National Geographic : 1951 Jun
© National Geographic Society 736 Air Force Color Photo Golden Gate Bridge, 220 Feet above the Tide, Spans the Entrance to San Francisco Harbor. Twin Towers Soar 746 Feet Geologists say the Golden Gate was once a river gorge. Erosion, scouring the channel, permitted the Pacific to back in,forming San Francisco Bay (right). Spanish explorers sailed past the narrows without suspecting the enormous harbor. Engineers, with earthquakes in mind, built the bridge soitcould sway 21feet ineither direction. Its stretch between towers is 4,200 feet; approaches boost the length to 9,266 feet. Here Redwood Highway(toOregon) enters Marin County.