Great Sand Dunes National Park & Preserve
If you want to see a cyclical environment, you can’t get a much more perfect example than Great Sand Dunes National Park and Preserve. The formation of the dunes began in the San Luis Valley about 440,000 years ago. Glaciers melted, creating a lake. When its water evaporated, sand and soil accumulated on the high desert plain. The Rio Grande and its tributaries contributed to those deposits, which were picked up by westerly winds. When the winds came up against the mountain range they lost some of their oomph, and since they could no longer carry the extra baggage, they dropped it and the dunes were born.