Belle Fourche Formation
The Belle Fourche Formation or Belle Fourche Shale is a fossiliferous early Late-Cretaceous geologic formation classification in Wyoming. Named for outcrops in Belle Fourche River, Wyoming, this unit name is also used in Montana, North Dakota, and South Dakota.
The unit records the gradual opening and expansion of the Greenhorn Cycle of the Western [Interior Seaway], and as such is lithologically identical to the Graneros Shale Formation.