DOI: 10.5066/p1vrszle
title: Digital surfaces and extents of selected hydrogeologic units within the Mississippi Embayment Aquifer System

description: Note that this data release has been modified from its original version. This data release was originally published on the U.S. Geological Survey (USGS) Water Mission Area NSDI Node (Node) in 2008.  The Node has since been deprecated, and the data release was revised and, in 2023, the files were moved over to Sciencebase, which is a USGS trusted digital repository. When this migration of files initially took place, each unit extent and surface file for the Mississippi Embayment aquifer system was given its own landing page.  The 2025 version of this data release revised the 2023 revision. This 2025 version regrouped the extents, surfaces, and metadata files, presenting them on one Sciencebase landing page. A new master metadata file was compiled to document all the datasets and each surface altitude raster is presented in three formats: ASCII, GRID, and TIFF (a new format). The 2025 version of the data release was created to make the spatial data more accessible to the user and to simplify the ScienceBase catalog.
 
This data release provides outcrop and subcrop extents and digital surfaces containing the top altitude of the following hydrogeologic units in Arkansas, Alabama, Louisiana, Missouri, Mississippi, and Tennessee. The abbreviations used for each hydrogeologic unit is listed below.  These abbreviations are used in names of the data release files. 
 
1. alvm - Mississippi River Valley Alluvial Aquifer (extent only)
2. vkbg - Vicksburg-Jackson Group                                 
3. ucaq - Upper Claiborne aquifer                                 
4. mccu - Middle Claiborne confining unit                         
5. mcaq - Middle Claiborne aquifer                                
6. lccu - Lower Claiborne confining unit                          
7. lcaq - Lower Claiborne aquifer                                 
8. mwaq - Middle Wilcox aquifer                                   
9. lwaq - Lower Wilcox aquifer                                    
10. mdwy - Midway confining unit                                   
  
The hydrogeologic unit surface datasets contain 414 rows and 394 columns representing 1-mile grid spacing. In general, limitations of data interpolation included areas of sparse geophysical log control points, log datums not clearly defined for some logs, unknown exact extent of each hydrogeologic unit in subcrop, interpolation limitations, and values averaged over 1-mile grid spacing.
 
This data release contains data sets that characterize the  Mississippi Embayment aquifer system. These data sets were assembled as part of the Mississippi Embayment Regional Aquifer Study (MERAS) as described in the associated report (Hart, R.M., Clark, B.R., and Bolyard, S.E., 2008, Digital surfaces and thicknesses of selected hydrogeologic units within the Mississippi Embayment Regional Aquifer Study (MERAS): U.S. Geological Survey Scientific Investigations Report 2008-5098, 33 p.) and utilized in the MERAS groundwater-flow model (Clark, B.R., Hart, R.M., and Gurdak, J.J., 2011, Groundwater availability of the Mississippi embayment: U.S. Geological Survey Professional Paper 1785, 62 p.).