Oregon Coast Range Pillow Basalts

The Coast Range in Oregon lies to the west of the more well-known Cascade Range, creating the other side of the Willamette Valley and providing spectacular views of the Cascades and the seashore on a clear day. However, unlike the Cascades, which are composed of andesites and rhyolites (silica-rich, viscous rocks characteristic of continental volcanic arcs), the Coast Range is composed of basalts and sandstones. How did these oceanic rocks end up forming mountains up to 1249 m (4097 ft) high?

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