Geology deals with the study of rocks in laymen's terms. And Big Bend National Park certainly has its share of rocks. Due to sparse vegetation and recent erosion, the rocks that lay in the Big Bend are clearly exposed. Geologic processes in volcanoes, landslides, flashfloods, fossils, etc.
During the Cretaceous Period, about 135 million years ago, a warm, shallow sea existed in the Big Bend. Lime mud and remains of sea life deposited creating visible limestone layers. Evidence of this process can be seen in all three river canyons, Santa Elena, Mariscal, and Boquillas, the Dead Horse Mountains, and the cliffs of the Sierra Del Carmen in Coahuila, Mexico. About 100 million years ago, the sea retreated to the current-day Gulf of Mexico. Fossil remains from this include ammonites, giant clams, oysters, and other aquatic life. The shores of the sea left behind petrified forests and fossils of turtles and crocodiles. Fossil remnants of dinosaurs were deposited even farther inland.
In general, dinosaur remains are as common as one would think. However, remains of duck-billed, horned, and large sauropod and carnivorous dinosaurs have been discovered. Fossils of crocodiles have also been found. Near Glen Springs in the National Park, the skull and jaws of a fifty foot long crocodile was discovered and is presently on display at the American Museum of Natural History located in New York City.
In 1971, the largest known flying creature, a giant pterosaur, was discovered. Quetzalcoatlus northopi was named after an Aztec God, Quetzalcoatl. Quetzalcoatl was believed to have taken the form of a feathered serpent. This amazing flier has a wingspan up to 39 feet and is believed to have been covered with hair. A typical dinner for most Quetzalcoatlus consisted of fish and crustaceans, while others had a palette of insects. A life size replica of the wing bones of this amazing pterosaur can be located at the Panther Junction Visitor Center in the National Park.
The next major mountain building phase occurred in the Big Bend towards the close of the Cretaceous Period. A compression of the earth's crust, beginning in Canada, gradually moved south. Due to uplifting and folding of ancient sediments, the Rocky Mountains began to form.
Volcanic eruptions became the next form of geologic processes to occur in the region. Volcanic activity can be seen in the area around the South Rim of the Chisos Mountains, Pine Canyon, Burro Mesa, near Castolon, and numerous other places in the National Park and throughout the Big Bend. Ash spewing forth from an erupting volcano blankets the ground, creating a lot of the present-day colorful rock. The Ross Maxwell Scenic Drive in the National Park has some of the best examples of volcanic activity in the region.