To most, sand dunes are as synonymous with deserts as water is to an ocean. However, the deserts of the southwest are certainly no American Sahara. Sand dunes cover but a small percentage of the total land area, with the vast majority made up of silica, composed of weathered quartz. What makes the white sands of New Mexico’s White Sands National Monument, located just outside of Alamogordo, special is their composition- gypsum. There are only a few gypsum sand dune fields in the world, with those preserved at White Sands National Monument being by far the largest. Since gypsum is a water soluble mineral, and is usually carried by rivers away to the sea, a perfect coincidence of environmental conditions must exist to form a gypsum dune field. In additional to the snow white color, which turns sublime shades of pink and purple under the right light, gypsum sands differ from silica in being much softer and less abrasive. This sand actually feels like talcum powder between your fingers and toes!
So where did all this gypsum sand originate? During the age of the dinosaurs, a shallow sea covered much of the interior of North America. Gypsum, a salt of calcium sulfate, was dissolved in the water and formed sediments when the seas dried up. The sediments were lifted into a giant dome in southern New Mexico 70 million years ago, during the same period that the Rocky Mountains were formed. The dome began to collapse 10 million years ago, forming the Tularosa basin. The lowest point in the basin, Lake Lucero, is the main source of material from which the dunes have been carved. Large crystals of gypsum known as selenite can be found there. The constant action of southwesterly winds has eroded these deposits into tiny particles and blown them into the dune field. The dunes are constantly being moved to the southwest and reshaped by these winds.
Life forms at White Sands are specially rutas de senderismo adapted to the challenging conditions of the dunes. Yuccas grow at a rate fast enough to keep up with the advancing sand, ultimately developing stems over 30 feet long, mostly covered by sand. When the dunes move on, the plant collapses and dies. Other plants have strong roots which hold in place pedestals of raised sand, forming an island for life in the harsh dune environment. Much of the fauna found at White Sands, including lizards, toads, pocket mice, crickets, and beetles, have evolved white forms that are camoflauged with their environment. In order to cope with the extremes of temperature and dryness, many animals remain underground by day and emerge at only night. A morning hike through the dunes will reveal copious evidence of their nocturnal activities.
Although the road in White Sands National Monument leads directly into the dune field, the best way to experience this place is to leave the car and hike some of the trails. The Big Dune Nature trail, located on the edge of the dune field, allows for close observation of many of the plants and animals adapted to life there. Animals are especially active early in the moring and at dusk. The Interdune Boardwalk goes through an area densely populated by wildflowers during the blooming season. For a true wilderness experience, the Alkalai Flats trail will take you deep into the heart of the dunes- a sea of white surrounded by rugged mountains! The 4.6 mile loop leads to the dry lakebed of Lake Otero and back, and is marked by orange plastic markers anchored to the dunes. The color and forms of the dunes there are very reminiscent of snow- a surreal environment. While hiking this trail, several times I had to remind myself that I was in New Mexico, not Antarctica! Like snow, they reflect the sunlight fiercely, so high strength sunblock is a must. Also, the plastic markers are the only landmarks, so be sure to stay in sight of them. Being on the dunes at dusk or dawn and watching the sands glow different shades of pink and purple in the low rays of the sun is an experience not soon to be forgotten. It’s also a great place to bring the kids, or to let out your inner child, and romp about in the soft sand.