Pierre Shale, undivided
Late Cretaceous, about 84 to 76 million years old. 4 crags on this site have their map point on it.
What the map says
The sheet gives no description for this unit. Lithology: shale.
1:500,000 sheet: Horton and others, 2017, U.S. Geological Survey Data Series 1052 (4 crags). A contact line at that scale is about 500 m wide on the ground.
Served by Macrostrat (CC BY 4.0). The wording is the map's own, quoted as a fact about the mapped unit, not about any one wall.