This brown juvenile gull looks like a Thayer's Gull (darker brown primaries with frosted edges, solid-centered tertials, small rounded head). However it seems large-bodied and large-billed, so it could be a hybrid Herring x Gloucous-winged Gull (also known as Cook Inlet Gull, named for a location in Alaska where many of these hybrids originate). If it were a Thayer's, the large body would indicate male gender. Yet the head may be too round for a male. If it were the hybrid, the small head indicates female gender. The very long wings is a strike against the hybrid theory, as neither parent is particularly long-winged. So, the most likely identity is a small-headed male Thayer's Gull. The three identifiable adult gulls on the left side of the photo are three different species: California, Ring-billed, and American Herring, from front to back.