OK, so here's what we (may) have so far. Our hero (in the campaign hat) retrieves two bodies from their cabin, lashing them to his own horse and walking them out. The two corpses were presumably the two guys in the ghost images in the background, implying that they rode together for a while. Their hats could also be campaign-style, although not as certainly as our hero's hat. SO it looks like all three may have ridden together at some point.
Wagga says the hat is not Mountie or Ranger, but did not say it is not US Army, which I also suggested, so let's assume that's what it is. The saddle also suggests military, not a Western/stock saddle. This is further suggested by q's ID of the VFW insignia.
SO we have three Army vets, either Spanish American War or WWI, or Villa campaign, cavalry probably . Could be as far back as war w/Mexico, although the possible Montana crease in the hat suggests not. So its early 1900s, but maybe as far back as 1850.
One alive, maybe returning to the camp where all three hung out, (Hunters, trappers, prospectors?) or maybe going to look for his buddies. In any event, he finds them dead. Murdered, no doubt, since there is a hanging involved later. Returns the bodies to civilization, for decent burials no doubt. Then goes after the killer.
Sounds like FRB or one of his buddies, BP or the other guy, whose initials are too famous to mention,, but I can't find anything in his or their bios to match up with it. FRB retired to California, Three Rivers, in fact, but I think it was a vacation to SF in BCATSK.