It contains fossils characteristic of the Atokan and Desmoinesian Ages of the Pennsylvanian.

The Pinkerton Trail Formation is the lowest member of the Hermosa Group, a group of geological formations deposited in the interior and margins of the Paradox basin during the Pennsylvanian.

The Pinkerton Trail Formation consists of gray limestone with occasional beds of black shale.

It was named for exposures at the Pinkerton Trail, about 12 miles (19 km) north of Durango, Colorado.

[4] Baars, Parker, and Chronic proposed a subsurface reference section in 1967 in the Paradox basin.