San Francisco Bay

Cells within Alcatraz Prison, California, USA. Alcatraz, situated on an island in the middle of San Francisco Bay, is arguably the most notorious prison in the world. Isolated and formidable, it has inspired numerous films and books about daring escapes. The prison has been closed since 1963, and Alcatraz is now part of the Golden Gate National Recreational Area.

Crescent-shaped bay in western California. Running parallel to the Pacific coast and linked to the ocean by a narrow strait known as the Golden Gate, it measures 100 km/60 mi from north to south and is 5–20 km/3–12 mi wide. With depths of up to 30 m/100 ft, it is an excellent natural harbour and an busy international port. The major cities around the bay are San Francisco, San Mateo, and Palo Alto (to the west) and Richmond, Berkeley, and Oakland (to the east). Notable sights include the Golden Gate Bridge and the former prison island of Alcatraz.

San Francisco Bay was overlooked by various European navigators who explored the Pacific coast in the 16th and 17th centuries. It was ultimately sighted by a Spanish overland expedition in 1769, and settlement began in 1776. In recent times, the computer and electronics industries of Silicon Valley and numerous military installations have contributed to the prosperity of the Bay Area.

San Francisco Bay is an ancient river valley in the Coast Ranges, lying between the Hayward (east) and San Andreas (west) faults. Its northeastern arm, San Pablo Bay, connects via Suisun Bay with the Sacramento–San Joaquin river system and California's Central Valley. Islands within the bay include Angel, Treasure, and Yerba Buena, and it is spanned by a number of bridges, such as the San Mateo, and those crossing between Richmond and San Rafael, and San Francisco and Oakland. Over time, land reclamation and other human activities have reduced the bay's size by as much as 40%.