Wow! We almost skipped this stop. What a mistake that would have been. (Click on pic to make it bigger)
These massive dunes of powdery gypsum (a mineral used in everything from cement to toothpaste) stretch for 30 miles along a wide valley set between the Sacramento and San Andres mountain ranges.
The highest dunes stand 60 feet. The sand is what's left of an ancient lake that began drying 10,000 years ago, exposing deposits of crystallized gypsum that for millions of years had washed into the pool from the surrounding mountains. Fierce winds pounded the crystals into the sand that forms the dunes.