Image Description from historic lecture booklet: "Valleys through which glaciers pass are widened and deepened, and their walls made smoother. The deepening of a mountain valley by glacial erosion sometimes brings about a curious relation between it and its tributaries. The lower ends of the tributary valleys are much higher than the valleys which they join. Such valleys are called hanging valleys. They abound in the mountains of the western part of the United States, and in other mountains where glaciers formerly existed. The tributary may be left hanging, because the main valley is deepened by glacial erosion, while the tributary is not; or in some cases both the main and the tributary valley are deepened, but the former much more than the latter."
