Toroweap Formation

The Toroweap Formation is a Permian geologic unit of darker, interbedded slope- and cliff-forming rock lying between the Kaibab Limestone above and the Coconino Sandstone below, exposed on both rims of the Grand Canyon as well as in southeast Utah, west-central Nevada and elsewhere in Arizona. It dates to the late Early Permian, roughly 273 to 272 million years ago, and comprises three members: the cliff-forming limestone and dolomite of the Brady Canyon Member sandwiched between the softer, slope-forming red beds, gypsum and fossiliferous limestone of the Seligman and Woods Ranch Members, reaching about 200 feet thick and creating a distinctive slope-cliff-slope pattern visible throughout the canyon. McKee formally named it in 1938 for Toroweap Valley, Arizona.