Geology of San Francisco, California

San Francisco packs a lot of geological features into its territory. If you want something more than great culture, local color and tourism, come get to know its rocks and landforms and beaches. Most of the city's rocks belong to the Franciscan Complex, a large assemblage of rock bodies, or terranes, that came here on the back of a subducting oceanic plate and piled together in a great accretionary wedge against the North American continent. Starting about 25 million years ago, the San Andreas fault system took this wedge and spread slices of it sideways up the California coast, raising the Coast Ranges at the same time.