After spending time and photographing the desert, I conclude that the sun rules. It dictates the structure of the shadows, and it decides whether to gently or harshly light the sand. In evening or early morning, the sunlight tickles the sand and creates sensuous shapes and sub-images. These images often "fool the eyes".
Bravo! Ed, if the sun does rule it certainly dominants ... that is till the wind blows, especially at 110˚ +.