(From Sharp, 1995)

Exploring dunes is fun. They can be mysterious and beautiful. Many are alive, changing shape with each shift in the wind. The witching time for dunes is just before sunset and just after sunrise, when shadows are long and deep. Then one appreciates the remarkable grace of curving dune crests and the complicated intermingling of geometrical forms. Walking through dunes at sunset, when the western sky reflects its twilight glow onto the sand, can be a mystical, magical, almost religious experience. Kelso Dunes lie in the eastern Mojave Desert, about midway between the diverging paths of Interstate 15 to the north and Interstate 40 to the south. Kelso is an abandoned section station of unusual elegance, size, and history on the Union Pacific Railway. It was established in 1906 as a station along the San Pedro, Los Angeles, and Salt Lake Railroad, which later became a subsidiary of Union Pacific. Best seasons to visit the dunes are winter, spring, and fall.

Kelso Dunes rise from a broad alluvial apron that slopes very gently down to the north from the Granite Mountains. Projection of this smooth surface under the highest dunes suggests a sand thickness of at least 700 feet. The dunes lie at the end of an umbilical cord supply line of wind blown sand four to five miles wide that extends 35 miles east and southeast from the mouth of Afton Canyon ). This long trail of sand includes the sand-covered Devil's Playground just northwest of the dunes, which receives additional sand from the north. The rugged Providence Mountains to the east were named by early Mormon travelers in appreciation for their springs.

Prevailing winds in the Mojave Desert blow from the western quadrants. Here at Kelso Dunes, the shape of the landscape channels the winds into the prevailing west-northwesterlies, although ripple marks and dune forms show that strong winds occasionally attack the dunes from all directions. These storm winds cause profound changes in dune shapes.

Four large, linear ridges that bear east to northeast are the main features of the Kelso dunes complex. Many smaller transverse ridges cover their flanks and the areas between them. A typical transverse ridge is 200 to 300 feet long. Its broad windward flank slopes 10 to 15 degrees and has a firm surface commonly decorated with little ripples. The windward slope climbs to a smooth crest, which drops off into a steep leeward face that stands at the angle of repose of dry sand, up to 34 degrees. The upper edge of the steep lee face generally ends a bit lower than the dune crest, which typically is gently rounded. Lee faces range in height from a few to 30 feet and vary along a dune's length. The somewhat sinuous crestline alternates between broad, rounded summits and open intervening saddles.

The wind rolls some sand grains along and bounces others across the dune surface in a series of short hops. The bouncing grains knock others across the surface as they crash-land back on the dune. Those impacts kick large grains along in a series of sudden jerks, like a small boy kicking a tin can down the sidewalk. Bouncing, the most efficient means of wind movement of sand, accounts for about three-quarters of the total sand transport. The difference between rolling and bouncing resembles the difference in mobility between a child that crawls and one that walks. The latter covers more ground and gets into twice as much mischief.

Bouncing sand grains cover distances up to several feet with each hop, angling back into the dune at nearly the speed of the wind. When a strong wind blows across a dune, you can see the cloud of bouncing sand grains blurring the view of its crest and windward slope. The cloud of sand is rarely more than 12 to 16 inches high, so you can stand comfortably in it, and someone with bare legs can tell you how high the grains are bouncing. Avoid the lee side of the dune, where you will be deluged by a rain of falling sand grains.

Sand grains blowing up the windward slope of a dune enjoy a free ride at the expense of the wind until they reach the brink where the lee face drops off. Here, grains moving along the surface are unceremoniously dumped down the lee face, and the bouncing grains make their last leap, coming to rest somewhere below, sheltered from the wind. The net effect of removing sand from the windward slope and depositing it on the lee slope is to cause the dune to migrate, or advance, downwind.

Since the cloud of bouncing grains is denser near the bottom, you can be sure that most grains are bouncing to low heights and consequently making short leaps. As a result, most of the bouncing grains that cross the crest land on the upper part of the lee face, making it steeper. When it reaches an angle of about 34 degrees, the upper part of the lee face slides in a tongue of avalanching sand toward the bottom of the slope. When strong winds are moving sand, those avalanches occur repeatedly on the lee face of a rapidly advancing dune. If you visit dunes shortly after a storm wind, you will find it easy to generate avalanches by stomping along the upper part of the lee face. It is fascinating to watch them run down a lee slope. Nearly all sand on lee slopes has been moved by avalanches.

A transverse dune, with its crest at right angles to the wind, is an efficient sand trap; very little sand escapes it. Wind that has passed over a dune, having lost much of its sand, starts to pick up sand from the succeeding hollow and from the lower windward slope of the next downwind dune. By the time it gets part way up the windward slope of the succeeding dune, the wind is loaded with sand and ready to deposit part of its burden. This type of deposit is called accretion sand. Experienced dune hikers know that accretion sand is made firm by the impact of bouncing grains. You hardly leave a footprint in it. The upper part of the windward slope has the thickest and firmest mantle of accretion sand. However, near the brink of a rapidly advancing dune, accretion sand may be so thin that a hiker breaks through into the soft, avalanche sand on the lee slope beneath. Avalanche sand is so loosely packed that a walker sinks in up to the ankles. It is smart to keep on, or a little windward of, the dune crest for easiest walking.

Like those of dunes everywhere, sand grains in the Kelso Dunes are smoothly worn and nicely rounded. If you look at the grains under a strong hand lens or microscope, however, you will find that the almost perfectly round surfaces are covered with tiny pits caused by the impact of one grain against another. Grab a handful anywhere, and you will see that the grains are all about the same size, a result of the powerful winnowing force of the wind. Most of the sand is composed of the minerals quartz and feldspar. Thin layers of black sand, mostly the magnetic iron oxide mineral magnetite, catch your eye, especially where they make a patch on the surface rather than just a streak. Children enjoy dragging a magnet through the black sand, covering it with magnetite hair. Kelso sand is so rich in magnetite that a Texas entrepreneur once staked parts of the dunes as placer claims and planned to separate the magnetite to sell to a steel company. Fortunately for the dunes, this project seems to have languished.

Wind ripples are among the most intriguing features on dune surfaces. Most are a few inches from crest to crest and a fraction of an inch high. They are miniature models of transverse dunes, and like dunes, they are symmetrical, with a long, gentle windward side and a short, steep lee face. They make interesting patterns around surface irregularities and obstacles, such as bushes, These patterns show that the shape of the surface strongly affects wind currents along the ground, causing the currents to depart considerably from the prevailing direction. At times, one can see active wind ripples on dune surfaces oriented at right angles to the general direction of the wind aloft.

Ripples form when the wind is strong enough, about 25 miles per hour, to raise a good cloud of bouncing sand grains. Impacts of incoming bouncing grains drive the coarser "creeping" grains up the windward slope of the ripple. Some linger in the ripple crest, others tumble down the steep lee face.

A wind blowing 30 miles per hour can drive sand ripples along at a speed of several inches per minute. To demonstrate this, take some toothpicks or medium-sized finishing nails into dunes on a windy day, stick them into several successive ripple crests, and watch the ripples migrate. Another fun experiment is to erase the ripples in a patch of sand two or three feet square by smoothing with your hands and watch the wind make new ones in a matter of minutes.

Long ago, a famous British hydraulic engineer, reasoning from the behavior of ripple marks made by water flowing through laboratory flumes, concluded that strong transverse winds must maintain a powerful eddy over the lee slope of a dune. He suggested that the eddy would undercut the lee side of the dune, making sand avalanche down the slope. Modern experiments with smoke bombs in Kelso Dunes and elsewhere have shown that the idea was wrong. Temporary eddies occasionally form along the lee side of a dune, especially under oblique winds, but no permanent eddy powerful enough to move sand exists there. Under a strong transverse wind, the lee side of a dune is largely becalmed. You can demonstrate this by watching strands of dead grass that you toss onto the lee slope. They move intermittently, usually in a leisurely and aimless way, up, down, or along the lee slope. No determined eddy drives them along.

Dunes provide an unusual ecological niche in the harsh desert environment because they save water. Their porous sand absorbs essentially all the rain that falls on them. After a rain, evaporation from the upper few inches of sand produces a dry layer that insulates the moist sand below from heat and evaporation. This happens because the uniform size of the sand grains minimizes the number of capillary passageways that connect to the surface. Months after any rain, a hole dug several feet into soil adjoining dunes will bebone dry, whereas a hole dug on the windward side of a transverse dune will usually penetrate moist sand within a few inches, at most within a foot or two. At any time of year, strong winds may blow dry sand off the dune surface, exposing moist sand beneath.

The twenty-two clusters of desert willow trees that grow well up on the south face of the Kelso Dunes not far east of their highest point demonstrates the availability of water. Some trees are dead, but many more are living, blossoming, and making seed pods – all signs of good health. Individual tree trunks approach one foot in diameter, and the height can reach 20 feet. The willows grow right out of dune sand, which is hundreds of feet thick. These trees probably established themselves under climatic conditions more moist than the present, but they survive because the dunes hold water.

Burrowing animals, reptiles, and bugs know they have a temperature- controlled system in the dune sand. By burrowing to a chosen depth, they select a comfortable temperature and humidity. One of the most interesting denizens of the dunes is a little lizard that loves to lie burrowed in sand. The pressure of a passing hiker's foot inspires it to boil out of its burrow and take off across the surface like a streak of light. It can disappear before your eyes, either by stopping and holding still – its coloration providing almost perfect camouflage - or, more likely, by burrowing into the sand. The lizard knows the difference between accretion and avalanche sand. When wanting to escape in a hurry, it heads for the lee face of a dune and literally dives into the loose avalanche sand. Children love these astute creatures.

Inspecting dune surfaces in early morning after a windless night reveals a world of tracks etched on the soft sand. A lizard leaves tail streaks between its footprints. A sidewinder rattlesnake leaves a distinctive series of cuspate curves. You have to see a beetle in action to appreciate how its track is made, and that is easy because they are about in the daytime. Tracks of larger animals, such as rabbits, foxes and coyotes also show up well in the sand.

Indians camped near the Kelso Dunes in bygone days. Artifacts, such as arrow points, are still occasionally found and large grinding stones were once abundant in the vicinity. Stones, carried into the dunes and reddened by fire, mark sites where Indians had campfires. They reputedly washed blankets and furs by impregnating them with sand and then shaking them out to remove grease, dirt, and vermin.

Dunes are normally quiet, but occasionally, they break the silence with a deep, low-pitched sound like the moaning of a diesel locomotive far, far away. This happens during or shortly after periods of strong wind. The phenomenon, known as singing dunes, has attracted considerable attention. Scientists attribute the sound to sand avalanching down lee slopes. You can make the noise by walking down the lee face of a dune after a strong wind, starting large sand avalanches.

So, where did all sand come from? Why are the dunes so far out in the Kelso Valley, rather than tucked up against one of the bordering mountain ranges? And, finally, how old are they?

The first question is the easiest. About 35 miles west, the Mojave River flows east from narrow Afton Canyon to build a broad alluvial plain. Every time it floods, the river renews the supply of raw, loose rock debris, much of it sand, on the surface of this plain. The prevailing westerly winds blow the sand off the alluvial plain, east into the Kelso Dunes. The uncommonly large amount of magnetite in the Kelso Dunes probably comes from Afton Canyon, where mines have produced the mineral in commercial quantities. Strong north winds blowing out of the valley of dry Soda Lake near Baker probably contribute additional sand.

The location of Kelso Dunes well out in a valley is by no means unique. The huge dune in Eureka Valley and the Death Valley dunes near Stovepipe Wells also lie in valleys. A long study of the behavior of transverse dunes in the Kelso complex provided a possible explanation. It showed that individual transverse dune ridges moved back and forth cumulative distances well in excess of several hundred feet in ten to twelve years, but ended up within a few feet of their initial position. During this same period, the wind removed and redeposited a thickness of several hundred feet of sand on dune crests, with an almost perfect balance between accumulation and erosion. Although the dunes have been very active, they have not moved far in any direction.

The ability of wind to transport sand increases with approximately the cube of its speed, so doubling the wind speed increases its carrying power by a factor of eight. Occasional very strong storm winds from south, north, or east are able to balance the effects of the more prevalent, but usually gentler, winds blowing from the west.

So what caused the dunes to start to grow about where they are now? One possibility is that some perturbation on the valley floor, such as a low, rough outcropping of bedrock, localized the initial accumulation of sand. A seemingly more likely explanation, in view of the fact that other large dune masses also prefer valley floors, is that their location reflects a node condition within the complex of conflicting wind patterns. The surrounding mountain terrain could play a part in creating such a node.