Los Osos Valley. Boysen Ranch Wetland Mitigation area between Los Osos Valley Road and O'Connor Way west of Foothill Road. West of city limits of San Luis Obispo. Shallow ponds excavated in summer 2005 in grassy ranchland area to enhance wetland characteristics of area. These fields have historically flooded during times of high precipitation. The ponds impound water for longer periods of time with open water lasting into spring or early summer.