In my opinion, the cause was the signs warning the driver of upcoming big rock problems – FALLING ROCK – as in you should be looking up at that cliff ahead of you to see if any big rocks are in the midst of falling, thereby taking your eyes of the road and inadvertently drifting over the cliff!
All those FALLING ROCK signs should say FALLEN ROCK so that you will keep your eyes on the road and not get killed.
Joel FlemingDurango