The conglomerates, breccias, sandstones, and argillites vary in color from purple-brown to dark red and reddish brown.

They include ripple marks; mudcrack covered surfaces; cone-in-cone structures; interformational breccias/conglomerates; both normal and reversed small-scale, graded bedding; and local channel fills.

Veins of asbestos with fibers up to 10 cm (3.9 in) in length, often commonly occur within 3 m (9.8 ft) of the upper and lower contacts of the sills.

The thin section of Bass Formation at Crystal Creek likely reflects the presence of a Vishnu Basement Rocks topographic high in the paleosurface on which it accumulated.

Where it has not been removed by erosion, prior to, and during the deposition of the overlying Bass Formation, a residual regolith developed by subaerial weathering of the underlying basement rocks – is present.

Typically, this regolith consists of a dark-reddish brown, structureless, ferruginous sediment that is usually a few centimeters to 30 cm (0.98 ft) thick.

For example, in Red Canyon, the contact consists of an interval in which stromatolitic limestone of the Bass Formation is intimately interbedded with coarse clastic sedimentary rock of the overlying Hakatai Shale.

These monadnocks served locally as sources of coarse-grained sediments during the marine transgression that deposited the Tapeats Sandstone and other members of the Tonto Group.

The contact between the Bass Formation and the Tapeats Sandstone forms part of a relative flat surface that lies between the monadnocks.

In addition, fossils of a bivalve of unknown affinity, which were reported from the Bass Formation, are now judged to be rounded mud-flakes or pellets that are likely oncolites of algal origin.

[11][12][13] The lithology and sedimentary structures observed in the Bass Limestone indicate that, except for the Hotauta Member, it accumulated beneath a sea that transgressed from the west.

The Hotauta Member consists of fluvial sands and gravels that accumulated within valleys on an eroded surface of the Vishnu Basement Rocks.

The quartzite gravel indicates that the conglomerates of the Hotauta Member were deposited by river systems that extended some unknown distance outside of the Grand Canyon region.

This limestone largely accumulated in clear, relatively warm, shallow marine waters by both biological and abiological processes.

Following the maximum incursion of marine waters, the sea slowly regressed, and it accumulated in nearshore and coastal environments as indicated by ripple marks, mudcracks, oxidized shales, and other evidence of periodic subaerial exposure found in the upper part of the Bass Formation.

Eventually, a shallow, near-shore marine environment, coastal plain mudflats, and deltas that marked the beginning of Hakatai Shale deposition – dominated the Grand Canyon area.

[5][9] The presence of chrysotile asbestos veins in the Bass Formation was first noted in early exploration of the Grand Canyon by the Powell expedition.

As in the case of the Bass Formation, these chrysotile asbestos deposits are of the contact metamorphic type that occur in magnesium-bearing Mesoproterozoic dolomites and limestones altered by basaltic dikes and sills.

As in the case of the Grand Canyon asbestos deposits, dolomite and limestone reacted with silica-bearing fluids, heated by the basalt intrusions, forming the serpentine mineral chrysotile.