The thicker limestone beds typically consist mostly of fragments of crinoids.

[4] The formation is thought to have been laid down in the Horquilla Seaway, a continental shelf environment on the southwest coast of Pangaea.

The most numerous fossils at the type section are brachiopods (such as Neospirifer, Composita, and Dictyoclostus) and fusulinids (such as Fusulina and Fusulinella).

[5] Exposures in the Organ Mountains include fossils of Chaetetes, Petalaxis, Fusulinella, and cordaite leaf impressions.

The type section is on an eastern spur of Horquilla Peak in the Tombstone Hills of southern Arizona.