California Gull
The first impression you get of this bird is its long lean look. The bill is long and thin, with a distinct dark band near the tip. The body is fairly slender and the dark wings appear very long. Despite the strong light in this photo, you can still make out the bluish gray color on the joints of the yellowish legs.
Western Gull
Two words: Bulky and Dark. The bill is very thick. Although shades of gray are very hard to judge in photos, the mantle color of this bird seems pretty dark. The tertials are blackish. The primaries and tail are black. This much contrast on a large pink-footed gull points toward Western.
Glaucous-winged Gull
Like the other age classes of Glaucous -winged Gull, this bird shows a general lack of contrast. The mantle is a little gray, the primaries are a little brown, but everything on this bird blends together really well. A Glaucous Gull would show lighter primaries, while a Western hybrid would show much darker.
Ethical Birder 