The Frontier Formation is a sedimentary geological formation whose strata date back to the Late Cretaceous

Late Cretaceous

The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...

. The formation's extents are: northwest Colorado

Colorado

Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...

, southeast Idaho

Idaho

Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

, southern Montana

Montana

Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

, northern Utah

Utah

Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...

, and western Wyoming

Wyoming

Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

. It occurs in many sedimentary basins and uplift areas.

The formation is described by W.G. Pierce as thick, lenticular, grey sandstone, gray shale, carbonaceous shale, and bentonite.

Dinosaur

Dinosaur

Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

 remains are among the fossils that have been recovered from the formation.

Vertebrate paleofauna

• Nodosaurus
  Nodosaurus
  Nodosaurus was a genus of herbivorous ankylosaurian dinosaur from the Late Cretaceous, the fossils of which are found in North America. Two incomplete specimens have been discovered in Wyoming and Kansas, and no skulls...
  
   textilis
• Stegopelta
  Stegopelta
  Stegopelta is a genus of armored dinosaur. It is based on a partial skeleton from the latest Albian-earliest Cenomanian-age Lower and Upper Cretaceous Belle Fourche Member of the Frontier Formation of Fremont County, Wyoming....
  
  landerensis - "Partial postcranium, osteoderms, [and] fragments of skull."