I don't know if you care for hints, but note that the leg colour is yellow. This rules out Thayer's (now rolled into Iceland Gull, sadly), Western, Herring, and Glaucous-winged. It leaves Mew, Ring-billed, and California as the expected options. I believe you can figure it out from there based on bill pattern.
Good birding,
Jeremy Gatten
Saanichton, BC