Paleozoic and Mesozoic 

stratigraphy of the northern 

part of the Ruby Range, 

southwestern Montana

GEOLOGICAL SURVEY BULLETIN 1405-1

Paleozoic and Mesozoic 

stratigraphy of the northern 

part of the Ruby Range, 

southwestern Montana

By RUSSELL G. TYSDAL

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1405-1

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1976
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress Cataloging in Publication Data

Tysdal, Russel G.

Paleozoic and Mesozoic stratigraphy of the northern part of the Ruby Range, southwestern

Montana. (Contributions to stratigraphy)

(Geological Survey Bulletin 1405-1)

Bibliography.

Supt. of Docs, no.: I 19.3:1405-1.

1. Geology, Stratigraphic-Paleozoic. 2. Geology, Stratigraphic-Mesozoic. 3. GeologyMontana-Ruby Mountains. I. Title. II. Series. III. Series: United States Geological 

Survey Bulletin 1405-1..

QE75.B9no. 1405-I[QE654] 557.3'08s [557.86'663] 76-608035

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

Washington, D. C. 20402

Stock Number 024-001-02854-9
CONTENTS

Page

Abstract ______________________________________________________________ II

Introduction ______________________________________________________ 1

Acknowledgments ____________________________________________ 3

Geologic setting __________________________________________ 4

Paleozoic rocks ________________________________________________________ 4

Cambrian System ________________________________________________ 5

Flathead Sandstone ______________________________________ 5

Wolsey Shale _______________________________________________ 8

Meagher Limestone ____________________________________________ 11

ParkShale_____-____________________________________-______ _ 12

Pilgrim Dolomite ________________________________________________ 13

Red Lion Formation ____________________________________________ 14

Devonian System _____________________________________________ 15

Jefferson Formation _______________________-___-___-________ 15

Devonian and Mississippian Systems ________________________________ 16

Three Forks Formation ________________________________________ 16

Mississippian System _______________________________________ 17

Madison Group__________________________________________ 17

Lodgepole Limestone ________________________________________ 17

Mission Canyon Limestone ____________________________ 18

Kibbey(?) Formation _____________________________ 20

Pennsylvanian System ________________________________________________ 21

Quadrant Sandstone ______________________________________ 21

Mesozoic rocks _________________________________________________ 21

Cretaceous System ______________________________________________ 22

Beaverhead Formation _________________________________--__-_---_- 22

References cited __________________________________________ 23

ILLUSTRATIONS

Page

FIGURE 1. Sketch map of southwestern Montana showing area of report and

paleotectonic features.. ___________________.__________-__--___-_ 13

2. Generalized columnar section of Paleozoic and Mesozoic rocks in northern part of Ruby Range ______________________-______----------_-- 6

3. Generalized stratigraphic cross section of Paleozoic rocks in northern 

part of Ruby Range---__-_-__---__---_---_---_------_----_------- 8

4. Correlation chart for Middle and Upper Cambrian rocks in Montana._ 10

III
IV CONTENTS

TABLE

Page

TABLE 1. Stratigraphic position of fossils collected from Mississippian Lodgepole

Limestone ____________________________________________________I19
CONTRIBUTIONS TO STRATIGRAPHY

PALEOZOIC AND MESOZOIC

STRATIGRAPHY OF THE

NORTHERN PART OF THE RUBY RANGE,

SOUTHWESTERN MONTANA

Bv RUSSELL. G. TVSDAL

ABSTRACT

The northern third of the Ruby Range, southwestern Montana, contains about 5,000 

feet (1,525 m) of Paleozoic marine sedimentary rocks overlying a basement of Precambrian metamorphic rocks. Mesozoic rocks are represented by a nonrnarine conglomerate, the Beaverhead Formation.

The Cambrian sequence, composed largely of carbonate rocks, comprises the 

Flathead Sandstone at the base, Wolsey Shale, Meagher Limestone, Park Shale, Pilgrim Dolomite, and the Red Lion Formation. The Meagher Limestone is mainly dolomite in the southern part of the area, limestone in the northern part. The Pilgrim 

Dolomite is divisible into two main parts: cyclically interbedded dolomitic strata 2- to 

10-inch (5-25 cm) thick in the lower part, mainly dolomitic quartz sandstone and sandy 

dolomite in the upper part. The Red Lion Formation is composed mainly of dolomite; 

the upper third is dominated by bedded, dome-shaped, and columnar stromatolites.

The Devonian is represented by the Jefferson Formation, a dolomite unit containing 

several interstratified units of silty shale, and the lower part of the Three Forks 

Formation. The Three Forks is composed largely of clay shale but contains a prominent 

medial limestone unit. The upper (Mississippian) part of the Three Forks is overlain by 

three Mississippian formations. The Lodgepole Limestone is constituted of limy shale 

in the lower half and fossiliferous limestone in the upper half. It is overlain by the 

Mission Canyon Limestone, a formation that locally contains solution breccias and 

minor amounts of interbedded dolomite. The overlying red beds, made up of dolomite 

and sandstone, are questionably assigned to the Kibbey Formation. Pennsylvania 

rocks are represented by the Quadrant Sandstone, made up of interbedded limestone 

and sandstone in nearly equal amounts.

The Mesozoic is represented by a nonmarine conglomerate that is correlated with the 

Beaverhead Formation. It is composed of clasts derived from Paleozoic carbonate units 

and Precambrian (Belt Supergroup) quartzite.

INTRODUCTION

The Ruby Range is a north-trending block of mountains about 

30 mi (50 km) long and 12 mi (20 km) wide, nearly surrounded by 

intermontane basins containing broad benchlands and alluvial surII
12 CONTRIBUTIONS TO STRATIGRAPHY

faces that slope gently away from the mountains. The mapped area 

makes up the northern third of the Ruby Range and the adjoining 

parts of the adjacent basins. The relief in the area ranges from about 

5,000 feet (1,525 m) in the northernmost part of the area to 9,391 feet 

(2,862 m) atop Ruby Peak in the central part, a difference of 4,300 

feet (1,310 m).

There is a close correspondence between topographic expression 

and lithology. The more rugged ridges are held up by Paleozoic carbonate rocks, the broad-backed and rounded ridges by Precambrian 

metamorphic rocks, and the benchlands and gently sloping surfaces 

by Cenozoic deposits.

The first geologic notation on the Ruby Range was recorded by a 

Hayden survey party that passed near the mountains in September 

1871; they referred to the mountains as the Stinking Water Range 

(Hayden, 1872, p. 36-39, 143, 259-261). In 1902 and again in 1905 

Earl Douglass collected Cambrian and Mississippian fossils from the 

northeastern part of the range (Douglass, 1905, 1909). Much later 

Hanson (1952) measured a Cambrian section near McHessor Creek; 

he used the section for regional correlation in southwestern Montana. 

A small Precambrian sedimentary iron-ore deposit in the southeastern part of the mapped area was studied by James and Wier (1972), 

and Tertiary -rocks at the northern tip of the range were noted briefly 

in a report of Fields and Petkewich (1967).

Studies of the Ruby Range south of the area of this report include 

those of Klepper (1950), Dorr and Wheeler (1964), Wier (1965), and 

James, Wier, and Shaw (1969). Heinrich (1960) referred to many 

papers on the economic geology.

This report on the general stratigraphy of the Paleozoic and 

Mesozoic rocks of the northern part of the Ruby Range complements 

U.S. Geological Survey Miscellaneous Investigations Map 1-951 

(Tysdal, 1976). The map includes a brief description of the Precambrian metamorphic rocks underlying the sedimentary sequence and 

of the Tertiary rocks flanking the range. Detailed measured sections 

of the Paleozoic formations are given in an open-file report of the U.S. 

Geological Survey (Tysdal, 1970) that discusses and illustrates the 

carbonate petrology of some Cambrian units and presents a structural interpretation of the area.

The mapped area constitutes the mountainous parts of four IVz 

quadrangles: Beaverhead Rock SE, Beaverhead Rock NE, Sheridan, 

and Laurin Canyon. It is delimited by 45°15' to 45°24' N. lat. and 

112°07'30" to 112°22'30" W. long. (fig. 1).

The terms "thin-, medium-, and thick-bedded" as used throughout 

this report refer, respectively, to beds up to 6 in. (15 cm) thick, 6-18 

in. (15-45 cm), and greater than 18 in. (45 cm) thick. "Massive" as
PALEOZOIC AND MESOZOIC STRATIGRAPHY, RUBY RANGE 13

113 112

45

10 15 20 MILES

10 20 30 KILOMETRES

FIGURE 1. Sketch map of southwestern Montana, showing area of report and

paleotectonic features.

used here does not describe bedding thickness but rather describes 

the homogeneous weathering profile of a group of beds. Color terms 

used in the measured sections and in most of the text are from the 

"Rock Color Chart of the National Research Council" (Goddard and 

others, 1948).

ACKNOWLEDGMENTS

The north end of the Ruby Range was suggested as a study area by 

the late W. J. McMannis, of Montana State University, Bozeman. For 

stimulating discussions on the geology of the Ruby Range, I am indebted to J. A. Peterson and G. W. Crosby, both of the University of 

Montana, Missoula; E. T. Ruppel, of the U.S. Geological Survey; R. M. 

Petkewich, then a student at the University of Montana; and
14 CONTRIBUTIONS TO STRATIGRAPHY

McMannis. I should like to thank Mr. and Mrs. George Knaggs of 

Sheridan, Mont., for their hospitality, and the ranchers of the area for 

their cooperation and helpfulness.

GEOLOGIC SETTING

The Ruby Range is one of several mountain ranges in southwestern 

Montana that contains a core of Precambrian metamorphic rock overlain by Paleozoic and younger sedimentary rocks. The range lies east 

of the Paleozoic hinge zone that separated the craton from the 

miogeosyncline to the west, and it is thought to be part of the nowsegmented Blacktail-Snowcrest arch (fig. 1), a large southwestplunging anticlinorium (Scholten, 1967). The range is broken by 

numerous so-called Laramide faults; its present block outline is the 

result of later Tertiary normal faulting. It is flanked by basins filled 

with Tertiary continental sedimentary rocks.

Precambrian metamorphic rocks, chiefly hornblende and biotite 

gneisses, the Dillon Granite Gneiss of Heinrich (1953), dolomitic 

marble, and numerous units of quartzo-feldspathic gneiss, are exposed mainly in the southern part of the mapped area. Sillimanite 

schist is present locally. Iron formation and associated quartzite and 

diopsidic gneiss are present in the southeastern part of the mapped 

area (James and Wier, 1972). Radiometric age determinations indicate that the last metamorphic event in the range took place about 

1,600 m.y. ago (Giletti and Gast, 1961; Giletti, 1966, 1968). Detailed 

structural and petrographic studies of metamorphic rocks in the 

northern half of the Ruby Range were made by Heinrich (1960), 

James, Wier, and Shaw (1969), and Garihan (1973).

Tertiary rocks composed of dark-green-gray mudstone with interbedded poorly sorted locally conglomeratic siltstone and sandstone 

crop out at the northern tip of the range (Fields and Petkewich, 1967); 

these rocks have yielded late Eocene and Oligocene vertebrate fossils 

(Petkewich, 1972). A similar sequence of rocks occur along the western margin of the range. Miocene and Pliocene sedimentary rocks 

crop out locally in the basins beyond the margins of the range (Fields 

and Petkewich, 1967; Petkewich, 1972).

Quaternary deposits within the range are tufa, an unnamed conglomerate, alluvium, colluvium, landslides, and glacial deposits. The 

conglomerate, present on both the eastern and western flanks of the 

range, intertongues with tufa at one locality. Small basalt, andesite, 

and rhyolite intrusive bodies occur along some faults in the range.

PALEOZOIC ROCKS

Paleozoic rocks constitute most of the sedimentary sequence pre-
PALEOZOIC AND MESOZOIC STRATIGRAPHY, RUBY RANGE 15

served in the Ruby Range, aggregating a thickness of about 5,000 ft 

(1,640 m). Cambrian rocks, which make up little more than a fifth of 

this sequence, were studied in greatest detail. Ordovician, Silurian, 

and Permian rocks are not present in the range, probably as a result 

of erosion rather than nondeposition. The sequence of rocks is shown 

in figure 2.

The generalized stratigraphic relations derived from mapping and 

the stratigraphic position of the measured sections are shown 

schematically in figure 3. Detailed measured sections were published 

in an earlier report (Tysdal, 1970).

CAMBRIAN SYSTEM

FLATHEAD SANDSTONE

The oldest Paleozoic rocks in the area are those of the Flathead 

Sandstone of Middle Cambrian age (fig. 3, sections G and L). This 

formation, which unconformably overlies Precambrian metamorphic 

rocks, is well exposed only in cliff-forming outcrops and is commonly 

about 60 ft (18 m) thick. It consists mainly of light-brown to orange, 

fine- to medium-grained quartz sandstone in beds 1-2 ft (30-60 cm) 

thick. The basal part of the formation includes lenses of subangular 

to subrounded granules and pebbles of quartz in a coarse-grained 

sand matrix; similar lenses are present locally in the upper part of 

the formation. Pebbles of clay shale to 3 cm long and a few millimetres thick and locally surrounded by coarse grains of sand were 

observed at the top of the Flathead in the rocks about ll/2 mi (3 km) 

southwest of Section J (fig. 3) in SEViNWA sec. 2, T. 7 S., R. 6 W. 

(Beaverhead Rock SE quadrangle).

Examination in thin section shows that the Flathead Sandstone is 

more than 98 percent quartz with minor amounts of chert, mica, 

hematite, limonite, heavy minerals, metamorphic rock fragments, 

and wisps of clay. Glauconite occurs locally in the uppermost part of 

the formation. The sandstone is mostly moderately to well sorted; the 

moderately sorted sands are bimodal and consist of coarse sand interlaminated with fine- to medium-grained sand. Most quartz grains are 

subrounded to rounded (3.5 to 5, classification of Powers, 1953) and 

are cemented by optically continuous overgrowths. Abundant double 

overgrowths and one grain with a triple overgrowth were seen in a 

thin section from one locality (about IVfe mi (2.5 km) west-southwest 

of section J), suggesting that some of the sand is recycled from older 

sandstone.

The parts of the shale section that are exposed reveal that the 

upper contact is gradational with the Wolsey Shale. Following Robinson (1963), I placed the upper contact at the base of the lowest shale
16 CONTRIBUTIONS TO STRATIGRAPHY

Period

MISSISSIPPIAN

|DEVONIAN 

| CAMBRIAN

| PRE-CAMBRIAN

c. 

u 

o

Q. 

Ill

X 

<0

111

so

a 

a

a 

TJ 

TJ

I

\

a 

o Formation 

O

Q. 

3 

O

13 Lodgepole 

§ Limestone

1

Three Forks 

Formation

Jefferson 

Formation

Red Lion 

Formation

Pilgrim 

Dolomite

Park 

Shale

Meagher 

Limestone

Wolsey 

Shale

Flathead

Metamorphic 

rocks

Thickness, in 

feet 

(metres)

594

(181)

150

250- 

268

(76-82)

0-170

(0-52)

295- 

390 

(90-119)

150-196 

(47-60)

745

227)

58-100 

(18-30.5)

52(16)

7

Graphic log Rock description

J | I ) | gray thinly bedded argillaceous lime- 

-i i T' T 4 '-T T i-4-y stone. Forms slopes

J*-i7-i u-i Til 1^3^ / Sappington Member is grayish-orange 

 j-T-i-r-LT-L i -i~i r-J / calcareous siltstone. Trident Member 

 J.T f |-t ' 4.1 .j._i 4= 7 / js mainly olive clay shale. Logan Gulch

^;Lj_.JL*--jJii-nV^ip' limestone and minor shale andevapor- 

~~[~rT"'°T"'r~| c' r\ ite breccia

-!<*& jj^ *g_ JLff>^. / Birdbear Member (at top) is brown doloOi3C> a®£0 0 tpQp v£V& is yellowish-brown medium- to thirk-

~fy7'j '/'r/^/ >/^\ bly weathering dolomite. Brownish silty

/ "j ,'-7-"-7-"7 's ( rn ehaly rlnlnmita intarhorl« at «a»ar9l

'T/ /" / ////~( horizons

^> -= ; - $-/ /£' 7*T~~ Sage Dolomite Member is largely brownish

^S^r^JES^z-^^j siliceous laminae. Stromatolites present 

1, I, *i i -Lr~^ r-ir^A in upper part. Dry Creek Shale Member

 '. ^ t'f . <( . '' ' _; -: ' ] Upper one-third is mainly thin- to mediumfJ&?S.'lf/'f/fy!r} ? f/n bedded sandy dolomite and crossbedded

//////// / flan dolomite, witn tnin units of silty shaly

"^Wi^po ~^c^Y^ Grayish-olive finely micaceous clay shale 

rr=-~~^^ -tJHET/ with limonitic limestone nodules locally 

^^^E^f-f^^. present in basal part and dolomite nod-

////// A

' S S / / / / S\

';' ' s^s^/^/^s*/^/ ( third is thin to medium bedded, formirrg a 

/ / / / / /' / J ledae or cl if f

/ / / / / / A ^^ Mainly nhua-graan tn raddish-hro\A/n miray/ / / / / /j'J/'^ ceous clay shale; siltstone in basal part 

L=.-^r=^^^j / Fine- to coarse-grained locally conglomerrfTVr'^T'Tl^rr-TrV-^/ atic quartz sandstone

^'I'.y-^iiij&'.-^pi^vi^/ Dominant rock types are dolomitic marble.

^fif/yj[/t///////\ gneiss, and sillimanite schist. Minor gran- 

''// ff?ffs///f/\ ite 8 n«iss a nd iron-formation

FIGURE 2. Generalized columnar section of Paleozoic and Mesozoic rocks in northern part of Ruby Range.

unit that is more than 5 feet (1.5 m) thick. Where the shale section is 

covered, I placed the contact above the highest sandstone ledge beneath the dip slope of the Wolsey.

No fossils were found in the Flathead in the Ruby Range. Middle 

Cambrian trilobites of the genus Glossopleura are present in the
PALEOZOIC AND MESOZOIC STRATIGRAPHY, RUBY RANGE 17

? i i p

[E?^E^rnA SNDPENNSYLVANIAN Y

MISSISSIPPIAN

a 

TJ 

TJ

i

o 

a

Ul

0)

X "w

a

Ul

a

3 

O

O

Formation

Beaverhead 

Formation

Quadrant 

Sandstone

Kibbeyf?) 

Formation

| Madison Group

Mission 

Canyon

Limestone

Thickness, in 

feet 

(metres)

150-? 

(47-7)

1204?

(367)

20-138 

(6-42)

1370

(418)

Graphic log

S / / 7 / ?"\ \

' / / / / / / \\

K 1 1 1 1 1

1 1 i 1 1 1 ^

.i..t..l.'i . L L.I;

: :::: :':'"'.-.::::.^

 .' .'.| .-1-/-|- : . \

1 1 1 i I r i

i i i i i i i i i i i i i i

-.-' A-liMpM 

.. .-.. .. .. -.-.. .1. i i i i i i \ i i i i i j 1 1

J i i J i i j

,'...L..'. j... ..i $ )

.1. j. . i.-X-.i. y i

\ vf ^r^r'l^x

i i i i i i i

i i i i i i i

^rV 

ii ii

ii iii ii 

^^^^- i^^i^i ^i^i^i^ ^

iii iii

i i i i i i i

1,1,1 i i i <

I^I^I^I^I^I^IA.

i i i i ii i i i i i i i

i i i i i _!__r

l-a. ^.|^|A|ii ^|^

1 '-1,1, 1

1 \ III

II 1 1 1 1

\' \' \' \' \' \ f \'

1 1 1 1 1 1 1

\

/

/

Rock description

Mainly conglomerate composed of multicolored well-rounded cobbles of quartz ite; 

cobbles and boulders of subrounded carbonate rocks in reddish calcareous sandstone 

matrix; metamorphic rock clasts present 

locally

Light-gray-weathering medium- to thickbedded limestone, interbedded with palebrown thin- to medium-bedded fine-grained 

quartzite and sandstone; dolomite present 

locally

Pale-reddish-brown thin- to medium-bedded 

finely crystalline dolomite, dolomitic limestone, silty dolomite, siltstone, and sandstone

Light-gray-weathering pale- to dark-yellowishbrown medium- and thick-bedded cliffforming limestone. Chert stringers present 

locally in lower part. Evaporite-solution 

breccia zones present locally in middle to 

upper part

EXPLANATION 

(£^j Dolomite, mat-algal

1 (yi\ '. 1 Dolomite, sandy 

Y/{\ Dolomite, silty 

\ //'/\ Dolomite 

17 71 Limestone, argillaceous 

|i| |' J 1 Limestone, silty 

1 '^ l| Limestone, dolomitic

H Limestone &£> Evaporite-solution 

breccia

Shale, silty ^^ Chert 

L =J shale <Z><2> Nodules, dolomite

11 < o . \ o c? Nodules, limestone 

\JtOg" Conglomerate 

_ <* <3 Stromatolites, 

$£$ Sandstone dome shaped

I,, .. ,,i © 61 Stromatolites, 

kH Siltstone columnar

\yfffl Metamorphic rock

FIGURE 2. Continued.

lower part of the Wolsey Shale that overlies the Flathead in the 

Three Forks area (fig. 4) about 40 mi (64 km) north of the mapped 

area (Alexander, 1955). As sedimentation was apparently continuous
18 CONTRIBUTIONS TO STRATIGRAPHY

R. 6 W.

012 MILES 

0 1 2 KILOMETRES

Plane of stratigraphic 

cross section

Three Forks Formation

K196) Jefferson Formation

Dry Creek Shale Member f12)

Metamorphic rocks

FIGURE 3. Generalized stratigraphic cross section of Paleozoic rocks in northern part of Ruby Range. Locations of measured sections and plane of cross 

section shown in inset map.

from the base of the Flathead to fossiliferous rocks in the lower part of 

the overlying Wolsey, it is reasonable to infer that the Flathead is 

only slightly older than the Wolsey. The Flathead of the Ruby Range, 

therefore is believed to belong to the Glossopleura zone and (or) the 

Albertella zone (fig. 4). Chadhuri and Brookings (1969), who 

radiometrically dated glauconite from the upper part of the Flathead, 

obtained an age of 542 m.y., which they consider Middle Cambrian.

WOLSEY SHALE

The Wolsey Shale (fig. 3, section G) is of Middle Cambrian age, 

ranges from 58 to 100 ft (18-30 m) thick, commonly forms broad 

benches or grass-covered slopes above the Flathead Sandstone, and is
PALEOZOIC AND MESOZOIC STRATIGRAPHY, RUBY RANGE 19

EC D F 

K

Fault

Quadrant Sandstone

Kibbey(?)

FaultFault(?K

1204

Fault(?)\

Formation

\

Madison 

Group

Mission Canyon 

1370

Limestone

Lodgepole Limestone

594

"fhVee Forks^orrnaTion

u(40) Jefferson Formation u(55)

._ _,

Dry Creek Sh' 

Mbr. (1 1) 295

150

565«§v

M(63.5) ^^e^tTo^ Formation'" TEtTbKSO)

-u(85) Pilgrim Dolomite c 9|>NDry 

1(210) a Fault creek

Park Shale 196 | Sh(vftbr'

Covered -JQQ |

 Covered Meagher Limestone

Wolsey Shale\

Flathead Sandstone/

Metamorphic rocks

EXPLANATION

Contact, 

uncon- / 

f ormable-~- -

Thickness 

of 425 J

formation,] 

in feet

Fault

tT{100), 

_upper unit

1(325), 

lower unit

- Contact, 

Contact,--- conformable -- 

covered

1.0 ft = 0.3 0 5 m

VERTICAL 

EXAGGERATION X 5

1 MILE

I I I

0 .5 1 KILOMETRE

FIGURE 3. Continued.

exposed only in a mining exploration trench cut into the basal part of 

the formation (SEV* sec. 34, T. 6 S., R. 6 W. Beaverhead Rock SE 

quadrangle). It is chiefly brown, thin-bedded coarse-grained micaceous glauconitic quartzose siltstone and intercalated olive-green and 

reddish-brown coarsely micaceous clay shale. Shale in the upper part 

of the formation is like that below, except that reddish rocks were not 

observed. Examination of siltstone by microscopy shows quartz 

(85-90 percent), feldspar (5-10 percent), glauconite (1-10 percent), 

mica (1-2 percent), and hematite (1 percent). Most of the grains are 

angular to subangular (except the glauconite grains which are round) 

and are cemented with silica along sutured grain contacts.
Series

Upper Cambrian

Middle Cambrian

& 

to

C/3

jauan

to

0) 

Q.

E

0)

H

c 

to'c

0 

0

c

(D

ul

Dresbachian

0)

E 

to

c

0) 

O)

to

0

Z

Faun7r--\^^ MoVitl 

zonex ^"^-\ 1

Saukia

Prosaukia

Idahoia

Taenicephalus

Elvinia

Dunderbergia

Aphelaspis 

^ Dev

Gle 

Crepicephalus Dolort

Cedar ia

Switchb 

Bolaspidella 

Steamb

Bathyuriscus- Pentagc

G 1 osso pleura _Damr\at_

uoraon 

Albert ella _ __ __

PlaguriaPoueiia TmmnTr

m Drummond Ru 

na vie mty 

2 3

Red L on r 

Format on /

.' -Lion 

.-^Formatic

s Hasmark Pilgrim 

n Formation Dolomite 

lite

ack_Sh. Park Shale ( 

aat Ls.

> n Sh - Meagher Ls.( 

3 Ls.

"orTCT s lver H " WolseySh 

~ Format on _ __ __ __ 

Sha e Flathead Ss

d Ss.

Three 

Forks 

4 

M

/Red Lion Fm

Pil 9 r rn 

Limestone 

B) Park Shale 

C) Meagher Ls. 

WolseySh. 

Flathead Ss.

FIGURE 4. Correlation chart for Middle and Upper Cambrian rocks in Mont

proximate because of limited data and recent revis
PALEOZOIC AND MESOZOIC STRATIGRAPHY, RUBY RANGE II1

Regionally, the Wolsey is divisible into three parts: a basal shale 

unit with intercalated sandstone, siltstone, and shale; a medial limestone unit; and an upper shale unit that grades into the overlying 

Meagher Limestone (Hanson, 1952; Lebauer, 1965). The middle unit, 

or float from it, was not seen in the Ruby Range, and the topographic 

pattern does not suggest the presence of a carbonate unit.

The Wolsey-Meagher contact was not observed in the Ruby Range, 

but in a few places where stratified dolomite crops out near the base 

of the Meagher, the transitional beds must be only a few feet thick. 

The contact was placed at the break in slope below the outcropping 

carbonate beds typical of the Meagher Limestone and at the break in 

slope where the carbonate beds do not crop out.

No fossils were found in the Wolsey in the Ruby Range. Those 

reported from nearby areas include Glossopleura-zone faunas in the 

Jefferson Canyon and Three Forks regions (Hanson, 1952; Alexander, 1955; Robinson, 1963).

MKAGHER LIMESTONE

The Meagher Limestone (fig. 3, sections F, G, I) is Middle Cambrian in age and is the thickest Cambrian formation in the Ruby 

Range, ranging from 565 to 745 ft (172-227 m) thick. It is generally 

well exposed, except for the basal one third, and consists of pale- to 

dark-yellowish-brown dolomite in the McHessor Creek drainage and 

southward but mainly medium-gray limestone north of this drainage. 

The limestone and dolomite are of fine crystallinity. The middle third 

of the Meagher is thin and medium bedded, appears massive, and 

contains surficial yellowish dolomitic mottles, pisolites, and locally 

oolites. The lower and upper thirds are mostly thin bedded; they 

contain irregular yellowish mottles, the "blue-and-gold" mottled 

limestone (for photographs see Hanson, 1952, pi. 3-H; Lebauer, 

1965). The uppermost 100 ft (30 m) of the formation is locally dolomitic limestone, pale- to dark-yellowish-brown and mottled grayish 

orange, and is intercalated with gray-green clay shale laminae. It 

contains flat- and locally edgewise-pebble conglomerate, oolites, 

brachiopod and trilobite fragments, and glauconite.

Lebauer (1965) described each unit of the Meagher Limestone in 

detail. Microscopic examination of the middle part of the Meagher 

shows the pisolites to be oncolites of algal filaments similar to those 

termed Girvanella. Whitish twiglike structures 1-3 mm in diameter 

and to 1 cm long are commonly associated with the oncolites or with 

aggregates of pellets; such structures have been noted elsewhere in 

the Meagher by Sloss and Moritz (1951), Hanson (1952), and Robinson (1963). Subtle small-scale long-angle crossbedding and pellets 

were seen in thin sections of thin-bedded limestone from the upper
112 CONTRIBUTIONS TO STRATIGRAPHY

part of the formation.

Carbonate beds in the upper 50 to 100 ft (15-30 m) of the Meagher 

commonly intertongue with shale like that of the overlying Park 

Shale. The contact is therefore placed at the uppermost outcrop of 

Meagher-like carbonate rock. No interbedded shale is present in the 

thin (565 ft (172 m)) Laurin Canyon section (fig. 3, section G) so the 

contact must be fairly sharp.

Poorly preserved fossils from the upper 100 ft (30 m) of the 

Meagher in section F (fig. 3) were identified by A. R. Palmer (written 

commun., 1968). They include the brachiopods Micromitra and Opisthotreta, and the trilobites Kootenia?, a pygidium of either Kootenia 

or Olenoides, and indeterminate marjumid and bynumiid 

brachiopods. Palmer stated that "the total aspect***is of faunas of 

late Middle Cambrian age."

PARK SHALE

The Park Shale (fig. 3, sections E, G, and I) is Middle Cambrian in 

age, is 150 ft (46 m) to more than 196 ft (60 m) thick, and commonly 

forms a gently sloping grass-covered bench above the Meagher. It 

consists mainly of grayish-olive, finely micaceous fissile clay shale 

with thin-bedded yellow and orange limestone nodules near the base 

and dolomite nodules near the top. The limestone nodules, which 

weather out of the shale, contain abundant trilobite fragments, phosphatic brachiopods, oncolites, or limestone pebbles. Lochman (1957) 

termed the fossiliferous nodules coquina.

The dolomite nodules in Robinson Canyon (fig. 3, section E) are 

"pod" shaped with dimensions averaging 5 by 3 by % in. (13 by 7.5 by 

2 cm). Silty dolomite forms the core of each pod, and the outer part is 

micaceous dolomitic siltstone. The pods are confined to the clay shale 

of the formation where many are present at the same stratigraphic 

level.

The upper contact of the Park is commonly covered, but it is exposed in Robinson Canyon (fig. 3, section E), where it is marked by an 

abrupt change from nonfissile dolomite mudstone in the upper 15 in. 

(38 cm) of the Park to dolomite pebble conglomerate in the basal 6 in. 

(15 cm) of the Pilgrim Dolomite. The contact here, which is not gradational, certainly indicates an abrupt change in environment if not an 

unconformity.

Poorly preserved fossils were collected from limestone nodules that 

had weathered out of the lower part of the Park in SEV4NE& sec. 13, 

T. 6 S., R. 6 W. (Beaverhead Rock SE quadrangle). These fossils were 

identified by M. E. Taylor (written commun., 1970) as Kootenia or 

Olenoides, indeterminate ptychoparioids, and an indeterminate orthid brachiopod. Taylor assigned the fossils to the Middle Cambrian.
PALEOZOIC AND MESOZOIC STRATIGRAPHY, RUBY RANGE 113 

PILGRIM DOLOMITE

The Pilgrim Dolomie (fig. 3, sections G, H, J, and K) ranges in 

thickness from 295 to 390 ft (90-119 m) and is well exposed in the 

Ruby Range, except for the basal few tens of feet. Two distinct units 

make up the formation in the Ruby Range. The lower unit, 210-278 ft 

(64-82 m) thick, consists of light-gray-weathering, pale-yellowishbrown dense dolomite. The upper unit is 85-122 ft (26-38 m) thick 

and consists mainly of pale-yellowish-brown sandy laminated dolomite, fine- to medium-grained crossbedded quartz sandstone, and 

yellowish-brown finely crystalline dolomite in the upper part of the 

unit.

The lower and upper few tens of feet of the lower unit are medium 

to thick bedded and intensely dolomitized. Polished slabs of the rock 

show local occurrences of faint mottling, glauconite, white twiglike 

structures similar to those noted in the Meagher, and ghosts of replaced oolites.

The middle part of the lower unit is characterized by repeated 

alternations of thin beds of shaly laminated dolomite, laminated 

dolomite, mottled dolomite, dolomite-pebble conglomerate, and fossil 

fragmental dolomite.

The upper unit of the Pilgrim contains abundant quartz sand in 

laminated dolomitic rocks. In outcrop its expression is more like the 

Sage Dolomite Member of the overlying Red Lion Formation than the 

underlying part of the Pilgrim. The rocks are assigned to the Pilgrim 

because they underlie, and are distinct from, the olive-gray shale of 

the Dry Creek Shale Member of the Red Lion (Emmons and Calkins, 

1913; Lochman, 1950). The sandy laminated dolomite forms thinbedded sequences, from 4 to 35 feet (1-10.5 m) thick, throughout the 

upper unit of the Pilgrim. The sand grains make up 20-25 percent of 

the rock, are subangular to subrounded, and form flat or wavy 

laminae that weather in relief. Crossbedded quartz sandstone occurs 

in only one interval in the upper unit and ranges from 4 to 12 ft (1-3.5 

m) thick; tabular and local trough crossbeds are present with the 

crossbed sets ranging from 2 to 12 in. (5-25 cm) in thickness.

Other rocks of the upper unit of the Pilgrim include (1) lightgray-weathering dolomite, which is thinly bedded but appears massive and forms sequences 4 to 6 ft (1-2 m) thick; (2) bioclastic dolomite; (3) reddish-nodular-weathering dolomite; and, (4) at the top of 

the formation, reddish-mottled sandy crystalline dolomite.

The contact of the Pilgrim Dolomite with the overlying Red Lion 

Formation is sharp. No evidence of a disconformity was observed 

although Palmer (written commun., in Witkind, 1969, p. 20) notes 

that one may exist in southwestern Montana.

No identifiable fossils were found in the Pilgrim, presumably be-
114 CONTRIBUTIONS TO STRATIGRAPHY

cause of dolomitization; fossil debris is present in the bioclastic rocks. 

The Pilgrim is considered Late Cambrian in age (Lochman-Balk, 

1956; Robinson, 1963).

RED LION FORMATION

The Red Lion Formation (fig. 3, sections G, H, and K) is Late Cambrian in age and ranges in thickness from about 115 to 170 ft (35- 

52 m); it is absent m the Trout Creek drainage area. The Dry Creek 

Shale Member, which occurs at the base of the formation, is poorly 

exposed, is 11-12 (3.5-4 m) thick, and consists of grayish-olive soft 

fissile finely micaceous clay shale with 6-12 in. (15-30 cm) of 

blackish-red shale at the bottom. A few thin beds of pale-yellowishbrown glauconitic dolomitic quartz sandstone are present locally at 

the top of the member. The overlying Sage Dolomite Member is well 

exposed. Its basal part is characterized by 1- to 3-in. (2.5-7.5 cm) 

thick beds of pale yellowish-brown dolomite with intercalated 

reddish-brown silty dolomite laminae. These "ribboned" beds are 

overlain by yellowish-brown finely crystalline dolomite beds V2-2 in. 

(1-5 cm) thick, locally mottled grayish-red, and contain thin interbeds of bioclastic dolomite. The upper part of the Sage consists of 

light-gray-weatheriiig, thin- to thick-bedded dense dolomite.

Polished slabs of the ribboned beds in the lower part of the Sage 

Dolomite Member show that each bed is actually a sandwich of 

medium-crystalline dolomite between thin layers of quartz silt. The 

thinner beds of dolomite commonly occur as boudins. Thin interbeds 

of mud-cracked dolomite occur in the lower part of the Sage; they 

consist of flat chips enveloped in reddish silt laminae that are strung 

out in discrete discontinuous layers.

In a small area north of McHessor Creek (section H) (sec. 13 and 18, 

T. 6 S., R. 5 W., Beaverhead Rock SE quadrangle), the light-grayweathering unit in the upper part of the Sage contains a variety of 

dolomitized stromatolites that form finely laminated beds ¥2-to 2-in. 

(1-5 cm) thick; small columns in 6- to 18-in. (15-46 cm) thick beds; 

dome-shaped mounds measuring 1- to 2-ft (30-60 cm) high and 2- to 

4-ft (60-120 cm) wide; and columnar structures to 5 ft (1.5 m) high. 

The finely laminated algal beds dip beneath the dome-shaped mounds 

and are flexed over them or sharply abut them. The 6- to 18-in. (15-46 

cm) thick beds of stromatolites extend laterally for more than 100 ft 

(30 m); locally the stromatolites have a thin unit of dolomite pebble 

conglomerate at their base. The few stromatolites preserved in the 

beds are columnar, 2- to 4-in. (5-10 cm) wide at the base and 4- to 

8-in. (10-20 cm) high. The small columns commonly are separate, but 

some are linked laterally. Dome-shaped mounds are composed 

mainly of many individual stromatolites similar in size to those of the
PALEOZOIC AND MESOZOIC STRATIGRAPHY, RUBY RANGE 115

6- to 18-in. (15-46 cm) thick beds. Each of the observed stromatolites 

is made of concentrically stacked hemispheroids although other types 

of stacking may be obscured by dolomitization. Dolomite pebble conglomerate is common at the base of each dome-shaped mound. Columnar stromatolites 4- to 5-ft (1-1.5 m) high are typically 1- to 2-ft 

(30-60 cm) wide at the base and taper upward. The form is discrete, 

being composed of vertically stacked hemispheroids in which the 

upper laminae do not reach the base of the preceding ones.

The upper part of the Sage Dolomite Member was mistakenly assigned to the Bighorn Dolomite (Ordovician) by Hanson (1952). It is 

conformable with the underlying part of the Sage, and a Late Cambrian (conaspid) trilobite was obtained from its uppermost part about 

165 ft (50 m) above the base of the Red Lion. Fossils collected about 60 

ft (18 m) above the base of the Red Lion in measured section H were 

identified by A. R. Palmer (written commun., 1968; 1970). They include the brachiopod Billingsella and the trilobite Taenicephalus. 

The fossils are of Late Cambrian (Franconian) age.

DEVONIAN SYSTEM

JEFFERSON FORMATION

The Jefferson Formation (fig. 3, sections H and J), of Late Devonian 

age, unconformably overlies the Red Lion Formation, ranges from 

250 to 268 ft (76-82 m) thick, and is well exposed. Sandberg (1962, 

1965) divided the formation into a lower unnamed member and the 

overlying Birdbear Member. The lower member is marked by repetition of three kinds of rock: (1) yellowish-brown to grayish-orange silty 

shaly dolomite "detrital units" of Benson (1966); (2) pale- to darkyellowish-brown medium- to thick-bedded fine- to mediumcrystalline rubbly weathering dolomite; and (3) pale- to darkyellowish-brown, medium- and thick-bedded, finely crystalline dense 

fetid and, locally, sugary dolomite. The Birdbear Member, which 

ranges from 54 to 68 ft (16-21 m) thick in the Ruby Range, contains 

thinly bedded dolomite in its basal 9-12 ft (3-4 m) but is mainly 

ledge-forming dolomite breccia and "pseudobreccia" (Sandberg, 

1965). The massive unit is mostly pale yellowish brown; locally the 

upper few feet are mottled grayish orange.

The silty, shaly, and detrital dolomite beds of the lower member are 

thinly bedded and locally consist of fine laminae that weather into 

1-mm-thick "pages" to form "books." The uppermost detrital unit 

marks the top of the lower member; according to Benson (1966), it is 

traceable from northeastern Montana to northeastern Utah.

The rubbly-weathering dolomite has a very uneven, weathered 

outcrop face on each bed. At one place, where a rubbly bed was traced
116 CONTRIBUTIONS TO STRATIGRAPHY

laterally into a less well exposed outcrop, the outcrop face was much 

smoother. The origin of the rubbly beds is uncertain, but the beds 

may have formed by evaporite solution.

The Jefferson is thinner in the Ruby Range than in nearby areas to 

the east, north, or west (compare Mann, 1954, 1960; Hadley, 1960; 

Karlstrom, 1948; Johns, 1961); it overlies an erosionally thinned 

Cambrian section in the southern part of the map area. These data, 

and the regional data of Benson (1966), suggest depositional thinning 

of the formation southward toward a positive area in the Devonian 

sea, the Tendoy dome (Lemhi Arch) (Sloss, 1954; Scholten, 1957, 

1960; Scholten and Hait, 1962), and the Yellowstone Park uplift 

(Sandberg and Mapel, 1967; Mapel and Sandberg, 1968).

Except for Amphipora, fossils were not found in the Jefferson of the 

Ruby Range. The Late Devonian age of the formation is based on 

regional faunal data (compare Robinson, 1963; Sandberg and Mapel, 

1967; Witkind, 1969).

DEVONIAN AND MISSISSIPPIAN SYSTEMS

THREE FORKS FORMATION

The Three Forks Formation (fig. 3, section D) is about 150 ft (47 m) 

thick; except for a medial limestone unit, it is poorly exposed. It 

consists of three members, in ascending order, the Logan Gulch, Trident, and Sappington Members (Sandberg, 1965). The Logan Gulch 

Member is 110 ft (34 m) thick in the Ruby Range; its lower half 

consists of yellowish-brown, thin- to thick-bedded dolomite and limestone evaporite-solution breccia, and a few interbeds of greenish-gray 

clay shale. The upper half of the member is composed mainly of 

gray-weathering, thin- and thick-bedded, finely crystalline limestone. It forms a prominent ledge that serves as an excellent marker 

unit throughout the range. The rest of the formation is covered, except for 7 ft (2 m) of grayish-orange thin- to medium-bedded, calcareous siltstone in the upper part of the covered interval assigned to the 

Sappington Member.

Between the exposed parts of the Logan Gulch Member and the 

Sappington Member is a covered interval about 25 ft (8 m) thick that 

may represent both the Trident Member and parts of the Sappington 

Member. Float from the basal half of the covered interval is mostly 

pale-olive chips of micaceous clay shale similar to that described at 

the type area of the Three Forks by numerous workers. An attempt 

was made, without success, to expose beds immediately beneath the 

siltstone in search of a black shale unit that occurs at the base of the 

Sappington as defined by McMannis (1955) in the Three Forks region. 

It is therefore uncertain if the black shale unit is present here.
PALEOZOIC AND MESOZOIC STRATIGRAPHY, RUBY RANGE 117

The Jefferson-Logan Gulch contact is sharp and appears conformable. The Logan Gulch-Trident, Trident-Sappington, and 

Sappington-Lodgepole contacts are all covered.

The faunal elements listed below, collected from the Logan Gulch 

Member in NWi/iSE1^ sec. 18, T. 6 S., R. 5 W. (Beaverhead Rock SE 

quadrangle) (section not measured), were identified by J. T. Dutro, Jr. 

(written commun., 1968). They are of Late Devonian age, probably 

middle Famennian.

Schuchertella sp.

"Camarotochia" sp.

Crytospirifer monticola (Haynes)

Crytospirifer sp.

Crytiopsis sp.

Cleiothyridina devonica Raymond

MISSISSIPPIAN SYSTEM

MADISON GROUP

A thick sequence of carbonate beds, about 1,960 ft (588 m), overlying the Devonian rocks makes up the Madison Group. The lower 

one-third of the sequence is assigned to the Lodgepole Limestone, the 

remaining two-thirds to the Mission Canyon Limestone. The group 

forms prominent outcrops along much of the east and north flanks of 

the range.

LODGEPOLE LIMESTONE

The Lodgepole Limestone (fig. 3, section C) is 594 ft (181 m) thick 

near Robinson Canyon in the northern part of the mapped area, and 

this thickness seems uniform throughout the range. The upper half is 

commonly well exposed throughout the mapped area; the lower half 

is well exposed mainly along the eastern margin of the range where 

the beds dip steeply. Most of the lower 300 ft (91 m) of the Lodgepole 

is made up of pale- to dark-yellowish-brown-weathering, 2- to 5-in. 

(5-13 cm) thick beds of dark-gray laminated argillaceous limestone; 

the laminae weather into "books" of 1-mm-thick "pages." The upper 

part of the formation is composed of light-gray-weathering mediumand thick-bedded finely crystalline limestone, and locally of 

medium-crystalline beds containing clastic debris.

Limited thin-section studies of the argillaceous limestone reveal an 

abundance of clay pellets 15-60 /it m in diameter; the size range in 

any one thin section is commonly much narrower. Cherty particles 

constitute 10 percent or more of the beds; finely comminuted fossil 

debris makes up a smaller fraction. The matrix of the rock is finely 

crystalline limestone.
118 CONTRIBUTIONS TO STRATIGRAPHY

The lower rocks of the Lodgepole in the Ruby Range differ from 

those in nearby areas where they have been described as thinly 

bedded limestone with partings of shaly limestone or calcareous 

shale. In the Ruby Range, it is the shaly rocks that make up most of 

the sequence.

The Cottonwood Canyon Member of the Lodgepole (Sandberg and 

Klapper, 1967), a thin black shale unit present at the base of the 

formation in much of Montana and northern Wyoming, was not observed in the Ruby Range, but as the contact interval is not exposed, 

the unit may be present but concealed. If present, the member must 

be thin, for the covered interval is only 9 ft (3 m) thick where the 

Three Forks was measured. Isopach maps of Benson (1966) and 

Sandberg and Klapper (1967) show the unit to be absent or very thin 

(2-3 ft (60-90 cm)) in the general area, and Sando and Dutro (1960) 

state that it is absent in the nearby Gravelly Range.

Sloss and Hamblin (1942) divided the Lodgepole into the Paine 

Member and the overlying Woodhurst Member, placing the contact at 

the base of massive beds of crinoidal debris. Massive beds were not 

observed in the Lodgepole in the Ruby Range, and the contact between the lower and upper parts is transitional through tens of feet. 

Therefore the Paine-Woodhurst terminology is not used here.

The contact of the Lodgepole with the overlying Mission Canyon 

Limestone, which is conformable, was placed at the base of the first 

cliff-forming outcrop.

Many fossils occur in the Lodgepole, particularly in the upper half; 

their stratigraphic distribution is shown in table 1. (See section C of 

open-file report (Tysdal, 1970) for detailed description of rocks.) The 

fossils are Early Mississippian. They were identified by J. T. Dutro, 

Jr. (written commun., 1968), who states, "the assemblage is typical of 

the middle and upper parts of the Lodgepole Limestone in southwestern Montana and can be assigned to Zone Ci of Sando and Dutro 

(I960)."

MISSION CANYON LIMESTONE

The Mission Canyon Limestone (fig. 3, section C) forms the steep 

eastern slopes of the Ruby Range and is well exposed in narrow canyons cut across the strike of the beds. The beds are not so well exposed 

elsewhere in the range. A thickness of 1,370 ft (418 m) was measured 

near Robinson Canyon; this figure is considered approximate because 

the measurement was necessarily made on a dip slope.

The Mission Canyon consists mainly of pale- to dark-yellowishbrown, medium- and thick-bedded limestone that weathers light gray 

and forms ledges and cliffs. The only dolomite observed was a 30-ft 

(9 m) thick interval in the lower one-fourth of the formation. Crystal-
PALEOZOIC AND MESOZOIC STRATIGRAPHY, RUBY RANGE 119

TABLE 1. Stratigraphic position of fossils collected from the Mississippian Lodgepole

Limestone

[Identifications by J. T. Dutro, Jr ]

U.S. Geological Survey

Locality No.

 p -i Feet above base.

Echinoderms: 

Platycrinites

Echinoderm debris, indet

Coelenterates: 

Horn coral, indet

Conularia? sp.

Bryozoans: 

Sulcoretopora sp.

Ptilopora sp.

Fenestrate bryozoans, indet

Ramose bryozoans, indet

Bryozoans, indet

Brachiopods: 

Rhipidomella sp

Leptagonia cf. L. analoga

Schuchertella! sp

Axiodeanial sp

Rhynchonellid brachiopods, indet

Retichonetes logani 

(Norwood and Pratten)

Rugosochonetes cf. R. loganensis 

(Hall and Whitfield) _______________

Productoid brachiopod, indet

Unispirifer sp

Spirifer cf. S. gregeri Weller

Actinochonchus sp.

Syringothyroid, indet

Cleiothyridina cf. 

C. tenuilineata (Rowley)

C. cf C. obmaxima (McChesney)

Punctospirifer cf. P. solidirostis (White )_ 

Ambocoelia? sp

Eumetrial sp

Gastropods:

Trace Fossils: 

Worm tubes and burrows, indet

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Unity ranges from fine to coarse; much of the rock is coarsely recrystallized. A few chert stringers are present in the middle third of the 

formation.

Solution breccias that fill cavities 20-50 ft (6-15 m) across in the 

upper part of the Mission Canyon consist of fragments of Mission 

Canyon Limestone to 3 ft (1 m) in diameter; the fragments are chaotically arrayed and are cemented by grayish-orange silty limestone
120 CONTRIBUTIONS TO STRATIGRAPHY

that is silicified locally. Similar breccias have been described in the 

Mission Canyon at numerous localities in Montana (compare Sloss 

and Hamblin, 1942; and Roberts, 1966).

The lower contact is conformable with the Lodgepole, as noted. The 

upper contact, though not observed, is inferred to be unconformable 

with the Kibbey(?) Formation on the basis of data from nearby areas 

(Robinson, 1963; Huh, 1967; Witkind, 1969).

No fossils were found in the Mission Canyon Limestone. Its age is 

considered Early and Late Mississippian.

KIBBEY(?) FORMATION

The Kibbey(?) Formation (fig. 3, section B) ranges in thickness 

from 20 to 138 ft (6-42 m), is poorly exposed, and makes a reddish 

soil-covered interval except for the well-exposed outcrop near Big 

Dry Creek that was measured for section B. At this outcrop the unit 

consists mainly of pale-reddish-brown, thin- to medium-bedded, 

finely crystalline silty dolomite or dolomitic limestone, with localized 

interbeds of calcareous quartz sandstone. Some of the beds are mottled; the mottled parts are rounded dolomite intraclasts as much as 

8 mm in diameter. A few other beds contain algal laminations. 

Quartz silt grains ranging from 20 to 60 /a m in diameter make up 

10-20 percent of some beds. The sandstone interbeds are composed 

largely of rounded fine- to medium-grained quartz, but chert grains 

locally constitute 10-15 percent of the rock.

The difficulty in distinguishing red beds of the Mississippian Kibbey Formation of the Big Snowy Group from those of the Mississippian and Pennsylvanian Amsden Formation has long been recognized (McMannis, 1965; Maughan and Roberts, 1967). A recent study 

of the Big Snowy Group (Harris, 1972) and its relation to the Amsden 

Formation in central and part of southwestern Montana traces the 

Big Snowy and Amsden rocks into the Three Forks-Jefferson Canyon 

area (fig. 1); there Harris distinguishes the red beds in the Kibbey 

from those in the Amsden on the basis of color, presence or absence of 

pinkish chert, and presence or absence of quartz sand. The Kibbey is 

characterized by an intense red color, the Amsden by somber hues of 

grayish red, maroon, and pale brown. Pinkish chert is common in the 

Kibbey but apparently absent from the Amsden. The Kibbey contains 

a significant amount of quartz sand but quartz sand is nearly absent 

from the Amsden. Using these criteria, the red beds in the Ruby 

Range are more like those of the Kibbey than the Amsden, therefore 

they are questionably assigned to the Kibbey.

The contact of the Kibbey(?) with the overlying Quadrant Sandstone is sharp. Red rocks are not interbedded with the Quadrant.

Fossils were not found in the Kibbey(?), but the age is considered
PALEOZOIC AND MESOZOIC STRATIGRAPHY, RUBY RANGE 121

Late Mississippian, the age of the Kibbey in the nearby Gravelly 

Range (Hadley, 1960) and the Three Forks area (Robinson, 1963).

PENNSYLVANIA SYSTEM

QUADRANT SANDSTONE

The Quadrant Sandstone is present only at the north end of the 

range (fig. 3, section A) in an exposure containing 1,200 ft (366 m) of 

contorted, brecciated, and faulted limestone, dolomite, and sandstone; the minimum thickness is about 300 ft (91 m), the maximum 

more than 1,200 ft (366 m). The formation consists of well-exposed 

light-gray-weathering medium- and thick-bedded limestone in intervals as much as 40 ft (12 m) thick; the limestone is interbedded with 

poorly exposed pale-brown thin- to medium-bedded quartzite in 

intervals of similar thickness. The limestone, and locally dolomite, is 

finely crystalline; it contains varying percentages of fossil debris, 

algal-laminated limestone, and calcareous pellets. Recrystallization 

has obscured most of the fauna. The quartzitic sandstone is well 

sorted; it is composed of grains ranging between 60 and 150 /xm in 

diameter which are cemented mostly by silica overgrowths. Float 

from the covered intervals in the section is composed largely of the 

quartzitic sandstone.

The actual thickness of the Quadrant is uncertain because of deformation and the absence of younger Paleozoic rocks. The minimum 

unfaulted thickness, about 300 ft (91 m), is consistent with that measured northward in the Jefferson Canyon area (Berry, 1943; Alexander, 1955; Robinson, 1963) and eastward and southeastward in the 

Gravelly and Madison Ranges, and the Centennial Mountains (Condit, 1918; Scott, 1935; Gardner and others, 1945; Honkala, 1949; Sloss 

and Moritz, 1951; Hadley, 1960; and Maughan and Roberts, 1967). 

Thicker sequences, more than 700 ft (213 m), have been reported in 

the area of McCartney Mountain west of the Ruby Range (Pardee, in 

Richards and Pardee, 1925; Sloss and Moritz, 1951); more than 500 ft 

(152 m) is present in the northern Snowcrest Range (Mann, 1954), 

and more than 1,000 ft (305 m) is reported in the Blacktail Range 

south of the Ruby Range (Scholten and others, 1955).

Fossils collected from the Quadrant, about 910 ft (277 m) above the 

base of the measured section, are Anthracospirifer aff. A. occidus 

(Sadlick) and Composite, aff. C. subtilita Hall. They were identified 

and assigned an Early or Middle Pennsylvanian age by J. T. Dutro, 

Jr. (written commun., 1968).

MESOZOIC ROCKS

The only Mesozoic rocks preserved in the Ruby Range are those of
122 CONTRIBUTIONS TO STRATIGRAPHY

the Beaverhead Formation, the lower part of which is Cretaceous. 

Triassic, Jurassic, and pre-Beaverhead Cretaceous rocks are absent, 

largely due to erosion, but in part to nondeposition (see isopach maps 

of McMannis, 1965; Peterson, 1972; and McGookey and others, 1972). 

In the nearby Gravelly and Greenhorn Ranges to the east of the 

mapped area, Hadley (1960) measured 225-375 ft (67-114 m) of 

Triassic rocks, 330-400 ft (100-122 m) of Jurassic rocks, 750-1,300 ft 

(229-396 m) of Lower Cretaceous rocks, and about 3,000 ft (915 m) of 

Upper Cretaceous rocks.

CRETACEOUS SYSTEM

BEAVERHEAD FORMATION

The Beaverhead Formation in the Ruby Range is made up of three 

types of conglomerate; the first type is composed of carbonate clasts 

derived largely from the Madison Group, the second is composed of 

poorly exposed quartzite clasts eroded from the Precambrian Belt 

Supergroup, and the third, present only locally, is composed of clasts 

derived from the Meagher and Flathead Formations, the Belt Supergroup, and metamorphic rocks.

The carbonate conglomerate is made up of poorly sorted subrounded cobbles and boulders 2-3 ft (0.5-1.0 m) in diameter in a 

matrix of fine- to coarse-grained sand of limestone, quartz, and chert 

that is cemented by calcite and stained red by iron oxide. This conglomerate is the oldest unit of the Beaverhead in the northern part of 

the Ruby Range. It is exposed along the western margin of the range, 

where it overlies formations ranging from the Cambrian Meagher 

through the Mississippian Mission Canyon. It is in contact with Precambrian metamorphic rocks only along faults.

The quartzite conglomerate overlying the carbonate conglomerate 

is composed of well-sorted, rounded to well-rounded cobbles and locally boulders in a matrix of medium- to coarse-grained quartz sand 

stained red with iron oxide. Many of the clasts are highly polished 

and some exhibit percussion marks.

The third type of conglomerate is composed of clasts derived from 

the Meagher, Flathead, Belt, and metamorphic rock units and has a 

reddish sandstone matrix of quartz and limestone grains. It is present 

in only two places in the mapped area, both high up in the northern 

part of the Ruby Range: one about 1 mi (1.5 km) southwest of section 

J, the other about 1.5 mi (2.5 km) south-southwest of this section. 

This conglomerate unit is considered to be the youngest part of the 

Beaverhead because it contains clasts derived from the oldest part of 

the sequence in the range and thus from rock units that would have 

been exposed late in the course of uplift and erosion of the range. The 

cobbles of Belt present in the unit were derived from rocks several
PALEOZOIC AND MESOZOIC STRATIGRAPHY, RUBY RANGE 123

miles west of the Ruby Range and transported into the area by 

streams.

The thickness of the Beaverhead was not measured but is probably 

several hundreds of feet.

Fossils were not found in the Beaverhead in the Ruby Range. A 

minimum age is late Eocene, as Petkewich (1972) found vertebrate 

fauna of that age in the lower part of basinal deposits that lap onto 

the north end of the range. In its type area, the Beaverhead contains 

fossils of Late Cretaceous and Paleocene age (Yen, in Lowell and 

Klepper, 1953; Wilson, 1970; Ryder and Ames, 1970). Ryder and 

Scholten (1973) believe the uppermost part of the formation may be 

as young as Eocene.

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 &GPO 691- 627-1976
Contributions to 

Stratigraphy, 

1976________

GEOLOGICAL SURVEY BULLETIN 1405

This volume was published 

as separate chapters A-I
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

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

Washington, D. C. 20402
CONTENTS

[Letters designate the chapters]

(A) Changes in stratigraphic nomenclature by the U.S. Geological Survey, 1974, 

by George V. Cohee and Wilna B. Wright.

(B) A Summary of Tertiary volcanic stratigraphy of the southwestern, high 

plateaus and adjacent Great Basin, Utah, by Peter D. Rowley, John J. Anderson, and Paul L. Williams.

(C) Revision of the lower part of the Tertiary system in the central and western 

Uinta Basin, Utah, by Thomas D. Fouch.

(D) Stratigraphy of the layered gabbroic Dufek intrusion, Antarctica, by Arthur B.

Ford. 

(E) McGowan Creek Formation, new name for lower Mississippian flysch sequence

in east-central Idaho, by Charles A. Sandberg. 

(F) The Buffalo Peaks andesite of central Colorado, by George F. Sanders, Jr.,

Glenn R. Scott, and Charles W. Naeser. 

(G) Upper Cambrian Orr Formation: Its subdivisions and correlatives in western

Utah, by Lehi F. Hintze and Allison R. Palmer. 

(H) Silurian nomenclature and correlations in southwest Virginia and northeast

Tennessee, by Ralph L. Miller. 

(I) Paleozoic and Mesozoic stratigraphy of the northern part of the Ruby Range,

southwestern Montana, by Russell G. Tysdal.