[EBB Sightings] Lake Merrit - Slaty-back Gull

I stopped briefly this morning just after 9 a.m. to
look for the TUFTED DUCK. After a while I found him
swimming around the first island w/ a group of Lesser
Scaup.
In the fenced enclosure (the Rotary Nature Center) a
gull caught my eye. I looked it over for 10 - 15 secs.
to make note of field marks before I got out my
Sibley's guide. It was a near perfect match w/ his
illustration of a 2nd cycle SLATY-BACKED GULL. Here
are a few field marks of the gull -

Size - about the size of a med. Western or Herring;
stocky
Mantle & Scapulars - solid, med. dark gray
Coverts & Tertials - tan/creamish w/ light markings;
the tertials had broad light ends
Primaries - solid dark med. brown; no spotting on tips
or light edges
Tail - dark
Legs - darkish pink
Bill - medium large, smaller than other gulls its size
I've seen, w/ smallish gonydeal angle; it was mostly
dark w/ a little light color around the base, mainly
on the lower mandible
Head/eye - I remember a shadow around the top of the
eye w/ a sort of thin, dark "eyebrow".

After I opened my guide, took a look, then looked up
again, the bird had disappeared. I had limited time,
but couldn't refind it in the immediate vicinity.
Hopefully someone else has or will see this bird since
I got no pics (didn't want to lug the camera out in
the drizzle).

Joe Devine
Modesto, Ca