Large-volume lava flows of tholeiitic basalt, basaltic andesite, and subordinate andesite in western Idaho; consists of Imnaha Basalt (17.5-16.5 Ma), Grande Ronde Basalt (16.5-15.6 Ma), Wanapum Basalt (15.6-14.5 Ma), and Saddle Mountains Basalt (14.5-6 Ma). Includes porphyritic basalt and basaltic andesite in western Owyhee County. (Quaternary to Eocene Continental Volcanic and Intrusive Rocks).
Flows and cinder cones of olivine tholeiite basalt, and shallow basalt intrusives (~15-3 Ma); includes basalt in Owyhee County and southwest of Twin Falls, basalt of Weiser (basalt to andesite), basalt of Cuddy Mountain (alkali basalt and picro-basalt) north of Cambridge, basalt in Mount Bennett Hills north of Gooding, andesite at Square Mountain near Magic Reservoir, and Cub River diabase sill east of Preston. Includes gabbro at depth in cross section D-D’-D”. (Quaternary to Eocene Continental Volcanic and Intrusive Rocks).
Fluvial and lacustrine deposits associated with Columbia River Basalt Group and equivalent basalts (17-8 Ma); consolidated to weakly consolidated sandstone, siltstone, arkose, conglomerate, claystone, and tuffaceous sediment; subordinate intercalated basalt and rhyolitic tuff. Includes Payette and Sucker Creek formations in southwestern Idaho, sediments associated with basalt of Weiser in western Idaho, and Latah Formation in northern Idaho. Includes sedimentary rocks of uncertain origin in southwest corner of Idaho. (Quaternary to Eocene Continental Sediments and Sedimentary Rocks).
Deposits in valleys consisting of gravel, sand, and silt. Includes younger terrace deposits. May contain some glacial deposits and colluvium in uplands. (Quaternary Sediments).
Marine mudstone and subordinate conglomerate and sandstone of the Coon Hollow Formation south of Lewiston and turbiditic sandstone, mudstone, volcanic conglomerate, and andesite and rhyolite tuff of the Weatherby Formation north of Weiser. (Mesozoic-Paleozoic Rocks of the Blue Mountains Island-Arc Complex).
Massive and ribbon chert, phyllite, argillite, cherty limestone, and limestone deposited in relatively deep water, possibly in a forearc basin setting. (Mesozoic-Paleozoic Rocks of the Blue Mountains Island-Arc Complex).
Basaltic to rhyolitic (largely intermediate) arc-derived volcanic and volcaniclastic rocks of the Huntington Formation; includes minor chert and limestone. (Mesozoic-Paleozoic Rocks of the Blue Mountains Island-Arc Complex).
Gravel and subordinate sand and silt deposited at mouths of canyons; largest fans are in Basin and Range Province in east-central and southeastern Idaho. (Quaternary Sediments).
Older gravel, sand, and silt deposited in fans, streams, and lakes. Includes older terrace gravels and Tuana Gravel northwest of Twin Falls. (Quaternary to Eocene Continental Sediments and Sedimentary Rocks).
Silt, clay, sand, and gravel deposited in and at margins of former Lake Bonneville (33-11 calibrated ka) and sand and gravel deposited in giant flood bars by outburst floods from the lake (17.4 calibrated ka). The 1,575-m (5,170 ft) Lake Bonneville shoreline was used to determine the maximum extent of the lake deposits. Flood deposits follow Bonneville flood path from near Downey and the Portneuf River westward along the Snake River to Lewiston. They include sand and silt deposited in slack-water areas to 740 m (2,430 ft) elevation in the Boise, Weiser, Payette, and Snake river drainages. (Quaternary Sediments).
Primarily quartz diorite, with subordinate diorite, gabbro, granite, and amphibolite; largely undeformed except near eastern part of Blue Mountains island-arc complex; wide age range (160-90 Ma). (Mesozoic-Paleozoic Rocks of the Blue Mountains Island-Arc Complex).
Unsorted gravel, sand, and clay of landslide origin; includes rotational and translational blocks and earth flows. (Quaternary Sediments).
Biotite- and hornblende-biotite tonalite and biotite-muscovite trondhjemite (120-110 Ma); rocks contain conspicuous magmatic epidote in plutons along eastern edge of arc complex. Includes tonalitic part of Hazard Creek complex northwest of McCall, Blacktail pluton southeast of Grangeville, and Sixmile Creek pluton southeast of Orofino. (Mesozoic-Paleozoic Rocks of the Blue Mountains Island-Arc Complex).
Diorite, tonalite, granodiorite, gabbro, norite, quartz diorite, and trondhjemite; basement of, and feeders to, volcanic rocks in Seven Devils Group (Wallowa terrane) and Olds Ferry terrane. (Mesozoic-Paleozoic Rocks of the Blue Mountains Island-Arc Complex).
Sand, gravel, and silt forming flood plains and filling channels of present streams. In places includes talus and slope wash. Locally includes soils containing abundant organic material, and thin peat beds
Olive-drab, pale-brown, dark-gray, and black volcanic graywacke and siltstone; lesser conglomerate and slate, and minor limestone and chert. Includes more extensive outcrops of Triassic or Jurassic limestone at north base of Juniper Mountain in northern Malheur County and near Huntington in southeastern Baker County. Interlayers of silicic and intermediate volcanic rocks are rare. Locally metamorphosed to prehnite-pumpellyite and zeolite facies and in places to greenschist facies. Folded, sheared, and locally foliated. Includes the Weatherby Formation of Brooks (1979). Age is Late Triassic(?) and Early and Middle Jurassic (Sinemurian-Callovian)
Mostly coarse-grained, plagioclase porphyritic basalt; flows commonly contain zeolite amygdules and montmorillonitic alteration is widespread. Potassium-argon ages mostly 16 to 17 Ma (McKee and others, 1981)
Green to gray spilite and keratophyre flows and flow breccia; and subordinate amounts of coarse volcaniclastic sandstone, tuff, sandstone, siltstone, chert, conglomerate, and limestone. Marine fauna from interlayered sedimentary rocks indicates unit is mostly of Karnian (Late Triassic) age. Includes Late Triassic "andesitic and basaltic rocks" of Nolf and Taubeneck (1963), and the basaltic to rhyolitic metavolcanic rocks and interbedded sedimentary rocks of the Huntington Formation of Brooks (1979). Equivalent, in part, to unit TrPv
Poorly bedded argillite, chert, phyllite, phyllitic quartzite, calc-phyllite, impure limestone, and marble. In places rocks are strongly foliated. Sparse fossils (Fusilina, corals, and crinoids) indicate that the unit includes rocks of Leonardian, Ochoan, and Late Triassic age (OR084). Includes Elkhorn Ridge Argillite (OR035), Mesozoic and Paleozoic sedimentary rocks of Brown and Thayer (OR008), and the Permian Coyote Butte Formation (OR085). In Baker County includes "sedimentary and volcanic rocks" (MzPza) of Brooks and others (OR039) and metamorphosed sedimentary and minor volcaniclastic rocks containing mineral assemblages indicative of quartz-albite-muscovite-chlorite subfacies and quartz-albite-epidote-biotite subfacies of the greenschist facies. In Jefferson and Wasco Counties north of Prineville, includes "phyllite and sedimentary rocks " of Swanson (OR031). Includes part of the Burnt River Schist (OR035; OR081) and volcaniclastic facies of several metavolcanic units of Permian and Late Triassic age. Not on State map (OR001) in area of La Grande 100K quadrangle, butmapped in OR291 as Elkhorn Ridge Argillite (Triassic Permian, Pennsylvannian, and Devonian?)