The Bonny Doon Ecological Reserve is a nature preserve of 552 acres (2.23 km2) in the Santa Cruz Mountains of California, United States. The reserve protects several rare and endangered plant and animal species within an area known as the Santa Cruz Sandhills, an ancient seabed containing fossilized marine animals. The land was purchased in 1989 by The Nature Conservancy which deeded the property to the state, and is now managed by the California Department of Fish and Wildlife. It is adjacent to the Laguna parcel of the San Vicente Redwoods protected area.