Treasure Island is a San Francisco island built for an exposition

Treasure Island was constructed on landfill for the 1939–1940 Golden Gate International Exposition and is legally part of the City and County of San Francisco despite being an artificial island in the middle of San Francisco Bay. The island is connected to Yerba Buena Island and the Bay Bridge and has been subject to redevelopment overseen by San Francisco city agencies, an example of municipal boundaries extending into the Bay. Treasure Island's ZIP code is 94130.