The area is located in Eagle and Summit counties in west-central Colorado. Two new late-Paleozoic formational names are proposed. In the area the name Battle Mountain formation is given for the clastics which were originally assigned to the Weber shale, Weber grit, and Maroon formation. The Belden shale member of this same formation is proposed to include the lower dark shale originally called the Weber shale. Much of the Battle Mountain formation is found to be of Des Moines age. The name State Bridge formation (of Donner) is applied to the red siltstones and shales which lie between the Battle Mountain formation and the Triassic sediments. These beds may be either Pennsylvanian or Permian in age. At least a part of the gypsum of the Eagle Basin is shown to belong in the Des Moines series.

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