On back: "SAN FRANCISCO-OAKLAND BAY BRIDGE; Walter G. Swanson; 500 Sansome St. - GA rfield 1415. File 900.11 B-12/AA. THE WORLD'S LARGEST CAISSON WHICH WILL FORM THE BASE OF THE GREAT CONCRETE CENTER ANCHORAGE OF THE SAN FRANCISCO-OAKLAND BAY BRIDGE. 11-8-33".