South Cascades Arc Volanism, California and Southern Oregon: Red Bluff to Redding, California, July 20-26, 1989

Published by the American Geophysical Union as part of the Field Trip Guidebooks Series.

The Cascade Range is a late Tertiary and Quternary volcanic arc that extends north from northeastern California through Oregon and Washington into British Columbia. The volcanic arc lies above an easterly dipping active subduction zone along which the Juan de Fuca, Gorda, and Explorer plates are thrust beneath the North American Plate (Riddington, 1984). In Addition to the major composite volcanoes that have erupted andesites, dacites, and even rhyolites, there are many smaller, commonly monogenetic vents that erupted primarily calc-alkaline basalt and basaltic andesites throughout the history of the arc (McBirney, 1978; Luedke and Smith, 1981, 1982; Smith and Luedke, 1984; Guffanti and Weaver, 1988). The volcanic arc is active, with certain historic eruptions at Lassen Peak (1914-17) and Mount St. Helens (mid-1800's; 1980-86), and possible historic eruptions at Mt. Shasta (1786), Mt. Baker (mid-1800's), Mt. Hood (mid-1800's), Mt. Rainier (mid-1800's) and Cinder Cone (east of Lassen Peak; 1851?).