Dacite to rhyolite (or rhodacite) ignimbrites; Eocene rhyodacitic cauldron complex; east-central Idaho, central Challis volcanic field (IDTevf;0)

State	Idaho
Name	Dacite to rhyolite (or rhodacite) ignimbrites; Eocene rhyodacitic cauldron complex; east-central Idaho, central Challis volcanic field
Geologic age	Eocene
Original map label	Tev; Tei
Comments	Tev consists mostly of thick caldera-fill and thinner outflow deposits of major rhyodacitic ash-flow tuffs, minor rhyodacitic lava flows, plugs, dikes and sills, minor rhyolitic ash-flow tuffs and flows, incidental quartz-latitic, dacitic, and andesitic to basaltic lava flows, and volcaniclastic megabreccia, breccia, and volcano-sedimentary deposits. Large explosive eruptions formed volcano-tectonic grabens, calderas, cauldron complexes, and dated ignimbrites, as follows: Panther Cr. Graben (48.6 Ma), Custer Graben (48.5 Ma), Van Horn Pk cauldron complex: tuff of Ellis Cr. (48.4 Ma), tuff of Eightmile Cr. (46.9 Ma); Twin Peaks caldera: tuff of Challis Creek (45 Ma) (ID137, ID139). Also includes Yearian Volcanics, which consist moslty of light-colored pyroclastic rocks in the middle of the Challis Volcanic Group in the Salmon area (ID140).
Primary rock type	rhyodacite
Secondary rock type	ignimbrite
Other rock types	lava flow; rhyolite; quartz latite; dacite; andesite; basalt; volcanic breccia (agglomerate); mixed clastic/volcanic
Lithologic constituents	Major Igneous > Volcanic > Felsic-volcanic > Dacite (Pyroclastic, ash-flow)mostly "rhyodacite" on source maps (trachydacite, chemically) Minor Igneous > Volcanic > Felsic-volcanic > Rhyolite (Pyroclastic, ash-flow)rhyolitic ignimbrites Igneous > Volcanic > Felsic-volcanic > Dacite (Flow)mostly "rhyodacite" on source maps (trachydacite, chemically) Incidental Sedimentary > Clastic > Mixed-clastic > Sandstone-Mudstone (Tuffaceous)alluvial and lacustrine tuffaceous sedimentary deposits Sedimentary > Clastic > Sedimentary-breccia (Tuffaceous)mudflow breccia and conglomerate Igneous > Volcanic > Felsic-volcanic (Volcaniclastic, volcanic breccia)megabreccia, explosion breccia, flow breccia Igneous > Volcanic > Mafic-volcanic > Basaltic-andesite (Flow)High-K andesite, basaltic andeside, basalt, shoshonite flows Igneous > Volcanic > Felsic-volcanic > Quartz-latite (Flow)quartz latite to rhyolite Igneous > Hypabyssal > Felsic-hypabyssal > Hypabyssal-dacite (Dike or sill)mostly "rhyodacite" on source maps (trachydacite, chemically) Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow)rhyolitic lava flows
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. Fisher, F.S., McIntyre, D.H., and Johnson, K.M., 1992, Geologic map of the Challis 1o x 2o quadrangle, Idaho: U.S. Geological Survey Miscellaneous Investigations Series Map I-1819, scale 1:250,000 with pamphlet, 39 p. [http://pubs.er.usgs.gov/publication/i1819] Evans, K.V. and Green, G.N., 2003, Geologic map of the Salmon National Forest and vicinity, east-central Idaho: U.S. Geological Survey Geological Investigations Series I-2765, scale 1:100,000 with pamphlet, 19 p. [http://pubs.er.usgs.gov/publication/i2765] 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, E.H., 1979, Geologic map of the Challis quadrangle, Idaho: Moscow, Idaho, Idaho Bureau of Mines and Geology, Geologic Map Series, Challis 2o quadrangle, scale 1:250,000. Moye, F.J., Hackett, W.R., Blakely, J.D., and Snider, L.G., 1988, Regional geologic setting and volcanic stratigraphy of the Challis Volcanic Field, central Idaho: in Link, P.K., and Hackett, W.R., eds., Guidebook to the Geology of central and southern Idaho: Moscow, Idaho, Idaho Geological Survey Bulletin 27, p. 87-97. [http://www.idahogeology.org/PDF/Bulletins_(B)/B-27Full.pdf] Christiansen, R.L., and Yeats, R.S., 1992, Post-Laramide geology of the U.S. Cordilleran region: in Burchfiel, B.C., Lipman, P.W., and Zoback, M.L., eds., The Cordilleran Orogen: Conterminous U.S.: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G-3, p. 261-406. 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 Kiilsgaard, T.H., 1946, Compiled geologic map of Latah County: Moscow, Idaho, Idaho Bureau of Mines and Geology, 1:190,080 scale (1inch = 3 miles).
Geographic coverage	Blaine - Boise - Butte - Clark - Custer - Elmore - Lemhi - Owyhee - Valley