South Rim Tour - the Great Unconformity

This zoomed-in view shows the Great Unconformity above the Precambrian metamorphic rocks exposed along the inner gorge along the Colorado River downstream of Phantom Ranch. Precambrian-age sedimentary rocks of the Grand Canyon Supergroup are exposed to the right of the inner gorge (beyond the butte in the right foreground). Above the Great Unconformity along the inner gorge are cliffs formed by the Tapeats Sandstone. Above the Tapeats Sandstone is a gentle plateau and slopes formed by the overlying Bright Angel Shale (called the Tonto Platform in the region of the canyon). The first cliff above the Bright Angel Shale is the Muav Limestone. The Tapeats, Bright Angel, and Muav are all of Cambrian age. The prominent, high cliff along the top of the image consists of the Temple Butte Limestone (Devonian age) and and overlying, massive Redwall Limestone (Mississippian age). The lower slope-forming units of Supai Group (Pennsylvanian and Permian age) overly the Redwall Limestone. Upper sedimentary units of the Supai Group form the slopes and butte in the foreground. See also Billingsley, 2000; and Timmons and others, 2009.