Fox Hills Formation

Fox Hills Formation
Stratigraphic range: Late Cretaceous,
A ridge capped by a sandstone bed of the Fox Hills Formation west of Limon, Colorado
Type	Geological formation
Unit of	Montana Group (MT, ND)
Sub-units	Fairpoint member (SD), Trail City member (ND, SD), Timber Lake (ND, SD), Lincoln member (CO), etc.
Underlies	Lance (WY)/Hell Creek (MT) Laramie Formation (CO)
Overlies	Pierre (USA)/Bearpaw (CAN) Lewis Shale (WY, MT)
Thickness	75-225 feet
Lithology
Primary	Sandstone
Other	Shale
Location
Region	Alberta, Colorado, Montana, North Dakota, South Dakota and Wyoming
Country	United States/Canada
Type section
Named for	Fox Hills between Cheyenne and Moreau Rivers, South Dakota
Named by	Meek and Hayden
Year defined	1862

The Fox Hills Formation is a Cretaceous geologic formation in the northwestern Great Plains of North America. It is present from Alberta on the north to Colorado in the south.

Fossil remains of dinosaurs, including tyrannosaurs, as well as large marine reptiles, such as mosasaurs, have been recovered from the formation.

Lithology

The Fox Hills Formation consists of marginal marine yellow to grey sandstone with shale interbeds. It was deposited as a regressive sequence of barrier islands during the retreat of the Western Interior Seaway in Late Cretaceous time. In its eastern extents, the formation is underlain by the marine Pierre Shale in the United States and by the equivalent Bearpaw Formation in Canada, while in western ranges in Montana and Wyoming it overlies the Lewis Shale. The Fox Hills is overlain by continental sediments of the Laramie Formation in Colorado and the Lance Formation in Wyoming, the later being the equivalent of the overlying Hell Creek Formation in Montana.

See also

• List of dinosaur-bearing rock formations
  • List of stratigraphic units with indeterminate dinosaur fossils