If you are traveling through during wet or snowy times you should keep a close eye out. Rocks can and do roll onto road and have been known to hit cars or take out undercarriages. It doesn't happen too often but it does happen.
A few years ago we were in Sacramento Ca. on new years. Theweather got very bad and we heard I80 was closed back to Reno. Turns out the whole side of the mountain let go and the rocks and mud were bad enough that it knocked cars out of there lanes and even trapped someone. I have also had to dodge smaller rocks in the mountains but never as bad as that
Chris