Rhyolite and dacite (ORTrh;0)

Rhyolite and dacite

Ash-flow tuff, lava flows, pumice-lapilli tuff, coarse pumicite, flow breccia, and domal complexes of rhyolitic, rhyodacitic, and dacitic composition; in places includes peralkaline rhyolite and some andesite and andesite breccia. Locally porphyritic with phenocrysts of alkali feldspar, plagioclase, and minor augite, ferro-hedenbergite, hornblende, hypersthene, or biotite. Commonly flow banded; locally glassy. Many of the ash--flow tuffs exhibit flow features and only obscure vitro-clastic textures. In places includes interlayers of silicic volcaniclastic rocks and tuffaceous sedimentary rocks. Includes rhyolite at Owyhee Dam, Jump Creek Rhyolite, and Littlefield Rhyolite, all of Kittleman and others (1965); Dooley Rhyolite Breccia of Gilluly (1937), radiometrically dated at 14.7 ñ 0.4 Ma by potassium-argon methods (Fiebelkorn and others, 1983); resurgent domal masses in McDermitt caldera area; and extensive unnamed flows and ash-flow tuffs in the central and southern part of the Owyhee Upland. Also includes isolated masses of dacitic and rhyodacitic flows, breccia, and ash-flow tuff along eastern slope of Cascade Range that are lapped by flows and sediments of the Madras (or Deschutes) Formation. Potassium-argon ages on rocks in unit from southeast Oregon range from about 13 to 16 Ma; lenses of interbedded tuffaceous sedimentary rocks locally contain a Miocene (Barstovian) vertebrate fauna

State	Oregon
Name	Rhyolite and dacite
Geologic age	Miocene to Pliocene
Lithologic constituents	Major Igneous > Volcanic > Felsic-volcanic > Dacite (Flow, Pyroclastic-ash flow) Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow, Pyroclastic-ash flow, Volcaniclastic-volcanic breccia)Also contains rhyodacite and andesite Minor Igneous > Volcanic > Mafic-volcanic > Andesite (Flow) Sedimentary > Clastic > Siltstone (Bed)
Comments	Includes rhyolite of the Silver City Range, (15.6-17.8+0.3 Ma (K-Ar; OR060; OR159; OR165; OR185; OR195); Littlefield Rhyolite (OR023; OR024), 15.2-16.8 Ma (40Ar/39Ar; OR179); rhyolite of McIntyre Ridge (OR170; formerly Dooley Rhyolite Breccia; OR035) the uppermost rhyolite member of which was dated at 14.7+0.4 Ma (K-Ar; OR010); tuff of Swisher Mountain, 13.1+0.2-14.7 Ma (K-Ar; OR159; OR160; OR161; OR162; OR196; OR197); rhyolite domes, plugs, and dikes 14.9+0.4 Ma-15.2+0.5 Ma; Rhyolite of Bully Creek canyon [sic] (OR158; same as rhyolite of Cottonwood Mountain; OR285; OR286; possibly slightly older than Littlefield Rhyolite); rhyolite of McCain Creek (OR007), a large-volume rheomorphic ash-flow tuff chemically similar to tuff of Swisher Mountain (OR159; OR160; OR161; OR162) that is widespread in southeastern Malheur County; rhyolite of Mahogany Mountain (OR166); rhyolite and rhyodacite of Cry Creek (OR167); unnamed silicic flows, tuffs, and welded tuff north of the town of Ironside that lie below Dooley Volcanics (OR287); rhyolite domes, plugs, and dikes (OR198; OR199); and Dam Rhyolite, 13.5+3.4-22.8+2.6 Ma (K-Ar; OR200; OR137)
Stratigraphic units	Rhyolite at Owyhee Dam (OR023), Jump Creek Rhyolite (OR023), Rhyolite of Double Mountain (OR136), Littlefield Rhyolite (OR023; OR024), Dooley Volcanics (OR170; formerly Dooley Volcanic Breccia; OR035), Rhyolite of Cottonwood Mountain (OR285; OR286; formerly rhyolite of Bully Creek canyon; OR158), Rhyolite of McCain Creek (OR007), Tuff of Swisher Mountain(?) (OR159; OR160; OR161; OR162; OR163), Rhyolite of McIntyre Ridge (OR164), Rhyolite of Silver City Range (OR159; OR165), Rhyolite of Mahogany Mountain (OR166), Rhyolite of Dry Creek (OR167)
References	Walker, G.W. and MacLeod, N.S., 1991, Geologic map of Oregon: U.S. Geological Survey, scale 1:500,000. Walker, G.W. and Repenning, C.A., 1966, Geologic map of the west half of the Jordan Valley quadrangle, Malheur County, Oregon: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-457, scale 1:250,000. https://pubs.er.usgs.gov/publication/i457 Ferns, M.L., Evans, J.G., and Cummings, M.L., 1993a, Geologic map of the Mahogany Mountain 30 x 60 minute quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-78, scale 1:100,000. Ferns, M.L., Brooks, H.C., Evans, J.G., and Cummings, M.L., 1993b, Geologic map of the Vale 30 x 60 minute quadrangle, Malheur County Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-77, scale 1:100,000. Fiebelkorn, R.B., Walker, G.W., Macleod, N.S., McKee, E.H., and Smith, J.G., 1983, Index to K-Ar determinations for the State of Oregon: Isochron/West, no. 37, p. 3-60. Kittleman, L.R., Green, A.R., Hagood, A.R., Johnson, A.M., McMurray, J.M., Russell, R.G., and Weeden, D.A., 1965, Cenozoic stratigraphy of the Owyhee region, southeastern Oregon: Eugene, University of Oregon Museum of Natural History Bulletin 1, 45 p. Kittleman, L.R., Green, A.R., Haddock, G.H., Hagood, A.R., Johnson, A.M., McMurray, J.M., Russell, R.G., and Weeden, D.A., 1967, Geologic map of the Owyhee region, Malheur County, Oregon: Eugene, University of Oregon Museum of Natural History Bulletion 8, scale 1:125,000. Gilluly, James, 1937, Geology and mineral resources of the Baker quadrangle, Oregon: U.S. Geological Survey Bulletin 879, 199 p. https://pubs.er.usgs.gov/publication/b879 Brooks, H.C., McIntyre, J.R., and Walker, G.W., 1976, Geology of the Oregon part of the Baker 1o by 2o quadrangle: Oregon Department of Geology and Mineral Industries Geologic Map Series GMS-7, scale 1:250,000. Walker, G.W., 1973, Reconnaissance geologic map of the Pendleton quadrangle, Oregon and Washington: U.S. Geological Survey Miscellaneus Geologic Investigations Map I-727, scale 1:250,000. https://pubs.er.usgs.gov/publication/i727 Walker, G.W., 1977, Geologic map of Oregon east of the 121st meridian: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-902, scale 1:500,000. https://pubs.er.usgs.gov/publication/i902 MacLeod, N.S. and Sherrod, D.R., 1992, Reconnaisance geologic map of the west half of the Crescent quadrangle, central Oregon: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-2215, scale 1:250,000. https://pubs.er.usgs.gov/publication/i2215 Wolff, E.N., 1965, The geology of the northern half of the Caviness quadrangle, Oregon: Eugene, University of Oregon, Ph.D. dissertation, 214 p. Evans, J.G., 1990b, Geology and mineral resources map of the South Mountain quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geologic Map Series GMS-67, scale 1:24,000. Brooks, H.C. and McIntyre, J.R., 1977, Preliminary geologic map of the Bowen Valley quadsrangle, Baker County, Oregon: Oregon Department of Geology and Mineral Industries, scale 1:24,000. Evans, J.G., Geologic map of the Dooley Mountain quadrangle, Baker County, Oregon: U.S. Geological Survey Geological Quadrangle GQ-1694, scale 1: 24,000. https://pubs.er.usgs.gov/publication/gq1694 Ferns, M.L., 1989, Geology and mineral resources map of the Owyhee Dam quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-55, scale 1:24,000. Ferns, M.L., 1989, Geology and mineral resources map of the Graveyard Point quadrangle, Malheur Count Oregon, and Owyhee County, Idaho: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-54, scale 1:24,000. Ferns, M.L., 1988, Geology and mineral resources map of the Owyhee Ridge quadrangle. Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-53, scale 1:24,000. Ramp, Len, and Ferns, M.L., 1989, Geology and mineral resources map of the Double Mountain quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-58, scale 1:24,000. Ferns, M.L. and Cummings, M.L., 1992, Geology and mineral resources map of The Elbow quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-62, scale 1:24,000. MacLeod, N.S., 1990, Geology and mineral resources map of the Sheaville quadrangle, Malheur County, Oregon, and Owyhee County, Idaho: Oregon Department of Geology and Mineral Industries Geological Map Series, GMS-64, scale 1:24,000. MacLeod, N.S., 1990, Geology and mineral resources map of the Mahogany Gap quadrangle, Malheur County, Oregon: Oregon Departmernt of Geology and Mineral Industries Geological Map Series GMS-65, scale 1:24,000. Ferns, M.L. and O'Brien, J.P., 1992, Geology and mineral resources map of the Harper quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-69, scale 1:24,000. Brooks, H.C. and O'Brien, J.P., 1992, Geology and mineral resources map of the Harper quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-71, scale 1:24,000. Brooks, H.C. and O'Brien, J.P., 1992a, geology and mineral resources map of the Westfall quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-71, scale 1: 24,000. Ekren, E.B., McIntyre, D.H., Bennett, E.H., and Marvin, R.F., 1982, Cenozoic stratigraphy of western Owyhee County, Idaho, in Bonnichsen, Bill and Breckenridge, R.M., eds., Cenozoic geology of Idaho: Idaho Geolological Survey Bulletin 26, p. 215-235. Ekren, E.B., McIntyre, D.H., and Bennett, E.H., 1984, High-temperature, large-volume, lavalike ash-flow tuffs without calederas in southwestewrn Idaho: U.S. Geological Survey Professional Paper 1272, 76 p. https://pubs.er.usgs.gov/publication/pp1272 Evans, J.G., 1987, Geologic map of the Owyhee Canyon Wilderness Study Area, Malheur County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-1926, scale 1:62,500. https://pubs.er.usgs.gov/publication/mf1926 Ferns, M.L., 1992b, Preliminary geologic map of the Cedar Mountain quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral industries Open-File Map O-92-05, scale 1:24,000. Minor, S.A., King, H.D., Kulik, D.M., and Sawatzky, D.L., 1987, Mineral resources of the Upper Deep Creek Wilderness Study Area, Owyhee County, Idaho: U.S. Geological Survey Bulletin 1719-B, 14 p. https://pubs.er.usgs.gov/publication/b1719B Vander Meulen, D.B., Griscom, Andrew, King, H.D., and Benham, J.R., 1989, Mineral resources of the Upper Leslie Gulch and Slocum Creek Wilderness Study Areas, Malheur County, Oregon: U.S. Geological Survey Bulletin 1741-D, 20 p. https://pubs.er.usgs.gov/publication/b1741D Ekren, E.B., McIntyre, D.H., Bennett, E.H., and Malde, H.E., 1981, Geologic map of Owyhee County, Idaho, west of longitude 116o W: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-1256, scale 1:125,000. https://pubs.er.usgs.gov/publication/i1256 Rytuba, J.J., Vander Meulen, D.B., Barlock, V.E., and Ferns, M.L., 1990, Field Guide to hot-spring gold deposits in the Lake Owyhee Volcanic Field, eastern Oregon, in Geology and ore deposits of the Great Basin: Geological Society of Nevada Field Trip Guide no. 10, 119 p. Brooks, H.C., 1992a, Preliminary geologic map of the Avery Creek quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-16, scale 1:24,000. Lees, K.R., 1994, Magmatic and tectonic changes through time in the Neogene volcanic rocks of the Vale area, Oregon, northwestern USA: Milton Keynes, U.K., The Open University, Ph.D. dissertation 284 p. Dalrymple, G.B., 1979, Critical tables for conversion of K-Ar ages from old to new constants: Geology, v. 7, no. 11, p. 558-560. Roback, R.C., Vander Meulen, D.B., King, H.D., Plouff, Donald, Munts, S.R., and Willett, S.L., 1987, Mineral resources of the Pueblo Mountains Wilderness Study Area, Harney County, Oregon, and Humboldt County, Nevada: U.S. Geological Survey Bulletin 1740-B, 30 p. https://pubs.er.usgs.gov/publication/b1740B Armstrong,, R.L., Taubeneck, W.H., and Hales, P.O., 1977, Rb-Sr and K-Ar geochronometry of Mesozoic granitic rocks and their Sr isotopic composition, Oregon, Washington, and Idaho: Geological Society of America Bulletin, v. 88, p. 397-411. Neil, W.M., 1975, Geology of the southeastern Owyhee Mountains and environs, Owyhee County, Idaho: Stanford, California, Stanford University, master's thesis, 59 p. Rytuba, J.J., Vander Meulen, D.B., and Barlock, V.E., Tectonic and stratigraphic controls on epithermal precious metal mineralization in the northern part of the Basin and Range, Oregon, Idaho, and Nevada, in Buffa, R.H. and Conyer, A.R., eds., Geology and ore deposits of the Great Basin field trip guidebook compendium: Geological Society of Nevada, v. 2, 633-644. Brown, D.E. and Petros, J.R., Jr., 1985, Geochemistry, geochronology, and magnetostratigraphy of a measured section of the Owyhee Basalt, Malheur County, Oregon: Oregon Geology, v. 47, p. 15-20. Evans, J.G. and Binger, G.B., 1998, Geologic map of the Little Black Canyon quadrangle, Malheur County, Oregon: U.S. Geological Survey Open-File Report 98-493, scale 1:24,000. https://pubs.er.usgs.gov/publication/ofr98493 Evans, J.G. and Binger, G.B., 1998, Geologic map of the Alder Creek quadrangle, Malheur County, Oregon: U.S. Geological Survey Open-File Report 98-484, scale 1:24,000. https://pubs.er.usgs.gov/publication/ofr98484 Evans, J.G. and Binger, G.B., 1999, Preliminary geologic map of the Skull Springs quadrangle, Malheur County, Oregon: U.S. Geological Survey Open-File Report 99-381, scale 1:24,000. https://pubs.er.usgs.gov/publication/ofr99381 Evans, J.G. and Binger, G.B., 1998, Geologic map of the Shumway Reservoir quadrangle, Malheur County, Oregon: U.S. Geological Survey Open-File Report 98-138, scale 1:24,000. https://pubs.er.usgs.gov/publication/ofr98138 Evans, J.G., 1996, Geologic map of the Monument Peak quadrangle, Malheur County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-2317, scale 1:24,000. https://pubs.er.usgs.gov/publication/mf2317 Evans, J.G. and Keith, W.J., 1996, Geologic map of the Tims Peak quadrangle, Malheur County, Oregon: U. S. Geological Survey Miscellaneous Field Studies Map MF-2316, scale 1:24,000. Evans, J.G., 1993, Geologic map of the Brannan Gulch quadrangle, Baker County, Oregon: U.S. Geological Survey Geological Quadrangle GQ-1744, scale 1:24,000. https://pubs.er.usgs.gov/publication/gq1744 Prostka, H.J., 1968, Geologic map of the Ironside 15' quad, Oregon: Oregon Department of Geology and Mineral Industries, scale 1:62,500. Ferns, M.L., 1992, Preliminary geologic map of the Jordan Craters South quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-09, scale 1:24,000. Brooks, H.C., 1992, Preliminary geologic map of the Avery Creek quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-16, scale 1:24,000. Brooks, H.C., 1992, Preliminary geologic map of the Rufino Butte quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-17, scale 1:24,000. Brooks, H.C., 1993, Preliminary geologic map of the Copeland Reservoir quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral industries Open-File Map O-93-3, scale 1:24,000. Brooks, H.C. and O'Brien, J.P., 1992b, Geology and mineral resources of the Little Valley quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-72, scale 1:24,000. Ferns, M.L., 1992, Preliminary geologic map of the McCain Creek quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-10, scale 1:24,000. Ferns, M.L., 1992, Preliminary geologic map of the Sacramento Butte quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-13, scale 1;24,000. Ferns, M.L. and Evans, J.G., 1993c, Preliminary geologic map of the Rinehart Canyon quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-93-5, scale 1: 24,000. Ferns, M.L. and Gilbert, Deborah, 1992, Preliminary geologic map of the Rockville quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-12, scale 1:24,000. Ferns, M.L. and Macleod, N.S., 1992, Preliminary geologic map of the Cow Lakes quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-06, scale 1:24,000. Ferns, M.L.1992, Preliminary geologic map of the Downey Canyon quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-07, scale 1:24,000. Ferns, M.L. and O'Brien, J.P., 1991, Preliminary geologic map of the Keeney Ridge quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-91-3, scale 1:24,000. Ferns, M.L. and O'Brien, J.P., 1992, Geology and mineral resources map of the Namorf quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-74, scale 1:24,000. Ferns, M.L. and Urbanczyk, K., 1990, Preliminary geologic map of the Kane Spring Gulch quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-90-03, scale 1:24,000. McMurray, J.M., 1962, Geology of the Freezeout Mountain area, Malheur County, Oregon: Eugene, University of Oregon, master's thesis, 87 p. Minor, S.A., Rytuba, J.J., Goeldner, C.A., and Tegtmeyer, K.J., 1987, Geologic map of the Alvord Hot Spring quadrangle, Harney County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-1916, scale 1:24,000. https://pubs.er.usgs.gov/publication/mf1916 Minor, S.A., Vander Meulen, D.B., Rytuba, J.J., and Vercoutere, T.L., 1989, Geologic map of The V quadrangle, Harney County, Oregon: U.S. Geological Survey Open-File Report 89-351, scale 1:24,000. https://pubs.er.usgs.gov/publication/ofr89351 Camp, V.E., Ross, M.E., and Hanson, W.E., 2003, Genesis of flood basalts and Basin and Range volcanic rocks from Steens Mountain to the Malheur River Gorge, Oregon: Geological Society of America Bulletin, v. 115, no. 1, p. 105-128. Rytuba, J.J., Vander Meulen, D.B., Vercoutere, T.L., and Minor, S.A., 1982b, Reconnaissance geologic map of the Borax Lake quadrangle, Harney County, Oregon: U.S. Geological Survey Open-File Report 82-1126, scale 1:24,000. https://pubs.er.usgs.gov/publication/ofr821126 Evans, J.G., unpub. mapping, 1994, Fields quadrangle, Harney County Evans, J.G., unpub. mapping, 1994, Ladycomb Peak quadrangle, Harney County Rytuba, J.J., Bateson, J.T., Curtis, D.L., Jr., and Cox, G.A., 1983, Geologic map of the Little Whitehorse Creek quadrangle, Harney and Malheur Counties, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-1472, scale 1:24,000. https://pubs.er.usgs.gov/publication/mf1472 Rytuba, J.J., Minor, S.A., Conrad, W.K., and Vander Meulen, D.B., 1982, Geologic map of the Trout Creek Canyon quadrangle, Harney County, Oregon: U.S. Geological Survey Open-File Report 82-281, scale 1:24,000. https://pubs.er.usgs.gov/publication/ofr82281 Rytuba, J.J., Minor, S.A., Miller, R.J., and Vander Meulen, D.B., 1983, Geologic map of the Red Mountain quadrangle, Harney County, Oregon: U.S. Geological Survey Open-File Report 83-0282, scale 1:24,000. https://pubs.er.usgs.gov/publication/ofr83282 Rytuba, J.J., Minor, S.A., and Vander Meulen, D.B., 1983, Reconnaissance geologic map of the Whitehorse Ranch quadrangle, Harney and Malheur Counties, Oregon: U.S. Geological Survey Open-File Report 83-0284, scale 1:24,000. https://pubs.er.usgs.gov/publication/ofr83284 Vander Meulen, D.B., Rytuba, J.J., Grubensky, M.J., and Goeldner, C.A., 1987, Geologic map of the Bannock Ridge 7.5' quadrangle, Malheur County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-1903A, scale 1:24,000. https://pubs.er.usgs.gov/publication/mf1903 Vander Meulen, D.B., Rytuba, J.J., Minor, S.A., and Harwood, C.S., 1989, Preliminary geologic map of the Three Fingers Rock quadrangle, Malheur County, Oregon: U.S. Geological Survey Open-File Report 89-344, scale 1:24,000. https://pubs.er.usgs.gov/publication/ofr89344 Vander Meulen, D.B., Rytuba, J.J., Vercoutere, T.L., and Minor, S.A., 1987, Geologic map of the Rooster Comb 7.5' quadrangle, Malheur County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-1902C, scale 1:24,000. https://pubs.er.usgs.gov/publication/mf1902 Whitsun, N.W., 1988, Geochemical stratigraphy of the Dooley Rhyolite Breccia and Tertiary basalts in the Dooley Mountain quadrangle, Oregon: Portland, Oregon, Portland State University, master's thesis, 122 p. Evans, J.G., unpub. mapping, Hope Butte quadrangle, Malheur County Evans, J.G., unpub. mapping, Swede Flat quadrangle, Malheur County Evans, J.G., unpub. mapping, Devils Heel quadrangle, Malheur County
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Counties	Baker - Clackamas - Crook - Deschutes - Harney - Jefferson - Klamath - Lake - Malheur

Rhyolite and dacite

Walker, G.W. and MacLeod, N.S., 1991, Geologic map of Oregon: U.S. Geological Survey, scale 1:500,000.

Walker, G.W. and Repenning, C.A., 1966, Geologic map of the west half of the Jordan Valley quadrangle, Malheur County, Oregon: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-457, scale 1:250,000.

Ferns, M.L., Evans, J.G., and Cummings, M.L., 1993a, Geologic map of the Mahogany Mountain 30 x 60 minute quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-78, scale 1:100,000.

Ferns, M.L., Brooks, H.C., Evans, J.G., and Cummings, M.L., 1993b, Geologic map of the Vale 30 x 60 minute quadrangle, Malheur County Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-77, scale 1:100,000.

Fiebelkorn, R.B., Walker, G.W., Macleod, N.S., McKee, E.H., and Smith, J.G., 1983, Index to K-Ar determinations for the State of Oregon: Isochron/West, no. 37, p. 3-60.

Kittleman, L.R., Green, A.R., Hagood, A.R., Johnson, A.M., McMurray, J.M., Russell, R.G., and Weeden, D.A., 1965, Cenozoic stratigraphy of the Owyhee region, southeastern Oregon: Eugene, University of Oregon Museum of Natural History Bulletin 1, 45 p.

Kittleman, L.R., Green, A.R., Haddock, G.H., Hagood, A.R., Johnson, A.M., McMurray, J.M., Russell, R.G., and Weeden, D.A., 1967, Geologic map of the Owyhee region, Malheur County, Oregon: Eugene, University of Oregon Museum of Natural History Bulletion 8, scale 1:125,000.

Gilluly, James, 1937, Geology and mineral resources of the Baker quadrangle, Oregon: U.S. Geological Survey Bulletin 879, 199 p.

Brooks, H.C., McIntyre, J.R., and Walker, G.W., 1976, Geology of the Oregon part of the Baker 1o by 2o quadrangle: Oregon Department of Geology and Mineral Industries Geologic Map Series GMS-7, scale 1:250,000.

Walker, G.W., 1973, Reconnaissance geologic map of the Pendleton quadrangle, Oregon and Washington: U.S. Geological Survey Miscellaneus Geologic Investigations Map I-727, scale 1:250,000.

Walker, G.W., 1977, Geologic map of Oregon east of the 121st meridian: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-902, scale 1:500,000.

MacLeod, N.S. and Sherrod, D.R., 1992, Reconnaisance geologic map of the west half of the Crescent quadrangle, central Oregon: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-2215, scale 1:250,000.

Wolff, E.N., 1965, The geology of the northern half of the Caviness quadrangle, Oregon: Eugene, University of Oregon, Ph.D. dissertation, 214 p.

Evans, J.G., 1990b, Geology and mineral resources map of the South Mountain quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geologic Map Series GMS-67, scale 1:24,000.

Brooks, H.C. and McIntyre, J.R., 1977, Preliminary geologic map of the Bowen Valley quadsrangle, Baker County, Oregon: Oregon Department of Geology and Mineral Industries, scale 1:24,000.

Evans, J.G., Geologic map of the Dooley Mountain quadrangle, Baker County, Oregon: U.S. Geological Survey Geological Quadrangle GQ-1694, scale 1: 24,000.

Ferns, M.L., 1989, Geology and mineral resources map of the Owyhee Dam quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-55, scale 1:24,000.

Ferns, M.L., 1989, Geology and mineral resources map of the Graveyard Point quadrangle, Malheur Count Oregon, and Owyhee County, Idaho: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-54, scale 1:24,000.

Ferns, M.L., 1988, Geology and mineral resources map of the Owyhee Ridge quadrangle. Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-53, scale 1:24,000.

Ramp, Len, and Ferns, M.L., 1989, Geology and mineral resources map of the Double Mountain quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-58, scale 1:24,000.

Ferns, M.L. and Cummings, M.L., 1992, Geology and mineral resources map of The Elbow quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-62, scale 1:24,000.

MacLeod, N.S., 1990, Geology and mineral resources map of the Sheaville quadrangle, Malheur County, Oregon, and Owyhee County, Idaho: Oregon Department of Geology and Mineral Industries Geological Map Series, GMS-64, scale 1:24,000.

MacLeod, N.S., 1990, Geology and mineral resources map of the Mahogany Gap quadrangle, Malheur County, Oregon: Oregon Departmernt of Geology and Mineral Industries Geological Map Series GMS-65, scale 1:24,000.

Ferns, M.L. and O'Brien, J.P., 1992, Geology and mineral resources map of the Harper quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-69, scale 1:24,000.

Brooks, H.C. and O'Brien, J.P., 1992, Geology and mineral resources map of the Harper quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-71, scale 1:24,000.

Brooks, H.C. and O'Brien, J.P., 1992a, geology and mineral resources map of the Westfall quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-71, scale 1: 24,000.

Ekren, E.B., McIntyre, D.H., Bennett, E.H., and Marvin, R.F., 1982, Cenozoic stratigraphy of western Owyhee County, Idaho, in Bonnichsen, Bill and Breckenridge, R.M., eds., Cenozoic geology of Idaho: Idaho Geolological Survey Bulletin 26, p. 215-235.

Ekren, E.B., McIntyre, D.H., and Bennett, E.H., 1984, High-temperature, large-volume, lavalike ash-flow tuffs without calederas in southwestewrn Idaho: U.S. Geological Survey Professional Paper 1272, 76 p.

Evans, J.G., 1987, Geologic map of the Owyhee Canyon Wilderness Study Area, Malheur County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-1926, scale 1:62,500.

Ferns, M.L., 1992b, Preliminary geologic map of the Cedar Mountain quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral industries Open-File Map O-92-05, scale 1:24,000.

Minor, S.A., King, H.D., Kulik, D.M., and Sawatzky, D.L., 1987, Mineral resources of the Upper Deep Creek Wilderness Study Area, Owyhee County, Idaho: U.S. Geological Survey Bulletin 1719-B, 14 p.

Vander Meulen, D.B., Griscom, Andrew, King, H.D., and Benham, J.R., 1989, Mineral resources of the Upper Leslie Gulch and Slocum Creek Wilderness Study Areas, Malheur County, Oregon: U.S. Geological Survey Bulletin 1741-D, 20 p.

Ekren, E.B., McIntyre, D.H., Bennett, E.H., and Malde, H.E., 1981, Geologic map of Owyhee County, Idaho, west of longitude 116o W: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-1256, scale 1:125,000.

Rytuba, J.J., Vander Meulen, D.B., Barlock, V.E., and Ferns, M.L., 1990, Field Guide to hot-spring gold deposits in the Lake Owyhee Volcanic Field, eastern Oregon, in Geology and ore deposits of the Great Basin: Geological Society of Nevada Field Trip Guide no. 10, 119 p.

Brooks, H.C., 1992a, Preliminary geologic map of the Avery Creek quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-16, scale 1:24,000.

Lees, K.R., 1994, Magmatic and tectonic changes through time in the Neogene volcanic rocks of the Vale area, Oregon, northwestern USA: Milton Keynes, U.K., The Open University, Ph.D. dissertation 284 p.

Dalrymple, G.B., 1979, Critical tables for conversion of K-Ar ages from old to new constants: Geology, v. 7, no. 11, p. 558-560.

Roback, R.C., Vander Meulen, D.B., King, H.D., Plouff, Donald, Munts, S.R., and Willett, S.L., 1987, Mineral resources of the Pueblo Mountains Wilderness Study Area, Harney County, Oregon, and Humboldt County, Nevada: U.S. Geological Survey Bulletin 1740-B, 30 p.

Armstrong,, R.L., Taubeneck, W.H., and Hales, P.O., 1977, Rb-Sr and K-Ar geochronometry of Mesozoic granitic rocks and their Sr isotopic composition, Oregon, Washington, and Idaho: Geological Society of America Bulletin, v. 88, p. 397-411.

Neil, W.M., 1975, Geology of the southeastern Owyhee Mountains and environs, Owyhee County, Idaho: Stanford, California, Stanford University, master's thesis, 59 p.

Brown, D.E. and Petros, J.R., Jr., 1985, Geochemistry, geochronology, and magnetostratigraphy of a measured section of the Owyhee Basalt, Malheur County, Oregon: Oregon Geology, v. 47, p. 15-20.

Evans, J.G. and Binger, G.B., 1998, Geologic map of the Little Black Canyon quadrangle, Malheur County, Oregon: U.S. Geological Survey Open-File Report 98-493, scale 1:24,000.

Evans, J.G. and Binger, G.B., 1998, Geologic map of the Alder Creek quadrangle, Malheur County, Oregon: U.S. Geological Survey Open-File Report 98-484, scale 1:24,000.

Evans, J.G. and Binger, G.B., 1999, Preliminary geologic map of the Skull Springs quadrangle, Malheur County, Oregon: U.S. Geological Survey Open-File Report 99-381, scale 1:24,000.

Evans, J.G. and Binger, G.B., 1998, Geologic map of the Shumway Reservoir quadrangle, Malheur County, Oregon: U.S. Geological Survey Open-File Report 98-138, scale 1:24,000.

Evans, J.G., 1996, Geologic map of the Monument Peak quadrangle, Malheur County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-2317, scale 1:24,000.

Evans, J.G. and Keith, W.J., 1996, Geologic map of the Tims Peak quadrangle, Malheur County, Oregon: U. S. Geological Survey Miscellaneous Field Studies Map MF-2316, scale 1:24,000.

Evans, J.G., 1993, Geologic map of the Brannan Gulch quadrangle, Baker County, Oregon: U.S. Geological Survey Geological Quadrangle GQ-1744, scale 1:24,000.

Prostka, H.J., 1968, Geologic map of the Ironside 15' quad, Oregon: Oregon Department of Geology and Mineral Industries, scale 1:62,500.

Ferns, M.L., 1992, Preliminary geologic map of the Jordan Craters South quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-09, scale 1:24,000.

Brooks, H.C., 1992, Preliminary geologic map of the Avery Creek quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-16, scale 1:24,000.

Brooks, H.C., 1992, Preliminary geologic map of the Rufino Butte quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-17, scale 1:24,000.

Brooks, H.C., 1993, Preliminary geologic map of the Copeland Reservoir quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral industries Open-File Map O-93-3, scale 1:24,000.

Brooks, H.C. and O'Brien, J.P., 1992b, Geology and mineral resources of the Little Valley quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-72, scale 1:24,000.

Ferns, M.L., 1992, Preliminary geologic map of the McCain Creek quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-10, scale 1:24,000.

Ferns, M.L., 1992, Preliminary geologic map of the Sacramento Butte quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-13, scale 1;24,000.

Ferns, M.L. and Evans, J.G., 1993c, Preliminary geologic map of the Rinehart Canyon quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-93-5, scale 1: 24,000.

Ferns, M.L. and Gilbert, Deborah, 1992, Preliminary geologic map of the Rockville quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-12, scale 1:24,000.

Ferns, M.L. and Macleod, N.S., 1992, Preliminary geologic map of the Cow Lakes quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-06, scale 1:24,000.

Ferns, M.L.1992, Preliminary geologic map of the Downey Canyon quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-07, scale 1:24,000.

Ferns, M.L. and O'Brien, J.P., 1991, Preliminary geologic map of the Keeney Ridge quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-91-3, scale 1:24,000.

Ferns, M.L. and O'Brien, J.P., 1992, Geology and mineral resources map of the Namorf quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Geological Map Series GMS-74, scale 1:24,000.

Ferns, M.L. and Urbanczyk, K., 1990, Preliminary geologic map of the Kane Spring Gulch quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-90-03, scale 1:24,000.

McMurray, J.M., 1962, Geology of the Freezeout Mountain area, Malheur County, Oregon: Eugene, University of Oregon, master's thesis, 87 p.

Minor, S.A., Rytuba, J.J., Goeldner, C.A., and Tegtmeyer, K.J., 1987, Geologic map of the Alvord Hot Spring quadrangle, Harney County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-1916, scale 1:24,000.

Minor, S.A., Vander Meulen, D.B., Rytuba, J.J., and Vercoutere, T.L., 1989, Geologic map of The V quadrangle, Harney County, Oregon: U.S. Geological Survey Open-File Report 89-351, scale 1:24,000.

Camp, V.E., Ross, M.E., and Hanson, W.E., 2003, Genesis of flood basalts and Basin and Range volcanic rocks from Steens Mountain to the Malheur River Gorge, Oregon: Geological Society of America Bulletin, v. 115, no. 1, p. 105-128.

Rytuba, J.J., Vander Meulen, D.B., Vercoutere, T.L., and Minor, S.A., 1982b, Reconnaissance geologic map of the Borax Lake quadrangle, Harney County, Oregon: U.S. Geological Survey Open-File Report 82-1126, scale 1:24,000.

Evans, J.G., unpub. mapping, 1994, Fields quadrangle, Harney County

Evans, J.G., unpub. mapping, 1994, Ladycomb Peak quadrangle, Harney County

Rytuba, J.J., Bateson, J.T., Curtis, D.L., Jr., and Cox, G.A., 1983, Geologic map of the Little Whitehorse Creek quadrangle, Harney and Malheur Counties, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-1472, scale 1:24,000.

Rytuba, J.J., Minor, S.A., Conrad, W.K., and Vander Meulen, D.B., 1982, Geologic map of the Trout Creek Canyon quadrangle, Harney County, Oregon: U.S. Geological Survey Open-File Report 82-281, scale 1:24,000.

Rytuba, J.J., Minor, S.A., Miller, R.J., and Vander Meulen, D.B., 1983, Geologic map of the Red Mountain quadrangle, Harney County, Oregon: U.S. Geological Survey Open-File Report 83-0282, scale 1:24,000.

Rytuba, J.J., Minor, S.A., and Vander Meulen, D.B., 1983, Reconnaissance geologic map of the Whitehorse Ranch quadrangle, Harney and Malheur Counties, Oregon: U.S. Geological Survey Open-File Report 83-0284, scale 1:24,000.

Vander Meulen, D.B., Rytuba, J.J., Grubensky, M.J., and Goeldner, C.A., 1987, Geologic map of the Bannock Ridge 7.5' quadrangle, Malheur County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-1903A, scale 1:24,000.

Vander Meulen, D.B., Rytuba, J.J., Minor, S.A., and Harwood, C.S., 1989, Preliminary geologic map of the Three Fingers Rock quadrangle, Malheur County, Oregon: U.S. Geological Survey Open-File Report 89-344, scale 1:24,000.

Vander Meulen, D.B., Rytuba, J.J., Vercoutere, T.L., and Minor, S.A., 1987, Geologic map of the Rooster Comb 7.5' quadrangle, Malheur County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-1902C, scale 1:24,000.

Whitsun, N.W., 1988, Geochemical stratigraphy of the Dooley Rhyolite Breccia and Tertiary basalts in the Dooley Mountain quadrangle, Oregon: Portland, Oregon, Portland State University, master's thesis, 122 p.

Evans, J.G., unpub. mapping, Hope Butte quadrangle, Malheur County