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."
Did You Know?
In 1915, a tragic fire at the Presidio claimed the lives of General Pershing’s wife and his three daughters. Pershing's son, Francis Warren, survived the blaze and chose to enlist in the army as a private during World War II. By the end of the war he had achieved the rank of major.