Skunkbush Sumac - a woody plant that flourish in the dune field. (Rhus trilobata). White Sands National Monument, New Mexico, USA. As the dunes move on, the Sumac's roots allow the plant to hold on to the sand soil needed to keep it alive and at the same height as when the dune was present. The glistening dunes of White Sands in the Tularosa Basin are not sand, but fine gypsum, deposited on an ancient seabed 250 million years ago. Gypsum, a form of calcium sulfate, is water soluble and washes away. But geological forces here created a basin with no outlet.