

16. Sandstone, like bed 19; contains marine pelecypod fragments

near top (FC-3); forms blocky projecting ledge._________ 5

Thickness of Pine Butte Member________.---__--_ 62
CHINLE AND SUNDANCE FORMATIONS, COLORADO N17

SECTION A. Elk Creek Continued

Sundance Formation Continued

Canyon Springs Sandstone Member: Feet

15. Sandstone, moderate-orange-pink, very fine grained, locally 

limy, well-sorted; contains orange and black chert grains; 

massive; contains a platy-fissile grayish-green clayey zone 

5 ft thick 20-25 ft below top; forms rounded ledges. _____ 68

14. Sandstone, like unit 15; weathers yellowish gray; makes

rounded ledges_____________________________________ 61

13. Sandstone, like unit 15___-______________.______________ 41

12. Sandstone, like unit 15; base of unit marked by zone of 

black limy schist pebbles as much as 2.5 in. long; forms 

rounded ledges_____________________________________ 18

Thickness of Canyon Springs Sandstone Member____ 188

Thickness of Sundance Formation________________ 259

Unconformity. 

Chinle Formation:

Upper and middle members undivided:

11. Siltstone, pale-red, tightly lime-cemented, ripple-laminated

at top 1 ft; forms massive rounded ledge._______________ 9

10. Siltstone, pale-reddish-brown, and grayish-red silty claystone; 

contains a few grayish-red lime-cemented siltstone pebbles; 

forms slope________________________________________ 4

9. Siltstone, pale-reddish-brown, tightly lime-cemented; forms

rounded ledge.______________________________________ 16

8. Claystone, grayish-red, very silty; forms slope.____________ 2

7. Limestone, light-gray, dolomitic; makes square-faced ledge

that weathers to thin plates.__________________________ 2

6. Siltstone, moderate-reddish-brown, clayey, slightly limy,

micaceous; subfissile to blocky; forms slope____________ 31

5. Claystone, reddish-purple, silty; forms slope containing 

0.5-ft-thick ledge 9 ft above base; ledge is pale-reddishpurple slightly clayey laminated micaceous siltstone_-____ 28

Thickness of upper and middle members undivided, _ 92

Lower member:

4. Siltstone, dark-reddish-brown, mixed with dark-reddishbrown silty sandy claystone and greenish-gray fine-grained 

sandstone; unit is especially sandy in lower 10 ft; forms 

slope interrupted by projecting ledge of limestone pebble 

conglomerate 5 ft below top and thin sandstone ledge in 

lower part________________________________________ 20

3. Sandstone, mottled light-gray and grayish-red, medium- to 

coarse-grained, poorly sorted, contains a few chert pebbles; 

forms rounded ledges.______-__-_--__-____-________-__ 12
N18 CONTRIBUTIONS TO STRATIGRAPHY 

SECTION A. Elk Creek Continued

Chinle Formation Continued

Lower member Continued Feet 

2. Sandstone, light-gray, coarse-grained, with, quartz, chert, 

and quartzite pebbles as much as 1 in. in diameter; upper 

2 ft contains grayish-purple shale and makes slope; basal 

1 ft makes projecting ledge..._____.-__.__._______.__._ 3

Thickness of lower member._____________________ 35

Thickness of Chinle Formation___-_--__-_-___-____ 127

Unconformity.

Triassic and Permian red beds (in part):

1. Siltstone, reddish-brown and grayish-red in top 5 ft, micaceous, subfissile; forms slope containing thin ledges_--___- 100 +

SECTION B. Radium SW

[In Leadville quadrangle (A.M.S.), across the graded road 0.5 mile southwest of Radium, Colo., in the 

SWJ4NWJ4 sec. 27, T. 1 S., R. 82 W.; attitude of beds ranges from N. 5° E., 11° NW. at base of Chinle 

Formation to N. 11° E., 14° NW. at base of upper part of Entrada Sandstone and averages about N. 

7° E., 13° NW. Measured by G. N. Pipiringos and A. A. Bookstrom, July 1963]

Morrison Formation (in part):

18. Limestone, olive-gray, aphanitic; weathered surfaces show

fine laminae of algal (?) origin; forms hard ledge. __ _______ 1

17. Sandstone, greenish-white, very fine to fine-grained, tightly 

lime-cemented; makes hard ledge separated by partings of 

soft sandstone._____________________________________ 7

16. Sandstone, greenish-gray, very clayey; forms soft slope.___. 4

15. Claystone, greenish-gray and dark-purplish-gray, silty;

forms slope______________________________---------_ 20

14. Sandstone, light-gray, very fine grained; interbedded with 

medium-gray dense aphanitic limestone; forms rounded 

ledge._--___-______________-_-____-----_-__-_------- 1

Partial thickness of Morrison Formation.___________ 33

Sundance Formation:

Windy Hill Sandstone Member:

13. Sandstone, light-gray, very fine grained, well-sorted, slightly 

limy, orange and black chert grains; middle of unit contains a 1.5-ft-thick bed of medium-gray poorly laminated 

claystone that contains ostracodes (FC-1); forms slope. _ 

12. Sandstone, light-gray, very fine grained, weU-sorted, slightly 

limy, porous; contains varicolored chert and quartzite 

grains; middle 2 ft forms a slope capped by a 1-ft-thick 

ledge; basal 3 ft makes a massive to platy ledge; locally 

ripple marked.______________________________________

Thickness of Windy Hill Sandstone Member._.....- 10
CHINLE AND SUNDANCE FORMATIONS, COLORADO N19

SECTION B. Radium SW Continued

Unconformity. feet 

Pine Butte Member:

11. Clay shale, medium-gray; forms slope_______-_--_________ 2

10. Sandstone, light-gray, yellowish-gray-weathering, very fine 

grained, well-sorted, limy; forms slope with ledges at top 

and bottom.________________________________________ 8

9. Sandstone, light-gray, very fine grained, limy, clayey; forms

slope.___-___-___--__--__-___-_______-----__.-______ 7

8. Sandstone, light-gray, very fine grained; basal 2 ft contains 

medium-gray shale partings; two thin ledges at 3 and 5 ft 

below top contain marine pelecypod fragments and casts 

throughout (FC-4); unit forms slope capped by 3-ft-thick 

fossiliferous ledge.___________________________________ 13

Thickness of Pine Butte Member__________________ 30

Canyon Springs Sandstone Member:

7. Sandstone, light-gray, white- and pink-weathering, finegrained, limy, clayey, friable; forms slope _______________ 17

6. Sandstone, like bed 7 but obscurely crossbedded; forms

massive cliff_________________________________________ 18

5. Clay shale, very light green and very dusky red, limy, silty; 

contains glauconitic aggregates, chlorite and biotite flakes; 

shale is interbedded with very thin green and red clayey to 

silty sandstone beds; makes chippy slope____--__--_____ 21

4. Sandstone, light-gray, grayish-orange-weathering, finegrained, well-sorted, weakly lime-cemented, friable; contains chert granules 2 ft above base; 0.2 mile to west the 

basal foot of unit contains pebbles as much as 6 mm in 

diameter; forms massive rounded cliff_________________ 60

Thickness of Canyon Springs Sandstone Member.___ 116

Thickness of Sundance Formation....._____-____--- 156

Unconformity. 

Chinle Formation: 

Lower member:

3. Sandstone, siltstone, and claystone. Lower third of unit is 

mottled grayish-purple silty sandy claystone mixed with 

light- to medium-gray sandstone; claystone is swelling clay; 

silt and sand grains float in claystone matrix; micaceous. 

Upper two-thirds of unit is pale-reddish-brown-weathering 

sandstone and siltsone. Unit forms slope.___--_---___-_- 18 

2. Sandstone, light-gray, gritty, slightly limy; contains a few 

chert and quartzite grains and a few scattered reddishbrown siltstone fragments; forms ledge__:_-___-,_____- 3

Thickness of Chinle Formation______-_--__--_----_ 21
N20 CONTRIBUTIONS TO STRATIGRAPHY 

SECTION B. Radium SW Continued

Unconformity.

Triassic and Permian rocks (in part): -Feet 

1. Siltstone, grayish-red, micaceous (chlorite and white mica),

clayey, subfissile; forms 8lope___-_-_--_-_______-_-_____ 20+

SECTION C. Radium SE

[In Leadville quadrangle (A.M.S.), along the road 1.5 miles southeast of Radium, Colo., in the SWMNEJ4 

sec. 26, T. 1 S., R. 82 W.; attitude of beds ranges from N. 45° W., vertical dip at base of Canyon Springs 

Sandstone Member to N. 68° W., 70° SW. in the Windy Hill Sandstone Member. Measured by Q. N. 

Pipiringos and A. A. Bookstrom, July 1963]

Morrison Formation (in part): feet

19. Limestone, grayish-brown, smooth, has faint algallike 

laminae; lower part is sandy and clayey; upper part makes 

projecting ledge, lower part makes slope ________________ 2

18. Sandstone, pink and green, very fine grained, very clayey,

limy; makes slope__-___________________________-_____ 2

17. Sandstone, grayish-white, very fine to fine-grained; has 

chalky calcite matrix; contains 1-ft-thick shale parting 5 ft 

below top; unit makes moderately projecting slabby ledge. 12

16. Claystone, red and green; interbedded with thin sandstone

and limestone beds; unit forms ledges and slopes.________ 9

15. Sandstone, greenish-gray, very fine grained, limy; grades 

downward into sandy grayish-pink limestone; upper part of 

unit forms slabby ledge, lower 2 ft makes hard squarefaced ledge______________________________________ 3

14. Siltstone, greenish-gray, clayey, slightly micaceous; contains

ostracodes; forms slope_______.__________.____________ 2

Partial thickness of Morrison Formation._ __________ 30

Sundance Formation:

Windy Hill Sandstone Member:

13. Sandstone, light-greenish-gray, very fine grained, silty, 

clayey, laminated, glauconitic, oolitic; upper part has 

bottom-dweller trails on bedding planes; lower part is ripple 

marked and weathers grayish yellow; forms slabby ledge. _

Unconformity.

Pine Butte Member:

12. Shale, grayish-green, silty, sandy, limy; forms slope_______

11. Sandstone, light-greenish-gray, very fine to fine-grained, limy, 

hard; makes square-faced ledge.... __.____-_-______-___

10. Sandstone, light-greenish-gray, very fine-grained, limy, silty,

clayey, glauconitic; has wavy laminations; forms slope.__

9. Sandstone, light-greenish-gray, very fine grained, limy,

slightly micaceous; forms ledge__________________---__-
CHINLE AND SUNDANCE FORMATIONS, COLORADO N21

SECTION C. ^Radium SE Continued

Sundance Formation Continued

Pine Butter Member Continued Feet 

8. Sandstone, like bed 10, but platy; interbedded with thin beds 

of gray shale in middle and laminated reddish-brown siltstone in lower part; hard square-faced ledge 1 ft thick 0.5 

ft below top of unit._-_-_--_____-_-__-__-_-____-_-__. 6

Thickness of Pine Butte Member._________________ 22

Canyon Springs Sandstone Member:

7. Sandstone, reddish-brown, very fine grained, clayey; locally 

cut out by greenish-gray limy very fine grained sandstone 

that makes a square-faced ledge._-__-_-___________._-_ 2

6. Sandstone, light-brown, very fine-grained, well-sorted, massive; makes rounded ledge_____.__._.._.____._____._ 27

5. Siltstone, greenish-gray, clayey, sandy, shaly, laminated,

micaceous, limy; contains sparse glauconite; forms slope.. 7

4. Sandstone, light-gray to pink, very fine grained; crossbedded; 

quartz granules and pebbles are concentrated in lower 2 ft; 

a few quartz, chert, and quartzite granules are scattered 

throughout; forms rounded ledges._____________________ 31

Thickness of Canyon Springs Sandstone Member ____ 67

Thickness of Sundance Formation________________ 96

Unconformity.

Chinle Formation (in part):

3. Claystone, mottled grayish-purple and light-gray, silty and

sandy; bed is highly sheared_________________________ 2

Fault.

2. Siltstone, moderate-reddish-brown, slightly clayey, micaceous;

resembles lithology of older red beds; bed is highly sheared. 5 

Unconformity. 

Precambrian:

1. Gneiss.

SECTION D. Kremmling

[In Kremmling quadrangle, about 4.5 miles southwest of Kremmling, Colo., on north side of an irrigation 

ditch in the center of the N>_N^ sec. 21, T. 1N., R. 81W.; beds strike N. 12° W. and dip 13° NE., except 

units 8-12 which strike N. 15° W. and dip 30" NE. Measured by O. N. Pipiringos and C. S. V. Barclay, 

June 1963]

Morrison Formation (in part): feet 

16. Sandstone, thin-bedded; interbedded with clay shale; topmost bed is a 2-ft-thick grayish-brown limestone; thin 

conglomeratic sandstone bed in middle of unit contains 

fragments of limestone similar to topmost bed; unit forms 

ledges and reentrants.._______________________________ 20

15. Sandstone, white and yellow, thin-bedded; interbedded with 

gray clay shale, claystone, and limestone; sandstone is 

similar to that in unit 11; unit forms ledges and reentrants.. 9
N22 CONTRIBUTIONS TO STRATIGRAPHY

SECTION D. Kremmling Continued

Morrison Formation (in part) Continued Feet 

14. Claystone, greenish-gray and light-pinkish-gray; makes 

slope; topmost 0.5 ft is dense gray sandy limestone that 

makes ledge_________________________________________ 1. 5

13. Sandstone, light-gray, very fine grained, slightly limy; interlayered with greenish-gray waxy clay shale; appears 

transitional between units 14 and 12; unit forms slopes 

and ledges-..._______________________________________ 2. 5

Partial thickness of Morrison Formation____________ 33

Sundance Formation:

Windy Hill Sandstone Member:

12. Sandstone, pale-yellowish-orange, very fine grained, clean, 

well-sorted, slightly limy, ripple-marked; greenish-gray 

clayey shaly siltstone near middle of unit; sandstone 

forms ledges separated by siltstone reentrants-__________ 4. 5

11. Sandstone, pale-yellowish-orange, very fine grained, clean, 

well-sorted, slightly limy, ripple-marked; light-gray shaly 

silty limy claystone in upper half foot; unit forms ledge.__ 3

Thickness of Windy Hill Sandstone Member._______ 7. 5

Unconformity.

Pine Butte Member:

10. Siltstone and very fine grained sandstone; both light greenish 

gray, limy, clayey, micaceous; contains some bottomdweller trails; middle part of unit forms ledges, rest of 

unit forms slopes_____--_______________-_-_---_----- 5

9. Sandstone, light-greenish-gray, very fine grained; contains 

casts of marine pelecypods and bottom-dweller trails; 

forms rounded ledge_________--____-___---------.--- 2

8. Sandstone, light-greenish-gray, yellowish-brown-weathering,

very fine grained, clayey; forms slopes and ledges _____ 6

Thickness of Pine Butte Member._________________ 13

Canyon Springs Sandstone Member:

7. Sandstone, light-yellowish-brown, very fine grained, slightly 

clayey; basal 1 ft contains vuggy calcite aggregates; forms 

ledges _______-________________-____-_____-_-__------ 12

6. Bentonite, white, waxy, mixed with some light-greenish-gray

silty sandstone and clay shale; forms slope._____________ 1

5. Sandstone, light-yellowish-brown, very fine grained, clayey,

locally limy, shaly; forms slope.________________-_----- 2

4. Sandstone, light-yellowish-brown, very fine grained, calcitecemented, well-sorted, fairly clean, massive; has shale 

partings; grades laterally into shale; contains ripple marks 

and bottom-dweller trails and borings; unit forms rounded 

ledge.-_______-_____-_-_-_____--------_------_------ 17
CHINLE AND SUNDANCE FORMATIONS, COLORADO N23 

SECTION D. Kremmlmg Continued

Sundance Formation Continued

Canyon Springs Sandstone Member Continued Feet

3. Siltstone, very light greenish gray, well-sorted, limy, slightly 

clayey; upper part is more clayey and shaly and is mottled 

purple; contains a few thin beds of light-gray calcitecemented sandstone; unit forms slopes and thin ledges____ 14

2. Partly covered; light-gray, micaceous, limy sandstone, contains granules and pebbles near base. Most granules are 

white, some are black, and some are pink chert; pebbles are 

light-gray chert. Thin bedded; forms slope.___._._._._.. 5

Thickness of Canyon Springs Sandstone member _____ 51

Thickness (rounded) of Sundance Formation._______ 71

Unconformity. 

Precambrian:

I. Biotite gneiss and migmatite.

SECTION E. Lazy Bear

[In Gore Pass quadrangle, about 9.5 miles northwest of Kremmling, Colo., on north side of a road leading 

to the Lazy Bear Ranch (formerly the Lone Cow Ranch) in the NEJ^NWJi sec. 7 and the SEK8W)i 

sec. 6, T. 2 N., R. 81 W.; beds strike N. 40° W. and dip about 2}_° SW. Measured by O. N. Pipiringos 

and W. J. Hail, Jr., September 1963]

Sundance Formation, not measured; base of exposure is in fault contact with

beds similar to those in unit 12. 

Chinle Formation (in part): 

Middle member:

13. Claystone, grayish-red and yellowish-orange, weathers to 

popcorn surface, soft and sticky when wet; top is in fault 

contact with beds similar to those in unit 12; forms slope 10+ 

Lower member: ^== 

12. Sandstone, mottled light-gray and grayish-purple, very coarse 

grained, poorly sorted, granulitic, arkosic; contains thin 

partings of grayish-purple silty sandy claystone; forms 

rounded ledges and slopes; ledge at top _________________ 44

II. Siltstone and claystone, grayish-purple; mixed with finegrained mottled poorly sorted sandstone and swelling claystone; shaly in basal few feet; contains black iron oxide 

nodules 3 ft above base; unit forms badland topography__ 25

Thickness of lower member______________________ 69

Partial thickness of Chinle Formation ______________ 79+
N24 CONTRIBUTIONS TO STRATIGRAPHY

SECTION E. Lazy Bear Continued

Unconformity.

Triassic and Permian red beds: Feet 

10. Siltstone and shale; upper par.t is reddish-brown limy siltstone; lower part is reddish-brown shale with thin platy 

limy siltstone ledges; unit forms slopes and ledges._______ 6

9. Siltstone, reddish-brown, slightly clayey, limy, micaceous

(biotite, chlorite, and white mica); forms ledgy slope.____ 35

8. Claystone, reddish-brown, subfissile, inter-laminated with thin

siltstone layers; unit forms ledges and slopes___________ 10

7. Siltstone, like bed 9; contains greenish-gray arkosic bed at

top; unit forms ledges and slopes_____________________ 10

6. Siltstone, like bed 9; contains a 1.5-ft-thick ledge at top and

a 0.5-ft-thick ledge in middle._________________________ 8

5. Siltstone, like bed 9; interbedded with a few 1-in .-thick layers

of conglomerate; topmost 0.5 ft makes ledge___________ 13. 5

4. Sand^fone, reddish-brown, very coarse to fine-grained, poorly 

sorted, clayey and silty, micaceous, conglomeratic; fragments are as much as 4 in. long and are especially abundant 

in a zone 3-5 ft above base; forms slopes and rounded 

ledges. _____________________________________________ 15

3. Siltstone, reddish-brown, slightly clayey, slightly limy,

micaceous, laminated; forms slope._____________________ 1

2. Sandstone, reddish-brown, very coarse to fine-grained, 

conglomeratic, arkosic, poorly sorted; makes rounded 

ledge______________________________________.______ 2. 5

Thickness of Triassic and Permian red beds- ________ 101

Unconformity. 

Precambrian:

1. Crystalline rocks.

SECTION F. Snowshoe Ranch

[In Gore Pass quadrangle, about 10.5 miles northwest of Kremmling, Colo., along a road in the NWJ^NWJi 

SEJi sec. 1, T. 2 N., R. 82 W.; beds strike N. 10° E., dip 40° SE. Measured by G. N. Pipiringos and W. B. 

Cashion, September 1957]

Morrison Formation (in part):

14. Sandstone, light-gray, clear- to chalky-calcite-cemented, 

glauconitic(?), well-sorted, massive friable; forms rounded 

ledge_____________________________________________ 15

13. Claystone, greenish-gray and red, limy, sandy near top,

blocky; forms slope________________________________ 2

Partial thickness of Morrison Formation._________ 17

Sundance Formation (in part):

Windy Hill Sandstone Member:

12. Sandstone, light-gray, fine-grained, calcite-cemented, fairly 

clean, well-sorted, sparsely oolitic; forms ledge; sharp 

contact with unit 11________________________________ 2. 5
CHINLE AND SUNDANCE FORMATIONS, COLORADO N25

SECTION F. Snowshoe Ranch Continued 

Sundance Formation (in parO Continued 

Unconformity.

Pine Butte Member: feet

11. Claystone, medium-gray, sandy, subfissile, limy; forms slope. 4 

, 10. Claystone, medium-gray, silty, subfissile, limy; forms slope; 

overlain by laminated silty sandstone that forms a weak 

ledge; unit is fossiliferous.-_-____,____________________ 2. 5

9. Sandstone, light-gray, very fine grained, locally limy, interbedded with medium-gray limy shale; contains gray sandy

/ nodular limestone bed 0.5 ft thick at base; sandstone contains marine pelecypod casts (FC-5); unit forms ledge____ 2. 5

} 8. Claystone, yellowish-gray, limy, sandy, chunky; forms 

slope ___________-_-___---_-----_---__-_-____-_______ 1

7. Sandstone, yellowish-gray, very fine to fine-grained, chalkycalcite-cemented; makes weak inconspicuous ledge. ______ 1

6. Claystone, yellowish-gray, limy, silty, chunky; forms slope.. 1 

, 5. Sandstone, grayish-yellow, very fine to fine-grained, tightly

calcite-cemented; forms a platy, ripple-marked ledge. _. _ _ _ 1 

j 4. Claystone, yellowish-gray, limy, silty, chunky; forms slope._ 2

Thickness of Pine Butte Member _________________ 15

, Canyon Springs Sandstone Member (in part):

3. Sandstone, yellowish-gray, very fine-grained, limy, sparsely

glauconitic; forms slope__..____.______________________ 9. 5

2. Sandstone, light-gray, very fine to fine-grained, cemented

with chalky to clear calcite; interbedded with gray-green

^ shale; unit forms ledgy slope; sandstone contains marine

pelecypods (FC-ll)--__---_-_____-___.._._...__.._. 2

1. Sandstone, moderate-reddish-orange, silty, limy, fairly soft; 

contains a few limy nodules; topmost few feet are green; 

J' forms slope; base concealed__________________________ 8+

'^ Partial thickness of Canyon Springs Sandstone

j Member_____________________________________ 19.5 +

J Partial thickness (rounded) of Sundance Formation__ 37 +

-/, SECTION G. Tyler Mountain

.-j [In Gore Pass quadrangle, about 11.5 miles northwest of Kremmling, Colo., on southwest side of Tyler

Mountain on north side of Deer Creek in the NW^SEJ^ sec. 25, T. 3 N., R. 82 W.; beds nearly horizontal.

j Measured by G. N. Pipiringos, W. J. Hail, Jr., G. A. Izett, and C. S. V. Barclay, June and September 1963

Sundance Formation:

 Windy Hill Member: Feet 

18. Sandstone, pale-yellowish-gray, yellowish-orange-weathering, 

fine-grained, limy; contains a few rounded medium chert

, grains; bedding surfaces are ripple marked; freshly fractured surfaces show calcite cleavage faces; contact with

* Morrison Formation not exposed; forms slabby ledge.__._ 3
N26 CONTRIBUTIONS TO STRATIGRAPHY

SECTION G. Tyler Mountain Continued

Sun dance Formation Continued 

Unconformity.

Pine Butte Member: Feet 

17. Sandstone, light-gray, very fine grained, friable, well-sorted, 

fairly clean, locally ripple marked, massive; contains a few 

shale partings; topmost 8 ft are covered; contains marine 

pelecypods in basal 5 ft (FC-6); unit forms rounded ledges 

and reentrants_____________________________________ 18

Canyon Springs Sandstone Member:

16. Sandstone, moderate-reddish-orange, very fine grained, silty 

and clayey, limy, laminated; slope is littered with ripplelaminated platy chips of sandstone; forms soft slope__-___ 29

15. Sandstone, pale-reddish-brown to yellowish-gray, very fine 

grained, tightly lime-cemented, laminated; forms slab by 

ledge._-__-______-___-__-__---_--_--__-_____-__--___ 4

\- 

Thickness of Canyon Springs Sandstone Member.___ 33

Thickness of Sundance Formation._________________ 54

Unconformity. v 

Chinle Formation (in part): 

Middle member:

14. Claystone, grayish-red with pinkish-gray bands, bentonitic,

smooth, waxy, weathers to popcorn surfaces; makes soft * 

deeply weathered slope.______________________________ 19

13. Claystone, light-yellowish-orange, sandy, bentonitic; makes

slope _______________________________________________ 1

12. Siltstone, pale-reddish-brown, very clayey, very sandy; makes

slope. ______________________________________________ 3 i.

Thickness of middle member._____________________ 23

Lower member (in part):

11. Claystone, dusky-red, locally mottled light-gray, silty, sandy,

blocky; contains black iron oxide nodules; forms slope.... 3. 5

10. Sandstone, gray to purplish-red, very fine grained, tightly

lime-cemented; makes hard square-faced ledge.__________ 3

9. Claystone, sandy; and clayey sandstone; mottled purplish

black to grayish purple; forms slope.___________________ 26

8. Sandstone, mottled purple, yellow, and red, fine- to coarsegrained, conglomeratic, poorly sorted; contains claystone 

and siltstone fragments as much as 10 mm long; arkosic; 

upper part cross laminated; upper part makes slope, lower 

1.5 ft makes prominent ledge--_-------__-_-__-_------- 3.5

7. Claystone, sandy, and clayey sandstone; mottled purplish

black and grayish purple; forms slope__________---_-_- 3

6. Sandstone, mottled pale-reddish-brown, grayish-purple, and 

pale-yellowish-orange, fine-to coarse-grained, poorly sorted; 

contains clay galls and chips, arkosic; forms ledge._.____. 1
CHINLE AND SUNDANCE FORMATIONS, COLORADO N27 

SECTION G. Tyler Mountain Continued

Chinle Formation (in part) Continued

Lower member (in part) Continued Feet

5. Claystone, mottled like bed 6, silty and very sandy, micaceous,

laminated to blocky; forms slope and platy ledges________ 10

4. Sandstone, mottled like bed 6, fine-grained, silty and clayey, 

not well-sorted, fairly well indurated; contains trail casts 

and borings; forms ledge__-_-_---_--_---_---__-_-_--__ 1

3. Sandstone, mottled like bed 6, fine-grained, silty, poorly 

sorted, blocky; interbedded with silty shale; unit forms 

ledges._____-_____--___----_-_-_--__--__--______._-_ 15+

Partial thickness of lower member.________________ 66 +

Partial thickness of Chinle Formation______________ 89+

2. Covered; contact of Chinle with Triassic and Permian red

beds concealed in this interval 1 __________--_-.__-__-___ 56

Triassic and Permian red beds (top and bottom not exposed, thickness 

estimated):

1. Siltstone, reddish-brown, micaceous, locally laminated; 

contains thin beds of reddish-brown sandstone; unit forms 

slopes and ledges__-___-_--__-__--__--------_-_-____ 80+

Unconformity.

Precambrian crystalline rocks.

SECTION H. McMahon Reservoir

[In Gore Pass quadrangle, at north end of McMahon Reservoir about 15 miles northwest of Kremmling, 

Colo., in the SWHNEH and the SE^NWH sec. 21, T. 3 N., R. 82 W.; beds 1-14 strike N. 38° W. and 

dip 13° NE., beds 16-21 strike N. 28° E. and dip 46° SE. Measured by O. N. Pipiringos, A. A. Bookstrom, and C. S. V. Barclay, June 1963]

Morrison Formation (in part): Feet

22. Limestone, gray, very sandy, cherty; forms ledge__________ 2

21. Claystone, green, subfissile; forms slope.______--_-.___-___ 10

Partial thickness of Morrison Formation__.___-_._ 12

Sundance Formation:

Windy Hill Sandstone Member:

20. Sandstone, light-greenish-gray, mottled red in lower part, 

very fine grained, limy, glauconitic, sparsely oolitic; contains 

a few laminations of greenish-gray shaly siltstone; upper 

0.5 ft forms ledge, rest forms slope_____.----_-__-_--___ 5. 5

1 At a locality about 0.7 mile southeast of the Tyler Mountain section along the road near a steel gate in 

the SEHNEMNEH sec. 36, T. 3 N., R. 81 W., the lower part of the lower member consists of quartz granules 

and pebbles in a coarse quartzose sandstone matrix and is about 10 ft thick. It overlies the Triassic and 

Permian red beds and is overlain by about 5 ft of purple and gray siltstone and sandstone beds whose top 

is concealed. Consequently, the minimum thickness of the Chinle in this area Is about 105 ft. The maximum 

thickness is about 125 ft (exposed Chinle plus unit 2).
N28 CONTRIBUTIONS TO STRATIGRAPHY

SECTION H. McMahon Reservoir Continued

Sundance Formation Continued

Unconformity.

Pine Butte Member: Feet

19. Sandstone, light-gray, very fine grained, slightly limy, / 

slightly glauconitic, oolitic(?), well-sorted, fairly clean; 

stained with iron oxides 3.5 to 4.5 ft below top; makes 

slope.______________________________________________ 10

18. Sandstone, greenish-white, very fine to fine-grained, weakly

calcite-cemented; contains shaly partings in lower part; »

lower part forms slopes, upper part forms weak ledges;

thin weak ledges at top and bottom of unit are oolitic. _.._ 15 k

17. Claystone, medium-gray, very sandy, very limy, crudely

fissile; contains ostracodes; makes slope.________________ 7

16. Sandstone, light-gray, fine-grained, calcite-cemented wellsorted, contains abundant white chalky ooliths; top 0.2 ft 

makes ledge, rest forms slope._--____._._____._-___.___ 8

15. Limestone, light-olive-gray, dense, slightly sandy; contains ' 

ostracodes; no fissility apparent, but edges of bed weather . 

to an irregularly bladed appearance parallel to bedding; ' 

makes weak ledge___________________________________ . 5

Offset northward on limestone in unit 15. About 200 ft north,

there is a 1-ft-thick oolitic sandstone bed about 23 ft above \

the limestone. The slope between the limestone and the

oolitic sandstone is mostly covered and consists in part

of greenish-gray clayey, silty limy sandstone locally L

mottled pale red. About 100 feet still farther north, the

limestone contains a few ostracodes and occurs 5-7 below v

a thin oolitic sandstone bed; the limestone grades down- fl

ward into unit 14.

14. Slope, mostly covered; upper half is light-gray highly calcareous

claystone that contains ostracodes; lower half is medium- \ 

gray fine-grained sandstone that is calcite cemented, oolitic; 

contains large glauconite pellets and grades downward into ^ 

unit 13___-_--_--____________-____._____________-. 5

13. Limestone, light-greenish-gray, oolitic, sandy; contains large ^ 

glauconite pellets and fragments of Camptonectes; forms t 

prominent ledge.____-_-_-_-_------_-________-_------ 2. 5 '

Thickness of Pine Butte Member._________________ 48

Lak(?) Member:

12. Sandstone, light-gray, yellow-gray-weathering, fine-grained,

silty, limy, glauconitic, friable; makes rounded slope.._ -_ 37

Canyon Springs Sandstone Member:

11. Sandstone, moderate-reddish-orange, fine-grained, well-sorted, 

limy; contains well-rounded quartz grains and a few magnetic dark mineral grains; friable; forms slope; middle third 

of unit is covered-_____-_______-____-_____-__-_-_-_-- 30

10. Clay shale, greenish-gray, bentonitic; basal 0.3 ft is greenishgray bentonite_________________--_-________------_- 1
CHINLE AND SUNDANCE FORMATIONS, COLORADO N29

SECTION H. McMahon Reservoir Continued

Sundance Formation Continued

Canyon Springs Sandstone Member Continued Feet

9. Sandstone, moderate-reddish-orange; except beds of top few 

feet which are gray and yellow; very fine grained, silty, 

clayey, limy, friable; contains magnetic dark mineral grains; 

contains a few l-in.-thick layers of brown silty and sandy 

clay shale in lower 10 ft; unit forms ledges and slopes___ 30

8. Sandstone, moderate-reddish-orange to light-brown, very fine 

to fine-grained, well-sorted, firmly calcite-cemented to 

friable; contains magnetite and some other dark mineral 

grains; thin-bedded, forms platy ledge__________________ 2

7. Claystone, light-greenish-gray, limy, slightly sandy and

silty, crudely fissile, laminated to blocky; forms slope_____ 6

6. Sandstone, light-greenish-gray locally mottled pink and 

yellow, very fine grained, limy silty, thin-bedded to finely 

laminated, varvelike; interbedded with greenish-gray 

shale near base; platy to papery, fissile throughout; some 

bedding surfaces are irregularly pustulate, especially near 

base; unit forms slope._-_---_______._.____----_-_-___ 8

5. Sandstone, moderate-reddish-orange, very fine grained, wellsorted, limy, massive; contains well-rounded medium- to 

coarse-size quartz grains; friable, clean; base of exposure is 

at creek level on the east side of Red Dirt Creek___-_--__ 2+

Partial thickness of Canyon Springs Sandstone

Member. _--__-----____________---_----__-__-_ 79+

Partial thickness (rounded) of Sundance Formation.. 170+

4. Covered by alluvial deposits; contact between Sundance 

Formation and Chinle Formation concealed; position of 

this contact shown in figure 3 is arbitrary.-___-__---_--- 68 

Chinle Formation (in part): 

Lower member (in part):

3. Sandstone, silty sandstone, sandy siltstone, interbedded; the 

sandstone is light gray, coarse grained to pebbly, quartzose; 

the silty sandstone and the sandy siltstone are pale red to 

dusky red, mottled pinkish gray, noncalcareous, clayey, 

poorly sorted; the silty sandstone is fine to medium grained; 

entire unit is friable and makes a short steep slope in the 

west bank of a meander of Red Dirt Creek; top and bottom 

of unit are concealed---_--___________._-_-_____-_-___ 20+

Offset to northwest on west side of Red Dirt Creek in the 

NEtfSEtfNWi sec. 21, T. 3 N., R. 82 W.

2. Sandstone, pinkish-gray, very coarse to fine-grained, quartzose; contains a few chert and quartzite granules and 

pebbles; forms weak crossbedded slabby ledge that 

grades up into lithology like that of unit 3; top concealed. _ 3+

Partial thickness of lower member of Chinle Formation 23+
N30 CONTRIBUTIONS TO STRATIGRAPHY 

SECTION H. McMahon Reservoir Continued

Unconformity.

Triassic and Permian red beds (in part): Feet 

1. Clay shale, moderate-reddish-brown, silty, sandy, noncalcareous, micaceous, laminated; forms slope; sharp contact 

with bed 2; base concealed_-_____-___________-__.___.. 20+

Partial thickness of Triassic and Permian red beds. __ 20+

SECTION I. McMahon Reservoir, north

(In Gore Pass quadrangle, about 16 miles northwest of Kremmling, Colo., about 1 mile north of McMahon 

Reservoir near the center W>iNWJ4 sec. 16, T. 3 N., R. 82 W.; beds strike N. 34° W. and dip 13° NE . 

Measured by W. J. Hail, Jr., and G. N. Pipiringos, September 1963]

Morrison Formation (in part) : Feet 

16. Limestone, medium-gray; shows concentric algal structures; 

contains charophyte oogonia; forms ledge; stratigraphically 

higher beds concealed_____--__--__--__-_--_____--_____ 0. 5 

15. Covered interval_-----------------------------_---_--__ 2

Partial thickness of Morrison Formation. ___________ 2. 5

Sundance Formation (in part):

Windy Hill Sandstone Member:

14. Sandstone, light-gray, light-brown-weathering, very fine 

grained, well-sorted; calcite cemented; fractured surfaces 

show calcite cleavage faces; ripple marked; salt crystal 

casts on under side of bedding surfaces; forms slabby 

ledge.____-___----__-__-__-__--___-______--_-______- 1

Unconformity.

Pine Butte Member:

13. Sandstone, light-gray, fine-grained, slightly limy, oolitic; 

interbedded with gray calcareous clay stone; unit forms 

slope.-_-___-_-----_-------_-----_-__-----__---___-- 1

12. Limestone, light-gray, sandy, oolitic; contains large glauconite 

pellets and fragments of echinoid spines; forms prominent 

ledge and ridge; base concealed-_______________________ 10

Offset 200 feet southeast across stream.

11. Sandstone, yellowish-gray, very fine grained, well-sorted, 

clean, limy, glauconitic, oolitic; contains light-olive-gray 

claystone layers; unit forms partly covered slope.-------- 10

10. Sandstone, light-gray, fine-grained, slightly limy; contains 

abundant white chalky ooliths and a few dark mineral 

grains; friable; forms weak rounded ledge.--------- 2

9. Sandstone, light-gray, very fine grained, well-sorted, clean, 

cemented with chalky calcite, oolitic; top 0.5 ft is finegrained and makes weak rounded ledge; lower part is soft 

and forms partly covered slope_.________-____----_--- . 5

8. Limestone, light-greenish-gray, very samdjy, contains biotite 

and other dark minerals; upper part is smooth, medium

--__--_____-----_---_-_--_-____-_------------ . 5
CHDSTLE AND SUNDANCE FORMATIONS, COLORADO N31 

SECTION I. McMahon Reservoir, north Continued

Sundance Formation Continued

Pine Bute Member Continued Feet

7. Sandstone, light-greenish-gray, yellowish-gray-weathering, 

limy; contains biotite and other dark minerals; basal 1 ft 

contains beds of medium-gray sandy calcareous clay shale; 

unit forms slope_____---___---________-____-__._____ 9

6. Limestone, light-greenish-gray, yellowish-gray-weathering, 

very sandy; contains biotite flakes and other dark minerals; 

contains a shaly sandstone parting near base; unit makes a 

weak slabby ledge_-_____-__-_--__-____-_-_____._.____ 1.5

5. Shale, light-greenish-gray; contains ostracodes (FC-7); interbedded with clayey silty sandstone that contains marine 

pelecypods; unit forms ledges and slopes.___-.___._..___ 4

4. Sandstone, very light greenish gray, fine-grained, calcareous, 

abundantly oolitic; contains clay galls; grades downward 

into sandy light-gray dense limestone with smooth conchoidal fractures; unit forms rounded ledge____________ 1

3. Shale, light-olive-gray; calcareous; contains ostracodes (FC-8); 

includes two thin light-gray silty and sandy limestone beds; 

unit forms slope____________________________________ 5

2. Sandstone, very light greenish gray, very fine grained, glauconitic, limy, ripple-marked, thin-bedded, cherty; forms 

ledge.______________________________________________ 1

Thickness of Pine Butte Member.__.______-_-__-__ 50

Lak(?) Member (in part):

1. Sandstone, light-gray to yellowish-gray, very fine grained, 

cemented with chalky calcite, glauconitic, well-sorted, 

friable; forms soft smooth slope; base concealed-_________ 26 +

Partial thickness of Sundance Formation._________ 77 +

SECTION J. Frantz Creek

[In Lake Agnes quadrangle, about 18 miles northwest of Kremmling, Colo., in the NE'ANW'ASE1 /* sec. 

32, T. 4 N., R. 82 W.; beds strike about north and dip 10° E. Measured by W. J. Hail, Jr., and Q. N. 

Pipiringos, September 1963]

Morrison Formation (in part): feet 

18. Limestone, gray, calcareous; middle is shaly and makes reentrant between two ledges________._____-____--__--- 1

17. Claystone, medium-gray, calcareous, chunky; contains

ostracodes; makes slope..______________________________ 5

Partial thickness of Morrison Formation.
N32 CONTRIBUTIONS TO STRATIGRAPHY

SECTION J. Frantz Creek Continued

Sundance Formation:

Windy Hill Sandstone Member: Feet 

16. Sandstone, grayish-yellow, very fine grained, cemented with

chalky calcite, ripple-marked; makes weak slabby ledge.__ 1

Pine Butte Member:

15. Clay shale, greenish-gray mottled purple, calcareous, crudely

fissile; makes slope. _-__---_-----__-_-._._-_____-_____ 4

14. Sandstone, yellowish-gray, very fine grained, calcareous, 

glauconitic; beds in upper 2 ft contain grayish-green shale 

partings, middle is shaly, basal 1 ft is grayish white; unit 

makes slope interrupted by weak ledges _ ______________ 7

13. Sandstone, like unit 14; central part makes slope _ ________ 3

12. Covered___--__--_--___---__------_---.__. ----_---__._ 2

11. Sandstone, grayish-yellow, very fine grained, cemented with

chalky calcite, friable; makes slope_____-___-_-___--____ 1

10. Clay shale, light-greenish-gray, limy, irregularly fissile, laminated; bottom-dweller trails along bedding planes; contains ostracodes (FC-9); limy parts form thin ledges __ __ 10

Thickness of Pine Butte Member. _________________ 28

Lak(?) Member:

9. Sandstone, light-gray, very fine grained, well-sorted, slightly 

limy, glauconitic, fairly well indurated; makes slope, basal 

1 ft makes ledge.------_--_------__-________-________ 14

8. Sandstone, light-yellowish-brown, very fine grained, wellsorted, slightly limy; makes slope._____________________ 5

7. Claystone, olive-gray, limy, crudely fissile; plant microfossils

(FC-10); forms slope____-___-______-____________.____ 5

6. Sandstone, brownish-yellow, very fine grained, limy; upper

part forms slope, lower 1 ft forms ledge.________________ 5

5. Claystone, gray, limy, crudely fissile, hard; forms slope.____ 10

4. Siltstone, gray, limy, sparsely glauconitic, biotitic; interbedded with yellowish-gray limy silty sandstone; bottomdweller burrow casts common; unit forms ledges and 

slopes; grades downward into unit 3___.____-____.-_____ 8

Thickness of Lak(?) Member____._________________ 47

Canyon Springs Sandstone Member:

3. Sandstone, buff and moderate-reddish-orange, calcareous, 

friable; gradational downward into bed 2; contains a bed 

of green bentonitic clay shale 0.1 ft thick about 15 ft 

below top; unit forms steep slope.___-_____--_____---__ 164
CHINLE AND SUNDANCE FORMATIONS, COLORADO N33

SECTION J. Fr<mtz Creek Continued

Sundance Formation Continued

Canyon Springs Sandstone Member Continued Feet 

2. Sandstone, light-gray, very fine grained, calcareous, wellsorted, friable; basal 1 in. is biotitic, platy, gritty, and 

shaly and contains quartz, quartzite, and chert pebbles as 

much as 0.2 in. in diameter and iron oxide at the base____ 2

Thickness of Canyon Springs Sandstone Member ____ 166

Thickness of Sundance Formation__..__.._._.____ 242

Unconformity.

Triassic and Permian red beds:

1. Siltstone, moderate-reddish-brown, some parts bleached

gray, clayey, sandy, calcareous, micaceous, thin-bedded;

claystone partings are noncalcareous, unit forms chippy

slope, contact with bed 2 is sharp; basal 10 ft concealed;

contact with Precambrian approximately at creek level.. 100

Thickness of Triassic and Permian red beds.__--._.. 100

Unconformity. 

Precambrian granite.

SECTION K. Barber Basin

[In Lake Agnes quadrangle, about 20.5 miles northwest of Kremmllng, Colo., at north end of Barber Basin 

In the NEJiSW^NE^ sec. 17, T. 4 N., R. 82 W.; beds strike N. 10° W. and dip 11° NE. Measured by 

W. J. Hail, Jr., and G. N. Pipiringos, September 1963]

Sundance Formation (in part):

Pine Butte Member (in part): Feet 

8. Sandstone, yellowish-orange, very fine grained, poorly sorted, 

silty, limy, glauconitic; makes reentrants and slopes broken 

by ledges of coquinal sandstone similar to bed 7; top of unit 

concealed.________-_---_-----____------_-___-___-____ 5+

7. Sandstone, yellowish-orange, very fine grained, cemented by 

chalky calcite, glauconitic, cherty, contains Camptonectes 

and Ostrea shell fragments; forms square-faced ledge_-____ 4

Partial thickness of Pine Butte Member.____________ 9 +

Lak(?) Member:

6. Sandstone, yellowish-gray, clayey; forms slope.__.__-_____.- 19

5. Claystone, yellowish-gray, silty, calcareous, crudely fissile; contains scattered lenses of platy limy glauconitic sandstone; 

unit forms slope____--___-_-___-____-_-_-_-_________- 3

4. Sandstone, yellowish-gray, very fine grained, calcareous,

clayey, silty, glauconitic; forms slope._.----_____-_____._ 3

3. Claystone, yellowish-gray, silty, calcareous, crudely fissile;

forms slope; grades downward into bed 2_________.___-__- 16
N34 CONTRIBUTIONS TO STRATIGRAPHY

SECTION K. Barber Basin Continued

Sundance Formation Continued

Lak(?) Member Continued Feet 

2. Siltstone, yellowish-gray, calcareous, clayey, sparsely glauconitic; forms slope; grades downward into bed !__________ 2

Thickness of Lak(?) Member____-__________________ 43

Canyon Springs Sandstone Member:

1. Sandstone, fine-grained, well-sorted, clean, friable; a few 

percent chert and quartzite grains; upper part is gray with 

pink bands, lower part is orange pink with light-gray bands; 

beds of top few feet weather yellow and contain burrow casts; 

unit forms slope; base concealed_____---__--------__--_- 60+

Partial thickness of Sundance Formation ____________ 112 +

REFERENCES CITED

Baker, A. A., Dane, C..H., and Reeside, J. B., Jr., 1936, Correlation of the Jurassic

formations of parts of Utah, Arizona, New Mexico, and Colorado: U.S. Geol.

Survey Prof. Paper 183, 66 p. 

Beekly, A. L., 1915, Geology and coal resources of North Park, Colorado: U.S.

Geol. Survey Bull. 596,121 p. 

Burbank, W. S., Lovering, T. S., Goddard, E. N., and Eckel, E. B., 1935, Geologic

map of Colorado: Washington, D.C., U.S. Geol. Survey, Geol. Map, scale

1:500,000 (repr. 1959). 

Donner, H. F., 1949, Geology of the McCoy area, Eagle and Routt Counties,

Colorado: Geol. Soc. America Bull., v. 60, no. 8, p. 1215-1247. 

Hail, W. J., Jr., 1965, Geology of northwestern North Park, Colorado: U.S. Geol.

Survey Bull. 1188, 133 p.

Heaton, B. L., 1933, Ancestral Rockies and Mesozoic and late Paleozoic stratigraphy of Rocky Mountain region: Am. Assoc. Petroleum Geologists Bull., v.

17, no. 2, p. 109-168. 

Imlay, R. W., 1947, Marine Jurassic of Black Hills area, South Dakota and

Wyoming: Am. Assoc. Petroleum Geologists Bull., v. 31, no. 2, p. 227-273. 

 1964, Marine Jurassic pelecypods from central and southern Utah: U.'S.

Geol. Survey Prof. Paper 483-C, p. C1-C42,4 pis. 

Izett, Glen, 1968, Geology of Hot Sulphur Springs quadrangle, Grand County,

Colorado: U.S. Geol. Survey Prof. Paper 586, 79 p. 

Jenkens, M. A., Jr., 1957, Stratigraphy of the Red Dirt Creek area, Grand County,

Colorado, in Rocky Mtn. Assoc. Geologists Guidebook, 9th Ann. Field Conf.,

North and Middle Park Basins, Colorado, 1957: p. 51-54. 

Kinney, D. M., 1955, Geology of the Uinta River-Brush Creek area, Duchesne and

Uintah Counties, Utah: U.S. Geol. Survey Bull. 1007, 185 p. 

Lovering, T. S., and Johnson, J. H., 1933, Meaning of unconformities in stratigraphy of central Colorado: Am. Assoc. Petroleum Geologists Bull., v. 17, no.

4, p. 353-374.
CHINLE AND SUNDANCE FORMATIONS, COLORADO N35

Pipiringos, G. N., 1953, Correlation of marine Jurassic and related rocks in the 

Laramie Basin, Wyoming, in Wyoming Geol. Assoc. Guidebook, 8th Ann. 

Field Oonf., Laramie Basin, Wyoming, and North Park, Colorado, 1953: 

p. 34-39.

 1957, Stratigraphy of the Sundance, Nugget and Jelm formations in the 

Laramie Basin, Wyoming: Wyoming Geol. Survey Bull. 47, 63 p.

 1968, Correlation and nomenclature of some Triassic and Jurassic rocks

in south-central Wyoming: U.S. Geol. Survey Prof. Paper 594-D, 26 p.

Poole, F. G., and Stewart, J. H., 1964, Chinle Formation and Glen Canyon Sandstone in northeastern Utah and northwestern Colorado, in Geological Survey 

research 1964: U.S. Geol. Survey Prof. Paper 501-D, p. D30-D39.

Whitfield, R. P., and Hovey, E. O., 1906, Remarks on and descriptions of Jurassic 

fossils of the Black Hills: Am. Mus. Nat. History Bull. 22, p. 389-402, pis. 

42-62.

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