1. Bailey, Robert G. 1995. Description of the ecoregions of the United States. 2nd edition revised and expanded (1st edition 1980). Misc. Publ. No. 1391. Washington, DC: USDA Forest Service. 108 pages with separate map at 1:7,500,000.
2. Identifying Ecoregion Boundaries
3. McNab, W. Henry; Avers, Peter E. 1994. Ecological Subregions of the United States: Section Descriptions. WO-WSA-5. Washington, DC: USDA Forest Service. Variable pagination.
4. Delineation of ecosystem regions