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Contra Costa County was one of the original 27 counties of California, created in 1850 at the time of statehood. The county was originally to be called Mt. Diablo County, but the name was changed prior to incorporation as a county. The county’s Spanish language name means opposite coast, because of its location opposite San Francisco, in an easterly direction, on San Francisco Bay. Southern portions of the county’s territory, including all of the bayside portions opposite San Francisco and northern portions of Santa Clara County, were given up to form Alameda County effective March 25, 1853.

In 1821 Mexico gained independence from Spain. While little changed in ranchero life, the Mexican War of Independence resulted in the secularization of the missions with the re-distribution of their lands, and a new system of land grants under the Mexican Federal Law of 1824. Mission lands extended throughout the Bay Area, including portions of Contra Costa County. Between 1836 and 1846, during the era when California was a province of independent Mexico, 15 land grants were made in Contra Costa County.

The land titles in Contra Costa County may be traced to multiple subdivisions of a few original land grants. The grantee’s family names live on in a few city and town names such as MartinezPacheco and Moraga and in the names of streets, residential subdivisions, and business parks. A few mansions from the more prosperous farms have been preserved as museums and cultural centers and one of the more rustic examples has been preserved as a working demonstration ranch, Borges Ranch.


#312: John Muir Home
#356: Castro Home
#455: Don Fernando Pacheco Adobe
#509: Joaquin Moraga Adobe
#511: Vicente Martinez Adobe
#512: Alvarado Adobe
#515: Don Salvio Pacheco Adobe
#722: Site of the Murder of Dr. John Marsh

#731: The Old Homestead
#853: Captain Pedro Fages Trail
#905: Mount Diablo
#932: Mount Diablo Coal Field
#951: Light Stations of California (Thematic) -East Brother Light Station
#1002.1: Site of Giant Powder Company (Point Pinole)
#1032: Richmond Shipyards District