In a corner of the remote high-mountain Sangre De Cristo Mountains, in San Luis Valley are the tallest sand dunes in North America. They achieve nearly 750 feet. The dunes cover approximately 39 mils². It is estimated that there is 4 billions cubic meters of sand.For centuries the Rio Grande meandered through the San Luis Valley, much as it does today, carrying sand and other sediments and depositing them in its riverbed and along its shores. Most of the sand was eroded bits and pieces of the San Juan Mountains brought to the Rio Grande by tributary streams. In time, the Rio Grande changed its course, and these great deposits of sand were exposed to the winds that swept across the board, flat valley. These winds, blowing toward the northeast, pushed and bounced the grains of sand barred the way. In the sand you can find trace of Kangaroo rat, Giant sand treader camel cricket, or Scurfpea
Temperature of sand can achieve 60 oC at sunny day. On the dunes´ border is a visitor center, camp and also petrol station.