Where in California was this? Some areas have high concentration of Olympic hybrids. The best thing to look for his wing color. A GWGU should have wingtips that match the color of the mantle, or close to it.Olympic hybrids will have darker wing tips. Some areas actually have a higher chance of herring- glaucus hybrids. The gene pool can get very messy in gulls on the West Coast. It’s hard to say for certain with these photos.