In the late 1950s, the United States government procured Mount Umunhum to build the Almaden Air Force Station, an early warning radar station that operated from 1957 to 1980. The station was constructed as part of a network of radar stations used to keep watch over the nation’s airspace during the Cold War. The radar tower on Mount Umunhum was one of a system of 23 similar stations in California and one of hundreds across the country that fed radar signals into the Semi-Automatic Ground Environment (SAGE) defense system.

This eight-story concrete tower was once a base holding a large radar dish operated by the US Air Force. Between 1957 and 1980, the Air Force used Mount Umunhum’s spectacular views to help protect the West Coast from the possible threat of Soviet planes during the Cold War. The Almaden Air Force Station permanently closed in 1980 when satellite technology made the radar station here obsolete. Some military veterans who worked at the Air Force Station took their technical skills down the mountain and contributed them to the growth of Silicon Valley.