First thing is go to any fish and wildlife office and get the gold and fish book, or you can download and print (will take quite a few sheets). That is the end all "bible" for WA. Got to have it with you, at least in the vehicle if checked.
Next, look at the online guide for the claims available. Also get in touch with a chapter near you. Lot of knowledge to be had, most are more than willing to help, just have to show up and ask.
Don't know about the other chapters up there, only had interaction with the Southwest chapter in Vancouver, great bunch of folks.
If you're down south, can suggest Cape Disappointment. Gold in the black sand on the beach, but is super fine and tough panning.