[1] It preserves fossils dating back to the early Mississippian.

[2] The formation is mostly crystalline or calcarenite limestone with a total thickness of up to 130 ft (40 m).

[3] The formation is divided into the Macho Member, which is a massive ledge-forming limestone breccia (thickness 30 feet (9.1 m));[1][4] the Turquillo Member, a thick-bedded mudstone;[3] the Manuelitas Member, which is a light to medium gray calcarenite, limestone-pebble conglomerate, and finely crystallized locally cherty limestone (thickness 39 feet (12 m)); and the Cowles Member, which is a light yellow gray to olive yellow cross-bedded silty calcarenite (thickness 50 feet (15 m).

[2] The Macho, Turquillo, and Manuelitas Members contain microfossils characteristic of the Meramecian while the Cowles Member contains microfossils characteristic of the Chesterian (late Visean and Serpukhovian).

[1] Armstrong and Mamet included it as the upper formation of their Arroyo Penasco Group in 1974 and added the Turquillo Member.