• East view from Crissy Field overlook with old Coast Guard station on left and city on right

    Presidio of San Francisco

    California

Graywacke Sandstone

Graywacke sandstone

Bedded graywacke sandstone at Baker Beach.

Will Elder, NPS

Graywacke sandstone is the product of underwater landslides that carry sand, silt, rock fragments, and plant and animal debris off of the continental margin and rapidly deposit them in deep ocean environments. Graywacke is associated with subduction zones, where sediments are being shed off a continent at high rates. Little sorting of mineral types, rock types, or particle size occurs before deposition of these rocks; hence their other name, "dirty sandstone."

Learn more about graywacke sandstone.

 
Ammonite Sandstone from Baker Beach in the Presidio
This ammonite (Douvilleiceras mammillatum) was found
in the sandstone near Baker Beach, indicating that these
continental derived sediments of the Marin Headlands Terrane
are about 100 million years old.

Did You Know?

The San Francisco National Cemetery at the Presidio

The National Cemeteries Act was based on the principles articulated by President Lincoln in his Gettysburg Address--"that these dead shall not have died in vain." Passed by Congress in 1863, the law established thirteen cemeteries to inter veterans of the Armed Forces and their families.