USDA Ecosystem Unit Name

http://www.fws.gov/stand/standards/econame_rev3.txt

Official names used by the Service to identify the ecosystem unit boundaries of the United States, which are drawn primarily along watershed boundaries. The Service originally chose the U.S. Geological Survey's Hydrologic Unit Map as the foundation for delineating ecosystem unit boundaries on a national scale. Since that time, boundaries in some of the regions have been moved to the closest county boundaries to simplify management responsibilities. The current unit boundaries reflect this combination.