From much of San Jose, you can see a concrete box on a peak in the Santa Cruz Mountains.
The Cube
The Cube is a radar tower built in 1962 that housed an 85.5-ton AN/FPS-24 radar to watch for hostile aircraft during the Cold War, according to Wikipedia. Its signal caused electronic interference for radios, TVs and sound systems within about 250 miles. After the Air Force station closed, Midpeninsula Regional Open Space District removed 3,000 cubic yards of hazardous materials in 2009 with federal funding. The tower was given historic status to protect it from demolition. On Sept. 18, 2017, the summit road and a hiking and biking trail opened to the public. Wikipedia says the name comes from Ohlone and means "Resting Place of the Hummingbird."
The preserve
Midpen says Sierra Azul is the largest of the lands it manages, protecting more than 19,000 acres above Lexington Reservoir, Los Gatos and south San Jose, topped by the 3,486-foot summit. It has 26 miles of trails for hiking, dog walking, biking and horseback riding, and it is prime mountain lion habitat. Midpen says Mount Umunhum figures prominently in the Amah Mutsun people's creation story.
Hours
The preserve opens a half-hour before sunrise and closes a half-hour after sunset. The Mount Umunhum area is open from 7 a.m., and its gate closes at sunset so visitors have time to leave.