While driving North on the only paved road out of the "Grand Canyon" national paark after veiwing the sunset there we saw a very, very bright and large white light "zoom" through the trees to our left, going South. It made no noise that I could tell. {the windows were rolled up and the stereo was playing at a moderate volume as my wifes son was a sleep in the back seat. As this white light flashed through the trees past us, going South in the opposite direction of our travel; I looked in the rear view mirror out of reflex and as I did my wife turned her head and looked over her left shoulder, out the back window. Of course we both saw the same thing. Pitch black. We looked at each other for a second but said nothing about the incident to one another till much later. ((name deleted))