UNITED STATES DEPARTMENT OF THE INTERIOR

Base from U. S. Geological Survey map of
the Johnson Creek quadrangle, Idaho

M R1293

and S.E. Clabaugh, 1948-50, aided by
E. R. Cressman, N. K, Flint, S. Tuttle, and J.

Krauskopf,
|. Hill

Bend in section

SSSssss=:

BULLETIN 1042 PLATE 1
GEOLOGICAL SURVEY shonerr
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; 111°30° R. 42 E.R. 43 E. 27'30" 25! inteRIoR—GEOLOGICAL SURVEY. WASHINGTON, D.c. Geology by R.A. Gulbrandsen, K. P. McLaughlin, F. S. Honkala 11 1°22’30””

Thaynes formation

Dinwoody formation

Phosphoria formation

Wells formation

L

EXPLANATION

Qal

Alluvium
Mostly fine-grained sediments

ANGULAR UNCONFORMITY

Conglomerate, travertine, and gravel
ANGULAR UNCONFORMITY

Member D

Poorly exposed thick-bedded gray limestone
‘and brown sandstone, possibly as much as
500 fect thick. Top of Thaynes formation
not represented

Thick-bedded brownish-gray calcareous silt-
stone with irregular bedding surfaces, con-
tains gray limestone nodules and lenses and
some fissile gray siltstone at base; 500 to 900

‘feet thick

Member B

Thin-bedded calcareous siltstone, weathers to
light-brown, large, smooth, thin plates that
tend to thicken and whose surfaces are irreg-
ular in upper part; 600 to 800 feet thick

ess

Member A
Fissile and thin-bedded dark-gray and brown
calcareous siltstone and tee beled black
brittle limestone; basal 10 to 20 feet composed
of gray limestone and thin bedded calcareous
eae that contain the regionally distine-
tive Meekoceras fauna; 500 to 800. feet thick

Thick-bedded (as much as 8 feet) gray limestone
with some interbedded thin- and thick-bedded
olive-gray siltstone; 800 to 1200 feet thick

Me

Lower member
Dusky-yellow and light-olive-gray shale, fissile
‘in part, containing some very fossiliferous
limestone beds generally less than 1 foot in
thickness that weather purplish and brown-
ish-gray; grades upward to thick-bedded
calcareous siltstone that weathers brownish-
gray and black; 1000 to 1400 feet thick in

most pl
Par |

Rex chert member
Massive medium-gray to black ledge-forming
chert; lower half is very distinctive over

the region; upper half consiste of poorly ex-
pooed Uen-bedded dark gray to black chert;
200 to 300 feet thick

Phosphatic shale member
‘No natural exposures; in trenches it is grayish-

brown to black shale including a lower phos-
phate zone, a. middle mudstone zone, and an
upper phosphate zone; some limestone beds
are present; phosphate rock is generally
oolitie; 100 to 200 feet thick in most places

E

Upper member

Thick-bedded brown and gray sandstone with
some interbedded limestone; very distinctive
thick-bedded gray limestone in upper 30 feet
contains silicified fossils (mostly brachio-
pods) and lenses and beds of black and bluish-
gray chert; used as marker for overlying
phosphate beds; 1100 to 1300 feet thick

\\

Lower member

Thick-bedded gray limestone with abundant
‘fossil fragments and calcareous sandstone,
‘weathering brownish-gray; about 800 or 900
Seet thick

Brazer limestone
Distinctive ledge-forming massive gray lime-
stone and perp and brown sandstone
‘in lower part; limestone contains large silici-
fied horn corals; about 1000 feet thick; base
not exposed

Long dashed where approximately located,
short dashed where gradational, indefinite,
or inferred; queries indicate doubiful position

Limit of outcrop

Strike and dip symbols outside of outcrop areas
indicate location of outcrops of unmappable size
ee

U_ Fault
Dashed where approximately located or infer-
red, dotted where covered; U, upthrown

side; D, downthrown side; queries indicate
doubtful position

Showing location of trace of axial plane, dashed
where approximately located, dotted where
concealed; queries indicate doubtful position

Bisa

Showing approximate location of trace of axial
plane, dotted where concealed; queries indi-
cate doubtful position

eo |
Overturned anticline
Showing approximate location of trace of axial
plane; queries indicate doubtful position

ae aS
Overturned syncline

Showing approsimate location of trace of axial
plane; queries indicate doubtful pen be

oes
Plunge of minor anticline
“25
Strike and dip of beds
ao
Strike and dip of overturned beds
=e?
Strike of vertical beds

@
Horizontal beds
x
Portal of adit

Trench or prospect pit
1206 and 1209 are lot numbers of
sampling-program trenches

io}
Diamond-drill hole

1274, 1275, and 1276 are lot numbers
of sampling-program drill holes

TRUE NORTH

APPROXIMATE MEAN
DECLINATION 1949

GEOLOGIC MAP AND SECTIONS OF THE JOHNSON CREEK QUADRANGLE, CARIBOU COUNTY, IDAHO

Scale 1:24,000
0

1Mile

Contour interval 20 feet
Datum is mean sea level

TERTIARY QUATERNARY

QUATERNARY (?)

TRIASSIC

PERMIAN

PENNSYLVANIAN Pine

MISSISSIPPIAN

CARBONIFEROUS