Geologic units in Idaho county, Idaho

Additional scientific data in this geographic area

Granodiorite and granite. (Paleocene and Cretaceous) at surface, covers 17 % of this area

Granodiorite and granite containing biotite and local muscovite (66-54 Ma); composes northern (Bitterroot) lobe of batholith and is ~20 Ma younger than southern (Atlanta) lobe. (Paleocene and Cretaceous Idaho Batholith and Older Cretaceous and Jurassic Intrusive Rocks).

Challis intrusive rocks. (Eocene) at surface, covers 15 % of this area

Shallow roots of Challis volcanic field. Older suite of granodiorite and quartz monzodiorite and subordinate diorite, granite, and subvolcanic dacite; includes Jackson Peak, Beaver Creek, Marsh Creek, and Summit Creek stocks (49-45 Ma). Younger suite of granite and minor syenite and subvolcanic rhyolite; includes Sawtooth, Casto, Bungalow, and Lolo Hot Springs plutons (47-43 Ma). (Eocene Challis Magmatic Complex and Related Sedimentary Rocks).

Columbia River Basalt Group. (Miocene) at surface, covers 13 % 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).

Granodiorite and two-mica granite. (Cretaceous) at surface, covers 10 % of this area

Granodiorite and granite containing biotite, commonly with muscovite; includes bulk of Atlanta lobe (85-67 Ma) and isolated plutons in northern Idaho (107-67 Ma). (Paleocene and Cretaceous Idaho Batholith and Older Cretaceous and Jurassic Intrusive Rocks).

Tonalitic orthogneiss and foliated granodiorite. (Cretaceous) at surface, covers 7 % of this area

Orthogneiss (primarily tonalite) and foliated granodiorite (~90 to ~80 Ma). Includes early phases of the Idaho batholith, migmatite, intrusions along major structures, and plutonic rocks of uncertain age along the Salmon River northwest of Salmon. (Paleocene and Cretaceous Idaho Batholith and Older Cretaceous and Jurassic Intrusive Rocks).

Gneissic and schistose metasedimentary rocks. (Mesoproterozoic) at surface, covers 6 % 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).

Tonalite, granodiorite, and quartz diorite. (Cretaceous) at surface, covers 4 % 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).

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).

Riggins Group, Orofino series, and related rocks. (Cretaceous to Permian) at surface, covers 3 % 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).

Windermere Supergroup. (Cambrian and Neoproterozoic) at surface, covers 3 % 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).

Quartzitic metamorphic rocks. (Mesoproterozoic) at surface, covers 3 % of this area

Feldspathic quartzite and subordinate schist and calc-silicate rocks of central Idaho. Includes the Golden metamorphic sequence east of Grangeville that is probably metamorphosed western facies of Lemhi subbasin. (Mesoproterozoic Metasedimentary Rocks of Lemhi Subbasin of Belt Basin).

Piegan Group. (Mesoproterozoic) at surface, covers 2 % of this area

Calcareous and dolomitic siltite, quartzite, and subordinate argillite of the Helena and Wallace formations in northern Idaho; south of St. Joe River, correlative rocks include garnet grade feldspathic quartzite and calc-silicate gneiss. (Mesoproterozoic Belt Supergroup).

Glacial deposits. (Pleistocene) at surface, covers 2 % of this area

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).

Lower Missoula Group. (Mesoproterozoic) at surface, covers 2 % of this area

Siltite, argillite, and dolomitic siltite in northern Idaho; includes Snowslip and Shepard formations, rocks previously mapped as upper member of Wallace Formation, and correlative garnet-grade phyllite and schist south of St. Joe River. Also includes schist, micaceous quartzite, and calc-silicate rocks in lower part of Meadow Creek metamorphic sequence east of Elk City, and argillite, siltite, phyllite, and calc-silicate rocks south of Lost Trail Pass. (Mesoproterozoic Belt Supergroup).

Upper Missoula Group. (Mesoproterozoic) at surface, covers 1 % of this area

Feldspathic quartzite and subordinate siltite and argillite. Includes Mount Shields, Bonner, Striped Peak, and Libby formations in northern Idaho and possibly correlative quartzite north of Salmon and in the Meadow Creek metamorphic sequence east of Elk City. (Mesoproterozoic Belt Supergroup).

Plutonic rocks along the western Idaho shear zone. (Cretaceous and Jurassic) at surface, covers 1 % of this area

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).

Intrusive rocks (Triassic and Permian). (Triassic and Permian) at surface, covers 1 % 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).

Tonalite and trondhjemite. (Cretaceous) at surface, covers 0.8 % of this area

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).

Quartz diorite. (Cretaceous and Jurassic) at surface, covers 0.8 % 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).

Ravalli Group. (Mesoproterozoic) at surface, covers 0.8 % of this area

Feldspathic quartzite and subordinate siltite and argillite of the Burke, Revett, and St. Regis formations in northern Idaho; south of St. Joe River, includes correlative garnet-grade quartzite and schist. (Mesoproterozoic Belt Supergroup).

Sedimentary and volcanic rocks. (Jurassic and Triassic) at surface, covers 0.5 % 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).

Landslide deposits. (Quaternary) at surface, covers 0.3 % of this area

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

Sedimentary rocks associated with flood basalts. (Miocene) at surface, covers 0.3 % of this area

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).

Augen gneiss. (Mesoproterozoic) at surface, covers 0.3 % of this area

Biotite granite and granitic augen gneiss near Elk City and northwest of Salmon (~1380 Ma). Abundant alkali feldspar and high iron content indicate A-type granite composition. (Mesoproterozoic Intrusive Rocks).

Intrusive rocks (Neoproterozoic). (Neoproterozoic) at surface, covers 0.3 % of this area

Syenite and diorite of the Acorn Butte, Ramey Ridge, and Rush Creek stocks along Big Creek northeast of McCall (665-650 Ma), and ~726 Ma granitic gneiss in lower part of House Mountain metamorphic complex southeast of Boise. A 695 Ma orthogneiss in the Pioneer Mountains is too small to show at map scale and is included in XAm. (Paleocene to Neoproterozoic Sedimentary and Igneous Rocks of the Cordilleran System).

Amphibolite. (Mesoproterozoic) at surface, covers 0.2 % of this area

Amphibolite formed from metamorphism of mafic sills; includes rocks north- west of Salmon (~1380 Ma) and east of Elk City. (Mesoproterozoic Intrusive Rocks).

Alluvial deposits. (Quaternary) at surface, covers 0.2 % 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).

Volcanic rocks. (Oligocene) at surface, covers 0.2 % of this area

Alkali olivine basalt and trachyte of the ~26 Ma Potlatch volcanics; basalt, andesite, and rhyolite of the ~32 Ma Kamiah volcanics; and olivine basalt and andesite of the 26-31 Ma Salmon Creek volcanics southwest of Nampa. (Quaternary to Eocene Continental Volcanic and Intrusive Rocks).

Gneiss, schist, and quartzite. (Mesoproterozoic) at surface, covers 0.1 % of this area

Kyanite and sillimanite gneiss, schist, quartzite, and amphibolite that is metamorphosed lower part of Prichard Formation (Hauser Lake Gneiss) and underlying quartzite of Gold Cup Mountain in the Priest River metamorphic complex. (Mesoproterozoic Belt Supergroup).

Metasedimentary rocks. (Paleozoic to Mesoproterozoic) at surface, covers 0.1 % of this area

Quartzite, feldspathic quartzite, calc-silicate gneiss, biotite gneiss, schist, and amphibolite north and east of McCall and as pendants in the southern part of the Idaho batholith; schist, quartzite, and marble in southwestern Idaho; argillite, siltite, quartzite, carbonate bearing quartzite, dolomite, phyllite, and conglomerate of the Deer Trail Group in northwest corner of state; and quartzite, Hayden Creek diamictite, and siltite stratigraphically above(?) the Swauger Formation south of Salmon. (Metasedimentary Rocks of Uncertain Age (Neoproterozoic to Paleoproterozoic)).

Lemhi Group. (Mesoproterozoic) at surface, covers < 0.1 % of this area

Feldspathic fine-grained quartzite, siltite, and subordinate argillite and carbonate-bearing rocks in east-central Idaho; includes Apple Creek, West Fork, Inyo Creek, Big Creek, and Gunsight formations. (Mesoproterozoic Metasedimentary Rocks of Lemhi Subbasin of Belt Basin).

Sediments and sedimentary rocks (Pleistocene and Pliocene). (Pleistocene and Pliocene) at surface, covers < 0.1 % of this area

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).

Coon Hollow and Weatherby formations. (Cretaceous and Jurassic) at surface, covers < 0.1 % 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).

Granitic rock (Cretaceous) at surface, covers < 0.1 % of this area

Granitic rock

Challis Volcanic Group. (Eocene) at surface, covers < 0.1 % of this area

Dacite, andesite, and rhyolite tuffs and flows and subordinate basalt and latite flows; covers large area in south-central Idaho. Includes Absaroka Volcanic Group near Henrys Lake and scattered volcanic rocks in eastern and northern Idaho. (Eocene Challis Magmatic Complex and Related Sedimentary Rocks).

Granitic rock (Tertiary) at surface, covers < 0.1 % of this area

Granitic rock

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).

Piegan Group: Helena and Wallace Formations (Middle Proterozoic) at surface, covers < 0.1 % of this area

Helena Formation (Yh): Northwestern Montana: (formerly “lower Wallace”): cycles of basal white quartzite or intraclast beds overlain by couplets of green siltite and argillite, capped by dolomite beds. Calcite pods and ribbons (molar tooth structure) common. West-central Montana: gray to dark gray limestone and dolomitic limestone with siltite partings. Thickness as much as 2,000 m (6,562). Wallace Formation: Tan-weathering, dolomitic quartzite and siltite, and black argillite with calcite ribbons (molar tooth structure) in graded pinch-and-swell couples and couplets. Thickness as much as 2,500 m (8,202 ft).

Lake Bonneville deposits. (Pleistocene) at surface, covers < 0.1 % 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).

Metasedimentary rock: Variously assigned to the Swauger Formation, Yellowjacket Formation, Lemhi Group, and/or Belt Supergroup along southest Montana-Idaho border (Middle Proterozoic) at surface, covers < 0.1 % of this area

Beaverhead Mountains, southwestern Montana - Light gray quartzite with subordinate argillite, siltite, and calc-silicate rocks; unresolved unit that has been variously assigned to Yellowjacket Formation, Lemhi Group, Swauger Formation, or Belt Supergroup. Thickness as much as 2,700 m (8,858 ft).

Amphibolite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Amphibolite

Volcanic rock: locally includes Challis Volcanics in southwestern Montana (Tertiary) at surface, covers < 0.1 % of this area

Volcanic rock; In southwestern Montana - Challis Volcanics: Basaltic andesite, andesite, quartz latite, latite, rhyodacite, and rhyolite flows, and tuff, most of which is nonporphyritic and commonly spherulitic; glassy to devitrified. Subordinate water-laid tuff.

Belt Supergroup (Middle Proterozoic) at surface, covers < 0.1 % of this area

Extremely large lumping of over 25+ formations. See individual unit descriptions. Belt Supergroup consists of: Missoula Group (Ym, Ymu, Yml), Piegan Group (Ypg, Yh), Ravalli Group (Yr, Ye, Ysp), and all the Lower Belt Formations (Ypu, Ypl, Yaw, Yla, Yg, Yn, Ynla, Ych, Yne).

Missoula Flood deposits. (Pleistocene) at surface, covers < 0.1 % of this area

Gravel, sand, and silt near Coeur d'Alene and Sandpoint that were carried by outburst floods from Glacial Lake Missoula (20-15 ka). Floods also flowed back up the Snake and Clearwater rivers to Kamiah. Missoula Flood slack-water deposits cover Lake Bonneville deposits in the Lewiston area. (Quaternary Sediments).

Granite and diorite (Triassic to Jurassic) at surface, covers < 0.1 % of this area

Felsic to intermediate, granitoid intrusive rocks. Includes Jurassic muscovite granodiorite, hornblende gabbro, tonalite, and quartz diorite of southwest Oregon (Smith and others, 1982)

Imnaha Basalt (Early Miocene) at surface, covers < 0.1 % of this area

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)

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 and volcanic rocks, partly metamorphosed (Permian to Triassic) at surface, covers < 0.1 % of this area

Complexly folded, locally highly foliated and recrystallized undifferentiated sedimentary and volcanic rocks that in places are lithologically similar to Jurassic and Triassic rocks in the Aldrich Mountains of the Blue Mountains province and in other places resemble Elkhorn Ridge Argillite, Clover Creek Greenstone, and Burnt River Schist (Gilluly, 1937). Age probably mostly Late Permian to Late Triassic, but, as shown, may include some Early Jurassic rocks

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)