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

Geologic units in Idaho county, Idaho

[Additional scientific data in this geographic area]

Garnet-sillimanite-biotite gneiss, quartzite, and amphibolite; Middle Proterozoic Lemhi Group; southern Belt trans-Idaho metamorphic provinces (Middle Proterozoic) at surface, covers 0.6 % of this area

Precambrian high-grade metamorphic rock; metasediment; kyanite-sillimanite-garnet-mica coarse-grained schist and gneiss; minor quartzite

Lithology: gneiss; quartzite; amphibolite

Rhyolite ignimbrites, latite and basalt lava flows, late Eocene rhyolitic ignimbrite cauldron complex; east-central Idaho, northern Challis volcanic field (Eocene) at surface, covers < 0.1 % of this area

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

Lithology: rhyolite; latite; ignimbrite; lava flow; mixed clastic/volcanic; basalt

Tertiary volcanic rocks (Phanerozoic | Cenozoic | Tertiary) at surface, covers < 0.1 % of this area

Tertiary volcanic rocks: Flows and associated pyroclastic deposits, with subordinate amounts of intercalated sedimentary beds and lignite. The volcanic material is mostly latite, quartz latite, and andesite but includes some rhyolite and basalt. The distinction between Tertiary and pre-Tertiary volcanic rocks was not made in some of the reports used in the complilation. Hence in the less well-known areas some pre-Tertiary volcanic rocks may be included.

Lithology: volcanic rock (aphanitic); mixed clastic/volcanic; coal

Quartz diorite, metasedimentary rock, metavolcanic rock, and migmatite; Cretaceous to Jurassic plutons in Triassic to Permian metamorphic host rocks, undivided; western Idaho (Cretaceous to Permian) at surface, covers 0.9 % of this area

Mixed, highly altered and migmatitic rocks; derived from imbrication and dynamic events

Lithology: quartz diorite; metasedimentary rock; metavolcanic rock; trondhjemite; quartz monzonite; migmatite

Sedimentary and volcanic rocks (Upper? Triassic) (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

Lithology: mixed clastic/volcanic

Argillite, quartzite, and calc-silicate rock; Middle Proterozoic Yellowjacket Formation; southern Belt province (Middle Proterozoic) at surface, covers < 0.1 % of this area

Intermediate Precambrian sediments, dark-colored, feldspathic quartzite with minor limestone beds of southern Idaho.

Lithology: meta-argillite; quartzite; calc-silicate rock

Metamorphosed granitoid plutonic rocks and metasedimentary rocks, undivided; Cretaceous orthogneiss in Middle Proterozoic metasedimentary host rocks; west-central Idaho (Cretaceous to Middle Proterozoic) at surface, covers 3 % of this area

Highly metamorphosed rock of central Idaho; age and origin of rock questionable.

Lithology: granitoid; quartzite; pelitic schist; orthogneiss; calc-silicate rock

Metamorphosed granodiorite, quartz monzonitek tonalite, quartz diorite; mostly Cretaceous orthogneiss and migmatite; northern and Atlanta batholith; margins of Bitterroot and Atlanta batholiths (Cretaceous) at surface, covers 9 % of this area

Metamorphosed granitic intrusive rock; associated with pluton margins and stress areas.

Lithology: granodiorite; quartz monzonite; tonalite; quartz diorite; orthogneiss; migmatite

Quartz monzodiorite, monzogranite, granodiorite, monzonite, diorite; Eocene phaneritic to porphyro-aphanitic intrusions of the quartz monzodiorite suite; Challis magmatic belt (Eocene) at surface, covers < 0.1 % of this area

Eocene intrusions of intermediate (mafic to felsic) composition

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

Rhyolite, andesite, dacite, quartz latite; Oligocene to Eocene volcanics; northern Idaho; (Paleogene, possibly Oligocene) at surface, covers 0.2 % of this area

Lower Tertiary, possibly Oligocene, flows and tuffs of northern Idaho.

Lithology: rhyolite; andesite; ignimbrite; lava flow; volcanic breccia (agglomerate)

Open Water (Holocene) at surface, covers 0.2 % of this area

Lakes and streams

Lithology: water

Sedimentary and volcanic rocks, partly metamorphosed (Triassic and Permian) (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

Lithology: meta-argillite; greenstone; slate

Imnaha Basalt (lower Miocene) (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)

Lithology: basalt

Garnet-mica schist, gneiss, and quartzite; Proterozoic high-grade metasedimentary rocks; trans-Idaho metamorphic province (Late to Early Proterozoic) at surface, covers 6 % of this area

Precambrian high-grade metamorphic rock; metasediment; Kyanite-sillimanite-garnet-mica schist and gneiss; minor quartzite

Lithology: mica schist; paragneiss; quartzite; orthogneiss

Amphibolite after gabbro, diabase, and diorite; Middle Proterozoic sill-like intrusions; southern and northern Belt provinces (Middle Proterozoic) at surface, covers < 0.1 % of this area

Younger or Intermediate Precambrian age intrusive rock undifferentiated; Intrusive rock of eastern Idaho; appears older than Cretaceous, possibly Precambrian; Highly metamorphosed rock of central Idaho; age and origin of rock questionable.

Lithology: amphibolite; gabbro; diabase; diorite

Argillite, siltite, quartzite, carbonate; Middle Proterozoic Belt metasedimentary rocks (subunits are Y1s, Y2s, Y3s, and Y4s); southern Belt province (Middle Proterozoic) at surface, covers < 0.1 % of this area

Intermediate Precambrian sediments, northern and southern Idaho; northern Idaho subdivisions are (Y4n, Y3n, Y2n, Y1n) and southern Idaho subdivisions are (Y4s, Y3s, Y2s, Y1s).

Lithology: quartzite; siltstone; meta-argillite

Quartzite and muscovite schist; Middle Protrerozoic metasedimentary rocks of the Ravalli Group; northern Belt province (Middle Proterozoic) at surface, covers 0.4 % of this area

Intermediate Precambrian age metasediments; dominantly quartzite with minor micaceous layers and mica schists of northern Idaho.

Lithology: quartzite; mica schist

Idaho batholith and associated masses (Phanerozoic | Mesozoic Cenozoic | Cretaceous-Late Tertiary) at surface, covers < 0.1 % of this area

Idaho batholith and associated masses: faintly gneissic quartz monzonite, granodiorite, and similar rocks. The extreme eastern part of the Idaho batholith extends into Ravalli County, Mont. This and nearby masses of similar rocks are shown as associated with the Idaho batholith and designated Ki. Future studies may show that some granitoid masses further east are also allied to the Idaho batholith or that a few of the masses now grouped with that batholith are younger. Precise dating is impossible at present.

Lithology: granitoid

Syenite, quartz syenite, monzodiorite, quartz diorite, gabbro, pyroxenite, and hornblendite; Late Proterozoic plutons; east-central Idaho (Late Proterozoic) at surface, covers 0.3 % of this area

Younger or Intermediate Precambrian age intrusive rock undifferentiated.

Lithology: syenite; quartz syenite; monzodiorite; quartz diorite; gabbro; pyroxenite; hornblendite

Glacial debris; Late Pleistocene glacial till, outwash, and alluvium of continental glaciers; northern Idaho (Late Pleistocene ) at surface, covers < 0.1 % of this area

Pleistocene till, moraines and similar unsorted glacial debris.

Lithology: till; outwash; alluvium

Glacial debris; Late Pleistocene till, outwash, and alluvium of valley glaciers; high mountain valleys (Late Pleistocene ) at surface, covers 0.4 % of this area

Pleistocene upland valley deposits; commonly derived from alpine glaciation.

Lithology: till; outwash; alluvium

Garnet-sillimanite-biotite schist; Middle Proterozoic Prichard Formation, northern Belt province (Early Middle Proterozoic) at surface, covers 0.1 % of this area

Precambrian high-grade metamorphic rock; metasediment; kyanite-sillimanite-garnet-mica coarse-grained schist and gneiss; minor quartzite

Lithology: schist; gneiss; quartzite

Felsic augen gneiss after porphyritic granite; Middle Proterozoic; southern Belt province (Middle Proterozoic) at surface, covers < 0.1 % of this area

Augen gneiss, amphibolite and other metamorphosed igneous rocks; possibly Precambrian.

Lithology: peraluminous granite; orthogneiss; diabase; amphibolite

Basalt lava flows; Early Miocene valley-filling basalt flows of subunit 1b; Columbia Plateau (Miocene) at surface, covers 2 % of this area

Miocene basalt flows of western Idaho; commonly porphyritic and exposed on lower slopes.

Lithology: tholeiite; lava flow

Tuffaceous shale, sandstone, conglomerate, and lignite; Eocene to Pliocene alluvial and lacustrine deposits; central and southern Idaho (Tertiary) at surface, covers 0.2 % of this area

Tertiary continental sediments; predominantly Upper Tertiary in age; subdivisions are:(Tpd, Tmd, and Ted).

Lithology: shale; sandstone; conglomerate; tuff; siltstone; lignite; bentonite; claystone; limestone

Metavolcanic and metasedimentary rocks, diorite, trondhjemite, and migmatite; Cretaceous to Jurassic quartz dioritic plutons in Mesozoic to Permian greenschist-facies rocks; western Idaho, Blue Mountains island-arc complex (Cretaceous to Permian) at surface, covers 3 % of this area

Triassic and possibly Permian submarine metavolcanic rocks of west-central Idaho.

Lithology: metavolcanic rock; meta-argillite; migmatite; amphibolite; serpentinite

Basalt lava flows; Middle to Late Miocene local basalt flows of subunit 3b; Columbia Plateau (Late Miocene) at surface, covers < 0.1 % of this area

Upper Miocene valley-filling basalt flows of western Idaho.

Lithology: basalt; lava flow

Rhyolite ignimbrites; Early Pleistocene felsic volcanics; Yellowstone Plateau (Early Pleistocene) at surface, covers < 0.1 % of this area

Lower Pleistocene silicic volcanic units of the Island Park-Yellowstone area.

Lithology: rhyolite; ignimbrite

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

Quartzite, siltstone, conglomerate, and metavolcanic rocks; Late and Middle Proterozoic, undivided; Atlanta batholith roof pendants (Late and Middle Proterozoic, undivided) at surface, covers 2 % of this area

Precambrian, high-grade metamorphic rock

Lithology: quartzite; meta-argillite; metaconglomerate; schist; calc-silicate rock; marble; amphibolite; mafic metavolcanic rock; felsic metavolcanic rock

Basalt dikes; Miocene basaltic feeder dikes of subunit ib; Columbia Plateau (Miocene) at surface, covers < 0.1 % of this area

Miocene intrusions including basalt feeder dikes and sills of western Idaho.

Lithology: basalt

Clastic debris; Quaternary colluvium, fanglomerate, talus, and glacial deposits; upland-valley margins (Quaternary) at surface, covers 0.3 % of this area

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

Lithology: alluvium; glacial drift; colluvium

Ravalli group (Proterozoic | Mesoproterozoic) at surface, covers < 0.1 % of this area

Ravalli group: a diverse assemblage with numerous subdivisions, only a few of which have been recognized over large enough areas to be distinguished here. Near Idaho the rocks are light colored and siliceous, ranging from pure white quartzite to siliceous shale, mostly in subdued tones of gray, green, purple, and red. Near Missoula the rocks are dark-gray quartzite and quartzitic argillite. In and near Glacier National Park the Grinnell, Appekunny, and Altyn formations are distinguished.

Lithology: meta-argillite; quartzite

Quartzite, mica schist, and calc-silicate rock; Proterozoic high-grade metasedimentary rocks; trans-Idaho metamorphic province (Proterozoic) at surface, covers 4 % of this area

Precambrian, high-grade metamorphic rock; metasediments; kyanite-sillimanite schist, and micaceous quartzite

Lithology: quartzite; mica schist; calc-silicate rock

Intermediate intrusions; mostly Late Cretaceous dioritic to granodioritic plutons of the Idaho batholithic assemblage (Cretaceous) at surface, covers 1 % of this area

Cretaceous plutons; intermediate; as granodiorite or diorite; probably includes unmapped older and younger crystalline bodies.

Lithology: tonalite; granodiorite; quartz diorite; trondhjemite

Alluvium (Phanerozoic | Cenozoic | Quaternary) at surface, covers < 0.1 % of this area

Alluvium: mainly valley fill consisting of silt, sand, and gravel; includes some terrace deposits and glacial drift of Pleistocene age in some areas; locally includes hot spring tufa. The older part of the alluvium, where present, is probably of Pliocene age.

Lithology: alluvium; glacial drift; carbonate

Metavolcanic and metasedimentary rocks; Middle to Lower Triassic greenschist-facies metamorphic rocks; western Idaho, Blue Mountains island-arc complex (Middle and Early Triassic) at surface, covers 3 % of this area

Middle and Lower Triassic metabasalt and submarine volcaniclastics of western Idaho

Lithology: mafic metavolcanic rock; metasedimentary rock; quartzite; meta-conglomerate; meta-argillite; marble; keratophyre

Shale, limestone, and sandstone; Triassic marine to non-marine epicontinental deposits (subunits are TRl and TRu) (Triassic) at surface, covers < 0.1 % of this area

Triassic shallow-marine to non-marine sediments of eastern Idaho; subdivisions are (TRu and TRl).

Lithology: shale; limestone; sandstone; chert; conglomerate

Gravel, sand, and clay; Quaternary-Tertiary colluvium and fanglomerate; western Idaho (Pleistocene and Pliocene) at surface, covers 0.5 % of this area

Pleistocene and Pliocene fanglomerate, colluvium, and poorly sorted gravel deposits.

Lithology: alluvial fan; colluvium; residuum; gravel; clay or mud; sand; silt

Sedimentary rocks (Jurassic) (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)

Lithology: shale; siltstone; graywacke

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 < 0.1 % of this area

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

Lithology: basalt; latite; lava flow

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 31 % 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)

Border zone of Idaho batholith and associated masses (Proterozoic Phanerozoic | Mesozoic Cenozoic | Cretaceous-Late Tertiary) at surface, covers < 0.1 % of this area

Border zone of Idaho batholith and associated masses: granitic gneiss and sedimentary rocks, mainly of Belt age, impregnated with granitic material. Because of lack of information they are not distinguished aournd some of the smaller granitic masses that have such border zones.

Lithology: granitoid; metasedimentary rock

Tuff, arkose, claystone, siltstone, conglomerate, lignite; Miocene alluvial and lacustrine deposits (Miocene) at surface, covers < 0.1 % of this area

Miocene stream and lake deposits; generally associated with volcanic episodes.

Lithology: tuff; arkose; claystone; conglomerate; siltstone; mixed clastic/coal

Open Water (Holocene) at surface, covers < 0.1 % of this area

water

Lithology: water

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 4 % of this area

Precambrian high-grade metamorphic rock; metasediment

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

Limestone, sandstone, shale, and chert; Pennsylvanian marine epicontinental-basin deposits; southeastern Idaho (Pennsylvanian) at surface, covers < 0.1 % of this area

Pennsylvanian beds; lowermost portion of the southern Idaho sequence (PPNs).

Lithology: limestone; sandstone; shale; chert

Quartz diorite, tonalite, granodiorite, orthogneiss, migmatite; Cretaceous to Jurassic quartz dioritic plutons; western Idaho, Blue Mountains island-arc complex (Early Cretaceous to Late Jurassic) at surface, covers 2 % of this area

Lower Cretaceous to Upper Jurassic intrusions in west-central Idaho.

Lithology: quartz diorite; tonalite; granodiorite; orthogneiss; migmatite; gabbro; trondhjemite; aplite

Granite and diorite (Jurassic and Triassic) (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)

Lithology: granite; quartz diorite

Gravel, sand, and silt; Quaternary; alluvium (Quaternary) at surface, covers 0.1 % of this area

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

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

Quartzite and marble; Middle Proterozoic Hoodoo Quartzite; southern Belt province (Middle Proterozoic) at surface, covers < 0.1 % of this area

Intermediate Precambrian sediments, light-colored, massive quartzite of southern Idaho.

Lithology: quartzite; marble

Monzogranite, syenogranite, and syenite; Eocene phaneritic to porphro-aphanitic intrusions of the pink monzogranite suite; Challis magmatic belt (Eocene) at surface, covers 3 % of this area

Eocene intrusions of predominantly felsic (pink granite) composition

Lithology: granite; quartz syenite

Granitoid intrusions, metasedimentary rocks, and migmatite, undivided; Cretaceous intrusions and Proterozoic host rocks, undivided; northern and central Idaho (Cretaceous to Early Proterozoic) at surface, covers 0.6 % of this area

Mixed, highly altered and migmatitic rocks; derived from imbrication and dynamic events

Lithology: granitoid; metasedimentary rock; migmatite

Limestone, slate; Upper Triassic greenschist-facies metamorphic rocks; western Idaho, Blue Mountains island-arc complex; (Late Triassic) at surface, covers 0.6 % of this area

Upper Triassic shale overlying reefal limestone and dolomite in west-central Idaho.

Lithology: limestone; slate; shale; dolostone (dolomite); phyllite; marble; skarn (tactite); amphibolite schist; greenschist

High-grade metasedimentary biotite schist, biotite gneiss, and calc-silicate gneiss; Middle Proterozoic northern Belt province near Idaho batholith (Middle Proterozoic) at surface, covers 2 % of this area

Precambrian high-grade metamorphic rock; kyanite-sillimanite calc-silcate bearing schist and gneiss; scapolite common

Lithology: mica schist; paragneiss; calc-silicate rock

Basalt lava flows; Middle Miocene flood-basalt flows of subunit 2b; Columbia Plateau (Miocene) at surface, covers 12 % of this area

Miocene basalt flows of western Idaho; commonly finely crystalline and exposed on upper slopes.

Lithology: basalt; lava flow

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 8 % of this area

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

Lithology: granite; quartz monzodiorite; granodiorite

Diorite, gabbro, and granite; Jurassic to Triassic plutons; western Idaho, Blue Mountains island-arc complex (Jurassic to Triassic) at surface, covers 0.5 % of this area

Lower Mesozoic intrusions; localized near the Snake Canyon of western Idaho.

Lithology: diorite; quartz diorite; gabbro; norite; alkali-granite (alaskite); greenschist