The National Natural Landmarks (NNLs) in Florida include 18 of the almost 600 such landmarks in the United States. They cover areas of geological, biological and historical importance, and include springs, swamps, marshes and seashore. Several of the sites provide habitat for rare or endangered plant and animal species. The landmarks are located in 14 of the state's 67 counties. Four counties each contain all or part of two or more NNLs, while two landmarks is split between two counties. The first designation, Corkscrew Swamp Sanctuary, was made in 1964, while the most recent designation, Archbold Biological Station, was made in 1987. Natural Landmarks in Florida range from 593 to 14,000 acres (240.0 to 5,665.6 ha; 0.9 to 21.9 sq mi) in size.