A stream valley is a natural geographic formation that is characterized by a narrow and elongated depression or lowland. There are many synonyms for this term, including ravine, gully, dell, hollow, canyon, gorge, coulee, arroyo, and gulch. Each of these words captures a slightly different aspect of a stream valley, such as the depth, width, slope, or vegetation cover. Some of these terms are also associated with particular regions or types of terrain, such as the arid southwest of the United States where arroyos are common. Despite their differences, all of these words describe a landscape that has been shaped by the erosive power of water carving a channel through rock or soil.