The Mesilla Valley Shale is a geologic formation in southern New Mexico, northern Chihuahua, and far west Texas.

[2][3] The formation is particularly well exposed at Cerro de Cristo Rey, near El Paso, Texas, where it is part of a thick sequence of uplifted Cretaceous beds that record transgressions (advances of the sea onto land) and regressions (retreats of the sea from the land) of the Western Interior Seaway during the mid-Cretaceous.

Trigonia emery Conrad, Helicocryptus mexicanus Bose, and Turritella granulata Sowerby var.

[2] The formation also contains ammonoids, brachiopods, foraminiferans (especially Cribratina texana), dinoflagellates, serpulid worms, corals, ostracods, calcareous algae, and some terrestrial plant fragments.

These include Ancorichnus, Arenicolites, Bergueria, Bichordites, Cardioichnus, Chondrites, Cochlichnus, Coprulus, Gordia, Helicodromites, Lockeia, Ophiomorpha, Palaeophycus, Planolites, Protovirgularia, Rhizocorallium, Skolithos, Spongeliomorpha, Taenidium, Thalassinoides, Treptichnus, and a biofilm, Rugalichnus.