National Park Service White Sands U.S. Department of the Interior A Source of Gypsum Forming the Tularosa Basin An Ancient Lake White Sands National Monument The geologic story of White Sands began 250 Beginning about 70 million years ago, pressure During the last ice age, 24,000 to 12,000 years million years ago when earth’s continents were from colliding tectonic plates pushed up the ago, the climate in this region was considerably still joined in the megacontinent Pangaea. At land from Colorado to Mexico. These forces colder and wetter. A large cap of glacial ice Geology of a this time much of the Southwest was covered eventually formed the Rocky Mountain range. was perched atop present-day Sierra Blanca. by the shallow Permian Sea, including parts of As the earth warmed approximately 11,000 Gypsum Dunefield present-day Arizona and New Mexico. The plates began pulling years ago, ice melt and rain in the opposite direction flowed down the mountains Over millions of years, sea levels rose and about 30 million years into Lake Otero. Water fell many times. In times of evaporation, ago, pulling the crust flowing down the mountains concentrations of calcium and sulfate in the apart and forming dissolved gypsum in the water increased enough to combine and mountains and low- surrounding rocks and

form the mineral gypsum (CaSO4•2H2O). lying basins along fault carried it to the bottom of Thick layers of gypsum were deposited in lines. The Tularosa Basin the basin. sedimentary rocks on the bottom of this sea. and its surrounding Sacramento and San Gradually, the climate Andres mountains became more arid and Lake formed at this time. Otero receded, leaving behind large deposits of Utah Colorado Two to three million gypsum on the floor of the years ago the ancient Rio Tularosa Basin. Lake Otero Grande flowed along disappeared by about 10,000 the southern edge of the years ago. Today, all that Arizona New Mexico Tularosa Basin. Sand remains of Lake Otero is a deposits from the river small remnant called Lake curious white line on the horizon, blocked off the southern Lucero at the foot of the AW hite Sands has long sparked wonder edge of the basin, San Andres Mountains in in people passing through the Tularosa Basin. Ancient Landscapes of the Colorado Plateau preventing snowmelt the southwest corner of the Standing on top of a dune overlooking this and rainfall from monument. The gypsum sea of sand, it can be difficult to imagine flowing out of it. This Lake Otero once covered much of the Tularosa Basin. dunefield began to form where all the brilliant white sand came from. When it dried, gypsum deposits were left behind on © Ron Blakey, from from © Ron Blakey, allowed for the formation shortly after Lake Otero the basin floor. To understand the origins of the world’s Extent of the Permian Sea about 280 million years ago of the 1,600-square-mile dried up. largest gypsum dunefield, we must look Lake Otero back over millions of years during which just the right geologic and climatic processes took place in just the right order. Many of these processes continue today, allowing us to witness the formation of these unusual sands. 250 million years ago 70 million years ago 30 million years 2-3 million 24,000-12,000 years ago 10,000 years ago Gypsum was formed and deposited in the Permian Sea. Tectonic forces pushed ago years ago Ice age conditions formed a Ice age ended. Lake up the land and The crust began The Ancient Rio glacier on Sierra Blanca. Rain Otero dried up. the ancient seabed pulling apart, Grande River and snowmelt fill Lake Otero. Dunes began to Scan for a more in-depth explanation of the containing gypsum creating Tularosa blocked off form. geologic story of White Sands and the deposits Basin. southern part of Tularosa Basin. basin, allowing formation of Lake Otero. Lake Lucero From Crystals to Fine Grains A Sea of White Sand A Secret Key Ingredient Today, rainfall in the mountains still flows The dunes at White Sands probably began Gypsum is a common mineral in rocks all over down the sides of the Tularosa Basin. Water forming as late as 7,000 to 10,000 years ago, the world. Basins are common too, even here dissolves gypsum in rocks as it travels and when Lake Otero started to dry up. The dunes in New Mexico. So, why is White Sands the settles in low areas of the basin. Much of it are shaped by prevailing southwesterly winds, world’s largest gypsum dunefield? Water! settles in Alkali Flat and Lake Lucero. These which pile the sand up and push dunes into areas are ephemeral lakes, or playas, that various shapes and sizes. The different types of Water is the secret ingredient necessary fill with water only parts of the year. On the dunes depend on the amount of sand available, for gypsum sand to form. Although it is surface of these playas, the final steps in the the power of the wind in a particular spot, and not obvious, White Sands is actually a very formation of rare gypsum sand can still be the vegatation anchoring sand in place. wet environment. These dunes are at one seen today. hundred percent humidity. Only a few feet Because of the consistent wind, dunes are under interdunal areas lies what is called a evershifting. Some dunes in the heart of the perched water table—water that is held above Selenite crystals on the surface of Lake Lucero dunefield can travel twelve to thirteen feet per the normal water table found in the rest of year, keeping any thing but the occassional the basin by a barrier, in our case a layer of Each year some of the crystals emerge from grasses from taking root. Others, on the edges of impermeable clay. This shallow water table the protective mud surface of Lake Lucero as the dunefield, move only inches to a few feet per acts like a glue holding the dunes in place, wind and rain remove sediments from around year and are firmly held in place by a variety of preventing them from blowing away with them. Once exposed, crystals begin the gradual desert plants. the wind. process of erosion into smaller and smaller pieces. Lake Lucero is a remnant of ancient Lake Otero. The same processes that formed crystals in Lake Otero continue today in this playa. Gypsum is a soft mineral—softer than a human fingernail—so it breaks down easily. Water with dissolved gypsum in it flows to Water seeps into cracks, freezes, and breaks Alkali Flat and Lake Lucero during wet parts fragile sheets of selenite apart. The process of the year, usually during July and August continues over time until large crystals become monsoons. There, the heat of the sun causes small shards. the water to evaporate, leaving the gypsum behind. Gypsum precipitates out of the water When pieces become small enough that they in the form of crystals. Smaller crystals form can be picked up by the wind they are known on the surface of these playas. Larger crystals as “cornflakes,” and this is when things really form under the muddy surface of Lake speed up. Grains of gypsum picked up by the Lucero and are shaped like long jagged spars wind bounce along the surface and leap-frog and round segmented disks the size of bicycle over each other, breaking down into smaller tires. The crystal form of gypsum is known and smaller pieces. as selenite. As the soft grains collide with the ground and Although crystal growth continues in with one another their surfaces get scuffed. These scuffs reflect light rather than letting Alkali Flat and Lake Lucero, most of the sand Heavy rain in 2006 flooded interdunal areas throughout the monument. Normally, White Sands has a perched in the dunefield came from crystals formed in it pass through and give the gypsum sand its water table that lies one to two feet below the surface of interdunal flats. During this storm, the unusually heavy ancient Lake Otero, which was much larger. distinctive snowy appearance. rainfall raised the water table to the surface, which resulted in extensive flooding in the dunefield for six months.