This publication provides digital flight line data for a high-resolution horizontal magnetic gradient and radiometric survey over an area of southeast Missouri, southern Illinois, and western Kentucky. The survey was conducted in collaboration with the Missouri Geological Survey as part of the U.S. Geological Survey (USGS) Earth Mapping Resource Initiative (Earth MRI) effort (Day, 2019). Earth MRI is a cooperative effort between the USGS, the Association of American State Geologists, and other Federal, State, and private sector organizations to improve our knowledge of the geologic framework of the United States. Data for this survey were collected by Terraquest, Ltd. under contract with the USGS using a fixed-wing aircraft with magnetometers mounted in the tail stinger and each wing tip pod and a fully calibrated gamma ray spectrometer. The survey operated out of the Farmington, Missouri airport from March of 2021 to July of 2021. The survey covers a 88-kilometer x 160-kilometer area covering the major cities of Cape Giradeau, Illinois and Carbondale, Illinois. Data were collected along east-west flight lines spaced 250 meters (m) apart with north-south tie lines flown every 3500 m. A mean terrain clearance of 100 m was maintained except where safety dictated a higher elevation. A total of 64,233-line kilometers (km) of data were collected. Files that are available in this publication include flight line data for the magnetic gradient survey, flight line data for the radiometric survey and a report describing the survey parameters, field operations, quality control and data reduction procedures. A zip file is provided that contains the contractor's deliverable products that includes Geosoft databases and grids for the magnetic and radiometric survey and the report describing the survey and data reduction. The Gap survey was designed to fill the gap between two previous USGS airborne geophysical surveys. Adjacent surveys include magnetic and radiometric surveys flown in 2018 (McCafferty and Johnson, 2019) over southeast Missouri and western Illinois and a magnetic and radiometric survey flown in 2019 that is centered on the Hicks Dome area of Illinois (McCafferty and Brown, 2020). References: Day, W.C., 2019, The Earth Mapping Resources Initiative (Earth MRI)—Mapping the Nation's critical mineral resources (ver. 1.2, September 2019): U.S. Geological Survey Fact Sheet 2019–3007, 2 p., https://doi.org/10.3133/fs20193007. McCafferty, A.E., and Johnson, M.R., 2019, Airborne magnetic and radiometric survey, southeast Missouri and western Illinois, 2018-2019: U.S. Geological Survey data release, https://doi.org/10.5066/P9PBDSA1. McCafferty, A.E., and Brown, P.J., 2020, Airborne magnetic and radiometric survey, southeastern Illinois, western Kentucky, and southern Indiana, 2019: U.S. Geological Survey data release, https://doi.org/10.5066/P9R05B0M.