Bill Tyler (Charlton Heston) is an argumentative, curmudgeonly mountain man. Henry Frapp (Brian Keith) is Tyler’s good friend and fellow trapper. Together, they trap beaver, fight Native Americans, and drink at a mountain man rendezvous while trying to sell their “plews”, or beaver skins, to a cutthroat French trader named Fontenelle.
Tyler looks for a legendary valley, in Blackfoot territory, “so full of beaver that they just jump in the traps.” Running Moon (Victoria Racimo) leaves her abusive husband, a ruthless Blackfoot warrior named Heavy Eagle (Stephen Macht), and comes across the two trappers in the dying days of the fur trapping era. While at first Bill only wants to take her to safety at the rendezvous, she eventually becomes his woman. While trapping Bill and Henry are attacked by Blackfeet and Henry is scalped by Heavy Eagle in front of Bill. Bill runs back to camp and he and Running Moon flee only to be caught. Later, Bill (thinking Running Moon has also been killed) is given a chance to run (similar to the real life event of John Colter) and is chased by warriors whom he initially eludes by hiding in a beaver den. They pursue him until he and Heavy Eagle fall into a raging river. Heavy Eagle makes it to shore and Bill goes over a waterfall. Heavy Eagle tries to make Running Moon his woman again which he cannot do. He knows Bill Tyler survived and will come for her as he had done.
On his survival trek Bill comes across Henry who had survived the scalping and eventually learns that Running Moon is still alive. He and Henry set out to rescue her while they are followed by a pair of trappers (Cassell and Lucking) also looking for the valley of beavers.
The story takes place during 1838, although it’s never stated in the film, based on the fact that the beaver market was declining and the rendezvous was held on the Popoagie River. The “Era of the Mountain Man” ended two years later.
The story was written by Heston’s son. The film was Lang’s directorial debut. This was Victor Jory’s last film. John Glover’s character Nathan Wyeth (John Glover) was clearly inspired by the historical Nataniel Wyeth, a New England ice merchant who pioneered the marketing of Northwest salmon. Keith’s character Henry Frapp could have been inspired by Henry Fraeb, a nineteenth century trapper and fur trader.