Caribou County,

o Tincup o 112 00’ Mtn 111 10’ PPPs Qb Qs PPP s Gray’s TR s o Qb Qb Ms Lk. 43 00’ Tps Ms Qa Qa Ks Putnam Qs Qb Ms Qb PPPs Thrust OCs Chesterfield Wayan Gannett Hills Qb Ks Js Fort Hall Ind. Res. TTR R ss TR s Qa Tps Portneuf Js Qs OCs PPP s Blackfoot CZb Ms Qs Res. M Qs PPP s e Tps TR s a PPP s TR s Henry de Chesterfield TR s Rge. T Rv h Ms PPP s ru Portneuf Rge Qa Tps s t Js Portneuf Valley Ms Qf Js Tps PPP s Qs Qf China Qa Qa TR s Ks Qb Qf Cap TR s CZb Ms Blackfoot China Hat Qb Lava Field Qa Qa Bonneville TR s Pk. Conda TR s O Qs PPPs Tps ld Os TR s Qs H Paris Qs Tps wy Qs Ms Ds Paris Qa 3 PPPs Bancroft 0 Ds Aspen Rge Fish Crk. Rge. Ss TR s TR s Qa Os Os Qa

Thrust Qa Ds Thrust PPPs 30 Soda Ms Tps Qa Springs TR s Gem Valley Tps PPPs

Qb Qa PPPs Ms Os Tps 30 Ms PPPs Ms Grace Ms Ms Ms Js Ks Os 34 Preuss Cs Qa Os Qa Rge Ms Ms Cs o PPPs 42 30’ Cs Cs Qs Qa Qs CZb Os

05 10 miles

08 16 kilometers 1:500,000

Digital Atlas of Idaho, Nov. 2002 http://imnh.isu.edu/digitalatlas Compiled by Paul K. Link, Idaho State University, Geosciences Dept. http://www.isu.edu/departments/geology/ Caribou County Caribou County has the forested mountains of the Idaho-Wyoming thrust belt on its eastern side, and the wide Bear Lake and Gem valleys on its west, part of the Basin and Range province. Pleistocene volcanic rocks, mainly , fill the Blackfoot Lava field and much of Gem Valley to the west. China Hat and China Cap are Pleistocene rhyolite domes. Phosphate mining still controls the economy of Caribou County, with active mines operated by Simplot, FMC, Monsanto, and Agrium between Soda Springs and Afton, Wyoming. For more information see geology text from Rocks, Rails and Trails (page 83). Also see the Fortsch and Link field trip from “Geologic Guidebook to Eastern Idaho” (”Regional Geology and Sites from Pocatello to Montpelier, Feedom, and Wayan, Southeastern Idaho and Western Wyoming”, page 281). P.K. Link, 10/02

Descripton of Units for Caribou County, Idaho 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). Qb Pleistocene lava, 2 million to 12,000 years old, flows have some vegetation and surface weathering. Tps Pliocene and Upper Miocene stream and lake deposits (Salt Lake Formation, Starlight Formation, Idaho Group). Ks Cretaceous sedimentary rocks. Js Jurassic sedimentary rocks.

TR s Triassic sedimentary rocks. PPPs Permian and Pennsylvanian sedimentary rocks. Ms Mississippian sedimentary rocks. Ss Silurian sedimentary rocks. Ds Devonian sedimentary rocks. Os Ordovician sedimentary rocks. OCs Ordovician and Cambrian sedimentary rocks. Cs Cambrian sedimentary rocks. CZb Cambrian to Neoproterozoic Brigham Group.

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