Identification: The upperparts appear to be a medium gray, noticeably paler than Western Gull, but darker than Herring Gull. The upperside of the wingtip is short of being a true black, suggesting a hybrid between a species with a black wingtip and a paler wingtip. Glaucous-winged influence immediately comes to mind. The gray underside to the wingtip also suggests a four year hybrid. This is a large, thick-billed bird with dark eye and very smudgy head markings. Given the slightly darker gray upperparts, we can be confident this isn't a Herring x Glaucous-winged. Western x Glaucous-winged makes more sense and that's what it was identified as in the field.
Another image below. The pinkish orbital ring and dark eye is typical of Glaucous-winged. The stocky, bulbous-tipped bill, smudgy head markings and medium gray upperparts are typical of this hybrid combination. Note the less than black primaries here.