``The soil is the one indestructible, immutable asset that the nation possesses. It is the one resource that cannot be exhausted.''

-- Federal Bureau of Soils, 1878

Seventy-five years ago, America's southern plains were learning otherwise. Today, amid warnings of environmental apocalypse, it is well to recall the real thing. It is a story about the unintended consequences of technological progress and of government policies. Above all, it is an epic of human endurance.

Who knew that when the Turks closed the Dardanelles during World War I, it would contribute to stripping the topsoil off vast portions of Texas, Oklahoma, Colorado and Kansas? The closing cut Europe off from Russian grain. That increased demand for U.S. wheat. When America entered the conflict, Washington exhorted farmers to produce even more wheat, and guaranteed a price of $2 a bushel, more than double the 1910 price. A wheat bubble was born. It would burst with calamitous consequences recounted in Timothy Egan's astonishing and moving book, ``The Worst Hard Time: The Untold Story of Those Who Survived the Great American Dust Bowl.''

After the war, the price plunged and farmers, increasingly equipped with tractors, responded by breaking up more prairie, plowing under ever more grassland in desperate attempts to compensate for falling wheat prices with increased volume. That, however, put additional downward pressure on the price, which was 40 cents a bushel by 1930.

The late 1920s had been wet years, and people assumed that the climate had changed permanently for the better. In that decade, another 5.2 million acres -- equivalent, Egan says, to the size of two Yellowstone Parks -- were added to the 20 million acres previously in cultivation. Before the rains stopped, 50,000 acres a day were being stripped of grasses that held the soil when the winds came sweeping down the plain.

In 1931, the national harvest was 250 million bushels, perhaps the greatest agricultural accomplishment in history. But Egan notes that it was accomplished by removing prairie grass, ``a web of perennial species evolved over 20,000 years or more.'' Americans were about to see how an inch of topsoil produced over millennia could be blown away in an hour. Continued...