Geology and geologic history: Overview of the geology of the San Francisco Bay region

The geology of San Francisco and the surrounding northern and central California area has played a pivotal role in the development of our understanding of Earth processes, especially the process of tectonic accretion at a continental margin and the development of transform plate margins. The Franciscan Complex, which underlies most (or perhaps all) of the City and County of San Francisco, is widely considered the "type" accretionary complex. More regionally, the Sierra Nevada, Great Valley, and Coast Ranges are often used as an illustration of the arc-forearc-accretionary prism geometry of a continental convergent margin, and the San Andreas Fault, just offshore to the west of San Francisco, serves as the prototype transform plate margin, although as illustrated below the actual geometry and geologic history is more complicated.