The terrain along the northern Parkway differs from that further south. Here, the land is rocky. Erosion is at work . The combined efforts of the stream, rain, and plants form a powerful force. Bedrock is being reduced to boulders, and boulders to stone, gravel, and sand. The eroded bedrock is then washed downstream. In the flatlands along most of the Parkway, sediments carried downstream settle out and come to rest, forming a soft, silty bottom. But a glance at the rocky streambed of Sweetwater Branch provides a vivid lesson in erosive power and undercuts the notion of “solid rock.”
National Park Service
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