undifferentiated rock units

Paleontology and geology

Early Devonian rocks are absent, as the state was above sea level during this time and any deposits have eroded away. Later Devonian rocks in Idaho are mostly shallow to moderate-depth marine sediments in the central and southeastern parts of the state, plus a few river deposits in parts of the southeast. Only one rock unit has yielded a variety of well-preserved marine fossils — it includes corals, brachiopods, stromatoporids, crinoids, sponges, gastropods, pelecypods, ostracods, cephalopods, conodonts, and fishes. Scattered river deposits in the northern part of southeastern Idaho have produced fossils of a variety of primitive fishes.