Putting horror in a Wild West setting is a challenge. The thing is, that time was brutal and rough so it's actually an appropriate setting for horror. Can you imagine the number of creatures that were actively out to kill you in 19th-century America?
It made sense to put werewolves into that environment since the wild nature of those beasts was a natural fit for the natural environment. From there, it was interesting to think of the types of shapeshifters that could roam these lands - would Native Americans know more about shapeshifting than white men given their deeper cultural roots in the land? How would werewolves look depending on their ethnicity? On their gender?
The clash of danger, wilderness, and dangerous creatures made for a ripe terrain of horror and mayhem. And of course, a little Wild West cowboy fun is always a bonus :)
Where do you think the horror part should come from in a Western? Can we go with classic werewolf lore or should we push further? Could the horror actually be in the humans rather than the beasts? What kind of relationship do you think there could be between werewolves, Native Americans, and the average person trying to get by on the Frontier?
Let's go Wild in this Western, shall we?