Seen from the bird’s point of view, most of these desert sand dunes have a crescent shape, like the new moon. The horns of the crescent point downwind, with the slip face on the inside of the curve. This type of dune is called a barchan—a Russian term. (A sea of sand, as in Mexico’s Gran Desierto near the mouth of the Colorado River, is called an erg, a Hamitic word.) Dunes sometimes take other forms. There are transverse dunes, ridges of sand lying at a right angle to the course of the wind, and longitudinal dunes, which lie parallel to the wind. And there are parabolic dunes—barchans in reverse. Why dunes assume these different shapes is a question not yet resolved by those who have studied the problem.

How fast does a sand dune move? About twenty-five feet, sometimes up to fifty feet, in a year. Eventually the dunes achieve a point where they can advance no farther, climb no higher. When this happens, they resume the equally ancient process of consolidating themselves into sandstone. Into rock. We are talking here of a leisurely natural process, of millions of years. Sand and rock may observe a cosmic timetable, may follow some kind of pulse of their own, but if so this lies beyond human comprehension.

In our traditional conception of the desert we imagine it consisting entirely of billowing seas of sand, with here and there a palm tree, a gaunt saguaro cactus, the skull of a cow emerging from the sandy waves. Not so. Most of the Great American Desert is made up of bare rock, rugged cliffs, mesas, canyons, mountains, separated from one another by broad flat basins covered with sunbaked mud and alkali, supporting a sparse and measured growth of sagebrush or creosote or saltbush, depending on location and elevation. In the American desert sand dunes are rather rare, relative to the size of the area of which they are a part. Death Valley; the San Luis Valley in Colorado; Monument Valley in Arizona and Utah; the White Sands of New Mexico; the sand dunes near Yuma, Arizona, and in the Mojave Desert of Southern California; a few places in Nevada—that sums it up. But like many things that are rare, a field of dunes makes up in beauty what it lacks in vast expanse.

A simple but always varied beauty. Shades of color that change from hour to hour—bright golden in morning and afternoon, a pallid tan beneath the noon sun, platinum by moonlight, blue-sheened under snow, metallic silver when rimed with hoarfrost, glowing like heated iron at sunrise and sunset, lavender by twilight. With forms and volumes and masses inconstant as wind but always shapely. Dunes like nude bodies. Dunes like standing waves. Dunes like arcs and sickles, scythe blades and waning moons. Virgin dunes untracked by machines, untouched by human feet. Dunes firm and solid after rain, ribbed with ripple marks from the wind. Dunes surrounding ephemeral pools of water that glitter golden as tiger’s eye in the light of dawn. The clearcut cornice of a dune, seen from below, carving out of the intense blue of the sky a brazen, brassy arc of monumental particulars. Yes—and the dunes that flow around and upon a dying mesquite tree in the Mojave, suffocating a stand of junipers and yellow pine in some lovely piece of back-country Utah. Sand and beauty. Sand and death. Sand and renewal.