Continuity mistake: The white handkerchief in the breast pocket of McCready's dark suit, which he wears throughout the film, changes position in just about every indoor/studio shot when it cuts to an outside shot. At one point it disappears altogether.
Revealing mistake: Whilst Spencer Tracy is driving the Jeep through the desert at high speed, during one of the long shots the rough terrain causes the vehicle to bounce violently; if you look carefully you can just make out the stunt-driver's "missing" arm coming out from beneath his jacket to help wrestle with the steering wheel.
Continuity mistake: During the desert chase sequence, when our hero is run off the road by Ernest B. his missing arm is momentarily transposed when he steps from the jeep.
Factual error: The opening scene shows Spencer Tracy on a crack streamliner in the desert east of Los Angeles, featuring red and orange coaches. Such equipment was used by the railroad on only two trains, neither of which crossed the desert east of Los Angeles, and both of which had matching red and orange locomotives. In the film the train is pulled by a dark gray locomotive normally used only to haul freight, and in a close-up shot the number in the locomotive is preceded by an X, which in the language of railroading refers to an extra train.