Surface electrical resistivity tomography (ERT), magnetics, and gravity data were acquired in July 2017 in the greater East River Watershed near Crested Butte Colorado with a focused effort in Redwell Basin. Five ERT profiles were acquired within Redwell Basin and Brush Creek to map geologic structure at depths up to 40 meters, depending on the subsurface resistivity, using the Advanced Geosciences, Inc. SuperSting R8 resistivity meter. Approximately ten kilometers of total field magnetics data were acquired with a Geometrics G-858 cesium vapor magnetometer that detects changes in deep (tens of meters to kilometers) geologic structure based on variations in the magnetic properties of different formations. Ten gravity stations were acquired with a LaCoste and Romberg G-model relative gravimeter to map density variations. This data release includes raw data for all methods as well as processed and/or inverted resistivity or water content models. Digital data from all methods are provided, and data fields are defined in respective data dictionaries.

Surface geophysical surveys were conducted in July 2017 in the greater East River Watershed near Crested Butte Colorado with a focused effort in Redwell Basin as part of a broader study of the role of bedrock groundwater in the hydrogeology of mineralized mountain watersheds. Ten gravity stations were acquired with a LaCoste and Romberg G-model relative gravimeter to map density variations. This data release includes principal facts for the gravity stations provided as digital data. Data fields are defined in the data dictionary.

Surface electrical resistivity tomography (ERT), magnetic, and gravity surveys were conducted in July 2017 in the greater East River Watershed near Crested Butte Colorado with a focused effort in Redwell Basin as part of a broader study of the role of bedrock groundwater in the hydrogeology of mineralized mountain watersheds. Five electrical resistivity tomography profiles were acquired within Redwell Basin and Brush Creek to map geologic structure at depths up to 40 meters, depending on the subsurface resistivity, using the Advanced Geosciences, Inc. SuperSting R8 resistivity meter. This data release includes the raw and processed resistivity data as well as inverted resistivity models. All are provided as digital data, and data fields for each file type are defined in the respective data dictionary.

In June 2017, U.S. Geological Survey (USGS) collected geophysical measurements to help map variations in electrical properties to infer shallow flowpaths and storage zones influenced by residual spilled unconventional oil and gas (UOG). Two survey profiles were collected, each including dipole-dipole and Wenner-Schlumberger configurations. For each survey a total of 56 electrodes spaced 1.0 meter (m) apart were used. During the ERT measurement, current is injected through two current electrodes and voltage is measured sequentially across multiple pairs of potential electrodes; the known current and the measured voltages are used to determine the apparent resistivity of the subsurface. Inverse modeling of ERT survey results provide profiles of resistivity that can be interpreted for subsurface layers. This data release provides the raw ERT data and output from inversion.

Geophysical measurements and related field data were collected by the U.S. Geological Survey (USGS) at the Alaska Peatland Experiment (APEX) site in Interior Alaska from 2018 to 2020 to characterize subsurface thermal and hydrologic conditions along a permafrost thaw gradient. The APEX site is managed by the Bonanza Creek LTER (Long Term Ecological Research). Nine instrument monitoring sites (APEX1-APEX9) were established in April 2018. To quantify permafrost and thaw zone characteristics along the instrumented gradient, electrical resistivity tomography (ERT) data were collected in August 2018 along four 82 meter (m)-long transects between select sites: APEX1-3, APEX5-3, APEX5-7, and APEX6-8. Data were collected for both dipole-dipole (DD) and inverse Schlumberger (IS) survey geometries. Inverted models of electrical resistivity were produced from the separate DD and IS datasets, as well as the combination of both datasets inverted jointly (labeled DDIS). The resulting models of electrical resistivity revealed the spatial variability in soil lithology and thermal state (frozen vs. thawed) to depths up to 10-15 m below the surface. Manual permafrost-probe measurements of thaw depths were collected at set intervals along each ERT transect and used for comparison to the resistivity models.

This data release includes raw and processed (inverted) data for three different geophysical methods, continuous resistivity profiles (CRP), direct current electrical resistivity tomography (ERT), and frequency domain electromagnetic induction (FDEM) data. These surface geophysical methods were used as a proxy for groundwater salinity in the Paradox Valley in western Colorado to investigate temporal and spatial variations in the position of brine-rich groundwater under the Dolores River. Continuous resistivity profile surveys along a 8-10 km reach of the Dolores River were conducted on March 7, May 16, and September 13 of 2017. The ERT surveys were conducted along 3 lines crossing the river and 1 line parallel to it during March 6-10, 2017. The FDEM surveys were conducted along the same paths as the CRP and ERT surveys. Some additional land-based FDEM surveys were conducted using an all-terrain vehicle (ATV). Below is a brief description of each attached file in the data release: 1. The file 'CRP_data.csv' includes raw data for all 4 of the CRP surveys of the river including one in March, two in May, and one in September. The columns titled 'date' and 'time' in the file differentiate data from the 4 surveys. 2. The file 'ERT_data.csv' includes data for all the ERT surveys, 3 crossing the river and 1 parallel to it. The columns titled 'Survey Description', 'survey geometry', and 'electrode spacing' can be used to differentiate data for the individual surveys. 3. The file ‘ERT_electrode_positions.csv’ includes the coordinates for the 56 electrodes in each ERT survey. 4. The file ‘FDEM_data.csv' includes GEM-2 data from the river and ATV land-based surveys. The columns titled 'Description', 'Land or Water', 'Mode', 'Date', and 'Run' can be used to differentiate data for the individual surveys. 5. The file 'QW_data.csv' includes GPS coordinates and water depth, temperature, and specific conductance for the CRP river surveys. The column titled 'DateTime' differentiates data for the March, May, and September surveys. 6. The image 'River_surveys.jpeg' shows the approximate path of each river-based CRP and FDEM survey and apparent conductivity based on 1530 Hz FDEM data. 7. The image 'ERT_survey_location_map.jpg' shows the approximate path of each ERT survey. 8. The image 'FDEM_ATV_surveys.jpg' shows the path of the ATV surveys and apparent conductivity based on 1530 Hz FDEM data collected in May 2017. 9. The file 'PVU_RiverCRP_inverted_conductivity.csv' contains the CRP inversion results from the four different river surveys (March, May first run, May 2nd run, and September). 10. The file 'PVU_ERT_inverted_conductivity.csv' contains the inversion results from the March 2017 ERT surveys. 11. The file 'PVU_RiverFDEM_inverted_conductivity.csv' contains the FDEM inversion results from the four different river surveys (March, May first run, May 2nd run, and September). 12. The file 'PVU_FDEM_inverted_conductivity.csv' contains inversion results from all of the March 2017 FDEM surveys (including walking, river, and ATV).

Electrical resistivity tomography (ERT) surveys were done northwest of the Air Force Research Laboratory (AFRL) at Edwards Air Force Base. ERT surveys were done at four locations in May through June of 2018 to refine the understanding of the bedrock-alluvial aquifer transition zone downgradient from the AFRL. The ERT technique injects direct-current electricity with known voltage and current into the earth using a series of electrodes and measures the resulting resistivity. This technique is generally limited to investigations of aquifer properties less than 100 meters below land surface. Data from other geophysical techniques co-located with the ERT data, including time-domain electromagnetics and horizontal-to-vertical spectral ratio passive seismic, are made available in other child pages within this data release: https://doi.org/10.5066/P9ZGZTA4. This page contains the ERT data, spatial information for the ERT transects, and preliminary processed ERT data.