The National Parks website explains how the White Sands National Monument was created over the last 280 million years.  From a sea, to a mountain range, to a rift basin, to a lake, to a playa, to a desert, to the dunes.  More sediment is added to the dunes by wind and water breaking down and transporting selenite crystals.

https://www.nps.gov/whsa/learn/geology-of-white-sands.htm

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