Fort Mason is built on landfill at the easternmost tip of Marina District. The site was a defense base for the Spanish and the Americans during the American Indian wars in the 19C. In the wake of Pearl Harbor in 1941, Fort Mason served as the strategic embarkation point and headquarters of the Pacific fleet, through which 1.5 million soldiers transited. The base was abandoned by the army in 1962 and is now the site of a youth hostel.