FLORIDA KEYS

island chain, in Monroe and Dade counties, southern Florida, U.S. Composed of coral and limestone, the islands curve southwesterly for about 192 miles (309 km) into the Gulf of Mexico from Virginia Key, just south of Miami Beach, to Loggerhead Key in the Dry Tortugas (q.v.). Waters between the keys and the mainland include Biscayne and Florida bays. The western terminus of the Florida Keys is sometimes considered to be Key West (q.v.), the most important of the islands. The Overseas Highway, running from the mainland to Key West, is the longest overwater road in the world, with 42 bridges, including one 7-mile (11-kilometre) span; completed in 1938, the highway was built over the route of the Florida East Coast Railroad, begun in 1912 by Henry M. Flagler and destroyed by the 1935 hurricane. Largest of the keys is Key Largo, about 30 miles (50 km) long and known for its lime plantations. The John Pennekamp Coral Reef State Park, which contains the largest living coral formations in North America, is the first underseas park in the United States. It is 21 miles (34 km) long and 6.5 miles (about 10 km) wide and lies along Key Largo's east coast. Islamorada, on Upper Matecumbe Key, has a monument to World War I veterans and victims of the 1935 hurricane. The largest town of the middle keys is Marathon, a centre of extensive resort development. Nearby is the Southeast Museum of the North American Indian and a porpoise-training school. Bahia Honda State Park, on Bahia Honda Key, has 77 acres (31 hectares) of tropical palms and beach recreation facilities. The northern shores of the lower keys have been designated the Great White Heron National Wildlife Refuge. The 7,700-acre (3,116-hectare) Big Pine Key, largest of the lower keys, is a refuge for the tiny key deer and has unusual displays of cacti. More than 600 varieties of fish are found in the waters of the keys.