The film was initially titled Guns of Rio Conchos, after the 1964 novel by Clair Huffaker upon which it was based. Twentieth Century-Fox Film Corp. optioned the book in spring 1962, as stated in a 16 May 1962 DV item, and filmmaker George Sherman, who’d recently collaborated with Clair Huffaker on the 1961 film The Comancheros (see entry), was brought on to produce and direct. John Wayne was named as a potential leading man, and while a 14 Jun 1963 LAT brief reported that both Wayne and actor Gregory Peck had signed on, neither remained with the project.
       An item in the 19 Dec 1963 DV made no mention of George Sherman’s former involvement when it announced that Gordon Douglas and David Weisbart had been hired to direct and produce, respectively. A month later, a 14 Jan 1964 DV brief noted that Stephen Boyd might join the cast.
       Principal photography began on 16 Mar 1964 in Moab, UT, according to that day’s DV. Four weeks of exterior shooting in Moab was cut short by inclement weather. Filmmakers arranged to shoot interiors on an improvised soundstage at a Moab Airport hangar, the 27 Mar 1964 DV reported. However, “snow and extreme cold” forced the cast and crew to move to Los Angeles, CA, earlier than planned, on 6 Apr 1964. Two weeks of interior shooting in Los Angeles were set to precede a final ten days of shooting back in Moab. On 8 May 1964, a DV item confirmed that production had returned to Moab. Location scenes were also filmed in Monument Valley and elsewhere in Arizona.
       Richard Boone was injured on set when a pony “bolted and dragged the actor nearly 100 yards," the 8 May 1964 DV stated. Boone was hospitalized overnight for bruises and lacerations, prompting Douglas to rearrange the shooting schedule so that Boone would only appear in “long shots” for the few days following the accident. Around the same time, cast member Edmond O’Brien endured an eye injury that required an emergency flight back to Los Angeles for treatment at Cedars-Sinai Medical Center, according to the 13 May 1964 DV. Principal photography wound the first week of Jun 1964, “several days behind schedule because of weather problems,” as noted in the 9 Jun 1964 DV.
       The world premiere was scheduled to occur on 23 Oct 1964 in Cleveland, OH, the hometown of cast member Jim Brown, a professional football player who made his acting debut in the picture. The 12 Nov 1964 Los Angeles Sentinel claimed that proceeds from the event would go to the American Cancer Society’s Ohio division, of which Brown was a co-chairman. A Los Angeles, CA, opening was set to follow on 12 Nov 1964. Coinciding with the film’s debut, Gold Medal Books planned to release 400,000 paperback copies of Huffaker’s novel, according to the 13 Aug 1964 DV.
       For the role of “Rodriguez,” actor Tony Franciosa (a.k.a. Anthony Franciosa) received a Golden Globe Award nomination for Best Performance by an Actor in a Motion Picture – Drama.
       The cast was said to include Bob Adler , Jorge Moreno, Robert Contreras, and Abel Fernandez, according to the 9 Apr 1964 and 30 Apr 1964 issues of DV. Also, a 5 Nov 1964 LAT item noted that 200 Navajo Indians appeared in the film as Apaches.