A broken concretion with fossils inside; Late Cretaceous Pierre Shale near Ekalaka, Montana
Contact (red arrow) between the underlying marine shales of the Bearpaw Formation and the coastal Horseshoe Canyon Formation.
Bearpaw shale being excavated to recover ammonites for ammolite production.
A specimen of Placenticeras ammolite from the Bearpaw Formation.

It is correlative with other marine shales that occur farther west, such as the Bearpaw Shale, Mancos Shale and the Lewis Shale.

- Pierre Shale

To the east, it merges into the Pierre Shale.

- Bearpaw Formation
A broken concretion with fossils inside; Late Cretaceous Pierre Shale near Ekalaka, Montana

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A ridge capped by a sandstone bed of the Fox Hills Formation west of Limon, Colorado

Fox Hills Formation

Cretaceous geologic formation in the northwestern Great Plains of North America.

Cretaceous geologic formation in the northwestern Great Plains of North America.

A ridge capped by a sandstone bed of the Fox Hills Formation west of Limon, Colorado

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.