Step one: Slow down. Step two: If you can't see around a curve, slow some more.
If you come speeding around a curve in the mountains and find a big rock in the middle of the road, you may wind up with a pretty banged up rig. And if it's a big boulder, well, the boulder will win.
The chances of being hit by a rolling rock are pretty small. The chances of seeing a big one in the middle of the road are a good deal better (but still pretty small). The chances of seeing smaller rocks in the road are better still, especially after rains. And even a smaller rock (say, 3 or 4 inches) can do some major damage to your tires if you hit it.
:)
Lynn