Deep channels make San Francisco’s protected harbor accessible to immense ships, but swift currents, high winds, rocks, and fog make the narrow Golden Gate treacherous to navigate. Early mariners relied on on-shore bonfires, painted rocks, and natural landmarks, while later navigators used buoys, beacons, foghorns, charts, sonar, and satellite global positioning systems. Distinctive lighthouse flash patterns and foghorn sounds helped sailors and ship pilots determine their location in poor visibility, yet numerous ships were still lost at the Golden Gate. Traffic in, out, and around the bay is coordinated by the U.S. Coast Guard’s Vessel Traffic Service, and the Coast Guard maintains the bay’s buoys, lights, and fog horns. A whitewashed patch of cliff called the Painted Rock at Lands End once served as a navigation aid when aligned with Mile Rock lighthouse. Alcatraz has the oldest still-operating beacon on the West Coast; its light has shone since 1854, was moved to a taller lighthouse in 1909, and was automated in 1963. Nautical charts show water depths, potential hazards, and the identifying frequencies of foghorns, and in the late 1820s Point Bonita’s fog cannon became the first fog signal on the Pacific Coast.
