Many of the white animals you see in the dunes were once darker. Thousands of years ago before the white sands were here, the landscape was much darker. As the gypsum dunes began to form, however, the landscape became more and more white. Lighter animals could better match their white surroundings and were thus more likely to survive and reproduce. As a result, after about 7,000 years and thousands of generations of living here in the white gypsum sand dunes, many animal species are now a lighter color than their relatives living outside the dunes just a few miles away.