The Lower Triassic marine formations of the Cordilleran miogeosyncline (Dinwoody, Thaynes, and Moenkopi) make up a wedge-shaped body that intertongues on the east with redbed shelf deposits (Chugwater and Moenkopi). The miogeosynclinal strata are limestones with minor amounts of shale, siltstone, and sandstone. The shelf deposits are redbeds with tongues of nonred siltstone, sandstone, dolomite, limestone, and evaporites.

Carbonate tongues in the redbeds in eastern Utah consist of oolites and poorly sorted echinoderm-rich limestones. There are no obvious lateral facies changes and the deposits appear to have formed in a shallow, laterally extensive sea.

In most areas, however, lacustrine or shallow-marine redbed environments passed westward into a sand channel--oolite bar complex or into tidal flats with intraformational conglomerate channels. Seaward, lagoons (burrowed muds) and offshore banks (echinoderm-rich wackestones and oolites) were present. Farther seaward open marine (gray bioclastic limestones and tan calcareous siltstones) and euxinic basin (black limestones and shales) conditions existed.

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Thin chert-rich conglomerates and sandstones and the absence of much of the Lower Triassic in eastern Nevada indicate a positive area in that region. Evidence of Lower Triassic volcanism is present in western Utah and eastern Nevada.

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