Big Bend National Park has national significance as the largest protected area of Chihuahuan Desert topography and ecology in the United States. Few areas exceed the park s value for the protection and study of geologic and paleontologic resources . Cretaceous and Tertiary fossil organisms exist in variety and abundance. Archeologists have discovered artifacts estimated to be 9,000 years old, and historic buildings and landscapes offer graphic illustration of life along the international border at the turn of the century. Dry, hot late spring and early summer days often exceed 100 degrees in the lower elevations.
Winters are normally mild throughout the park, but sub-freezing temperatures occasionally occur.
Because of the range in altitude from approximately 1,800 feet along the river to 7,800 feet in the Chisos Mountains, a wide variation in available moisture and in temperature exists throughout the park. These variations contribute to an exceptional diversity in plant and animal habitats. The 118 river miles that form the southern park boundary include the spectacular canyons of Santa Elena, Mariscal, and Boquillas. The Rio Grande, meandering through this portion of the Chihuahuan Desert, has cut deep canyons with nearly vertical walls through three uplifts comprised primarily of limestone. Throughout the open desert areas, the highly productive Rio Grande riparian zone includes various plant and animal species and significant cultural resources.