Adults are similar in appearance to the herring gull, but with brown eyes, yellow legs, and a more rounded head.

They frequently beg for food at public beaches, parks and other locations where people will hand feed them.

[10] Although these subspecies are not well distinguishable by mtDNA allozyme variation,[11] they breed true and the low genetic divergence can be explained by separation during the Pleistocene and renewed contact in Montana during more recent times.

These California gulls now inhabit large, remote salt-production ponds and levees and have a very large food source provided by nearby landfills from San Francisco, San Jose and other urban areas, all the way up into the Sacramento area.

This population boom has resulted in large resident flocks of gulls that will opportunistically prey on other species, particularly the eggs and nestlings of other birds.

Efforts are underway to reduce habitat for this species and find other ways to disperse the large numbers of gulls.