Klamath Mountains - Geology

Geology

The rocks of the Klamath Mountains originated as islands in the Pacific Ocean. The islands were created by plate tectonics and volcanic activity as early as 500 million years ago, in the early Paleozoic era. The islands moved eastward on the Farallon plate and smashed several times into the North American continent from 260 to about 130 million years ago. Each accretion left a terrane of rock of a single age. After accretion, subduction of the plate formed intrusions of plutons and metamorphic rocks. Serpentinite — a toxic metamorphic rock mixed with seawater — and granite from the North American plate are common rocks within the Klamath terranes.

Subsequent lava flows from active volcanoes in the Cascade Range and erosion from the Oregon Coast Range to the north partially covered these rocks with basalt and sediments.