Franciscan Assemblage

The Franciscan Assemblage is a geological term for an accreted terrane of heterogeneous rocks found on and near the San Francisco Peninsula. It was named by geologist Andrew Lawson who also named the San Andreas Fault which bounds the Franciscan Assemblage.

Also known as the "Franciscan Formation," "Franciscan Series," "Franciscan Group," "Franciscan assemblage," or "Franciscan Complex," it includes altered mafic volcanic rocks (greenstones), deep-sea radiolarian cherts, greywacke sandstones, limestones, serpentinites, shales, and high-pressure metamorphic rocks, all of them faulted and mixed in a seemingly chaotic manner.

It forms the major component of the Pacific Coast Ranges of California.

Wentworth and others interpreted the juxtaposition of the Franciscan Assemblage and the section consisting of the Coast Range ophiolite and the Great Valley sequence to have happened through landward movement of the Franciscan Assemblage as a tectonic wedge, largely seafloor sediments and bits of ocean crust pushed upward and into the previous coastline as a berm as the Farallon Plate moved into a coastal subduction zone.