But these dinosaurs have been found in Utah as well. Coal-bearing rocks, including the Blackhawk Formation, were formed from extensive swamps along the edge of this retreating sea. Fossil trees, upright in growth position, have been found surrounded by the tracks of dinosaurs that fed upon their leaves. Above the coal beds, deposits of the Cretaceous-Tertiary North Horn Formation occur, mostly on the Wasatch Plateau. The lower part of the formation has yielded the remains of Upper Cretaceous dinosaurs, including the Cretaceous sauropod Alamosaurus , Arrhinoceratops and other ceratopsian dinosaurs, and hadrosaurs.
Dinosaur eggshells as well as teeth and bones from tiny Mesozoic mammals are found as well.
The upper part of the formation contains the fossil remain of larger Paleocene mammals. Further examination of this formation, which spans the Cretaceous-Tertiary boundary may help to answer questions about the extinction of the dinosaurs. William Lee Stokes, Geology of Utah . Utah Museum of Natural History and Utah Geological Survey, 1986. Paleontology and Geology of the Dinosaur Triangle .