Geology of the California Coast
Friday July 18, 2008
I've been putting together this photo introduction to the geology of the California coast, and I realized that the Franciscan is the key to it all. Northern California is defined by the Franciscan Complex rocks lining the coast; they peter out just north of San Luis Obispo, and except for a few bits of granite and Tertiary sediments, the northern California coast is dark, rugged, isolated and rocky offshore. The southern California coast is light, rugged, and isolated but there are few rocks offshore and there's the huge beaches of Los Angeles that set the tone for the region. But the fog covers north and south alike. This set of pictures goes from Trinidad to San Diego, and there's fog, or the promise of fog, in most of them.Baker Beach, San Francisco — Geology Guide photo
Comments
I am an amateur at this, but the geology of NorCal in general has been a preoccupation of mine for years. I have a theory about the overall dynamics of the geology of NorCal. I propose that the last piece of the Farallon plate (eastern side of the Pacific plate) did not subduct, but rather rode up onto the North American plate which is why we have a gentle west sloping granite Sierra batholith. Also, the action of the ocean floor plate allowed a large access or crack to form along the northeastern portion of this region allowing a massive release of magma across northern CA, southern OR and ID. I also believe the sediment on this young portion of the Farallon plate slid and fold back towards the west as the plate rose up onto the No. American plate. Has anyone else suggested this as a possible explanation of the formation of NorCal?
Why would a plate made of heavy basalt and peridotite rise over a nice buoyant continent? And where is all that oceanic crust to be seen?