The Cloverly Formation rests disconformably on the Morrison Formation and is conformably overlain by the Thermopolis Shale. It is subdivided into a variety of members, depending on the location. In the Bighorn Basin along the Montana-Wyoming border, Moberly divided the Cloverly into the following three members:
The Pryor Conglomerate lies at the base and contains abundant black chert. It is named from thick beds exposed on the west side of the Pryor Mountains.
The uppermost unit is the Himes Member, which contains some coarse-grained channel sandstone deposits, but consists primarily of brightly multicolored mudstones.
In contrast, Ostrom divided the formation into four units, which he named Units IV-VII:
Unit IV equates to the Pryor Conglomerate of Moberly and consists of a conglomerate or conglomeratic sandstone.
Unit V, overlaying Unit IV, consists of a lower grey-to-purple claystone with abundant fist-sized chalcedony and barite concretions; the unit is highly bentonitic and contains occasional channel sands.
Unit VI is a discontinuous "salt and pepper" cross-stratified channel sandstone with occasional conglomerate, considered by Moberly to be part of the Himes Member.
Unit VII, the uppermost, is a maroon to orange claystone with occasional highly rounded and polished pebbles of silica.
Age
by the fission track method has yielded dates of 115 ± 10 Ma for the lower part of the Little Sheep Member and 108.5 ± 0.2 Ma near the top of that member, confirming that the Cloverly Formation is of Aptian to Albian age.
Depositional environment
The sediments of the Cloverly Formation were deposited in alluvial and floodplain environments. The basal conglomerates probably represent braided river deposits, while the sandstones were deposited in fluvial channels. The mudstones that contain most of the fossils represent overbank, lacustrine, and pedogenic deposits.
Vertebrate fauna
Animals recovered include the dinosaurs Deinonychus, Microvenator, Tenontosaurus, Zephyrosaurus and Sauropelta as well as fragmentary remains of Titanosaurs and Ornithomimids. As well, two genera of turtle Naomichelys and Glyptops and the lungfish Ceratodus. Dinosaur eggs have been found in Montana. References for data: Ostrom 1970; Cifelli et al. 1998; Cifelli 1999; Nydam and Cifelli 2002. Possible goniopholidid remains are known from the formation.
Ornithischians
Saurischians
Theropod eggshell fragments are known from the formation. Unidentifiable ornithomimid remains are present and most commonly represented by toe bones. Indeterminate allosauroid remains are known from the formation. Remains identified by John Ostrom as Ornithomimus are suspected by Jack Horner to be of a new ornithomimid genus.
Mammals
Turtles
Bony fish
Indeterminate amiiformes are known from the formation.
