By Karen Kahler
Big Bend National Park Geologic History
The striking landscapes of Big Bend National Park in southwest Texas reflect the area's rich geologic history. Plant cover is sparse throughout most of this isolated desert park, allowing visitors a clear view of its dramatic rock formations.
Oldest Outcrops
The park's oldest rocks, sedimentary outcrops at Persimmon Gap, are 500 million years old. These rocks formed from sediments deposited in a deep-ocean trough that once extended along the southern edge of present-day North America.
Boquillas Formation
About 100 million years ago, a warm shallow sea covered what is now the Midwestern United States. The limestone of the Boquillas Formation (100 to 95 million years old) contain marine fossils ranging from small invertebrates to a 30-foot-long mosasaur.
Aguja Formation
As the Cretaceous period (144 to 65 million years ago) went on, the Big Bend area emerged from the sea. The Aguja Formation (80 to 75 million years old) contains the fossils of palms, ferns and other tropical swamp plants, as well as the fossils of almost 70 dinosaur species.
Volcanism
A series of volcanic eruptions began roughly 42 million years ago near what is now the park's northwest boundary. Magma welled up beneath the earth's surface, lifting the overlying area or escaping to the surface through fractures to form massive lava flows.
The Rio Grande and Erosion
Over the past two million years, the Rio Grande has eroded the strata of Big Bend to form picturesque canyons.
Resources
About the Author:
Karen Kahler began writing and editing technical documentation in 1986. She has since contributed articles on science topics to Salem Press reference works. A professional actor/dancer/choreographer, she also writes for the performing arts. She received a Bachelor of Arts degree in geology from Yale and currently resides near L.A.
Photo Credits:
Photo courtesy U.S. National Park Service/Eric Leonard
