Shadow Cliffs Regional Recreation Area is a regional park on the border of Pleasanton, California, and Livermore, California that is part of the East Bay Regional Parks system on Stanley Blvd. The lake was once a gravel pit, but now includes a sandy beach with swimming, waterslides and it supports fishing and recreational boating. The park is also a popular picnic ground.
Shadow Cliffs Regional Recreation Area official web page
Coordinates: 37°40′10″N 121°50′22″W / 37.66944°N 121.83944°W