Sierra Azul Open Space Preserve is managed by the Midpeninsula Regional Open Space District in Santa Clara County, California. It's approximately 17,000 acres (69 km2) in area. The park features the Sierra Azul range's peaks of Mount Umunhum, Mount Thayer, and El Sombroso. Trails connect from Lexington Reservoir on the western edge of the park, to Hicks Road on the eastern edge.
Parts of Sierra Azul are not yet open to the public, but many sections are, and these include miles of trails, old roads (some paved, some not), a manmade lake, Cherry Springs Lake, and other amenities. The terrain varies from wooded creek canyons to chaparral hills with views to open meadows.