Bulletin of the Museum of Natural History, University of Oregon

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Cenozoic Stratigraphy of the Owyhee Region, Southeastern Oregon
(Museum of Natural History, University of Oregon, 1965-12) Kittleman, Laurence R.; Green, Arthur R.; Hagood, Allen R.; Johnson, Arvid M.; McMurray, Jay M.; Russell, Robert G.; Weeden, Dennis A.
Late Cenozoic terrestrial sedimentation and volcanism produced more than 6000 ft of complexly interstratified rocks in the Owyhee region, southeastern Oregon. Deposition upon a basement of peripherally exposed Paleozoic and Mesozoic rocks began in Miocene time and continued intermittently through the Pleistocene. High-angle block faulting related to the adjacent Basin and Range Province created hundreds to thousands of feet of structural relief. Faulting and concomitant erosion formed north-trending basins that received Miocene, Pliocene, and Pleistocene deposits. The rocks described range from late Miocene to sub-historic. They are dated through mammalian chronology, stratigraphic relations, and potassium· argon chronology. About 30 stratigraphic units are discussed, of which 12 are named and defined. Extrusive rocks are olivine-poor clinopyroxene basalts, porphyritic andesine rhyolites, and rhyolitic welded ash-flow tuffs. Clastic rocks are arkoses, granite-cobble conglomerates, air-fall tuffs, and fluviatile and lacustrine bentonitic volcaniclastic rocks variously adulterated with plutonic detritus.