At one point, Cora Dufrayne (Telford's girlfriend) is trying to seduce gunslinging anti-hero Reb Kittridge. And, when he mentions having been driven out of Arizona, New Mexico, and Wyoming, she replies: "You're running out of states." Wyoming, however, did not gain statehood until 1890. While Arizona and New Mexico remained territories until 1912.
The song "The Boys in the Back Roon" was written in 1940 and first sung by Marlene Dietrich in the film "Destry Rides Again" (1939), but is not an authentic song from the 1800s, just another Hollywood fantasy.
When Audie Murphy tells Jesse White to turn his chuck wagon around to avoid the grass fire, a pair of arms can clearly be seen behind White and in the back of the wagon, holding the real reins to the horse team.