Muav Limestone


The Cambrian Muav Limestone is the upper geologic unit of the 3-member Tonto Group. It is about thick at its maximum. It is a resistant cliff-forming unit. The Muav consists of dark to light-gray, brown, and orange red limestone with dolomite and calcareous mudstone. The Muav is overlain in some areas by the Devonian Temple Butte Formation, but the major unit above, are the vertical cliffs of Mississippian Redwall Limestone. The Muav is located in the lower elevations of the Grand Canyon, Arizona.
The Muav is in part younger than, and in-part grades into, the Bright Angel Shale, which is less erosion resistant and is categorized as a slope-forming unit. The Muav is about 350 feet thick in the east and reaches about 600 feet thick in the western part of its exposure area in the Grand Canyon. The two units lie above the erosion-resistant cliff-forming Tapeats Sandstone.
In the eastern canyon, the Tapeats Sandstone creates the extremely horizontal Tonto Platform. In west Grand Canyon, the north-south Toroweap Fault is the west perimeter of the Tonto Platform, and west Grand Canyon is dominated by the erosion resistant unit of the Esplanade Sandstone. The Tonto Trail is a mostly horizontal trail on the south side of Granite Gorge, on the Tonto Platform.
cliff example, below Redwall Limestone cliff, on the North Kaibab Trail

The Tonto Group units were deposited on an ancient erosion surface on the Vishnu Basement Rocks. The Vishnu sequence has a dip of about 45 degrees. As this long-timeframe unconformity represents about 1,000 million years of non–deposition, tectonic activity and erosion, on the Vishnu Basement Rocks, is called the Great Unconformity.
Beyond the Grand Canyon area the Muav occurs in southern Utah, southern Nevada and southern California. In the California occurrence it is known as the Muav Marble.

Geologic sequence

The units of the Tonto Group: