Airborne electromagnetic (AEM) and magnetic survey data were collected during October 2016 along 1,443 line kilometers in the southwestern San Joaquin Valley near Lost Hills, California. These data were collected in support of groundwater salinity mapping and hydrogeologic framework development as part of the U.S. Geological Survey California Oil, Gas, and Groundwater program and the California State Water Resources Control Board’s Program of Regional Monitoring of Water Quality in Areas of Oil and Gas Production. Data were acquired by SkyTEM ApS with the SkyTEM 312 time-domain helicopter-borne electromagnetic system together with a Geometrics G822A cesium vapor magnetometer. The survey was designed to cover the region hydrogeologically downgradient and within 5 km of the Lost Hills, North Belridge, and South Belridge oil fields. Additional lines were extended to the west, east, and south for hydrogeologic context. The AEM typical maximum depth of investigation is about 300 m. The survey was flown at a nominal flight height of 35 m above terrain along block-style lines with a nominal spacing of 150 to 300 m. This data release includes minimally processed (raw) AEM data, fully processed AEM data used for resistivity model development, and laterally constrained inverted resistivity models along all flight lines. This release also includes raw and processed magnetic data.

Airborne electromagnetic (AEM) and magnetic survey data were collected during October 2016 along 1,443 line kilometers in the southwestern San Joaquin Valley near Lost Hills, California. These data were collected in support of groundwater salinity mapping and hydrogeologic framework development as part of the U.S. Geological Survey California Oil, Gas, and Groundwater program and the California State Water Resources Control Board’s Program of Regional Monitoring of Water Quality in Areas of Oil and Gas Production. Data were acquired by SkyTEM ApS with the SkyTEM 312 time-domain helicopter-borne electromagnetic system together with a Geometrics G822A cesium vapor magnetometer. The survey was flown at a nominal flight height of 35 m above terrain along block-style lines with a nominal spacing of 150 to 300 m. The survey was designed to cover the region hydrogeologically downgradient and within 5 km of the Lost Hills, North Belridge, and South Belridge oil fields. Additional lines were extended to the west, east, and south for hydrogeologic context. The survey was flown at a nominal flight height of 35 m above terrain along block-style lines with a nominal spacing of 150 to 300 m. The AEM typical maximum depth of investigation is about 300 m. The data provided includes minimally processed (raw) AEM data and unprocessed and processed magnetic data. Digital data from production flights are provided and described in the data dictionary. The complete data package received from the contractor is included in separate zip-file directory and described in the contractor's report.

Airborne electromagnetic (AEM) and magnetic survey data were collected during October 2016 along 1,443 line kilometers in the southwestern San Joaquin Valley near Lost Hills, California. These data were collected in support of groundwater salinity mapping and hydrogeologic framework development as part of the U.S. Geological Survey California Oil, Gas, and Groundwater program and the California State Water Resources Control Board’s Program of Regional Monitoring of Water Quality in Areas of Oil and Gas Production. Minimally processed binary AEM data received from the contractor were imported into the Aarhus Workbench software (v. 5.6.3.0, Aarhus Geosoftware, Aarhus, Denmark) and processed. Filters were applied to inclinometer and spatial positioning data to smooth raw data and remove sensor drop outs. Altimeter data were filtered, smoothed, and manually edited to correct false altitudes associated with trees and other obstacles, resulting in processed altitude representative of the distance between the AEM sensor airframe and bare earth. Ground surface elevations were imported from the 1/3 arc second USGS National Elevation Dataset (U.S. Geological Survey, https://www.usgs.gov/core-science-systems/ngp/3dep/3dep-product-metadata). The elevations were extracted using bilinear interpolation at the intersection of the AEM measurement points and the 1/3 arc second digital elevation model. Raw electromagnetic data were visually examined for couplings and noise associated with infrastructure and considered in the context of the locations of known or suspected infrastructure (power lines, pipe lines, etc...) and magnetic anomalies; impacted data were manually removed. Culled electromagnetic data were averaged using a filter width of 4 seconds applied to high moment and low moment data. Low-signal data were removed from the averaged data through a combination of filters and manual culling. The data provided include fully processed electromagnetic data produced from minimally processed contractor-delivered data, also provided with this data release. The digital data are described in the data dictionary, additional documentation is provided in the metadata.

Airborne electromagnetic (AEM) and magnetic survey data were collected during October 2016 over a total distance of 262 line kilometers in the southeastern San Joaquin Valley near Cawelo, California. These data were collected in support of groundwater salinity mapping and hydrogeologic framework development as part of the U.S. Geological Survey California Oil, Gas, and Groundwater program and the California State Water Resources Control Board’s Oil and Gas Regional Monitoring Program. Deterministic spatially constrained inversions of the processed AEM data were conducted using the AarhusINV code (Auken and others, 2015) implemented in Aarhus Workbench software (Aarhus Geosoftware, Aarhus, Denmark). Inversion parameters were selected by running a series of test models with varying starting model resistivity values, layer discretization, horizontal/lateral constraints, and other inversion parameters. A 30-layer fixed-depth smooth inversion model was developed with layer top depths ranging between 4 and 400 meters and layer thickness increasing with depth. Inversions were run with vertical and lateral constraints of values of 2.0 and 1.6, respectively, and a 30 ohm-meter homogeneous half-space starting model. Sensor altitude was treated as a free parameter after the 5th iteration. Depth of investigation was calculated with a minimum and maximum depth of 5 and 500 meters. The data provided include inverted resistivity models along all flight lines. Digital data are described in the data dictionary, additional details regarding data inversion are described in the metadata processing steps.

Airborne electromagnetic (AEM) and magnetic survey data were collected during October 2016 over a total distance of 262 line kilometers in the southeastern San Joaquin Valley near Cawelo, California. These data were collected in support of groundwater salinity mapping and hydrogeologic framework development as part of the U.S. Geological Survey California Oil, Gas, and Groundwater program and the California State Water Resources Control Board’s Oil and Gas Regional Monitoring Program. Data were acquired by SkyTEM ApS with the SkyTEM 312 time-domain helicopter-borne electromagnetic system together with a Geometrics G822A cesium vapor magnetometer. The survey was flown at a nominal flight height of 35 m above terrain along block-style lines with a nominal spacing of 300 m. The survey was designed to cover the region hydrogeologically downgradient of the Poso Creek Oil Field. Minimally processed electromagnetic and magnetic data from production flights are provided and described in the data dictionary and contractor's report. The complete data package received from the contractor is included in separate zip-file directory and described in the contractor's report.