Processes of a tectonically-active continental margin

The continental margin of California was a subduction zone until the mid-Cenozoic. The Farallon tectonic plate subducted under the North American plate and was eventually consumed, sedimentary and crustal material was accreted to the continental margin, and the granite batholiths in the Sierra Nevada range were emplaced.

The tectonics of central California changed with the passage through the area of the triple-junction now off Mendocino; subduction is still occurring off Oregon and Washington. Now our continental margin is being deformed by the generally strike-slip motion of the San Andreas fault, as the Pacific plate moves north-west relative to the North American plate, carrying the sliver of coastal California with it. Adjustments to the motions of the plates have occurred, which in some places generated tensional forces and subsequent volcanic activity (see the continental margin seamounts page), and in other places generated compressional forces, such as are currently uplifting the Santa Cruz mountains.