Sierra del Carmen is a rugged, 40-mile-long section in the northern end of the eastern Sierra Madre range. Much of it is a so-called "sky island,"
with ridges and peaks rising more than 5,000 feet from the floor of the Chihuahuan Desert.
With high, striated cliffs above Boquillas Canyon on the Rio Grande river, the Carmen mountains are just across the Texas/Mexico border.
These limestone cliffs are often called Sierra del Carmen, and the forested summits to the south are called Maderas del Carmen.

Although it looks desolate, researchers documented 300 bird species, 65 species of reptiles and amphibians and 91 species of mammals (including 23 species of bats).