The late Triassic (?) and early Jurassic Nugget and Navajo Sandstones are compositionally and texturally extremely homogeneous, mature, feldspathic quartz arenites extending over vast areas in the western United States. They have long been considered as "classic" eolian sandstones, deposited within great interior, sub-tropical deserts.

Trough-shaped "festoon" cross-bedding predominates and most tabular-planar and irregular sets are modifications of this basic style. Large scale simple, non-erosional, wedge-shaped sets are subordinate and are restricted stratigraphically to the middle part of the Navajo Sandstone. Ripple-marked, wavy-bedded horizons, plane bedded to massive units, and interbedded shale seams associated with horizontal truncation planes are common, particularly in the Nugget Sandstone. Very thin dolomitic carbonate lenses are found in the Navajo. While the sparse fossil evidence is indicative of terrestrial, but not necessarily extremely arid, conditions, these latter characteristics, as well as widespread contortion of inclined laminae, are apparently the result of subaqueous processes.

Sediment volume, grain composition, and textural maturity indicate a predominantly sedimentary provenance. No areal compositional or textural trends are discernible but south- and southeasterly-directed paleocurrents suggest a source along the western margin of the Canadian Shield. Textural parameters derived from recent sediments fail to clearly identify Nugget and Navajo depositional environments.

The weight of all evidence indicates, however, that both formations consist of a complex of shallow-marine, littoral, and coastal dune deposits laid within, and in advance of, an east- and southward-transgressing sea. Although temporary regressive oscillations may have at times exposed large areas of marine sand to the action of the wind, the majority of Nugget and Navajo cross-bedding is aqueous in origin. Preserved eolian structures are remnants of transverse coastal dune belts rather than vast interior dune fields, and paleocurrent directions thus reflect both marine current and coastal onshore

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wind regimes rather than simply ancient tradewind circulations.

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