San Francisco Bay Area

The San Francisco Bay Area, commonly known as the Bay Area, is a region of California centered around the San Francisco, San Pablo, and Suisun estuaries in Northern California. The Association of Bay Area Governments defines the Bay Area as including the nine counties that border the aforementioned estuaries: Alameda, Contra Costa, Marin, Napa, San Mateo, Santa Clara, Solano, Sonoma, and San Francisco. Other definitions may be either smaller or larger, and may include neighboring counties that do not border the aforementioned estuaries, such as the Central Coast counties of Santa Cruz, San Benito, and Monterey, or the Central Valley counties of San Joaquin, Merced, and Stanislaus.

The Bay Area is known for its natural beauty, progressive politics, prominent universities, technology companies, and affluence. The Bay Area contains many cities, towns, airports, and associated regional, state, and national parks, connected by a complex multimodal transportation network. The most populous cities of the Bay Area are Oakland, San Francisco, and San Jose, the latter of which in 2022 had population of 971,233, making it the third-most populous city in California, after Los Angeles and San Diego, and the 12th-most populous in the United States.

The nine-county Bay Area is home to approximately 7.52 million people. The larger federal classification, the combined statistical area of the region which includes 13 counties, 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. The Bay Area's population is ethnically diverse: roughly three-fifths of the region's residents are Hispanic, Asian, African American, or Pacific Islander, all of whom have a significant presence throughout the region. Most of the remaining two-fifths of the population is non-Hispanic White American. As of 2022, 70,717 residents of the nine-county Bay Area and 100,325 residents of the thirteen-county Bay Area—approximately 1% of the population of both—identify as Native American.

The earliest archaeological evidence of human settlements in the Bay Area dates back to 8000–10,000 BC from shell mounds in the Coyote Hills. The oral tradition of the Ohlone and Miwok people suggests they have been living in the Bay Area for several hundreds if not thousands of years. Anthropological evidence suggests Ohlone ethnogenesis occurred around 700 CE following a wave of migration from the Central Valley.

Despite being unaware of its existence, the Spanish empire claimed the Bay Area beginning in the early period of Spanish colonization of the Americas. In 1535, the empire established kingdom of New Spain which inherited the empire's claims to much of what is now the western United States, including the Bay Area. However despite its claims, the region remained a distant frontier land, largely outside of the kingdom's control for centuries. The earliest Spanish exploration of the Bay Area took place in 1769, and the earliest European settlements in the area date this time period. The Mexican government controlled the area from 1821—following the Mexican War of Independence—until the 1848 Treaty of Guadalupe Hidalgo which ended the Mexican–American War.

Coincidentally also in 1848, James W. Marshall discovered gold in nearby mountains, resulting in explosive immigration to the area and the precipitous decline of the Native population. The California Gold Rush brought rapid growth to San Francisco specifically, transforming it from an unimportant hamlet into a busy port and the largest city on the West Coast at the time. The city's population grew from 200 in 1846 to about 35,000 in 1852 and about 150,000 in 1870. From 1870 to 1900, approximately one quarter of California's population resided in the city proper. California was admitted as the 31st state in 1850, and during the early years of statehood, state legislative business was briefly conducted in the Bay Area cities of San José, Vallejo, and Benicia, before being permanently relocated to Sacramento in 1854. San Francisco served as the temporary capital during the Great Flood of 1862. A major earthquake and fire leveled much of San Francisco in 1906, but the city was quickly rebuilt in time to host the 1915 Panama-Pacific Exposition.

During World War II, the Bay Area played a major role in America's war effort in the Asiatic-Pacific Theater, with the San Francisco Port of Embarkation, of which Fort Mason was one of 14 installations and location of the headquarters, acting as a primary embarkation point for American forces. In 1945, the United Nations Charter was signed in San Francisco, establishing the United Nations before permanently relocating to Manhattan, and in 1951, the Treaty of San Francisco re-established peaceful relations between Japan and the Allied Powers. Since then, the Bay Area has experienced numerous political, cultural, and artistic movements, developing unique local genres in music and art and establishing itself as a hotbed of progressive politics. Economically, the post-war Bay Area saw large growth in the financial and technology industries, creating an economy with a gross domestic product of over $700 billion. In 2018 it was home to the third-highest concentration of Fortune 500 companies in the United States.

Despite its urban character, the 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. In addition, the Bay Area is known for its stands of coast redwoods, many of which are protected in state and county parks. The region is additionally known for the complexity of its landforms, the result of millions of years of tectonic plate movements. Because the Bay Area is crossed by 6 major earthquake faults, the region is particularly exposed to hazards presented by large earthquakes. The climate is temperate and conducive to outdoor recreational and athletic activities such as hiking, running, and cycling. The Bay Area is host to 6 professional sports teams and is a cultural center for music, theater, and the arts. It is also host to numerous higher education institutions, including research universities such as Stanford University and the University of California, Berkeley. Home to 101 municipalities and 9 counties, governance in the Bay Area involves numerous local and regional jurisdictions, often with broad and overlapping responsibilities.