Paleontology and geology
Through most of the Permian, Arizona was mainly a low-lying area that continued to receive sediment from tectonic activity in the southeast. The floodplains and rivers of central Arizona channeled this sediment to the coast (which stretched along the present-day border between Arizona and California), forming extensive dune fields. By the Late Permian, sea level rose and most of Arizona consisted of marine and shoreline habitats, which were home to an extensive fauna of nautiloids, ammonoids, bivalves, and other invertebrates. The limestones, shales, and sandstones that originated as sediment on the Permian sea floor are now exposed in the spectacular walls of the Grand Canyon of northern Arizona.