Though it's never explicitly stated in the film, the story takes place during 1838. This is 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.
During the chase sequence, after Heavy Eagle passes a rock on the top of a ridge and goes to the left of the camera, a bush is moved violently at the bottom right of the screen, clearly by someone off camera.