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Correlation Of The Upper Ellensburg Formation With The Old Scab Mountain Eruptive Center, East-Central Cascade Range, Washington, Christopher Charles Humphrey
Correlation Of The Upper Ellensburg Formation With The Old Scab Mountain Eruptive Center, East-Central Cascade Range, Washington, Christopher Charles Humphrey
Dissertations and Theses
The Ellensburg Formation, preserved in the Nile basin 50 km northwest of Yakima, Washington, consists of a series of middle to late Miocene epiclastic and pyroclastic rock assemblages rich in porphyritic hornblende-biotite dacite. Geochemical, petrographic, and stratigraphic correlations indicate that Old Scab Mountain, a dacite porphyry intrusion, located at the western margin of the basin (lat. 46°53'30", long. 121°13'00"), is the probable source for much of the upper Ellensburg volcaniclastic material in the basin. The dacite intrusion exposed at Old Scab Mountain was emplaced at depths of 1 to 3 km and underlaid a now eroded volcanic edifice. This volcanic …