The fight on the top of the train was performed by stuntmen Howard Curtis, doubling Charles Bronson, and Tony Brubaker, doubling Archie Moore, and was directed by stunt coordinator Yakima Canutt, his last screen credit in a career that lasted 60 years and included directing the chariot race in Ben-Hur (1959).
Railway scenes were shot on the Camas Prairie Railroad around Lewiston, ID.
Although set in Nevada, the film was shot in Idaho and Arizona.
At one point Nathan Pierce refers to Maj. Claremont as Colonel, to which Claremont replies, "Major." In Alistair MacLean's original novel, Claremont's rank is Colonel.