Atlas of American Agriculture. Physical Basis including Land Relief, Climate, Soils, and Natural Vegetation of the United States. Prepared under the Supervision of O.E. Baker, Bureau of Agricultural Economics. Contributions from the Weather Bureau, Willis R. Gregg, Chief; Bureau of Chemistry and Soils, H.G. Knight, Chief; Bureau of Plant Industry, Frederick D. Richey, Chief; Forest Service, F.A. Silcox, Chief; Bureau of Agricultural Economics, A.G. Black, Chief. United States Department of Agriculture, Washington, D.C., United States Government Printing Office, Washington: 1936