Almaden Air Force Station
was a US Air Force early warning radar base in operation from 1958 to 1980. It is located on the summit of Mount Umunhum
in the Santa Cruz Mountains & sits about 3,486 feet (1062 m) above Almaden Valley. The station was constructed in 1957 to keep watch over Northern California's airspace as part of the NORAD defense system. A GATR (Ground Air Transmitter Receiver) was located about a mile (1,5 km) away on Mount Thayer. The station was manned by the 682d Radar Squadron, and at its peak housed about 120 people in eighty four buildings. The Air Force Station was closed down in 1980, and in 1986 it was acquired by the MROSD (Midpeninsula Regional Open Space District
). The base is now a part of the Sierra Azul Open Space Preserve although it is not yet open to the public because of environmental hazards (asbestos and lead-based paint). The MROSD estimates it will take about US$2 million to clean up the base for public use.