If the Rio Grande River interrupts the Big Bend country as a linear oasis, the Chisos Mountains interrupt it as a green island in a desert sea. The presence of the river and the mountains brings together creatures that you might not otherwise expect to find in desert areas.
Several species are quite rare. Isolation—set in motion thousands of years ago as the great ice age drew to a close—accounts for their rarity. As colder, moister climates retreated northward many plants and animals became stranded in the Chisos Mountains by the increasing aridity of the lowlands that surround them.
Carmen Mountains white-tailed deer provide a graphic example. Within the United States these deer live only in the Chisos Mountains. Also occupying several nearby mountain ranges in Mexico, they are unknown outside this area that the Rio Grande bisects.
White-tailed deer are not adapted to
desert conditions. They may have had a much wider range in this region
during the much cooler ice age. As the climate warmed, cooler conditions
prevailed only in the mountains because of their higher elevations.
Today, the fate of this smaller white-tailed deer can be monitored by
watching the desert mule deer gradually encroach on mountain foothills.
Adapted to desert life, mule deer appear to be usurping some of the whitetailed deer’s range.
Average rainfall at the Basin, a Chisos Mountains location popular with both people and animals, is twice that at Rio Grande Village along the river.
Approaching the mountains through Green Gulch, you pass grasslands punctuated by century plants and sotol, but soon you will notice green, leafy shrubs. Then the bushes get taller, with evergreen sumac, mountain mahogany, Texas madrone, and common beebrush.
You see both evergreen and deciduous trees. At an elevation of 4,500 feet, the first tall trees begin to appear. Higher up in the drainages you see masses of trees—junipers, small oaks, and pinyon pines. Some tree species grow at the extreme southern limit of their United States ranges in the Chisos Mountains. Arizona pine, Douglas fir, Arizona cypress, quaking aspen, and bigtooth maple are the last remnants of ice age-influenced forests once widespread here.
Some Big Bend plant species are found nowhere else in the world. The Chisos oak grows only in the Chisos Mountains highcountry. A number of plant species grow in the United States only in the Chisos Mountains, but they also are found in Mexico and elsewhere. Drooping juniper that looks as though it needs a good watering is such a plant.
To see all the bird species that occur in the United States, you eventually must come to the Chisos Mountains to see the Colima warbler. It nests here after wintering in Mexico.
Also found here is the mountain lion, locally called a panther. This cat has given its name to the lion’s share of park places, including Panther Pass and Panther Junction.