These pinyon-juniper-oak woodlands are pretty typical of the dry Southwest. Chisos woodlands include only one pine, three junipers, and many varieties of oak. You can easily identify pinyon and juniper trees, but the oaks are often hard to tell apart because they tend to hybridize. The different tree species have different soil and water requirements and where moisture is harder to come by they grow smaller and more widely spaced. You’ll find redberry juniper at drier, lower elevations, such as Green Gulch. This is a rather scraggly shrub or small tree whose lower branches often touch the ground. It has scale-like yellow-green leaves, and red berry-like cones. It will often invade abused grasslands. The gray oak, an evergreen with small olive-green leaves and dark gray bark, also prefers drier soils. On exposed slopes it too takes on shrub-like proportions but grows to 20 meters (65 feet) in protected canyons. Birds, peccaries, and deer feed on gray oak acorns. The Indians preferred the acorns of the Emory oak.
Startling plant combinations comprise this forest floor on the South Rim of the Chisos. Such biotic richness and surprise led to the park’s designation as an International Biosphere Reserve.
Volcanic spires remind us that change has not always come slowly in the Big Bend. Molten rock under intense pressure created these spires as plugs inside softer rock, which has long since eroded away.
The other narrowleaf evergreens prefer intermediate to moister soils and the Chisos Basin is a good place to see both drooping and alligator junipers, the latter named for the square scales that make its bark look like alligator hide. This slow-growing, long-lived tree has bluish-green needles, and gray fox and rock squirrel relish its berry-like cones. Drooping juniper all but cries out for recognition. Its wilted leaves and drooping branches seem to be dying of thirst, but in fact are perfectly healthy, as is the bark that shreds in long, fibrous strips. You’ll find plenty of drooping juniper in Mexico, but the only place you can see it in the United States is right here in the Chisos Mountains.
The Chisos Basin has been hollowed out of volcanic rock by stream erosion. The peaks that ring the Basin all came into being when molten rock squeezed up under enormous pressure from deep within the Earth. Some of the red hot stuff poured out over the land surface in lava flows which cooled so quickly that they cracked in long vertical fissures. Then as the ages passed, joints toppled and square-faced peaks, buttresses, and free-standing spires emerged. So the Basin wall took shape from Casa Grande southward through Emory Peak. Later on, more molten rock pushed up from below, bulging the surface rocks upward without breaking through. Again the eons passed and the softer surface rocks wore away, exposing the dome-shaped peaks which now rim the Basin to the north and west. Today, loose rocks and clays still inch downhill toward the Window. All Basin runoff heads for this chute, and when it storms in the heights, the dry waterfall turns into a torrent, with boulders bouncing along like so many corks. Growling and grumbling, the big rocks plunge over the pouroff in a 67-meter (220-foot) free fall, coming to Earth in a great rubble pile below.
Pinyon pines grow abundantly across both Mexico and the American Southwest. In the Chisos you’ll find them almost anywhere above 1,500 meters (4,800 feet) of elevation, and at lower elevations they will be the only pines. Short of trunk, with spreading lower branches, egg-sized cones, and short, slender, bluish-green needles, pinyons range from dwarf size to a tree 15 meters (50 feet) tall. Many birds and mammals eat its delicious nuts.
As elevation increases you may find fewer junipers, while more pinyons appear on the open slopes and more oaks along drainages. The deciduous Graves oak requires more moisture than other oaks, so you find it putting forth its shiny, dark green leaves in high moist canyons. The Emory oak also prefers high drainages but it grows at slightly lower elevations. It has small lance-shaped leaves. The Chisos oak, a small, graceful tree with narrow, leathery leaves, requires a high water table. In all the world it grows only in the Chisos Mountains’ Blue Creek Canyon.
