The southwestern margin of the Cretaceous Western Interior Seaway laid extensive deposits in Arizona from the westernmost exposures near Pinedale to the Arizona-New Mexico border along the Mogollon Rim. Consisting of the intertongueing Dakota and Mancos Formations, it ranges in age from Cenomanian to Turnonian. The transgressive-regressive sediments consist of a sequence of sandstones, shales and limestones and represent fluvial, coastal and marine shelf environments.

The stratigraphic units in Arizona have been primarily extended from the New Mexico terminology by Wolfe and others to the following units: A basal unit, consisting of primarily a conglomerate of erosional clasts from the pre cretaceous underlying units of the Triassic Chinle formation, and meta sedimentary deposits from pre-Paleozoic volcanics. This unit has been named the Cliff Dwellers Sandstone of the Dakota formation and is up to 15 meters thick towards the eastern extensions of this study area.

Overlying the Cliff Dwellers Member of the Dakota is an intertongueing series of shaley beds that are three separate formations in New Mexico that pinch out around the Show Low area. They are in ascending sequence, the Clay Mesa Shale, Paguate Sandstone, and the Whitewater Arroyo members of the Mancos Shale. However, around the study area, the three are very thin, and have been combined to one 10 to 20m thick bed called the Clay Mesa/Whitewater Arroyo tongue of the Mancos Shale.

Conformably overlaying the above group is the Twowells Tongue of the Dakota Formation. This is the commonly seen yellow sandstone beds in and around the Show Low area, forming sometimes highly crossbedded massive cliffs and escarpments. It ranges in thickness from 10 to 20 meters in the study area and usually contains several limestone shell lag beds near the top ranging in thickness up to 10 meters and containing dominantly the mollusks Exogyra Levis and Pinna Petrina.

A tertiary basalt cap overlies the previous formation in much of the area especially in the eastern end of the section.

The Cretaceous sediments in Show Low - Pinedale area are locally fossiliferous, containing a dominantly molluscan macrofauna including oysters, ammonites, nautiloids and Pinnas, with an occasional shark or crocodile tooth. Terrestrial deposits include large amounts of permineralized wood, impressions of leaves and plant parts, and freshwater clams.