Alkali Flat Trail At White Sands -- Continued

   The trail heads two and a half miles to the western edge of the dune field and out onto the playa, remnant of the glacial Lake Otero. Farther west, accessible only over missile range property, is Lake Lucero, the true remnant of the ancient lake. During the rainy season, Lucero often has water, perhaps a surface area the size of a football field and maybe four to six inches deep. The balance of the year it’s dry. The lake is the source of the gypsum sand comprising the dunes.

   This part of New Mexico, maybe 250 million years ago, was a shallow sea. Gypsum in the water settled in bottom sediments. Later, when the sea was long gone, the San Andres Mountains were thrust up, carrying the sediments several thousand feet aloft. And after that, Lake Otero was formed. Wind and weather eroded the white layers in the mountains and carried the gypsum into the lake. Time advanced. Ice ages came and went. Finally, with no water running out of Lake Otero, the gypsum reached the point of saturation and it precipitated into crystals buried in the lake’s sediments. What remained were the substantially smaller Lake Lucero and the playa of the ancient lake.

   That playa is where I am heading today. All along the loop road of the national monument, dunes are scarred with footprints and sled tracks. People come here to take pleasure in the dunes. For them, they are a playground, and the air is filled with the happy sounds of people enjoying themselves.

   I want to see dunes untrammeled by feet, except by those of a kit fox or a porcupine. I want to find sand pillars Rangers talk about on nature hikes and sunset strolls. I want to see the ancient lake bed.

   At the trail head kiosk, Rangers warn, if you don’t see the next orange marker, turn around and return. That’s common sense but, as you’ll learn, I often lack common sense. And so I trek west following the orange markers.

   The Rangers who laid out the trail were kind to me. They don’t make me tramp up slip faces and down windward sides of dunes. Instead, they take me through interdunal areas and over less steep and more compact faces. Sometimes, the trail leads up a dune and carries me along the crest line. At this height, I can see skunkbush sumac here and there peeking over a dune. I know beneath this scruffy tree stands a sand pillar. I want to get close to one but I also want to get to the alkali flats so I stay the course.

   Finally, I drop down the last dune onto the flat. The surface is crusty; the crust maybe a quarter-inch thick. Beneath the crust, the sand is moist, almost pasty. What strikes me is the surface. This may be a dry lake bed, but it is rippled just like the surface of water−only the ripples on water are ephemeral, constantly changing as the wind moves over the surface. The dry lake ripples are also moving, only much slower. I notice fine white sand grains in the troughs of darker, crusty sand ripples. These are the next line of the moving surface.

   The playa is vast. Long enough from north to south to pass beyond the five-mile horizon of a man standing on the ground. While principally an empty expanse, it is not totally devoid of life. Creosote and other scruffy shrubs dot the land. Tufts of alkali-resistant grass stand on small mounds like hairs in a mole.

   The trail I have been following turns north and angles east, looping back toward the trail head kiosk. Here’s where my real adventure begins, the point at which I leave my common sense behind.

   I head south in search of those sand pillars and views of dunes untrammeled by human feet. I pick out a dune with a particularly clear pyramidal shape and hike toward it. Once I climb up its windward side, I can see the sumac and I can plot a course into the interdunal area and around the steep dunes.

   In this part of White Sands, the dunes are barchans, a technical term for a dune with a long, gentle windward slope and a steep leeward slope, the slip face. These dunes are shaped like crescent moons as the wind blows sand around the mounting windward face, curving it into the crescent. The crest has a sharp edge, almost as if someone had sculpted it that way, but it’s a natural phenomenon.

   Sand grains have tiny sharp edges and angles. Dunes form when wind blows the grains, which bounce along the ground rather than fly. Lighter ones bounce a few inches. Heavier ones bounce an inch or less. As they bounce and stick to each other, the dune forms. Grains bounce to the top and fall down the other side. Most stay on the windward side and the dune gets higher. There is a specific angle after which the stickiness of the grains is overcome by gravity. It’s called the angle of repose and, when the sand along the crest exceeds the angle of repose, an avalanche occurs. Sand slides down the slip face and the dune advances.

   The dunes, too, are rippled, much like the playa. But these ripples change more rapidly. The sand is looser and moves more readily. This is an exceptionally dynamic natural phenomenon−advancing grains forming ripples, exceeding angles of repose along crest lines, slipping down a leeward face, advancing a dune that may be a couple hundred yards long and as high as 200 feet.

   The sand in the eastern dune field is nearly pure white and very fine. If you let it slide through your fingers, you might think of it as sifted flour, although it’s much grainier. The gypsum crystals from which the sand comes are actually a golden brown. At Lake Lucero, there are crystals exposed and they often remind me of fins along a dragon’s back. Here in the western dunes, the sand is newly minted and so it’s darker. As they advance, the grains get scratched and begin to reflect more and more light until what we see is white.

   The dunes are also more compact. There seems to be a lot more moisture in them. And each dune is still a unique structure. These barchans dunes are not yet connected to each other. As they advance and as the wings on the ends of each reach out, they eventually overlap forming long, interconnected ridges. Individuality is lost. I come over the final mound and slip into a large interdunal area. I feel like I am in a bowl. High dunes surround me. I can’t see the mountains. Everything at ground level is white. Everything beyond that is a flawless dome of blue silk, embroidered with lacy clouds.

   In the center of the area is the subject of my search, a sand pillar. This one is a column perhaps 40 feet wide at its base and 30 feet or so at its peak. I can’t easily determine its height since a rather large skunkbush sumac is in residence at the top.

   Pillars form when a tree like this one takes root on a dune or is growing ahead of a dune. As the sand advances, the sumac is one of the few plants that can extend its roots and keep drawing moisture from a water table rarely more than two feet beneath the interdunal surface. The dune advances. The tree grows, staying on top of the sand. At some point, it reaches the crest line and from there it’s downhill. But the tree’s roots are now maybe thirty feet from the trunk to the water and the root ball dense enough to entrap thousands of pounds, if not tons, of sand. The dune continues to advance, but the tree remains stationary unable to reverse its growth and retract its roots.

   Eventually, what remains is what I’m seeing. A tall pillar of impacted sand captive in the root ball of this resilient tree. In time, the pillar will erode and the roots will be exposed to the drying effects of desert air. The tree will die in stages. Parts will succumb and fall away. It takes years or maybe even decades for dunes the size of those here to advance. If the tree is resilient enough, if the pillar is compact enough, some part of it may survive long enough to be overtaken by the next advancing dune. Most likely, though, it won’t survive and will pass into eternity as the rest of life on earth does.

   It’s time to find my way home. I climb the long, curving edge of the dune to the west and at the summit I look back at the sumac, now 150 feet below me. It reminds me of a green and while toadstool seen in some children’s amusement park.

   The playa is only a few hundred yards to the west and I stride back to it and turn north. I know if I walk north I’ll eventually cross the Alkali Flat trail. I haven’t figured my snaking around the dunes has taken me more than a mile from the trail. And so I trudge on until I find the orange markers and resume the proscribed hike. Instead of the four and a half miles indicated at the trail head, I expect I will have walked between six and a half and eight miles.

   As I walk east, I note when desert verbena, one of the few flowering plants in the dunes, begins to appear−along with gamma grasses, yucca, and other shrubs. Because of the alkalinity of the gypsum, there isn’t much growing in the western interdunal areas. In fact, there are curved ridges reminiscent of tracks made by some vehicle. They’re not. They’re just the hard ridges that remain after a dune moves on. They’re ridges that will stop advancing grains and start the next dune. Once plants can get established in these interdunal areas, they are able to keep abreast of the advancing dunes, casting seeds or feeding birds and insects that drop seeds well away from the dunes.

   As I said, this is a dynamic natural system. It’s almost as if it’s alive, and indeed it is. While the sand is inorganic and inanimate, the dune field is a complex, energetic ecosystem supporting insects, reptiles, rodents, birds, mammals, and the occasional Oryx, an exotic African antelope introduced by the White Sands Missile Range.

   I arrive at the kiosk. My long hike concluded. My leg muscles are spent, exhausted, and they let me know in no uncertain terms. But the stiffness and aches pale to insignificance as I reflect on this incredible marvel of Mother Nature.

Return to home