The Puget Sound subspecies has a yellow or yellow-orange bill, and a back pattern of blackish-centered feathers with buff edges; Gambel's has a orange or orange-pink bill, and a back pattern of reddish-centered feathers with light gray edges. Puget Sound White-crowns are much more common than Gambel's in the San Francisco Bay Area, but I photographed a Gambel's at the same spot in my back yard two days later, see http://www.pbase.com/image/75046702 .