www.gull-research.org

I am pretty sure this is a 1st winter Western Gull pictured in San Francisco in March but would appreciate any input please.

I can see the resemblance, but I doubt that this is a pure bird.
The plumage is rather pale overall for a 1st-cycle Western Gull in March. Especially the primaries look paler than usual.
Note also that a few juvenile scapulars have been retained, which is unseasonally late.
My guess would therefore be that this bird shows influence of Glaucous-winged Gull.

Interesting and very helpful thank you. It was the fact that the bird was noticeably more pale than other Westerns present that made me unsure about this one especially as I have very limited experience of this species. Also when trying to firm up IDs of my shots that day using mainly Olsen/Larsson there seemed to be more pale edges to the inner primaries than would be expected on a similarly aged Western. Unfortunately I could not get a shot of another standing young Western for comparison - lots of beautiful adults were very obliging though as were the Mews.
Thanks again.

Another shot of the same bird - a little more head-on.