| Sixtymile Formation | Kwagunt Formation | Galeros Formation | Nankoweap Formation |
| Cardenas Lava
| Dox Formation
| Shinumo Quartzite
| Hakatai Shale
| Bass Limestone |
The Shinumo Quartzite
The Shinumo Quartzite is a member of the Unkar Group formations and is the third oldest Supergroup formation. The Shinumo Quartzite was unconformably deposited atop the Hakatai Shale. The Hakatai emerged above sea level and eroded prior to the deposition of the sediments composing the overlying Shinumo Quartzite towards the end of the Middle Proterozoic Eon. The contact between the Hakatai and the Shinumo Quartzite truncates channel deposits and cross bedded structures in the Hakatai. Deposition of the Hakatai is believed to have been ended by tectonic activity producing a series of northwest trending, high angle reverse faults that was followed by a period of erosion prior to the deposition of Shinumo sands and sediments.
The photo at left depicts a view to the northwest from the Shinumo Quartzite on the west side of mesa cliffs surrounding the Utah Flats area, overlooking a side canyon separating the mesa and Cheops Pyramid in the background. This exposure of the Shinumo forms a ribbon of vertical cliffs beginning along the south and west sides of the mesa, around this side canyon, surrounding Cheops Pyramid on its east, south and west sides and then on along the south side of Isis Temple where it finally pinches out between the Hakatai and the Bright Angel Shale.
Below the Shinumo Quartzite at the base of Cheops Pyramid are spectacular orange and reddish purple outcrops of Hakatai Shale. Making up Cheops Pyramid above the Shinumo are the Paleozoic Bright Angel Shale, Muav Limestone and Temple Butte Formation, concealed for the most part beneath a good deal of talus, capped by a steep walled prominence composed of Redwall Formation. The normally ubiquitous Tapeats Sandstone is missing from below the Bright Angel Shale where hard, resistant quartzites and sandstones of the Shinumo eroded to a hilly topography with highs poking through and pinching out the much later deposited and subsequently eroded Paleozoic Tapeats.
A disconformity representing a gap in geologic time of roughly half a billion years exists where the Shinumo contacts overlying Paleozoic formations. In most places at Grand Canyon there are no remnants of the Middle to Late Proterozoic Grand Canyon Supergroup intervening between the Early Proterozoic Vishnu Group and the overlying Paleozoic formations. Where the Paleozoic column directly overlies the Vishnu Group, an even more tremendous gap spanning over a billion years, known as the Great Unconformity, is missing from the Precambrian geologic record at Grand Canyon.
Among the Unkar Group formations, the Shinumo Quartzite is second in thickness only to the Dox Sandstone, which conformably overlies it. Exposures of the Shinumo indicate a general thickening trend towards the west, ranging from about 1130 feet in the Papago Creek vicinity to reported thickness in the Shinumo Creek vicinity exceeding 1300 feet. Geologists have recognized four or five poorly defined members based on varying lithologies of the sandstones within the Shinumo. These consist of a bottommost member of conglomeratic subarkose and subminiature quartz sandstone, overlain by a mature quartz sandstone, followed by a brown quartz sandstone containing clay galls and fossilized mud cracks, followed by a hard, fine grained sandstone with rounded and well sorted quartz grains lithified with a siliceous cement.
The lithology and structure of sediments making up the Shinumo sandstones suggest a shallow marine environment with stream and river born sediments deposited in near coastal delta environments. The contact between the Shinumo and overlying Dox Formation is regarded as generally conformable, with the end of Shinumo time marked by a rapid transgression of the Dox sea and ensuing deposition of the lower shaley and mudstone members of the Dox.