[Birdtalk] California Gull vs Ring Billed Gull

[birdnet at skylace.net]

Is there any reliable way to distinguish
California Gulls from Ring Billed Gulls
at a distance?

The reason I ask, is that during the winter
I sat on the flyway where gulls were coming
in to spend the night on a lake. About 200
gulls came close enough for me to see the
eyes. Every gull who's eyes I could see 
had yellow eyes (ring-billed).  

The next day one of my favorite posters to
this group said that s/he had observed a flock
of California gulls at the lake.

So I went back to the lake and observed another
hundred gulls at close distance, and every
one of them had yellow eyes (ring-billed).

I think the other poster was wrong about the
identification even though s/he is very 
knowledgeable about the birds of Utah.

Beyond about 100 feet I am clueless about whether
a gull is a California Gull or a Ring-Billed Gull,
and if even an expert goofs I wonder if eBird might
benefit from a California/Ring-Billed category?