Ring-billed Gulls (easily identified by a black ring around their bill close to the tip) is a year around resident of much of the United States, including the Pacific, Atlantic and Gulf coasts.  The bird's territory extends inland from the Gulf Coast into the Midwest.  During Summer the Ring-billed Gull is found in the Upper Midwest extending well into Canada.  The bird is around 19" in length.

City Birds took this picture of a pair of Ring-billed Gulls on a sandy beach in Duluth, Minnesota on the shores of Lake Superior.  Duluth has a hilly geography quite similar to that of San Francisco.  Also, both cities have cool Summer weather with occasional hot spells.  In the Autumn the Ring-billed Gulls migrate South to warmer waters.