Geologic units in Nez Perce county, Idaho

Additional scientific data in this geographic area

Columbia River Basalt Group. (Miocene) at surface, covers 92 % of this area

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).

Seven Devils Group. (Triassic and Permian) at surface, covers 3 % of this area

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).

Sedimentary and volcanic rocks. (Jurassic and Triassic) at surface, covers 1 % of this area

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).

Quartz diorite. (Cretaceous and Jurassic) at surface, covers 1 % of this area

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).

Coon Hollow and Weatherby formations. (Cretaceous and Jurassic) at surface, covers 1.0 % of this area

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).

Landslide deposits. (Quaternary) at surface, covers 0.7 % of this area

Unsorted gravel, sand, and clay of landslide origin; includes rotational and translational blocks and earth flows. (Quaternary Sediments).

Alluvial deposits. (Quaternary) at surface, covers 0.6 % of this area

Deposits in valleys consisting of gravel, sand, and silt. Includes younger terrace deposits. May contain some glacial deposits and colluvium in uplands. (Quaternary Sediments).

Lake Bonneville deposits. (Pleistocene) at surface, covers 0.3 % of this area

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).

Intrusive rocks (Triassic and Permian). (Triassic and Permian) at surface, covers 0.2 % of this area

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).

Riggins Group, Orofino series, and related rocks. (Cretaceous to Permian) at surface, covers 0.2 % of this area

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).

Tonalite, granodiorite, and quartz diorite. (Cretaceous) at surface, covers < 0.1 % of this area

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).

Gneissic and schistose metasedimentary rocks. (Mesoproterozoic) at surface, covers < 0.1 % of this area

Biotite-rich paragneiss and schist, and subordinate feldspathic quartzite and calc-silicate rocks. Probably metamorphosed western facies of Lemhi subbasin. Characterized by igneous suite of Yam and Yag. Includes Elk City metamorphic sequence and metamorphic rocks east of Moscow, along Salmon River northwest of Salmon, and in Pioneer Mountains. (Mesoproterozoic Metasedimentary Rocks of Lemhi Subbasin of Belt Basin).

Windermere Supergroup. (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Upper part consists of shallow marine and fluvial quartzose sandstone, and minor siltite, shale, and limestone of the Brigham Group of southeast Idaho, Wilbert Formation of east-central Idaho, and quartzites of unknown affinity west of Borah Peak. More highly metamorphosed equivalents are quartzite, metaconglomerate, metasiltite, calc-silicate marble, and schist of Gospel Peaks successions C and D in central Idaho; mature quartzite, biotite schist, and minor calc-silicate rocks of Syringa metamorphic sequence east of Moscow; and schist and quartzite in the Albion Range (Elba Quartzite, schist of Upper Narrows, quartzite of Yost, schist of Stevens Spring, quartzite of Clarks Basin, schist of Mahogany Peaks, and Harrison Summit Quartzite). Lower part consists of diamictite, immature sandstone, and bimodal volcanic rocks related to continental rifting. Includes Pocatello Formation (700-665 Ma), formation of Leaton Gulch near Challis, Shedroof Conglomerate in extreme northwest Idaho, and metamorphic equivalents (schist, marble, calc-silicate rocks, metaconglomerate, and ~686 Ma metavolcanic rocks) of Gospel Peaks successions A and B in central Idaho. (Paleocene to Neoproterozoic Sedimentary and Igneous Rocks of the Cordilleran System).

Alluvial-fan deposits. (Quaternary) at surface, covers < 0.1 % of this area

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).

Sedimentary and volcanic rocks (Late Triassic) at surface, covers < 0.1 % of this area

Undifferentiated marine sedimentary rocks and volcanic rocks, locally slightly to moderately metamorphosed, of Late(?) Triassic age, exposed principally in Hells Canyon of Snake River, locally in tributary canyons of Imnaha River, and in several areas marginal to the Wallowa Mountains

Sedimentary rocks (Jurassic) at surface, covers < 0.1 % of this area

Black and gray mudstone, shale, siltstone, graywacke, andesitic to dacitic water-laid tuff, porcelaneous tuff, and minor interlayers and lenses of limestone and fine-grained sediments metamorphosed to phyllite or slate. Locally includes some felsite, andesite and basalt flows, breccia, and agglomerate. Marine invertebrate fauna indicates age range from Early Jurassic (Hettangian) to early Late Jurassic (Oxfordian). In northeast Oregon, includes Graylock Formation, Mowich Group, and Shaw Member (of Snowshoe Formation) of Dickinson and Vigrass (1965); Keller Creek Shale of Brown and Thayer (1966); Weberg, Warm Springs, Snowshoe, Trowbridge, and Lonesome Formations of Lupher (1941); the Coon Hollow Formation of Morrison (1964); and unnamed Jurassic rocks near Juniper Mountain in northern Malheur County (Wagner and others, 1963)