Today my dad and I attended the 2013 Oakland A's Fan Fest. Ray Fosse and Sal Bando were there, but the star of the show was a fairly clear-cut adult 'KUMLIEN'S' ICELAND GULL (although a Kumlien's/Thayer's hybrid probably can't be ruled out). The bird showed up in the gull flock in the Coliseum's south parking lot immediately after the fan fest. It was a fairly dark Kumlien's-type, but definitely seems to fall short of Thayer's, with slaty gray wingtips, no dark bar on P5, and an incomplete dark outer web on P9. Several THAYER'S GULLS were also in the gull flock.
 
Photos here: http://www.flickr.com/photos/73989529@N02/sets If this doesn't look good for Kumlien's please let me know! (I have been known to misidentify Thayer's as Kumlien's in the past...)
 
Go A's
Noah Arthur, Oakland