Long, long ago an old Indian chief was about to die, so he called for Geronimo and Falling Rocks, the two bravest warriors in his tribe.  The chief instructed each to go out and seek buffalo skins.  Whoever returned with the most skins would be chief.  About a month later Geronimo came back with one hundred pelts, but Falling Rocks never returned.  Even today as you drive throughout the West you can see signs saying:

WATCH OUT FOR FALLING ROCKS.