The Early Cretaceous Cedar Mountain Formation of east-central Utah has the most extensive record of Early Cretaceous terrestrial sedimentation of any comparably sized region in the world.

The latest Jurassic and earliest Cretaceous was an interval of tectonic quiescence, nondeposition, and erosion over most of the region leading to an unconformity representing 25 million years. During the Barremian around 125 million years ago, local salt tectonics in eastern Utah led to the local deposition of terrestrial sediments in the area around Arches National Park. The basal Yellow Cat Member of the Cedar Mountain Formation has been dated on the basis of charophytes, pollen, and dinosaurs as being Barremian in age. The dinosaurs include abundant polacanthine ankylosaurids, Gastonia burgei, the large ornithopods Iguanodon ottingeri, a sail‑backed iguanodontid (= I. ottingeri ?), a new small hypsilophodontid ornithopod, brachiosaurid Cedarosaurus with undescribed titanosaurid camarasaurid sauropods, a small coelurosaurian theropod, Nedcolbertia justinhofmanni, and the giant dromaeosaurid, Utahraptor ostrommaysorum . The polacanthine ankylosaurs, iguanodontids, and titanosaurid sauropods indicate close temporal and geographic ties to the Barremian of Europe.

The overlying Poison Strip Sandstone Member has yielded the large ornithopod Planicoxa, the titanosauromorph sauropod, Venenosaurus,  and  a new species of the polacanthine ankylosaurid, Gastonia indicating close ties to the fauna of the underlying Yellow Cat Member.

            Ruby Ranch Member of the Cedar Mountain Formation across eastern Utah preserves an dinosaur fauna that is as yet only partially studied and includes a large nodosaurid close to Sauropelta, the primitive iguanodontian Tenontosaurus, sauropods assigned to Pleurocoelus (= Astrodon), the dromaeosaurid teeth identified as Deinonychus, a large carnosaurid with coarsely serrated teeth, and the giant high‑spined theropod Acrocanthosaurus characterized by finely serrated teeth. Dinosaur faunas of this general composition are widely distributed across North America in the Cloverly Formation of Montana and Wyoming the Trinity Group of Texas and and the Arundle Formation of Maryland. The uniqueness of these dinosaurs suggests that with rising sealevels North America was isolated for much of the Aptian-Albian. The uppermost Ruby Ranch Member on the north end of the San Rafael Swell has also recently yielded the remains of several shamosaurine ankylosaurids Cedarpelta bilbyhallorum perhaps indicating early ties to Asia.

Along the western side of the San Rafael Swell in east‑central Utah, the Mussentuchit Member of the Cedar Mountain Formation spans the Albian/Cenomanian boundary based on radiometric dates (98.7 mya) and pollen. It preserves a very diverse terrestrial fauna known from both microvertebrate sites and skeletal remains. This fauna is dominated by the derived iguanodontian (hadrosauroid), Eolambia caroljonesa and also includes a small ornithopod, the small nodosaurid ankylosaur Anamantarx ramaljonesi, ceratopsian teeth, pachycephalosaur teeth, tiny sauropod teeth, a dromaeosaurid, possible troodontid teeth, cf. Richardoestesia teeth, cf. Paronychodon teeth, and an early tyrannosaurid. Additionally dinosaur egg-shell is abundant at many localities. 

Discovery of the Mussentuchit dinosaur fauna indicates that there is a dramatic faunal shift near the Albian ‑ Cenomanian boundary with replacement of dinosaurs typical of the

Aptian ‑ Albian by those characteristic of the Late Cretaceous. This dinosaur fauna is remarkably similar to those of the Campanian and Maastrichtian of western North America for which only the toothless theropods have not been recorded in the Mussentuchit fauna as yet. As the most likely ancestors of the tyrannosaurid, hadrosauroid and pachycephalosaur are from the Early Cretaceous of Asia, the dramatic shift to faunas typical of the North American Late Cretaceous is interpreted to result from opening migration corridors to and from Asia through Alaska at the end of the Early Cretaceous, when migration to eastern North America was still possible. However, flowering plants were coming into dominance during this same interval and may account for some of this faunal turnover.

The fossil record in the Cedar Mountain Formation of Utah indicates that a Barremian iguanodont‑polacanthid fauna with European affinities predating common flowering plants was replaced by an Aptian‑middle Albian Tenontosaurus‑Pleurocoelus fauna, perhaps representing an impoverished recovery fauna following a Early Cretaceous extinction event (endemic to North America). In turn, this was followed by a latest Albian‑earliest Cenomanian hadrosauroid dominated fauna with Asian affinities when flowering plants were co‑dominant in a considerably wetter habitat, which continued until the end of the Cretaceous.

The new Crystal Geyser Dinosaur Quarry is below beds preserving a typical Yellow Cat fauna. It has yielded the basal therizinosauroid Falcarius and parts of a new very large ankylosaur. Additional new sites preserving sauropods, theropods, and iguanodonts have been found this summer in the same general area and are going to be used to test the hypothesis that this level preserves the oldest Cretaceous dinosaur fauna in North America.