The Dox Formation, also known as the Dox Sandstone, is a Mesoproterozoic rock formation that outcrops in the eastern Grand Canyon, Coconino County, Arizona. The strata of the Dox Formation, except for some more resistant sandstone beds, are relatively susceptible to erosion and weathering. The lower member of the Dox Formation consists of silty-sandstone and sandstone, and some interbedded argillaceous beds, that form stair-stepped, cliff-slope topography. The bulk of the Dox Formation typically forms rounded and sloping hill topography that occupies an unusually broad section of the canyon.
Dox Formation at Tanner Graben-(photo left, on river) and upstream on Colorado River (from Comanche Point, East Rim)
Purple colored, layered Dox Formation, below black Cardenas Basalt. (shows the ~15 degree dip)
Basalt Creek cut into the Dox Formation. (At left-(northwest), entering the Colorado River at a small 'deltaic' region-(alluvial fan).)
Close-up view of Dox Formation at Basalt Creek, just downstream of Tanner Graben, Tanner Rapid, and Tanner Creek
The Unkar Group is a sequence of strata of Proterozoic age that are subdivided into five geologic formations and exposed within the Grand Canyon, Arizona, Southwestern United States. The 5-unit Unkar Group is the basal member of the 8-member Grand Canyon Supergroup. The Unkar is about 1,600 to 2,200 m thick and composed, in ascending order, of the Bass Formation, Hakatai Shale, Shinumo Quartzite, Dox Formation, and Cardenas Basalt. Units 4 & 5 are found mostly in the eastern region of Grand Canyon. Units 1 through 3 are found in central Grand Canyon. The Unkar Group accumulated approximately between 1250 and 1104 Ma. In ascending order, the Unkar Group is overlain by the Nankoweap Formation, about 113 to 150 m thick; the Chuar Group, about 1,900 m (6,200 ft) thick; and the Sixtymile Formation, about 60 m (200 ft) thick. These are all of the units of the Grand Canyon Supergroup. The Unkar Group makes up approximately half of the thickness of the 8-unit Supergroup.
Units 5 & 4 of the Unkar Group Reddish (unit 4)–Dox Formation below blackish (5)–Cardenas Basalt, upstream from Tanner Graben
View due-north, from Lipan Point, East Rim: Lava Butte, Temple Butte, Cardenas Basalt, Dox Formation, Palisades of the Desert – (on East Rim), etc. on Colorado River.
Close-up of Apollo Temple
(units 1-2-3 of 5 units) Shinumo Quartzite cliffs upon colorful Hakatai Shale upon horizontal thin beddings of Bass Formation (upon Vishnu Basement Rocks of Granite Gorge) (expandable high-resolution photo)