Geologic Trips, San Francisco

Golden Gate


San Francisco is built on a thick suite of unusual red, green, gray, black, blue, yellow, and brown rocks called the Franciscan. These rocks were formed in the Franciscan subduction zone as a result of a slow-motion collision between two of the large plates that covered the surface of the earth during Cretaceous time. San Francisco is one of the best place in the world to observe the innards of a subduction zone. The fraternity of rocks once housed in the subduction zone are well exposed and have been investigated by geologists and other scientists for over a hundred years. As a result of these studies we know where the rocks came from, how and when they got into the subduction zone, and what happened to them during the subduction process. Itís a fascinating story. And the story is written in the hills and sea cliffs of San Francisco and the Marin Headlands.

Related Links

Geologic background: San Francisco (pdf)

Geologic trips:†† Alcatraz Island††††††† Cliff House††††††† Fort Point†††††††† Golden Gate†††††††† Lands End††††††


Exterior Websites

Golden Gate National Parks Conservancy: Golden Gate Bridge

US Geological Survey: Geology of San Francisco Bay Area

Wikipedia: Golden Gate Bridge

The Golden Gate Bridge from the Marin Headlands.