This is a great classic John Ford Western, starring John Wayne, Henry Fonda, with a bit part by a taxidermied Gila Monster.

John Wayne and Henry Fonda are US Cavalry officers whose troops just fought a band of Apaches and rode to a trading post on a reservation for the Apaches. There we see a dead Gila Monster mounted and hung above a doorway.

One of the filming locations listed on IMDB is Goulding's Trading Post, Monument Valley, Utah. It might have been the location with the stuffed Gila Monster which would mean that it wasn't added just for the film. (Though Gila Monsters are not found in Monument Valley, so it would have been brought there, probably from Arizona.) The trading post is still there, now called Goulding's Trading Post and Museum. I've been through there a few times but I don't remember stopping there. Next time I'll check to see if the Gila Monster is still around.