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Mid-Tertiary Volcanic Rocks Of The Timberwolf Mountain Area, South-Central Cascades, Washington, Julianna M. (Julianna Maureen) Shultz

WWU Graduate School Collection

Over 3000 m of mid-Tertiary Cascade arc volcanics are exposed in the Timberwolf Mountain area of Washington's central Cascade Range. Arc rocks of the Ohanapecosh, Stevens Ridge, and Fifes Peak Formations overlie the Jura-Cretaceous Rimrock Lake inlier and sparse late Eocene(?) sedimentary rocks. Geochemical analyses of meta-basalts from the Russell Ranch and Indian Creek complexes that comprise the inlier indicate an island-arc or immature continental volcanic-arc tectonic environment for the inlier.

The early to mid Oligocene Ohanapecosh Formation is comprised of two facies within the study area. Distal, water-lain andesitic to dacitic lapilli-tuffs of the Wildcat Creek facies unconformably overlie …