A valley is a landform characterized by a low-lying area of land surrounded by high areas, such as mountains or hills. Valleys can be a wide variety of shapes and sizes. They are either erosional features, carved by water or glacial ice, or structural features, caused by rifting. A canyon is a type of erosional valley with extremely steep sides, frequently forming vertical or nearly vertical cliff faces.The term “gorge” is often used interchangeably with “canyon” and generally implies a smaller, particularly narrow feature.