undifferentiated rock units

Paleontology and geology

A shallow sea covered parts of Idaho during the Ordovician, and large thicknesses of Ordovician marine sediments are known from southeastern and central Idaho (included as undifferentiated on this map). These contain a variety of fossils including algae, brachiopods, trilobites, ostracods, graptolites, corals, gastropods, crinoids, sponges, nautiloids, and very large trace fossils.