George D, McCain,Jr.  age 15, of Jonesboro, La., for his question:

Why is White Sands, N. M. so white?

The sand of this snow white desert is gypsum, a mineral which is a water‑made mixtur<of sulphur and calcium. The desert is bounded by mountains under which large quantities of gypsum are buried. Ground water dissolves this soft mineral and brings it to the surface. From there it is carried off by rushing streams and left to dry in the hollow in which the desert is formed.

Southwest winds blow endlessly over the gypsum, breaking it into grins like powdered snow or granulated sugar. The winds also blow the sands into dunes, maybe 50 feet high, and the surface of the desert is rippled like eddying water.

The gypsum is so glistening white that a photograph taken during brilliant sunshine shows none of the dunes or ripples. The best time to photograph this dazzling expanse of gypsum is soon after sunrise or just before sunset.