This is the only movie that John Williams has scored for Clint Eastwood. He was suggested by the studio and producers 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.
Clint Eastwood performed 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 movie critic Roger Ebert that, during this movie's release, he donned a disguise and slipped into a screening of this movie 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."
Before being attached as the director, Clint Eastwood originally asked Don Siegel to direct this movie, as he personally felt that he wasn't capable of directing an action movie with dangerous stunts like this one had. After a long talk with Siegel, Eastwood took the reins as director.
One climber, David Knowles, was killed by a boulder on the second day of shooting. Clint Eastwood had been in the same position just a few minutes earlier.
Clint Eastwood did almost all of his own stunts, including the scene where he cuts his safety line over a drop of at least 1,000 feet. The only stunt he did not perform was a 2,500-foot drop, for which a dummy was used.