When Briggs threatens Marshall with the knife his gloves appear when showing Briggs front and disappear when showing his back.
When Ruth runs to hide in the barn, she drops a crossbar to lock the doors behind her. The barn doors slid open rather than swung open, making the crossbar useless.
At 1:06, a wide shot reveals a modern paved road cut through the mountain.
Upon reaching the final town of Santa Rosa, the first frontal shot of the outlaws approaching shows a wide modern tire mark in the dirt. Additional tire marks continue to be seen in the town throughout the remainder of the film.
When Briggs starts shooting at everyone at the start of the film, he shoots a man in a white T-shirt and you can clearly see the fake blood squib that explodes when Briggs shoots him (you can actually hear the pop sound on impact).