Basalt
Basalt & volcanic. Cenozoic, about 66 to 2.6 million years old. 1 crag on this site has its map point on it.
What the map says
Scoriaceous and vesicular lava capping Grand Mesa and Mount Callahan. Lithology: extrusive; mafic; basalt flows.
1:100,000 sheet: Day and others, 1999, U.S. Geological Survey Open-File Report 99-0427 (1 crag). A contact line at that scale is about 100 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.