The data in this release originate from a low-altitude, aeromagnetic survey of the Centralia and Chehalis area of southwestern Washington. The survey was conducted between September 22 and October 22, 2015, by Eon Geosciences, Inc, working under contract to the U.S. Geological Survey. The covered region extends from the Cascade Range in the east to Willapa Bay in the west, and includes the cities of Chehalis and Centralia, Washington, and a part of Interstate 5. Total magnetic field values were acquired using a fixed-wing aircraft flown at a target elevation of 200 m above terrain. Primary flight lines were oriented east-west and spaced 400 m apart; additional tie lines were oriented north-south and spaced 4000 m apart. Flight lines and tie lines together represent 23,051 line-km of data.