Alcatraz was barely affected by the 1906 San Francisco earthquake which devastated the city , and the prison population dramatically increased as prisoners were temporarily transferred to the island due to damage in the city . In 1907 , Alcatraz Citadel ceased function as a military defense and became the Pacific Branch , U.S. Military Prison solely . When the original 1860s citadel collapsed in 1908 , the Citadel was demolished in 1909 up to its basement over which the new prison was built by the military prisoners between 1909 and 1911 and named as " the Pacific Branch , U.S. Disciplinary Barracks for the U.S. Army , " which became popular as " The Rock . " The prison was entirely rebuilt in concrete in 1910-1912 under the command of Colonel Reuben Turner on a $ 250,000 budget on the site of the remains and short-lived upper prison building . Many of the former underground tunnels and chambers of the original fort remain today and are still accessible . This building was modernized in 1934 when it reopened as a federal penitentiary , the notorious Alcatraz prison which held America 's most ruthless criminals until 1963
1906 San Francisco earthquake
1906 San Francisco earthquake
Fort Alcatraz