undifferentiated rock units

Paleontology and geology

Much of Arizona was under a shallow sea during the Carboniferous. These marine waters were inhabited by a diversity of invertebrate organisms, including corals, crinoids, bryozoans, brachiopods, and bivalves. The crinoid-rich Redwall Limestone covers nearly half the state and provides evidence of an extensive shallow marine shelf. By the Late Carboniferous, however, tectonic activity along the west and south coasts of North America began to crumple this shallow shelf into several small basins.