White Sands National Monument, fifteen miles southwest of Alamogordo, is
another area of great interest to the geologist and biologist. But its
strangeness, the graceful contours of its snow-white dunes, and the
peculiar adaptations of some of the plants and animals that live among
its dunes are appreciated as fully by the nonscientist. More than
370,000 visitors come to marvel at the White Sands each year.
The Monument, some 230 square miles in extent, preserves the most
impressive part of the world’s largest gypsum desert. This is a
glistening sea of pure gypsum sand that the wind has drifted into huge
dunes that are almost bare of vegetation except along the fringes.
Wavelike, the restive dunes move slowly before the prevailing winds,
covering and uncovering the few plants that lie in their way. And
wavelike, their surfaces trace the vagaries of indecisive breezes in
tiny parallel ripplelike ridges.
Because of the almost constant wind and resulting gradual advance of the
dunes, most of the plants that are able to establish themselves in the
open flats between the dunes eventually become buried. A few species,
however, are able to survive the irresistible march of the sand. Through
rapid growth and elongation of the stems, the struggling crowns remain
on top of the rising crests of the dunes. Plants with stems more than
forty feet long have been found. As the dunes continue forward under the
pressure of the wind, they leave the plants elevated on columns of
compacted gypsum bound by their adventitious roots.
Animals, too, have become adapted to their unusual surroundings. The
small creatures, lizards, mice, and others, are picked off easily by
such predators as foxes, coyotes, and hawks when they are conspicuous.
Thus, through the centuries, only the lighter-colored individuals have
survived among the dunes and, through many generations, have developed
pale and elusive animals that blend inconspicuously with their white
surroundings. Pocket mice are a good example of this. Among the white
dunes, the pocket mice are white; in the nearby red hills, they are a
rusty color; and on the beds of black lava a few miles north of the
sand, the pocket mice are very dark.
A visitor to White Sands National Monument should stop at the visitor
center, where exhibits explain the geology of the duneland and others
describe the plants and animals that are able to live there.
But how and from where did this natural wonder come? The dunes of gypsum
lie in the Tularosa Basin, which stretches for more than 100 miles
between two north-south mountain ranges. All sides of the valley slope
gently inward, forming the basin, with Lake Lucero, its lowest point, at
the southwest end of the Monument. This valley was formed hundreds of
centuries ago, when a great section of the earth’s crust settled to form
the type of basin known geologically as a graben.
High above the basin floor, beds of gypsum are found to the north in the
mountain ranges flanking the valley. Similar gypsum beds lie far beneath
the floor of the basin. Thus, it was once a part of the high plateau, a
great blocklike section that slowly sank to form the basin at its
present level.
Percolating water from seasonal rains and melting snow carries tons of
gypsum, in solution, from the highlands at the north end of the basin
into Lake Lucero. During much of the year, cloudless skies and warm dry
winds evaporate Lake Lucero, and it shrinks to a crystal-encrusted
marsh. Capillarity draws the gypsum-laden underground water to the
surface; it, too, evaporates, depositing its burden of gypsum throughout
the extensive “alkali flats.” The persistent southwest wind picks up the
particles of gypsum and whirls them away, adding them to the gleaming
white dunes, the accumulation of centuries.
The best ways to see the dunes are by car and by foot. Along the drive
that leads into the heart of the duneland are numbered posts that
correspond to numbered paragraphs in the Monument’s informational
folder. These paragraphs explain the features that are of particular
significance. At pull-outs along the drive, park the car and walk among
the dunes.
[Illustration: Capulin Mountain National Monument]