A gorge is a narrow valley with steep, rocky walls located between hills or mountains. It is typically any narrow or deep valley between tall slabs of steep rock on either side and has a source of water flowing through the bottom of the valley. Gorges are formed by the interplay of several geological processes, including erosion, tectonic processes such as vertical uplift and cavern collapse. Erosion by the resident body of water is usually the primary contributor to gorge formation. Rivers carve gorges as they pass over the land by carrying rocks and soil away. The continuous flow of water and abrasion by debris in the water eventually cuts a deep trench through the landscape that exposes many layers of rock. Glaciers can also dig gorges into the land as they advance and retreat. These glacial gorges fill with water and become rivers, which in turn remove more rock and soil to form even deeper gorges. Gorges are usually located between mountains, hills or near-desert plateaus, at the point where a river cuts a channel into the land. Gorges, valleys, and canyons can be quite similar but their characteristics, composition, the ways in which they are created and where (the regions) make the difference in name.