A gorge is a narrow valley or chasm that has near-vertical sides.

A gorge.

Most gorges have been cut by fast flowing streams, often following a line of weakness in the rocks. A gorge is normally as wide as the river that flows in it, because the rate at which the river cuts into the rock is far greater than the rate at which the sides can erode to form a normal valley. Gorges are very common where rivers flow in glacial areas, and where they flow through deserts. Desert gorges are known by a variety of terms including box canyon (U.S.) and wadi (North Africa).