The area covers approximately 54 square miles ( 140 km ) , much of it open space .
The area contains Lake Elsman , Lexington , and Williams reservoirs , as well as the Lexington Reservoir County Park and Bear Creek Redwoods and Sierra Azul open space preserves .
The area covers approximately 54 square miles ( 140 km ) , much of it open space , and contains Lake Elsman , Lexington , and Williams reservoirs , as well as the Lexington Reservoir County Park and Bear Creek Redwoods and Sierra Azul open space preserves .