USGS Home
Contact USGS
Search USGS

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

Geologic units in Boise county, Idaho

[Additional scientific data in this geographic area]

Basalt flows, pyroclastic debris, clastic sediments, and diatomite; Pliocene basaltic volcanics and clastic sediments; Snake River Plain and vicinity (Pliocene) at surface, covers 0.2 % of this area

Pliocene olivine basalt flows and associated tuff and detritus of southern Idaho.

Lithology: basalt; lava flow; tuff; mixed clastic/volcanic

Glacial debris; Late Pleistocene till, outwash, and alluvium of valley glaciers; high mountain valleys (Late Pleistocene ) at surface, covers < 0.1 % of this area

Pleistocene upland valley deposits; commonly derived from alpine glaciation.

Lithology: till; outwash; alluvium

Gravel, sand, and silt; Quaternary basin-filling alluvium; Snake River Plain, Basin and Range provinces (Quaternary) at surface, covers 0.5 % of this area

Quaternary detritus; generally basin-filling deposits of central and southern Idaho.

Lithology: alluvium; alluvial fan; alluvial terrace

Glacial debris; Late Pleistocene glacial till, outwash, and alluvium of continental glaciers; northern Idaho (Late Pleistocene ) at surface, covers 1 % of this area

Pleistocene till, moraines and similar unsorted glacial debris.

Lithology: till; outwash; alluvium

Rhyolite ot trachyte ignimbrites and flows; Pliocene felsic volcanics; eastern Snake River Plain and vicinity (Pliocene) at surface, covers < 0.1 % 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 0.2 % 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 0.1 % 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

Quartz monzodiorite, monzogranite, granodiorite, monzonite, diorite; Eocene phaneritic to porphyro-aphanitic intrusions of the quartz monzodiorite suite; Challis magmatic belt (Eocene) at surface, covers 0.4 % of this area

Eocene intrusions of intermediate (mafic to felsic) composition

Lithology: quartz monzodiorite; monzogranite; granodiorite; quartz monzonite; quartz diorite

Dacite to rhyolite (or rhodacite) ignimbrites; Eocene rhyodacitic cauldron complex; east-central Idaho, central Challis volcanic field (Eocene) at surface, covers < 0.1 % of this area

Eocene mixed silicic and basaltic volcanic ejecta, flows and reworked debris.

Lithology: rhyodacite; ignimbrite; lava flow; rhyolite; quartz latite; dacite; andesite; basalt; volcanic breccia (agglomerate); mixed clastic/volcanic

Monzogranite, granodiorite, syenite, monzodiorite, monzonite, and diorite; Eocene phaneritic to porphyro-aphanitic intrusions (subunits are Teif and Teii); northern Idaho to central Idaho (Eocene) at surface, covers 0.2 % of this area

Eocene intrusions including large granitic plutons and dike swarms of central Idaho

Lithology: granite; quartz monzodiorite; granodiorite

Trachyandesite, latite, trachybasalt flows, dikes, and volcaniclastic debris; Eocene intermediate volcanics; central Idaho, southern Challis volcanic field (Eocene) at surface, covers < 0.1 % of this area

Eocene mixed silicic and basaltic volcanic ejecta, flows and reworked debris.

Lithology: trachyandesite; latite; trachybasalt; dacite; trachyte; lava flow; volcanic breccia (agglomerate)

Gravel, sand, and silt; Quaternary; alluvium (Quaternary) at surface, covers 0.4 % of this area

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

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

Monzogranite, syenogranite, and syenite; Eocene phaneritic to porphro-aphanitic intrusions of the pink monzogranite suite; Challis magmatic belt (Eocene) at surface, covers 4 % of this area

Eocene intrusions of predominantly felsic (pink granite) composition

Lithology: granite; quartz syenite

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

Mica schist, quartzite, gneiss, and amphibolite; Late to Early Proterozoic high-grade metasedimentary rocks (subunits are ZXmhs, ZXmhq, and ZXmhc); trans-Idaho metamorphic province (Proterozoic) at surface, covers 0.2 % of this area

Precambrian high-grade metamorphic rock; metasediment

Lithology: mica schist; quartzite; calc-silicate rock; paragneiss; amphiibolite

Clay, silt, and minor sand; Late Pleistocene distal glacial-flood deposits; western Snake River Plain (Late Pleistocene) at surface, covers 0.1 % 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 88 % 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 3 % of this area

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

Lithology: basalt; latite; lava flow

Clastic debris; Quaternary colluvium, fanglomerate, talus, and glacial deposits; upland-valley margins (Quaternary) at surface, covers 1 % of this area

Quaternary colluvium, fanglomerate, and talus plus some glacial debris in upland valleys.

Lithology: alluvium; glacial drift; colluvium

Gravel, sand, and silt; glacial outburst flood deposits, outwash, fanglomerate, and alluvium, undivided; Pleistocene (Pleistocene) at surface, covers < 0.1 % 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