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File - In this May 24, 1987 file photo, a crowd estimated at several hundred thousand jams the deck of the Golden Gate Bridge in San Francisco during a walk to celebrate the 50th anniversary of the bridge. The bridge was heralded as an engineering marvel when it opened in 1937. It was the world's longest suspension span and had been built across a strait that critics said was too treacherous to be bridged. But as the iconic span approaches its 75th anniversary, the engineers who have overseen it all these years say keeping it up and open has been a feat unto itself. (AP Photo/Doug Atkins, File)