California Gull
Larus californicus
Adults are similar in appearance to the herring gull, but with brown eyes, yellow legs, and a more rounded head. The body is mainly white with grey back and upper wings. The bill is yellow with a black ring and red spot near the tip. They have black primaries with white tips. Immature birds are also similar in appearance to immature herring gulls, with browner plumage than immature ring-billed gulls. Length can range from 46 to 55 cm (18 to 22 in), the wingspan 122–137 cm (48–54 in) and body mass can vary from 430 to 1,045 g (0.948 to 2.304 lb).
ID text from Wikipedia, CC BY-SA 4.0
Common Gull
Larus canus
Adult common gulls are 40–46 cm (16–18 in) long and a wingspan of 100–115 cm (39–45 in), noticeably smaller than the herring gull and slightly smaller than the ring-billed gull. It is further distinguished from the ring-billed gull by its shorter, more tapered bill, which is a more greenish shade of yellow and is unmarked during the breeding season. The body is grey above and white below. The legs are yellow in breeding season, becoming duller in the winter.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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