Big Bend National Park

Big Bend Through Time

The Indians said that after making the Earth, the Great
Spirit simply dumped all the leftover rocks on the Big Bend.

Big Bend Brochure (NPS)

By anyone's measure, Big Bend is beautiful country. To those of us with an interest in geology, Big Bend is more beautiful yet. By understanding the geologic history of Big Bend, we can understand the significance of some of the parks most interesting features: the Chisos Mountains, Mule Ear Peaks, Santa Elena Canyon, Persimmon Gap.

When viewing this site and reading through the geologic history, it is important to remember that the Earth's geologic history covers a time span of about 4.6 billion years! The oldest rocks presently exposed in Big Bend date to about 300 MYA (million years ago), so that only a small portion of the Earth's entire history is visible within Big Bend. However, through techniques of geologic interpretation, scientists have constructed a timeline of geologic events that affected Big Bend during the entirety of the Paleozoic, Mesozoic, and Cenozoic eras.

The rest of this page is a geologic timeline divided into significant periods in the development of Big Bend. Ancient history is at the top of the page, more recent history at the bottom. When you encounter the shape of Texas, it represents the level of the ocean during the time period it is directly adjacent. The blue represents ocean and the brown represents land above the ocean.

Paleozoic Era

570 MYA - 245 MYA

Cambrian -- North America is covered by a shallow ocean belt that trends northwest-southeast from the Gulf of Mexico to the Pacific Northwest. In Big Bend, the sediments deposited during the Cambrian were primarily sandstones, limestones, and dolomites. Marine life included trilobites, brachiopods, bryozoans, snails, clams, and sponges. The Cambrian Period marks the first time that multicellular organisms are known to have existed, but none of these organisms (or the rocks containing them) are presently exposed at the land surface.

Ordovician, Silurian, Devonian, Mississippian -- Shallow seas continue to cover the Big Bend region. Limestone and chert beds were deposited, some of which contain brachiopod, coral, cephalopod, and gastropod fossils. The numbers and diversity of corals increase dramatically, and the first land plants appear. Big Bend is still covered in shallow seas, but the character of sedimentation changes slightly to include shales (in addition to chert, limestone, and sandstone deposition).

The Devonian Period is known as the "Age of Amphibians" since this is when the first amphibians evolved. Marine life also showed great leaps in evolution, with the development of more complex and numerous species of fish. Occasionally the seas receded somewhat, and land plants thrived in a marshlands environment -- the most common plants were ferns, horsetail rushes, and huge decidious trees. Fern forests and amphibians thrived on land, and the seas (which still covered portions of Big Bend country) were filled with a multitude of developing organisms.

Pennsylvanian -- During most of the Pennsylvanian, Big Bend was covered by shallow seas. However, towards the end of the Pennsylvanian Period (approximately 300 MYA), the cataclysmic collision of North America with South American and Africa produced the Ouachita Mountain chain that ranges across the eastern seaboard and the Gulf states. In southwest Texas, the collision caused the entire Big Bend region to rise above sea level, exposing much of it to a land environment for the very first time. In the modern Big Bend region, remnants of the Ouachita Mountains are visible only at Persimmon Gap at the northern entrance to the park. Land organisms thrived during the Pennsylvanian, The Age of Reptiles.

Permian -- The Permian Period left no geologic record in Big Bend. We know from studies in other parts of the world that precursors to the dinosaurs were developing during the Permian, but Big Bend is missing the strata (rock layers) from this time period. A gap such as this one in the geologic record is known as an unconformity.

Mesozoic Era

245 MYA - 66 MYA

Triassic, Jurassic -- There is no record of Triassic/Jurassic aged rocks in Big Bend National Park. When there appears to be a gap in the rock record, it is called an unconformity.

Cretaceous (early) -- During the early Cretaceous, the Big Bend area was covered by ocean. Ammonites, mollusks, and other shellfish are predominantly found amongst the sandstones and limestones deposited during this time period. During the beginning of the Triassic, a thick layer of limestone known as the Glenrose formation was deposited in a deep sea environment. Following the deposition of the Glenrose formation, a very thin (3 meter) layer of sandstone known as the Maxon formation was deposited in a shallow sea environment. Because the sediments show that the ocean was first fairly deep then less deep, we can infer that the ocean was receding toward the end of the early Cretaceous.

Mid-Cretaceous -- For most of the mid-Cretaceous, Big Bend was covered by ocean. The beginning of the mid-Cretaceous in the park is characterized by thick (750-850 ft) beds of cherty limestone, the Santa Elena Canyon formation. The next layers of rocks deposited in the park indicate that the ocean levels were receding, although small transgressive/regressive cycles can be found. Later on, it is evident from coal beds, mudstone, and thick layers of continental clay that the Big Bend area had a swampy environment. Dispersed throughout the clay and mudstone layers are dinosaur fossils.

Late Cretaceous -- The late Cretaceous was a time of uplift in which the ocean receded. Vast swampland with dense vegetation marked the beginning of the of the late Cretaceous, depositing continental clays and with it dinosaur fossils. The Javelina Formation is one such layer of clay and fossils. It was during this time also that flowering plants first grew in the park. The end of the Cretaceous is marked by the extinction of all dinosaurs.

Cenozoic Era

66 MYA - Present

Paleocene -- The Paleocene epoch was the calm before the volcanic storm struck. The oceans receded to close to where they presently are. Terrestrial vegetation continued to evolve, and mammals appeared for the first time. Sandstone and clay with thin interbedded layers of conglomerate are deposited throughout the park during this time.
Eocene -- The beginning of the Eocene epoch is marked with strata very similar to that which was deposited in the Paleocene. However, this peaceful landscape was shortly transformed into an ash covered wasteland after a major volcanic eruption in the area. After all the ash and debris settled, rain and erosion occurred, leaving behind tuffaceous sandstones and tuffaceous clays. These layers are now known as the Canoe formation.

Toward the end of the Eocene another volcanic eruption marked the Big Bend region, throwing ash and pouring thick layers of lava over the landscape. Most of the extrusive igneous features seen in the park were formed at this time. These lava and ash flows coupled with their sedimentary counterparts are known as the Chisos formation and can be found scattered throughout the central and south sides of the park.

Oligocene -- The Oligocene marks another violent period of time in the history of Big Bend. During this time, yet another volcanic episode occurred. The resulting strata, the South Rim formation is a massive lava flow combined with ash beds, some sandstone, and conglomerate. The South Rim formation is exposed on the top of the Chisos mountains and is also present atop Burro Mesa.

Miocene, Pliocene, Pleistocene, Holocene (Quaternary Period) -- Since the formation of the South Rim Formation, the only depositional features that are really worth noting are alluvial features. Talus slopes formed and are continuing to form around the massive and resistant volcanic features of the park. Loads of sand and silt are carried from areas of high elevation to lower elevations by rainfall and are eventually swept to the Gulf of Mexico by way of the Rio Grande. Desert vegetation and sparse grasslands now cover the Big Bend area. Bears, javelina, rabbits, coyotes, and tourists inhabit the Big Bend.

Big Bend's geologic history is quite unique, a mixture of placid ocean deposition, murky swamps with large reptiles, and violent earth-shaking volcanic eruptions. Now that you know a bit about the geologic history of the park, visit the links on the image-map below to learn more about the geologic processes that occurred throughout the history of the Big Bend.