Não informado. (2011). U.S. Geological Survey Bulletin. U.S. Department of the Interior, Geological Survey.
Chicago-referens (17:e uppl.)Não informado. U.S. Geological Survey Bulletin. Washington: U.S. Department of the Interior, Geological Survey, 2011.
MLA-referens (8:e uppl.)Não informado. U.S. Geological Survey Bulletin. U.S. Department of the Interior, Geological Survey, 2011.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.