Bearpaw Shale

The Bearpaw Shale is a geological formation composed of dark gray clay and limestone concretions found across Montana and Wyoming. These rock layers formed within an ancient seaway and contain thin beds of bentonite mixed throughout the sequence.

This formation developed between 75 and 72 million years ago when a shallow seaway covered parts of central North America. The deposits accumulated as sediment gradually settled on the ancient seafloor.

Geological studies of the Bearpaw Shale contribute to research programs focused on understanding sedimentary basins and marine deposits in North America.

Access to this formation can be challenging as its layers appear in remote areas with rolling terrain. The best viewing occurs where natural erosion or roadcuts expose the rock sequences.

The layers preserve remains of ancient marine animals such as ammonites and large swimming reptiles from the Cretaceous era. These fossils reveal the types of creatures that lived in this prehistoric seaway.

Location: Montana

Location: Wyoming

Made from material: shale, claystone

GPS coordinates: 48.25000,-109.50000

Latest update: December 8, 2025 13:40