San Francisco’s harbor is accessible to immense ships through deep channels, but the Golden Gate is dangerous to navigate because of its narrow entrance, swift currents, high winds, rocks, and fog. Early mariners used on-shore bonfires, painted rocks, and natural landmarks to find their way, while modern navigators rely on buoys, beacons, foghorns, charts, sonar, and satellite-based global positioning systems. Individual navigation aids are identifiable by distinctive signals, including lighthouse flash patterns and foghorn sounds, allowing sailors and ship pilots to determine their location in poor visibility, yet many ships have still been lost there and entered shipwreck lore. Traffic in, out, and around the bay is coordinated by the U.S. Coast Guard’s Vessel Traffic Service, and the Coast Guard also maintains the bay’s buoys, lights, and foghorns. Alcatraz holds the oldest beacon on the West Coast still in operation, first lit in 1854 during the Gold Rush, moved into a taller lighthouse in 1909, and automated in 1963. Nautical charts show water depths, hazards, and the identifying frequencies of foghorns, while Painted Rock at Lands End once helped ships stay within the shipping lane when aligned with Mile Rock lighthouse. Mile Rock lighthouse was constructed in 1906 and converted to a helicopter landing pad with an automated light in 1966.
