Pierre Shale, Geological formation in South Dakota and North Dakota, United States and Alberta, Canada
Pierre Shale is a rock formation that extends across parts of South Dakota, North Dakota, and Alberta, composed of gray and olive-colored shale layers. The formation contains interbedded siltstone and sandstone deposits that create visible geological patterns in the landscape.
Geologists F.B. Meek and F.V. Hayden first documented this formation in 1862, initially calling it Formation No. 5 before it received its current name. The designation was updated to better identify and distinguish it from other rock layers.
Local communities view the lands where these rock layers emerge as part of their heritage and traditional territories passed down through generations. The exposed surfaces hold meaning in stories and knowledge systems that connect people to the landscape.
Access is easiest where the rock layers are exposed at the surface and do not require long hikes to reach. Visiting with a local guide or geologist helps make sense of the different layers and what they show.
The rock layers preserve fossils from ancient sea creatures that lived during the Cretaceous period, including shellfish and early marine reptiles. These remains come from about 70 million years ago when shallow seas covered this region.
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