The Shinumo Quartzite, the third from the bottom formation in the Grand Canyon Supergroup, is the hardest, most resistant formation in the entire Grand Canyon, and it forms steep cliffs that can reach a thousand feet in height. Few trails in the Grand Canyon spend much time in the Shinumo, preferring to follow much easier routes provided by the Hakatai Shale, the soft, easily eroded formation immediately beneath the Shinumo.The one trail where you get to experience the Shinumo in full is the Escalante Route, which passes though a series of supergroup formations, the Dox Formation, the Shinumo, and the Hakatai Shale, as it traverses northeast to southwest though the eastern inner canyon. All of these formations are tilted about ten degrees from horizontal. Pictured here, near the mouth of Escalante Creek, is the spot where the Shinumo first appears, rising up and out from the Colorado River. At this spot, the Escalante Route is deferring any attempt to pass through the Shinumo, and is simply following upward along a slanting platform formed by the top of the Shinumo. As hard and resistant as it is, streams flowing though the Shinumo can form steep, narrow slot canyons. Here the Escalante Route is descending through the upper half of the Shinumo Quartzite via a slot canyon formed by 75 Mile Creek. The Shinumo is informally divided into several geologic members based on color. Here, at the top of the Papago Slide on the Escalante Route, we are looking across the Colorado River at a massive cliff of Shinumo that has an upper tan member sitting on top of a purplish member. The Escalante Route at this point descends several hundred feet to the base of the Shinumo down a steep and treacherous scree slope, the only possible route. One way to identify the Shinumo is by the gigantic house-sized blocks that tumble down from it. Here, along the North Kaibab Trail, are a collection of massive blocks that have calved off from the Shinumo as the soft eroding Hakatai Shale undermines its cliffs. Another great spot to see these blocks is along the South Kaibab Trail just below the Tipoff, but you will see them wherever the Hakatai Shale has had a chance to widen out to a valley or shelf below the Shinumo. The Shinumo cliffs provide a fine opportunity for streams to form waterfalls cascading over it, such as here at Ribbon Falls near the North Kaibab Trail. The rounded, inverted cone below the waterfall is Travertine that has precipitated out from the falling water, molecule by molecule, over the millennia to form the cone. The Shinumo Quartzite is named for the Shinumo Canyon area, where, in its lower portions, not far up from the Colorado River, Shinumo Creek carves through the Shinumo Quartzite. Here, by Shinumo Creek on the North Bass Trail, we are looking up at just one of a series of dramatic Shinumo cliffs in the area that twist and turn in all directions, tossed about by a complex set of faults.
To read more detailed geological information about the Shinumo Quartzite, visit the excellent Wikipedia page for the Shinumo Quartzite.