ⓘ Muav Limestone. The Cambrian Muav Limestone is the upper geologic unit of the 3-member Tonto Group. It is about 650 feet thick at its maximum. It is a resistant ..


ⓘ Muav Limestone

The Cambrian Muav Limestone is the upper geologic unit of the 3-member Tonto Group. It is about 650 feet 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 creates the 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 platform.

The Tonto Group units were deposited on an ancient erosion surface angular unconformity on the Vishnu Basement Rocks. The Vishnu sequence has a dip of about 45 degrees. As this unconformity represents about 1.000 million years 1.0 billion 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.


1. Geologic sequence

The units of the Tonto Group:

  • 2-Bright Angel Shale
  • 3-Muav Limestone
  • 1-Tapeats Sandstone
  • 1-Temple Butte Formation, Devonian-409-363 Ma, channel deposits upon Muav Limestone
  • Tonto Group ~544-505 Ma

2. Popular Publications

  • Chronic, Halka. Roadside Geology of Arizona, c. 1983, 23rd printing, Mountain Press Publishing Co. 322 pages. pp. 229–232. softcover, ISBN 978-0-87842-147-3
  • Blakey, and Ranney, 2008. Ancient Landscapes of the Colorado Plateau, Ron Blakey, Wayne Ranney, c 2008, Grand Canyon Association publisher, 176 pages, with Appendix, Glossary, Index. Contains approximately 75 shaded topographic maps, for geology, etc., with 54 23 pairs, 46) for Colorado Plateau specifically; others are global, or North American.
  • Arizona Geological Society, Arizona Geological Survey, c. 1998 etc. Geologic Highway Map of Arizona. Contains geologic map, Arizona Shaded Relief Map, Geologic Cross Sections, Shaded Relief Map of Arizona, Geologic Map of the Grand Canyon in the Vicinity of the South Rim Visitor Center, etc.
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