All In response to my request, 3 people kindly sent images of the slaty-backed gull. One had a nice head shot of it. This photo matches the pattern I saw on the individual I saw last Thursday at Northridge Lakes so I'm confident that the bird I saw was indeed the slaty backed, which I hereby dub Smudgy.
Greg Seegert Beaver Dam....til next week
BTW, if anyone is interested, I limited out on whitefish both last Fri and Sat. Might have enough ice for one more trip.