The Marshall aquifer underlies much of the Lower Peninsula of Michigan and has a maximum thickness of 493 feet (Lampe, 2009). The aquifer consists mainly of medium-grained sandstone and is overlain by Pennsylvanian-age rocks and glacial deposits and underlain by the Devonian-Mississippian-age confining unit. The Marshall aquifer is one of the most productive aquifers in the state where unconfined conditions occur (HA 730-J). This product provides source data for the Marshall aquifer framework, including: Extent shapefiles: 1. p_32MRSHLL.shp: Polygon shapefile containing the areal extent of the Marshall aquifer (32MRSHLL_AqExtent). The extent file contains no aquifer subunits. Point shapefiles: 1. po_32MRSHLL_top.shp: Point dataset containing altitude values, in feet reference to North American Vertical Datum of 1988 (NAVD88), across the top of the Marshall aquifer (Lampe, 2009). These data were used to create the ra_32MRSHLL_top.tif raster dataset. 2. po_32MRSHLL_bot.shp: Point dataset containing altitude values, in feet reference to NAVD88, across the bottom of the Marshall aquifer (Lampe, 2009). These data were used to create the ra_32MRSHLL_bot.tif raster dataset. Altitude raster files: 1. ra_32MRSHLL_top.tif : Altitude raster dataset of the top of the Marshall aquifer. The altitude values are in meters reference to NAVD88 vertical datum. This raster was interpolated from the po_32MRSHLL_top.shp point dataset. 2. ra_32MRSHLL_bot.tif: Altitude raster dataset of the bottom of the Marshall aquifer. The altitude values are in meters reference to NAVD88 vertical datum. This raster was interpolated from the po_32MRSHLL_bot.shp point dataset. Depth raster files: 1. rd_32MRSHLL_top.tif: Depth raster dataset of the top of the Marshall aquifer. The depth values are in meters below land-surface (NED, 100-meter). 2. rd_32MRSHLL_bot.tif: Depth raster dataset of the bottom of the Marshall aquifer. The depth values are in meters below land-surface (NED, 100-meter).

This data set represents the extent of the Jacobsville aquifer in Michigan.

This geospatial dataset represents a prototype of a finer-scale representation of the principal aquifers of the United States, using four original principal aquifers in the Upper Midwest, United States, which were re-analyzed and condensed into three updated principal aquifers. The original principal aquifer definitions and extents were published in the Ground Water Atlas of the United States at a scale of 1:5,000,000. The updated version in this dataset are based on a reinterpretation of the original definitions using geologic data from the U.S. Geological Survey (USGS) State Geologic Map Compilation (v 1.1, 2017), which contains published state data at scales from 1:50,000 to 1:1,000,000. This shapefile includes fields describing the original principal aquifer definitions and data links as well as ages, major and minor lithologies, and source data for the updated aquifer unit polygons. A detailed description of the process followed to evaluate the old definitions of the principal aquifers in the Ground Water Atlas of the United States in the context of the State Geologic Map compilation datasets can be found in the related primary publication.

This data set represents the extent of the Ozark Plateaus aquifer system in the states of Missouri, Kansas, Oklahoma, Arkansas, and Illinois.

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

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 Ada-Vamoosa aquifer in Oklahoma.

This data set represents the extent of the Upper carbonate aquifer in Minnesota and Iowa.

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

This data set represents the extent of the Blaine aquifer in Texas and Oklahoma.