Now I’m not an expert (far from it) when it comes to gulls, but I’m going to say that this is a mature Ring-billed Gull in its winter plumage. Note the black ring at the end of the yellow bill and the yellowish legs. Heermann’s have a bright red bill (with a black ring as well) and black legs. We typically don’t get that many Heermann’s in this area (try Point Roberts in late summer) where Ring-billed’s are plentiful year round.
Someone else with more gull experience should confirm this though - it sure wouldn’t be the 1st time I was way off in identifying a gull