Gilliom, R. G., W. M. Alley, and M. E. Gurtz. 1995. Design of the National Water-Quality Assessment Program—Occurrence and distribution of water-quality conditions. U.S. Geological Survey Circular 1112, Reston, Virginia, 33 pp.
Hammond, E. H. 1964. Classes of land-surface form in the 48 states, USA. Annals of the Association of American Geographers 54, no. 1964, map supplement no. 4, 1:5,000,000 scale.
Hamon, W. R. 1961Estimating potential evapotranspiration. Journal of the Hydraulics DivisionProceedings of the American Society of Civil Engineers87107120Google Scholar
Hargrove, W. W., Hoffman, F. M., Law, B. E. 2003. New analysis reveals representativeness of the Ameriflux network. Eos 84:529, 535.Google Scholar
Hargrove, W. W., Hoffman, F. M. 1999Using multivariate clustering to characterize ecoregion bordersComputing in Science and Engineering11825Google Scholar
Helsel, D. R., and R. M. Hirsch. 2002. Statistical methods in water resources. U.S. Geological Survey Techniques of Water-Resources Investigations Book 4, Chapter A3 (http://water.usgs.gov/pubs/twri/twri4a3/)
Kuchler, A. W. 1964Manual to accompany the map, potential natural vegetation of the conterminous United StatesAmerican Geographical Society, Special Publication No. 36New York143Google Scholar
Meador, M. R., T. F. Cuffney, and M. E. Gurtz. 1993. Methods for sampling fish communities as part of the National Water-Quality Assessment Program. U.S. Geological Survey Open-File Report 93–104, 40 pp.
Murtagh, F. 1985Multidimensional clustering algorithmsPhysica-VerlagViennaGoogle Scholar
Omernik, J. M. 1987Ecoregions of the conterminous United StatesAnnals of the Association of American Geographers77118125CrossRefGoogle Scholar
Omernik, J. M., Griffith, G. E. 1991Ecological regions versus hydrologic units: frameworks for managing water qualityJournal of Soil and Water Conservation46334340Google Scholar
Owensby, J. R., and D. S. Ezell. 1992. Climatography of the United States No. 81—monthly station normals of temperature, precipitation, and heating and cooling degree days, 1961–90. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Climatic Data Center. Ashville, North Carolina.
Preston, S. D. 2000. Statistical identification of hydrochemical response units for hydrologic monitoring and modeling in Maryland. U.S. Geological Survey Water-Resources Investigations Report 00–4232. Reston, Virginia, 8 pp.
U.S. Department of Agriculture. 1994. State Soil Geographic (STATSGO) data base: data use information. Miscellaneous Publication Number 1492, 35 pp.
U.S. Environmental Protection Agency. 2002. Level III ecoregions of the continental United States (revision of Omernik 1987). U.S. Environmental Protection Agency, National Health and Environmental Effects Laboratory, Western Ecology Division, Corvallis, Oregon. Map M-1, various scales.
U.S. Geological Survey. 1990. Land use and land cover digital data from 1:250,000- and 1:100,000-scale maps: Data users guide 4 (US GeoData—National Mapping Program Technical Instructions). U.S. Department of Interior, U.S. Geological Survey. Reston, Virginia, 33 pp.
U.S. Geological Survey. 1998. Strategic directions for the U.S. Geological Survey Ground-Water Resources Program: A Report to Congress, 30 November 1998. (http://water.usgs.gov/ogw/gwrp/stratdir/stratdir.html).
U.S. Geological Survey. 2001. National atlas of the United States maps. U.S. Geological Survey Fact Sheet 086-01 (http://mac.usgs.gov/mac/isb/pubs/factsheets/fs08601.html).
Verdin, K. L., and S. K. Greenlee. 1996. Development of continental scale digital elevation models and extraction of hydrographic features. In Proceedings, Third International Conference/Workshop on Integrating GIS and Environmental Modeling, Santa Fe, New Mexico, 21–26 January 1996. Santa Barbara, California. National Center for Geographic Information and Analysis.
Winter, T. C. 2001The concept of hydrologic landscapesJournal of the American Water Resources Association37335349Google Scholar