Great Sand Dunes National Park and Preserve is located in the
easternmost parts of Alamosa County and Saguache County,
Colorado, United States. Originally designated Great Sand Dunes
National Monument, Great Sand Dunes National Park and Preserve
was created by an act of the United States Congress on September
13, 2004. The park contains approximately 85,000 acres.
Sand Dunes contain the tallest sand dunes in North America,
rising about 750 feet from the floor of the San Luis Valley on
the western base of the Sangre de Cristo Range, covering about
19,000 acres. They are perhaps 12,000 years old.
The dunes were formed from sand and soil deposits of the Rio
Grande and its tributaries, flowing through the San Luis Valley.
Over the ages, westerly winds picked up sand particles from the
river flood plain. As the wind lost power before crossing the
Sangre de Cristo Range, the sand was deposited on the east edge
of the valley. This process continues, and the dunes are slowly
growing. The wind changes the shape of the dunes daily.
There are several streams flowing on the perimeter of the dunes.
The streams erode the edge of the dune field, and sand is
carried downstream. The water disappears into the ground,
depositing sand on the surface. Winds pick up the deposits of
sand, and blow them up onto the dune field once again.
Digging a few inches into the dunes even at their peaks reveals
wet sand. Part of the motivation of turning the Monument into a
National Park was the extra protection of the water, which
Colorado's cities and agriculture covet.
It is very easy to experience the dune-building process. This is
a very windy region, as hikers on the Sand Dunes will attest, as
on many days they will be pelted by sand and even small rocks
when hiking on the dunes. The wind carries sand and rocks from
many miles away.