reef: see coral reef.

Kingman Reef, uninhabited reef, less than 1 sq mi (2.6 sq km), central Pacific, one of the Line Islands, 1,075 mi (1,730 km) SW of Honolulu. It was discovered by Americans in 1798 and annexed by the United States in 1922. Formerly an airport on the route from Honolulu to Pago Pago, Kingman Reef is now under the jurisdiction of the U.S. navy.

Great Barrier Reef, largest complex of coral reef in the world, c.1,250 mi (2,000 km) long, in the Coral Sea, forming a natural breakwater for the coast of Queensland, NE Australia. Composed of more than 2,800 individual reefs, the Great Barrier Reef is separated from the mainland by a shallow lagoon from 10 to 100 mi (16-161 km) wide. In some places it is more than 400 ft (122 m) thick. A major tourist attraction, the reef has many islets, coral gardens, and unusual marine life. The Great Barrier Reef Marine Park, more than 130,000 sq mi (340,000 sq km), encompasses most of the reefs and interreefal areas as well as the neighboring lagoon and a large section of the continental shelf. It is the largest UNESCO World Heritage Area.

Capitol Reef National Park: 241,904 acres (97,971 hectares), S Utah. The park features a dome-shaped white rock, said to resemble the U.S. Capitol, and a maze of deep canyons, arches, and monoliths cut through a 100-mi (160-km) uplift, known as the Waterpocket Fold, that geologists consider unique because of its size. Proclaimed a national monument in 1937, it was designated a national park in 1971. See National Parks and Monuments (table).

Buck Island Reef National Monument: see National Parks and Monuments (table).

Ridge or hummock formed in shallow ocean areas from the external skeletons of corals. The skeleton consists of calcium carbonate (CaCO₃), or limestone. A coral reef may grow into a permanent coral island, or it may take one of four principal forms. Fringing reefs consist of a flat reef area around a nonreef island. Barrier reefs may lie a mile or more offshore, separated from the landmass by a lagoon or channel. Atolls are circular reefs without a central landmass. Patch reefs have irregular tablelike or pinnacle features. Smaller patches occur inside atoll lagoons; larger patches occur as isolated parts of any of the other three reef categories, and they sometimes occur completely separate from other kinds of reefs.

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Extensive complex of coral reefs, shoals, and islets in the Pacific Ocean, off the northeastern coast of Australia. The largest deposit of coral in the world, it extends for more than 1,250 mi (2,000 km) along the coast of Queensland and has an area of some 135,000 sq mi (350,000 sq km). The reef has been formed over millions of years from the skeletons of a mass of living marine organisms. In addition to at least 300 species of hard coral, marine life includes anemones, worms, gastropods, lobsters, crayfish, prawns, crabs, and a variety of fishes. Encrusting red algae form the purplish red algal rim that is one of the reef's characteristic features. A major tourist attraction, nearly all of it is within Great Barrier Reef National Park; the reef was designated a UNESCO World Heritage site in 1981.

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Park, south-central Utah, U.S. Occupying 378 sq mi (979 sq km), it comprises great buttressed cliffs of coloured Navajo sandstone extending for 100 mi (160 km) along the western edge of the Waterpocket Fold. Established as a national monument in 1937, it became a national park in 1971. It is so named because its rock towers reminded geologists of coral reefs, while its dome-shaped formations suggest capitol architecture. The cliff walls are covered with pre-Columbian petroglyphs.

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