"Metal detecting is permitted at more than 67 state parks throughout Washington. Users of metal detectors must register first with Washington State Parks and comply with posted regulations. Rules are summarized in "Your Guide to Metal Detecting in Washington State Parks," available from park rangers or by calling (360) 902-8500; Telephone Device for the Deaf (360) 664-3133."
All that SOUNDS GOOD. just try it. I sat with park people in WA and read the rules to them. All I got was ,it was up to the district manager. No one ever asked before so the park people just could not figure out what to do. So you guessed it, the answere was no I could not.