The amount of men involved in the Mormon posse is not consistent. The posse started with 9 men. Cullen killed 1 en route to Cheyenne, which would leave 8, but 7 were shown in pursuit. In the city, it appears Cullen and crew killed 5, which left 2 Mormons (made sense when 1 came from behind to knock out Cullen). But later Cullen is shown being escorted by 4 Mormon members. Inconsistent.
The is no known 'Fort Smith" in Wyoming. Fort CF Smith is in Montana. North of the state of Wyoming. Mormon's did pass through Wyoming on their traverse between Illinois and Utah in the mid 1800's They didn't settle there, and were not a necessarily disagreeable people despite their mistreatment due to their differing religious beliefs.
Cheyenne is not in the mountains of Wyoming. It could be said to be in the 'foot hills' but actually is in the plains on the run-up to the Rockies from the east, and part of 'Buffalo Country'