Geology, Petrology, and Geochemistry of a Portion of the High Cascades in Southern Oregon-Northern California, South of the Klamath River Gorge Jennifer McIntosh Department of Geology, Whitman College, Walla Walla, WA 99362 The Secret Spring field area, south of the Klamath River gorge on the Oregon-California border, is part of the High Cascades, a volcanic region active since the mid-Miocene. Extrusive igneous rocks, volcaniclastic sediments, and pyroclastic flow deposits in the area have been dated at 19 to 4 Ma. The volcanic deposits are basaltic to andesitic with varying degrees of secondary hydrothermal alteration. At least one lava flow is related to the ca. 14 Ma Secret Spring volcano, remnants of which are located on the eastern side of the Secret Spring field area. Several andesitic dikes intrude volcanic deposits on the northern slope of a prominent mesa in the area. The dikes are unconformably overlain by a 4.4 +- 0.4 Ma mesa-capping basalt porphyry. The youngest pyroclastic flow deposit in the area, the 17.6 +-0.6 Ma lithic vitric tuff is most likely related to a pyroclastic unit north of the Klamath River gorge.     Return to the Geology Department homepage Return to the Whitman College homepage