Shot in 21 days.
Matthew Fox has said that he enjoyed making this movie more than any other film, and always wanted to be in a western.
The cave set in the last act of the movie was the same cave set used in Iron Man (2008) where Tony Stark is held captive and constructs the first iron man suit.
At Fantastic Fest, S. Craig Zahler said that he wanted much of the film's mysticism to remain ambiguous and debatable.
The final movie represents the first draft of the script.