Sigafoos, Robert S. Vegetation of Northwestern North America, as an aid in interpretation of Geologic Data / by Robert S. Sigafoos. -- Washington : United States Government Printing Office, 1958 - P. 165-183 + map. -- (Geological Survey Bulletin ; 1061-E). Subjects--Topical Terms: Estados UnidosFitogeografía Universal Decimal Class. No.: 581.9(73)