It preserves fossils dating back to the late Cambrian to early Ordovician periods.

The formation lies unconformably on Precambrian basement rock except in the Florida Mountains, where it overlies Cambrian syenite and granite.

[6] The formation is locally bioturbated and contains fossils of the brachiopods Obolus, Lingulella, and Lingulepis acuminata.

The best dated section is in the Flordillo Canyon in the central Caballo Mountains, which contains trilobite and conodont fossils that have helped determine its age.

[5] The lower beds are very scarce in fossils and difficult to date across the exposure area.