Its cliffs contrast sharply with the stair-stepped topography of typically brightly-colored (orange, red, yellow, etc) strata of the underlying slope-forming Hakatai Shale.

Overlying the Shinumo, dark green to black, fissile, slope-forming shales of the Dox Formation create a well-defined notch.

It and other formations of the Unkar Group occur as isolated fault-bound remnants along the main stem of the Colorado River and its tributaries in Grand Canyon.

The Unkar Group consists of a sequence of sedimentary rocks that accumulated in a variety of environments ranging from fluvial to shallow-marine.

The Unkar Group, as the base section of the Grand Canyon Supergroup, overlies deeply eroded granites, gneisses, pegmatites, and schists that comprise Vishnu Basement Rocks.

One conglomeratic sandstone layer that lies about 21 m (69 ft) above the base of the Shinumo Quartzite near the South Kaibab trail contains jasper pebbles.

As in the case of the Hotauta Conglomerate, the quartzite gravel of the lower member lacks any known equivalents in the Grand Canyon region.

In addition, the gray quartzite was subjected to cementation by silica and bleaching that removed its original reddish brown and purple hematite pigments, after its deposition.

The sandstones of the lower and lower-middle members exhibit centimeter- to meter-scale planar tabular cross-stratification and trough cross-beds.

[6][8] Within the Unkar Group, the upper contact of the Shinumo Quartzite with the Dox Formation appears to be gradational and is marked by a change in topographic expression and color.

The basal 12 m (39 ft) of the Dox Formation directly overlying Shinumo Quartzite consists of predominantly dark green to black, fissile, slope-forming shale that contains thin sandstone beds.

These monadnocks served locally as sources of coarse-grained sediments that accumulated during the marine transgression to form the Tonto Group.

The deformed strata of the upper member are interpreted as evidence of reoccurring earthshocks along regional fault and fold systems that were active during its deposition.

The Hakatai Shale, Shinumo Quartzite, and Dox Formation samples yield clusters of zircon as young as 1170 Ma.