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Big Bend National Park

Date of Submission: 12/04/2017
Criteria: (viii)(ix)
Category: Natural
Submitted by:
United States Department of the Interior
State, Province or Region:
Coordinates: 13 R 674200 E 3245500 N
Ref.: 6241
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Established in 1944, Big Bend National Park encompasses 324,153 hectares along the international border with Mexico.  As the largest protected portion of the Chihuahuan Desert in the United States, the park preserves vast desert landscapes, mountain ranges, desert springs, and riparian ecosystems along the Rio Grande. 

Elevation in the park ranges from 550 meters along the river to 2380 meters in the Chisos Mountains. While arid grasslands and desert scrub occupy the lower elevations, a cooler, wetter climate can be found in the “sky island” of the mountains.  This montane woodland ecosystem preserves relict forests of Arizona pine, Douglas fir, Arizona cypress, quaking aspen, and bigtooth maple that were widespread during the Pleistocene Ice Ages.  Overlapping ecotones in the mountains can create odd juxtapositions, such as cactus growing in a bed of moss.  Black bears, mountain lions, collared peccaries, mule deer and other large mammals inhabit the area.

Geologically, the park is highly diverse, with exposures of sedimentary, igneous, and metamorphic rocks from the Paleozoic, Mesozoic, and Cenozoic Eras.  Sedimentary deposits include marine, coastal, and continental rocks, including carbonates and clastics.  Igneous exposures include both basalt and rhyolitic rocks deposited as intrusions (dikes, sills, laccoliths) and extrusive volcanic rocks (lava domes, pyroclastic flows, volcanic tuffs).  Rare mineral deposits include cinnabar and other mercury minerals, fluorite, and a variety of agates. The park is located at the intersection of the 3 major North American mountain-building episodes (the Appalachian Mountains, the Rocky Mountains, and the Basin and Range Province), creating a unique location to study the interaction of tectonic forces.  Numerous scientifically-important fossils have been found in the park, including species new to science and some found nowhere else in the world.

Justification of Outstanding Universal Value

Big Bend NP is globally significant for its rich paleontological record. The park’s fossil record documents the end of the Age of Reptiles and much of the Age of Mammals.  Ecosystems changes over geologic time are recorded in an almost continuous rock record spanning 130 million years, from the Cretaceous Period through the Cenozoic Era to the present. 

Over 1200 different fossil taxa are known from the park, including fossils of plants and animals from marine environments, coastal ecosystems, and inland continental environments.  The park’s fossil record includes numerous species that are new to science, and some found nowhere else in the world. 

The diversity represented in this fossil record is rarely matched by any other site in the world. It includes dinosaurs, mosasaurs, pterosaurs, crocodiles, alligators, turtles, lizards, birds, insects, frogs, toads, salamanders, boney fish, sharks, rays, sawfish, bivalves, ammonites, nautiloids, gastropods, sea urchins, corals, worms, sponges, plankton, saber-toothed cats, primitive dogs, early primates, early horses, camels, rhinoceroses, weasels, gophers, marsupials, tortoises, brontotheres, mammoths, and numerous plants, including many kinds of trees, ferns, leaves, algae, and fungi.

The park’s most famous fossil is Quetzalcoatlus, a giant pterosaur with a 35-foot wingspan, making it the largest known flying creature of all time.  The park is home to several fossil forests, a very rare occurrence where petrified tree stumps stand in their growth position, creating extremely valuable opportunities for understanding ancient forest ecology. 

The park’s diverse geology creates remarkably diverse of habitats for plant and animal life.  More than 400 bird species have been recorded at Big Bend, and the park supports significant bat, reptile, insect, and mammal diversity, as well as a wide variety of cactus and other plants. The park protects numerous rare and endangered species, including Mexican long-nosed bats, Big Bend mosquitofish, black-capped vireo, Chisos hedgehog cactus, Guadalupe fescue grass, and others.

Criterion (viii):  The park preserves an exceptionally detailed paleontologic record of the past 130 million years, from the end of the Age of Reptiles (Mesozoic Era) through the Age of Mammals (Cenozoic Era).  Big Bend is one of very few places in the world to have exposures of strata laid down during the terminal Cretaceous extinction, the asteroid impact event that wiped out the dinosaurs and three-quarters of the plant and animal species on Earth. These strata, known as the Cretaceous-Paleogene (or K-Pg) boundary, are from the very end of the Cretaceous Period.  The K-Pg strata in the park are unique, because they are the only known non-marine or continental deposits in the world that are in relatively close proximity to the asteroid impact site that triggered the extinction episode.  Remarkably, the K-Pg boundary beds at Big Bend show evidence of the tsunami caused by the asteroid impact near the Yucatan Peninsula. 

The terminal Cretaceous extinction was one of the most significant episodes in the history of life on earth, and Big Bend NP preserves one of the world’s most important records of that dramatic event.  

Criterion (ix): Big Bend National Park protects the largest and most representative example of the Chihuahuan Desert ecosystem in the United States, and includes the entirety of the Chisos Mountains.  The mountain range functions as a cooler, wetter “sky island,” preserving a relict forest that is isolated by the surrounding desert.  The river corridor of the Rio Grande, along with the springs, desert, mountain, and grassland environments support extraordinary biological diversity including endemic and rare plants and animals.  In particular, the park supports notable diversity in birds, bats, butterflies, scorpions, ants, reptiles, and cacti.

Ranges of typically eastern and typically western species of plants and animals come together or overlap here and many species are at the extreme limits of their ranges. Latin American species, many from the tropics, range this far north, while northern-nesting species often travel this far south in winter. Endangered species found at Big Bend are the black-capped vireo, yellow-billed cuckoo, Mexican long-nosed bat, and Big Bend gambusia (a tiny fish found only in the park).  Threatened species include yellow-billed cuckoo and several cacti species including the Chisos agave, which lives nowhere else in the world.

Statements of authenticity and/or integrity

Big Bend National Park has preserved 324,153 contiguous hectares under the exclusive jurisdiction of the U.S. National Park Service since its establishment in 1944, and will continue to do so in perpetuity.  Park management includes dedicated scientists and resource professionals who protect intact ecosystems, perform restoration work, and collaborate with their peers in nearby U.S. and Mexican protected areas.  Collecting plants, animals, rocks, fossils, artifacts, or any other material from the park is strictly prohibited, and park law enforcement rangers ensure this resource protection. 

The park serves as the keystone for a group of surrounding large protected areas, including Big Bend Ranch State Park (Texas), Black Gap Wildlife Management Area (Texas), and three protected areas in Mexico:  Áreas de Protección de Flora y Fauna Cañón de Santa Elena, Maderas del Carmen, and Ocampo.  The Mexican protected areas encompass more than 800,000 hectares, and Big Bend park managers collaborate with Mexican managers on resource issues. The river corridor is also a protected area, designated and managed as the Rio Grande Wild and Scenic River on the U.S. side of the border and Monumento Natural Rio Bravo Del Norte on the Mexican side.

Comparison with other similar properties

Big Bend differs from other fossil localities by its span of geological time (130 million years), the completeness of the largely-uninterrupted geological record, and the diversity of the paleo-environments preserved.  Most localities measure time spans in millions or tens of millions of years, and very few would exceed 100 million years.  Even the remarkably complete record at John Day Fossil Beds National Monument (Oregon) only covers about 37 million years—roughly a quarter of Big Bend’s time span. Most world-class fossil localities exhibit excellent preservation within a single paleo-environment, such as the exquisite fossil record preserved in ancient lake beds at Florissant Fossil Beds National Monument (Colorado).  However, Big Bend preserves multiple paleo-environments, including marine, coastal, inland floodplain, volcanic upland, and ice age savannah.  The Cretaceous-Paleogene boundary beds preserved in the park are peerless.  They are the only known non-marine deposits in the world that are in relatively close proximity to the asteroid impact site that triggered extinction of some three-quarters of species on Earth.