Hi, I'm looking for help identifying this gull a friend of mine saw in Riverfront Park in downtown Spokane, Washington, USA yesterday. We're at a loss to specify it but have considered Iceland, Glaucous, Glaucous-winged, and Herring. All of these are rarities in Spokane. Glaucous and Glaucous-winged are super rare, and Iceland is much rarer than Herring. My friend says it was noticeably larger than Ring-billed Gulls close by. Specifically, he said it had about 4-6 inches more wingspan and about 4 inches more body length than Ring-billed Gulls. Would appreciate some help. Thank you!