Mount Burdell Open Space Preserve is a nature reserve in Marin County, California, United States, within the San Francisco Bay Area. It is managed by Marin County Parks. Mount Burdell rises 1,558 feet (475 m) above sea level. Hidden Lake, a seasonal pond located about halfway to the top, is home to frogs, salamanders and other creatures during the wet season. The Marin County Open Space District, with the help of local residents, purchased the 1,627-acre (658 ha) preserve in 1977.