Originally known as Government Island, this artificial island was formed in 1913 by the dredging project that extended the Oakland Estuary to San Leandro Bay. The Coast Guard first came to the island in 1926 when it established Base 11. An Executive Order signed in September 1931 gave title to a 15 acre tract for a permanent base. Improvements were started at that time and by 1933 included streets, utilities, spur tracks, a trestle bridge from Oakland, a transformer station, and rebuilding of the existing wharves. The cost was more than one and a half million dollars and provided facilities for Base 11 and the Coast Guard Store (warehouses).
http://www.uscg.mil/pacarea/morgenthau/