Clint Eastwood preformed the sequence where his character hangs off the side of a mountain by a cable himself without the use of a stunt double. Eastwood later told film critic Roger Ebert, that during the film's release, he donned a disguise and slipped into a screening of the film to judge the audiences reactions. To Eastwood's dismay, during the sequence a woman sitting in front of him asked her friend, "Gee, I wonder how they did that?", to which she responded, "Special effects."
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 twenty-five hundred-foot drop, for which a dummy was used.
This shoot marked the last time that anyone was allowed to climb the "Totem Pole" in Monument Valley, Arizona. 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.
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.
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 D. Zanuck and David Brown, after Jaws (1975), and because Williams knew that Eastwood was a huge fan of jazz. He did incorporate that style into his score, which also featured a classical, more traditional orchestral sound.
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.
In the vehicle chase scene, where Jonathan Hemlock (Clint Eastwood) was being pursued along a cliff road by Miles Mellough (Jack Cassidy) and his bodyguard Dewayne (Dan Howard), there was so much dust that Howard 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 Cassidy, that he demanded his stuntman take his place in the vehicle.
Clint Eastwood seriously considered abandoning the project after the death of climber David Knowles. However, he decided to continue on with the film so that Knowles' death was not in vain. There were several accidents, injuries, and mishaps during the filming of the climbing sequences, that were not reported to the media.
Brenda Venus was twenty-five-years-old when she played the role of "George". She became the pen pal, then lover and muse, of writer Henry Miller. She also became a successful author, writing books giving advice on seduction for men and women, and a regular column for Playboy Magazine.
According to local climber and mountain guides, when looking out and down the Eiger north face from the excavation tunnel's opening for the first time, Clint Eastwood cringed back onto safe ground saying "Let's get the sh..t out of here!"
Director Clint Eastwood used original oil paintings borrowed for the film. The piano nocturne in E flat major opus 9 number 2 by Chopin is during the Wormwood scene. The Pissarro painting on the black market is "Woman Digging in an Orchard" 1882. The sports car at Bowman's climbing school is a Bizzarrini 5300 GT. Eastwood is a jazz fan and Mellow Miles is the title of an album by Miles Davis. "Screw Marlon Brando" was about Brando, who supported Native American rights. The beer at the hotel and with Pope is Feldschlossen Original Lager. An alpine föhn wind forced the climbers to retreat.
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.