This data set represents the extent of the Silurian Devonian aquifers in the states of Michigan, Wisconsin, Illinois, Indiana, Ohio, Kentucky, and Tennessee.

This geodatabase includes spatial datasets that represent the Silurian-Devonian aquifers in the States of Illinois, Indiana, Iowa, Kentucky, Michigan, Missouri, Ohio, Tennessee, and Wisconsin. Included are: (1) polygon extents; datasets that represent the aquifer system extent, and the entire extent subdivided into subareas, (2) raster datasets for the altitude of the top and bottom surfaces of the entire aquifer (where data are available), and (3) altitude contours used to generate the surface rasters. The digitized contours are supplied for reference. The extent of the Silurian-Devonian aquifers is from the linework of the Silurian-Devonian aquifer extent maps in U.S. Geological Survey U.S. Geological Survey Hydrologic Atlas 730, Chapters J and K, (USGS HA 730-J, -K) and a digital version of the aquifer extent presented in the National Aquifer Code Reference List, available at http://water.usgs.gov/ogw/NatlAqCode-reflist.html , "silurian.zip". The extent was then modified for each subarea: Subarea 1 (sa1): Primarily in Ohio and Indiana, subject of U.S. Geological Survey Professional Paper 1423 B (USGS PP 1423B). Subarea 2 (sa2): In Iowa. Digital data were available from the Iowa Geologic Survey. Subarea 3 (sa3): Remaining area in Illinois, Wisconsin, Michigan, and Kentucky. Extent is that part of the National Aquifer Code Reference List polygon that remained when the areas of sa1 and sa2 were removed. The altitude and thickness contours that were available for each subarea were compiled or generated from georeferenced figures of altitude contours in USGS PP 1423B for sa1, digital data from IAGS for sa2. There were no vertical data for sa3. The resultant top and bottom altitude values were interpolated into surface rasters within a GIS using tools that create hydrologically correct surfaces from contour data, derive the altitude from the thickness (depth from the land surface), and merge the subareas into a single surface. The primary tool was an enhanced version of "Topo to Raster" used in ArcGIS, ArcMap, Esri 2014. The raster surfaces were corrected in the areas where the altitude of an underlying layer of the aquifer exceeded the altitude of an overlying layer.

This geodatabase includes spatial datasets that represent the Silurian-Devonian aquifers in the States of Illinois, Indiana, Iowa, Kentucky, Michigan, Missouri, Ohio, Tennessee, and Wisconsin. Included are: (1) polygon extents; datasets that represent the aquifer system extent, and the entire extent subdivided into subareas, (2) raster datasets for the altitude of the top and bottom surfaces of the entire aquifer (where data are available), and (3) altitude contours used to generate the surface rasters. The digitized contours are supplied for reference. The extent of the Silurian-Devonian aquifers is from the linework of the Silurian-Devonian aquifer extent maps in U.S. Geological Survey U.S. Geological Survey Hydrologic Atlas 730, Chapters J and K, (USGS HA 730-J, -K) and a digital version of the aquifer extent presented in the National Aquifer Code Reference List, available at http://water.usgs.gov/ogw/NatlAqCode-reflist.html , "silurian.zip". The extent was then modified for each subarea: Subarea 1 (sa1): Primarily in Ohio and Indiana, subject of U.S. Geological Survey Professional Paper 1423 B (USGS PP 1423B). Subarea 2 (sa2): In Iowa. Digital data were available from the Iowa Geologic Survey. Subarea 3 (sa3): Remaining area in Illinois, Wisconsin, Michigan, and Kentucky. Extent is that part of the National Aquifer Code Reference List polygon that remained when the areas of sa1 and sa2 were removed. The altitude and thickness contours that were available for each subarea were compiled or generated from georeferenced figures of altitude contours in USGS PP 1423B for sa1, digital data from IAGS for sa2. There were no vertical data for sa3. The resultant top and bottom altitude values were interpolated into surface rasters within a GIS using tools that create hydrologically correct surfaces from contour data, derive the altitude from the thickness (depth from the land surface), and merge the subareas into a single surface. The primary tool was an enhanced version of "Topo to Raster" used in ArcGIS, ArcMap, Esri 2014. The raster surfaces were corrected in the areas where the altitude of an underlying layer of the aquifer exceeded the altitude of an overlying layer.

This data set represents the extent of the Cambrian-Ordovician aquifer system in the states of Wisconsin, Michigan, Minnesota, Iowa, and Illinois.

This data set represents the extent of the Cambrian-Ordovician aquifer system in the states of Wisconsin, Michigan, Minnesota, Iowa, and Illinois.

This data set represents the extent of the Ordovician aquifers in Tennessee and Kentucky.

This data set represents the extent of the Ordovician aquifers in Tennessee and Kentucky.

This data set represents the extent of the Lower Cretaceous aquifers in the states of Montana, Wyoming, South Dakota, Kansas, Nebraska, Iowa, and Minnesota..

This data set represents the extent of the Lower Cretaceous aquifers in the states of Montana, Wyoming, South Dakota, Kansas, Nebraska, Iowa, and Minnesota..

This geodatabase includes spatial datasets that represent the Cambrian-Ordovician aquifer system in the States of Wisconsin, Michigan, Minnesota, Iowa, and Illinois. Included are: (1) a polygon dataset that represents the aquifer system extent, (2) raster datasets for the altitude of each aquifer subunit, (3) altitude, or if applicable, thickness contours used to generate the surface rasters, (4) georeferenced images of the figures that were digitized to create the altitude or thickness contours, (5) the line datasets representing the altitude contours that were digitized from the images, and (6) an ArcGIS Toolbox used to develop the surface raster datasets. The images and digitized contours are supplied for reference. The extent of the Cambrian-Ordovician aquifer system is from the linework of the Cambrian-Ordovician aquifer system extent maps in U.S. Geological Survey Professional Paper 1405-B (PP1405B), and a digital version of the aquifer extent presented in the Groundwater Atlas of the United States (the U.S. Geological Survey Hydrologic Atlas 730-J, (USGS HA 730-J) and 730-K (USGS HA 730-K)), available at http://water.usgs.gov/ogw/NatlAqCode-reflist.html . The Cambrian-Ordovician Aquifer System has four aquifer subunits, in order from the most surficial to the deepest: (A1) St. Peter Sandstone Aquifer, (A2) Prairie du Chien Aquifer, (A3) Ironton and Galesville Sandstone Aquifer, and (A4) Mt. Simon or Lamotte Sandstone Aquifer. The altitude contour line datasets for each subunit available were digitized from georeferenced figures of altitude contours in PP1405B, and the altitude values were interpolated into surface rasters within a GIS using tools that create hydrologically correct surfaces from contour data, derives the altitude from the thickness (depth from the land surface), and merges the subareas into a single surface. The primary tool was "Topo to Raster" used in ArcGIS, ArcMap, Esri 2014. (ArcGIS Desktop: Release 10.2 Redlands, CA: Environmental Systems Research Institute). The surface rasters were corrected for the areas where the altitude of the top of the aquifer exceeded the land surface, and where the bottom of an aquifer exceeded the altitude of the corrected top of the aquifer.