[15] The larger federal classification, the combined statistical area of the region which includes 13 counties,[9] is the second-largest in California—after the Greater Los Angeles area—and the fifth-largest in the United States, with over 9 million people.

[17][18] Despite its urban character, San Francisco Bay is one of California's most ecologically sensitive habitats, providing important ecosystem services such as filtering the pollutants and sediments from rivers and supporting a number of endangered species.

[19] It has been conjectured that the people living in the Bay Area at the time of first European contact were descended from Siberian tribes who arrived at around 1,000 BCE by sailing over the Arctic Ocean and following the salmon migration.

[20] However the current academic consensus is compatible with the oral tradition of the Ohlone and Miwok peoples, which suggests they have been living in the Bay Area for several hundreds if not thousands of years.

Soromenho set sail on Manila Galleon San Agustin on July 5, 1595 and in early November they reached land between Point St. George and Trinidad Head, north of the Bay Area, in the Lost Coast.

[28] The Bay Area estuaries remained unknown to Europeans until members of the Portolá expedition, while trekking along the California coast, encountered them in 1769 when the Golden Gate blocked their continued journey north.

[30] In 1821, Mexico gained its independence from Spain and the Bay Area became part of the Mexican province of Alta California, a period characterized by ranch life and visiting American trappers.

[38] The completion of the railroad connected the Bay Area with the rest of the United States, established a truly national marketplace for the trade of goods, and accelerated the urbanization of the region.

By 1915, the city had been sufficiently rebuilt and advertised itself to the world during the Panama Pacific Exposition that year, although the effects of the quake hastened the loss of the region's dominant status in California to the Los Angeles metropolitan area.

In 2009, an African-American man named Oscar Grant was fatally shot by Bay Area Rapid Transit police officers, precipitating widespread protests across the region and even riots in Oakland.

[80] The Bay Area is located in the warm-summer Mediterranean climate zone (Köppen Csb) that is a characteristic of California's coast, featuring mild to cool winters with occasional rainfall, and warm to hot, dry summers.

[83] Due to the Bay Area's diverse topographic relief (itself the result of the clashing tectonic plates), the region is home to numerous microclimates that lead to pronounced differences in climate and temperature over short distances.

Further north, the Carquinez Strait funnels the ocean weather into the San Joaquin River Delta, causing a cooling effect in Stockton and Sacramento, so that these cities are also cooler than their Central Valley counterparts in the south.

[84] The Bay Area is home to a diverse array of wildlife and, along with the connected San Joaquin River Delta represents one of California's most important ecological habitats.

[109] Bald eagles were once common in the Bay Area, but habitat destruction and thinning of eggs from DDT poisoning reduced the California state population to 35 nesting pairs.

[110] In 1927, zoologist Joseph Grinnell wrote that osprey were only rare visitors to the San Francisco Bay Area, although he noted records of one or two used nests in the broken tops of redwood trees along the Russian River.

[129] Today, the bay has been significantly altered heavily re-engineered to accommodate the needs of water delivery, shipping, agriculture, and urban development, with side effects including the loss of wetlands and the introduction of contaminants and invasive species.

The Visitacion Valley has a designated Pacific Islander district and Samoan and Tongans have a presence in Southeast San Francisco and Daly City's Bayshore neighborhood.

[173][174][175] Some observers have warned that this could lead to an economic doom loop for Bay Area cities, particularly San Francisco,[176] while others have argued that these concerns are restricted to the downtown cores.

Rising housing prices and gentrification in the San Francisco Bay Area are often framed as symptomatic of high-income tech workers moving in to previously low-income, underserved neighborhoods.

[189][190] As greater proportions of their incomes are spent on rent, many impoverished populations in the San Francisco Bay Area also face food insecurity and health setbacks.

[222] Transportation in the San Francisco Bay Area is reliant on a complex multimodal infrastructure consisting of roads, bridges, highways, rail, tunnels, airports, ferries, and bike and pedestrian paths.

[228] Additional damage that occurred in the wake of the 1989 Loma Prieta earthquake resulted in freeway segments being removed instead of being reinforced or rebuilt, leading to the revitalization of neighborhoods such as San Francisco's Embarcadero and Hayes Valley.

[240] According to the Cook Partisan Voting Index (CPVI), the Bay Area's districts tend to favor Democratic candidates by roughly 40 to 50 percentage points, considerably above the mean for California and the nation overall.

San Francisco, in particular, was the center of the counterculture movement in the 1960s, which directly led to the rise of several notable musical acts: The Grateful Dead, which formed in 1965, and Jefferson Airplane and Janis Joplin; all three would be closely associated with the 1967 Summer of Love.

[152] The Vietnam War was being fought at the time, and Bay Area bands such as Creedence Clearwater Revival of El Cerrito became known for their political and socially-conscious lyrics against the conflict.

[254] The 1990s also saw the emergence of the influential hyphy movement in hip hop, derived from the Oakland slang for "hyperactive", and pioneered by Bay Area rappers Andre "Mac Dre" Hicks, Mistah Fab, and E-40.

[267][268] Several famous actors have arisen from the Bay Area's theatre community, including Daveed Diggs from Hamilton and Darren Criss from Hedwig, A Very Potter Musical, and Glee.

The San Francisco Examiner, once the cornerstone of William Randolph Hearst's media empire and the home of Ambrose Bierce, declined in circulation over the years and now takes the form of a free daily tabloid, under new ownership.

[284] Non-English-language newspapers include several Chinese-language papers such as Sing Tao Daily, the largest in the Bay Area by circulation,[285] and El Mundo, a free Spanish-language weekly distributed by the Mercury News.