ABSTRACT
More than 75 sections of the Jurassic beds were measured along the eastern flank of the Rocky Mountains in Colorado and New Mexico and in the region comprising northern Utah and adjoining parts of Wyoming and Idaho. These, combined with measurements by other geologists, are here used in correlation sheets to show that the basal sandstone of the “Jurassic” of northern Colorado is probably partly Entrada and partly Upper Triassic; that the latter grades into red beds southward and the former continues into New Mexico where it is identical with the so-called Wingate; that it does not extend westward to the Arizona line but can be correlated with the lower LaPlata of the San Juan Mountains in Colorado.
The true Wingate of the Zuni Mountains grades marginally into red beds and may be of Upper Triassic age.
Type Nugget sandstone of southwestern Wyoming is equivalent to the Navajo of Utah and Arizona but the so-called Nugget of northwestern Colorado is Nugget and Entrada separated by a thin remnant of the Carmel formation.
