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San Francisco Bay
Coordinates	37°42′30″N 122°16′49″W / 37.70833°N 122.28028°W / 37.70833; -122.28028Coordinates: 37°42′30″N 122°16′49″W / 37.70833°N 122.28028°W / 37.70833; -122.28028
River sources	Sacramento River San Joaquin River
Ocean/sea sources	Pacific Ocean
Countries	United States
Max. length	60 mi (97 km)
Max. width	12 mi (19 km)
Surface area	400 to 1,600 sq mi (1,000 to 4,100 km2)
Settlements	San Francisco Oakland San Jose

San Francisco Bay is a shallow, productive estuary through which water draining from approximately forty percent of California, flowing in the Sacramento and San Joaquin rivers from the Sierra Nevada mountains, enters the Pacific Ocean. Specifically, both rivers flow into Suisun Bay, which flows 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. However, the entire group of interconnected bays is often referred to as “San Francisco Bay”.

San Francisco Bay is located in the U.S. state of California, surrounded by a contiguous region known as the San Francisco Bay Area (often simply "the Bay Area"), dominated by the large cities San Francisco, Oakland, and San Jose. The waterway entrance to San Francisco Bay from the Pacific Ocean is called the Golden Gate. Across the strait spans the Golden Gate Bridge.

Size[link]

The Bay covers somewhere between 400 and 1,600 square miles (1,040 to 4,160 square kilometers), depending on which sub-bays (such as San Pablo Bay), estuaries, wetlands, and so on are included in the measurement.^[1][2] The main part of the Bay measures 3 to 12 miles (5 to 20 km) wide east-to-west and somewhere between 48 miles (77 km)¹ and 60 miles (97 km)² north-to-south. It is the largest Pacific estuary in the Americas.

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 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.

San Francisco, Oakland, and the Bay Bridge

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 (1915), 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 in 1901. It is now predominately a bedroom 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.

San Francisco Bay, and the city skyline seen from Marin County in the Golden Gate National Recreation Area.

Geology[link]

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. During the last ice age, the basin now filled by the bay was a large linear valley with small hills, similar to most of the valleys of the Coast Ranges. The rivers of the Central Valley ran out to sea through a canyon that is now the Golden Gate. As the great ice sheets melted, sea level rose 300 feet (91 m) over 4,000 years, and the valley filled with water from the Pacific, becoming a bay. The small hills became islands.

History[link]

San Francisco Bay from space, September 1994

The first recorded European discovery of San Francisco Bay was on November 4, 1769 when Spanish explorer Gaspar de Portolà, unable to find the port of Monterey, California, continued north close to what is now Pacifica and reached the summit of the 1,200-foot (370 m) high Sweeney Ridge, where he sighted San Francisco Bay. Portola 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.

This famous bay was the center of American settlement in the Far West during the 19th century. From the 1820s onward, American presidents and expansionists coveted the bay as a great natural harbor in the Pacific. After many failed efforts to buy the bay and varying areas around it, the US Navy and Army seized the region from Mexico during the Mexican-American War (1845–1848). On February 2, 1848 California was annexed to the U.S. 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. During the California gold rush of 1848-1850s, San Francisco Bay instantly became one of the world's greatest seaports, dominating shipping and transportation in the American West until the last years of the 19th century. The bay's regional importance became paramount when the First Transcontinental Railroad reached its western terminus in Alameda on September 6, 1869.^[3] The terminus was switched to the Oakland Long Wharf two months later on November 8, 1869.^[4]

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 8 million residents.

Ecology[link]

Despite its urban and industrial character, San Francisco Bay and the Sacramento-San Joaquin 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.^[5]

Most famously, the bay is a key link in the Pacific Flyway. Millions of waterfowl annually use the bay shallows as a refuge. Two endangered species of birds are found here: the California least tern and the California clapper rail. Exposed bay muds provide important feeding areas for shorebirds, 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 artificial Lake Merritt, constructed in the 1860s, and America's first urban National Wildlife Refuge, the Don Edwards San Francisco Bay National Wildlife Refuge (SFBNWR) in 1972. The Bay is also plagued by non-native species.

Salt produced from San Francisco Bay is produced in salt 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.

Low-salinity salt ponds mirror the ecosystem of the bay, with fish and fish-eating birds in abundance. Mid-salinity ponds support dense populations of brine 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.

The seasonal range of water temperature in the Bay is from about 8 °C (46 °F) to about 23 °C (73 °F).

Humphrey the Whale entered San Francisco Bay twice on errant migrations, and was successfully rescued and redirected each time in the late 1980s and early 1990s. This occurred again with Dawn and Delta a mother and calf in 2007.

Industrial, mining, and other uses of mercury have resulted in a widespread distribution in the bay, with uptake in the bay's phytoplankton and contamination of its sportfish.^[6]In January 1971, two Standard Oil tanker collided in the bay, creating an 800,000 gallon oil spill disaster, which spurred environmental protection of the bay. In November 2007, a ship named COSCO Busan collided with the San Francisco – Oakland Bay Bridge and spilled over 58,000 gallons of bunker fuel, creating the largest oil spill in the region since 1996.^[7]

At times, San Francisco Bay is covered in fog.

For the first time in 65 years, Pacific Harbor Porpoise (Phocoena phocoena) returned to the Bay in 2009.^[8] Golden Gate Cetacean Research, a non-profit organization focused on research on cetaceans, 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.^[9] Pacific harbor porpoise range from Point Conception, California to Alaska and across to the Kamchatka 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.^[10]

City skyline through the fog, from the Golden Gate National Recreation Area.

Bay fill and depth profile[link]

San Francisco Bay's profile changed dramatically in the late 19th century and again with the initiation of dredging by the US Army Corps of Engineers in the 20th century. Before about 1860, most bay shores (exception: 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.

In the 1860s and continuing into the early 20th century, miners dumped staggering quantities of mud and gravel from hydraulic 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.

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.

(1) Richmond-San Rafael Bridge, (2) Golden Gate Bridge, (3) San Francisco-Oakland Bay Bridge, (4) San Mateo-Hayward Bridge, (5) Dumbarton Bridge

In the last years of the nineteenth- and first decades of the twentieth-centuries, at the behest of local political officials and following Congressional orders, the US 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, an enormous federal subsidy of San Francisco Bay shipping. Some of the dredge spoils were initially dumped in the bay shallows (including helping to create Treasure Island on the former shoals to the north of Yerba Buena Island) and used to raise an island 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 by dikes.

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 (3.7 to 4.6 m). Between Hayward and San Mateo to San Jose it is 12 to 36 in (300 to 910 mm). The deepest part of the bay is under and out of the Golden Gate Bridge, at 372 ft (113 m). ^[11]

In the late 1990s, a 12-year harbor-deepening project for the Port 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), but dredging 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 $432 million project, with $244 million paid for with federal funds and $188 million supplied by the Port of Oakland. Some 6,000,000 cubic yards (4,600,000 m³) of mud from the dredging was deposited at the western edge of Middle Harbor Shoreline Park to become a 188-acre (76 ha) shallow-water wetlands habitat for marine and shore life.^[12][13] Further dredging followed in 2011, to maintain the navigation channel.^[14][15] This dredging enabled the arrival of the largest container ship ever to enter the San Francisco Bay, the MSC Fabiola. Bay pilots trained for the visit on a simulator at the California 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.^[16]

Transportation[link]

San Francisco Bay was traversed by watercraft since before the coming of Europeans; the indigenous peoples used their canoes to fish and clam along the shoreline. The era of sail brought ships that communicated with the rest of the world and served as early 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 early established around the Bay, augmented during wartime. (See e.g. Kaiser Shipyards)

San Francisco Bay and the Golden Gate Bridge

San Francisco Bay is spanned by eight bridges, all of them dedicated to vehicle traffic: the Golden Gate Bridge on Highway 101 (which was the largest single span suspension bridge ever built at the time of its construction) which connects San Francisco and Marin counties and is the only bridge in the area not own by the State of California. The Richmond-San Rafael Bridge on Highway 580 which connects Marin and Contra Costa counties, the San Francisco – Oakland Bay Bridge on Highway 80 which connects Alameda and San Francisco counties, the Hayward-San Mateo Bridge on Highway 92 which connects Alameda and San Mateo counties and the Dumbarton Bridge on Highway 84 which connects Alameda and San Mateo counties. The Carquinez Bridge on Highway 80, the Benicia Bridge on Highway 680 and the Antioch Bridge on Highway 160 all connect Contra Costa and Solano county. The bay is also spanned by the Transbay Tube, an underwater tunnel through which BART runs. Prior to the construction of these infrastructures, transbay transportation was dominated by fleets of ferryboats operated by the Southern Pacific Railroad and the Key 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. (See article Ferries of San Francisco Bay).

The Bay also continues to serve as a major international shipping port, served by a large container facility operated by the Port of Oakland, and two smaller facilities in Richmond and San Francisco.

Port Of Oakland California

Recreation[link]

San Francisco Bay is a mecca for sailors (boats, as well as windsurfing and kitesurfing), due to consistent strong westerly/northwesterly thermally-generated winds (Beaufort force 6 (15-25 knots) is common on summer afternoons) and protection from large open ocean swells. Yachting and yacht racing are popular pastimes and the San Francisco Bay Area is home to many of the world's top sailors. A shoreline bicycle and pedestrian trail known as the San Francisco Bay Trail encircles the edge of the bay. Parks and protected areas around the bay include Eden Landing Ecological Reserve, Hayward Regional Shoreline, Don Edwards San Francisco Bay National Wildlife Refuge, Hayward Shoreline Interpretive Center, Crown Memorial State Beach, Eastshore State Park, Point Isabel Regional Shoreline, Brooks Island Regional Shoreline, and César Chávez Park.

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.

Kitesurfing and wind surfing are also popular in the bay.

San Francisco Bay panorama with a view of sailboats, kite boarders, and the Crissy Field Beach.

San Francisco Bay panorama with a view of sailboats, kite boarders, and the Crissy Field Beach.

Gallery[link]

• 

  "San Francisco Bay", painting by Albert Bierstadt, 1871-73

• 

  The City of Berkeley, the Bay and Marin County in the background as seen from the Claremont Canyon reserve

• 

  Mount Tamalpais view across San Pablo Bay at Point Pinole Regional Shoreline in Richmond

• 

  San Pablo Bay portion of San Francisco Bay at the Richmond-San Rafael Bridge

• 

  Alcatraz at dawn on San Francisco Bay

• 

  People also swim recreationally, at Kellar Beach in Richmond's Miller/Knox Regional Shoreline.

• 

  Oil Spill in the Bay

• 

  RMS Queen Mary 2 in San Francisco Bay

• 

  seen at night.

See also[link]

San Francisco Bay Area portal

• Islands of San Francisco Bay
• Golden Gate
• Mount Tamalpais State Park
• Mount Diablo State Park
• Napa Sonoma Marsh
• Point Pinole Regional Shoreline, Richmond
• Eastshore State Park
• Hydrography of the San Francisco Bay Area

People

• J.C. Barthel, who prepared "plans for the docks and other water-front improvements in the San Francisco Bay district"

References[link]

Further reading[link]

• 1999 Grolier Multimedia Encyclopedia.
• 1988 Encyclopædia Britannica.

External links[link]

Wikimedia Commons has media related to: San Francisco Bay

• San Francisco Bay: Portrait of an Estuary, David Sanger and John Hart, University of California Press
• Barging In - A Short History of Liveaboards on the Bay
• The Islands of San Francisco Bay, James A. Martin | Michael T. Lee, Down Window Press
• Army Corps of Engineers Bay Model: Working scale model of the Bay
• SF Bay Kayak, Canoe, and Boat Launch Ramp guide. A collaboratively edited guide to the SF bay.
• BoatingSF.com: Photos of SF Bay and its boats, plus online cruising guide
• SF Estuary Institute: San Francisco Bay Historical View Maps
• Save San Francisco Bay: Protect and Restore San Francisco Bay
• sfbaywildlife.info Guide to San Francisco Bay wildlife
• Early History of the California Coast, a National Park Service Discover Our Shared Heritage Travel Itinerary

v t e San Francisco Bay Area Bodies of water Bodega Bay Carquinez Strait Clifton Forebay Golden Gate Grizzly Bay Guadalupe River Half Moon Bay Lake Berryessa Napa River Oakland Estuary Petaluma River Richardson Bay Richmond Inner Harbor Russian River San Francisco Bay San Leandro Bay San Pablo Bay Sonoma Creek Suisun Bay Tomales Bay Counties Alameda Contra Costa Marin Napa San Francisco San Mateo Santa Clara Solano Sonoma Major cities San Jose San Francisco Oakland Cities and towns 100k–250k Antioch Berkeley Concord Daly City Fairfield Fremont Hayward Richmond Santa Clara Santa Rosa Sunnyvale Vallejo Cities and towns 25k–99k Alameda Belmont Benicia Brentwood Burlingame Campbell Castro Valley Cupertino Danville Dublin East Palo Alto Foster City Gilroy Livermore Los Altos Los Gatos Martinez Menlo Park Milpitas Morgan Hill Mountain View Napa Newark Novato Oakley Pacifica Palo Alto Petaluma Pittsburg Pleasant Hill Pleasanton Redwood City Rohnert Park San Bruno San Carlos San Leandro San Mateo San Pablo San Rafael San Ramon Saratoga South San Francisco Suisun City Union City Vacaville Walnut Creek Windsor Cities and towns 10k–25k Alamo Albany Alum Rock American Canyon Ashland Atherton Bay Point Blackhawk-Camino Tassajara Cherryland Clayton Discovery Bay Dixon El Cerrito El Sobrante Emeryville Fairview Half Moon Bay Healdsburg Hercules Hillsborough Lafayette Larkspur Los Altos Hills Millbrae Mill Valley Moraga North Fair Oaks Orinda Piedmont Pinole San Anselmo San Lorenzo Sonoma Stanford Tamalpais-Homestead Valley Sub-regions East Bay North Bay San Francisco Peninsula Silicon Valley South Bay

v t e San Francisco Bay watershed Outline Hydrography · Ecology · List of tributaries · List of lakes Subdivisions Major: San Francisco Bay · Suisun Bay · San Pablo Bay · Minor: Golden Gate · Grizzly Bay · Richardson Bay · San Rafael Bay · Richmond Inner Harbor · San Leandro Bay Waterways Rivers: San Joaquin · Sacramento · Napa · Guadalupe · Petaluma · Creeks (discharging into the Bay): Alameda · Baxter · Cerrito · Codornices · Coyote (Santa Clara) · Coyote (Marin) · San Leandro · San Lorenzo · Schoolhouse · Temescal · Sausal · Redwood · San Mateo · Sonoma · Corte Madera · Arroyo Corte Madera del Presidio · San Rafael · Miller · Novato · Tolay · San Francisquito · Pacheco · Alhambra · Adobe · Rodeo · Refugio · Pinole · Garrity · Rheem · Karlson · San Pablo · Castro · Wildcat · Fluvius Innominatus · Marin (Alameda County) · Strawberry · Reservoirs: Calaveras Reservoir · Straits and estuaries: Sacramento–San Joaquin River Delta · Carquinez Strait · Oakland Estuary · Raccoon Strait Parks and protected areas Don Edwards National Wildlife Refuge · San Pablo Bay National Wildlife Refuge · Eden Landing Ecological Reserve · Hayward Regional Shoreline · Hayward Shoreline Interpretive Center · Crown Memorial State Beach · Eastshore State Park · Emeryville Crescent State Marine Reserve · Point Isabel Regional Shoreline · César Chávez Park · Brooks Island Regional Shoreline · Point Pinole Regional Shoreline · Antioch Dunes National Wildlife Refuge · Coyote Point Park · Middle Harbor Shoreline Park · National Estuarine Research Reserve · China Camp State Park · Rush Ranch Open Space Preserve · San Francisco Maritime National Historical Park · SF Bay Trail Islands and peninsulas Major islands: Alameda · Alcatraz · Angel · Treasure · Yerba Buena · Minor: Brooks · Bair · Bay Farm · Belvedere · Brother · Castro Rocks · Coast Guard · Mare · Red Rock · The Sisters · Marin Islands · Roe · Ryer · Seal Islands · Peninsulas/infill: Albany Bulb · Point Isabel · Foster City · Hunters Point Wetlands Meeker Slough · Hoffman Marsh · Napa Sonoma Marsh · Mowry Slough · Seal Slough · Stege Marsh · Suisun Marsh · Westpoint Slough · Cordelia Slough · Crissy Field · Point Molate Marsh Bridges and tubes Bridges: San Francisco – Oakland · Richmond – San Rafael · San Mateo – Hayward · Dumbarton · Golden Gate · Benicia–Martinez · Antioch · Carquinez · Leimert · Fruitvale · Tubes: Posey/Webster Street · Transbay Ports and marinas Port of San Francisco · Port of Oakland · Port of Richmond · San Francisco Naval Shipyard · Mare Island Naval Shipyard · Port of Redwood City · Berkeley Marina · Oyster Point Marina/Park · Clipper Yacht Harbor · Foster City Marina (proposed) Other Discovery Site · Humphrey the Whale · COSCO Busan oil spill · Delta and Dawn · Golden Gate Biosphere Reserve · California Clapper Rail · Reber Plan · San Leandro Oyster Beds · Thicktail chub · Delta smelt · Richmond Shipyards · U.S. Army Corps of Engineers Bay Model · Guadalupe Watershed · Clifton Court Forebay · Conservation and Development Commission · The Watershed Project · Save The Bay · Harold Gilliam · Marincello · Citizens for East Shore Parks · Friends of Five Creeks · Urban Creeks Council · Cargill Salt infill · Ferry service/WETA · 1971 oil spill · Greenbelt Alliance · The Bay Institute  Portal  ·   Category

San Francisco
—  City and county  —
City and County of San Francisco
San Francisco from the Marin Headlands, with the Golden Gate Bridge in the foreground
Flag Official seal of San Francisco Seal
Nickname(s): The City by the Bay Fog City Frisco (deprecated)[1][2][3] The City that Knows How (antiquated)[4] Baghdad by the Bay (antiquated)[5] The Paris of the West[6]
Motto: Oro en Paz, Fierro en Guerra (Spanish for "Gold in Peace, Iron in War")
Location of San Francisco
San Francisco Location in the United States
Coordinates: 37°46′45.48″N 122°25′9.12″W / 37.7793°N 122.4192°W / 37.7793; -122.4192Coordinates: 37°46′45.48″N 122°25′9.12″W / 37.7793°N 122.4192°W / 37.7793; -122.4192
Country	United States
State	California
Founded	June 29, 1776
Incorporated	April 15, 1850[7]
Founder	Lieutenant José Joaquin Moraga and Francisco Palóu
Named for	Francis of Assisi
Government
• Type	Mayor-council government
• Mayor of San Francisco	Edwin M. Lee
• San Francisco Board of Supervisors	Supervisors Eric Mar Mark Farrell David Chiu Carmen Chu Christina Olague Jane Kim Sean Elsbernd Scott Wiener David Campos Malia Cohen John Avalos
• California State Assembly	Fiona Ma (D) Tom Ammiano (D)
• California State Senate	Mark Leno (D) Leland Yee (D)
• United States House of Representatives	Nancy Pelosi (D) Jackie Speier (D)
Area[8]
• City and county	231.89 sq mi (600.6 km2)
• Land	46.87 sq mi (121.4 km2)
• Water	185.02 sq mi (479.2 km2)  79.79%
• Metro	3,524.4 sq mi (9,128 km2)
Elevation	52 ft (16 m)
Highest elevation	925 ft (282 m)
Lowest elevation	0 ft (0 m)
Population (2010)[8][9]	CSA: 7,563,460
• City and county	805,235
• Density	17,179.2/sq mi (6,632.9/km2)
• Urban	3,273,190
• Metro	4,335,391
Demonym	San Franciscan
Time zone	Pacific Standard Time (UTC-8)
• Summer (DST)	Pacific Daylight Time (UTC-7)
ZIP Code	94101–94112, 94114–94147, 94150–94170, 94172, 94175, 94177
Area code(s)	415
Website	www.sfgov.org

San Francisco (/ˌsæn frənˈsɪskoʊ/), officially the City and County of San Francisco, is the financial, cultural, and transportation center of the San Francisco Bay Area, a region of 7.6 million people which includes San Jose and Oakland.^[10] The only consolidated city-county in California,^[11] it encompasses a land area of about 46.9 square miles (121 km²)^[12] on the northern end of the San Francisco Peninsula, giving it a density of about 17,179 people per square mile (6,632 people per km²). It is the most densely settled large city (population greater than 200,000) in the state of California and the second-most densely populated large city in the United States after New York City.^[13] San Francisco is the fourth most populous city in California and the 13th most populous city in the United States, with a population of 805,235 as of the 2010 Census. The San Francisco-Oakland-Fremont metropolitan area has a population of 4,335,391.^[14]

In 1776, colonists from Spain established a fort at the Golden Gate and a mission named for Francis of Assisi a few miles away.^[15] The California Gold Rush of 1849 propelled the city into a period of rapid growth, increasing the population in one year from 1,000 to 25,000,^[16] and thus transforming it into the largest city on the West Coast at the time. After three-quarters of the city was destroyed by the 1906 earthquake and fire,^[17] San Francisco was quickly rebuilt, hosting the Panama-Pacific International Exposition nine years later. During World War II, San Francisco was the port of embarkation for service members shipping out to the Pacific Theater.^[18] After the war, the confluence of returning servicemen, massive immigration, liberalizing attitudes, and other factors led to the Summer of Love and the gay rights movement, cementing San Francisco as a center of liberal activism in the United States.

Today, San Francisco is one of the top tourist destinations in the world,^[19] ranking 35th out of the 100 most visited cities worldwide,^[20] and is renowned for its cool summers, fog, steep rolling hills, eclectic mix of architecture, and landmarks including the Golden Gate Bridge, cable cars, and its Chinatown. The city is also a principal banking and finance center, and the home to more than 30 international financial institutions,^[21] helping to make San Francisco rank 18th in the world's top producing cities, 8th in the United States, and 12th place in the top twenty global financial centers.^[22]

History[link]

Mission San Francisco de Asís (Mission Dolores)

The earliest archaeological evidence of human habitation of the territory of the city of San Francisco dates to 3000 BC.^[23] The Yelamu group of the Ohlone people resided in several small villages when a Spanish exploration party, led by Don Gaspar de Portolà arrived on November 2, 1769, the first documented European visit to San Francisco Bay.^[24] Seven years later, on March 28, 1776, the Spanish established the Presidio of San Francisco, followed by a mission, Mission San Francisco de Asís (Mission Dolores).

Upon independence from Spain in 1821, the area became part of Mexico. Under Mexican rule, the mission system gradually ended and its lands began to be privatized. In 1835, Englishman William Richardson erected the first independent homestead,^[25] near a boat anchorage around what is today Portsmouth Square. Together with Alcalde Francisco de Haro, he laid out a street plan for the expanded settlement, and the town, named Yerba Buena, began to attract American settlers. Commodore John D. Sloat claimed California for the United States on July 7, 1846, during the Mexican-American War, and Captain John B. Montgomery arrived to claim Yerba Buena two days later. Yerba Buena was renamed San Francisco on January 30 of the next year,^[26] and Mexico officially ceded the territory to the United States at the end of the war. Despite its attractive location as a port and naval base, San Francisco was still a small settlement with inhospitable geography.^[27]

Portsmouth Square in 1851

The California Gold Rush brought a flood of treasure seekers. With their sourdough bread in tow,^[28] prospectors accumulated in San Francisco over rival Benicia,^[29] raising the population from 1,000 in 1848 to 25,000 by December 1849.^[16] The promise of fabulous riches was so strong that crews on arriving vessels deserted and rushed off to the gold fields, leaving behind a forest of masts in San Francisco harbor.^[30] California was quickly granted statehood, and the U.S. military built Fort Point at the Golden Gate and a fort on Alcatraz Island to secure the San Francisco Bay. Silver discoveries, including the Comstock Lode in 1859, further drove rapid population growth.^[31] With hordes of fortune seekers streaming through the city, lawlessness was common, and the Barbary Coast section of town gained notoriety as a haven for criminals, prostitution, and gambling.^[32]

Entrepreneurs sought to capitalize on the wealth generated by the Gold Rush. Early winners were the banking industry which saw the founding of Wells Fargo in 1852 and the Bank of California in 1864. Development of the Port of San Francisco and the establishment in 1869 of overland access to the Eastern U.S. rail system via the newly completed Pacific Railroad (the construction of which the city had only reluctantly helped support^[33]) helped make the Bay Area a center for trade. Catering to the needs and tastes of the growing population, Levi Strauss opened a dry goods business and Domingo Ghirardelli began manufacturing chocolate. Immigrant laborers made the city a polyglot culture, with Chinese railroad workers creating the city's Chinatown quarter. In 1870, Asians made up 8% of the population.^[34] The first cable cars carried San Franciscans up Clay Street in 1873. The city's sea of Victorian houses began to take shape, and civic leaders campaigned for a spacious public park, resulting in plans for Golden Gate Park. San Franciscans built schools, churches, theaters, and all the hallmarks of civic life. The Presidio developed into the most important American military installation on the Pacific coast.^[35] By 1890, San Francisco's population approached 300,000, making it the eighth largest city in the U.S. at the time. At the turn of the century, San Francisco was a major city known for its flamboyant style, stately hotels, ostentatious mansions on Nob Hill, and a thriving arts scene.^[36]

"Not in history has a modern imperial city been so completely destroyed. San Francisco is gone." –Jack London after the 1906 earthquake and fire^[37]

At 5:12 am on April 18, 1906, a major earthquake struck San Francisco and northern California. As buildings collapsed from the shaking, ruptured gas lines ignited fires that would spread across the city and burned out of control for several days. With water mains out of service, the Presidio Artillery Corps attempted to contain the inferno by dynamiting blocks of buildings to create firebreaks.^[38] More than three-quarters of the city lay in ruins, including almost all of the downtown core.^[17] Contemporary accounts reported that 498 people lost their lives, though modern estimates put the number in the several thousands.^[39] More than half the city's population of 400,000 were left homeless.^[40] Refugees settled temporarily in makeshift tent villages in Golden Gate Park, the Presidio, on the beaches, and elsewhere. Many fled permanently to the East Bay.

The Palace of Fine Arts at the 1915 Panama-Pacific Exposition

Rebuilding was rapid and performed on a grand scale. Rejecting calls to completely remake the street grid, San Franciscans opted for speed.^[41] Amadeo Giannini's Bank of Italy, later to become Bank of America, provided loans for many of those whose livelihoods had been devastated. The destroyed mansions of Nob Hill became grand hotels. City Hall rose again in splendorous Beaux Arts style, and the city celebrated its rebirth at the Panama-Pacific International Exposition in 1915.^[42]

In ensuing years, the city solidified its standing as a financial capital; in the wake of the 1929 stock market crash, not a single San Francisco-based bank failed.^[43] Indeed, it was at the height of the Great Depression that San Francisco undertook two great civil engineering projects, simultaneously constructing the San Francisco – Oakland Bay Bridge and the Golden Gate Bridge, completing them in 1936 and 1937 respectively. It was in this period that the island of Alcatraz, a former military stockade, began its service as a federal maximum security prison, housing notorious inmates such as Al Capone, and Robert Franklin Stroud, The Birdman of Alcatraz. San Francisco later celebrated its regained grandeur with a World's Fair, the Golden Gate International Exposition in 1939–40, creating Treasure Island in the middle of the bay to house it.

During World War II, the Hunters Point Naval Shipyard became a hub of activity, and Fort Mason became the primary port of embarkation for service members shipping out to the Pacific Theater of Operations.^[18] The explosion of jobs drew many people, especially African Americans from the South, to the area. After the end of the war, many military personnel returning from service abroad and civilians who had originally come to work decided to stay. The UN Charter creating the UN was drafted and signed in San Francisco in 1945 and, in 1951, the Treaty of San Francisco officially ended the war with Japan.

The USS San Francisco steams under the Golden Gate Bridge in 1942, during World War II.

Urban planning projects in the 1950s and 1960s involved widespread destruction and redevelopment of west-side neighborhoods and the construction of new freeways, of which only a series of short segments were built before being halted by citizen-led opposition.^[44] Port activity moved to Oakland, the city began to lose industrial jobs, and San Francisco began to turn to tourism as the most important segment of its economy. The suburbs experienced rapid growth, and San Francisco underwent significant demographic change, as large segments of the white population left the city, supplanted by an increasing wave of immigration from Asia and Latin America.^[45][46] From 1950 to 1980, the city lost over 10 percent of its population.

Over this period, San Francisco became a magnet for America's counterculture. Beat Generation writers fueled the San Francisco Renaissance and centered on the North Beach neighborhood in the 1950s.^[47] Hippies flocked to Haight-Ashbury in the 1960s, reaching a peak with the 1967 Summer of Love.^[48] In the 1970s, the city became a center of the gay rights movement, with the emergence of The Castro as an urban gay village, the election of Harvey Milk to the Board of Supervisors, and his assassination, along with that of Mayor George Moscone, in 1978.^[49]

Bank of America completed 555 California Street in 1969 and the Transamerica Pyramid was completed in 1972,^[50] igniting a wave of Manhattanization that lasted until the late 1980s, a period which saw extensive high-rise development downtown.^[51] The 1980s also saw a dramatic increase in the number of homeless people in the city, an issue that remains today, despite many attempts to address it.^[52] The 1989 Loma Prieta earthquake caused destruction and loss of life throughout the Bay Area. In San Francisco, the quake severely damaged structures in the Marina and South of Market districts and precipitated the demolition of the damaged Embarcadero Freeway and much of the damaged Central Freeway, allowing the city to reclaim its historic downtown waterfront and revitalizing the Hayes Valley neighborhood.

During the dot-com boom of the late 1990s, startup companies invigorated the economy. Large numbers of entrepreneurs and computer application developers moved into the city, followed by marketing, design, and sales professionals, changing the social landscape as once-poorer neighborhoods became increasingly gentrified.^[53] By 2000, the city's population reached new highs, surpassing the previous record set in 1950. When the bubble burst in 2001, many of these companies folded and their employees left. However, many new startups soon took their place during the Web 2.0 boom, and high technology and entrepreneurship continue to be mainstays of the San Francisco economy.^[54]

Geography[link]

The San Francisco Peninsula

San Francisco is located on the West Coast of the United States at the tip of the San Francisco Peninsula and includes significant stretches of the Pacific Ocean and San Francisco Bay within its boundaries. Several islands—Alcatraz, Treasure Island and the adjacent Yerba Buena Island, and a small portion of Alameda Island, Red Rock Island, and Angel Island are part of the city. Also included are the uninhabited Farallon Islands, 27 miles (43 km) offshore in the Pacific Ocean. The mainland within the city limits roughly forms a "seven-by-seven-mile square," a common local colloquialism referring to the city's shape, though its total area, including water, is nearly 232 square miles (600 km²).

Cars navigate Lombard Street to descend Russian Hill.

San Francisco is famous for its hills. There are more than 50 hills within city limits.^[55] Some neighborhoods are named after the hill on which they are situated, including Nob Hill, Pacific Heights, and Russian Hill. Near the geographic center of the city, southwest of the downtown area, are a series of less densely populated hills. Twin Peaks, a pair of hills resting at one of the city's highest points, forms a popular overlook spot. San Francisco's tallest hill, Mount Davidson, is 925 feet (282 m) high and is capped with a 103-foot (31 m) tall cross built in 1934.^[56] Dominating this area is Sutro Tower, a large red and white radio and television transmission tower.

The nearby San Andreas and Hayward Faults are responsible for much earthquake activity, although neither physically passes through the city itself. The San Andreas Fault caused the earthquakes in 1906 and 1989. Minor earthquakes occur on a regular basis. The threat of major earthquakes plays a large role in the city's infrastructure development. The city has repeatedly upgraded its building codes, requiring retrofits for older buildings and higher engineering standards for new construction.^[57] However, there are still thousands of smaller buildings that remain vulnerable to quake damage.^[58]

San Francisco's shoreline has grown beyond its natural limits. Entire neighborhoods such as the Marina and Hunters Point, as well as large sections of the Embarcadero, sit on areas of landfill. Treasure Island was constructed from material dredged from the bay as well as material resulting from tunneling through Yerba Buena Island during the construction of the Bay Bridge. Such land tends to be unstable during earthquakes; the resultant liquefaction causes extensive damage to property built upon it, as was evidenced in the Marina district during the 1989 Loma Prieta earthquake.^[59]

Climate[link]

A popular quote incorrectly attributed to Mark Twain is "The coldest winter I ever spent was a summer in San Francisco."^[60][61] San Francisco's climate is characteristic of the cool-summer Mediterranean climate^[62] of California’s coast, "generally characterized by moist mild winters and dry summers."^[63] Since it is surrounded on three sides by water, San Francisco's weather is strongly influenced by the cool currents of the Pacific Ocean, which moderates temperature swings and produces a remarkably mild year-round climate with little seasonal temperature variation.

Fog is a regular feature of San Francisco summers.

Among major U.S. cities, San Francisco has the coldest daily mean, maximum, and minimum temperatures for June, July and August.^[64] During the summer, rising hot air in California's interior valleys creates a low pressure area that draws winds from the North Pacific High through the Golden Gate, which creates the city's characteristic cool winds and fog.^[65] The fog is less pronounced in eastern neighborhoods and during the late summer and early fall, which is the warmest time of the year.

Because of its sharp topography and maritime influences, San Francisco exhibits a multitude of distinct microclimates. The high hills in the geographic center of the city are responsible for a 20% variance in annual rainfall between different parts of the city. They also protect neighborhoods directly to their east from the foggy and sometimes very cold and windy conditions experienced in the Sunset District; for those who live on the eastern side of the city, San Francisco is sunnier, with an average of 260 clear days, and only 105 cloudy days per year.

Temperatures exceed 75 °F (24 °C) on average only 28 days a year.^[66] The dry period of May to October is mild to warm, with average high temperatures of 64–71 °F (18–22 °C) and lows of 51–56 °F (11–13 °C). The rainy period of November to April is slightly cooler, with high temperatures of 58–64 °F (14–18 °C) and lows of 46–51 °F (8–11 °C). On average, there are 67 rainy days a year, and annual precipitation averages 20.4 inches (518.16 mm).^[66] Snow is extraordinarily rare, with only 10 instances recorded since 1852, most recently in 1976.^[67]

The highest recorded temperature at the official National Weather Service office was 103 °F (39 °C) on July 17, 1988, and June 14, 2000. The lowest recorded temperature was 27 °F (−3 °C) on December 11, 1932.^[68] The U.S. National Weather Service provides a helpful visual aid^[69] graphing the information in the table below to display visually by month the annual typical temperatures, the past year's temperatures, and record temperatures.

Cityscape[link]

San Francisco just before sunset from Twin Peaks.

San Francisco Cityscape from Treasure Island.

Neighborhoods[link]