Olivine basalt (Pliocene and Miocene)

Thin, commonly open-textured (diktytaxitic), subophitic to intergranular olivine basalt flows, intercalated with and grades laterally through palagonite breccia and tuff into tuffaceous sedimentary rocks (unit Ts). In places includes flows of platy olivine andesite or basaltic andesite. Several potassium-argon ages ranging from about 4 to 7 Ma indicate unit is mostly of early Pliocene and late Miocene age. Includes Shumuray Ranch Basalt and Antelope Flat Basalt of Kittleman and others (1965), Grassy Mountain Basalt of Corcoran and others (1962), Drinkwater Basalt of Bowen and others (1963), basalt formerly assigned to Danforth Formation by Piper and others (1939) (see Walker, 1979), Hayes Butte Basalt of Hampton (1964), Pliocene and upper Miocene basalt flows capping and interstratified with the Madras (or Deschutes) Formation, and basalt flows interstratified in the Dalles Formation of Newcomb (1966; 1969)
State Oregon
Name Olivine basalt (Pliocene and Miocene)
Geologic age Miocene to Pliocene
Primary rock type basalt
Secondary rock type andesite
Other rock types
Lithologic constituents
Major
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow)
Minor
Igneous > Volcanic > Mafic-volcanic > Basalt (Pyroclastic)
Igneous > Volcanic > Mafic-volcanic > Basaltic-andesite (Flow)
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow)
Map references
Walker, G.W. and MacLeod, N.S., 1991, Geologic map of Oregon: U.S. Geological Survey, scale 1:500,000.
Unit 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.
Walker, G.W. and Repenning, C.A., 1965, Geologic map of Adel quadrangle, Lake, Harney, and Malheur Counties, Oregon: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-446, 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.
Evans, J.G., Geologic map of the Lower Owyhee Wilderness Study Area, Malheur County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-2167, scale 1:50,000.
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., 1992, Preliminary geologic map of the Wrangle Butte quadrangle, Malheur County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Map O-92-15, scale 1:24,000.
Counties Deschutes - Harney - Lake - Malheur