Iron Mountain Trail.

Rex Allen and Slim Pickens are sent from Washington, D.C. to California in 1850 to speed up deliveries of mail to the goldfields, and find a destructive feud raging between two stage-line owners, Sam Sawyer and John Brockway. In their attempts to have their stages and drivers first on the dock to get the mail brought East by ship, the two have damaged each other's equipment and schedules to the point that no consignment of mail reaches the goldfields intact or on time.