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Mineral Resources > Online Spatial Data > Geology > by state > Idaho Geology

Geologic units in Gem county, Idaho

[Additional scientific data in this geographic area]

Gravel, sand, and silt; Quaternary; alluvium (Quaternary) at surface, covers 8 % of this area

Quaternary alluvium; may contain some glacial deposits and colluvium in uplands

Lithology: alluvium; alluvial terrace; floodplain; alluvial fan; colluvium

Tuff, arkose, claystone, siltstone, conglomerate, lignite; Miocene alluvial and lacustrine deposits (Miocene) at surface, covers 0.9 % of this area

Miocene stream and lake deposits; generally associated with volcanic episodes.

Lithology: tuff; arkose; claystone; conglomerate; siltstone; mixed clastic/coal

Clay, silt, and minor sand; Late Pleistocene distal glacial-flood deposits; western Snake River Plain (Late Pleistocene) at surface, covers 10 % of this area

Pleistocene waterlaid detritus; may be distal deposits of glacial floods and outwash.

Lithology: stratified glacial sediment; outwash; glaciolacustrine

Intrusive rocks: mostly Late Cretaceous granodioritic to granitic plutons of the Idaho batholithic assemblage, but including some Eocene intrusions; northern Idaho and Atlanta batholith (Cretaceous to Eocene) at surface, covers 12 % of this area

Cretaceous plutons; probably includes unmapped older and younger crystalline bodies.

Lithology: granodiorite; peraluminous granite; quartz monzonite; quartz diorite; tonalite; trondhjemite; pegmatite; alkali-granite (alaskite)

Basalt flows and incidental andesite, and latite flows; Miocene mafic to intermediate volcanics; subunits are Tmib, Tm1b, Tm2b, Tm3b; Columbia Plateau, Owyhee Plateau (Miocene) at surface, covers 41 % of this area

Miocene plateau basalt flows of western Idaho; subdivisions are (Tm3b, Tm2b, Tm1b).

Lithology: basalt; latite; lava flow

Gravel, sand, and silt; glacial outburst flood deposits, outwash, fanglomerate, and alluvium, undivided; Pleistocene (Pleistocene) at surface, covers 4 % of this area

Pleistocene outwash, fanglomerate, flood and terrace gravels; sudivisions are: (Qpug, Qpmg, and Qplg).

Lithology: stratified glacial sediment; alluvium; outwash; alluvial fan; alluvial terrace

Rhyolite ot trachyte ignimbrites and flows; Pliocene felsic volcanics; eastern Snake River Plain and vicinity (Pliocene) at surface, covers 0.2 % of this area

Pliocene silicic welded tuff, ash, and flow rock; most common in southwestern Idaho.

Lithology: rhyolite; trachyte; ignimbrite; lava flow; tuff; volcanic breccia (agglomerate)

Open Water (Holocene) at surface, covers 0.3 % of this area

Lakes and streams

Lithology: water

Sandstone, conglomerate, siltstone, tuff, claystone, limestone, and diatomite; Pliocene tuffaceous alluvial and lacustrine deposits; Snake River Plain and vicinity, southeastern Idaho (Pliocene ) at surface, covers 19 % of this area

Pliocene stream and lake deposits; may be due to volcanic and block-faulting events.

Lithology: sandstone; conglomerate; siltstone; tuff; claystone; shale; limestone

Metamorphosed granodiorite, quartz monzonitek tonalite, quartz diorite; mostly Cretaceous orthogneiss and migmatite; northern and Atlanta batholith; margins of Bitterroot and Atlanta batholiths (Cretaceous) at surface, covers 5 % of this area

Metamorphosed granitic intrusive rock; associated with pluton margins and stress areas.

Lithology: granodiorite; quartz monzonite; tonalite; quartz diorite; orthogneiss; migmatite