This data release provides access to a low-altitude aeromagnetic survey flown over a part of the Cascade Range of the US Pacific Northwest, approximately centered over the town of Packwood, Washington. The Packwood magnetic survey surrounds but does not include the edifice of Mount Rainier, the highest (4392 m; 14,410 ft) volcano of the conterminous United States. Data were acquired between September 18 and October 18, 2022, by KBM Resources Group, Thunder Bay, Ontario, Canada, working under contract to the U.S. Geological Survey. Survey procedures are described in detail in the document, Packwood_tech_report.pdf, also available in this data release. The survey is underlain by a diverse magnetic terrane of Tertiary to Quaternary volcanic and intrusive rocks of the Western and High Cascades. These strongly magnetic rocks produce many of the anomalies evident in these aeromagnetic data.
Data were acquired with a twin-engine, fixed-wing aircraft. Flight lines were spaced 400 m apart and directed east-west; tie lines were spaced 4000 m apart and directed north-south. A total of 11,790 line-kilometers of aeromagnetic data were acquired over an area of approximately 4335 square kilometers. These data are available in the database, Packwood_data_MAIN.csv, available in this data release. The flight altitude was based on a best-fit, pre-planned, three-dimensional drape surface targeted at 200 m above terrain, subject to aircraft climb and descent limitations.
Fixed-wing aeromagnetic surveys over rugged, mountainous terrain require significant increases in terrain clearance, especially over valleys. Variable terrain clearance should be considered when modeling and interpreting these data.
This data release includes an additional database, Packwood_data_PROFILES.csv, consisting of 35 lines flown as close to the ground as safely possible within and along prominent valleys within the study area, a total of 690 line-kilometers.