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."
in the sandstone near Baker Beach, indicating that these continental derived sediments of the Marin Headlands Terrane are about 100 million years old. |
Last updated: February 28, 2015