Description: Ecoregions, Levels III and IV, 1996 (1:250,000) -
Shows areas within which ecosystems (and the type, quality, and quantity of environmental resources) are generally similar. Level I divides North America into nine ecological regions. Level II divides the continent into 32 classes. Level III is the hierarchical level shown on this map. For portions of the United States the ecoregions have been further subdivided to level IV. Derived and modified from a preexisting shapefile by A. Woods and others, U. S. Geological Survey. Additional information is available from U.S. Environmental Protection Agency, National Health and Environmental Effects Laboratory (NHEERL).