References: (1) Ricketts, Taylor H., Eric Dinerstein, David M. Olson, Colby J. Loucks, et al. 1999. Terrestrial ecoregions of North America: A conservation assessment. Washington, DC: Island Press. (2) Omernik, James M. 1987. Ecoregions of the conterminous United States. Annals of the Association of American Geographers, 77(1):118-125.