Geology: The Bolinas shelf is less than 0.3 degrees tilted, meaning that it is quite flat. The seafloor of the bay area near the lagoon is shallow, and has large bedrock outcroppings from the shore to depths of about 25 m. The sediments date to the Neogene epoch.

Paleontology: Fossil hunters have determined that fossilized sand dollars are fairly common in the area.

Works Cited:

“Geology and geomorphology–Offshore of Bolinas Map Area, California,” (USGS 2015) http://pubs.usgs.gov/ds/781/OffshoreBolinas/metadata/Geology_OffshoreBolinas_metadata.html

Further Reading:

“Recent Marine Sediments of Bolinas Bay, California” (UC Berkeley 1968) http://escholarship.org/uc/item/2kf907bg#page-1