Miss Elaine and I just got back from Las Cruces and southeastern New Mexico. This was my favorite place. White Sands National Monument protects a big chunk of the world's largest area of gypsum sand dunes. Most sand is made of silica or other minerals and can range from yellow and light brown to black. The sand here is made of gypsum (hydrous calcium sulfate), a white, soft mineral that is often used in making the wallboard used in building our houses.
White Sands covers about 275 square miles. The sands come from playa lakes -- lakes fed totally by rainfall -- that dry up when the water evaporates. The minerals in the water are left behind and eventually break down and are carried by the wind.
The dunes don't stay in one place -- they shift with the winds. In some areas the dunes move 30 feet in one year. That's probably about the same distance as from the front to back of your classroom.
Are you surprised to see plants in the desert? The plants have to have special adaptive qualities to survive here. If they can get their roots down far enough, they can get to water that is stored under the desert floor.
Miss Elaine was very interested in all these details. Me -- I just wanted to slide down the dunes!