Further downstream, the First, Second, and Third Canyons were also unaffected by the direct power of glaciation. The canyons of the Nahanni River are somewhat unusual as a result. Usually when a river erodes the land, forming a valley, the valley takes the form of a V shape. The effect of glaciers on these V-shaped valleys is unmistakable, leaving a steeper U-shaped valley. Because the Nahanni's course was already established before the mountains rose, it formed steep canyon wall that plummet hundreds of feet to the river's edge. Relatively untouched by glaciation, these canyons continue in their ancient state.