Jerry Friedman

A towhee would have a thicker bill, since towhees are a kind of sparrow.

The tiny stubby little tail is also a good clue for Winter (or Pacific).

Those streaks are darker and less rufous than is typical for Sharpie. And "thin" probably isn't the right word. The people at the Raptor ID group on Facebook say "teardrop-shaped" for Cooper's, meaning exactly what your bird has--feathers with a dark spot and a dark shaft.

I mean, if it's a pure Snow. If it's a hybrid with white wingtips, would that probably be a hybrid with a domestic goose?

Shouldn't we be able to see black wingtips from this angle?

That's not actually the alula. This picture of a Red-tail shows both alulae, with a bonus king snake. The alula goes outboard from the "wrist", but the patagial mark is inboard of it. I think the left alula may actually be visible in "Art's" picture as a slight notch along the leading edge. While I'm at it, I'll say that Ferruges do show up in central N.M., but your chances are much better on the eastern plains.

No, the patagial bars make it a Red-tail--a juvenile with yellow eyes and apparently no rufous in the tail. If you want to see Ferruginous Hawks in New Mexico, try Las Vegas NWR. (And I've been sniped.)

The only new comment is from Shane Brown: 'The lighter “pants” than upper breast and largely white undertail coverts are neat for such an otherwise dark intermediate-morph. The wing linings are kinda light, too.'

I'd go with the first--whenever you're sure it's Larus, which I'll bet is pretty often, report it as Larus sp. with supporting material (which in my opinion could be just one or more photos, but maybe you prefer to add comments even when you have definitive photos).

Are people using "back" to mean the background or the back of the line?

People unsure of gull IDs haven't been able to eliminate the other genera or haven't thought about it? I imagine a lot of gull sp. reports have been of distant, quickly glimpsed, obscured, etc., birds whether the observer only knew it was a gull, not situations like this where only one species and two hybrids are being considered. Incidentally, I've just decided that when you report a sp., there should be a way to attach a link to a species you're (pretty) sure is involved, the way people here say "Glaucous-winged thing". That way future ornithologists could search for weird or hybrid forms of the species. This species would be reported as "Larus sp., Herring gull involved".

Yep. Also you get some information on where the bird is from, which is useful to ornithology if you report it.

Looks good to me. I don't know if anyone claims there are Northerns that color.

I'd call it a Coop. Head well clear of wings, straight leading edge to wings, body widest in the middle, outer tail feathers significantly shorter than the others, obvious white tip to the tail.

Great! And no problem about the time. Also, you should never apologize for birding... at least not here. I put them on Facebook. It's always good to include lots of shots that show different things.