Continuity mistake: At the start in the wide shot of town, when the stage coach enters town three horse back riders pass the coach. The very next shot from the town shows the riders now trailing the coach.
Revealing mistake: When McKay and Ramon are riding into Blanco Canyon to rescue Julie, you can see a diesel loading shovel with its bucket raised in the bottom of the frame of one of the scenic shots. Presumably the scene was shot in a quarry and they didn't get all the equipment out.
Continuity mistake: When Jim tries to ride "old Thunder" he bucks off and brushes all the straw out of his hair. Seconds later it is back.