The Wells Creek Dolomite is the lowest unit of the Stones River Group. The Wells Creek consists of cherty limestone that underlies the Murfreesboro Limestone of the Stones River Group of Middle Ordovician age, and directly overlies the Knox Group of early Ordovician and late Cambrian age. The unit ranges in thickness from less than 1.52 meters (5 feet) in the eastern part of the Central Basin to approximately 54.86 meters (180 feet) in Stewart County. The depth of the Wells Creek generally ranges from 121.92 meters to 457.2 meters (from 400 to 1500 feet) below land surface (Smith, 1959). The Wells Creek Dolomite does not yield water but it can be easily recognized when drilling wells and it overlies the Knox Group, a deep aquifer in middle Tennessee and a significant source of groundwater for some areas. For this data release, the raster interpolated for the top of the Knox Group in Middle Tennessee (ra_knx_tp.tif) was also used to represent the altitude of the bottom of the Wells Creek Dolomite (See process steps for more details). An isopach map of the thickness of the Wells Creek Dolomite in Middle Tennessee was prepared as a part of a cooperative groundwater study by the Tennessee Division of Geology and the U.S. Geological Survey (USGS) (Smith, 1959). The 43 x 71 cm map covers parts of Middle Tennessee, from Camden east to Crossville, and from the Kentucky border to the Alabama border. The map scale is approximately 1:600,000. Contour intervals are 5 feet (east of the 100-foot isopach) and 10 feet (west of the 100-foot isopach), which show the thickness of the Wells Creek Dolomite. The associated data are altitude values from a study of cuttings in 120 wells between the western boundary of the Cumberland Plateau and the Tennessee River (Smith, 1959). Prior to the current work, the Wells Creek Dolomite isopach map (Smith, 1959) existed in limited quantities, mainly restricted to the Nashville, TN offices of the Tennessee Department of Environment and Conservation (TDEC) and United States Geological Survey (USGS). The work for this project consisted of (1) scanning and georeferencing original paper maps to create georeferenced images (GRI), (2) digitizing well location points and contour lines, (3) populating well and contour attribute tables with data from maps and associated reports, and (4) interpolating raster surfaces for the thickness of the Wells Creek Dolomite using the data from the isopach map (Smith, 1959), altitude of the bottom of the Wells Creek Dolomite by using the data for the top of the Knox Group (Newcome, 1954), altitude of the top of the Wells Creek Dolomite using the bottom of the Wells Creek Dolomite added to the thickness of the Wells Creek Dolomite (Smith, 1959), and depth from land surface to the top and bottom of the Wells Creek (USGS, 2012). All raster surfaces were aligned to a modified version of the National Hydrogeologic Grid (Clark and others, 2018) to support USGS Lower Mississippi Gulf Water Science Center efforts to create a statewide hydrogeologic framework. All horizontal coordinated data are projected to NAD 1983 USGS Contiguous USA Albers. Raster vertical coordinate information was referenced to the North American Vertical Datum of 1988 (NAVD 88). Dataset types can be identified by the following naming convention: "i_" = georeferenced map images (GRI) "po_" = points "c_" = contours "p_" = extent polygons "ra_" = altitude raster "rd_" = depth from land surface raster "rt_" = thickness raster The datasets included on this child item page are as follows: wllscr_metadata.xml - metadata file wllscr_alldata.zip: GRI/ i_wllscr.tif - thickness contour map for the Wells Creek Dolomite (Smith, 1959) polygon/ p_wllscr_ext.shp - study area extent for the Wells Creek Dolomite rasters/ ra_wllscr_btm.tif - altitude raster for the bottom of the Wells Creek Dolomite (same dataset as ra_knx_tp.tif [Newcome, 1954; Smith, 1959]) (NAVD 88) (meters) ra_wllscr_tp.tif - altitude raster for the top of the

Data about the top and bottom altitude, depth from land surface and/or the thickness of three geologic units in Tennessee were converted into geospatial format for this USGS data release from previously published paper maps and converted into digital formats for use by the public. The three geologic units were the Chattanooga Shale of Mississippian-Devonian age (Moore and Horton, 1999), the Wells Creek Dolomite of middle Ordovician age (Smith, 1959), and the Knox Group of lower Ordovician age (Newcome, 1954). These geologic units represent important geologic horizons across Tennessee. Geologic structure maps provide important information and, in digital format, support investigative and modeling efforts pertaining to water and mineral resources. Prior to this work, the paper source maps used for this data release existed in limited quantities, mainly restricted to the Nashville, TN offices of the Tennessee Department of Environment and Conservation (TDEC) and United States Geological Survey (USGS). The work for this project included (1) scanning and georeferencing original paper maps to create georeferenced images (GRI), (2) digitizing well location points and contour lines, (3) populating well and contour attribute tables with data from maps and associated reports, and (4) when possible, interpolating raster surfaces for the three geologic units of top and bottom altitude, depth from land surface to the top and bottom surface, and thickness. All raster surfaces were aligned to a modified version of the National Hydrogeologic Grid (Clark and others, 2018) to support USGS Lower Mississippi Gulf Water Science Center efforts to create a statewide hydrogeologic framework. All horizontal coordinated data are projected to NAD 1983 USGS Contiguous USA Albers. The raster vertical coordinate information was referenced to the North American Vertical Datum of 1988 (NAVD 88). This data release includes GRIs, vector data of the wells and mapped contours of top, bottom, or thickness, raster data, and related metadata files for each three geologic units under the associated child item tab. Dataset types can be identified by the following naming convention: i_ = georeferenced map images (GRI) po_ = points c_ = contours and closed depressions f_= faults and other structural features p_ = extent polygon ra_ = altitude raster rd_ = depth from land surface raster rt_ = thickness raster The datasets included on this main landing page are as follows: project_metadata.xml – metadata file for general project information studyarea_ext.zip: p_chttshl_ext.shp - mapped extent of the Chattanooga Shale in Tennessee p_wllscr_ext.shp - mapped extent of the Wells Creek Dolomite in Tennessee p_knx_ext.shp - mapped extent of the Knox Group in Tennessee The datasets included on the child item pages are as follows: Chattanooga Shale: geospatial geologic structural datasets in Tennessee: chttshl_metadata.xml - metadata file chttshl_alldata.zip: GRI/ i_chttshl_btm.tif - structure contour map of the bottom of the Chattanooga Shale (Moore and Horton, 1999) i_chttshl_data.tif - map of data used to create structure and isopach maps (Moore and Horton, 1999) i_chttshl_thk.tif - thickness contour map for the Chattanooga Shale (Moore and Horton, 1999) polygons/ p_knx_ext.shp - study area extent for the Chattanooga Shale p_hohenwald.shp - polygon for extend of the Hohenwald Platform (Moore and Horton, 1999) - supplemental data rasters/ ra_chttshl_btm.tif - altitude raster for the bottom of the Chattanooga Shale ra_chttshl_tp.tif - altitude raster for the top of the Chattanooga Shale rd_chttshl_btm.tif - depth from land surface raster of the bottom of the Chattanooga Shale rd_chttshl_tp.tif - depth from land surface raster of the top of the Chattanooga Shale rt_chttshl.tif - thickness raster for the Chattanooga Shale vectors/ c_chttshl_btm.shp - structure contours for the bottom of the Chattanooga Shale c_chttshl_btm_modified.shp - modified structure contours for the bottom

Data about the top and bottom altitude, depth from land surface and/or the thickness of three geologic units in Tennessee were converted into geospatial format for this USGS data release from previously published paper maps and converted into digital formats for use by the public. The three geologic units were the Chattanooga Shale of Mississippian-Devonian age (Moore and Horton, 1999), the Wells Creek Dolomite of middle Ordovician age (Smith, 1959), and the Knox Group of lower Ordovician age (Newcome, 1954). These geologic units represent important geologic horizons across Tennessee. Geologic structure maps provide important information and, in digital format, support investigative and modeling efforts pertaining to water and mineral resources. Prior to this work, the paper source maps used for this data release existed in limited quantities, mainly restricted to the Nashville, TN offices of the Tennessee Department of Environment and Conservation (TDEC) and United States Geological Survey (USGS). The work for this project included (1) scanning and georeferencing original paper maps to create georeferenced images (GRI), (2) digitizing well location points and contour lines, (3) populating well and contour attribute tables with data from maps and associated reports, and (4) when possible, interpolating raster surfaces for the three geologic units of top and bottom altitude, depth from land surface to the top and bottom surface, and thickness. All raster surfaces were aligned to a modified version of the National Hydrogeologic Grid (Clark and others, 2018) to support USGS Lower Mississippi Gulf Water Science Center efforts to create a statewide hydrogeologic framework. All horizontal coordinated data are projected to NAD 1983 USGS Contiguous USA Albers. The raster vertical coordinate information was referenced to the North American Vertical Datum of 1988 (NAVD 88). This data release includes GRIs, vector data of the wells and mapped contours of top, bottom, or thickness, raster data, and related metadata files for each three geologic units under the associated child item tab. Dataset types can be identified by the following naming convention: i_ = georeferenced map images (GRI) po_ = points c_ = contours and closed depressions f_= faults and other structural features p_ = extent polygon ra_ = altitude raster rd_ = depth from land surface raster rt_ = thickness raster The datasets included on this main landing page are as follows: project_metadata.xml – metadata file for general project information studyarea_ext.zip: p_chttshl_ext.shp - mapped extent of the Chattanooga Shale in Tennessee p_wllscr_ext.shp - mapped extent of the Wells Creek Dolomite in Tennessee p_knx_ext.shp - mapped extent of the Knox Group in Tennessee The datasets included on the child item pages are as follows: Chattanooga Shale: geospatial geologic structural datasets in Tennessee: chttshl_metadata.xml - metadata file chttshl_alldata.zip: GRI/ i_chttshl_btm.tif - structure contour map of the bottom of the Chattanooga Shale (Moore and Horton, 1999) i_chttshl_data.tif - map of data used to create structure and isopach maps (Moore and Horton, 1999) i_chttshl_thk.tif - thickness contour map for the Chattanooga Shale (Moore and Horton, 1999) polygons/ p_knx_ext.shp - study area extent for the Chattanooga Shale p_hohenwald.shp - polygon for extend of the Hohenwald Platform (Moore and Horton, 1999) - supplemental data rasters/ ra_chttshl_btm.tif - altitude raster for the bottom of the Chattanooga Shale ra_chttshl_tp.tif - altitude raster for the top of the Chattanooga Shale rd_chttshl_btm.tif - depth from land surface raster of the bottom of the Chattanooga Shale rd_chttshl_tp.tif - depth from land surface raster of the top of the Chattanooga Shale rt_chttshl.tif - thickness raster for the Chattanooga Shale vectors/ c_chttshl_btm.shp - structure contours for the bottom of the Chattanooga Shale c_chttshl_btm_modified.shp - modified structure contours for the bottom

The Knox Dolomite is currently recognized as the Knox Group. The Mascot Dolomite, the upper unit of the Knox Group, is dolomite and dolomitic limestone of Lower-Ordovician-age that occurs in the subsurface of most of Tennessee. This data release will focus on Middle Tennessee, where the only outcrop of the Knox Group is in the Wells Creek basin in Stewart and Houston counties (Bradley, 1986; Wilson and Stearns, 1968). The top of the Knox Dolomite is an erosional surface that is useful as a structural datum because of the importance of the Knox Group for oil and gas resources, zinc mineralization, and domestic drinking water supplies. Since the upper approximately 30 meters of the Knox Group is paleokarst, groundwater is generally under confined conditions (Bradley, 1986; Wilson and Stearns, 1968). This upper portion of the Knox is often low-yielding and variable in water quality. However, it can be a reliable aquifer in specific areas - mostly in the Central Basin. A structure contour map on the Knox Group in Middle Tennessee was prepared by Newcome (1954) as a part of a cooperative program of groundwater investigations by the U.S. Geological Survey and the Tennessee Division of Geology at Nashville, Tennessee. Prior to this work, this paper map existed in limited quantities, mainly restricted to the Nashville offices of the Tennessee Department of Environment and Conservation (TDEC) and United States Geological Survey (USGS). The map measuring 46 x 64 cm, with an approximate scale of 1:500,000 was prepared with well elevation data, determined by aneroid barometer or from topographic quadrangle maps (Newcome, 1954). Structure contours were drawn on top of Knox Group at 100 feet intervals. The work for this project consisted of (1) scanning and georeferencing original paper maps to create georeferenced images (GRI), (2) digitizing well location points and contour lines, (3) populating well and contour attribute tables with data from maps and associated reports, and (4) interpolating raster surfaces for the top altitude of the Knox Group and depth from land surface to the top of the unit. All raster surfaces were aligned to a modified version of the National Hydrogeologic Grid (Clark and others, 2018) to support USGS Lower Mississippi Gulf Water Science Center efforts to create a statewide hydrogeologic framework. All horizontal coordinated data are projected to NAD 1983 USGS Contiguous USA Albers. Vertical coordinate information was referenced to the North American Vertical Datum of 1988 (NAVD 88). Dataset types can be identified by the following naming convention: i_ = georeferenced map images (GRI) po_ = points c_ = contours and closed depressions f_= faults and other structural features p_ = extent polygon(s) ra_ = altitude raster rd_ = depth from land surface raster rt_ = thickness raster The datasets included on this child item page are as follows: knx_metadata.xml - metadata file knx_alldata.zip: GRI/ i_knx_tp.tif - structure contour map on the top of the Knox Group (Newcome, 1954) i_knx_outcrop.tif - map of the Wells Creek Disturbance (Wilson and Stearns, 1968) polygons/ "p_knx_ext" - extent polygon for the Knox Group "p_knx_outcrop" - extent polygon the Wells Creek Structure - Knox Group outcrop rasters/ ra_knx_tp.tif - altitude raster for the top of the Knox Group (NAVD 88) (meters) rd_knx_tp.tif - depth from land surface raster of the top of Knox Group (meters) vectors/ c_knx_tp.shp - structure contours for the top of the Knox Group (NGVD 29) (feet) c_knx_tp_modified.shp - modified structure contours for the top of the Knox Group (hachures removed from closed basins). This vector used to interpolate raster for the top of the Knox Group (NGVD 29) (feet) po_knx_tp.shp - point data for the altitude of top of the Knox Group (NGVD 29) (feet) References: Bradley, M. W., 1986, Preliminary Evaluation of the Knox Group in Tennessee for Receiving Injected Wastes, U.S. Geological Survey, Environmental Protection Agency,

The Knox Dolomite is currently recognized as the Knox Group. The Mascot Dolomite, the upper unit of the Knox Group, is dolomite and dolomitic limestone of Lower-Ordovician-age that occurs in the subsurface of most of Tennessee. This data release will focus on Middle Tennessee, where the only outcrop of the Knox Group is in the Wells Creek basin in Stewart and Houston counties (Bradley, 1986; Wilson and Stearns, 1968). The top of the Knox Dolomite is an erosional surface that is useful as a structural datum because of the importance of the Knox Group for oil and gas resources, zinc mineralization, and domestic drinking water supplies. Since the upper approximately 30 meters of the Knox Group is paleokarst, groundwater is generally under confined conditions (Bradley, 1986; Wilson and Stearns, 1968). This upper portion of the Knox is often low-yielding and variable in water quality. However, it can be a reliable aquifer in specific areas - mostly in the Central Basin. A structure contour map on the Knox Group in Middle Tennessee was prepared by Newcome (1954) as a part of a cooperative program of groundwater investigations by the U.S. Geological Survey and the Tennessee Division of Geology at Nashville, Tennessee. Prior to this work, this paper map existed in limited quantities, mainly restricted to the Nashville offices of the Tennessee Department of Environment and Conservation (TDEC) and United States Geological Survey (USGS). The map measuring 46 x 64 cm, with an approximate scale of 1:500,000 was prepared with well elevation data, determined by aneroid barometer or from topographic quadrangle maps (Newcome, 1954). Structure contours were drawn on top of Knox Group at 100 feet intervals. The work for this project consisted of (1) scanning and georeferencing original paper maps to create georeferenced images (GRI), (2) digitizing well location points and contour lines, (3) populating well and contour attribute tables with data from maps and associated reports, and (4) interpolating raster surfaces for the top altitude of the Knox Group and depth from land surface to the top of the unit. All raster surfaces were aligned to a modified version of the National Hydrogeologic Grid (Clark and others, 2018) to support USGS Lower Mississippi Gulf Water Science Center efforts to create a statewide hydrogeologic framework. All horizontal coordinated data are projected to NAD 1983 USGS Contiguous USA Albers. Vertical coordinate information was referenced to the North American Vertical Datum of 1988 (NAVD 88). Dataset types can be identified by the following naming convention: i_ = georeferenced map images (GRI) po_ = points c_ = contours and closed depressions f_= faults and other structural features p_ = extent polygon(s) ra_ = altitude raster rd_ = depth from land surface raster rt_ = thickness raster The datasets included on this child item page are as follows: knx_metadata.xml - metadata file knx_alldata.zip: GRI/ i_knx_tp.tif - structure contour map on the top of the Knox Group (Newcome, 1954) i_knx_outcrop.tif - map of the Wells Creek Disturbance (Wilson and Stearns, 1968) polygons/ "p_knx_ext" - extent polygon for the Knox Group "p_knx_outcrop" - extent polygon the Wells Creek Structure - Knox Group outcrop rasters/ ra_knx_tp.tif - altitude raster for the top of the Knox Group (NAVD 88) (meters) rd_knx_tp.tif - depth from land surface raster of the top of Knox Group (meters) vectors/ c_knx_tp.shp - structure contours for the top of the Knox Group (NGVD 29) (feet) c_knx_tp_modified.shp - modified structure contours for the top of the Knox Group (hachures removed from closed basins). This vector used to interpolate raster for the top of the Knox Group (NGVD 29) (feet) po_knx_tp.shp - point data for the altitude of top of the Knox Group (NGVD 29) (feet) References: Bradley, M. W., 1986, Preliminary Evaluation of the Knox Group in Tennessee for Receiving Injected Wastes, U.S. Geological Survey, Environmental Protection Agency,

The Chattanooga Shale is relatively thin and generally continuous across the state, making it an important geologic horizon. In Tennessee, the Chattanooga Shale crops out along the escarpment between the Central Basin and the surrounding Highland Rim, in several river valleys and in folded areas outside the basin, and crops out around the Wells Creek, Howell, and Flynn Creek impact structures (Conant and Swanson, 1961). The Devonian-Mississippian-aged Chattanooga Shale is often abbreviated as "MDc.” Data related to the thickness, depth from land surface, and elevation of the unit are useful for resource exploration. Information from 1,615 oil well and surface data points were used to produce the structure map on the Chattanooga Shale in Tennessee by the Tennessee Department of Environment and Conservation, Division of Geology (Moore and Horton, 1999). The data used in 1999 were acquired from previously drawn structure maps on the base of the Chattanooga Shale and compiled into computer-generated contour lines and maps. The original publication, Structure and isopach maps of the Chattanooga Shale in Tennessee, included three 84x57 cm maps, at an approximate scale of 1:500,000. The paper maps include a structure map on the base of the formation, an isopach map, and a location map of the data points representing wells used to prepare the original structure maps. The three maps associated with the original publication were digitized and rasterized for this project. The work for this project consisted of (1) scanning and georeferencing original paper maps to create georeferenced images (GRI), (2) digitizing well location points and contour lines, (3) populating well and contour attribute tables with data from maps and associated reports, and (4) interpolating raster surfaces for the top and bottom altitude, depth from land surface to the top and bottom surface, and thickness of the Chattanooga Shale in Tennessee. All raster surfaces were aligned to a modified version of the National Hydrogeologic Grid (Clark and others, 2018) to support USGS Lower Mississippi Gulf Water Science Center efforts to create a statewide hydrogeologic framework. All horizontal coordinated data are projected to NAD 1983 USGS Contiguous USA Albers. Raster vertical coordinate information was referenced to the North American Vertical Datum of 1988 (NAVD 88). Dataset types can be identified by the following naming convention: i_ = georeferenced map images (GRI) po_ = points c_ = contours and closed depressions f_= faults and other structural features p_ = extent polygon ra_ = altitude raster rd_ = depth from land surface raster rt_ = thickness raster The datasets included on this child item page are as follows: chttshl_metadata.xml - metadata file chttshl_alldata.zip: GRI/ i_chttshl_btm.tif - structure contour map of the bottom of the Chattanooga Shale (Moore and Wilson, 1999) i_chttshl_data.tif - map of data used to create structure and isopach maps (Moore and Horton, 1999c) i_chttshl_thk.tif - thickness contour map for the Chattanooga Shale (Moore and Horton, 1999b) polygons/ p_chttshl_ext_ext.shp - study area extent for the Chattanooga Shale (Moore and Wilson, 1999) p_hohenwald.shp - polygon for extend of the Hohenwald Platform (Moore and Horton, 1999b) - supplemental data rasters/ ra_chttshl_btm.tif - altitude raster for the bottom of the Chattanooga Shale (NAVD 88) (meters) ra_chttshl_tp.tif - altitude raster for the top of the Chattanooga Shale (NAVD 88) (meters) rd_chttshl_btm.tif - depth from land surface raster of the bottom of the Chattanooga Shale (meters) rd_chttshl_tp.tif - depth from land surface raster of the top of the Chattanooga Shale (meters) rt_chttshl.tif - thickness raster for the Chattanooga Shale (meters) vectors/ c_chttshl_btm.shp - structure contours for the bottom of the Chattanooga Shale (NGVD 29) (feet) c_chttshl_btm_modified.shp - modified structure contours for the bottom of the Chattanooga Shale (hachures removed from closed

The Chattanooga Shale is relatively thin and generally continuous across the state, making it an important geologic horizon. In Tennessee, the Chattanooga Shale crops out along the escarpment between the Central Basin and the surrounding Highland Rim, in several river valleys and in folded areas outside the basin, and crops out around the Wells Creek, Howell, and Flynn Creek impact structures (Conant and Swanson, 1961). The Devonian-Mississippian-aged Chattanooga Shale is often abbreviated as "MDc.” Data related to the thickness, depth from land surface, and elevation of the unit are useful for resource exploration. Information from 1,615 oil well and surface data points were used to produce the structure map on the Chattanooga Shale in Tennessee by the Tennessee Department of Environment and Conservation, Division of Geology (Moore and Horton, 1999). The data used in 1999 were acquired from previously drawn structure maps on the base of the Chattanooga Shale and compiled into computer-generated contour lines and maps. The original publication, Structure and isopach maps of the Chattanooga Shale in Tennessee, included three 84x57 cm maps, at an approximate scale of 1:500,000. The paper maps include a structure map on the base of the formation, an isopach map, and a location map of the data points representing wells used to prepare the original structure maps. The three maps associated with the original publication were digitized and rasterized for this project. The work for this project consisted of (1) scanning and georeferencing original paper maps to create georeferenced images (GRI), (2) digitizing well location points and contour lines, (3) populating well and contour attribute tables with data from maps and associated reports, and (4) interpolating raster surfaces for the top and bottom altitude, depth from land surface to the top and bottom surface, and thickness of the Chattanooga Shale in Tennessee. All raster surfaces were aligned to a modified version of the National Hydrogeologic Grid (Clark and others, 2018) to support USGS Lower Mississippi Gulf Water Science Center efforts to create a statewide hydrogeologic framework. All horizontal coordinated data are projected to NAD 1983 USGS Contiguous USA Albers. Raster vertical coordinate information was referenced to the North American Vertical Datum of 1988 (NAVD 88). Dataset types can be identified by the following naming convention: i_ = georeferenced map images (GRI) po_ = points c_ = contours and closed depressions f_= faults and other structural features p_ = extent polygon ra_ = altitude raster rd_ = depth from land surface raster rt_ = thickness raster The datasets included on this child item page are as follows: chttshl_metadata.xml - metadata file chttshl_alldata.zip: GRI/ i_chttshl_btm.tif - structure contour map of the bottom of the Chattanooga Shale (Moore and Wilson, 1999) i_chttshl_data.tif - map of data used to create structure and isopach maps (Moore and Horton, 1999c) i_chttshl_thk.tif - thickness contour map for the Chattanooga Shale (Moore and Horton, 1999b) polygons/ p_chttshl_ext_ext.shp - study area extent for the Chattanooga Shale (Moore and Wilson, 1999) p_hohenwald.shp - polygon for extend of the Hohenwald Platform (Moore and Horton, 1999b) - supplemental data rasters/ ra_chttshl_btm.tif - altitude raster for the bottom of the Chattanooga Shale (NAVD 88) (meters) ra_chttshl_tp.tif - altitude raster for the top of the Chattanooga Shale (NAVD 88) (meters) rd_chttshl_btm.tif - depth from land surface raster of the bottom of the Chattanooga Shale (meters) rd_chttshl_tp.tif - depth from land surface raster of the top of the Chattanooga Shale (meters) rt_chttshl.tif - thickness raster for the Chattanooga Shale (meters) vectors/ c_chttshl_btm.shp - structure contours for the bottom of the Chattanooga Shale (NGVD 29) (feet) c_chttshl_btm_modified.shp - modified structure contours for the bottom of the Chattanooga Shale (hachures removed from closed

This digital dataset is a result from the goal within the U.S. Geological Survey’s (USGS) National Cooperative Geologic Mapping Program to convert surficial data that were previously published in non-digital format to digital, vector-based data suitable for use by the public and in USGS studies. The objective of the data conversion is to reproduce the original published mapping with little to no added interpretation. This digital data release captures subsurface geologic data within the Mississippi Embayment region, using two publications focusing on water resources and general geology to fulfill missing pieces of a larger network of data. These two legacy publications, ‘Maps of upper Mississippi embayment Paleozoic and Precambrian rocks’ by Richard L. Dart, 1995 and ‘General Geology of the Mississippi Embayment’ By E. M. Cushing, E. H. Boswell, And R. L. Hosman, 1964- were chosen due the focus on structural and isopach data within their publications. There were six selected map figures with structural data digitized, two from Dart, 1995 and four from Cushing, 1964. This does not include any additional input data or speculative interpretations, strictly published structural contour features. While there were six identified maps, there are only five sets of vector data, this is due to combining both sets of Paleozoic features into one feature class- one can differentiate the two based on the listed source attribute. This geologic data set includes structure contour data for the top of the Eocene Sparta Sand, the base of Eocene Cane River Formation and stratigraphic equivalents, the top of Cretaceous rocks, the top of Paleozoic rocks, and the top of Precambrian basement rock. The Sparta Sand is identified as the middle part of the Eocene and is a formation within the Claiborne Group, the Cane River Formation underlies the Sparta Sand and includes all rock from the top of the Carrizo Sand to the base of the Sparta Sand. The Mississippi embayment is an extensive sediment-filled geologic structure underlying parts of eight states in the southcentral U.S. that provides large quantities of groundwater from numerous aquifers to residential and industrious areas. Due to the large size of the Mississippi Embayment and its cross-cutting political boundaries, the names given to the many geologic units may vary from region to region. It is common to call a unit by the name given by the local area, for example; west Tennessee terms the Memphis aquifer the Sparta Sand and Corrizo Sand aquifers, additionally the Sparta Sand is referred to as the Cane River in Arkansas and Louisiana and is the equivalent to the Mount Selma Formation of Texas and the Tallahatta Formation in Mississippi and Alabama.

The karstic Edwards and Trinity aquifers are classified as major sources of water in south-central Texas by the Texas Water Development Board, and both are classified as major aquifers by the State of Texas. The purpose of this data release is to present the data that were collected and compiled to describe the geologic framework and hydrostratigraphy within parts of Bandera and Kendall Counties, Texas, in order to help water managers, water purveyors, and local residents better understand and manage water resources. The scope of the larger work and this accompanying data release is focused on the geologic framework and hydrostratigraphy of the outcrops and hydrostratigraphy of the Edwards and Trinity aquifers within parts of Bandera and Kendall Counties, Texas. These digital data accompany Clark and others (2024).

The karstic Edwards and Trinity aquifers are classified as major sources of water in south-central Texas by the Texas Water Development Board, and both are classified as major aquifers by the State of Texas. The purpose of this data release is to present the data that were collected and compiled to describe the geologic framework and hydrostratigraphy within parts of Bandera and Kendall Counties, Texas, in order to help water managers, water purveyors, and local residents better understand and manage water resources. The scope of the larger work and this accompanying data release is focused on the geologic framework and hydrostratigraphy of the outcrops and hydrostratigraphy of the Edwards and Trinity aquifers within parts of Bandera and Kendall Counties, Texas. These digital data accompany Clark and others (2024).