In the heart of southern Colorado sits the Great Sand Dunes National Park. It was established in 2004 and it is the newest park in the U.S. National Park system. Prior to 2004 most of the park was a part of the Great Sand Dunes National Monument which was established in 1932 to protect the tallest sand dunes in North America, rising approximately 750 feet off of the valley floor. The dunes were form from sand deposited by several rivers that run through the San Luis Valley. Strong winds blowing across the valley would pick up the sand and carry it until they lost steam when they ran into the Sangre de Cristo Mountain Range on the edge of the valley. No longer able to support the weight of the sand the wind deposits it at the foot of the mountains building up a large field of dunes over the past 440,000 years.