Lance Fm
Maastrichtian, about 72 to 66 million years old. 1 crag on this site has its map point on it.
What the map says
Shale, sandstone, and minor coal beds; Fox Hills equivalent at base Lithology: shale, sandstone, some coal.
1:500,000 sheet: Horton and others, 2017, U.S. Geological Survey Data Series 1052 (1 crag). 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.