Called a “geologist’s paradise” as well as a “geologist’s nightmare,” the geological history of Big Bend National Park is a complex, even chaotic story. This story includes mountain building, an influx of shallow seas, volcanism, vertical faulting, and subsequent erosion to produce the views you'll enjoy during a visit there.

Sunset over the Chihuahuan Desert and Chisos Mountains, Big Bend National Park / Rebecca Latson

Early Mountain Building

The landscape on which Big Bend sits has been around for some 500 million years, although most of the rocks exposed today range in age from 100 million years to younger. The pressures that created the Oachita Mountains in Arkansas and Oklahoma reached over into the northern part of Big Bend. Most of this has been eroded away, but you can still see remnants of the far western portion of the Ouachitas near Persimmon Gap. 

Shallow seas over Big Bend

Around 135 million years ago (mya), during the Cretaceous Period (145 mya – 66 mya), a vast, shallow sea invaded the Big Bend area. This sea also divided the western portion of North America from the eastern portion. An abundance of calcium-rich organisms thrived in this shallow sea and their shells were deposited as thick lime muds that created such limestone as what is viewed at Santa Elena Canyon. You can even see ancient seashells in this limestone along the Santa Elena Canyon Nature Trail.

Fossil seashells in the canyon wall along the Santa Elena Canyon Nature Trail, Big Bend National Park / Rebecca Latson

Volcanism

Between 38 and 32 mya a series of volcanic eruptions occurred within the park to create the colorful layers and tuffs of the Chisos Mountains and surrounding area. Head out toward Castolon along the Ross Maxwell Scenic Drive and you’ll see the red-brown igneous dikes of the Fins of Fire along the southern edge of the Chisos Mountains.

Fins of Fire igneous dikes alongside the Chisos Mountains, Big Bend National Park / Rebecca Latson

Created from intrusions of magma into joints in the existing rock and then solidifying, these dikes are highly visible because they are more resistant to erosion than the surrounding landscape.

Goat Mountain, about 14 miles (22.5 km) from the Ross Maxwell Scenic Drive entrance, is the result of tuff deposits (a highly-porous rock of consolidated volcanic ash) and volcanic vents from which oozed lava flows.

Goat Mountain has a jumbled volcanic history, Big Bend National Park / Rebecca Latson

Just before arriving at Castolon, you’ll see to your left the colorfully-layered Cerro Castellan, born of pyroclastic deposits (volcanic rocks and magma ejected from volcanic explosions) and tuff topped by a dense rhyolite lava flow.

Cerro Castellan, Big Bend National Park / Rebecca Latson

Vertical Faulting

Just after passing Castolon, on your way to Santa Elena Canyon, stop off at the pullout for a better view of the Chihuahuan Desert and Chisos Mountains to the north. This disparity in high and low land levels is the result of a down-dropped block of land (graben) created by faulting. Limestone layers at the base of the Sierra del Carmens range to the east, and Mesa de Anguila range on the west, thus match layers found at the tops of the mountains! 

Looking north across the desert to the mountains, Big Bend National Park / Rebecca Latson

Erosion

The last 10 million years or so have been dominated by erosion sculpting the modern Big Bend landscape. Erosion wore down the high places and sediments filled in the low places.

Big Bend National Park has plenty of superlatives, including the fact the park preserves fossils from a longer span of time (130 million years) than any other national park unit! This includes the dinosaur extinction event (aka KT extinction), and fossil dinosaur bones found in Big Bend and nowhere else (Bravoceratops).

If you drive the park road from Persimmon Gap to Panther Junction, stop off at the revamped Fossil Discovery Exhibit 8 miles (12.9 km) north of Panther Junction on the Persimmon Gap Entrance Road (Highway 385).

You can read more about Big Bend’s fossil finds here, and download a Big Bend Geologic Map as a PDF to see for yourself the stories in stone that created this 801,163-acre national park.