Heermann's Gull

This is the Heermann’s Gull in breeding plumage, which is characterized by the contrasting white mark on the gray parts of the wings towards the back of the bird. Wikipedia states, "This species looks distinctly different from other gulls. Adults have a medium gray body, blackish-gray wings and tail with white edges, and a red bill with a black tip. The head is dusky gray in non-breeding plumage and white in breeding plumage. "

Nice photo of a Heermann's gull with breeding plumage.