Metal Detecting in WA State parks is allowed (not all but most). You need to print out and bring a form, go to WA State parks web site for the form or PM me for it.
It's true MD'ing is allowed in many WA State parks, but not at Cama Beach SP on Camano Island. Used to be a private resort, with many families returning year after year for their summer vacations. Seemed a good place to find some bits of history. Unfortunately, the National Historical Society thought so too. It's now off limits as a National Historic Place, and the rangers will enforce No Metal Detecting.
MD'ing is allowed at Camano Island State Park, just down the road from Cama Beach, unfortunately there's a million bazillion pull tabs there!