Stevenson Ranch is an affluent census-designated place in Los Angeles County, California. The community is located in the Santa Clarita Valley. Often incorrectly referred to as part of the city of Santa Clarita, the community does not actually fall within the Santa Clarita city limits, and is instead in an unincorporated area. Stevenson Ranch encompasses about 6.4 square miles (17 sq. km). About 1,000 acres (4.0 sq. km) are set aside as parks, recreation areas and open space. Stevenson Ranch is set in the foothills of the Santa Susana Mountains and lies west of Interstate 5. This area backs up to the historic, oil-mining town of Mentryville, founded in 1875. A master planned community, it was approved by the county in 1987.