Washington aeromagnetic maps and data:

Online link http://pubs.usgs.gov/of/1998/ofr-98-0241/
Description Aeromagnetic surveys of Washington state, merged to form seamless grids across the state. Gravity anomaly data are provided as well.
Originators Finn, Carol A.; Brenner, K. C.; McCafferty, Anne E.; and Kucks, Robert P.
Publication U.S. Geological Survey Open-File Report 98-241

States or counties

Washington aeromagnetic anomaly map
Washington aeromagnetic anomaly map
Additional images
Washington isostatic gravity anomaly map
https://pubs.usgs.gov/of/1998/ofr-98-0241/iso_mag.gif