The San Francisco Bay Model was, like the Mississippi Basin Model, built by the Army Corps of Engineers to study the flow of water — in this case, simulating “the rise and fall of tide, flow, and currents of water, mixing of salt and fresh water, and… trends in sediment movement”, permitting the study of the impact of both natural events (such as floods) and human actions (such as dredging and industrial accidents). It is also, again like the Mississippi Basin Model, out of service, not having been used for active modeling since 2000, though — unlike the Mississippi Basin Model — it has found a second life as a public education center, open to guided and unguided public tours.
The San Francisco Bay Model is the only model of its size which remains intact and functional. (There were originally three comparable models built by the Army Corps, with the San Francisco and Mississippi Models joined by the Chesapeake Bay Model on Kents Island, MD. The Chesapeake Bay Model ran its last test in 1982 — successfully predicting the watery resting place of the body of the final victim of the Air Florida Flight 90 crash — and today occupies a mostly empty lot in Matapeake State Park.) Interestingly, the reason that the San Francisco Bay Model outlasted its contemporaries in active service was not only that it was indoors — the Chesapeake Bay Model was also indoors — but that “an ingenious system of 286 concrete slabs individually supported on adjustable jacks” permitted the model to be continuously reconfigured in geologic miniature to accurately represent the shifting fluid topography of the Bay area.
[The aerial image is via Google Maps; the interior shot is by flickr user chuck b.]