The sets in Old Tucson are built to 7/8th scale, so the performers look larger than life.
Howard Hawks did not want to cast Ricky Nelson, whom he considered to be both too young and too lightweight, and deliberately gave him the fewest possible number of lines for a third-billed star. However, he later admitted that having Nelson's name on the poster had probably added $2 million to the film's box office performance.
John Wayne had deliberately moved away from westerns after The Searchers (1956), but none of his films since then had been particularly successful or well received. This film was a return to the genre for him.
Howard Hawks always wanted someone who would connect with teenagers to play Colorado. Reportedly, his first choice was Elvis Presley, who was enthusiastic about the opportunity. Unfortunately, Presley's manager, Colonel Tom Parker, wanted too much money and top billing. Neither Hawks nor John Wayne would have any of it, so the search continued. Presley joined the U.S. Army in March 1958, two months before filming began.