The southern side of the entrance to the Golden Gate is dotted with a family of dangerous wave-swept rocks that includes Black Head Rock, Lobos Rock, and Pyramid Rock. The two northernmost, and thus most dangerous to navigation, are Mile Rock and Little Mile Rock, known together as Mile Rocks. Located only 0.4 miles from the closest shore, it seems Mile Rocks are so named because the rocks are one mile south of the main shipping channel leading into San Francisco Bay.
In November of 1889, the Lighthouse Service placed a bell buoy near the rocks. However, the strong currents in the area would pull the buoy beneath the surface of the water and even set it adrift. Frustrated lighthouse engineers concluded that the rocks “must always be a menace to navigation as long as they exist,” as building atop the rocks or dynamiting them below the surface didn't seem practical. Then on February 22, 1901 the City of Rio de Janeiro, inbound from Hong Kong in heavy fog, struck Fort Point Ledge and sunk in just eight minutes. Of the 210 aboard, 128 were lost. The Lighthouse Board concluded that the shipwreck, the worst in San Francisco’s history, might not have occurred if a fog signal could be heard considerably seaward of the ledge.
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