Pat Garrett & Billy the Kid (1973)

It's 1881 in New Mexico, and the times they are a'changing. Pat Garrett, erstwhile travelling companion of the outlaw Billy the Kid has become a sheriff, tasked by cattle interests with ridding the territory of Billy. After Billy escapes, Pat assembles a posse and chases him through the territory, culminating in a final confrontation at Fort Sumner, but is unaware of the full scope of the cattle interests' plans for the New West.