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

Geologic units in Clark county, Idaho

[Additional scientific data in this geographic area]

Dolostone, arenite, conglomerate, and chert; Silurian to Middle Ordovician marine outer continental-shelf deposits; east-central Idaho (Silurian to Middle Ordovician) at surface, covers < 0.1 % of this area

Silurian to Middle Ordovician marine carbonate-to-clastic strata of east-central Idaho.

Lithology: dolostone (dolomite); arenite; conglomerate; chert

Sandstone, siltstone, shale, limestone, and coal ; Early Cretaceous Cordilleran retroarc-foreland-basin deposits; southeastern Idaho (Early Cretaceous) at surface, covers 2 % of this area

Lower Cretaceous shale, siltstone, red-bed sandstone and fresh-water limestone.

Lithology: sandstone; siltstone; shale; limestone; coal

Basalt and gravel; Late Pleistocene basalt flows and interlayered gravel of subunit 2b; Snake River Plain (Late Pleistocene) at surface, covers 11 % of this area

Upper Pleistocene Snake Plain basaltic lava flows, unit 2.

Lithology: tholeiite; lava flow; gravel

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

Dolostone, limestone, sandstone, shale, and conglomerate; Devonian marine continental-shelf deposits; east-central and southeastern Idaho (Devonian) at surface, covers 0.3 % of this area

Devonian bedded dolomite and limestone interval of eastern and southern Idaho.

Lithology: dolostone (dolomite); limestone; sandstone; shale; conglomerate

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

Missoula group: chiefly red, maroon, or purple argillite; sandy or quartzitic argillite, and generally impure quartzite and limestone. The larger limestone masses are similar to the Siyeh limestone of the Piegan group. The Missoula group includes numerous named formations, most of which cannot be traced with confidence far from their type localities. Among these are the Marsh shale in the Helena region, the Striped Peak and Libby formations in northwestern Montana, five near Missoula, and others in and south of Glacier National Park.

Lithology: quartzite; meta-argillite; carbonate; meta-conglomerate

Sandstone, conglomerate, siltstone, tuff, claystone, limestone, and diatomite; Pliocene tuffaceous alluvial and lacustrine deposits; Snake River Plain and vicinity, southeastern Idaho (Pliocene ) at surface, covers < 0.1 % of this area

Pliocene stream and lake deposits; may be due to volcanic and block-faulting events.

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

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

Lakes and streams

Lithology: water

Colorado shale (Phanerozoic | Mesozoic | Cretaceous-Early Cretaceous-Middle(?) Cretaceous-Late) at surface, covers < 0.1 % of this area

Colorado shale: dark-gray shale and siltstone with many concretions and sandy units. Includes equivalents of Fall River, Skull Creek, Newcastle, Mowry, Belle Fourche, Greenhorn, Carlile, and Niobrara formations, and locally Telegraph Creek formation. In the less well-known areas beds of other ages may have been included.

Lithology: fine-grained mixed clastic

Rhyolite ot trachyte ignimbrites and flows; Pliocene felsic volcanics; eastern Snake River Plain and vicinity (Pliocene) at surface, covers 9 % of this area

Pliocene silicic welded tuff, ash, and flow rock; most common in southwestern Idaho.

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

Glacial debris; Late Pleistocene glacial till, outwash, and alluvium of continental glaciers; northern Idaho (Late Pleistocene ) at surface, covers 0.2 % of this area

Pleistocene till, moraines and similar unsorted glacial debris.

Lithology: till; outwash; alluvium

Devonian, undifferentiated (Phanerozoic | Paleozoic | Devonian) at surface, covers < 0.1 % of this area

Devonian, undifferentiated: comprises Three Forks formation consisting of carbonaceous and calcareous shale with some sandstone and limestone, Jefferson limestone, and unnamed units of Devonian age.

Lithology: carbonate; fine-grained mixed clastic; conglomerate; sedimentary breccia; evaporite

Quartzite, argillite, carbonate, meta-conglomerate, siltite, intermediate volcanic rock; Late Proterozoic rifted continental margin; southeastern Idaho (Late Proterozoic) at surface, covers 1 % of this area

Younger Precambrian detrital units of central and southeastern Idaho; subdivisions are (Z2s and Z1s).

Lithology: quartzite; argillite; carbonate; conglomerate; siltstone; intermediate volcanic rock

Gravel, sand, and silt; Quaternary basin-filling alluvium; Snake River Plain, Basin and Range provinces (Quaternary) at surface, covers 8 % of this area

Quaternary detritus; generally basin-filling deposits of central and southern Idaho.

Lithology: alluvium; alluvial fan; alluvial terrace

Basalt, clay, and gravel; Late Pleistocene basalt flows with interlayered alluvial and lacustrine sediments; Snake River Plain and vicinity (subunits are Qpu1b, Qpu2b, Qpu3b, and Qpu4b) (Late Pleistocene) at surface, covers 0.8 % of this area

Upper Pleistocene Snake Plain lava flows; local stratigraphic position shown by (Qpu4b, Qpu3b, Qpu2b, Qpu1b).

Lithology: tholeiite; lava flow; clay or mud; gravel

Conglomerate, sandstone, and siltstone; Eocene to Late Cretaceous alluvial-fan deposits; east-central Idaho, Cordilleran fold-thrust belt, piggyback basins (Eocene to Late Cretaceous ) at surface, covers 5 % of this area

Lower Tertiary to Upper Mesozoic breccia, conglomerate and sandstone; syntectonic in part.

Lithology: conglomerate; arkose; siltstone; limestone

Siltstone, shale, sandstone, and limestone; Jurassic Cordilleran retroarc-foreland-basin deposits (subunits are Jl and Ju); southeastern Idaho (Jurassic) at surface, covers 0.3 % of this area

Jurassic shallow-marine to non-marine sediments of eastern Idaho; subdivisions are (Jl and Ju).

Lithology: siltstone; shale; sandstone; limestone

Montana group, undifferentiated (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers < 0.1 % of this area

Montana group, undifferentiated: mainly sandstone and shale, soft and in part poorly consolidated; some coal; shown undivided only in areas where detailed data are lacking and in these areas some rocks not of Montana age may have been included. In particular, rocks designated Km in southwestern Montana may include some Tertiary strata.

Lithology: fine-grained mixed clastic; coal

Tuffaceous shale, sandstone, conglomerate, and lignite; Eocene to Pliocene alluvial and lacustrine deposits; central and southern Idaho (Tertiary) at surface, covers 4 % 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

Basalt flows, pumice, and tuff; Early Pleistocene to Pliocene basaltic volcanics; Snake River Plain (Early Pleistocene) at surface, covers < 0.1 % of this area

Lower Pleistocene to Pliocene basalts with associated tuffs and volcanic detritus.

Lithology: tholeiite; lava flow; pumice; tuff

Permian, undifferentiated (Phanerozoic | Paleozoic | Permian) at surface, covers < 0.1 % of this area

Permian, undifferentiated: chert, sandstone, limestone, quartzite, and shale with rock phosphate mostly at base; mainly Phosphoria formation

Lithology: fine-grained mixed clastic; carbonate; chert; phosphorite; black shale; oil shale

Basalt flows, pyroclastic debris, clastic sediments, and diatomite; Pliocene basaltic volcanics and clastic sediments; Snake River Plain and vicinity (Pliocene) at surface, covers 0.6 % of this area

Pliocene olivine basalt flows and associated tuff and detritus of southern Idaho.

Lithology: basalt; lava flow; tuff; mixed clastic/volcanic

Surficial sediments; Quaternary alluvial, lacustrine, eolian, and glacial-outwash deposits, undivided; Snake River Plain, and Basin-and-Range provinces (Quaternary) at surface, covers 1 % of this area

Quaternary surficial cover; Snake Plain stream, lake, wind and glacial-flood mantle.

Lithology: loess; colluvium

Sand; Holocene dunes; Snake River Plain (Holocene) at surface, covers < 0.1 % of this area

Recent active sand dunes and eolian deposits.

Lithology: dune sand; eolian

Jurassic, undifferentiated (Phanerozoic | Mesozoic | Jurassic) at surface, covers < 0.1 % of this area

Jurassic, undifferentiated: calcareous shale and sandstone; includes the Morrison formation, the Ellis group, Sundance formation, and other rocks of Jurassic age.

Lithology: fine-grained mixed clastic; limestone; evaporite

Limestone, dolostone, sandstone, siltstone, and chert; Lower Permian to Lower Pennsylvanian marine continental-shelf deposits; east-central Idaho (Early Permian to Early Pennsylvanian) at surface, covers 5 % of this area

Lower Permian to Lower Pennsylvanian (Carboniferous) shallow-water detritus.

Lithology: limestone; dolostone (dolomite); arenite; siltstone; chert

Rhyolite ignimbrites; Early Pleistocene felsic volcanics; Yellowstone Plateau (Early Pleistocene) at surface, covers 0.7 % 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 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

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

Tertiary sedimentary rocks, undifferentiated: clastic deposits in western Montana, mostly in valleys, and in most places not divided into formations; mostly poorly consolidated gravel, sand, silt, and clay; includes some tuffaceous material and locally lenses of lignite and bentonite; a little hot spring tufa; and in areas not yet mapped in detail, lava may be included. These rocks were in part laid down in lakes but a large part was formed in streams and alluvial fans. These rocks are Tertiary in age and as now mapped may even include some beds of Cretaceous age. Some late Tertiary terrace deposits may be included.

Lithology: medium-grained mixed clastic; coarse-grained mixed clastic; lava flow; ash-flow tuff; tuff; coal; bentonite; carbonate

Kootenai formation and associated rocks (Phanerozoic | Mesozoic | Jurassic Cretaceous-Early) at surface, covers < 0.1 % of this area

Kootenai formation and associated rocks: conglomerate, sandstone, shale, and mudstone; purplish and green beds are common; mainly the Kootenai; in southern Montana includes strata that have been mapped as Cloverly formation. Includes Second Cat Creek and Third Cat Creek sands of drillers in central part of State; Sunburst sand of drillers in north-central part; and Cut Bank sand of drillers in western part. As here mapped, may locally include thin units of Jurassic age.

Lithology: medium-grained mixed clastic; mudstone; limestone

Clastic debris; Quaternary colluvium, fanglomerate, talus, and glacial deposits; upland-valley margins (Quaternary) at surface, covers 2 % of this area

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

Lithology: alluvium; glacial drift; colluvium

Rhyolite ignimbrites, basalt flows, andesitic flows and tuffs, mudstone, conglomerate, and limestone; Quaternary to Tertiary volcanics and sediments; east-central Idaho (Pliocene) at surface, covers 5 % of this area

Pliocene silicic welded tuff, ash, and flow rock; most common in southwestern Idaho.

Lithology: rhyolite; ash-flow tuff; basalt; lava flow; andesite; tuff

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

Terrace deposits: gravel, sand, and silt of terrace remnants.

Lithology: alluvial terrace

Triassic, undifferentiated (Phanerozoic | Mesozoic | Triassic) at surface, covers < 0.1 % of this area

Triassic, undifferentiated: conglomerate, sandstone, shale, and impure limestone belonging to the Dinwoody and Thaynes formations and other units of Triassic age, and the Chugwater of Triassic and Permian age.

Lithology: fine-grained mixed clastic; limestone; medium-grained mixed clastic

Gravel, sand, and clay; Quaternary-Tertiary colluvium and fanglomerate; western Idaho (Pleistocene and Pliocene) at surface, covers 9 % of this area

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

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

Shale, limestone, and sandstone; Triassic marine to non-marine epicontinental deposits (subunits are TRl and TRu) (Triassic) at surface, covers 0.3 % of this area

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

Lithology: shale; limestone; sandstone; chert; conglomerate

Basalt flows, basaltic pyroclastic and clastic debris; Middle Pleistocene canyon-filling and plateau lava flows, pyroclastic debris, alluvium, and colluvium; Snake River Plain (Middle Pleistocene) at surface, covers < 0.1 % of this area

Middle Pleistocene plateau and canyon-filling basalt in and near Snake Plain.

Lithology: tholeiite; lava flow; pyroclastic; alluvium; colluvium

Chert, shale, phosphorite, and carbonates; Permian restricted marine epicontinental-basin deposits; southeastern Idaho (Permian) at surface, covers 0.2 % of this area

Permian phosphatic sandstone, mudstone and chert of east-central Idaho.

Lithology: chert; shale; phosphorite; dolostone (dolomite); arenite; limestone

Mississippian, undifferentiated (Phanerozoic | Paleozoic | Carboniferous Mississippian) at surface, covers < 0.1 % of this area

Mississippian, undifferentiated: sandstone, shale, and limestone, in part dolomitic, with chert nodules, some quartzite; includes Big Snowy group in central part of State, Madison group in central and southwestern parts; and Hannan and Brazer limestones in the northwestern part; may include small amounts of Pennsylvanian rocks in areas where stratigraphic studies are incomplete.

Lithology: carbonate; fine-grained mixed clastic; medium-grained mixed clastic; chert

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

Gravel, sand, and silt; Quaternary; alluvium (Quaternary) at surface, covers 12 % of this area

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

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

Trachyandesite, latite, trachybasalt flows, dikes, and volcaniclastic debris; Eocene intermediate volcanics; central Idaho, southern Challis volcanic field (Eocene) at surface, covers < 0.1 % of this area

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

Lithology: trachyandesite; latite; trachybasalt; dacite; trachyte; lava flow; volcanic breccia (agglomerate)

Sandstone, siltstone, dolostone, and chert; Pennsylvanian to Mississippian shallow marine inner continental-shelf deposits; eastern east-central Idaho (Pennsylvanian and Mississippian ) at surface, covers 0.9 % of this area

Pennsylvanian and Mississippian shallow-water carbonates of eastern Idaho.

Lithology: arenite; siltstone; dolostone (dolomite); chert

Basalt, gravel, and pumice; Late Pleistocene basaltic volcanics and interlayered sedimetnsof subunit 3b; Snake River Plain (Late Pleistocene) at surface, covers 13 % of this area

Upper Pleistocene Snake Plain basaltic lava flows, unit 3.

Lithology: tholeiite; lava flow; gravel; pumice

Limestone, shale, siltstone, chert, and conglomerate; Mississippian western turbiditic flysch to eastern shallow-water carbonates; east-central Idaho (Mississippian) at surface, covers 6 % of this area

Mississippian shallow-water carbonate-to-clastic sequence of east-central Idaho.

Lithology: limestone; shale; siltstone; sandstone; chert; conglomerate

Pennsylvanian, undifferentiated (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian) at surface, covers < 0.1 % of this area

Pennsylvanian, undifferentiated: in western Montana is mainly the Quadrant quartzite but includes limestone and other rocks of Pennsylvanian age so far as present data permit. Farther east other formations of Pennsylvanian or possible Pennsylvanian age are included.

Lithology: sandstone; mudstone; carbonate; conglomerate; chert

Dacite to rhyolite (or rhodacite) ignimbrites; Eocene rhyodacitic cauldron complex; east-central Idaho, central Challis volcanic field (Eocene) at surface, covers 0.4 % of this area

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

Lithology: rhyodacite; ignimbrite; lava flow; rhyolite; quartz latite; dacite; andesite; basalt; volcanic breccia (agglomerate); mixed clastic/volcanic