1. Life Areas of North America;Aldrich;U.S. Fish and Wildlife Service BSFW Poster 102,1966
2. The geographical distribution of North American mammals;Allen;Bull. Am. Museum Nat. Hist.,1892
3. Forest Regions of Montana;Arno;U.S. Forest Service Research Paper INT-218,1979
4. Ecoregions of the United States;Bailey,1976
5. Description of the Ecoregions of the United States;Bailey;U.S. Department of Agriculture Miscellaneous Publication 1391,1980