Treasure Island is a hydraulically-filled man-made structure in central San Francisco Bay, north of Yerba Buena Island, constructed for the 1939 Golden Gate International Exposition. The island was built in 1936 and 1937 by hydraulically pumping estuarine sediment behind a perimeter rip-rap dike. The silty, sandy fill averages about 7 m thick and overlies Holocene San Francisco Bay Mud and older Pleistocene estuarine and terrestrial deposits. The water table varied from 0 m (standing water) to 1.5 m below the ground surface while we occupied the site.

A View from north during the hydraulic filling of Treasure Island, 1937.
B Treasure Island Naval station at the time of the Loma Prieta event, 1989.