The state's most famous fossil site is exposed on the east bank of the Red River of the South at Montgomery Landing. Geological research has revealed a long and complex geological history for the regional now occupied by Louisiana. During the Late Proterozoic and Early Cambrian, the supercontinent of Rodinia was beginning to break up. This division created two landmasses, the northern Laurentia, consisting of the continental crust and overlying sedimentary cover of prehistoric North America and the southern Gondwana, which included South America. Much of the geology underlying the Louisiana area was detached from Laurentia in the process, and the Precordillaria terrane was shifted by plate tectonics until it collided with and attached to what is now Argentina. The gap between Laurentia and Gondwana, where most of modern Louisiana was situated, was filled by the Iapetus Ocean. The Iapetus continued to submerge Louisiana between Early Cambrian to Middle Mississippian times, eventually becoming a body of water known as the Rheic Ocean. Oceanic crust, island arcs, and trenches that formed and sediments that accumulated during this period have largely been consumed by subduction. No local fossils are known from this time, although fossils of Devonian to Mississippian brachiopods, crinoids, mollusca, trilobites and other invertebrates can be found in chert gravel found within the relatively recent Pliocene Citronelle and Willis formations. These fossils and gravels that contain them occur in were eroded and transported from the Nashville Dome in the state of Tennessee. Around this time, Laurentia and Gondwana began to reunite. During the collision between these continents, the remaining, small portion of oceanic crust and overlying sediment were shoved northward by Gondwana and incorporated into the Ouachita Mountains within Arkansas and Oklahoma during the Late Mississippian to the Early Pennsylvanian times. During the Middle Pennsylvanian, Permian, and Triassic, the region of Louisiana consisted entirely of dry land underlain by Gondwana-derived crust as part of the newly formed supercontinent of Pangea. During the Mesozoic breakup of Pangea, the Gulf of Mexico opened by the separation of the North and South American plates. Initially during the Triassic through early Jurassic, tensional deformation created a series of basement grabens and half grabens, which filled with terrestrial red beds and volcanic rocks. During the Middle Jurassic Bathonian and Callovian ages the stretching of the crust between North and South America created a broad basin within the continental crust that opened initially to the Pacific Ocean and later to the Atlantic Ocean.