Geologic Units

Tertiary sedimentary rocks, undifferentiated
Miocene basalt (Columbia River Basalt Group)
Oligocene volcanics (Potlatch volcanics and Salmon Falls Creek volcanics)
Eocene Challis Volcanic Group, volcanics and volcaniclastics
Cretaceous syenitic rocks
Cretaceous granite and granodiorite of the 2-mica suite (Idaho batholith)
Mesoproterozoic augen gneiss and porphyritic granite
Schist of the Wallace Formation and lower Missoula Group
Quartzite and calc-silicate gneiss of the Wallace Formation
Quartzite and schist of the Ravalli group
Upper Missoula Group.  Upper part Swauger Quartzite  (Mount Shields, Bonner, and Libby Fms.)
Lower Missoula Group.  Lower part-- Gunsight Formation  (Snowslip and Shepard) 
Metamorphic rocks, Elk City metamorphic sequence and related rocks, Syringa metamorphic sequence, and Priest River metamorphic complex

  Map Key
Geologic units with unit designation.
Normal Fault: certain; dashed where approximately located; dotted where concealed.
Thrust Fault: certain; dashed where approximately located; dotted where concealed.
Detachment Fault: certain; dashed where approximately located; dotted where concealed.
Interstate Route.
U.S. Route.
State Route.
Location of Rockwalk rock from the county.
Feature location.

Latah County

The rolling Palouse of western Latah County is underlain by loess hills deposited above Miocene Columbia River basalt that flowed eastward from vents in Washington. Miocene and younger sediments were deposited upstream of the ends of these basalt flows and underlie much of the farming country between Moscow and Bovill.

The unique Oligocene Potlach volcanics are found in the northwestern part of the quadrangle. The Potato Hill volcanics are found west of Bovill.

The eastern part of the county is underlain by Mesoproterozoic Belt Supergroup, with the metamorphosed garnet-bearing Wallace Formation exposed in the northeastern part of the county, south of Fernwood and the Emerald Creek garnet district.

The central part of the county is underlain by Cretaceous granodiorite, one of the northern parts of the Idaho batholith, that extends westward into eastern Washington.

Written by P.K. Link, 9/02

Additional Reading

Rocks Rails and Trails: page
References on Idaho Geology

Click here to see a correlation of geologic units, and the associated time scale.

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