Bright Angel Shale

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Bright Angel Shale
Stratigraphic range: Middle Cambrian[1][2]
Grand Canyon-Mather point.jpg
Muav Limestone-(dk or lt gray, brown, or orange-red subcliff at base of Redwall Limestone cliff) and Bright Angel Shale (greenish slope-former), resting on Tapeats Sandstone (short, dp brown vertical cliff) (Tapeats forms the "Tonto Platform"), inner canyon, Granite Gorge. (The 3 units–Muav, Bright Angel, and Tapeats, are easily seen below the red-stained Redwall Limestone (550 ft thick))
Type Geological formation
Unit of Tonto Group
Underlies Muav Limestone
Overlies Tapeats Sandstone
Thickness 500 feet (150 m) at its maximum
Primary micaceous siltstone and shale
Other sandstone and glauconitic sandstone
Region northern Arizona, southeast California, southern Nevada, and southcentral Utah
Country United States of America
Type section
Named for Bright Angel Canyon, Bright Angel quadrangle, Coconino Co., Arizona[3]
Named by Noble (1914)[3]

The Cambrian Bright Angel Shale is the middle member of the 3-member Tonto Group. It is about 500 feet (152 m) thick at its maximum.[4] It is a nonresistant slope-forming unit. The Bright Angel Shale consists of green and purple-red, siltstone and shale which is interbedded with red-brown to brown sandstone that is similar in lithology to the underlying Tapeats.[5] The Bright Angel Shale underlies and interfingers with Muav Limestone. The Bright Angel Shale is located in the lower elevations of the Grand Canyon, Arizona.[6]

Geologic sequence[edit]

The units of the Tonto Group:[4]

See also[edit]


  1. ^ Rose, E (2006) Nonmarine aspects of the Cambrian Tonto Group of the Grand Canyon, USA, and broader implications. Palaeoworld. 15:223–241.
  2. ^ Rose, E (2011) Modification of the nomenclature and a revised deposition model for the Cambrian Tonto Group of the Grand Canyon, Arizona. in JS Hollingsworth, FA Sundberg, and JR Foster, eds., pp 77-98, Cambrian Stratigraphy and Paleontology of Northern Arizona and Southern Nevada: Museum of Northern Arizona Bulletin 67, 321 p.
  3. ^ a b Noble, LF (1914) The Shinumo quadrangle, Grand Canyon district, Arizona. Bulletin no. 549, US Geological Survey, Reston, Virginia.
  4. ^ a b Chronic, H (1983) Roadside Geology of Arizona. The Mountaineers Books, Seattle, Washington. (softcover, ISBN 978-0-87842-147-3)
  5. ^ Anonymous (2006c) Bright Angel Shale, Stratigraphy of the Parks of the Colorado Plateau. U.S. Geological Survey, Reston, Virginia.
  6. ^ Hampton, HM (1998) Geologic Map of the Grand Canyon in the Vicinity of the South Rim Visitor Center. in Kamilli, RJ, and SM Richard, eds., Geologic Highway Map of Arizona, Arizona Geological Society and Arizona Geological Survey, 1 sheet, scale 1:62,500.

Popular Publications[edit]

  • Blakey, Ron and Wayne Ranney, Ancient Landscapes of the Colorado Plateau, Grand Canyon Association (publisher), 2008, 176 pages, ISBN 978-1934656037
  • Chronic, Halka. Roadside Geology of Arizona, Mountain Press Publishing Co., 1983, 23rd printing, pp. 229–232, ISBN 978-0-87842-147-3
  • Lucchitta, Ivo, Hiking Arizona's Geology, 2001, Mountaineers's Books, ISBN 0-89886-730-4

External links[edit]