Each year millions of tons of sediment wash out from the Central Valley through the Carquinez Strait and are deposited in the mudflats of the San Pablo and San Francisco bays. Because the docks on the opposite side of the island are a natural settling area for silt and mud, the berths and ship channel had to be constantly dredged to maintain an adequate depth for submarines and ships. The dredged materials were used to expand the island from 800 acres to its current 5,252 acres over a period of about 150 years. Where you are standing was once open water.