Oil Sand

See those dark hills below? When seen from below, on the ground, you can see the difference in the heights of the surrounding lands the Dark sand you see is the top of the hills. The natural tendency of oil to settle in these sands has kept these hills from blowing away with the rest of he sand that has been shifted to and fro across the desert floors. It makes a semi-hard surface to walk on, but I wouldn't put your hands in it. It has a grimy feeling to it when you pick it up.