Iowa Bedrock Surface Elevation

This Digital Elevation Model (DEM) of the bedrock surface elevation in Iowa was compiled using all available data, principally information from GEOSAM, supplemented with well and boring information from the Iowa DOT, exposure reports from Iowa Geological & Water Survey reports and files, and the Department of Soil Conservation county soil maps for Iowa. The soil maps were especially valuable, since they identified soils that encountered bedrock within the soil horizon, and less dependably also spot-located rock exposures. A 50 foot contour interval was chosen for the map because it was considered to best represent the accuracy of the well data, allowed for fairly good representation of the bedrock surface in areas with limited well control, and was mappable in high relief areas (the contours packed so close together that it precluded mapping or forced the software to snap-join contours). The 50 foot contour interval also allowed areas where bedrock was present within the soil horizon (2-3 feet) to be treated as areas of exposures. In these areas the bedrock elevation was mapped as only slightly below the surface elevation, so contours on the 7«' topographic maps were closely followed in mapping the bedrock elevation. Consequently, on the completed map of bedrock elevation, these areas display much more contorted and crenulated contour lines than the areas where only drill control was utilized.