Eleven stratigraphic sections were measured along the southwestern margin of the Colorado Plateau, from north-central Arizona to southeastern Nevada. The northwestern sections are thick and consist dominantly of limestones. The southeastern sections are thin and contain much clastic material.

The Cambrian rocks, which are almost 2,200 feet thick in extreme southeastern Nevada, wedge to extinction southeastward. They have complex facies relationships resulting from diverse shifting environments during a Lower-Middle Cambrian transgression and a Middle-Upper(?) Cambrian regression. The deposition of primary dolomitic limestones in two types of shallow-water environment is clearly demonstrated.

The Ordovician(?) is represented by a thin wedge of dolomitic limestones which occurs only at the northwest.

The Upper Devonian Muddy Peak and Martin limestones form a continuous limestone series across the area. In the southeast the Martin truncates the Middle Cambrian Tapeats sandstone and contains basal clastic beds. In the western Grand Canyon area the Martin limestone contains soft, argillaceous limestone beds of Temple Butte lithologic character.

The Rogers Spring and Redwall limestones, western and eastern equivalents, are remarkably uniform in thickness and in general lithologic character. They are of Kinderhookian and Osagian age and consist of thick-bedded, light gray, fine-grained, and oolitic limestones with persistent zones of bedded chert.

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Fig. 1. Outline map of northwestern Arizona showing location of stratigraphic sections.

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The Callville limestone, as restricted in this study, is entirely Pennsylvanian. It forms an eastward tapering wedge of two members, which intertongues and intergrades with lower Supai redbeds. The limestones were formed during a Late Pennsylvanian, Virgilian, transgression that extended almost across the area.

A new formation, the Pakoon limestone, is proposed for the dolomitic limestones conformably overlying the Callville limestone. These dolomitic limestones were deposited in a Wolfcampian regressive phase, which followed the Late Pennsylvanian transgression. They are overlain conformably by cross-bedded sandstones of Supai lithologic character.

The pink and gray, cliff-forming, cross-bedded sandstone overlying the Pakoon limestone is designated the Queantoweap sandstone. This formation is not present in the southwestern part of the area, where the Supai is undifferentiated. The southwestern Supai contains many thin limestone beds between red sandstones. The repetition of these limestones with redbeds suggests simple types of cyclothems.

The dominant direction of dip of cross-bedding in all formations between the lower Callville limestone and the Coconino sandstone is south and southeast. This suggests that the source of clastic material was on the northwest or north. The possibility is presented that the Supai redbeds were deposited in a wide mud-flat marginal to a clearer-water environment on the north, and that the repeated subsidence of the mud-flat allowed marine water to spread out cross-bedded sandstones, and at times to precipitate thin limestones.

The Coconino sandstone is the only formation which thins northwestward. The consistent dominant southward dip of the eolian, wedge-shaped, cross-beds in the formation indicates that the source of the sand was north of the area.

The Toroweap formation consists of two gypsiferous members separated by a middle limestone member. It is Leonardian in age. The aridity or semi-aridity of Coconino time persisted during the deposition of the evaporite members of the Toroweap formation.

The Kaibab limestone contains many chert-bearing beds and forms steep cliffs above the less conspicuous cliffs of the Toroweap formation. The Kaibab limestone is overlain by redbeds of the Triassic Moenkopi formation.