The shoot marked the last time that anyone was allowed to climb the "Totem Pole" in Monument Valley. In return for permission to film there, climbers with the production had to remove all of the pitons, which had accumulated from years of climbing, on their way down.
Clint Eastwood did all of his own stunts, including the scene where he cuts his safety line over a drop of at least one thousand feet. The only stunt he did not perform was a 2500-foot drop, for which a dummy was used.
Many of the names of characters were originally inside jokes; for example, in the novel the full name of the character 'Dragon' is 'Urassis Dragon' ("Your Ass is dragging"). Also, Hemlock (the name of the assassin) is a poison.
This is the only film that John Williams has scored for Clint Eastwood. He was suggested by the studio and the producers of the film, Richard Zanuck and David Brown, after Jaws and because Williams knew that Eastwood was a huge fan of jazz; he did incorporate that style into his score which also features a classical. more traditional orchestral sound.
In the car-chase scene, where Hemlock is being pursued along a cliff road by Miles Mellough and his bodyguard Dewayne, there was so much dust that Dan Howard, who played Dewayne, could not see where he was driving. To compensate, he drove looking up through the sunroof and followed the ridge line above. While effective, this driving method so unnerved actor Jack Cassidy that he demanded his stunt man take his place in the car.
Before being attached as the director, Clint Eastwood originally asked his friend Don Siegel to direct the film as he personally felt that he wasn't capable of directing an action film with dangerous stunts like this one had. After a long positive talk with Siegel, Eastwood took the reins as director.
In this movie, George Kennedy has a daughter who had been a drug user. In real life, George's daughter Shaunna was a chronic drug offender. George adopted Shaunna's daughter Taylor in March 2000 when Shaunna was declared an unfit mother.
Two custom 1975 Ford Broncos were specially built for this film, the one used in filming and a support vehicle, similar to the film truck but with a powerful winch and a much better sound system. The support truck is privately owned, while the film truck's fate is a mystery.