undifferentiated rock units

Paleontology and geology

Cretaceous-age igneous rocks that formed below the surface are exposed throughout most of the central part of the state. These rocks, referred to as the Idaho Batholith, do not contain any fossils. However, terrestrial and freshwater sediments in the eastern part of the state provide evidence of a diverse flora and fauna. Fossils from the Early Cretaceous include those of fish, turtles, crocodilians, freshwater gastropods, ostracods, bivalves, and plants, including freshwater algal fruiting (reproductive) bodies. In addition, a variety of dinosaur fossils (bone, teeth, eggshell fragments, and gastroliths) indicate the presence of ceratopsians, theropods, an ankylosaur, and a tenontosaur. Late Cretaceous deposits contain coal, angiosperm leaves, clams and crayfish burrows.