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.