Mile 20-30 - Roaring Twenties Rapids
As the Colorado River cuts deeper into the canyon’s geologic strata, Redwall Limestone begins to appear along both shorelines. This limestone represents an ancient deep-sea environment from 350 million years ago. Many fossils abound in the Redwall, perhaps most notably, conically-shaped nautiloids that once roamed the world’s oceans. Due to the hardness of the limestone and it’s resistance to erosion, rapids are larger and more frequent in this section. Because of the abundance in whitewater activity during this ten mile stretch, river runners refer to it as the Roaring Twenties.