there is a sand dune park at Monahans, Texas on I 20 out in west Texas. I have been to White Sands and there the mineral is Gypsum and is very white. Late in the day or first light. Isn't there a book you can subscribe to called something like "Photographing America." It has info on all the state and national parks and is published in CA. For the National Park Service ask for the "old farts pass" (age 65) costs $10 and is good for the rest of your life and anyone in the vehicle gets in free also. That would be my recommendation.