I've been in Oceanside, Tillamook for a couple weeks visiting family.
On the coast are many gulls, the great majority of which are Western. Some California, fewer Ring-billed, and a few Heermann's and Glaucus-winged. The GW I see generally show evidence of blending with Western. Two weeks and I've seen just a single really pure looking GW.
Nine miles east in the town of Tillamook are a good number of gulls, 100% of them so far are very 'pure' looking Glaucus-winged. I mean of the sort one might see in Alaska. Most of these are adult. I have yet to see a different species. There were half dozen in the Safeway Parking lot; all GW. This is an inland location (though granted not far from Tillamook Bay and Netarts Bay waters).
I always presumed Glaucus-winged are as Marine as Western.