Serpentinites along Baker Beach are exposed by landslides. There is a fault contact here juxtaposing serpentinite and sandstone.  Serpentinite is rock typically formed from water rising from subducted sediments along a subduction zone into the mantle and forming hydrous minerals.

Jack Crane

Mélange

In geology, a mélange is a large-scale breccia, a mappable body of rock characterized by a lack of continuous bedding and the inclusion of fragments of rock of all sizes, contained in a fine-grained deformed matrix. The mélange typically consists of a jumble of large blocks of varied lithologies. Large-scale melanges formed in active continental margin settings generally consist of altered oceanic crustal material and blocks of continental slope sediments in a sheared mudstone matrix. The mixing mechanisms in such settings may include tectonic shearing forces, ductile flow of a water-charged or deformable matrix (such as serpentinite), sedimentary action (such as slumping, gravity-flow, and olistostromal action), or some combination of these. Some larger blocks of rock may be as much as 1 kilometre (0.62 mi) across. Smaller-scale localized mélanges may also occur in shear or fault zones, where coherent rock has been disrupted and mixed by shearing forces.

• http://en.wikipedia.org/wiki/Mélange
• http://www.nps.gov/goga/forteachers/upload/Geology%20of%20the%20Golden%20Gate%20Headlands%20Field%20Guide.pdf