Stratigraphy of the

State Bridge Formation in the

Woody Creek Quadrangle,

Pit kin and Eagle Counties,

Colorado

By VAL L. FREEMAN

CONTRIBUTIONS TO STRATIGRAPHY 

GEOLOGICAL SURVEY BULLETIN 1324-F
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

W. A. Radlinski, Acting Director

Library of Congress catalog-card No. 77-169280

U.S. GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1971

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

Washington, D.C. 20402 - Price 20 cents

Stock Number 2401-1126
CONTENTS

Page

Abstract._____________________ __________________________________ Fl

Introduction. ________________-_____-______-_-_--------_-_-_-__--_- 1

Paleogeography _ _____________-____________--__-_--_-____--_-_- 3

Nomenclature-__ __________________________--_---_-_-____--__-- 4

Maroon Formation-_______________________________________________ 5

State Bridge Formation_____-_-____-__-_--_-------__----------__-_- 6

Sandstone of the Fryingpan River.______________________________ 8

Sloane Peak Member_______________---__-_-__-_--------_--_-_- 9

Coarse unit of Toner Creek______________________----____- ___. 10

Comparison with its occurrence in other areas___________________ 10

Chinle Formation______________________________________________ 11

Selected stratigraphic sections_____________________________________ 11

1. Fryingpan River___________________-__--_-_-----___-___--_ 12

2. Box Canyon___-_______________________________ 13

3. Bionaz Gulch_____________________________________________ 14

4. Toner Creek______________________________________________ 15

References cited_________________________________ _____________ 16

ILLUSTRATIONS

Page 

FIGURE 1. Index map of Colorado_______________________________ F2

2. Map of central Colorado showing locations of the stratigraphic 

sections of the State Bridge Formation and of places discussed in text____________--__-______________ 3

3. Schematic section showing relations of red-bed units across

Woody Creek and western part of Ruedi quadrangles____ 5

m

CONTRIBUTIONS TO STRATIGRAPHY

STRATIGRAPHY OF THE 

STATE BRIDGE FORMATION IN THE 

WOODY CREEK QUADRANGLE, PITKIN 

AND EAGLE COUNTIES, COLORADO

By VAL L. FREEMAN

ABSTRACT

Distinct lithologic units within a 6,300-foot-thiek red-bed sequence are of great 

help in interpreting the history and structure of the Woody Creek quadrangle, 

west-central Colorado. Three thousand feet of :the red beds are assigned to the 

Maroon Formation; they are overlain in sequence by 2,400 feet of State Bridge 

Formation and 900 feet of Chinle Formation. The State Bridge is bounded top 

and bottom by unconformities. Within the State Bridge three mappable units are 

designated: the sandstone of the Fryingpan River at the base; the Sloane Peak 

Member a new, formal name in the upper part; and the coarse unit of Toner 

Creek at the top. Only the Sloane Peak is recognized in the State Bridge type 

locality. The South Canyon Creek Member of the State Bridge is recognizable 

along the north edge of the Woody Creek quadrangle, but is only 30 inches thick 

and pinches out about 2 miles to the south.

The State Bridge Formation can be distinguished from the Maroon Formation 

by its content of well-rounded spherical coarse sand grains, by the presence of 

parallel symmetrical ripple marks with wavelengths of less than 2 inches, by 

generally thinner and more even beds, and by better sorting of the beds. The 

Chinle Formation is readily identified by the presence of the distinctive and 

continuous mottled member at the base.

INTRODUCTION

The Woody Creek quadrangle in west-central Colorado (figs. 1, 2) 

contains about 6,300 feet of red beds consisting of parts of the Pennsylvanian and Permian Maroon Formation and the Triassic Chinle 

Formation and the Permian and Triassic State Bridge Formation. The 

State Bridge is unusually thick and was divided during mapping as an 

aid to greater understanding of the structure and geologic history of 

the area. Three newly recognized members one formal and two inFi
F2 CONTRIBUTIONS TO STRATIGRAPHY

FIGUEE 1. Map of Colorado showing area of figure 2 (stippled) and structural 

elements during Pennsylvanian time (from Mallory, 1960).

formal of the State Bridge proved mappable are herein named and 

described: the sandstone of the Fryingpan River at the base, the 

Sloane Peak Member in the upper part, and the coarse unit of Toner 

Creek at the top. These members are separated by unnamed parts of 

the State Bridge. The State Bridge Formation unconformably overlies the Maroon Formation, within which is recognized an upper unit 

informally called the siltstone unit. Unconformably overlying the 

State Bridge is the Chinle Formation, which was recognized a few 

miles north and south of the quadrangle by Poole and Stewart (1964). 

The purpose of this report is to describe three units of the State 

Bridge Formation. The mapping of these units is essential to the 

understanding of the geologic history and structure of the Woody 

Creek and adjacent quadrangles. The lithology of each is distinct and 

clearly recognizable, and it undoubtedly reflects changes of depositional conditions within the State Bridge. The sandstone of the 

Fryingpan River and the coarse unit of Toner Creek are probably of 

local extent within the Eagle basin. The Sloane Peak Member is 

probably continuous as a lithologic unit across the basin from near 

Aspen to Kent (fig. 2).
STATE BRIDGE FORMATION, COLORADO

107" 00' 45' 30'

F3

106° 15'

FIGURE 2. Locations in central Colorado of the stratigraphic sections of the 

State Bridge Formation and of places discussed in text. 1, Fryingpan River 

section; 2, Box Canyon section; 3, Bionaz Gulch section (type section of the 

Sloane Peak Member) ; 4, Toner Creek section.

PALEOGEOGRAPHY

The Woody Creek quadrangle is near the southwest side of the Eagle 

basin, an elongated structural basin that lies between the Front Range 

uplift on the northeast and the Uncompahgre uplift on the southwest 

(fig. 1). From Middle Pennsylvanian through Early Triassic time, 

during which the Maroon and State Bridge Formations were deposited,
F4 CONTRIBUTIONS TO STRATIGRAPHY

the basin received a thick sequence of clastic sediments derived from 

the adjacent highlands. The clastic rocks are dominantly "red beds" 

that in general increase in grain size toward the basin margins. Limestones and evaporate beds \vere deposited sporadically near the center 

of the basin.

NOMENCLATURE

The Maroon Formation, originally the Maroon Conglomerate, was 

named for typical exposures on Maroon Creek a few miles south of 

the Woody Creek quadrangle by G. H. Eldridge (in Emnions and 

others, 1894). In the Crested Butte area, where Eldridge used the 

name, the Maroon sediments are unconformably overlain by Jurassic 

sediments; consequently Eldridge did not give criteria for identifying 

the top of the Maroon where younger red beds are present.

Triassic red beds overlying the Maroon Formation in the Aspen area 

were recognized by Spurr (1898), but recent mapping by Bruce Bryant 

(oral commun., 1968) reveals that Spurr's placement of the contact 

was not consistent. Poole and Stewart (1964) correlated the Triassic 

beds of the Aspen area with the Chinle Formation and summarized 

the distinctive characteristics of the Chinle in that area. Their (fig. 3) 

regional section showed that the Chinle rests on progressively older 

rocks as it is followed into the Aspen area from the northwest; however, Bryant's recent mapping (1971) shows that at the locality of 

Poole and Stewart's section, the Chinle rests upon the Sloane Peak 

Member of the State Bridge Formation.

Red beds between the Maroon Formation and the Chinle Formation 

are recognized as a mappable formation in the area near State Bridge, 

Colo., about 59 miles northeast of the Woody Creek quadrangle (fig. 2). 

The name State Bridge Siltstone Member of the Maroon Formation 

was applied to these beds by Dormer (1936, 1949). The State Bridge 

was raised to formation rank by Brill (1942) in the Gore Creek area. 

The State Bridge in these papers is considered to be conformable on 

coarser clastic sediments now7 called Maroon Formation and to be unconformably overlain by conglomerate now recognized as a basal unit 

of the Chinle Formation. The State Bridge was recognized throughout 

a larger area to the west and south (Sheridan, 1950); there it overlies 

the Schoolhouse Sandstone of Thompson (1949) or overlies Pennsylvanian arkoses (now Maroon Formation according to Brill, 1952) 

where the Schoolhouse Sandstone (now Weber Sandstone according 

to Brill, 1952) is not present. Murray (1958, p. 56) demonstrated that 

an unconformity is present at the base of the State Bridge Formation 

east of State Bridge and that the Weber is cut out beneath the conformity nearer to the Front Range uplift.
STATE BRIDGE FORMATION, COLORADO F5

Three units within the State Bridge Formation (fig. 3) have proved 

mappable in the Woody Creek quadrangle and are called herein: the 

sandstone of the Fryingpan River (at the base), the Sloane Peak 

Member (in the upper part), and the coarse unit of Toner Creek (at the 

top). The upper part of the Maroon Formation is distinct from the 

underlying parts and is informally called the siltstone unit, although 

it is not a mappable unit.

South Canyon Creek Member

FIGURE 3. Schematic section showing relations of red-bed units across Woody 

Creek and western part of Ruedi quadrangles. Not to scale.

MAROON FORMATION

In the Woody Creek quadrangle only parts of the Maroon Formation are exposed. A complete section of Maroon, however, crops out 

along Woody Creek and Little Woody Creek in the Ruedi and Aspen 

quadrangles east and south of the Woody Creek quadrangle. The 

Maroon in this section is about 15,000 feet thick. The base of the 

Maroon is placed at the gradatioiial contact between the interbeclded 

greenish-gray and grayish red beds of the Eagle Valley Formation 

and the dominantly red beds of the Maroon (Brace Bryant. oral commun., 1968). The Maroon is composed mostly of silty and clayey sandstone, clayey siltstone, and silty claystone with lesser amounts of conglomeratic sandstone, limestone, and limestone chip conglomerate. The 

clastic beds are arkosic, micaceous, and calcareous. The colors are 

mostly shades of grayish red in the lower part and mostly shades of
F6 CONTRIBUTIONS TO STRATIGRAPHY

reddish brown in the upper part. Beds of sandstone and conglomeratic 

sandstone are less abundant toward the top and are absent in an uppermost unit 2,000 feet thick. This upper unit is dominantly composed of 

slightly clayey moderate-reddish-orange siltstone with films and thin 

beds of somewT hat darker silty claystone.

In the Woody Creek quadrangle only about 3,000 feet of the Maroon 

Formation is exposed. Of this total, the upper 1,000 feet is composed of 

siltstone very similar to the siltstone unit at the Woody Creek-Little 

Woody Creek section. Here the siltstone is slightly clayey and occurs 

as thick to very thick beds, some of which show a few parallel laminae. 

Bedding-plane features include a peculiar small-scale lumpy feature 

resembling the Riwularites of White (1929, pis. 6, 7, 8), mud cracks, 

and poorly preserved trails or twig imprints. The remaining 2,000 feet 

of Maroon in the Woody Creek quadrangle is in isolated exposures 

but is probably older. It is generally coarser grained than the Maroon 

in the Woody Creek-Little Woody Creek section and consists of thinto thick-bedded sandstone, conglomeratic sandstone, conglomerate, 

clayey siltstone, silty claystone, and limestone. The clastic beds are 

commonly poorly sorted, micaceous, arkosic, and calcareous. Pebbles 

are commonly rounded or subrounded, but the sand grains are angular. 

The debris appears to have been derived mostly from Precambrian 

crystalline terranes nearby. Sedimentary structures are crossbeclding 

and scour of fluvial aspect, cusp or asymmetrical parallel ripple marks 

with wavelengths more than 2i/£ inches, flute casts, clay chips, mud 

cracks, and raindrop impressions. Limestone beds in the Maroon are 

thin, clayey, and mostly unfossiliferous. One limestone near the base 

of the exposures contains poorly preserved Foraminifera and ostracodes. The Maroon in the Woody Creek quadrangle consists mostly of 

first-cycle sediments deposited from fresh water. The main part was 

deposited as channel and overbank stream deposits, and the siltstone 

unit was deposited as ephemeral lake or playa deposits.

The lowest part of the Maroon Formation exposed in the Woody 

Creek quadrangle is in fault contact with the Eagle Valley Formation. 

The top of the Maroon Formation is at an angular unconformity. The 

difference in dip across this unconformity is so low as to be indiscernible in parts of the Woody Creek quadrangle, but it exceeds 60° 

locally. The angle of unconformity decreases northeastward from the 

center of the quadrangle, but an angle of 20° was noted at Gerard 

Gulch just east of its confluence with Gypsum Creek (about 10 miles 

to the north).

STATE BRIDGE FORMATION

The State Bridge Formation in the Woody Creek quadrangle ranges 

in thickness from about 650 feet to about 2,400 feet. The Weber Sand-
STATE BRIDGE FORMATION, COLORADO F7

stone that separates the State Bridge from the Maroon Formation to 

the north is not recognized here. Recognized only along the north edge 

of the Woody Creek quadrangle is the South Canyon Creek Member 

(termed the Yarmony Limestone Member by Sheridan, 1950) that 

serves to divide the State Bridge into lower and upper units in the 

Glenwood Springs and State Bridge areas. Three new members are 

recognized and mapped in the Woody Creek quadrangle: the sandstone of the Fryingpan River, the Sloane Peak Member, and the 

coarse unit of Toner Creek (fig. 3).

The Permian age of the South Canyon Creek Member of the State 

Bridge Formation is based on the determination of its fossils (Bass 

and Northrop, 1950) and its regional correlations. Consequently the 

lower unit and the sandstone of the Fryingpan River are Permian, 

and the lower unit is a correlative of the Park City Formation (McKee 

and others, 1967, table 1). The upper unit is assigned to the Early 

Triassic (M. E. MacLachlan in McKee and others, 1959, p. 8) and 

considered to be a correlative of the Moenkopi Formation (McKee and 

others, 1959, table 1). The Sloane Peak Member and the coarse unit 

of Toner Creek are therefore of Early Triassic age. No unconformities have been recognized within the State Bridge and the PermianTriassic boundary is not evident. M. E. MacLachlan (in McKee and 

others, 1959, p. 3) stated that the boundary is placed arbitrarily 100 

feet above the limestone now recognized as the South Canyon Creek 

Member.

The bulk of the State Bridge Formation between the Maroon 

Formation or the sandstone of the Fryingpan River where present 

(fig. 3) and the newly named Sloane Peak Member consists of fine 

clastic sediments and is mainly moderate reddish brown. This part of 

the formation thins abruptly to the west, and coarser clastic beds 

become more abundant in that direction, that is, toward the Uncompahgre uplift.. The most common rock type is clayey siltstone containing scattered coarse sand grains that are characteristically rounded 

and highly spherical. Some thin short lenses of the coarse grains occur 

in the clayey siltstone. Other rocks are medium-grained sandstones, 

commonly slightly silty and clayey; claystones, commonly silty; clean 

medium- to coarse-grained sandstones; and at the north edge of the 

quadrangle at least one thin discontinuous limestone, the South Canyon 

Creek Member. The fine clastic sedimentary rocks are micaceous, 

arkosic, and calcareous, but seemingly to a lesser degree than the sedimentary rocks of the Maroon. Bedding in the State Bridge is thin to 

thick, and crossbedding is present, especially in the western part of the 

quadrangle. The rocks of the State Bridge are less resistant to weathering than are those of the Maroon, probably owing to a lesser degree
F8 CONTRIBUTIONS TO STRATIGRAPHY

of compaction of the sediments. Sedimentary structures characteristic 

of the State Bridge are parallel ripple marks mostly symmetrical with 

wavelengths less than 2 inches, mud cracks and associated clay chips, 

and rare markings such as rain prints and salt crystal casts. In general, 

the bedding in the State Bridge is more even and regular and thinner 

than that in the Maroon. The rounded spherical sand grains of the 

State Bridge are nearly omnipresent, though rarely abundant, and are 

diagnostic in differentiating the State Bridge from the Maroon. Also 

diagnostic is the type of ripple marks.

The clastic material composing the State Bridge Formation appears 

to have been derived partly from preexisting sedimentary rocks of 

the Maroon Formation and to have been transported farther and 

reworked to a greater degree than Maroon material. Deposition of the 

State Bridge sediments was in widespread bodies of standing water 

that often dried up. A marginal marine environment is postulated.

SANDSTONE OF THE FRYINGPAN RIVER

The distinctive sandstone here called the sandstone of the Fryingpan 

Kiver occurs at the base of the State Bridge Formation in the northeastern part of the Woody Creek quadrangle and in the adjacent 

Ruedi, Toner Reservoir, and Red Creek quadrangles. A stratigraphic 

section (section 1) measured on the Fryingpan River 1 mile west of 

the Ruedi Dam shows the unit to be about 400 feet thick there. The 

unit thins to a pinchout about 3 miles to the south and southwest, 

about 4 miles to the west, and about 7 miles to the northwest. To the 

east and northeast of the measured section it is missing, because of 

erosion. The contact with the underlying siltstone unit of the Maroon 

Formation is sharp and is probably an angular unconformity of very 

low angle. The contact with the overlying clayey siltstone of the State 

Bridge is sharp and seemingly concordant.

The sandstone of the Fryingpan River is composed of moderatereddish-orange clay-free sandstone which is fairly well sorted. The 

constituent grains range from silt size to medium sand size and were 

originally mostly rounded but are now irregular in shape, owing to 

intergrowth of the grains during compaction. Pore space is now filled 

by secondary quartz and minor calcite. Bedding in the unit consists 

mostly of large-scale sweeping crossbeds with laminae of differing 

grain size and with rare black-sand concentrations. A few parallel 

partings of clay-rich beds are present. The dominant dip direction of 

the crossbeds is to the southwest. The unit is believed to be of eolian 

origin.

The sandstone of the Fryingpan River is resistant to erosion and 

typically forms vertical cliffs or underlies large dip-slope areas. The
STATE BRIDGE FORMATION, COLORADO F9

sandstone has, in the past, been quarried and marketed as building 

stone and is still used locally as flagstone.

SLOANE PEAK MEMBER

The Sloane Peak Member of the State Bridge Formation is here 

named for typical exposures capping Sloane Peak in the northeast 

corner of the Woody Creek quadrangle. The top of the member is not 

present on Sloane Peak, but full thicknesses occur to the west and 

southwest in the quadrangle. The type section (section 3) is 5 miles 

west of Sloane Peak in Bionaz Gulch. The member also occurs in the 

Toner Reservoir quadrangle to the north and in the Aspen quadrangle 

to the south. The Sloane Peak may prove to be the most widespread 

member of the State Bridge Formation.

The Sloane Peak Member of the State Bridge Formation is a 

homogeneous very fine grained sandstone that ranges in thickness 

from about 130 feet in the northwestern part of the quadrangle to 

about 250 feet in the northeastern part. The sandstone is very well 

sorted and marked by medium-scale crossbedding throughout its 

thickness. In most of the Woody Creek quadrangle a 10-foot-thick 

clayey siltstone above the basal 10 feet of sandstone appears as a darker 

band. In the easternmost exposures in the Woody Creek quadrangle 

this clayey siltstone grades laterally into a very fine grained sandstone that is like the rest of the member. Both the upper and lower 

contacts of the member are sharp but seemingly conformable.

This member is slightly more resistant than the overlying and 

underlying beds and tends to form cliffs or the capping unit on ridges. 

In many exposures it weathers to subhorizontal slabs that obscure the 

crossbedding.

Every place where it has been observed, the Sloane Peak Member 

lies near the top of the State Bridge not more than 300 feet below the 

unconformity at the base of the overlying Chinle Formation. In the 

northwest corner of the Woody Creek quadrangle, the Sloane Peak is 

about 900 feet above the base of the State Bridge. In the northeast 

corner of the quadrangle the member is about 2,100 feet above the base 

of the State Bridge. Similar sandstones near the top of the State 

Bridge Formation in the Kent, Squaw Creek, and Brush Creek areas 

are, believed to correlate with the Sloane Peak. The sandstone at Kent 

that is considered to be the Sloane Peak is about 10 feet thick and lies 

about 20 feet below the base of the Chinle and about 470 feet above the 

base of the State Bridge. In lower Squaw Creek, about 4 miles southeast of Kent, the Sloane Peak is 30 feet thick, about 35 feet beneath the 

Chinle Formation. On Hardscrabble Mountain, between the Kent area 

and the Woody Creek quadrangle, the Sloane Peak has not been 

measured but is well developed and resistant. It is tentatively suggested that the Sloane Peak Member formed as an offshore bar.
F10 CONTRIBUTIONS TO STRATIGRAPHY

COARSE UNIT OF TONER CREEK

The coarse unit of Toner Creek of the State Bridge Formation 

crops out in the western part of the Woody Creek quadrangle, in the 

Toner Reservoir quadrangle, and in a few places in the Basalt quadrangle. A stratigraphic section of this unit was measured (section 4) 

near Toner Creek. The unit is probably a tongue-shaped body of 

sediment derived from the southwest that never extended much farther 

northeast than its present known extent. The maximum measured 

thickness, near the center of the Woody Creek quadrangle, is 388 feet. 

This unit consists of clastic rocks coarser than those in any other beds 

in the formation and probably reflects a renewed uplift of the Uncompahgre uplift. In gross aspect the sediments of the Toner Creek 

resemble sediments of equivalent grain size in the Maroon Formation, 

but a close examination of Toner Creek sediments always reveals the 

spherical coarse sand grains typical of the State Bridge and absent in 

the Maroon.

The sedimentary rocks of the coarse unit of Toner Creek are poorly 

to moderately sorted sandstones, pebbly sandstones, conglomerates 

with pebbles as much as 6 inches across, and silty and sandy claystones. 

They are micaceous and arkosic in thin to thick beds. Crossbedding 

and scour fills are common. The unit may represent deposition in a 

fluvial environment.

The basal contact of the coarse unit of Toner Creek at the measured 

section is at the base of the lowest conglomerate. This contact is easily 

found and is sharp. A few coarse grained sandstones in the upper part 

of the underlying State Bridge, however, are probably thin wedges of 

the coarse unit that likely intertongue with the underlying beds. 

During mapping of the Woody Creek quadrangle, I used for the base 

of the coarse unit of Toner Creek a sandstone that is considerably finer 

grained than the basal conglomerate in the measured section. The 

upper contact of the Toner Creek is the regional unconformity at the 

base of the Chinle Formation. The beds above and below this contact 

are seemingly without angular discordance in the Woody Creek 

quadrangle.

COMPARISON WITH ITS OCCURRENCE IN OTHER AREAS

The State Bridge Formation in the Woody Creek quadrangle is 

distinctly different from the type State Bridge, yet correlation is not 

in doubt. In both areas the State Bridge unconf ormably underlies the 

Chinle Formation and unconformably overlies the Maroon Formation. The South Canyon Creek Member of the State Bridge area is 

present in the northern part of the Woody Creek quadrangle, and the 

Sloane Peak Member of the Woody Creek quadrangle extends as far
STATE BRIDGE FORMATION, COLORADO Fll

as Kent (fig. 2). A section at Kent was correlated with the type locality 

by Sheridan (1950). The main difference in the formation between the 

two areas is the thickness: about 500 feet in the type locality and about 

2,400 feet in the northeastern part of the Woody Creek quadrangle. 

Other differences result chiefly from the fact that the two areas are on 

opposite sides of the Eagle basin and received debris from different 

source areas. Wedges of coarse debris are present in both areas: the 

coarse unit of Toner Creek, derived from the Uncompahgre uplift, at 

the top of the formation in the Woody Creek quadrangle area; and the 

Sheephorn graywacke, a local unit used by Sheridan (1950, p. 132), 

derived from the Front Range uplift, at the base of the formation east 

of the type locality.

Between State Bridge and the Woody Creek quadrangle, the State 

Bridge Formation is exposed east of Gypsum Creek on the slope of 

Hardscrabble Mountain. This area is near the center of the Eagle 

basin, and the State Bridge Formation is thicker than known elsewhere. The Sloane Peak Member is well developed and locally caps 

Hardscrabble Mountain. The formation rests with noticeable angular 

unconformity upon the Maroon Formation and very locally upon preMaroon strata.

The State Bridge Formation in the Glenwood Springs area is little 

changed from the type locality, except that it rests conformably upon 

a tongue of the Weber Sandstone, which in this area is certainly a 

water-laid deposit. In the Woody Creek quadrangle the sandstone of 

the Fryingpan River may be about the same age as the tongue of the 

Weber Sandstone; however, it is of eolian origin and must have formed 

as a group of dunes in no way connected with eolian parts of the 

Weber.

CHINLE FORMATION

The Chinle Formation is easily separable from older red beds in the 

Woody Creek quadrangle. This formation, 900 feet thick, consists 

mostly of red siltstone that is very thin bedded, although the bedding 

is generally obscured on weathered slopes. A continuous unit, but less 

than 50 feet thick, of red and purple mottled siltstone and sandstone 

and lenses of gray quartzose sandstone makes up the base of the 

Chinle. This unit, the mottled member of Poole and Stewart (1964), 

contrasts with the underlying State Bridge Formation.

SELECTED STRATIGRAPHIC SECTIONS

Stratigraphic sections were measured by hand leveling with a 

Brunton compass. Color descriptions and numbers are from the Rockcolor Chart (Goddard and others, 1948).
F12 CONTRIBUTIONS TO STRATIGRAPHY

1. FRYINGPAN RIVER SECTION, RUEDI QUADRANGLE

[Composite section of the sandstone of tlie Fryingpan River, State Bridge Formation. 

Measured on the north side of the Fryingpan River. The tendency of this sandstone to 

occur as a very steep cliff or as broad dip slopes precluded measurement of a single 

complete section. The thickness of this section, present on the north side of the river, 

5.000 ft due wesi of the Ruedi Dam, was calculated from mapped contacts and is 400 

feet; the lower 150 ft was examined and is described below. The top 85 ft of the sandstone is described from exposures at the easternmost of the three quarries of the 

Western Slope Stone Co., on the north side of the river 2,600 ft east of the mouth of 

Saloon Gulch. The central part was examined in low outcrops on the dip slope north 

of the section where the lower 150 ft was examined. Measured June 1968]

Thickness

State Bridge Formation (part) : (feet) 

Siltstone and sandstone, moderate-reddish-brown (1072 4/6) ; sandstone very fine to medium grained; siltstone contains scattered 

spherical coarse grains; all beds more or less clayey, calcareous, 

and friable. Unit is much more easily weathered and eroded than 

underlying sandstone of the Fryingpan River. Contact 

sharp _____________________________ ____ Not measured 

Sandstone of the Fryingpan River:

Sandstone, pale-red to reddish-orange (1072 6/2, 572 6/2, 1072 6/4 

1072 7/4), mainly fine- to medium-fine-grained, some mediumand medium-coarse-grained; different grain sizes form distinct 

laminae; a few laminae have slight clay content or concentration 

of opaque grains, but most are very free of clay and are dominantly composed of quartz grains tightly packed, with interlocking grain boundaries and secondary outgrowths of quartz ; 

sand grains originally rounded. Bedding in large-scale sets of 

sweeping thin crossbeds internally laminated that approach 

underlying bed tangentially_______-___ _________ 85 

Sandstone like unit below, in outcrops on dip slope. No internal

break above or below unit________________________ 165 

Sandstone, between light-brown (SYR 6/6) and moderate-reddishorange (1072 6/6) ; moderate reddish brown (1072 4/6) at base; 

fine and medium-fine grained; a few laminae of rounded, wellsorted medium and medium-coarse grains; sandstone free of clay 

except in basal few feet. Sandstone is hard with siliceous cement 

except at base where sandstone is friable at surface and has 

calcite cement. Bedding thin in crossbedded sets, most thicker 

than 20 ft but some 2-3 ft thick; one bed 18 in. thick about 50 

ft above base is probably parallel to base and is composed of 

very fine grained sandstone that is not laminated. Crossbeds 

mostly with internal laminae, crossbeds tangential at base. Base 

not exposed but probably not more than basal 4 ft of unit 

is covered_________________________________ 150

Total sandstone of the Fryingpan River____________ 400

Maroon Formation, siltstone unit (part) :

Siltstone, reddish-brown (1072 4/4), clayey; faint streaks of increased 

clay content; thickly bedded with thin to thick interbeds of silty 

claystone of slightly darker color________________ Not measured
STATE BRIDGE FORMATION, COLORADO F13 

2. BOX CANYON SECTION, TONER RESERVOIR QUADRANGLE

[Traverse from NE^NE^ sec. 9, T. S S., R. 86 W., to SE%NE% sec. 4. T. 8 S., R. 86 W. 

Base of section in Box Canyon 250 fit south of powerline ; section proceeds eastnortheast to top of the ridge east of Box Canyon and then up ridge to north. 

Measured June 1968]

Top of section. Thickness 

State Bridge Formation (part) : (feet)

Siltstone, sandstone, and claystone, pale-reddish-brown. (10.R 5/4, 10/2 

6/4) ; mostly clayey siltstone, minor amount of very fine grained 

sandstone that is silty and clayey, very minor amount of coarsegrained sandstone with clay chips and rounded grains of moderate 

sphericity ; all beds calcareous and micaceous. Near base is claystone 

which is almost free of silt grains __________ _____ Not measured

Sandstone (Sloane Peak Member), light-brown (SYR 6/4), very fine 

grained, well-sorted ; essentially free of clay matrix ; homogeneous 

throughout ; calcareous. Very thin crossbeds in sets averaging 3-4 ft 

thick. On ridge forms a moderate slope, but in canyon wall forms 

a rough-faced cliff in which abundant partings subparallel to base 

cut through crossbeds __________________ _ 135

Poorly exposed but abundant float pieces. Siltstone and minor silty 

claystone, reddish-brown (10YJ?- 4/4, 1072 5/4) ; siltstone is generally clayey, micaceous, and calcareous ; rare claystone is dark 

reddish brown (WR 3/4). Probably most of the rocks in the interval 

are very thin bedded with some laminae that contain sparse clay. 

Unit is easily weathered and forms bench and slope above unit 

below. Top contact picked on float _____________ _ 290

Poorly exposed but abundant float on ridge, well exposed in canyon 

wall to west. Mostly siltstone, moderate-reddish-brown (WR 4/6) 

to dark-redd ish-brown (10J? 3/4) ; common very thin to thin beds 

of sandstone, fine or medium grain size, with some very coarse 

grains ; medium grains rounded and moderately spherical, very 

coarse grains rounded and highly spherical : abundant clay and mica 

on bedding surfaces ; most sandstone beds clayey, but some nearly 

free of clay ; siltstone is calcareous and in very thin beds. Some float 

chips of claystone contain coarse sand grains. Two sandstone beds 

about 1 ft thick >are crossbedded, with crossbed dips to the west. 

Sedimentary structures are symmetrical parallel ripple marks with 

wavelengths 1-2 in., some poorly developed cusp ripple marks, and 

rare marks like small raindrop imprints which may be bubble or 

foam marks. Ripple marks strike in two directions, north to N. 30° 

E. and at right angles to this. Top of this unit at break in slope at 

topographic map elevation 7,674 ft __ ___ ____ ___________ 412

Limestone (South Canyon Creek Member), very clayey, pale-red-purple 

(5RP 6/2) and light-olive-gray (5Y 6/1), very fine grained; no textures visible except faint lines of higher clay content _____ __ __ 0.5

Poorly exposed, but abundant float. Siltstone and sandstone, reddishbrown (10/2 4/4). Siltstone is slightly clayey with clay films on some 

bedding surfaces. Sandstone is fine grained but has floating grains 

medium to medium coarse in size that are rounded and spherical : 

slightly clayey, moderately sorted. Siltstone and sandstone are calcareous and micaceous but mica mostly on some bedding surfaces. 

Some parting lineation on bedding _______________ __ 160
F14 CONTRIBUTIONS TO STRAr NHY

Thickness 

State Bridge Formation Continued

Poor exposure of pebbly sandstone in old roadcut; pebbles as much as 

1 in. in diameter, mostly of rusty quartz, also of very fine to finegrained metamorphic rocks. Some sandstone grains are medium 

coarse, rounded, and moderately spherical. Some blotches of palered-purple (5RP 6/2) color. No pebbles above this unit. Unit probably marks an unconformity____________ _ - 

Total State Bridge Formation (part)____________-_ 999.5

Maroon Formation (part) :

Covered ___________________________-__ 23

Arkose, moderate-red (5R 5/4), like bottom unit in measured section 

but more granules and fewer pebbles, one disk-shaped pebble of mica 

schist 2 in. long. Forms ledge__________________ 7.

Siltstone and sandstone, moderate-reddish-brown (1(XR 4/6, 107? 4/4). 

Mostly clayey siltstone, well sorted, micaceous and calcareous. Sandstone is very fine grained, poorly sorted, clayey; grains as large as 

coarse, angular to rounded, mostly subangular, low to moderate 

sphericity, micaceous and calcareous. Unit thinly bedded, forms 

slope with thin ledges outcropping____________ 32

Arkose, conglomeratic, moderate-red (5R 5/4) to moderate-pink (5# 

7/4), poorly sorted, medium-grained; mostly angular grains with 

some subrounded; conspicuous cleavage faces on feldspar grains; 

clay matrix and streaks of greater than average clay content. 

Pebbles as large as 3 in., rounded, consist of vein quartz, fine- to 

coarse-grained igneous rocks with common pink feldspar, and d'ark 

schist, probably all from Precambrian rocks. Beds are calcareous 

but friable at surface. Bedding not clear, but some crossbedding 

cut off sharply at top of sets; no scour channels visible. Bedding 

sets thin to thick. Unit mostly forms rounded ledges with rough 

surfaces, some benches, one bench 17 ft thick covered 101

Total Maroon Formation (part)__________________- 163.5 

Base of section.

3. BIONAZ GULCH SECTION, WOODY CREEK QUADRANGLE

[Type section of the Sloane Peak Member, State Bridge Formation. SE*4SW% sec. 15, T. 8 

S., R. 86 W. Measured July 1968]

Top of section.

State Bridge Formation (part) : Thickness 

Coarse unit of Toner Creek: (feet)

Base is coarse-grained sandstone__________ Not measured 

Unnamed unit:

Siltstone, silty claystone, and sandy siltstone, pale-reddish-brown 

(1QR 5/4), claystone slightly darker; thinly bedded; some mica 

flakes concentrated in bedding, some parallel ripple marks with 

wavelengths from % to 2 in_______ _ _ _ 46
STATE BRIDGE FORMATION, COLORADO F15

State Bridge Formation Continued Thickness 

Unnamed unit Continued (f?et) 

Siltstone, pale-reddish-brown (107? 5/4) ; has coarse spherical 

sand grains, otherwise is well sorted; tightly cemented with 

clay and calcite. Beds 3 in. thick or less. Forms stepped moderate slope__________________________________ 10

Total unnamed unit__________________________ 56

Sloane Peak Member:

Sandstone, moderate-orange-pink (10K 7/4), very fine grained, 

very well sorted ; tightly compacted with some calcite cement. 

Beds 2 in. to 4 ft thick ; generally beds parallel to base are thin, 

and cross-laminated beds are thicker. Cross4aminations are 

planar and simple, low angle, medium size, tangential to underlying surface. Near base are some laminations darker in color, 

probably indicating higher clay content. Forms a cliff with 

rubble at bottom. Bubble covers basal contact __________ 150 

Base of section.

4. TONER CREEK SECTION, TONER RESERVOIR QUADRANGLE

[Traverse along ridge east of creek, from NBi4NE% sec. 3, T. 8 S., R. 86 W., to

SW%SW% sec. 35, T. 7 S., R. SG W. Measured June 1968] 

Top of section. 

Chinle Formation :

Not measured or described ; lower part covered. 

Regional unconformity not exposed.

State Bridge Formation (part) : Thickness 

Coarse unit of Toner Creek : (feet) 

Covered with debris from above. Upper contact picked at break in 

slope ___ __________________________________ 11

Siltstone, very poorly exposed, reddish-brown (107? 4/4), clayey, 

micaceous, seems homogeneous. Probably very thin bedded or 

laminated ________________________________ 40. 5 

Sandstone, arkosic, grayish-pink (5R 8/2) ; coarse grained and 

pebbles to 1 in. ; abundant clay chips, grayish-.red (10.R 4/2) to 

moderate^ reddish-brown (10R 4/6) ; seems loosely packed with 

clay matrix and calcite cement; appears speckled, owing to 

white grains which may be kaolinite after feldspar ; fresh feldspar present, also light-greenish-gray (5GY 8/1) clay grains ( ?). 

Sand grains are angular to rounded, mostly subangular, some 

spherical quartz grains. Twenty feet along strike unit is 7.5 ft. 

thick _____________________________________ 4 

Covered, in part sandstone like that at base of unit; pebbles in 

float not more than % in. in maximum diameter _ _ _ _ _ _ 23

Covered ; float indicates interval is continuation of sandstone 

unit below, maybe with siltstone interbed _ _ ____ _ 28

Sandstone, very conglomeratic, like sandstone at base of unit ; 

cobbles as large as 5 in. across, many of dark-gray and grayishred fine-grained igneous rock, some as large as 4 in. across of 

quartz or qviartzite. Crossbedded 31
F16 CONTRIBUTIONS TO STRATIGRAPHY

State Bridge Formation Continued Thickness 

Coarse unit of Toner Creek Continued (feet) 

Covered, at top some siltstone chips in float ___ 20 

Sandstone, conglomeratic, like sandstone at base of unit______ 3 

Covered; float chips of siltstone, clayey to very clayey; mica on

bedding surfaces_____________________________ 21 

Sandstone, conglomeratic, slightly arkosic, grayish-pink (5R 8/2), 

poorly sorted; mostly medium-coarse grains that are angular to 

rounded and of low to moderate sphericity. Friable but some 

clay coating grains, and calcareous. Pebbles as much as 1% in. 

long of metamorphic and pegmatitic rock, feldspar granules, 

clay chips probably from underlying beds. Low outcrops, bedding not apparent___________________________ 4. 5

Total coarse unit of Toner Creek________ __ 186.0

Unnamed unit:

Not described in detail. Interval is mostly siltstone and very fine 

grained sandstone. At 46 ft above base is a coarse sandstone; 

other coarse sandstone beds occur higher in unit and become 

more common upward, and unit becomes more like coarse unit 

of Toner Creek in appearance_____________________ 70 

Sloane Peak Member:

Not described-_________________ _ 170 

Base of section.

REFERENCES CITED

Bass, N. W., and Northrop, S. A., 1950, South Canyon Creek dolomite member, a 

unit of Phosphoria age in Maroon formation near Glenwood Springs, Colorado : Am. Assoc. Petroleum Geologists Bull., v. 34, no. 7, p. 1540-1551.

Brill, K. G., Jr., 1942, Late Paleozoic stratigraphy of Gore area, Colorado: Am. 

Assoc. Petroleum Geologists Bull., v. 26, no. 8, p. 1375-1397.

 1952, Stratigraphy in the Permo-Pennsylvanian zeugogeosyncline of Colorado and northern New Mexico: Geol. Soc. America Bull., v. 03, no. 8, p. 809- 

880.

Bryant, Bruce, 1971, Geologic map of the Aspen quadrangle, Pitkin County, 

Colorado : U.S. Geol. Survey Geol. Quad. Map GQ-933 (in press).

Donner, H. F., 1936, Geology of the McCoy area, Eagle and Routt Counties, 

Colorado: Michigan Univ. Sc. D. thesis.

 1949, Geology of the McCoy area, Eagle and Routt Counties, Colorado:

Geol. Soc. America Bull., v. 60, no. S, p. 1215-1247. 

Bmmons, S. F., Cross, Whitman, and Eldridge, G. H., 1894, Description of the

Elk Mountains quadrangle [Colo.]: U.S. Geol. Survey Geol. Atlas, Folio 9,

lip. 

Goddard, E. N., chm., and others, 3948, Rock-color chart: Natl. Research Council,

6 p. (repr., 1951, by Geol. Soc. America). 

Mallory, W. W., 1960, Outline of Pennsylvanian stratigraphy of Colorado, in

Rocky Mtn. Assoc. Geologists Guide to the geology of Colorado: p. 23-33. 

McKee, E. D., Oriel, S. S., and others, 1967, Paleotectonic maps of the Permian

System: U.S. Geol. Survey Misc. Geol. Inv. Map I -450, 164 p., 20 pis., text.
STATE BRIDGE FORMATION, COLORADO F17

McKee, E. D., and others, 1939, Paleotectonic maps of the Triassic system: U.S. 

Geol. Survey Misc. Geol. Inv. Map 1-300, 33 p., incl. geol. maps.

Murray, H. F., 1958, Pennsylvanian stratigraphy of the Maroon trough in Rocky 

Mtn. Assoc. Geologists, Symposium on Pennsylvanian rocks of Colorado and 

adjacent areas : p. 47-58.

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 [1965].

Sheridan, D. S., 1950 Permian(?), Triassic, and Jurassic stratigraphy of the 

McCoy area of west central Colorado: Compass, v. 27, no. 3, p. 126-147.

Spurr, J. E., 1898, Geology of the Aspen mining district, Colorado, with Atlas: 

U.S. Geol. Survey Mon. 31, 260 p.

Thompson, W. O., 1949, Lyons sandstone of Colorado Front Range: Am. Assoc. 

Petroleum Geologists Bull., v. 33, no. 1, p. 52-72.

White, C. D., 1929, Flora of the Hermit shale, Grand Canyon, Arizona: Carnegie 

Inst. Washington Pub. 405,221 p.

Contributions to

Stratigraphy,

1970

GEOLOGICAL SURVEY BULLETIN 1324

This volume was published as 

separate chapters A-F
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

W. A. Radlinski, Acting Director
CONTENTS

[Letters designate the separately published chapters]

(A) Changes in stratigraphic nomenclature by the U.S. Geological Survey, 1969 

by George V. Oohee, Robert G. Bates, and Wilna B. Wright.

(B) The Russell Mountain Formation, a new stratigraphic unit in western 

Massachusetts, by Norman L. Hatch, Jr., Rolfe S. Stanley, and Stewart 

F. Clark, Jr.

(C) Revision of the Precambrian stratigraphy in the Prescott-Jerome area, 

Yavapai County, Arizona, by C. A. Anderson, P. M. Blacet, L. T. Silver, 

and T. W. Stern.

(D) The Chopawamsic Formation a new stratigraphic unit in the Piedmont of

northeastern Virginia, by D. L. Southwick, John C. Reed, Jr., and R. B.

Mixon. 

(E) The Monteagle Limestone of south-central Kentucky, by Richard Q. Lewis,

Sr. 

(F) Stratigraphy of the State Bridge Formation in the Woody Creek quadrangle,

Pitkin and Eagle Counties, Colorado, by Val L. Freeman.