National Park Service White Sands U.S. Deoartment 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 was Geology of a this time much of the Southwest was covered eventually formed the Rocky Mountain range. perched atop present-day Sierra Blanca. As the by the shallow Permian Sea, including parts of earth warmed approximately 11,000 years ago, Gypsum Dunefield present-day Arizona and New Mexico. The plates began pulling ice melt and rain flowed in the opposite direction down the mountains into Over millions of years, sea levels rose and about 30 million years Lake Otero. Water flowing fell many times. In times of evaporation, ago, pulling the crust down the mountains' sides 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 (CaS04*2H20). 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 Two to three million gypsum on the floor of the ? Si 2S years ago the ancient Rio Tularosa Basin. Lake Otero a. •8 Grande flowed along disappeared by about 10,000 2 o the southern edge of the years ago. Today, all that 3 •c Tularosa Basin. Sand remains of Lake Otero is a o cu deposits from the river small remnant called Lake a curious white line on the horizon, 2 Lucero at the foot of the -S blocked-off the southern White Sands has long sparked wonder c A •Sc edge of the basin, San Andres Mountains in c in people passing through the Tularosa Basin. -a; preventing snowmelt the southwest corner of the Standing on top of a dune overlooking this o 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 o where all the brilliant white sand came from. Q allowed for the formation When it dried, gypsum deposits were left behind on shortly after Lake Otero To understand the origins of the world's the basin floor Extent of the Permian Sea about 250 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 containing gypsum creating Tularosa blocked off form. deposits Basin. southern part of basin, allowing the 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 various areas are ephemeral lakes, or playas, that shapes and sizes. The different types of dunes Water is the secret ingredient necessary fill with water only parts of the year. On the depend on the amount of sand available, the power for gypsum sand to form. Although it is not surface of these playas, the final steps in the of the wind in a particular spot, the vegetation, and obvious, White Sands is actually a very wet formation of rare gypsum sand can still be soil moisture anchoring sand in place. environment. These dunes are at one hundred seen today as the water evaporates. percent humidity. Only a foot under interdunal Because of the consistent wind, dunes are areas lies what is called a perched water table— ever-shifting. Some dunes in the heart of the water that is held by a barrier above the normal dunefield can travel twelve to thirteen feet water table found in the rest of the basin, in Selenite crystals on the surface of Lake Lucero per year, keeping anything but the occassional our case a layer of impermeable clay. This Each year some of the crystals emerge from grasses from taking root. Others, on the edges of shallow water table acts like a glue holding the the protective mud surface of Lake Lucero as the dunefield, move only inches to a few feet per dunes in place, preventing them from blowing wind and rain remove sediments from around year and are firmly held in place by a variety of away with the wind. them. Once exposed, crystals begin the gradual desert plants and soil crust. 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 Crystal growth continues in Alkali Flat and with one another their surfaces get scuffed. Lake Lucero as it has for thousands of years. These scuffs reflect light rather than letting Heavy rain in 2006 flooded interdunal areas throughout the monument. Normally, White Sands has a perched 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 distinctive snowy appearance. rainfall raised the water table to the surface, which resulted in extensive flooding in the dunefield for six months.

Revised 12/7/18