Actual size
Since the coming of the park, cottonwoods have returned to the floodplain, especially at Castolon. A stately colonnade of eastern cottonwoods lures ladderback woodpeckers and yellow-bellied sapsuckers to Cottonwood Campground. More than 100 lanceleaf cottonwoods may be seen along the road that leads to Santa Elena, Mexico. Standing as much as 30-meters (100-feet) tall, refreshingly green in summer and gorgeous gold in fall, cottonwoods seek water by spreading horizontal roots far and wide, and by sending taproots deep down to the water table. They propagate in early summer by shaking millions of cottony seeds upon the wind. These fuzzy white parachutes may lie in windrows or cover the ground downwind like new fallen snow.
Along the River Road from Castolon to Santa Elena Canyon, you get another glimpse of what water means in the desert. The road winds along the edge of an alluvial bench from 15 to 30 meters (50-100 feet) high. Atop this terrace you have the widely spaced shrubs of the Chihuahuan Desert, but peer over the edge and you find a dense green wilderness crowded between the benchface and the river. All that separates lifeless sand from green jungle is the vertical distance that stops the water. Down there salt cedars have packed themselves thickly into the narrow space.
Another water-loving plant prevalent along the river and dry washes is honey mesquite, a feathery, thorned shrub- or tree-sized member of the pea family. Its root system, with a deep tap root, is so extensive that more wood lies underground than shows above ground, and natives say you must “dig for wood” here. Mesquite trees multiply as persistently as salt cedar, but are highly useful to man and to wildlife. Honey bees and butterflies visit the yellow mesquite flowers, quail roost in the branches, and wood rats collect mesquite beans in tremendous numbers. Deer, horses, and cattle also relish the beans, while Indians and early settlers made a nutritious bread from mesquite bean flour. Honey mesquite carries the standard Kentucky-wonder type of bean. But the screwbean mesquite or tornillo—for which Tornillo Creek was named—puts out a curious cluster of corkscrew-shaped fruit pods. Mesquites often mass together in thickets, and they do very well in the drier soils of arroyos, often rubbing thorns with acacias, a family of sweet-smelling, flowering trees and shrubs attractive to honey bees and hummingbirds. The roots of these thickets provide apartments for scores of floodplain pocket gophers, kangaroo rats, and hispid cotton rats.
A greenbelt along a wash contrasts sharply with surrounding desert habitat.
Despite the luxuriance and rapid growth of floodplain flora, life along the greenbelt rests in precarious balance. The floodplain is the one place in the park from which domestic cattle have never been successfully removed. The problem is that Mexican cows, horses, and burros do not recognize international boundaries.
There was a day when cows grazed grasslands at higher elevations, and before the cows could be seen herds of pronghorns, golden, graceful, large-eyed, with black horns and white rump patches. Imagine if you can how Tornillo Flat must have looked at the turn of the century with fine grasses bending under the wind and the pronghorns flashing their rump patches in sudden semaphore. Depending on speedy flight for protection, pronghorns seek wide-open places where they can see a long way off. Today, Tornillo Flat is a bald shrub desert. The pronghorns vanished long ago. The small band sometimes seen north of Tornillo Creek is the remnant of a herd reintroduced in the 1940s.
The grass that flourished on Tornillo Flat in its heyday was a very good clump-forming grass called tobosa. To the first settlers it looked as though there was more grass along Tornillo Creek than could ever be eaten off. Yet the tobosa soon disappeared, falling first to mowing machines and finally to the domestic herds that cropped it out of existence. Hay balers plied Tornillo Flat into the 1930s.