San Francisco Bay drains water from approximately 40 percent of California. Water from theSacramento andSan Joaquin rivers, and from theSierra Nevada mountains, flow intoSuisun Bay, which then travels through theCarquinez Strait to meet with theNapa River at the entrance toSan Pablo Bay, which connects at its south end to San Francisco Bay. It then connects to thePacific Ocean via theGolden Gate strait. However, this entire group of interconnected bays is often calledSan Francisco Bay. The bay was designated aRamsar Wetland of International Importance on February 2, 2013, and thePort of Oakland on the bay is one of the busiest cargo ports on the west coast.
The bay covers somewhere between 400 and 1,600 square miles (1,000–4,000 km2), depending on which sub-bays (such as San Pablo Bay), estuaries,wetlands, and so on are included in the measurement.[4][5][6] The main part of the bay measures three to twelve miles (5–19 km) wide east-to-west and somewhere between 48 miles (77 km)1 and 60 miles (97 km)2 north-to-south.
San Francisco Bay is the second-largest estuary on the Pacific coast of the Americas, following theSalish Sea in Washington State and British Columbia, Canada.[7]
The bay was navigable as far south asSan Jose until the 1850s, whenhydraulic 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 andharbor, 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 ordredged from channels was often dumped onto the wetlands and other parts of the bay as landfill.[citation needed]
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 tosoil liquefaction during earthquakes, and most of the major damage close to the bay in theLoma Prieta earthquake of 1989 occurred to structures on these areas.[citation needed]
TheMarina District of San Francisco, hard hit by the 1989 earthquake, was built on fill that had been placed there for thePanama-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 internationalrunways 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 thePort 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. MountainousYerba Buena Island is pierced bya tunnel linking the east and west spans of theSan Francisco–Oakland Bay Bridge. Attached to the north is the artificial and flatTreasure Island, site of the 1939Golden 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 isAlcatraz, the site of the famous federal penitentiary. The federal prison onAlcatraz 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.
Population density and low elevation coastal zones in San Francisco Bay (2010). San Francisco Bay is especially vulnerable tosea level rise.
San Francisco Bay is thought to represent a down-warping of the Earth's crust between theSan Andreas Fault to the west and theHayward Fault to the east, though the precise nature of this remains under study. About 560,000 years ago, atectonic shift caused the large inlandLake Corcoran to spill out from thecentral valley and through theCarquinez Strait, carving out sediment and forming canyons in what is now the northern part of San Francisco Bay andGolden Gate strait.[8]
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.[9] During theWisconsin 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 theSacramento River through theGolden Gate Strait into the ocean.[9] 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.[10] 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.[10] By 5000 BC the sea level rose 300 feet (90 m), filling the valley with water from the Pacific.[10] TheFarallon Islands are what used to be hills along the old coastline,[10] and Potato Patch Shoal is an area of sand dunes now covered by the ocean.[9]
The indigenous inhabitants of San Francisco Bay areOhlone.[11] In the eastern part of the bay, the nativeChochenyo people called the bayommu, in theChochenyo language.[12]
The bay eluded discovery by passing European mariners for centuries, "because its entrance was narrow and often fog-shrouded".[13]
The first recorded European discovery of San Francisco Bay was on November 4, 1769, when Spanish explorerGaspar de Portolá, unable to find thePort of Monterey, continued north close to what is nowPacifica and reached the summit of the 1,200-foot-high (370 m)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 calledDrakes Bay.[16] At the time, Drakes Bay went by the nameBahia 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 nameSan Francisco Bay.[citation needed]
The first European to enter the bay is believed to have been the Spanish explorerJuan de Ayala, who passed through theGolden Gate on August 5, 1775, in his ship theSan Carlos and moored in a bay ofAngel Island now known as Ayala Cove. Ayala continued to explore theSan 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, includingPoint Reyes,Angel Island,Farallon Islands, andAlcatraz Island.[citation needed]
Alaskan Native sea otter hunters usingAleutian kayaks and working for theRussian–American Company entered San Francisco Bay in 1807 and again over 1810–1811. Led by the RussianTimofei Nikitich Tarakanov, these hunting raids probably wiped out sea otters in the bay. Thousands of sea otter skins were taken to Sitka, thenGuangzhou (Canton), China, where they commanded a high price.[17][18]
The United States seized the region from Mexico during theMexican–American War (1846–1848). On February 2, 1848, the Mexican province ofAlta California was annexed to the United States with the signing of theTreaty 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.[19][20]
San Francisco Bay Shoreline Tablet
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."[21]
The bay became the center of American settlement and commerce in the Far West through most of the remainder of the 19th century. During theCalifornia 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 thefirst transcontinental railroad was connected to its western terminus atAlameda on September 6, 1869.[22] The terminus was switched to theOakland Long Wharf two months later on November 8, 1869.[23]
Duck hunting on the Bay, 1915Mallard II, a clamshell dredge built in 1936 and used into the 21st century to dredge levees for Cargill's salt ponds in the bay
During the 20th century, the bay was subject to the 1940sReber Plan, which would have filled in parts of the bay in order to increase industrial activity along the waterfront. In 1959, theUnited 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 theSave the Bay movement in 1960,[32] 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.[33]
San Francisco Bay continues to support some of the densest industrial production and urban settlement in the United States. TheSan Francisco Bay Area is the American West's second-largest urban area, with approximately seven million residents.[34]
Most famously, the bay is a key link in thePacific Flyway. Millions ofwaterfowl annually use the bay shallows as a refuge. Twoendangered species of birds are found here: theCalifornia least tern and theRidgway's Rail. Exposedbay muds provide important feeding areas forshorebirds, but underlying layers of bay mud pose geological hazards for structures near many parts of the bay perimeter. San Francisco Bay provided the nation's first wildlife refuge, Oakland's artificialLake Merritt, constructed in the 1860s, and America's first urban National Wildlife Refuge, theDon Edwards San Francisco Bay National Wildlife Refuge (SFBNWR) in 1972. The bay is also plagued by non-native species.[citation needed]
Salt produced from San Francisco Bay is produced insalt evaporation ponds and is shipped throughout the Western United States to bakeries, canneries, fisheries, cheese makers and other food industries and used to de-ice winter highways, clean kidney dialysis machines, for animal nutrition, and in many industries. Many companies have produced salt in the bay, with theLeslie Salt Company the largest private land owner in theBay Area in the 1940s.[36][37]
Low-salinity salt ponds mirror the ecosystem of the bay, with fish and fish-eating birds in abundance. Mid-salinity ponds support dense populations ofbrine shrimp, which provide a rich food source for millions of shorebirds. Only salt-tolerant micro-algae survive in the high salinity ponds, and impart a deep red color to these ponds from the pigment within the algae protoplasm. Thesalt marsh harvest mouse is an endangered species endemic to the wetlands of San Francisco Bay with a high salt tolerance. It needs nativepickleweed, which is often displaced by invasive cordgrass, for its habitat.[38]
The seasonal range of water temperature in the bay is from January's 53 °F (12 °C) to September's 60 °F (16 °C) when measured atFort Point, which is near the southern end of theGolden Gate Bridge and at the entrance to San Francisco Bay.[39]
For the first time in 65 years,Pacific Harbor Porpoise (Phocoena phocoena) returned to the bay in 2009.[40] Golden Gate Cetacean Research, a non-profit organization focused on research oncetaceans, has developed a photo-identification database enabling the scientists to identify specific porpoise individuals and is trying to ascertain whether a healthier bay has brought their return.[41] Pacific harbor porpoise range fromPoint Conception, California, to Alaska and across to theKamchatka Peninsula and Japan. Recent genetic studies show that there is a local stock from San Francisco to the Russian River and that eastern Pacific coastal populations rarely migrate far, unlike western Atlantic Harbor porpoise.[42]
Thecommon bottlenose dolphin (Tursiops truncatus) has been extending its current range northwards from theSouthern California Bight. The first coastal bottlenose dolphin in the Bay Area in recent times was spotted in 1983 off theSan Mateo County coast in 1983. In 2001, bottlenose dolphins were first spotted east of the Golden Gate Bridge and confirmed by photographic evidence in 2007. Zooarcheological remains of bottlenose dolphins indicated that bottlenose dolphins inhabited San Francisco Bay in prehistoric times until at least 700 years before present, and dolphin skulls dredged from the bay suggest occasional visitors in historic times.[43]
San Francisco Bay faces many of the same water quality issues as other urban waterways in industrialized countries, or downstream of intensive agriculture. According to state water quality regulators, San Francisco Bay waters do not meet water quality standards for the following pollutants:[44]
Industrial, mining, and other uses ofmercury have resulted in a widespread distribution in the bay, with uptake in the bay'sphytoplankton and contamination of its sportfish.[45]
In January 1971, twoStandard Oil tankers collided in the bay, creating an 800,000-U.S.-gallon (3,000,000-liter)oil spill disaster, which spurred environmental protection of the bay. In November 2007, a ship namedCOSCO Busan collided with theSan Francisco–Oakland Bay Bridge and spilled over 58,000 U.S. gallons (220,000 liters) ofbunker fuel, creating the largestoil spill in the region since 1996.[46]
The bay also has some of the highest levels of dissolved inorganic nitrogen known from any coastal water body, mostly originating from treated wastewater fromPublicly owned treatment works.[47] In other bays, such nutrient levels would likely lead toeutrophication, but historically, the bay has had lessharmful algal blooms than other water bodies with similar nutrient concentrations. Potential explanations have included the presence of intensive "top-down control" from grazing clams likePotamocorbula, high sediment supply limiting light availability for the algae, and intensive tidal mixing. The occurrence of an unprecedented harmful algal bloom ofHeterosigma akashiwo in 2022, resulting in mass fish deaths and anoxia,[48] suggests that the mechanisms of control on algal growth may be eroding.
The bay was once considered a hotspot for polybrominated diphenyl ether (PBDE) flame retardants used to make upholstered furniture and infant care items less flammable. PBDEs have been largely phased out and replaced with alternative phosphate flame retardants. A 2019San Francisco Estuary Institute (SFEI) study assayed a wide range of these newer flame retardant chemicals in Bay waters, bivalveCalifornia mussels (Mytilus californianus), andharbor seals (Phoca vitulina) which haul out in Corkscrew Slough[49] onBair Island inSan Mateo County, with phosphate flame retardant contaminants such astris(1,3-dichloro-2-propyl)phosphate (TDCPP) andtriphenyl phosphate (TPhP) found at levels comparable to thresholds for aquatic toxicity.[50]
Thousands of man-made chemicals are found in Bay water, sediment, and organisms. For many of these, there is little or no data on their impacts on the environment or human health, and they are not regulated by state or federal law. These are often referred to as "contaminants of emerging concern." TheSan Francisco Estuary Institute has studied these chemicals in the Bay since 2001.[51] Scientists have identified the following most likely to have a negative impact on Bay wildlife:[52]
San Francisco Bay and the Golden Gate Bridge, looking southeast towards the City and East Bay.Alcatraz is the small islet in the upper-middle left.
San Francisco Bay's profile changed dramatically in the late 19th century and again with the initiation of dredging by theUS Army Corps of Engineers in the 20th century. Before about 1860, most bay shores (with the exception of rocky shores, such as those in Carquinez Strait; along Marin shoreline; Point Richmond; Golden Gate area) contained extensive wetlands that graded nearly invisibly from freshwater wetlands to salt marsh and then tidal mudflat. A deep channel ran through the center of the bay, following the ancient drowned river valley.[citation needed]
In the 1860s and continuing into the early 20th century, miners dumped staggering quantities of mud and gravel fromhydraulic mining operations into the upper Sacramento and San Joaquin Rivers. GK Gilbert's estimates of debris total more than eight times the amount of rock and dirt moved during construction of the Panama Canal. This material flowed down the rivers, progressively eroding into finer and finer sediment, until it reached the bay system. Here some of it settled, eventually filling in Suisun Bay, San Pablo Bay, and San Francisco Bay, in decreasing order of severity.[citation needed]
By the end of the 19th century, these "slickens" had filled in much of the shallow bay flats, raising the entire bay profile. New marshes were created in some areas.[citation needed]
Cargo ships in San Francisco Bay in 2012
In the decades surrounding 1900, at the behest of local political officials and following Congressional orders, the U.S. Army Corps began dredging the Sacramento and San Joaquin Rivers and the deep channels of San Francisco Bay. This work has continued without interruption ever since. Some of the dredge spoils were initially dumped in the bay shallows (including helping to createTreasure Island on the formershoals to the north ofYerba Buena Island) and used to raise islands in the Sacramento-San Joaquin Delta. The net effect of dredging has been to maintain a narrow deep channel—deeper perhaps than the original bay channel—through a much shallower bay. At the same time, most of the marsh areas have been filled or blocked off from the bay bydikes.
Large ships transiting the bay must follow deep underwater channels that are maintained by frequent dredging as the average depth of the bay is only as deep as a swimming pool—approximately 12 to 15 ft (4–5 m). BetweenHayward andSan Mateo toSan Jose it is 12 to 36 in (30–90 cm). The deepest part of the bay is under and out of the Golden Gate Bridge, at 372 ft (113 m).[53]
In the late 1990s, a 12-year harbor-deepening project for thePort of Oakland began; it was largely completed by September 2009. Previously, the bay waters and harbor facilities only allowed for ships with a draft of 46 ft (14 m), butdredging activities undertaken by the United States Army Corps of Engineers in partnership with the Port of Oakland succeeded in providing access for vessels with a 50-foot (15 m) draft. Four dredging companies were employed in the US$432 million project, with $244 million paid for with federal funds and $188 million supplied by the Port of Oakland. Some six million cubic yards (160 million cubic feet; 4.6 million cubic meters) of mud from the dredging was deposited at the western edge ofMiddle Harbor Shoreline Park to become a 188-acre (0.294 sq mi; 0.76 km2) shallow-waterwetlands habitat for marine and shore life.[54][55] Further dredging followed in 2011, to maintain the navigation channel.[56][57] This dredging enabled the arrival of the largestcontainer ship ever to enter San Francisco Bay, theMSC Fabiola. Baypilots trained for the visit on a simulator at theCalifornia Maritime Academy for over a year. The ship arrived drawing less than its full draft of 50 feet 10 inches (15.5 m) because it held only three-quarters of a load after its stop in Long Beach.[58]
San Francisco Bay was traversed by watercraft before the arrival of Europeans. Indigenous peoples used canoes to fish and clam along the shoreline. Sailing ships enabled transportation between the bay and other parts of the world—and served as ferries and freighters within the bay and between the bay and inland ports, such as Sacramento and Stockton. These were gradually replaced by steam-powered vessels starting in the late 19th century. Several shipyards were established around the bay, augmented during wartime (e.g., theKaiser Shipyards,Richmond Shipyards) nearRichmond in 1940 forWorld War II for construction of mass-produced, assembly lineLiberty andVictory cargo ships.[59]
San Francisco Bay is spanned by nine bridges, eight of which carrycars.[citation needed]
TheGolden Gate Bridge onU.S. Route 101/State Route 1 (US 101/SR 1) was the largest single spansuspension bridge ever built at the time of its 1937 construction. It spans theGolden Gate, the strait between San Francisco and Marin County, and is the only bridge in the area not owned by the State of California.
Prior to the bridges and, later, the Transbay Tube, transbay transportation was dominated by fleets offerryboats operated by theSouthern Pacific Railroad and theKey System transit company. However, in recent decades, ferries have returned, primarily serving commuters from Marin County, relieving the traffic bottleneck of the Golden Gate Bridge (seeFerries of San Francisco Bay).[citation needed]
The San Francisco Bay Area Water Trail is a planned system of designated trailheads designed to improve non-motorized small boat access to the bay. The California Coastal Conservancy approved funding in March 2011 to begin implementation of the water trail.
San Francisco Bay panorama with a view of sailboats, kite boarders, and the Crissy Field Beach
^abcdYabrove, Daniel (December 9, 2013)."How the Bay was Born".Save The Bay Blog. Save The Bay. Archived fromthe original on June 20, 2018. RetrievedJune 4, 2018.
^"Salt Marsh Harvest Mouse"(PDF).South Bay Salt Pond Restoration Project.Archived(PDF) from the original on March 20, 2017. RetrievedSeptember 25, 2019.
^United States. Army. Corps of Engineers. San Francisco District, Port of Oakland (1998).Oakland harbor navigation improvement (−50-foot) project: draft environmental impact statement/environmental impact report: executive summary. U.S. Army Corps of Engineers, San Francisco District.
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