Rocky island in San Francisco Bay , California, U.S. It has an area of 22 acres (9 hectares) and is located 1.
5 mi (2 km) offshore from the city of San Francisco . The site of the first lighthouse (1854) on the California coast, it became an army garrison (1859) and a military prison (1868). From 1934 to 1963 it served as a federal prison for dangerous civilian prisoners. Its famous inmates included Al Capone , George "Machine Gun" Kelly, and Robert Stroud, the "Birdman of Alcatraz." It is now open to the public.