Colorado City Formation

The Colorado City Formation is a Late Triassic geologic formation in the Dockum Group of Texas, United States. It has previously been known as the Iatan Member, Colorado City Member or  'Pre-Tecovas Horizon'  (as it is assumed to be older than the Tecovas Formation).

The Colorado City Formation is mostly restricted to Howard and Borden counties. The formation hosts the Otis Chalk fossil sites, named after a ghost town in Howard County. Despite their importance, the Otis Chalk localities have been difficult to resolve in the stratigraphy of Triassic Texas. They occupy a narrow band of sediments between the slightly older Camp Springs Formation and much younger Cretaceous deposits.

The first major excavations near Otis Chalk were led by UMMP paleontologists starting in 1927. Several new phytosaur species were discovered during these digs. University of Oklahoma paleontologists followed with their own expedition in 1931. The vast majority of fossils collected from the formation were recovered during a 1939–1941 state-sponsored Works Progress Administration paleontological survey. Several sites southeast of Big Spring were particularly productive. Fossils collected by these efforts were stored at the newly opened Texas Memorial Museum in Austin. Since the 1940s, collection from the Otis Chalk area has been more limited. One notable find is a pond deposit, the Schaeffer Fish Quarry, discovered in 1967 by AMNH paleontologist Bobb Schaeffer.

Biochronological significance
The Otis Chalk localities that are situated in the Colorado City Formation form the basis of the Otischalkian Land Vertebrate Faunachron (LVF), which is defined by the first appearance of Parasuchus.

Archosaurs
Other archosaur fossils include remains of an unnamed silesaurid and a partial femur of a theropod or herrerasaurian dinosaur referable to the Chindesaurus + Tawa clade.

Fish
Fish fossils from Quarry 1 (NMMNH 860 / TMM 31025) include lungfish teeth (Arganodus? ), coelacanth scales, "palaeoniscid" scales (aff. Turseodus ), and hybodont shark teeth and spines (Lissodus? or Lonchidion?).