Situated in northern California, Contra Costa County is one of nine counties that make up the San Francisco Bay Area. It extends from San Francisco Bay north to the San Joaquin Delta and east to the western edge of the Central Valley. Located in the heart of the county is Mount Diablo, a major geographic feature and focal point. These diverse regions contribute to the avian richness of the county, which supports habitats for such nesting species as the Black Oystercatcher, Swainson’s Hawk, and probably the Black Rail. Additional breeding birds of conservation concern include the Tricolored Blackbird, Yellow-billed Magpie, and Least Tern. In size, Contra Costa County ranks 48th among California’s 58 counties, but as of 2008, it was the ninth most populated, with over a million people.