Looks good for a California Gull to me. My points of reference are--- black and red spots near the tip of the bill, dusky brownish-yellow eye, what looks like dark gray wings and the obvious down-turned gape. I'm only going by my reference guides so wait for a more experienced birder.
Seems to match the description for a Willow. Shallow forehead, peaked crown, indistinct eye-ring, medium bill with orange lower mandible, dull wingbars and short fat tail. I'm not an expert. (Also, Alder would seem to be rare at this location.)