Portland State University. Department of Geology
Paul E. Hammond
Date of Publication
Master of Science (M.S.) in Geology
Stratigraphic geology -- Oligocene, Geology -- Washington (State) -- Ohanapecosh Formation, Volcanism -- Washington (State) -- Ohanapecosh Formation, Sedimentation and deposition -- Washington (State) -- Ohanapecosh Formation
1 online resource (94 p.)
Over 1055 m of early Oligocene andesitic-dacitic volcaniclastic rocks and minor interbedded andesitic lava flows of the Ohanapecosh Formation are exposed in a dissected structural high in the southern Washington Cascade Range, about 22 km southwest of Packwood, Washington.
The exposed sequence of rocks in the study area are located approximately 250 m above the base of the Ohanapecosh Formation. A lower sequence of deposits, about 350 m in thickness, are dominated by primary and reworked lithic lapilli-tuff and epiclastic channelized volcanic sandstone and conglomerate. These sediments are interpreted as pyroclastic flows and stream deposits, respectively. The upper sequence, about 455 m thick is dominated by volcanic diamictites interpreted as lahars, with minor lithic lapilli-tuff and epiclastic volcanic sandstone.
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Stine, Cynthia Marie, "Stratigraphy of the Ohanapecosh Formation north of Hamilton Buttes, southcentral Washington" (1987). Dissertations and Theses. Paper 3762.