Rock of Ages Light stands on a tiny rock outcropping in Lake Superior west of Washington Island and Isle Royale, where reefs and frequent fog made navigation especially dangerous. Built beginning in 1908 as part of a Great Lakes push to replace vulnerable lightships with permanent offshore towers, it used a concrete-filled steel caisson base and an unusual tall tower design for the region. A powerful second-order Fresnel lens was installed in 1910. The reef had already wrecked major ships before the lighthouse was built, and the danger persisted afterward, notably in the 1933 rescue of George M. Cox survivors. Automated in 1978, it remains an active aid to navigation.