I've lived in Washington State my whole life and am completely unaware of any iconic dishes. Maybe apple pie . . .?
Same here - 61 years next month.
I picked the cedar planked salmon simply for its advertising value. I've never had it, or geoduck for that matter. I can think of a lot of things I've eaten growing up that are spectacular and regional; but they all fly well below the radar.
The most common and overlooked would be Dungeness crab and the Pacific oyster. The best fish I've ever eaten was river caught steelhead. There is simply no comparison to any other fish I've eaten.
I could go on and on about the PNW food, but you'd have to have lived here for a long time to get any meaning out of it.
Not sure that's a good thing or not. Maybe it's best that some things are forgotten...