San Francisco Bay Area Combined Statistical Area

The San Jose-San Francisco-Oakland, CA Combined Statistical Area is a 12-county Combined Statistical Area (CSA) designated by the United States Office of Management and Budget in Northern California that includes the San Francisco Bay Area. The CSA is more extensive than the popular local definition of the Bay Area, which consists of only the nine counties bordering San Francisco and San Pablo Bays: Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, and Sonoma. This group of counties also elects boards for regional planning and air quality control regulation. The CSA includes the three counties of San Joaquin, Santa Cruz, and San Benito that do not border San Francisco or San Pablo Bay, but are economically tied to the nine counties that do.

The CSA ranks as the fifth most populous combined statistical area of the United States, and second in California.

The CSA includes the vast geographic diversity of the traditional nine-county region, composed of at least six terranes (continental, seabed, or island arc fragments with distinct characteristics) pushed together over many millions of years by the forces of plate tectonics. These landscapes range from cool foggy mountains and temperate forests on the San Francisco Peninsula and Marin County, to the semi-arid, near-desert terrain in the easternmost portions of the East Bay.

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