Sierra Azul Open Space Preserve (closed areas)

Sierra Azul Open Space Preserve is managed by the Midpeninsula Regional Open Space District in Santa Clara County, California. It is approximately 19,300 acres in area. The preserve is named for the Sierra Azul or "Blue Mountains", the name the colonizing Spanish used for the half of the Santa Cruz Mountains south of today's California Highway 17.

The park features the peaks of Mount Umunhum 3,486 feet, Mount Thayer 3,478 feet, and El Sombroso peak 2,999 feet. El Sombroso is about 2 miles north by northeast of Mount Umunhum. Trails connect from Lexington Reservoir, on the western edge of the park, to Hicks Road on the eastern edge.