Herring Gull was the most common answer for this bird, with Thayer's Gull also mentioned more than once. Wng and mantle color is too dark for American Herring Gull. The white primary tips are usually more extensive on Thayer's Gull, and the underside of the end of the primaries (look closely at the right wing) would appear as mostly white. I added an additional photo of this bird (next), which provides easier clues such as eye color and bill shape....but we all know that lots of the gulls we try to I.D. are sleeping individuals like this one