National Park Service statistical abstract.

MLA

United States., Public Use Statistics Program Center (U.S.) and Natural Resource Program Center (U.S.). National Park Service statistical abstract. Denver, Colo. : Statistical Office, U.S. Dept. of Interior, National Park Service, 1989-

APA

United States., Public Use Statistics Program Center (U.S.) & Natural Resource Program Center (U.S.). (1989). National Park Service statistical abstract. Denver, Colo. : Statistical Office, U.S. Dept. of Interior, National Park Service.

Chicago

United States., Public Use Statistics Program Center (U.S.) and Natural Resource Program Center (U.S.). National Park Service statistical abstract. Denver, Colo. : Statistical Office, U.S. Dept. of Interior, National Park Service, 1989-