Spreading before us are the famous walking half-moons of La Joya. They are crescent-shaped sand dunes ranging from about 100 fett in width to 15 feet in height, and of such exact shape that no human agency could make them mathematically more perfect than the constant winds of this plateau. This unfailing wind is the true explanation of why the dunes creep across the desert in a true northerly course at an even rate of fifty to sixty feet a year.
The wind, always blowing from one direction, blows the ashen colored sand up the convex side of the crescent from whence it drifts down into the hollow side in such perfect and regular fashion that the entire dune seems to dreep across the plateau without a single variation in size or shape, and with a movement that marks the years with the same accuracy that an hour-glass marks the hours.
One has to look back but half a mile to see where a dune was fifty years ago when this railroad was built; and if you look back five miles you can see where it was when the Inca sent messages to his people that strange white man with hair on their faces were coming up from the sea. [...]
Ripley's Believe it or Not!