The Rock: Alcatraz

December 01, 2017

Alcatraz741c_25june17 (1)

Photographer: Ray Boren 
Summary Author: Ray Boren 

Alcatraz, the notorious island in California’s San Francisco Bay, is almost as well-known today by its nickname — The Rock — as it is by its exotic geographic place name. Besides the obvious geologic connotations, that may be in part a result of the 1996 Hollywood thriller with that title, starring Sean Connery and Nicolas Cage. But according to the Federal Bureau of Prisons, calling Alcatraz the Rock dates at least to the early 20th century when a new military prison was built on the island — using the labor of the isolated convicts themselves

"The Rock" seems appropriate. As illustrated in this photograph, taken from a ferry on June 25, 2017, small but prominent Alcatraz Island, sprouting various old prison buildings, guard towers and a lighthouse, rises in the bay 1.25 miles (2.01 km) off San Francisco’s piers. Alcatraz was fortified by the U.S. military as early as 1850. Before, during and after the Civil War, the island’s guardhouse was employed as a military prison. Early inmates included captured Confederate privateers and suspected Confederate sympathizers. The facilities on Alcatraz were designated the Pacific Branch, U.S. Military Prison, in 1907, and then were transferred to the civilian Federal Bureau of Prisons in 1933. Until it was decommissioned in 1963, the maximum-security penitentiary housed many an infamous or troublesome convict, including Al Capone, George "Machine Gun" Kelly and "the birdman of Alcatraz,” Robert Stroud. Since 1973, Alcatraz has hosted public history tours, courtesy of the National Park Service.

Alcatraz has also loaned its name to a geologic formation, the Alcatraz terrane, part of California’s Franciscan Complex, according to the Park Service’s Golden Gate National Recreation Area, of which Alcatraz is a component. The complex includes eight terranes, with rocks from about 80 million to 200 million years old, which underlie as well as form hills and headlands in and around San Francisco Bay and the Golden Gate. The terranes have been much disrupted and contorted by the subduction and uplift of the colliding Farallon, Pacific and North American tectonic plates, as well as the feared San Andreas Fault. The Alcatraz terrane, exposed in the island’s cliffs — and underlying San Francisco’s Telegraph Hill and Nob Hill, among others — is chiefly composed of sandstone, which contains fossil mollusks that lived during the Early Cretaceous, about 130-140 million years ago.

Photo Details: Camera Model: NIKON D3200; Lens: AF-S DX VR Zoom-Nikkor 18-55mm f/3.5-5.6G; Focal Length: 44mm (35mm equivalent: 66mm); Aperture: ƒ/11.0; Exposure Time: 0.0020 s (1/500); ISO equiv: 360.