I have to disagree with both you & John C, as the upper-wing outer primaries are much too dark for Glaucous-winged Gull. In addition, that species doesn't show any contrast between the inner & outer primaries. Some other species do show the pale inner 'window'.
Initial impression was a bird with a rather delicate almost 'Common Gull like' appearance. Leg colour is completely wrong for that species & is a very rare visitor anyway. I do have some ideas, but would like to confirm orbital ring colour as this could be yellow, orange & even with some red spots from the posted image. Perhaps a close-up of the head could be posted to this thread. If you have any other captures of this bird, particularly from above, then this will also help the ID process.