Cascades Geothermal Region

The Cascade Range is part of a vast mountain chain that extends from British Columbia to northern California and has been volcanically active for ~ 40 million years as a result of the convergence of the of the Juan de Fuca and Pacific plates. Two physiographic sub-provinces make up the Cascade Range; the Western Cascades and the High Cascades on the east. Middle Eocene to early Pliocene (40 – 5 million years) thick mafic lava flows, primarily of andesitic composition are associated with ash flows, tuffs, and silicic intrusive bodies and stocks that decrease in age eastward to the High Cascades. Miocene to Holocene volcanic rocks make up the modern volcanic arc of the high Cascades. Lava flows, 2- to 3 km thick, fill an a graben developed in older rocks that are intruded and overlain by stratovolcanoes of Quaternary age. Their composition varies from rhyolitic to basaltic associated with interlayered ash flows and pryroclastic deposits. The High Cascades are situated at the western margin of the Basin and Range in the zone of crustal extension. This has had control over the volcanic history and the north-south alignment of volcanic activity (Cashman, K.V. and others, 2009). Assessment of Moderate- and High-Temperature Geothermal Resources of the United States^[1]