The prison set took seven weeks to build. When construction began, it was snowing. When it ended, the temperature was 100 degrees. Upon completion of filming, the entire set had to be removed and the area it occupied restored to its original pristine state so that no trace would be left.
Hume Cronyn was diagnosed with optic cancer, which required the surgical removal of an eye. Cronyn volunteered to work past 5 p.m. and revamp his shooting schedule so he could finish up his role as soon as possible. Although the situation was very stressful for director Joseph L. Mankiewicz, Cronyn handled the situation very professionally.
The Warner Brothers front office was very worried about this film. It was shot over a five-month period in the first half of 1969, but it was well over a year before it was given any commercial showings. Like Joseph L. Mankiewicz's previous film, The Honey Pot (1967), it opened in Britain some two months before the US, in late 1970. According to Mankiewicz's biographer, Kenneth Geist, his preferred version of the film ran to 165 minutes; however, Warner Brpthers objected to this and re-cut the film, to his great irritation, to a more manageable 126 minutes. One notable casualty of this re-cutting was the prominently-billed Lee Grant, a very well-known actress at the time, whose appearance is now barely a couple of minutes in length.
Much of the filming was done in the Joshua Tree National Monument, 50 miles northeast of Indio, California. This was the first time a movie was allowed to be filmed in the 500,000-acre National Park. The location was so remote that a wagon-rutted road had to be bulldozed and widened for a distance of three miles to provide vehicular access.
Twelve rattlesnakes were used for a key scene but failed to hiss on cue. The hissing had to be dubbed in during post-production.