It is home to the now-abandoned prison, the oldest operating lighthouse on the West Coast of the United States, early military fortifications, and natural features such as rock pools[?], a seabird colony[?], and unique views of the coastline.
Alcatraz was a military fort from 1850 to 1933. The island became a federal prison on January 1, 1934. During the 29 years it was in use, the jail held such notable criminals as Al Capone and Robert Franklin Stroud, the Birdman of Alcatraz. The penitentary was closed for good on March 21, 1963.
The island is also known as 'The Rock', and it featured in a movie of the same name.
This image is from the GIMP photo library (http://GIMP-savvy.com/cgi-bin/img.cgi?noaauH1zY36LdMg2344).