Sierra Azul Open Space Preserve

Sierra Azul Open Space Preserve is the largest of Midpen's lands, more than 19,000 acres of rugged Santa Cruz Mountains wilderness above Lexington Reservoir, Los Gatos, and south San Jose, crowned by 3,486-foot Mount Umunhum. The mountain's name comes from the Mutsun language and is usually translated as "resting place of the hummingbird"; the mountain figures in the Amah Mutsun creation story. From 1957 to 1980 the summit was the Almaden Air Force Station, and the square concrete tower still standing was the base of a Cold War radar. After Midpen acquired it, crews removed more than 3,000 cubic yards of hazardous material and recycled most of the demolished buildings, and the summit reopened in 2017.

Two of the preserve's four areas are open. In the Mount Umunhum area, the 3.9-mile Mount Umunhum Trail climbs from the Bald Mountain lot to the summit, the highest point on the Bay Area Ridge Trail, and a 0.3-mile accessible path at the top leads to a ceremonial circle, viewpoints, and exhibits with views from the Pacific to the Sierra Nevada. The Kennedy-Limekiln area has steep multiuse trails toward Mount El Sombroso. Across 26 miles of trails you may see serpentine wildflowers (about 350 species have been counted), golden eagles, and signs of mountain lions.

Leashed dogs are allowed on more than 12 miles of trail, including Limekiln, Priest Rock, and Kennedy, but not anywhere on Mount Umunhum, even in cars. The summit lot has 57 spaces at the end of Mount Umunhum Road.