Yellow-footed Gull, adult: Salton Sea, California, USA - 18th November 2009: This is/was a large gull with slate grey upper-parts, not truly black, and large and obvious white tertial tips.
The black primaries are short, only extending a little way beyond the tail tip.
The eye is dark however the most striking features of the bird are the bill and legs.
Firstly the bill is bright yellow, deep based with huge Gonydeal expansion and blunt tip, in general it looks massive.
The legs are long, thick and bright mustard yellow.
Other large dark backed gulls that do occur at the Salton Sea are scarce to rare with Western Gull the most likely confusion species but it has pink legs and is actually quite rare whilst Lesser Black-backed Gull has also occured as a vagrant. So basically any large black backed, yellow legged gull seen at the Salton Sea is going to be this species.