 During the gold rush, a large number of goats were pastured on the island, and the name "Goat Island" came into popular use.It was changed back to Yerba Buena Island on June 3, 1931.The idea of a military post on Yerba Buena Island originated during the American Civil War, when it was feared a raiding Confederate warship could slip past Fort Point and Alcatraz Island during a foggy night.