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Great Sand Dunes National Park is a United States national park as of September 13, 2004 in the southern part of the American state of Colorado, in the American Southwest.
The sand dunes rise close to 230 meters (about 750 feet) from the floor of the San Luis Valley in front of the Sangre de Cristo Mountains, covering about 78 square kilometers (about 30 square miles). They are the tallest sand dunes in North America.
They were made a national monument in 1932. On November 22 2000, United States President Bill Clinton signed the Great Sand Dunes National Park and Preserve Act of 2000, aiming at ultimate national park status, after more land was acquired.
According to the ski the dunes.
You might imagine you're in the Sahara Desert or a Western movie. Hiking is permitted, with the warning the sand can get hot in the summer, up to 60 Celsius (~140 Fahrenheit). The area gets snow in the winter. Some go on pack trips with horses.
The closest city is Alamosa, Colorado, though Colorado Springs, Denver and Albuquerque, New Mexico are not far off. Consult the references for more information.
Anyone who visits the dunes has to wonder, "Where did such a bizarre feature come from? Why here?" They trace to perhaps 12,000 years ago.
The dunes were formed from sand deposits of the Rio Grande River and its tributaries, flowing through the San Luis Valley. Over the ages, westerly winds have picked up sand particles as they flew over the Rocky Mountains and down over the river flood plain. As the wind lost power before crossing the Sangre de Cristo mountains, the sand was deposited on the east edge of the valley. This continues, and the dunes are slowly enlarging by the wind that daily changes the shape of the dunes. There are areas of black sand which are deposits of magnetite, a crystalline black oxide of iron.