When Marshall and Mary are driving across the desert (supposedly toward El Paso), two consecutive shots of Marshall show the same sign (back of sign) behind him through the truck window, though in between the camera shows Mary responding to his lines.
The road from Albuquerque to El Paso, Tx is shown as a rural empty 1 lane highway curving thru flat high desert terrain. In reality, Interstate 25 is a large, mostly straight, 2 lane major highway, well traveled, with terrain nothing like was shown in the scene.