Any use of trade, firm, or product names is for descriptive purposes 

only and does not imply endoresement by the U.S. Government.

If printed on an electronic plotter directly from digital files, note that 

dimensional calibration may vary between electronic plotters and 

between X and Y directions on the same plotter, and paper 

may change size due to atmospheric conditions; therefore, scale and 

proportions may not be true on plots of this map.

Digital files available at https://doi.org/10.3133/sim3215

Suggested citation: Oberlindacher, H.P., Hovland, R.D., Miller, S.T. , 

Evans, J.G., and Miller, R.J., 2018, Geologic map of the Lower Valley 

quadrangle, Caribou County, Idaho: U.S. Geological 

Survey Scientific Investigations Map 3215, 6 p., 1 sheet, scale 

1:24,000, https://doi.org/10.3133/sim3215.

Geologic Map of the Lower Valley Quadrangle, Caribou County, Idaho

By

H. Peter Oberlindacher, R. David Hovland, Susan T. Miller, James G. Evans, and Robert J. Miller

2018 ISSN 2329-132X (online)

https://doi.org/10.3133/sim3215

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B-2

1 Table 1. Potassium-argon age determination.

number K-Ar age Description, unit 

B-1 2.1 ± 0.9 Ma basalt, QTb

By Teledyne Isotopes Inc., Westwood, New Jersey, 1981

B-3 1.6 ± 0.7 Ma basalt, QTb

B-2 2.2 ± 1.0 Ma basalt, QTb

Sample

1

Disturbed surface, as of field mapping in 1979 and 1980; may include open pits, waste disposal areas, and mining 

facilities; where dsm overlaps with disturbed surface as of 1984 photorevision, dsm is generally less extensive, and faults, contacts, and structures are commonly concealed, except in open pits that have not been 

backfilled

Alluivum (Holocene)—Unconsolidated, poorly sorted gravel, sand, silt, and clay

Surficial deposits (Holocene and Pleistocene)—Undifferentiated older alluvium and hillwash

Basalt (Pleistocene or Pliocene)—Dark gray crystalline vesicular olivine basalt; sample B-1 was dated at 2.1 ± 0.9 

Ma; sample B-2 was dated at 2.2 ± 1.0 Ma, sample B-3 was dated at 1.6 ± 0.7 Ma (Teledyne Isotopes, written 

commun., 1981, see table 1)

Sedimentary deposits (Quaternary and (or) Tertiary)

Landslide deposits (Quaternary and (or) Tertiary)

Thaynes Formation (Lower Triassic)

Portneuf Limestone Member

Upper part—Yellowish-beige to reddish-brown sandstone and blue-gray limestone; local crossbedding and 

dolomitization of sandstone; limestone locally contains gray chert nodules; about 107 m thick, top not exposed

Lower part—Gray limestone, generally cliff-forming; minor very fine-grained sandstone and siltstone; about 

153 m thick

Member C—Olive to brown siltstone containing dark-gray limestone nodules in upper part; interbedded with 

yellowish-brown sandstone and limestone near top; gray to black fissile siltstone and minor dark-gray 

limestone in lower part; about 213 m thick

Member B—Yellowish-brown calcareous platy siltstone and minor nodular gray limestone; about 183 m thick

Member A—Dark-gray to black silty limestone; Meekoceras ammonite zone at base; 

 about 168 m thick

Ankareh Formation (Lower Triassic)

Lanes Tongue—Reddish-brown to red sandstone and siltstone; 60 m thick; top not exposed; where present, 

separates upper and lower parts of the Portneuf Limestone Member of the Thaynes Formation

Dinwoody Formation (Lower Triassic)—Consists mainly of interbedded siltstone, limestone, and subordinate 

sandstone. The true thickness of the Dinwoody Formation in the quadrangle cannot be determined because of 

poor exposure and structural complications. Cross-sectional data yield a thickness of about 519–610 meters. 

The Dinwoody Formation is mapped as undifferentiated except in the southern part of the quadrangle, where it 

is divided into five informal units:

Upper part—Brownish-gray limestone and siltstone 

Middle and upper parts—Undifferentiated

Middle part—Blocky-weathering olive-gray to brownish-gray siltstone and minor very fine-grained sandstone 

and limestone

Lower and middle parts—Undifferentiated

Lower part—Olive-gray shaly siltstone and minor silty limestone 

Phosphoria Formation (lower Permian)

Cherty shale member—Dark-gray to grayish brown cherty siltstone and mudstone and minor phosphatic 

siltstone and phosphatic mudstone; 48 m thick

Rex Chert and cherty shale members—Undifferentiated

Rex Chert Member—Gray to bluish-gray chert, locally light gray to white; minor argillaceous chert; ledge 

forming; 10–12 m thick

Meade Peak Phosphatic Shale Member—Dark-brown phosphorite, siltstone, mudstone and minor limestone 

and sandstone; phosphorite concentrated in upper and lower parts of member; swale-forming; rarely exposed; 

about 40–50 m thick

Park City Formation (lower Permian)

Grandeur Tongue—Light-gray to brownish-gray dolomite and minor siltstone, chert, and phosphatic chert; 

ledge-forming

Wells Formation (Permian and Pennsylvanian)

Upper member (lower Permian)—Brownish-gray to reddish-brown quartzose sandstone and quartzite and 

dark- to light-gray dolomite beds, lenses, and nodules; quartzose sandstone and quartzite are locally 

crossbedded; about 520 m thick

Lower member (lower Permian and Middle Pennsylvanian)—Gray limestone and quartzite and siltstone; 

limestone locally cherty and sandy; 293 to 316 m thick

Phosphatic marker bed—In upper part of lower member of Wells Formation; a 0.5- to 1.2-m-thick 

phosphorite and phosphatic silty mudstone bed occurs 33 m below top of formation

Chesterfield Range Group (Upper Mississippian)

Monroe Canyon Limestone—Dark gray limestone and minor siltstone and sandstone; locally dolomitic; 

contains large horn corals and brachiopods near top of formation; at least 281 m thick; base not exposed

EXPLANATION OF MAP SYMBOLS 

Disturbed surface, as 1984 photorevision; present topography differs from that shown on map; faults, contacts, 

and structures originally mapped in disturbed surface areas may be concealed, or removed, or their 

locations may be altered as a result of subsequent mining activity; open pits, where present, are large 

elongate trenches that follow the locus of the Meade Peak Phosphatic Shale Member of the Phosphoria 

Formation; may include dsm

Contact—Dotted where concealed; dashed where approximate

Fault—Dotted where concealed

Normal fault—Ball and bar on downthrown side 

Strike-slip fault—Arrows indicate relative horizontal movement

Thrust fault—Sawteeth on upper plate

Generic fault—Unknown or unspecified orientation

Fold—Showing trace of axial surface; dotted where concealed

Anticline—Showing crestline and direction of plunge

Syncline—Showing troughline and direction of plunge 

Overturned anticline—Showing crestline and direction of plunge 

Overturned syncline—Showing troughline and direction of plunge 

Strike and dip of bedding

Strike and dip of overturned bedding

Horizontal bedding

Sample location for K-Ar determination (see table 1)

DESCRIPTION OF MAP UNITS

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

Holocene

Holocene and 

Pleistocene

Pleistocene or

Pliocene

Lower Triassic

Lower Permian

Lower Permian and

Middle Pennsylvanian

Upper Mississippian

QUATERNARY

QUATERNARY AND (OR) TERTIARY

TRIASSIC

PERMIAN

PERMIAN AND

PENNSYLVANIAN

MISSISSIPPIAN

CORRELATION OF MAP UNITS

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IDAHO

MAP LOCATION

SCALE 1:24,000

1 .5 0 1 MILE

1 .5 0 1 KILOMETER

APPROXIMATE MEAN

DECLINATION, 2018

111

/

2

°

MAGNETIC NORTH

TRUE NORTH

Base from U.S. Geological Survey

1:24,000 Lower Valley, 1984

Transverse Mercator

UTM 1927

Zone 12

Geology mapped in 1979 and 1980 by H. Peter 

Oberlindacher, R. David Hovland, and Susan T. 

Miller and compiled in 1998 by James G. Evans.

GIS database and digital cartography by Robert J. 

Miller and Barry C. Moring.

Edited by Claire Landowski; digital cartographic 

production by Donna L. Knifong

Manuscript approved for publication May 5, 2012

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3215

Pamphlet accompanies map

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0

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ENOCH

VALLEY

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WOOLEY

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111°22'30

111°22'30"

111°30'

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42°52'30" 42°52'30"

42°45' 42°45'