The Dakota Group of northeastern New Mexico and southern Colorado
— Niall J. Mateer

The history of Dakota Group terminology is briefly reviewed in northeastern New Mexico and southeastern Colorado and traced from the type area in northeastern Nebraska. Component formations of the Dakota Group in this region are reviewed with the purpose of providing correlations between northeastern New Mexico and Colorado and placing northeastern New Mexico stratigraphic terminology within the larger framework of the Western Interior. The twofold division of the Dakota Group (Purgatoire and Dakota formations) is rejected in favor of a fourfold division comprising the Lytle, Plainview (not present in northeastern New Mexico), Glencairn (and Tucumcari) and Muddy formations. The Muddy Formation of Wyoming is extended
along the Colorado Front Range into northeastern New Mexico, and component members are also correlated: the Mesa Rica Sandstone is correlated with the lower sandstone unit and Kassler Sandstone of Colorado; the Pajarito Shale with the Dry Creek Canyon Member and Van Bibber Shale; and the "Dakota" Sandstone (a term rejected here) with the upper "J" Sandstone and Horsetooth Member. Primary effects on deposition of the Dakota Group appear to be related to sea-level and sediment-influx fluctuations, although contemporaneous basement movements had strong local effects.