The Collaborative International Dictionary
Colorado group
Colorado group \Col`o*ra"do group\ (Geol.) A subdivision of the cretaceous formation of western North America, especially developed in Colorado and the upper Missouri region.
Wikipedia
Colorado Group
The Colorado Group, also called the Colorado shale, is a stratigraphical unit of Cretaceous age in the Western Canadian Sedimentary Basin.
It was first described in the Rocky Mountains front ranges of Colorado by A. Hague and S.E. Emmons in 1877.