This raster is a highly detailed (delineations made at the 1:15,840 scale) map of geologic materials at the surface, covering the entire state of Iowa. The map is based on the interpretations of the US Soil Survey, which regularly needs to assess the soil parent material in their mapping activities. The raster was generated from the USDA-NRCS gSSURGO spatial database (10 m resolution). The attributes were extracted from the NRCS official soil series descriptions (OSD), but at times some additional interpretation was needed based on typical soil profile properties and spatial relationships with better-defined soil series. Because of the common relationship between surficial geology and topography, digital elevation models or derived hillshades from the USGS would be complementary to this data set.
Miller, B.A. and C.L. Burras. 2015. Comparison of surficial geology maps based on soil survey and in depth geological survey. Soil Horizons 56(1). doi:10.2136/sh14-05-0005.
Soil Survey Staff. 2014. Official Soil Series Descriptions (OSD). United States Department of Agriculture, Natural Resources Conservation Service. https://soilseries.sc.egov.usda.gov/osdname.asp
Soil Survey Staff. 2014. Gridded Soil Survey Geographic (gSSURGO). United States Department of Agriculture, Natural Resources Conservation Service. http://datagateway.nrcs.usda.gov