In a Western, outlaws will lie in wait at the top of a ravine, or narrow valley, until they see a traveler entering at the bottom. Then, the outlaws will come pounding down the ravine's steep sides.
Ravines can be lonely and violent places averse to settlement as nothing can be built along their steep sides. The word ravine itself derives from the archaic rapin, which is a violent seizure of property. During times of heavy rains and snow melt, a ravine may be filled with violent, rushing water.