Redwall Limestone

The Redwall Limestone is an erosion resistant, cliff forming rock formation of Mississippian age found across northern Arizona, southeastern California, New Mexico, southern Utah and Nevada, forming some of the most prominent, distinctively red-stained escarpments of the Grand Canyon, where it is also among the most fossiliferous formations in the canyon's walls. It consists mainly of fossiliferous limestone with secondary dolomite and chert, light olive gray to light gray and fine to coarse grained, reaching a maximum thickness of about 244 meters and divided into four members, in ascending order the Whitmore Wash, Thunder Springs, Mooney Falls and Horseshoe Mesa. The limestone accumulated in shallow marine conditions as shallow seas repeatedly advanced and retreated over northern Arizona during the Mississippian period, roughly 340 to 330 million years ago, with cycles of deposition, erosion and weathering creating the unconformities that separate its members.