Surficial Geology of Iowa GIS Data
Author: Bradley Miller
This raster dataset presents a highly detailed map of surface geologic (parent) materials across Iowa. It was compiled from detailed soil maps at scales ranging from 1:24,000 to 1:12,000 and merged by USDA-NRCS into the gSSURGO spatial database at 10-meter resolution. The Geospatial Laboratory for Soil Informatics (GLSI) at Iowa State University interpreted this data to classify parent materials to a depth of 2 meters.
Interpretation Method
Parent material classifications were derived from NRCS Official Soil Series Descriptions (OSD), with supplemental interpretation based on soil morphology, spatial relationships, and geomorphic context. Mapped categories include glacial till, loess, alluvium, outwash, residuum, and bedrock.
Applications and Visualization Tips
This dataset is ideal for understanding soil formation processes, landform history, and subsurface material distribution. Visualization is enhanced by overlaying the data on fine-resolution hillshades or digital elevation models (DEMs), which emphasize the strong connection between topography and geologic origin.
Resolution and Coverage
10-meter raster resolution covering the entire state of Iowa.
GIS Map Folder Download
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GIS Map Details
This raster is a highly detailed map of geologic materials at the surface (delineations made from maps at 1:24,000 to 1:12,000 scale). The smaller extent maps were merged together by USDA-NRCS to produce the gSSURGO spatial database, covering the entire state at a 10m resolution. The gSSURGO map was then interpreted by Iowa State University’s Geospatial Laboratory for Soil Informatics (GLSI) for parent material, which is equivalent to the geologic material to a depth of 2 meters from the surface. Surficial material 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 would be complementary to this data set. Draping this surfical geology data set over hillshades derived from fine resolution elevation data works especially well.
References
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