Não informado. (2001). Annual report of the United States Geological Survey. U.S. Geological Survey.
Chicago-referens (17:e uppl.)Não informado. Annual Report of the United States Geological Survey. Washington: U.S. Geological Survey, 2001.
MLA-referens (8:e uppl.)Não informado. Annual Report of the United States Geological Survey. U.S. Geological Survey, 2001.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.