West Coast Tectonic Evolution—20 Million Years Ago [2 of 3]

As the mid-ocean ridge separating the Farallon and Pacific Plates entered the subduction zone, the Farallon Plate separated into the Juan de Fuca and Cocos Plates. A transform plate boundary developed where the Pacific Plate was in contact with the North American Plate and the volcanism ceased in central California. Farther east, the continent began to rift apart in the Basin and Range Province.