High-Resolution Aeromagnetic Survey Over Cascade Locks, Oregon, and Surrounding Areas

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 Cascade Locks, Oregon. The Cascade Locks magnetic survey encompasses two large stratovolcanoes of the Cascade Range: Mt. Hood (3426 m) in Oregon and Mt. Adams (3742 m) in Washington. Data were acquired between October 17, 2021, and February 26, 2022, by KBM Resources Group, Thunder Bay, Ontario, Canada, working under contract to the U.S. Geological Survey. The survey is underlain by a diverse magnetic terrane, including Miocene flood basalts of the Columbia River Basalt Group and 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. Flying was conducted 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 25,600 line-kilometers were acquired over an area of approximately 8975 square kilometers of Oregon and Washington. Survey procedures are described in detail in the document, CascadeLocks_tech_report.pdf, available in this data release. The target 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. A fixed-wing survey over Mt. Hood and Mt. Adams requires significant increases in terrain clearance over large distances from the two edifices. To reduce terrain clearance over the majority of the study area, the Cascade Locks magnetic survey was divided into three parts: the MAIN survey was flown over the entire study area excluding the two stratovolcanoes, and the ADAMS and HOOD surveys were flown directly over the stratovolcano summits. The ADAMS and HOOD surveys were able to achieve 200-m terrain clearance directly over the summits but elsewhere deviated significantly from that target clearance, reaching 2324 m for ADAMS and 2293 m for HOOD. The MAIN survey also required significant terrain clearance over steep canyons, notably the Columbia River Gorge. Variable terrain clearance should be considered when modeling and interpreting these data. This data release includes an additional low-altitude magnetic profile (PROFILE) flown within and along the Columbia River Gorge where the Gorge crosses the study area.