Nodular calcareous paleosols are common in the upper member of the Upper Triassic Dolores Formation in the San Juan Mountains of southwestern Colorado. These soils are developed in reddish brown, very fine-grained sandstone and siltstone of a sand-sheet facies that was deposited by eolian and aqueous processes on the margins of a large Triassic erg. Characteristics of these paleosols include nearly complete destruction of physical sedimentary structures, extensive mottling associated with burrows and root trace fossils, poorly sorted textures, and abundant carbonate nodules.

Vegetative stabilization of the sand sheet is recorded by trace fossils of long, monopodial root systems, and...