Trachyandesite, latite, trachybasalt flows, dikes, and volcaniclastic debris; Eocene intermediate volcanics; central Idaho, southern Challis volcanic field (IDTevi;0)

State	Idaho
Name	Trachyandesite, latite, trachybasalt flows, dikes, and volcaniclastic debris; Eocene intermediate volcanics; central Idaho, southern Challis volcanic field
Geologic age	Eocene
Original map label	Tev; Tei
Comments	In the lower part of the Challis Volcanics, erosionally exposed in the southern part of the Challis Volcanic Field, Tevi includes dark-colored K-rich andesite, andesite, latite, and K-rich basalt, mostly as flows that emanated from many small, widely scattered vents, and coallesced to form an extensive lava plateau by filling about 300 m of pre-Challis relief. Arkosic conglomerate at base grades upward into tuffaceous conglomerate and volcanic breccia. Light-colored dacite to rhyodacite in small stratovolcanoes and dome complexes, formed before large-volume explosive eruptions formed and filled calderas. In the Salmon area, Cheney Volcanics are latitic and andesitic flows of the lower Challis Volcanic Group (ID150).
Primary rock type	trachyandesite
Secondary rock type	latite
Other rock types	trachybasalt; dacite; trachyte; lava flow; volcanic breccia (agglomerate)
Lithologic constituents	Major Igneous > Volcanic > Felsic-volcanic > Latite (Flow)latite lava flows, small composite volcanoes Igneous > Volcanic > Mafic-volcanic > Andesite (Flow)K-rich andesite, andesite, basaltic andesite lava flows Minor Igneous > Volcanic > Mafic-volcanic > Basalt (Flow)Mg-rich basalt, K-rich basalt, shoshonite lava flows Incidental Sedimentary > Clastic > Conglomerate (Bed)basal arkosic conglomerate grades up to tuffaceous conglomerate Igneous > Hypabyssal > Mafic-hypabyssal > Hypabyssal-basaltic-andesite (Dike or sill)discordant subvolcanic intrusions (plugs, dikes, sills) Igneous > Volcanic > Felsic-volcanic (Volcaniclastic, volcanic breccia)felsic flow breccia Igneous > Volcanic > Mafic-volcanic (Volcaniclastic, volcanic breccia)mafic flow breccia Igneous > Volcanic > Felsic-volcanic (Dome)felsic dome complexes Igneous > Volcanic > Felsic-volcanic > Trachyte (Flow)trachytic lava flows Igneous > Volcanic > Felsic-volcanic > Dacite (Flow)dacitic lava flows, small composite volcanoes
Map references	Bond, J.G., Kauffman, J.D., Miller, D.A., and Venkatakrishnan, Ramesh, 1978, Geologic map of Idaho: Moscow, Idaho, Idaho Bureau of Mines and Geology, with contributions from U.S. Geological Survey, scale 1:500,000.
Unit references	Bond, J.G., Kauffman, J.D., Miller, D.A., and Venkatakrishnan, Ramesh, 1978, Geologic map of Idaho: Moscow, Idaho, Idaho Bureau of Mines and Geology, with contributions from U.S. Geological Survey, scale 1:500,000. Hardyman, R.F., 1989, Eocene magmatism, Challis volcanic field, central Idaho: in 28th International Geological Congress Field Trip Series, Volcanism and Plutonism of western North America, Vol. 2, Washington D.C., American Geophysical Union, p. T337: 32-38. Witkind, I.J., 1972, Geolgic map of the Henrys Lake quadrangle, Idaho and Montana: U.S. Geological Survey Map I-781-A, 1:62,500 scale. [http://pubs.er.usgs.gov/publication/i781A] Rember, W.C., and Bennett, E.H., 1979, Geologic map of the Dubois quadrangle, Idaho: Moscow, Idaho, Idaho Bureau of Mines and Geology Map Series, Dubois 2o quadrangle, scale 1:250,000. Rember, W.C., and Bennett, E.H., 1979, Geologic map of the Idaho Falls quadrangle, Idaho: Moscow, Idaho, Idaho Bureau of Mines and Geology, Geologic Map Series, Idaho Falls 2o quadrangle, scale 1:250,000. Rember, W.C. and Bennett, Earl H., 1979, Geologic map of the Hailey quadrangle, Idaho: Moscow, Idaho, Idaho Bureau of Mines and Geology, Geologic Map Series, Hailey 2o quadrangle, scale 1:250,000. Worl, R.G., Kiilsgaard, T.H., Bennett, E.H., Link, P.K., Lewis, R.S., Mitchell, V.E., Johnson, K.M., and Snyder, L.D., 1991, Geologic map of the Hailey 1o x 2o quadrangle, Idaho: U.S. Geological Survey Open-File Report 91-340, 1:250,000 scale. [http://pubs.er.usgs.gov/publication/ofr91340] McIntyre, D.H., Ekren, E.B., and Hardyman, R.F., 1982, Stratigraphic and structural framework of the Challis Volcanics in the eastern half of the Challis 1o x 2o quadrangle, Idaho: in Bonnichsen, Bill, and Breckenridge, R.M., eds., Cenozoic geology of Idaho: Moscow, Idaho, Idaho Bureau of Mines and Geology Bulletin 26, p. 3-22 Anderson, A.L., 1961, Geology and mineral resources of the Lemhi quadrangle, Lemhi County, Idaho: Moscow, Idaho, Idaho Bureau of Mines and Geology Pamphlet no. 124.
Geographic coverage	Blaine - Boise - Butte - Camas - Clark - Custer - Elmore - Fremont - Gooding - Lemhi - Valley