Protected as a National Park in 1944, the Big Bend of West Texas harbors one of the best concentrations of geologic formations on the planet. Spanning 500 million years of Earth's history, these rock layers represent the last three chapters of geologic time: the Paleozoic, Mesozoic and Cenozoic Eras.
In the early Paleozoic, some 500 million years ago (MYA), a seaway curved into the south-central region of North America, from Mexico to the latitude of Oklahoma and Arkansas. Over the following 200 million years, this shallow arm of the sea filled with sand, mud and gravel which hardened into layers of sandstone, shale and conglomerate rock. When North America and South America collided during the assembly of Pangea, 300-270 MYA, these sediments were lifted and folded into the Ancestral Ouachitas, which have since eroded into relatively low ridges across this region; stumps of the ancient mountains represent the oldest rocks in Big Bend National Park. About 135 MYA, a broad sea cut across North America, from eastern Mexico to northwest Canada, covering what is now the High Plains and Rocky Mountain corridor; after depositing thick layers of limestone, this Cretaceous Sea retreated, leaving younger sandstones and mudstones (with their cargo of dinosaur and marine life fossils) atop the limestone. The Cretaceous limestone now forms towering cliffs along the Rio Grande River and is the primary component of Big Bend's Deadhorse Range.
Following the Laramide Orogeny (Rocky Mountain uplift, 65 MYA), volcanism developed in the Big Bend region and occurred intermittently from the Eocene to the Miocene (from 42 to 22 MYA). The earliest eruptions formed the Christmas Mountains, in the northwest area of the Park, while later volcanism formed the Chisos Mountains, which include Big Bend's highest point, Emory Peak (7832 feet). Further uplift of the Mountain West during the Miocene has stretched the crust between Big Bend and the Colorado Plateau, triggering formation of the Rio Grande Rift and producing fault-block ranges across West Texas and eastern New Mexico. Finally, heavy precipitation during the Pleistocene molded the varied strata of Big Bend and the dry climate of the Holocene has served to protect and highlight the Park's geologic wonders.
