San Mateo County, California in the context of "Santa Clara County, California"

The San Francisco Bay Area, commonly known as the Bay Area, is a region of California surrounding and including San Francisco Bay, and anchored by the cities of Oakland, San Francisco, and San Jose. The Association of Bay Area Governments defines the Bay Area as including the nine counties that border the estuaries of San Francisco Bay, San Pablo Bay, and Suisun Bay: 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 which are not officially part of the San Francisco Bay Area, 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, 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 earliest archaeological evidence of human settlements in the Bay Area dates back to 8000–10,000 BC. 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. The Spanish empire claimed the area beginning in the early period of Spanish colonization of the Americas. The earliest Spanish exploration of the Bay Area took place in 1769. The Mexican government controlled the area from 1821 until the 1848 Treaty of Guadalupe Hidalgo. 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. California was admitted as the 31st state in 1850. A major earthquake and fire leveled much of San Francisco in 1906. 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. 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. The postwar 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.

Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides occur in a variety of environments, characterized by either steep or gentle slope gradients, from mountain ranges to coastal cliffs or even underwater, in which case they are called submarine landslides.

Gravity is the primary driving force for a landslide to occur, but there are other factors affecting slope stability that produce specific conditions that make a slope prone to failure. In many cases, the landslide is triggered by a specific event (such as heavy rainfall, an earthquake, a slope cut to build a road, and many others), although this is not always identifiable.

The Association of Bay Area Governments (ABAG) is a regional planning agency incorporating various local governments in the San Francisco Bay Area in California. It encompasses nine counties surrounding the San Francisco Bay. Those counties are Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, and Sonoma. It has the ability to establish housing and transportation goals for cities to minimize urban sprawl by requiring that housing be zoned for near new workplace construction. It deals with land use, housing, environmental quality, and economic development. Non-profit organizations as well as governmental organizations can be members. All nine counties and 101 cities within the Bay Area are voluntary members of ABAG.

As an advisory organization, ABAG has limited statutory authority. It is governed by its General Assembly, which consists of an elected official (delegate) from each city and county which is a member of the organization. The General Assembly determines policy, adopts the annual budget and work program, and reviews policy actions taken or proposed by the organization's Executive Board. A majority of city and county votes are required for action.

The San Francisco Police Department (SFPD) is the municipal law enforcement agency of the City and County of San Francisco, as well as San Francisco International Airport in San Mateo County. In 2000, the SFPD was the 11th largest police department in the United States.

The SFPD (along with the San Francisco Fire Department and the San Francisco Sheriff's Department) serves an estimated population of 1.2 million, including the daytime-commuter population and thousands of other tourists and visitors.

San Mateo is the most populous city in San Mateo County, California, United States, on the San Francisco Peninsula. It is part of the San Francisco Bay Area metropolitan region, and is located about 20 miles (32 km) south of San Francisco. San Mateo borders Burlingame to the north, Hillsborough to the west, San Francisco Bay and Foster City to the east and Belmont to the south. The population was 105,661 at the 2020 census. Some of the biggest economic drivers for the city include technology, health care and education.

The San Francisco Peninsula is a peninsula in the San Francisco Bay Area that separates San Francisco Bay from the Pacific Ocean. On its northern tip is the City and County of San Francisco. Its southern base is Palo Alto, Mountain View, Los Altos and Sunnyvale, in Santa Clara County. Most of the Peninsula is occupied by San Mateo County, which is between San Francisco and Santa Clara counties, and the Peninsula includes the cities and towns of Atherton, Belmont, Brisbane, Burlingame, Colma, Daly City, East Palo Alto, El Granada, Foster City, Half Moon Bay, Hillsborough, La Honda, Loma Mar, Los Altos, Los Altos Hills, Menlo Park, Millbrae, Mountain View, Pacifica, Palo Alto, Pescadero, Portola Valley, Redwood City, Redwood Shores, San Bruno, San Carlos, San Mateo, South San Francisco, Sunnyvale, West Menlo Park and Woodside.

Whereas the term peninsula in a geographical sense technically refers to the entire San Francisco Peninsula, in local jargon, "The Peninsula" does not include the city of San Francisco.

San Francisco International Airport (IATA: SFO, ICAO: KSFO, FAA LID: SFO) is the primary international airport for the San Francisco Bay Area in the U.S. state of California. Owned and operated by the City and County of San Francisco, the airport has a San Francisco mailing address and ZIP Code, although it is situated in an unincorporated area of neighboring San Mateo County, approximately 12 miles (19 km; 10 nmi) southeast of San Francisco.

SFO is the largest airport in the Bay Area and the second-busiest in the US State of California, following Los Angeles International Airport (LAX). In 2024, it ranked as the 13th-busiest airport in the United States and the 36th-busiest in the world by passenger traffic. It is a hub for United Airlines, acting as the airline's primary transpacific gateway, and as a major maintenance facility. Additionally, SFO functions as a hub for Alaska Airlines.