First described by H. Peirce of the Arizona Geological Survey, and J. Dale Nations of Northern Arizona University, this relatively little known tertiary outcrop on the Mogollon Rim near the town of Clints Well offers insights to the climate of the Rim area during no later than Miocene Tertiary times. This section, called the Blue Ridge Tertiary section is a bed of plant bearing carbonate rocks underlain and overlain by a conglomerate sequence, then finally topped by a basalt flow of probable Miocene age of approximately 22 Million Years old. The conglomerate unconformably lies on the Triassic Moenkopi Formation, and contains clasts of Precambrian rocks including basalts, granites and mostly quartzites. In fact, the composition is very near that of the Rim Gravels, however the upper conglomerate bed is mostly white cherts in a salmon colored matrix of sandstones.
Our exploration of this outcrop revealed another section behind the roadcut with beds representing a more terrestrial origin. Fossil rhizomes (root casts) were evident in a more calcitic sandy matrix. Certain beds just above both conglomerate sequences were fossiliferous, containing the molds of stems and reeds of aquatic plants.
This section of the cut shows the gravely basal conglomerate overlain by a limestone with interbedded shales, capped by basalt at the very top.
Closer view of the roadcut basal unit. The clasts ranged up in size to about 3 inches.
Mostly quartzites and basalts up to 3 inches are seen here in this closer examination of the basal conglomerate.
The upper part of the conglomerate bed is composed of white cherty clasts, up to an inch in size. They are much more angular, and thus were not transported from their original source as far as the the lower unit.
Travertine like deposits are throughout the calcareous member, but contain no fossils.
Fossil reeds - possibly cattails in middle member are in a two foot thick bed.
Block of fossil reeds found loose from the lower member of the fossiliferous unit. We found fossil roots and rhizomes in the upper fossiliferous unit, but few reed casts.