"That stereotypical Western backdrop isn’t typical of the West.
...
Towering red rock formations and big blue sky make up the classic backdrop of the American West. But the rocks we see in so many movies aren't typical of the area at all. In fact, they are unique to one place: Monument Valley.

Monument Valley is on the Utah-Arizona border inside the Navajo Nation Reservation, and until the 20th century, it had barely been visited by non-indigenous people. But when John Ford made Stagecoach — the 1939 blockbuster that mainstreamed Western movies and the actor John Wayne — that all changed. More filmmakers followed suit and used the location as their movie backdrop, creating a deep association between Monument Valley’s iconic landscape and the mythic American West..."