Rock formations from over a million years ago!
These rocks began their migration over one hundred million years ago from as far south as what today we call "Los Angeles".
These are located at the Hawk Hill area in the Marin Headlands in San Francisco.
These are part of a fascinating geological formation created by the accretion of oceanic sediments onto the North American Plate from the Pacific Plate.
The primary components of Headlands geology include graywacke sandstone, radiolarian chert, serpentinite, pillow basalts, and shale (courtesy Wikepedia).