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).
Basaltic to rhyolitic (largely mafic) arc-derived volcanic and volcaniclastic rocks of the Wallowa terrane; includes minor limestone. Composed of Windy Ridge, Hunsaker Creek, Wild Sheep Creek, and Doyle Creek formations. (Mesozoic-Paleozoic Rocks of the Blue Mountains Island-Arc Complex).
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).
Deformed granodiorite, tonalite, and quartz diorite; includes Little Goose Creek complex northwest of McCall dominated by porphyritic granodiorite (~105 Ma) and subordinate 160-87 Ma tonalite and quartz diorite. (Paleocene and Cretaceous Idaho Batholith and Older Cretaceous and Jurassic Intrusive Rocks).
Metasedimentary and metavolcanic schist, gneiss, amphibolite, and marble, all of uncertain age, along eastern margin of island-arc complex; typically hornblende-rich. Includes Pollock Mountain amphibolite southeast of Riggins and gneiss of Swiftwater Creek near Lowell. (Mesozoic-Paleozoic Rocks of the Blue Mountains Island-Arc Complex).
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).
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).
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).
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).
Till and outwash consisting of gravel, sand, silt, and clay. Formed by valley glaciers at higher elevations and by the Cordilleran ice sheet in northern Idaho. Includes deposits of several glacial episodes. Includes rock glacier deposits and some modern alluvium derived from reworked till and outwash. (Quaternary Sediments).
Marine limestone and marble of the Martin Bridge Formation and calcareous mudstone and phyllite of the Hurwal Formation exposed west of Riggins and south of Lewiston; basaltic andesite, rhyolite tuff (~202 Ma), and conglomerate along Salmon River southwest of Grangeville; and rhyolite tuff at Pittsburg Landing (~198 Ma). (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).
Unsorted gravel, sand, and clay of landslide origin; includes rotational and translational blocks and earth flows. (Quaternary Sediments).
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).
Tonalite, granodiorite, and quartz diorite, typically hornblende-bearing; includes the Payette River tonalite (~90 Ma) along western border zone of the Atlanta lobe, and the ~99 Ma Croesus pyroxene-biotite quartz diorite south of Hailey. Also includes granodiorite with potassium feldspar megacrysts that is typically hornblende-bearing and foliated (~90 Ma in central Idaho and ~100 Ma in northernmost Idaho) and early mafic phases of the Bitterroot lobe (~70 Ma). (Paleocene and Cretaceous Idaho Batholith and Older Cretaceous and Jurassic Intrusive Rocks).
Syenite, monzonite, quartz monzonite, and subordinate pyroxenite (115-110 Ma); includes Gem stocks north of Wallace, Gold Hill stock northeast of Potlatch, Benning Mountain stock along the Montana-Idaho border east of Sandpoint, syenite of Wall Mountain north of Bonners Ferry, monzonite of Long Canyon (~88 Ma) northwest of Bonners Ferry, and no Business Mountain pluton (uncertain age) west of Donnelly. (Paleocene and Cretaceous Idaho Batholith and Older Cretaceous and Jurassic Intrusive Rocks).
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).
Epiclastic and volcaniclastic rocks, chert, limestone, and lava flows of mid- or Early Permian(?) age that are moderately to intensely metamorphosed. Includes part of Hunsaker Creek Formation of Vallier (1977), in the eastern Blue Mountains province, composed mostly of keratophyre flows, keratophyric volcaniclastic rocks and minor spilite, mudstone, and limestone. In Wheeler County, includes phyllite, chert, and fusulinid-bearing crystalline limestone of probable Early Permian (Wolfcampian?) age (Oles and Enlows, 1971), associated with phyllite, chlorite, and muscovite schist, and lawsonite-crossite blueschist (Swanson, 1969b)
Black, green, and gray argillite, mudstone, and shale; graywacke, sandy limestone, tuff, and some coarse volcaniclastic rocks; chert, sandstone comprised of chert clasts, and chert pebble conglomerate; thin-bedded and massive limestone. Locally contains some interbedded lava flows, mostly spilite or keratophyre. In places metamorphosed. Invertebrate marine fauna indicates unit mostly of Late Triassic (Karnian and Norian) age. Includes the Begg and Brisbois Formations of Dickinson and Vigrass (1965; Vester Formation of Brown and Thayer, 1966) and the Rail Cabin Argillite of Dickinson and Vigrass (1965); Fields Creek Formation and Laycock and Murderers Creek Graywackes of Brown and Thayer (1966); Martin Bridge Formation and lower sedimentary series in and near the Wallowa Mountains (Prostka, 1962; Nolf, 1966); and Doyle Creek and Wild Sheep Creek Formations (Vallier, 1977). Probably partly age correlative with rocks of the Applegate Group (Wells and Peck, 1961) of southwestern Oregon
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)