Katie (KT) M. Hulsey Burke J. Minsley Daniel R. Hadley Daniel B. Abrams Andrew C. Phillips Emilia L Bristow 20251204 raster digital data https://doi.org/10.5066/P1DYYM2G In support of the U.S. Geological Survey (USGS) Illinois River Basin (IRB) Next Generation Water Observing System (NGWOS) program, a top of bedrock elevation surface was generated to improve understanding of the bedrock elevation, subsurface geologic structure, and unconsolidated materials thickness across IRB and the State of Illinois. The surface was derived primarily from models of electrical resistivity values collected along flight paths from a regional scale airborne electromagnetic (AEM) survey over IRB in 2023. The AEM derived estimate of the top of bedrock elevation was then interpolated with available bedrock elevation surfaces from the Illinois State Geological Survey (ISGS) and Indiana Geological and Water Survey (IGWS), where AEM data was absent. Top of bedrock elevation surface was generated to improve understanding of bedrock elevation in IRB. The surface is primarily intended to inform hydrologic models at a regional scale and support Integrated Water Availability Assessments (IWAAs) program studies in IRB. 2023 2025 ground condition Complete None planned -91.6996 -85.7851 43.0397 37.0862 None geophysics bedrock elevation airborne electromagnetic AEM Next Generation Water Observing Systems NGWOS USGS Metadata Identifier USGS:68489d7dd4be02423f6a9b4d USGS Thesaurus geophysics None Illinois River Basin Illinois Indiana Wisconsin Michigan None. Please see 'Distribution Info' for details. None. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. Katie M. Hulsey U.S. Geological Survey - Central Midwest Water Science Center Hydrologist mailing

401 NW Capital Drive

Lees Summit MO 64086 816-554-3489 khulsey@usgs.gov Data were collected as part of the U.S. Geological Survey (USGS) Next Generation Water Observing System (NGWOS) Illinois River Basin project to improve understanding of top of bedrock elevation within the Illinois River Basin, in collaboration with the Illinois State Water Survey (ISWS) and the Illinois State Geological Survey (ISGS). Elevation of the top of bedrock is provided as a Elevation of the top of bedrock is provided as a Tagged Image File Format (TIFF) image with georeference information. Data were developed in ArcGIS Pro, Geoscene3D, and QGIS software. Brian R Clark Paul M Barlow Steven M Peterson Joseph D Hughes Howard W Reeves Roland Viger 2018 dataset https://www.sciencebase.gov U.S. Geological Survey https://doi.org/10.5066/f7p84b24 Jennifer E Carrell Andrew C Phillips Riley Balikian Curtis C Albert 2023 publication Model of the bedrock topography of Illinois, updated from Herzog et al. (1994) with newer large scale mapping results and additional water well, engineering, and petroleum boring pick. Esri 2024 ArcGIS Pro version 3.3.2 application/service https://www.esri.com/en-us/home Indiana Geological Survey 20250828 publication https://geo.btaa.org/catalog/80e4c937-6bfa-4b98-9a16-80cfb20165c1 Daniel B Abrams Devin H Mannix Daniel R Hadley George S Roadcap 2018 publication https://hdl.handle.net/2142/102968 IGIS GeoScene3D 2024 application/service https://i-gis.dk/geoscene3d/ Jade W. Crosbie Burke J Minsley Katie (KT) M. Hulsey James J Duncker 2024 dataset https://www.sciencebase.gov U.S. Geological Survey https://doi.org/10.5066/p13q93jm Katie (KT) M. Hulsey Burke J Minsley Jade W. Crosbie Ryan F Adams Carole D Johnson Eric A White Emilia L Bristow Amy M Gahala 2025 dataset https://www.sciencebase.gov U.S. Geological Survey https://doi.org/10.5066/p13whwzr QGIS 20250805 application/service QGIS version 3.40.10-Bratislava https://qgis.org/ Resistivity models from the 2023 airborne electromagnetic survey of Illinois River Basin were imported into the Geoscene3D software (v. 12.0.0.702) and visually inspected for consistency with terrain and other geospatial datasets. The top of bedrock elevation surface was visually inspected relative to other bedrock digital datasets available from the Illinois State Water Survey (ISWS), Illinois State Geologic Survey (ISGS), and Indiana State Geological and Water Survey in grid and tabular format in the Geoscene 3D software for reasonableness, regional geologic trends, and spatial consistency. Data set is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details. Generation of contiguous, published bedrock elevation raster: The National-scale grid (Clark and others, 2018) was imported into ArcGIS Pro. The National-scale grid raster was clipped to the bounding polygon “National_Grid” and resampled at 100-meter (m) cell size. This resampled portion of the National-scale grid was utilized for all subsequent raster snapping in following process steps for the generation of “Bedrock_elevation.tif” raster. Three bedrock elevation surfaces were imported to ArcGIS Pro; The Bedrock Topography of Illinois, 2023 for the state of Illinois (Carrell and others, 2023), the Bedrock Surface Elevation DEM : Indiana (IGWS, 2015) for the portion of the Illinois River Basin within the state of Indiana, and the bedrock surface from Groundwater Flow Models of Illinois (Abrams and others, 2018) for the portion of the Illinois River Basin within the state of Wisconsin. Each of these bedrock surfaces were resampled at 100-meter cell size, snapped to the national scale grid, and clipped using polygons Illinois, IRB_IN, and IRB_WI, respectively, to ensure no overlap of cells.See Data_extent_poly.zip for shapefile. The three resampled, snapped, and clipped bedrock elevation surfaces were mosaic combined in ArcGIS Pro resulting in a contiguous bedrock elevation surface. 2023 Generation of AEM resistivity model indicated top of bedrock elevation pointset: Resistivity models from the 2023 airborne electromagnetic survey of the Illinois River Basin (USGS, 2024) and the 1-D time domain electromagnetic geophysical data (USGS, 2025) were imported into GeoScene3D software. Bedrock elevation points were manually picked along AEM survey flight lines as defined by resistivity transitions, indicative of subsurface material composition changes from unconsolidated materials to bedrock. These points were visually inspected relative to other publicly available geospatial data sets related to bedrock geology and topography from the ISWS, ISGS, and IGWS. AEM derived top of bedrock elevation points were reviewed and manually adjusted in select areas by the USGS together with ISWS and ISGS. 2024 Generation of regional scale “Bedrock_elevation.tif” surface: The following workflow was implemented to generate a regional scale bedrock elevation surface for use in regional scale (Illinois State and Illinois River Basin) groundwater modeling that (1) integrates, the bedrock elevation trends indicated by AEM resistivity models within the footprint of the Illinois River Basin AEM survey, (2) preserves smaller scale bedrock elevation trends between the roughly 20-km spaced AEM flight paths, and (3) smoothly transitions to bedrock elevation surfaces beyond the AEM survey footprint: 1. The AEM-derived top of bedrock elevation pointset and contiguous, published bedrock elevation surface were imported to QGIS geospatial software. 2. The elevation difference value in meters between the AEM-derived top of bedrock elevation pointset and the contiguous, published bedrock elevation surface was calculated at each point. 3. A 10-km buffer polygon (AEM_footpring) was generated around the AEM-derived top of bedrock elevation pointset to represent the footprint of the AEM survey. A ‘buffering’ pointset was generated along the buffer polygon with a 1,000 m spacing. The ‘buffering’ pointset was assigned an elevation difference value of 0 meters. 4. The AEM-derived top of bedrock elevation pointset and the ‘buffering’ pointset elevation difference values were interpolated using kriging in QGIS software to produce a 100-m cell sized ‘elevation difference’ raster, snapped to the National-scale grid, within the footprint of the regional Illinois River Basin AEM survey. 5. To produce the “Bedrock_elevation.tif” file. The AEM-derived elevation difference raster was added to the contiguous, published bedrock elevation raster. 2025 Raster Grid Cell 7026 4477 1 Albers Conical Equal Area 29.5 45.5 -96.0 23.0 0.0 0.0 row and column 100.00000000000016 100.0000000000004 meters North_American_Datum_1983 GRS 1980 6378137.0 298.257222101004 Bedrock_elevation.tif Single-band raster geospatial data file containing elevation of top of bedrock values derived from AEM resistivity models. Producer Defined Value Unique numeric values contained in each raster cell. Elevation value (North American Vertical Datum of 1988) of the top of bedrock. Producer Defined -9999 no bedrock elevation value Producer defined 43.765674591064 368.58447265625 meters Data_extent_poly.shp Attribute Table Table containing attribute information associated with the data set. Producer Defined FID Internal feature number. ESRI Sequential unique whole numbers that are automatically generated. Shape Feature geometry. ESRI Shape type. Name Names of individual polygons. Polygons illustrate the data extent of various input rasters and or snapped rasters as described in the Process Steps workflow in the metadata file. Producer Defined National_Grid Polygon representing the extent of the National-Scale Grid (Clark and others, 2018), re-sampled at 100 meter cell size, used for snapping throughout workflow. See Process Steps in metadata file. Producer defined AEM_footprint Polygon of the extent of the AEM difference grid. See Process Steps in metadata file. Producer defined Bedrock_clip Used for clipping contiguous, published bedrock surface and "Bedrock_elevation.tif" raster. Producer defined IRB_WI Wisconsin portion of the Illinois River Basin. Used for clipping bedrock surface from Abrams and others, 2018. See Process Steps in metadata file. Producer defined Illinois Illinois state boundary. Used for clipping bedrock surface from Carrell and others, 2023. See Process Steps in metadata file. Producer defined IRB_IN Indiana and Michigan portion of the Illinois River Basin. Used for clipping bedrock surface from IGWS, 2015. See Process Steps in metadata file. Producer defined GS ScienceBase U.S. Geological Survey mailing address

Denver Federal Center, Building 810, Mail Stop 302

Denver CO 80225 United States 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Digital Data https://doi.org/10.5066/P1DYYM2G None 20251204 Katie M. Hulsey U.S. Geological Survey- Central Midwest Water Science Center Hydrologist mailing

401 NW Capital Drive

Lees Summit MO 64086 816-554-3489 khulsey@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998