At Sweeney Ridge, on November 4, 1769, hunters from Portola's expedition sighted what would become one of the world's greatest seaports. Today, monuments mark the "Portola Discovery Site." Hikes along the ridge also pass the ruins of a former U.S. Army Nike missile control station. Nike Missile Site SF-51, which helped protect the peninsula from 1956 to 1974, held three radar dishes to find, track and guide missiles (based at Milagra Ridge) to enemy aircraft.