People forget the Bay Bridge came first. It beat the Golden Gate by six months. To build it, divers plunged 242 feet into the dark, freezing mud of the bay to sink massive caissons, shattering depth records. Twenty-eight men died. Chief engineer Charles Purcell faced a nightmare of deep water, treacherous currents, and unstable mud. But he pulled it off. The double-decker giant opened in November 1936, boasting the world's largest bore tunnel through Yerba Buena Island.

Before the bridge, commuters relied entirely on slow, crowded ferries. The crossing killed that industry. Actually, it welded San Francisco and Oakland into a single economic powerhouse. Then came the trains. The Interurban electric lines carried millions of commuters on the lower deck until highway greed cleared them out in 1958. It was pure Depression-era muscle. Funded by federal Reconstruction Finance Corporation loans, the construction project put thousands of desperate, jobless men back to work. The western suspension span still stands as a monumental workhorse.