This layer averages about 265 million years old and is composed of soft, easily eroded shales which have formed a slope. As the shales erode they undermine the layers sandstone and limestone layers above which causes huge blocks to fall off and into the lower reaches of the Canyon. Many of these blocks end up in the side drainages and down on the Tonto Platform. The color of this layer is a deep, rust-colored red. Fossils to be found in this layer consist of ferns, conifers and other plants, as well as some fossilized tracks of reptiles and amphibians.
 
Grand Canyon Rock Layers
 

Copyright © 2001, www.kaibab.org, all rights reserved.