When the train collides with the water tower, it is on dual gauge track, with three rails. When Grant gets up to walk along the track, it is now single gauge with only two rails.
When the gang returns to their hideout after robbing the train, Latigo holds up the bottle of whiskey he took from the train. The card players all come to the bar for a glass. When the bottle is carried to the table it is still full.
When Utica and Joey leave the abandoned mining camp during the shootout, the shadows are high on the mountain range, a sign that the sun is just coming up. The same is true when Grant, Verna and Charlotte leave after them. But a few minutes later as they ride out in the open, the horses' shadows are much shorter, as if the sun were at mid-morning height in the sky.
At the old mill during the shootout, you can clearly see an airplane contrail in the sky.
Eighty-three minutes into the film, a bullet hole suddenly appears on a steel cable car right behind Charlie as she ducks bullets with Grant. Charlie looks behind her, apparently reacting to the sound of the bullet hitting the car - but there is no sound whatsoever.
Grant McLaine finds the hideout much too easily.