Hidden Valley (formerly, Union House)[2] is a housing development in an unincorporated area of Placer County, California, adjacent to Granite Bay.

[1] Hidden Valley is located 4.25 miles (6.8 km) east-southeast of Rocklin.

[1] Hidden Valley was established in 1950 and consists of semi-rural housing lots surrounding 180 acres of pasture and small lakes.

It was once informally called the "Aerojet enclave" for the large number of executives of the aerospace company who resided in the area.

This Placer County, California-related article is a stub.