The irrigation of the Ogallala region, which has occurred almost entirely since the Second World War, is, from a satellite's point of view, one of the most profound changes visited by man on North America; only urbanization, deforestation and the damming of rivers surpass it. In the space of twenty years, the high plains turned from brown to green as if a tropical rainbelt had installed itself between the Rockies and the hundredth meridian. From an airplane, much of semiarid west Texas appears as lush as Virginia.

Regarding the knowledge needed to avoid the human destruction of arid environments:

… it is safe to say that we have today not all the knowledge we need, but a great deal more than we use.

In terms of the “greening” by irrigation of the arid San Luis Valley of Colorado:

… even the most prosperous farmers there know that from nature's point of view this is cosmetology. The place is still a desert, harsher yet for their efforts than the one their ancestors settled. If the water table drops, if credit dries up, if prices fall, if soil salinity increases, if fuel and chemical costs rise, if exotic pests multiply, the green makeup will crack right off the hard dry face of it.