112°

30'

11

2° 3

7' 3

0"

112°

30'

112°

37'

30"

32' 3

0"

35'

32' 3

0"

35'

40'

40'

42' 3

0"

47' 3

0"

46°

37' 3

0"46

° 37

' 30"

46°

45'

46°

45'

T 12

NT

11 N

T 12

NT

11 N

T 11

NT

10 N

T 11

NT

10 N

R 8

W

R 7

W

R 8

W

R 7

W

50

5025

30

2830

40

5

35

15

913

6

23

14

15

30

15

10

20

2060

45

17

45

22

60

23

25

14

22

30

30

50

12

14

48

23

5835 34

33

40

65

50

55

80

38

40

30

38

11

1520

17

30

29

47

35

60

35

1870

18

2516

13

25

17

30

27

42

21

19

21

24

4045

Qgo

Qal

Trca

Tba

Qac

Trca

Trca

Qgr

Qgr

Qgr

Qgr

Qgr

Tba

Qgr

Trca

Qal

o

Trca

Qal

Qac

Qal

oTr

p

Tba

Tgr

Tba

Tba

Qgr

Trca

Qgr

Qls

Qgr

Trca

Trca

Tba

Trca

Trca

pl pl

Taf

Qgo

Trca

Qal

Qal

oTg

r

Qgr

Trca

Trca

Qal

o

MmKqm

Qgr

Qal

Qal

Qac

Qac

Kqm

Mm

Mm

Qal

o

pl plK

qm

pl plK

qmpl pl

pl pl

Trca

Qls

Trca

Qac

Qac

Mm

Taf

Tri

Qal

o

Kqm

P*Mps

Qgo

Qaf

Qls

Qal

o

Qgr

Ybo

Ybo

Kqm

Qgr

Qls

Taf

Taf

Ym

pl pl

_pm

Kqm

Taf

_pm

Mm

Qal

o

Qls

Qls

Taf

Qls

Qgt

Qls

Qls

Ybo

_wf

Dj

Qal

o

Trca

Qaf

Qaf

Qgt

Qgt

Taf

Taf

Taf

_pm

_wf

_pm

Qls

Qls

Taf

Qls

Qaf

Qls

Ybo

_m

Tri

Tri

Tri

_wf

Ym

Ym

s3

Taf

Taf

Ybo

Qgt

Ym

s3

Ym

Qgt

Taf

Ym

s2

Ym

s2

Ybo

Ym

s3

Ysh

Ysn

QmTrca

Qm

Qls

Trca

pl pl

pl pl

Trca

Qal

Qls

Qal

o Trca

Qls

Tba

Tri

pl pl

D_mp

D_mp

D_mp

D_mp

D_mp

D_mp

pl pl

pl pl

Qgt

Ym

s3

Trca

Qal

BLA

CK

FOO

T

CIT

Y

STO

CK

Black

Mountain

Syncline

A

A'

SC

ALE

: 1:2

4,00

0

feet

met

ers

010

0020

0030

00

010

0020

0030

0040

0050

0060

0070

0080

0090

0010

,000

Cro

ss S

ectio

n A

–A'

AA

' 2000

3000

4000

5000

6000

7000

8000

1000

2000 50

0

1500

2500

Elevation above sea level (meters)

Elevation above sea level (feet)

Ybo

Yms3

Yms2

Ysh

Tri

Taf

_wf

Ym

Ybo

Yms3

Yms2

Ysh

Ysn

Ym_wf

Ym

Ybo

Yms3

Yms2

Ysh

Ysn

Trca

Trca

Qgo

Qalo

Qgr

Taf

Ybo

Yms2Yms3

No

verti

cal e

xagg

erat

ion

Threemile Creek

3544

63 51

Strik

e an

d di

p of

incl

ined

bed

s

Faul

t: sh

ort-d

ashe

d w

here

infe

rred

, bar

and

bal

l on

dow

nthr

own

side

; arr

ows

indi

cate

mov

emen

t

Rev

erse

or t

hrus

t fau

lt: te

eth

on u

pthr

own

bloc

k; s

hort-

da

shed

whe

re in

ferr

ed; d

otte

d w

here

con

ceal

ed

Con

tact

: das

hed

whe

re a

ppro

xim

atel

y lo

cate

d

Strik

e an

d di

p of

cle

avag

e

Strik

e an

d di

p of

vol

cani

c fo

liatio

n

MA

P SY

MB

OLS

pl

Pla

cer w

orki

ngs

Syn

clin

e: s

how

ing

appr

oxim

atel

y lo

cate

d tra

ce o

f axi

al

plan

e an

d pl

unge

dire

ctio

n

Strik

e an

d di

p of

Bel

t Sup

ergr

oup

rock

s w

here

top

of

bedd

ing

is c

erta

in

Tgr

P*Mps

Pennsylvanian

Perm

ian

Mississippian

Devo

nian

Cambrian

Cretace

ous

Meso

proterozo

ic

Tertiary

Quaternary

Holoce

ne

Pleistoce

ne

CO

RR

ELAT

ION

DIA

GR

AM

Plioce

ne

Mioce

ne

Oligoce

ne

Eoce

ne

Qal

Qaf

Qgt

Taf

Tri

Trca

Trp

Qac

Qm

Qls

Qgr

Qgo

Qalo

Tba

Kqm

Dj

_pm

_wf

Ym

Ybo

Yms3

Yms2

Ysh

Ysn

Late

Cretace

ous

Mm

Bel

tS

uper

grou

p

D_mp

_m

? ?

? ?? ??

Geo

logi

c Su

mm

ary

Th

e no

rthea

ster

n th

ird o

f the

qua

dran

gle

is u

nder

lain

by

Mes

opro

tero

zoic

Bel

t Su

perg

roup

, Pal

eozo

ic se

dim

enta

ry ro

cks,

and

Cre

tace

ous t

o Eo

cene

igne

ous r

ocks

. Alth

ough

W

inst

on (1

986)

pro

pose

d th

at a

n ea

st–w

est M

esop

rote

rozo

ic d

own-

to-th

e-no

rth g

row

th fa

ult

trave

rsed

the

quad

rang

le, w

e sa

w n

o th

ickn

ess c

hang

es in

Bel

t Sup

ergr

oup

Form

atio

ns in

the

area

. The

sout

hwes

tern

2/3

of t

he m

ap is

und

erla

in b

y C

enoz

oic

volc

anic

and

sedi

men

tary

de

posi

ts o

f the

Avo

n Va

lley.

St

ruct

ure

is d

omin

ated

by

the

north

–nor

thw

est-t

rend

ing

Bla

ck M

ount

ain

sync

line

(Bie

rwag

en, 1

964)

and

nor

thw

est-s

triki

ng th

rust

and

nor

mal

faul

ts. N

orth

east

-stri

king

hig

h-an

gle

faul

ts c

ut th

e no

rthw

est s

truct

ures

. The

thru

st fa

ults

and

the

Bla

ck M

ount

ain

sync

line

may

be

kine

mat

ical

ly li

nked

; the

sync

line’

s age

is b

rack

eted

by

the

youn

gest

rock

s tha

t are

invo

lved

in

the

fold

ing

and

by th

e cr

oss-

cutti

ng B

lack

foot

City

stoc

k, a

nd is

ther

efor

e in

ferr

ed to

be

77–9

7 M

a (S

chm

idt a

nd o

ther

s, 19

94).

The

north

wes

t-tre

ndin

g, c

ontra

ctio

nal s

truct

ures

incl

udin

g th

is

fold

, and

the

reve

rse

faul

ts, a

re p

ostu

late

d to

be

part

of th

e Le

wis

and

Cla

rk L

ine,

a si

nist

ral

trans

pres

sive

stru

ctur

e th

at fo

rmed

sync

hron

ousl

y w

ith S

evie

r thr

ustin

g du

ring

the

Cre

tace

ous

that

was

late

r rea

ctiv

ated

dur

ing

Terti

ary

exte

nsio

n (S

ears

and

Hen

drix

, 200

4). N

orth

wes

t- st

rikin

g, d

own-

to-th

e-so

uthw

est,

norm

al fa

ults

con

trol m

uch

of th

e no

rthea

st si

de o

f the

Ter

tiary

Av

on V

alle

y. T

hey

form

ed p

aral

lel t

o th

e co

ntra

ctio

nal s

truct

ures

. Rel

ativ

ely

min

or

north

east

-stri

king

, hig

h-an

gle

faul

ts a

ppea

r to

cut a

ll th

e ot

her s

truct

ures

.

Lo

en (1

990)

des

crib

ed fo

ur ty

pes o

f Ter

tiary

dep

osits

: Plio

cene

(?) p

edim

ent g

rave

l, M

ioce

ne(?

) fan

glom

erat

e, M

ioce

ne (?

) silt

ston

e an

d sa

ndst

one,

and

Olig

ocen

e B

lack

foot

City

be

ds. O

n th

e cu

rren

t Oph

ir C

reek

qua

dran

gle

thes

e de

posi

ts a

re sh

own

resp

ectiv

ely

as G

rave

l (Ts)

, Allu

vial

-fan

dep

osit

(Taf),

Ren

ova

Form

atio

n—A

ntel

ope

Hill

mem

ber (Trah

), an

d R

enov

a Fo

rmat

ion—

Clim

bing

Arr

ow M

embe

r (Trca

).

Des

crip

tion

of M

ap U

nits

Qal

A

lluvi

um (Q

uate

rnar

y: H

oloc

ene)

—G

rave

l, sa

nd, s

ilt, a

nd c

lay

alon

g st

ream

s and

thei

r tri

buta

ries.

Cla

sts g

ener

ally

roun

ded

to su

brou

nded

cob

ble

size

and

smal

ler,

but

boul

ders

als

o pr

esen

t.

Qaf

A

lluvi

al-f

an d

epos

it (Q

uate

rnar

y: H

oloc

ene)

—G

rave

l, sa

nd, s

ilt, a

nd c

lay

in d

epos

it w

ith fa

n-sh

aped

mor

phol

ogy

near

Thr

eem

ile C

reek

and

alo

ng B

alla

rat C

reek

, bot

h on

th

e w

este

rn si

de o

f the

map

are

a. C

last

s prim

arily

der

ived

from

Qgt a

nd Taf.

Qac

A

lluvi

um a

nd c

ollu

vium

(Qua

tern

ary:

Hol

ocen

e)—

Silt,

sand

, gra

nule

s, an

d pe

bble

s de

posi

ted

on sl

opes

by

shee

twas

h al

luvi

um in

corp

orat

ed w

ith lo

cally

der

ived

fin

e-gr

aine

d co

lluvi

um.

Qm

M

antle

(Qua

tern

ary:

Hol

ocen

e an

d Pl

eist

ocen

e)—

Dep

osit

that

incl

udes

shee

twas

h al

luvi

um, c

ollu

vium

, coa

rse-

grai

ned

(peb

ble,

cob

ble,

smal

l bou

lder

) lag

from

old

er

depo

sits

, and

rego

lith.

Qls

L

ands

lide

depo

sit (

Qua

tern

ary:

Hol

ocen

e or

Ple

isto

cene

)—M

ass-

was

ting

depo

sit o

f ro

tate

d or

cha

otic

bed

s tha

t slid

dow

nslo

pe. T

he b

ento

nitic

Clim

bing

Arr

ow M

embe

r an

d un

its th

at im

med

iate

ly o

verli

e it

are

parti

cula

rly p

rone

to d

evel

opin

g la

ndsl

ide

depo

sits

.

Qgr

G

rave

l (Q

uate

rnar

y: P

leis

toce

ne)—

Dep

osits

rew

orke

d fr

om Taf a

nd Q

go

on

slop

es

belo

w th

e so

urce

dep

osits

.

Qal

o A

lluvi

um, o

lder

than

Qal

(Qua

tern

ary:

Ple

isto

cene

)—D

epos

its in

bro

ad v

alle

ys w

ith

unde

rfit

stre

ams.

Cla

sts l

ocal

ly d

eriv

ed.

Qgt

G

laci

al ti

ll (Q

uate

rnar

y: P

leis

toce

ne)—

Poor

ly so

rted,

suba

ngul

ar to

subr

ound

ed

gran

ules

, peb

bles

, cob

bles

, and

bou

lder

s in

a sa

ndy

to lo

cally

cla

yey

mat

rix. I

nclu

des

boul

ders

as m

uch

as 3

m (1

0 ft)

in d

iam

eter

, dom

inan

tly o

f qua

rtzite

and

lim

esto

ne.

Qgo

G

laci

al o

utw

ash

(Qua

tern

ary:

Ple

isto

cene

)—D

epos

its a

long

Six

mile

Cre

ek th

at

repr

esen

t the

term

inus

of a

larg

e gl

acia

l out

was

h fa

n th

at c

ontin

ues i

nto

the

Gra

vely

M

ount

ain

7.5'

qua

dran

gle

to th

e w

est.

Fan

is a

bout

6.5

km

(4 m

i) lo

ng. R

ewor

ked,

su

brou

nded

, iro

n-st

aine

d pe

bble

s and

cob

bles

that

are

dom

inan

tly c

last

-sup

porte

d.

Tgr

Gra

vel d

epos

it (T

ertia

ry: P

lioce

ne)—

Poor

ly to

wel

l-stra

tifie

d bo

ulde

r, an

d pe

bble

-cob

ble

grav

el, s

and,

silt,

and

cla

y. In

clud

es so

me

lag

depo

sits

. Loc

ally

con

tain

s pl

acer

gol

d. A

fter L

oen,

199

0.

Taf

Allu

vial

-fan

dep

osit

(Ter

tiary

)—D

omin

antly

mat

rix-s

uppo

rted,

but

loca

lly c

last

- su

ppor

ted

depo

sit t

hat o

ccur

s prim

arily

adj

acen

t to

rang

e-fr

ont f

ault.

Cla

sts r

ange

from

pe

bble

to la

rge

boul

der s

ize

in c

lay/

silt/

sand

mat

rix. C

last

com

posi

tion

dom

inan

tly

Bel

t Sup

ergr

oup

quar

tzite

with

subo

rdin

ate

Pale

ozoi

c, v

olca

nic,

and

plu

toni

c ro

ck.

Incl

udes

loca

l ext

rem

ely

larg

e bo

ulde

rs. S

ome

smal

l are

as sh

own

as P

aleo

zoic

out

crop

w

ithin

the

fan

depo

sits

on

prev

ious

map

s are

inte

rpre

ted

as b

urie

d bo

ulde

rs. D

epos

it ha

s pre

viou

sly

been

inte

rpre

ted

as M

ioce

ne(?

) (Lo

en, 1

990;

Sch

mid

t and

oth

ers,

1994

) bu

t may

be

as o

ld a

s Eoc

ene

base

d on

inte

rfin

gerin

g re

latio

nshi

p w

ith C

limbi

ng A

rrow

Fo

rmat

ion

prim

arily

obs

erve

d in

Fin

n 7.

5' q

uadr

angl

e to

the

north

. Dep

osit

cont

ains

pl

acer

gol

d (L

oen,

199

0). M

ay b

e as

thic

k as

300

m (9

85 ft

).

Tba

Bas

alt (

Tert

iary

: ear

ly O

ligoc

ene

or la

te E

ocen

e?)—

Bla

ck to

dar

k re

ddis

h br

own

mas

sive

flow

s tha

t wea

ther

yel

low

ish

red

to y

ello

wis

h br

own.

Flo

w to

ps v

esic

ular

w

ith c

aviti

es st

retc

hed

para

llel t

o flo

w d

irect

ion.

As m

uch

as 3

0% o

f the

ves

icle

s are

fil

led

with

cha

lced

ony

and/

or c

alci

te. R

ange

s mic

rosc

opic

ally

from

aph

aniti

c to

sl

ight

ly p

orph

yriti

c. A

ugite

and

pla

gioc

lase

phe

nocr

ysts

1–5

mm

(0.0

4 to

0.2

0 in

) lon

g oc

cur i

n a

pilo

taxi

tic m

atrix

of s

ubor

ient

ed p

lagi

ocla

se la

ths.

Acc

esso

ry m

iner

als

incl

ude

biot

ite a

nd ti

tano

mag

netit

e or

ilm

enite

. Sec

onda

ry m

iner

als i

nclu

de h

emat

ite

and

epid

ote.

Afte

r Loe

n, 1

990.

Trca

R

enov

a Fo

rmat

ion:

Clim

bing

Arr

ow M

embe

r (T

ertia

ry: E

ocen

e)—

Pale

oliv

e, li

ght

oliv

e gr

ay, m

oder

ate

oliv

e br

own,

and

med

ium

ligh

t gra

y, b

ento

nitic

mud

ston

e an

d ye

llow

ish

gray

silts

tone

. Con

tain

s len

ses o

f bro

wni

sh g

ray

sand

ston

e, a

nd

grav

el/c

ongl

omer

ate

usua

lly w

ith p

ebbl

e-si

ze c

last

s dom

inat

ing

the

coar

ser c

last

s in

a sa

nd/g

ranu

le m

atrix

. San

dsto

ne d

omin

antly

med

ium

- to

coar

se-g

rain

ed.

Gra

vel/c

ongl

omer

ate

cons

ists

of c

last

-sup

porte

d le

nses

of r

ound

ed g

ranu

les,

pebb

les,

and

cobb

les o

f rhy

olite

por

phyr

y an

d ot

her d

omin

antly

vol

cani

c lit

holo

gies

in a

sand

y m

atrix

. Uni

t typ

ical

ly d

ispl

ays “

popc

orn”

wea

ther

ing,

larg

e de

sicc

atio

n cr

acks

, and

is

pron

e to

land

slid

e de

velo

pmen

t. Ex

pose

d th

ickn

ess a

ppro

xim

atel

y 90

m (3

00 ft

).

Tri

Rhy

olite

plu

gs a

nd d

ikes

(Ter

tiary

: lat

e E

ocen

e?)—

Ligh

t gra

y to

ligh

t bro

wn,

no

n-fo

liate

d, p

orph

yriti

c, w

ith 1

0–40

% p

heno

crys

ts o

f san

idin

e an

d qu

artz

. Dik

es a

t Eu

reka

Gul

ch a

re m

iner

aliz

ed a

nd o

ccur

in th

e so

urce

are

a fo

r pro

duct

ive

gold

pla

cers

. A

cces

sory

min

eral

s inc

lude

iron

oxi

des a

nd a

patit

e. D

ikes

in T

iger

Gul

ch c

onta

in

anhe

dral

sani

dine

and

qua

rtz p

heno

crys

ts 1

–6 m

m (0

.04–

0.24

in) l

ong

in a

fin

e-gr

aine

d m

atrix

of f

elds

par a

nd c

lay,

and

are

typi

cally

hyd

roth

erm

ally

alte

red.

D

ump

spec

imen

s at T

ier G

ulch

are

inte

nsel

y si

licifi

ed. I

ntru

sive

rhyo

lite

in th

e m

ount

ain

area

is h

ydro

ther

mal

ly a

ltere

d an

d co

mm

only

con

tain

s dis

sem

inat

ed p

yrite

. A

fter L

oen,

199

0.

Trp

Rhy

olite

por

phyr

y (T

ertia

ry: E

ocen

e)—

Porp

hyrit

ic rh

yolit

e la

va fl

ows a

re ty

pica

lly

gray

, whi

te, t

an, r

ed, a

nd/o

r pur

ple

wea

ther

ing.

Cen

timet

er- t

o m

eter

-sca

le fl

ow

folia

tions

giv

e rh

yolit

e ou

tcro

ps a

blo

cky

wea

ther

ing

char

acte

ristic

. Phe

nocr

ysts

co

mpo

se u

p to

30%

of t

he ro

ck a

nd in

clud

e qu

artz

, san

idin

e, o

ligoc

lase

, bio

tite,

and

am

phib

ole

in a

mat

rix o

f gla

ss, c

lay,

and

cry

ptoc

ryst

allin

e m

ater

ial.

Dev

itrifi

catio

n of

th

e m

atrix

var

ies f

rom

non

e to

com

plet

e. L

ithop

hysa

e up

to 1

0 ce

ntim

eter

s in

diam

eter

ar

e lo

cally

abu

ndan

t and

typi

cally

ero

ded

and

parti

ally

fille

d w

ith c

halc

edon

y.

Dis

cont

inuo

us z

ones

of v

itrop

hyre

and

aut

obre

ccia

sepa

rate

indi

vidu

al fl

ows.

Kqm

Q

uart

z m

onzo

nite

of t

he B

lack

foot

City

stoc

k (U

pper

Cre

tace

ous)

—M

ediu

m-

grai

ned,

hyp

idio

mor

phic

gra

nula

r, eq

uigr

anul

ar, a

nd p

orph

yriti

c, b

iotit

e-ho

rnbl

ende

m

onzo

nite

, qua

rtz m

onzo

nite

, and

gra

nodi

orite

. Com

posi

tion

45%

pla

gioc

lase

, 8–2

0%

pota

ssiu

m fe

ldsp

ar, 1

6–25

% q

uartz

, 8–1

0% h

ornb

lend

e, 4

–7%

bio

tite.

Por

phyr

itic

and

folia

ted

near

con

tact

s. B

iotit

e yi

elde

d a

K-A

r age

of 7

7 M

a. A

fter S

chm

idt a

nd o

ther

s, 19

94.

P*M

Ph

osph

oria

and

Qua

dran

t For

mat

ions

, and

Sno

wcr

est R

ange

Gro

up, u

ndiv

ided

(P

erm

ian

thro

ugh

Upp

er M

issi

ssip

pian

)

Ph

osph

oria

For

mat

ion

(Per

mia

n)—

Gra

y fin

e- to

med

ium

-gra

ined

qua

rtz a

reni

te a

t to

p, g

ray

to p

ale

brow

n, th

inly

inte

rbed

ded

oolit

ic, p

hosp

hatic

sand

ston

e, sh

ale,

and

ch

ert i

n th

e m

iddl

e, a

nd y

ello

wis

h lim

esto

ne, c

herty

lim

esto

ne, s

iltst

one,

and

qua

rtz

aren

ite a

t bot

tom

. Thi

ckne

ss a

bout

50

m (1

60 ft

).

Q

uadr

ant F

orm

atio

n (P

enns

ylva

nian

)—G

ray

to ta

n, th

ick-

bedd

ed, v

itreo

us,

fine-

grai

ned

quar

tzite

. Thi

ckne

ss 4

5 m

(145

ft).

Afte

r Sch

mid

t and

oth

ers,

1994

.

Sn

owcr

est R

ange

Gro

up (L

ower

Pen

nsyl

vani

an to

Upp

er M

issi

ssip

pian

)—R

ed,

purp

le, g

ray,

and

tan

shal

e an

d si

ltsto

ne w

ith in

terb

edde

d re

d, y

ello

w, a

nd g

ray

limes

tone

and

dol

omite

. Abo

ut 4

0 m

(130

ft) t

hick

. Afte

r Sch

mid

t and

oth

ers,

1994

.

Mm

M

adis

on G

roup

(Upp

er a

nd L

ower

Mis

siss

ippi

an)—

Upp

er p

art i

s gra

y, m

assi

ve

bios

parit

e, b

iom

icrit

e, a

nd m

icrit

e. L

ower

par

t is t

hin-

bedd

ed g

ray

limes

tone

that

co

ntai

ns sc

atte

red

dark

gra

y, b

lack

, and

bro

wn

cher

t nod

ules

and

lens

es. T

hick

ness

450

m

(1,4

60 ft

). A

fter S

chm

idt a

nd o

ther

s, 19

94.

Dj

Jeff

erso

n Fo

rmat

ion

(Upp

er D

evon

ian)

—G

ray

to b

lack

, thi

ck-b

edde

d, c

oars

ely

crys

talli

ne, f

etid

dol

omite

with

thin

inte

rbed

s of l

ight

gra

y lim

esto

ne. T

hick

ness

230

m

(750

ft).

Afte

r Sch

mid

t and

oth

ers,

1994

.

D_m

M

ayw

ood,

Red

Lio

n, a

nd P

ilgri

m F

orm

atio

ns, u

ndiv

ided

(Upp

er D

evon

ian

to U

pper

C

ambr

ian)

May

woo

d Fo

rmat

ion

(Upp

er D

evon

ian)

—R

ed, g

ray,

and

gra

yish

gre

en sh

ale,

si

ltsto

ne, l

imes

tone

, and

dol

omite

. App

roxi

mat

ely

10 m

(30

ft) th

ick.

Afte

r Sch

mid

t an

d ot

hers

, 199

4.R

ed L

ion

Form

atio

n (U

pper

Cam

bria

n)—

Ligh

t gra

y m

ediu

m- t

o th

in-b

edde

d co

ntai

ning

thin

inte

rbed

s of o

rang

e an

d re

d w

eath

erin

g si

liceo

us a

nd a

rgill

aceo

us

dolo

mite

. Abo

ut 1

00 m

(325

ft) t

hick

. Afte

r Sch

mid

t and

oth

ers,

1994

.Pi

lgri

m F

orm

atio

n (U

pper

Cam

bria

n)—

Ligh

t gra

y, m

assi

ve to

thin

ly la

min

ated

, fin

ely

crys

talli

ne a

nd m

icro

crys

talli

ne d

olom

ite. A

bout

185

m (6

00 ft

) thi

ck. A

fter

Schm

idt a

nd o

ther

s, 19

94.

_pm

Pa

rk a

nd M

eagh

er F

orm

atio

ns, u

ndiv

ided

(Mid

dle

Cam

bria

n)Pa

rk F

orm

atio

n (M

iddl

e C

ambr

ian)

—G

rayi

sh g

reen

fiss

ile, w

axy

shal

e an

d in

terb

edde

d si

ltsto

ne a

nd g

ray

limes

tone

. Ver

y po

orly

exp

osed

. App

roxi

mat

ely

80 m

(2

60 ft

) thi

ck. A

fter S

chm

idt a

nd o

ther

s, 19

94.

Mea

gher

For

mat

ion

(Mid

dle

Cam

bria

n)—

Gra

y th

in- t

o th

ick-

bedd

ed m

icrit

e an

d bi

omic

rite

cont

aini

ng d

istin

ctiv

e th

in in

terb

eds o

f une

ven

and

disc

ontin

uous

gol

d an

d or

ange

wea

ther

ing

silic

eous

and

arg

illac

eous

dol

omite

. Thi

ckne

ss a

ppro

xim

atel

y 18

0 m

(590

ft).

Afte

r Sch

mid

t and

oth

ers,

1994

.

_wf

Wol

sey

and

Flat

head

For

mat

ions

, und

ivid

ed (M

iddl

e C

ambr

ian)

Wol

sey

Form

atio

n (M

iddl

e C

ambr

ian)

—G

reen

ish

gray

mic

aceo

us sh

ale

and

glau

coni

tic si

ltsto

ne in

terb

edde

d w

ith th

in b

eds o

f gra

y lim

esto

ne n

ear t

he to

p an

d w

ith g

lauc

oniti

c qu

artz

ite n

ear t

he b

ase.

Ver

y po

orly

exp

osed

. Thi

ckne

ss

appr

oxim

atel

y 90

–120

m (2

95–3

90 ft

). A

fter S

chm

idt a

nd o

ther

s, 19

94.

Flat

head

For

mat

ion

(Mid

dle

Cam

bria

n)—

Gra

y to

pur

ple,

thin

- to

thic

k-be

dded

fin

e- to

med

ium

-gra

ined

to c

ongl

omer

atic

, cro

ssbe

dded

qua

rtz a

reni

te. C

onta

ins

com

mon

wel

l-rou

nded

coa

rse

quar

tz g

rain

s. Th

ickn

ess 0

–30

m (0

–100

ft).

Afte

r Sc

hmid

t and

oth

ers,

1994

.

Ym

M

cNam

ara

Form

atio

n (M

esop

rote

rozo

ic)—

Cou

plet

s and

mic

roco

uple

ts o

f var

iega

ted

red

and

gree

n fin

e-gr

aine

d qu

artz

ite, s

iltite

, and

wax

y ar

gilli

te c

onta

inin

g di

agno

stic

re

d or

gre

en c

hert

beds

and

che

rt rip

-up

clas

ts. M

ud c

rack

s and

mud

rip-

up c

last

s co

mm

on. T

op p

art i

s lig

ht g

ray,

thic

k-be

dded

, fin

e- to

med

ium

-gra

ined

, cro

ssbe

dded

qu

artz

ite c

onta

inin

g ab

unda

nt re

d m

ud ri

p-up

cla

sts,

unco

mm

on re

d ch

ert r

ip-u

p cl

asts

, and

abu

ndan

t thi

n, re

d, m

ud c

rack

ed a

rgill

ite in

terb

eds.

Abo

ut 7

70 m

(2,5

00 ft

) th

ick.

Ybo

B

onne

r Fo

rmat

ion

(Mes

opro

tero

zoic

)—Pi

nk to

red,

med

ium

- to

coar

se-g

rain

ed, p

oorly

so

rted,

ver

y fe

ldsp

athi

c qu

artz

ite. A

bund

ant t

roug

h an

d pl

anar

cro

ssbe

ds in

bed

s ty

pica

lly 0

.5–1

.0 m

thic

k. B

eds o

ften

sepa

rate

d by

thin

(0.1

–1.0

cm

) red

to m

aroo

n ar

gilli

te b

eds.

Con

tain

s abu

ndan

t wel

l-rou

nded

coa

rse

quar

tz g

rain

s, an

d sp

arse

su

bang

ular

gra

nule

s and

smal

l peb

bles

. Fiv

e sl

abbe

d an

d st

aine

d sa

mpl

es c

onta

ined

50

–75

perc

ent q

uartz

, 15–

35 p

erce

nt p

otas

sium

feld

spar

, and

5–1

5 pe

rcen

t pl

agio

clas

e. P

oorly

exp

osed

con

tact

s mak

e th

ickn

ess e

stim

ates

pro

blem

atic

, but

are

re

porte

d to

be

460

m (1

,495

ft) t

hick

in th

is a

rea

(Sch

mid

t and

oth

ers,

1994

).

Ym

s3

Mou

nt S

hiel

ds F

orm

atio

n, m

embe

r 3

(Mes

opro

tero

zoic

)—R

ed q

uartz

ite to

arg

illite

co

uple

s and

cou

plet

s with

abu

ndan

t mud

cra

cks,

mud

chi

ps, a

nd d

iagn

ostic

, w

ell-f

orm

ed c

ubic

salt

cast

s. In

clud

es g

reen

inte

rbed

s and

som

e re

d m

icro

lam

inae

. A

bout

275

m (9

00 ft

) thi

ck o

n th

e no

rth-a

djac

ent N

evad

a M

ount

ain

7.5'

qua

dran

gle

(McD

onal

d an

d Lo

nn, 2

015)

.

Ym

s2

Mou

nt S

hiel

ds F

orm

atio

n, m

embe

r 2

(Mes

opro

tero

zoic

)—Pi

nk to

red,

poo

rly so

rted,

m

ediu

m- t

o co

arse

-gra

ined

, fel

dspa

thic

qua

rtzite

. Abu

ndan

t pla

nar a

nd tr

ough

cr

ossb

eds.

Con

tain

s spa

rse

suba

ngul

ar g

ranu

les.

Low

er p

art i

s thi

nner

bed

ded,

co

nsis

ting

of c

oupl

es o

f whi

te to

pin

k, m

ediu

m-g

rain

ed q

uartz

ite a

nd th

in re

d ar

gilli

te

that

con

tain

abu

ndan

t red

mud

chi

ps a

t the

bas

es o

f the

qua

rtzite

bed

s and

was

in

clud

ed in

the

top

part

of m

embe

r 1 o

f Sch

mid

t and

oth

ers (

1994

). In

con

trast

to

Bon

ner F

orm

atio

n, w

hich

has

pot

assi

um fe

ldsp

ar in

exc

ess o

f pla

gioc

lase

, tw

o sl

abbe

d an

d st

aine

d sa

mpl

es c

onta

ined

65–

75 p

erce

nt q

uartz

, 5–1

5 pe

rcen

t pot

assi

um

feld

spar

, and

20

perc

ent p

lagi

ocla

se. V

ery

diffi

cult

to d

istin

guis

h in

the

field

and

in

hand

sam

ple

from

the

Bon

ner F

orm

atio

n (u

nit Y

bo

). Th

ickn

ess a

ppro

xim

atel

y 46

0 m

(1

,500

ft).

Ysh

Sh

epar

d Fo

rmat

ion

(Mes

opro

tero

zoic

)—D

olom

itic

and

non-

dolo

miti

c, d

ark

gree

n si

ltite

and

ligh

t gre

en a

rgill

ite in

mic

rola

min

ae a

nd c

oupl

ets o

f non

-dol

omiti

c re

d qu

artz

ite to

arg

illite

. Poo

rly e

xpos

ed, b

ut w

eath

ers i

nto

thin

pla

tes t

hat w

hen

dolo

miti

c ha

ve a

cha

ract

eris

tic o

rang

ish

brow

n w

eath

erin

g rin

d. R

ippl

es a

nd lo

ad

cast

s are

com

mon

; mud

cra

cks a

re ra

re. T

he u

pper

hal

f con

tain

s int

erva

ls o

f pin

k to

gr

ay fi

ne-g

rain

ed fe

ldsp

athi

c qu

artz

ite th

at w

ere

incl

uded

in M

ount

Shi

elds

mem

ber 1

by

Sch

mid

t and

oth

ers (

1994

). H

owev

er, w

e pl

ace

the

uppe

r con

tact

at t

he to

p of

a 5

0 m

(160

ft) t

hick

inte

rval

of d

istin

ctiv

e ro

se-c

olor

ed d

olom

itic

silti

te–a

rgill

ite c

oupl

ets

as w

as d

one

in a

reas

to th

e w

est (

Lonn

and

oth

ers,

2010

). Th

e lo

wer

con

tact

is p

lace

d at

the

botto

m o

f the

low

est d

olom

ite-b

earin

g be

ds, a

lthou

gh in

are

as to

the

wes

t the

Sn

owsl

ip F

orm

atio

n al

so c

onta

ins d

olom

ite-b

earin

g in

terv

als (

Lonn

and

oth

ers,

2010

). A

cal

citic

stro

mat

olite

bed

is ty

pica

lly fo

und

near

the

base

. Thi

ckne

ss is

abo

ut

650

m (2

,100

ft),

sim

ilar t

o th

at in

the A

ustin

7.5

' qua

dran

gle

to th

e ea

st (B

erg

and

Lonn

, 201

1).

Ysn

Sn

owsl

ip F

orm

atio

n (M

esop

rote

rozo

ic)—

Inte

rbed

ded

inte

rval

s of q

uartz

ite to

red

argi

llite

cou

plet

s, an

d da

rk g

reen

silti

te to

ligh

t gre

en a

rgill

ite c

oupl

ets a

nd

mic

rola

min

ae. D

esic

catio

n cr

acks

and

mud

rip-

up c

last

s are

com

mon

thro

ugho

ut.

Arg

illite

bed

s ofte

n co

ntai

n irr

egul

ar “

bum

ps”

that

may

be

ill-d

efin

ed sa

lt ca

sts o

r st

ruct

ures

rela

ted

to a

lgal

mat

s. C

onta

ins b

eds a

nd le

nses

of d

istin

ctiv

e w

hite

, co

arse

-gra

ined

, wel

l-sor

ted,

feld

spar

-poo

r qua

rtzite

that

con

tain

s som

e w

ell-r

ound

ed,

fros

ted

quar

tz g

rain

s. Lo

wer

50

m (1

60 ft

) dom

inat

ed b

y m

icro

lam

inat

ed g

reen

do

lom

itic

silti

te a

nd a

rgill

ite. U

pper

50–

75 m

(160

–245

ft) i

s red

, fla

t-lam

inat

ed

med

ium

-gra

ined

qua

rtzite

in b

eds 0

.5–1

.0 m

eter

s thi

ck. T

hick

ness

app

roxi

mat

ely

1,07

5 m

(3,5

00 ft

) on

the

north

-adj

acen

t Nev

ada

Mou

ntai

n qu

adra

ngle

(McD

onal

d an

d Lo

nn, 2

015)

.

Ref

eren

ces

Ber

g, R

.B.,

and

Lonn

, J.D

., 20

11, G

eolo

gic

map

of t

he A

ustin

7.5

' qua

dran

gle,

cen

tral M

onta

na:

Mon

tana

Bur

eau

of M

ines

and

Geo

logy

Ope

n-Fi

le R

epor

t 603

, 10

p., s

cale

1:2

4,00

0.*B

ierw

agen

, E.E

., 19

64, G

eolo

gy o

f the

Bla

ck M

ount

ain

area

, Lew

is a

nd C

lark

, and

Pow

ell

Cou

ntie

s, M

onta

na: P

rince

ton,

N.J.

, Prin

ceto

n U

nive

rsity

, Ph.

D. d

isse

rtatio

n, 2

31 p

.*L

oen,

J.S.

, 199

0, L

ode

and

plac

er g

old

depo

sits

in th

e O

phir

Dis

trict

, Pow

ell,

and

Lew

is a

nd

Cla

rk C

ount

ies,

Mon

tana

: For

t Col

lins,

Col

o., C

olor

ado

Stat

e U

nive

rsity

, Ph.

D.

diss

erta

tion,

268

p.

Lonn

, J.D

., M

cDon

ald,

C.,

Sear

s, J.W

., an

d Sm

ith, L

.N.,

2010

, Geo

logi

c m

ap o

f the

Mis

soul

a Ea

st 3

0' x

60'

qua

dran

gle,

wes

tern

Mon

tana

: Mon

tana

Bur

eau

of M

ines

and

Geo

logy

O

pen-

File

Rep

ort 5

93, 2

shee

ts, s

cale

1:1

00,0

00.

McD

onal

d, C

., an

d Lo

nn, J

.D.,

Geo

logi

c m

ap o

f the

Nev

ada

Mou

ntai

n an

d G

rani

te B

utte

qu

adra

ngle

s, w

est-c

entra

l Mon

tana

: Mon

tana

Bur

eau

of M

ines

and

Geo

logy

O

pen-

File

Rep

ort 6

65, s

cale

1:2

4,00

0.*S

chm

idt,

R.G

., Lo

en, J

.S.,

Wal

lace

, C.A

., an

d M

ehne

rt, H

.H.,

1994

, Geo

logy

of t

he E

llist

on

regi

on, P

owel

l, an

d Le

wis

and

Cla

rk C

ount

ies,

Mon

tana

: U.S

. Geo

logi

cal S

urve

y B

ulle

tin 2

45, 2

5 p.

, sca

le 1

:62,

500.

Sear

s, J.W

., an

d H

endr

ix, M

., 20

04, L

ewis

and

Cla

rk L

ine

and

the

rota

tiona

l orig

in o

f the

Alb

erta

an

d H

elen

a sa

lient

s, N

orth

Am

eric

an C

ordi

llera

, in

Suss

man

, A.J.

, and

Wei

l. A

.B.,

Oro

geni

c C

urva

ture

: Int

egra

ting

Pale

omag

netic

and

Stru

ctur

al A

naly

ses:

Geo

logi

cal

Soci

ety

of A

mer

ica

Spec

ial P

aper

383

, p. 1

73–1

86.

Win

ston

, Don

, 198

6, S

edim

enta

tion

and

tect

onic

s of t

he M

iddl

e Pr

oter

ozoi

c B

elt B

asin

, and

thei

r in

fluen

ce o

n Ph

aner

ozoi

c co

mpr

essi

on a

nd e

xten

sion

in w

este

rn M

onta

na a

nd

north

ern

Idah

o, in

Pet

erso

n, J.

A.,

ed.,

Pale

otec

toni

cs a

nd S

edim

enta

tion

in th

e R

ocky

M

ount

ain

Reg

ion,

Uni

ted

Stat

es: A

mer

ican

Ass

ocia

tion

of P

etro

leum

Geo

logi

sts

Mem

oir 4

1, p

. 87–

118.

*Sou

rces

of g

eolo

gic

map

info

rmat

ion

Qac

Qaf

Qal

Qalo

Qgo

Qgr

Qgt

Qls

Qm

Taf

Tba

Tgr

Trca

Tri

Trp

P*Mps

Mm

D_mp

Dj

_m

_pm

_wf

Ybo

Ym

Yms2

Yms3

Ysh

Ysn

Kqm

11/

20

1 M

ILE

SC

ALE

1:2

4,00

0

1000

010

0020

0030

0040

0050

0060

0070

00 F

EE

T

1.5

01

KIL

OM

ETE

R

CO

NTO

UR

INTE

RVA

L 40

FE

ET

NAT

ION

AL

GE

OD

ETI

C V

ER

TIC

AL

DAT

UM

OF

1929

Bas

e m

ap p

rodu

ced

by th

e U

nite

d St

ates

Geo

logi

cal S

urve

yC

ontro

l by:

US

GS

, NO

S/N

OA

A an

d U

SFS

Com

pile

d fro

m a

eria

l pho

togr

aphs

take

n 19

84Fi

eld

chec

ked:

198

5; M

ap e

dite

d: 1

989

Pro

ject

ion:

Lam

bert

Con

form

al C

onic

Grid

:100

0 m

eter

Uni

vers

al T

rans

vers

e M

erca

tor Z

one

12U

TM g

rid d

eclin

atio

n: 1

° 08

' Eas

t19

89 M

agne

tic N

orth

Dec

linat

ion:

16°

30'

Eas

tVe

rtica

l Dat

um: N

atio

nal G

eode

tic V

ertic

al D

atum

of 1

929

Hor

izon

tal D

atum

: 192

7 N

orth

Am

eric

an D

atum

Loca

tion

Map

90

94

15

15

90

90

Kal

ispe

ll

Mis

soul

a

Hel

enaGre

at F

alls

Bill

ings

Boz

eman

But

te

116°

104°

106°

108°

110°

112°

114°

49° 45

°

46°

47°

48°

MO

NT

AN

A

100

010

0 M

iles

160

016

0 K

ilom

eter

sAv

onE

llist

on

Finn

Oph

irC

reek

Gra

nite

B

utte

Esm

eral

da

Hill

Luke

M

ount

ain

Gra

vely

M

ount

ain

Nev

ada

Mou

ntai

n

MO

NTA

NA

BU

REA

U O

F M

INES

AN

D G

EOLO

GY

A D

epar

tmen

t of M

onta

na T

ech

of T

he U

nive

rsity

of M

onta

naM

BM

G O

pen-

File

Rep

ort 6

66; P

late

1 o

f 1G

eolo

gic

Map

of t

he O

phir

Cre

ek 7

.5' Q

uadr

angl

e, 2

015

Com

pile

d an

d m

appe

d by

Jeffr

ey D

. Lon

n an

d Su

san

M. V

uke

201

5

N

MB

MG

Ope

n-Fi

le R

epor

t 666

Map

s m

ay b

e ob

tain

ed fr

om:

Pub

licat

ions

Offi

ce

Mon

tana

Bur

eau

of M

ines

and

Geo

logy

1300

Wes

t Par

k S

treet

But

te, M

onta

na 5

9701

-899

7P

hone

: (40

6) 4

96-4

167

Fax

: (40

6) 4

96-4

451

http

://w

ww

.mbm

g.m

tech

.edu

Parti

al su

ppor

t has

bee

n pr

ovid

ed b

y th

e ST

ATEM

AP

com

pone

nt o

f the

Nat

iona

l Coo

pera

tive

Geo

logi

c M

appi

ng P

rogr

am o

f the

U.S

. Geo

logi

cal S

urve

y un

der c

ontra

ct n

umbe

r G12

AC

2027

7.

GIS

pro

duct

ion:

Yiw

en L

i, K

en S

anda

u an

d Pa

ul T

hale

, MB

MG

. Map

layo

ut: S

usan

Sm

ith, M

BM

G.

Geo

logi

c M

ap o

f the

Oph

ir C

reek

7.

5' Q

uadr

angl

e, L

ewis

and

Cla

rk,

and

Pow

ell C

ount

ies,

Mon

tana