Visible crew/equipment: During the final montage, in the shot flying under the Golden Gate Bridge, a piece of camera machinery can be seen spinning in the right third of the frame. Evidently the camera was inside a protective box with a transparent pane at the front. The Sun is in front of the camera, shining brightly, and the illuminated camera is reflected in that pane.
Revealing mistake: During the fight at the river pirates land base, Jimmy Stewart throws a small keg of gunpowder at a fire. Seconds later there is a very large explosion. Frame by frame slow motion reveals that the keg hits the log behind the fire and totally shatters spilling its contents over the fire and nearly putting it out. Had the keg contained gunpowder it would have instantly caught fire.
Continuity mistake: Approximately 46 minutes into the film, Robert Preston is testing a new bullwhip. The whip is in his left hand as he brings his arm back and cracks the whip. He brings the left arm back for a second crack, and the shot changes to a closer angle just as he brings the whip down, only now it is suddenly in his right hand and not the left. The editing, the sound effect, the arm swing all seem perfectly coordinated, except that the whip changed hands between camera set-ups.