The Tatacoa is not a desert. It is tropical dry forest that erosion has stripped down to bare clay, red on one side and grey on the other, in the Huila department of southern Colombia beside the town of Villavieja. Rain here is rare and heavy, and it does all the work. Where it has cut the crimson clay of El Cuzco, the ground is a maze of walls, spires and dead ends narrow enough to lose your bearings in, so you walk it with a local guide. Late afternoon is when it repays you. The low sun turns the iron in the walls copper, rakes shadow down each gully and picks out every fine ridge and hollow the water has etched. From the air the whole thing resolves into a branching web of ravines, with the ochre sector and the grey sector of Los Hoyos lying side by side like two different planets.
Almost nothing grows on it. What does sends roots as far as thirty metres sideways and fifteen straight down after whatever water the ground still holds, while the columnar cacti take the other approach and store it in trunks four or five metres tall. The name is a sound: Tatacoa imitates the dry buzz of a rattlesnake's tail, though no rattlesnake lives in these badlands now. After dark the dryness pays again. With no city light anywhere near, a guide at the roadside observatory swings a telescope for you onto Saturn's rings and star clusters. But the rain is still the point. Every hard fall strips a little more clay away, and what surfaces underneath is bone. A younger bed carries the last Ice Age; below it lie giant crocodiles, freshwater turtles and the richest set of fossil monkeys known in South America. The rain that stripped the forest off this ground keeps handing up what was under it.