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.
Revealing mistake: In the final scene in the belltower you can see shadows from the surrounding trees. That's because this scene was shot at 3 in the afternoon. They just used a filter to make it look like it was night.
Revealing mistake: In the opening credits, Richard Widmark is driving a car with Doris Day in the passenger seat. Widmark does not turn the steering wheel, even though the rear-screen projection shows him going around a curve.