The Supai Group is a slope-forming section of red bed deposits found in the Colorado Plateau.

[6] The Supai beds range from siltstones and mudstones deposited in a continental environment, which contain fossils of land plants and structure such as shrinkage cracks and raindrop impressions, to limestone beds deposited in a marine environment, which contains fossils of marine animals such as crinoids, brachiopods, and corals.

The fossils found in the Redwall Limestone are also characteristic of the Mississippian Subperiod, while the lower beds of the Supai Group are Pennsylvanian in age.

[9] The disconformity between the Redwall Limestone and the Supai Group records a time of regional uplift, in which the Grand Canyon area was elevated by at least several hundred feet.

Erosion carved channels in the Redwall Limestone that reach a maximum depth of 400 feet (120 m) in the western Grand Canyon.

[11] The Supai Group was originally regarded as a single formation,[3] but further study showed that there were three disconformities within this set of beds that could be traced throughout the Grand Canyon.

This formation records a marine transgression (an advance of the sea inland) from the west and northwest across the future Grand Canyon area.

[10] Fossils in the formation show that deposition of the Watahomigi began in the very late Mississippian and continued into the early Pennsylvanian.

Deposition resumed in the Virgilian Age with the Wescogame Formation, beginning with another basal conglomerate bed.

As a result, the Esplanade Sandstone is the thickest and most widespread formation of the Supai Group, extending into southeastern Arizona[16] and southwest Utah.

The subsections are sometimes separated by unconformities, due to changing ocean levels, glaciation, or regional subsidence.

[2]: xviii Because marine transgressions cover distances, over time, the coeval units are separated by distance, and type of deposition material; the local subsidence, or uplift, as well as glaciation, and sea level changes, can cause variations in the deposition sequences of transgression-regressions.