San Francisco Bay is a large tidal estuary in the U.S. state of California, which gives its name to the San Francisco Bay Area. It is dominated by the cities of San Francisco, San Jose, and Oakland.
San Francisco Bay drains water from approximately 40 percent of California. Water from the Sacramento and San Joaquin rivers, and from the Sierra Nevada mountains, flow into Suisun Bay, which then travels through the Carquinez Strait to meet with the Napa River at the entrance to San Pablo Bay, which connects at its south end to San Francisco Bay. It then connects to the Pacific Ocean via the Golden Gate strait. However, this entire group of interconnected bays is often called San Francisco Bay. The bay was designated a Ramsar Wetland of International Importance on February 2, 2013, and the Port of Oakland on the bay is one of the busiest cargo ports on the west coast.
Geography The bay covers somewhere between , depending on which sub-bays (such as San Pablo Bay), estuaries, wetlands, and so on are included in the measurement.San Francisco Bay Watershed Database and Mapping Project The main part of the bay measures wide east-to-west and somewhere between 1 and 2 north-to-south.
San Francisco Bay is the second-largest estuary on the Pacific coast of the Americas, following the Salish Sea in Washington State and British Columbia, Canada.
The bay was navigable as far south as San Jose until the 1850s, when hydraulic mining released massive amounts of sediment from the rivers that settled in those parts of the bay that had little or no current. Later, wetlands and inlets were deliberately filled in, reducing the bay's size since the mid-19th century by as much as one third. Recently, large areas of wetlands have been restored, further confusing the issue of the bay's size. Despite its value as a waterway and harbor, many thousands of acres of marshy wetlands at the edges of the bay were, for many years, considered wasted space. As a result, soil excavated for building projects or dredged from channels was often dumped onto the wetlands and other parts of the bay as landfill.
From the mid-19th century through the late 20th century, more than a third of the original bay was filled and often built on. The deep, damp soil in these areas is subject to soil liquefaction during earthquakes, and most of the major damage close to the bay in the Loma Prieta earthquake of 1989 occurred to structures on these areas.
The Marina District of San Francisco, hard hit by the 1989 earthquake, was built on fill that had been placed there for the Panama-Pacific International Exposition, although liquefaction did not occur on a large scale. In the 1990s, San Francisco International Airport proposed filling in hundreds more acres to extend its overcrowded international runways in exchange for purchasing other parts of the bay and converting them back to wetlands. The idea was, and remains, controversial. (For further details, see the "Bay fill and depth profile" section.)
There are five large islands in San Francisco Bay. Alameda, the largest island, was created when a shipping lane was cut to form the Port of Oakland in 1901. It is now a suburban community. Angel Island was known as "Ellis Island West" because it served as the entry point for immigrants from East Asia. It is now a state park accessible by ferry. Mountainous Yerba Buena Island is pierced by a tunnel linking the east and west spans of the San Francisco–Oakland Bay Bridge. Attached to the north is the artificial and flat Treasure Island, site of the 1939 Golden Gate International Exposition. From the Second World War until the 1990s, both islands served as military bases and are now being redeveloped. Isolated in the center of the bay is Alcatraz, the site of the famous federal penitentiary. The federal prison on Alcatraz Island no longer functions, but the complex is a popular tourist site. Despite its name, Mare Island in the northern part of the bay is a peninsula rather than an island.
Geology
San Francisco Bay is thought to represent a down-warping of the Earth's crust between the San Andreas Fault to the west and the Hayward Fault to the east, though the precise nature of this remains under study. About 560,000 years ago, a tectonic shift caused the large inland Lake Corcoran to spill out from the central valley and through the Carquinez Strait, carving out sediment and forming canyons in what is now the northern part of San Francisco Bay and Golden Gate strait.
San Francisco Bay has been filled and emptied of sea water many times during the Pleistocene in accordance with sea level changes caused by glacial advances and retreats. During the Wisconsin Glaciation, between 15,000 and about 10,000 years ago, the basin which is now filled by San Francisco Bay was a large river valley with small hills, channeling the Sacramento River through the Golden Gate Strait into the ocean. When the great ice sheets began to melt, around 11,000 years ago, the sea level started to rise rapidly, by about 1 inch per year. Melting glaciers in the Sierra Nevada washed huge amounts of sediment down the Sacramento and San Joaquin rivers, which accumulated on the shores of the bay, forming huge mudflats and marshes that supported local wildlife. By 5000 BC the sea level rose , filling the valley with water from the Pacific. The Farallon Islands are what used to be hills along the old coastline, and Potato Patch Shoal is an area of sand dunes now covered by the ocean.
History
The indigenous inhabitants of San Francisco Bay are Ohlone. In the eastern part of the bay, the native Chochenyo people called the bay ommu, in the Chochenyo language.
The bay eluded discovery by passing European mariners for centuries, "because its entrance was narrow and often fog-shrouded".
The first European to see San Francisco Bay is likely N. de Morena, who was left at New Albion at Drakes Bay in Marin County, California, by Sir Francis Drake in 1579 and then walked to Mexico.
The first recorded European discovery of San Francisco Bay was on November 4, 1769, when Spanish explorer Gaspar de Portolá, unable to find the Port of Monterey, continued north close to what is now Pacifica and reached the summit of the Sweeney Ridge, now marked as the place where he first sighted San Francisco Bay. Portolá and his party did not realize what they had discovered, thinking they had arrived at a large arm of what is now called Drakes Bay. At the time, Drakes Bay went by the name Bahia de San Francisco and thus both bodies of water became associated with the name. Eventually, the larger, more important body of water fully appropriated the name San Francisco Bay.
The first European to enter the bay is believed to have been the Spanish explorer Juan de Ayala, who passed through the Golden Gate on August 5, 1775, in his ship the San Carlos and moored in a bay of Angel Island now known as Ayala Cove. Ayala continued to explore the San Francisco Bay Area and the expedition's cartographer, José de Cañizares, gathered the information necessary to produce the first map of the area. A number of place names survive (anglicized) from that first map, including Point Reyes, Angel Island, Farallon Islands, and Alcatraz Island.
Alaskan Native sea otter hunters using Aleutian kayaks and working for the Russian–American Company entered San Francisco Bay in 1807 and again over 1810–1811. Led by the Russian Timofei Nikitich Tarakanov, these hunting raids probably wiped out sea otters in the bay. Thousands of sea otter skins were taken to Sitka, then Guangzhou (Canton), China, where they commanded a high price.
The United States seized the region from Mexico during the Mexican–American War (1846–1848). On February 2, 1848, the Mexican province of Alta California was annexed to the United States with the signing of the Treaty of Guadalupe Hidalgo. A year and a half later, California requested to join the United States on December 3, 1849, and was accepted as the 31st State of the Union on September 9, 1850.
In 1921, a tablet was dedicated by a group of men in downtown San Francisco, marking the site of the original shoreline. The tablet reads: "This tablet marks the shore line of San Francisco Bay at the time of the discovery of gold in California, January 24, 1848. Map reproduced above delineates old shore line. Placed by the Historic Landmarks committee, Native Sons of the Golden West, 1921."
The bay became the center of American settlement and commerce in the Far West through most of the remainder of the 19th century. During the California Gold Rush (1848–1855), San Francisco Bay suddenly became one of the world's great seaports, dominating shipping in the American West until the last years of the 19th century. The bay's regional importance increased further when the first transcontinental railroad was connected to its western terminus at Alameda on September 6, 1869.Alta California, September 7, 1869 The terminus was switched to the Oakland Long Wharf two months later on November 8, 1869.
In 1910, the Southern Pacific railroad company built the Dumbarton Rail Bridge, the first bridge crossing San Francisco Bay. The first automobile crossing was the Dumbarton Bridge, completed in January 1927. More crossings were later constructed – the Carquinez Bridge in May 1927,The Barrier Broken – Vallejo Evening Chronicle, May 21, 1927 the San Francisco–Oakland Bay Bridge in 1936, the Golden Gate Bridge in 1937, the Richmond–San Rafael Bridge in 1956, and the San Mateo–Hayward Bridge in 1967.
During the 20th century, the bay was subject to the 1940s Reber Plan, which would have filled in parts of the bay in order to increase industrial activity along the waterfront. In 1959, the United States Army Corps of Engineers released a report stating that if current infill trends continued, the bay would be as big as a shipping channel by 2020. This news led to the creation of the Save the Bay movement in 1960, which mobilized to stop the infill of wetlands as well as the bay itself, which had shrunk to two-thirds of its size in the century before 1961.
On September 17, 1965, the California State Legislature enacted the McAteer-Petris Act, which created the San Francisco Bay Conservation and Development Commission. Since then, the commission has strictly regulated bay fill. Foster City, Redwood Shores, Paradise Cay, and Emeryville's western expansion were among the last developments along the bay shoreline before McAteer-Petris limited additional filling of the bay.
San Francisco Bay continues to support some of the densest industrial production and urban settlement in the United States. The San Francisco Bay Area is the American West's second-largest urban area, with approximately seven million residents.
Ecology
Despite its urban and industrial character, San Francisco Bay and the Sacramento–San Joaquin River Delta remain perhaps California's most important ecological habitats. California's Dungeness crab, California halibut, and Pacific salmon fisheries rely on the bay as a nursery. The few remaining salt marshes now represent most of California's remaining salt marsh, supporting a number of endangered species and providing key ecosystem services such as filtering pollutants and sediments from the rivers. San Francisco Bay is recognized for protection by the California Bays and Estuaries Policy, with oversight provided by the San Francisco Estuary Partnership.State Water Resources Control Board Water Quality Control Policy for the Enclosed Bays and Estuaries of California (1974) State of California