thousand feet more, with the production of a narrow gorge having precipitous walls, not yet widened into a mature valley. Channels like that of the Colorado also occur crossing submarine plateaus.
The short tributaries of these high plateau valleys may be likened to gigantic washouts. Such short, deep valleys commonly form at their heads amphitheaters, which may be a few miles in length, as is illustrated in Plate II. These are sometimes so precipitous