Chapter 6.8, Page 1 of 4

The Dakota/Cheyenne Group is an assemblage of sandstones, shales, and mudstones that were typically deposited in deltaic environments along an ancient seaway that covered much of Colorado during the Cretaceous period. The formation is present throughout most of Colorado, and is an important aquifer in many locations (Figure 6.8-1). Where these units are close to the surface, the Dakota-Cheyenne aquifer is the most extensive water-yielding unit in eastern Colorado.

The geologic deposits of the Cretaceous period were controlled by
the interior seaway covering most of Colorado.

paleo-reconstruction by Ron Blakey of Northern Arizona University.

Figure 6.8-1 Location and extent of the Dakota-Cheyenne aquifer,
outside of designated basins and the High Plains aquifer, showing the
distribution of permitted water wells.
(Click image to zoom .6MB)

Chapter 6.8, Page 1 of 4