The Redwall Limestone is very hard stone, which causes it to break down at harsh angles, creating pillars such as these. NPS Photo by Kristen M. Caldon

Redwall Limestone - thickness: 500-800 ft.

The Redwall Limestone forms distinct red cliffs about mid-level in the canyon. It was deposited 340 million years ago, during the Paleozoic Era - Late Early to Middle Mississippian Period.

The Redwall Limestone was deposited in a shallow to deep sea environment. A variety of fossilized sea life is preserved within the formation, including brachiopods and crinoids.

Although its name implies that the Redwall Limestone is a red rock, it is in fact a gray stone. It gains its reddish appearance from the rocks above.

Both the Supai Group and the Hermit Formation are red in color due to their high iron oxide content. Over time, rain has continually washed these eroding red sediments over the Redwall, staining it red.

The Redwall Limestone contains thousands of caves. Limestone is a water soluble rock, meaning that it can be slowly dissolved by water, eventually resulting in caves of various sizes.

Many animals, such as the California condor, now make these caves their homes, just as giant Shasta ground sloths made them their homes 11,000 to 20,000 years ago.