It is typically gray on fresh exposure and weathers to a light buff color. The Greenhorn is a persistent slabby ledge-former around the Black Hills and in the center of Chadron Dome. It is typically rich in fossils, especially the large bivalve Inoceramus labiatus , of which some beds are entirely composed. This is probably the part of the Graneros group exposed on Chadron Dome . On fresh exposures, the Mowry is a hard, dark gray to black, siliceous shale with some thin sandstones and siltstones and abundant bentonite beds.
Fish scales are abundant throughout.
The Mowry weathers to a silvery-gray color and frequently has coniferous trees growing on its slopes. Dark gray to black, soft splintery shale with few thin soft beds and some septarian concretions. Fall River Fm. May be interbedded at certain localities in the Black Hills with shale and coal. A fine-grained pink, white, buff, or purple sandstone, massive in outcrop.