Gorges, also called ‘ravines’, ‘flumes’ or ‘canyons’, are deep, narrow valleys with sharply steep cliffs. They are formed mostly due to the action of flowing water when a stream or a river digs into the surrounding rock. The most famous gorge is the Grand Canyon in the USA, Arizona; it is almost 1800 m deep in places. Over a period of 600 million years, the Colorado River carved the Grand Canyon by eroding the surface of the Colorado Plateaus, which are to a large extent made up of sandstone and argillite.
