Geologic Trips, San Francisco

Alcatraz Island


Alcatraz Island is one of the best places in the Bay Area to see the Alcatraz terrane of the Franciscan. The Alcatraz terrane is characterized by thick-bedded sandstones. These sandstones form many of the hills that give downtown San Francisco its unique character, including Telegraph Hill, Russian Hill, Rincon Hill and Nob Hill. However, in San Francisco, the Alcatraz sandstone is almost everywhere covered by buildings, streets and cable car tracks, so that good exposures are hard to find. The steep cliffs on the southwest shore of Alcatraz Island, seen in this photograph, are formed from thick beds of the Alcatraz sandstone. There are also good exposures of the sandstone along many of the paths on the island.

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: Alcatraz Tours

Golden Gate National Recreation Area: Alcatraz Island

Wikipedia: Alcatraz Island

Alcatraz Federal Penitentiary on top of Alcatraz Island.