The Corps of Discovery descended the Columbia River in five dugout canoes made from pines felled at the mouth of the North Fork of the Clearwater River in Idaho. Before McNary Dam harnessed this segment of the Columbia, the river plunged through the fierce Umatilla Rapids. William Clark observed banks of mussel shells there and called it Muscle Shell rapid. As the canoes carefully shot the rapids, Clark climbed a nearby cliff and discovered a high snow-covered mountain, which he incorrectly identified as Mount Saint Helens; it was actually Mount Adams. The sight of the snow-capped peaks of the Cascade Range, some named by George Vancouver in 1792, showed that the expedition was approaching charted territory.