Pennsylvanian and Lower Permian sedimentary rocks of the southern Colorado Plateau have been the subject of controversy concerning their correlation and origin. Paralic sediments of the Supai group (Morrowan, Atokan, Virgilian, and Wolfcampian) were deposited in the Grand Canyon embayment. A persistent southwest-trending unstable area, herein named the Sedona arch, confined all Supai sediments, except Virgilian, to the Grand Canyon and western Mogollon Rim regions; older strata are truncated by the sub-Virgilian unconformity.

Marine rocks of the Naco Group (Desmoinesian, Missourian, and Virgilian) were deposited on the Mogollon Shelf. Only Virgilian rocks cross the Sedona arch. Thus the bulk of Supai and Naco sedimentary rocks are not as closely related as most previous workers had thought.

The northwest-trending Kaibab arch provided the barrier between the Hermosa Group of the Paradox basin and the Supai and Naco to the south; therefore, most of the Supai, Naco, and Hermosa groups were deposited in distinctly separate basins.

The Wolfcampian Esplanade and Cedar Mesa Sandstone Members and Halgaito formation form a distinct eastward-thinning wedge of sedimentary rocks west of the Sedona arch. These high-energy marine shoreline and supratidal sedimentary rocks grade westward into thick marine carbonate rocks of the Cordilleran geosyncline. A widespread red-bed sequence comprising continental and possibly tidal shoreline deposits of the Hermit and Organ Rock formations was deposited across the entire study area.

The youngest sequence studied consists of sandstone, red beds, evaporites, and carbonate rocks of the Schnebly Hill formation and DeChelly Sandstone (Leonardian). These units are centered around the Holbrook basin and represent a complex of shallow-marine, high- and low-energy shoreline, eolian, and sabkah depositional environments. Both formations grade upward into the overlying Coconino Sandstone and related rocks.

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