Bannock County, Idaho

PPPs Qs Qw Qa Qw TRs Qa Qw OCs Qw 43o00’00” Ms Qw Cs Tps American 91 Os Qw Cs CZb Falls Qs Tps CZb Res Qbf Ss Qa Cs Cs Chubbuck 15 86 Tps CZb Cs Pocatello Zp CZb Tov Qbf Cs CZb CZb CZb 91 Zp CZb Cs Zp Qs o CZb Qb Cs 42 50’00” InkomInkom CZb Qa Qb CZb Cs Tps Zp Qb Tps Bonneville CZb Qw Cs Cs Os Peak CZb P Tov Qw 15 o OCs r Tps t

Qa n CZb e Tps Tps Cs Cs u Cs f Cs R i Os v Cs Os Zp e Tps Ss o Tov r 42 40’00” McCammon CZb Ss Tps Cs Qb Qa Scout Os Ss Mtn Os CZb Qbf Qa 31 Cs Qs Os Qb Os Lava Hot Os Cs Qs Springs Tps Zp Qa Qs Qs Os Qs Tps SOs Os Tps Cs Os Tov Os Tps Os OCs Ps Qs Tps CZb Qs Tpf Tov OCs OCs Tps Tps Qbf CZb Tps CZb Qs OCs OCs CZb Qa CZb CZb Tov 91 Downey 15 Qa CZb OCs CZb CZb Qs Tps OCs Tps CZb Tps Tps Qa CZb OCs OCs CZb OCs OCs CZb OCs 112o10’00” Qa Tps CZb Zp Qbo Tps CZb 112o00’00” Qbo Qa Tps

0 5 10 miles Digital Atlas of Idaho, Nov. 2002 http://imnh.isu.edu/digitalatlas Compiled by Paul K. Link, 0 8 16 kilometers Idaho State University, Geosciences Dept. http://www.isu.edu/departments/geology/ 1:500,000 Bannock County Bannock County straddles the boundary between the Basin and Range, Idaho-Wyoming thrust belt, and Snake River Plain. There are extensive discussions of the geology of Bannock County, including Marsh Valley and Lava Hot Springs in Rocks, Rails and Trails. Bannock County contains folded and thrust-faulted Neoproterozoic and Paleozoic strata in the Bannock and Portneuf Ranges. The intervening Marsh Valley is a Miocene to recent feature, bounded by a normal fault on the east side. The Basalt of Portneuf Valley flowed down the Portneuf River path about 600,000 years ago, and now forms inverted topography in the middle of Marsh Valley. The Lake Bonneville flood broke out at Red Rock Pass in southern Bannock County about 14,500 years ago and flowed north through Marsh Valley and Portneuf Narrows before is spread out in the Pocatello area as it emptied onto the Snake River Plain. Flood boulders are distinctive landscape elements in the Pocatello and Chubbuck areas. See Geology and regional sections of Rocks, Rails and Trails. P.K. Link, 10/02

Description of Geologic Units

Qa Quaternary alluvial deposits Qs Quaternary surficial cover, including colluvium, fluvial, alluvial fan, lake, and windblown deposits. Included fluveolian cover on Snake River Plain, (Snake River Group). Qw Quaternary windblown deposits; sand dunes and loess. Qbf Bonneville Flood gravels, including boulder and gravel bars north and west of Red Rock Pass through Marsh Valley and along Snake River west of Pocatello to Hells Canyon. Town of Lewiston is underlain by Bonneville gravels. Tps Pliocene and Upper Miocene stream and lake deposits (Salt Lake Formation, Starlight Formation, Idaho Group). Tpf Pliocene and Upper Miocene felsic volcanic rocks, rhyolite flows, tuffs, ignimbrites. (in Owyhee County and Mt. Bennett Hills, this should be Tmf). Ps Permian sedimentary rocks.

TR s Triassic sedimentary rocks.

PPPs Permian and Pennsylvanian sedimentary rocks.

PPPMs Permian and Carboniferous sedimentary rocks (Snaky Canyon Formation).

PPs Pennsylvanian sedimentary rocks.

Ms Mississippian sedimentary rocks.

MDs Mississippian and Devonian sedimentary rocks.

Ds Devonian sedimentary rocks.

Ss Silurian sedimentary rocks. DSs Devonian and Silurian sedimentary rocks.

DSOs Devonian, Silurian, and Ordovician sedimentary rocks.

SOs Silurian and Ordovician sedimentary rocks.

Os Ordovician sedimentary rocks.

Oi Ordovician intrusive rocks (includes Beaverhead pluton).

OCs Ordovician and Cambrian sedimentary rocks.

Cs Cambrian sedimentary rocks. OCZ Ordovician, Cambrian, and Neoproterozoic sedimentary rocks, Bannock and Portneuf Ranges. CZb Cambrian to Neoproterozoic Brigham Group.

Zp Pocatello Formation; diamictite, sandstone, conglomerate, mafic.

Symbols

Geologic unit contacts with unit Overturned anticline: trace of axial Yp designation. plane.

Normal fault: certain; dashed where Overturnedsyncline: trace of axial approximately located; dotted where plane. concealed. Location of ISU Rockwalk rock Thrust fault: certain; dashed where from each county. approximately located; dotted where concealed. Cities Detachment fault: certain; dashed Feature location where approximately located; dotted where concealed. Roads Anticline: trace of axial plane: large Interstate Route arrow indicates direction of plunge. 15 U.S. Route Syncline: trace of axial plane: large 95 arrow indicates direction of plunge. 1 State route