Frances Ann Juarez, Age 1.7., Of Mammoth, Ariz., For Her Question:

How deep is the sand on the Sahara desert?

The sand of the Sahara is not spread out in an even layer. The gritty grains are dry and light enough to be lifted by the winds, and the great desert is a windy place. The loose sand is just a surface layer, and below it is a bumpy bed of solid rock. The bedrock forms flat plateaus, dipping valleys and rising hills. Gentle breezes lift and twirl the sand from place to place. Deep layers of sand tend to collect in the hollows and the strong wind strips the hilltops down to the bare rock. Steady breezes pile up hilly sand dunes perhaps 30 feet high. The restless sands may be a few inches or many feet deep, and day by day the winds shift it from place to place.