Hakatai Shale

Hakatai Shale Stratigraphic range: Meso-Proterozoic, 1,200±50 Ma?
Three approximate equal-thickness formations outcropping below Isis Temple at north perimeter, Granite Gorge Unkar Group, Shinumo Quartzite (vertical cliffs), upon basalt sills, upon orange-red Hakatai Shale, upon Bass Formation.
Type	Geological formation
Unit of	Unkar Group
Underlies	Shinumo Quartzite
Overlies	Bass Formation
Thickness	985 feet (300 m) approximate maximum
Lithology
Primary	shale
Other	siltstone, sandy siltstone, and sandstone (subarkose, arkose and quartz arenite)
Location
Region	Arizona, Grand Canyon Isis Temple region, southwest Bright Angel Canyon, at north side, Granite Gorge, and along Colorado River
Country	United States of America
Type section
Named for	Hakatai Canyon
Named by	Noble (1914)

The Hakatai Shale is a Mesoproterozoic rock formation that outcrops in the Grand Canyon, Coconino County, Arizona. It consists of colorful strata that exhibit colors that vary from purple to red to brilliant orange on outcrop. The colors are the result of the oxidation of iron-bearing minerals in the Hakatai Shale. It consists of lower and middle members that consist of bright-red, slope-forming, highly fractured, argillaceous mudstones and shale and an upper member composed of purple and red, cliff-forming, medium-grained sandstone. Its thickness, which apparently increases eastwards, varies form 137 to 300 m (449 to 984 ft). In general, the Hakatai Shale and associated strata of the Unkar Group rocks dip northeast (10°-30°) toward normal faults that dip 60° or more toward the southwest. This can be seen at the Palisades fault in the eastern part of the main Unkar Group outcrop area (below East Rim). In addition, thick, prominent, and dark-colored basaltic sills and dikes cut across the purple to red to brilliant orange strata of the Hakatai Shale.

The bright orange-red slopes of the Hakatai Shale contrasts sharply against the grayish outcrops of the Bass Formation. The outcrop of the Hakatai Shale also contrasts greatly with the steep cliffs formed by Shinumo Quartzite as seen at the base of Isis Temple. In the central Grand Canyon north of Grand Canyon Village and viewed from the south at the South Rim, the bright orange-red unit can be seen below the Isis Temple and Cheops Pyramid landforms at the intersection of Bright Angel Canyon and Granite Gorge; the Bright Angel Trail from the South Rim traverses through the geographic region to the north, the North Kaibab Trail in Bright Angel Canyon.

The Hakatai Shale is part of a conformable sequence of sedimentary strata that comprise the Unkar Group. The Unkar Group is about 1,600 to 2,200 m (5,200 to 7,200 ft) thick and composed, in ascending order, of the Bass Formation, Hakatai Shale, Shinumo Quartzite, Dox Formation, and Cardenas Basalt. In ascending order, the Unkar Group is overlain by the Nankoweap Formation, about 113 to 150 m (371 to 492 ft) thick; the Chuar Group, about 1,900 m (6,200 ft) thick; and the Sixtymile Formation, about 60 m (200 ft) thick. The Grand Canyon Supergroup, of which the Unkar Group is the lowermost part, overlies deeply eroded granites, gneisses, pegmatites, and schists that comprise Vishnu Basement Rocks.