Abstract

The Entrada Sandstone, of Upper Jurassic age, is here divided into 3 named members in E.-central Utah and W.-central Colorado. They are, from bottom to top, the Dewey Bridge Member, the Slick Rock Member, and the Moab Member. The text description of these members is supplemented with graphic columns of 20 sections, histograms of grain-size distribution and mineral composition, and appended type sections. The Dewey Bridge Member is reddish brown sandy siltstone. Its strata are here transferred from the Carmel Formation to the Entrada because they are lithologically like and continuous with the siltstone of the Entrada at its type locality in central Utah, and because they intergrade in eastern Utah with the Slick Rock Member. The Slick Rock Member is quartzose sandstone, previously mapped as the lower part of the Entrada Sandstone in this area. Three subdivisions, based on distinctive bedding styles, can be recognized at many places within this extensive member. The previously defined Moab Member is extended from E.-central Utah into the Grand Junction area of Colorado. The western limit of the Moab is a prominent tongue in the Summerville Formation, but its eastern limit is the pinchout of thin inconspicuous tongues in the Summerville and gradation into less distinct sandstone beds included within the Summerville.

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