An extremely widespread intra-Permian transgression eroded and successively truncated beds from Middle Permian (Guadalupian) to Mississippian (Meramecian) in age.

On this erosion surface are lag gravels in a phosphatic matrix, with associated corrosion breccias. The breccias are developed where planate beds of calcilutite, dololutite, and chert are infiltrated, corroded, and brecciated in situ by the phosphate and then partly or totally replaced by chalcedony. Fragments from the breccias may be incorporated in the overlying

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conglomerate, although every gradation may be seen from mosaic brecciation of bedrock to moderately well-rounded material in the lag gravels.

The breccias and conglomerates are unconformably and diachronously overlain by Middle or Upper Permian clastic sedimentary rocks that were deposited in an evaporitic environment.

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