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Geologic units in Washington county, Idaho
[Additional scientific data in this geographic area]
- 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 3 % of this area
Pliocene stream and lake deposits; may be due to volcanic and block-faulting events.
- Metasedimentary and meta-igneous rocks; Triassic to Mississippian greenschist-facies dismembered ophiolite, western Idaho, Blue Mountains island-arc complex (Triassic to Mississippian) at surface, covers 2 % of this area
Jurassic marine wacke, volcanic, or carbonate metasediments of western Idaho.
- Alluvial deposits (Holocene) (Holocene) at surface, covers < 0.1 % of this area
Sand, gravel, and silt forming flood plains and filling channels of present streams. In places includes talus and slope wash. Locally includes soils containing abundant organic material, and thin peat beds
- Basalt lava flows; Early Miocene valley-filling basalt flows of subunit 1b; Columbia Plateau (Miocene) at surface, covers 0.5 % of this area
Miocene basalt flows of western Idaho; commonly porphyritic and exposed on lower slopes.
- Open Water (Holocene) at surface, covers 0.8 % of this area
Lakes and streams
- 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)
- Gravel, sand, and silt; Quaternary basin-filling alluvium; Snake River Plain, Basin and Range provinces (Quaternary) at surface, covers 1 % of this area
Quaternary detritus; generally basin-filling deposits of central and southern Idaho.
- Clastic debris; Quaternary colluvium, fanglomerate, talus, and glacial deposits; upland-valley margins (Quaternary) at surface, covers 1 % of this area
Quaternary colluvium, fanglomerate, and talus plus some glacial debris in upland valleys.
- 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 2 % of this area
Middle and Lower Triassic metabasalt and submarine volcaniclastics of western Idaho
- Basalt lava flows; Middle to Late Miocene local basalt flows of subunit 3b; Columbia Plateau (Late Miocene) at surface, covers 0.2 % of this area
Upper Miocene valley-filling basalt flows of western Idaho.
- Gravel, sand, and silt; glacial outburst flood deposits, outwash, fanglomerate, and alluvium, undivided; Pleistocene (Pleistocene) at surface, covers 0.6 % of this area
Pleistocene outwash, fanglomerate, flood and terrace gravels; sudivisions are: (Qpug, Qpmg, and Qplg).
- Volcanic and metavolcanic rocks (Upper Triassic) (Late Triassic) at surface, covers < 0.1 % of this area
Green to gray spilite and keratophyre flows and flow breccia; and subordinate amounts of coarse volcaniclastic sandstone, tuff, sandstone, siltstone, chert, conglomerate, and limestone. Marine fauna from interlayered sedimentary rocks indicates unit is mostly of Karnian (Late Triassic) age. Includes Late Triassic "andesitic and basaltic rocks" of Nolf and Taubeneck (1963), and the basaltic to rhyolitic metavolcanic rocks and interbedded sedimentary rocks of the Huntington Formation of Brooks (1979). Equivalent, in part, to unit TrPv
- Gravel, sand, and silt; Quaternary; alluvium (Quaternary) at surface, covers 8 % of this area
Quaternary alluvium; may contain some glacial deposits and colluvium in uplands
- Sedimentary rocks, partly metamorphosed (Triassic and Paleozoic) (Paleozoic to Triassic) at surface, covers < 0.1 % of this area
Poorly bedded argillite, chert, phyllite, phyllitic quartzite, calc-phyllite, impure limestone, and marble. In places rocks are strongly foliated. Sparse fossils (Fusilina, corals, and crinoids) indicate that the unit includes rocks of Leonardian, Ochoan, and Late Triassic age (OR084). Includes Elkhorn Ridge Argillite (OR035), Mesozoic and Paleozoic sedimentary rocks of Brown and Thayer (OR008), and the Permian Coyote Butte Formation (OR085). In Baker County includes "sedimentary and volcanic rocks" (MzPza) of Brooks and others (OR039) and metamorphosed sedimentary and minor volcaniclastic rocks containing mineral assemblages indicative of quartz-albite-muscovite-chlorite subfacies and quartz-albite-epidote-biotite subfacies of the greenschist facies. In Jefferson and Wasco Counties north of Prineville, includes "phyllite and sedimentary rocks " of Swanson (OR031). Includes part of the Burnt River Schist (OR035; OR081) and volcaniclastic facies of several metavolcanic units of Permian and Late Triassic age. Not on State map (OR001) in area of La Grande 100K quadrangle, butmapped in OR291 as Elkhorn Ridge Argillite (Triassic Permian, Pennsylvannian, and Devonian?)
- Metavolcanic and metasedimentary rocks; Jurassic greenschist-facies metamorphic rocks; western Idaho, Blue Mountains island-arc complex (Jurassic) at surface, covers 4 % of this area
Jurassic mixed marine detrital and volcanic rocks of western Idaho.
- Basalt lava flows; Middle Miocene flood-basalt flows of subunit 2b; Columbia Plateau (Miocene) at surface, covers 8 % of this area
Miocene basalt flows of western Idaho; commonly finely crystalline and exposed on upper slopes.
- 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 50 % of this area
Miocene plateau basalt flows of western Idaho; subdivisions are (Tm3b, Tm2b, Tm1b).
- 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 3 % of this area
Lower Cretaceous to Upper Jurassic intrusions in west-central Idaho.
- Tuff, arkose, claystone, siltstone, conglomerate, lignite; Miocene alluvial and lacustrine deposits (Miocene) at surface, covers 14 % of this area
Miocene stream and lake deposits; generally associated with volcanic episodes.
- Sedimentary and volcanic rocks (Jurassic and Upper Triassic?) (Late Triassic? to Jurassic) at surface, covers < 0.1 % of this area
Olive-drab, pale-brown, dark-gray, and black volcanic graywacke and siltstone; lesser conglomerate and slate, and minor limestone and chert. Includes more extensive outcrops of Triassic or Jurassic limestone at north base of Juniper Mountain in northern Malheur County and near Huntington in southeastern Baker County. Interlayers of silicic and intermediate volcanic rocks are rare. Locally metamorphosed to prehnite-pumpellyite and zeolite facies and in places to greenschist facies. Folded, sheared, and locally foliated. Includes the Weatherby Formation of Brooks (1979). Age is Late Triassic(?) and Early and Middle Jurassic (Sinemurian-Callovian)
- Open Water (Holocene) at surface, covers < 0.1 % of this area