A narrow gorge is a deep, steep-sided RAVINE with a small opening at the top. A DEFILE is a narrow passageway between mountains or hills, often with a river running through it. A GULCH is a narrow, steep-sided RAVINE or canyon, usually dry or containing a small stream. Finally, a CHASM is a deep, steep-sided crack or fissure in the earth's surface, often with a river running through it. All of these terms refer to a narrow gorge, which is a deep, steep-sided RAVINE with a small opening at the top.