Hidden Valley, Placer County, California

Hidden Valley (formerly, Union House) is a housing development in an unincorporated area of Placer County, California, adjacent to Granite Bay. Hidden Valley is located 4.25 mi east-southeast of Rocklin. It lies at an elevation of 436 feet (133 m).

Hidden Valley was established in 1950 and consists of semi-rural housing lots surrounding 180 acres of pasture and small lakes. It was originally planned as a retirement community, due to its rural setting, but it has since become a bedroom community for the Sacramento metropolitan area. It was once informally called the "Aerojet enclave" for the large number of executives of the aerospace company who resided in the area.