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The Great Plains
The grass built the soil, and the plow found out
The soil here is deep because the grass built it. For millennia, root systems reaching meters down died and rotted in place, laying up the dark, fertile mollisols that would make the Great Plains one of the most productive farming regions on the planet — and that plowing would then expose to the wind. The plains are the vast grassland apron east of the Rocky Mountains, running from the Canadian prairie provinces down through the American heartland into northern Mexico, about 1.3 million square kilometers of gently rising ground. They look flat and are not: the land climbs steadily westward, which is why the rivers all run east and why the rain thins as you go.
Rainfall is the organizing fact. A gradient runs from wetter tallgrass prairie in the east to shortgrass steppe hard against the Rockies, and the old rule of thumb — the 100th meridian, roughly the 500-millimeter rain line — still separates farming that works without irrigation from farming that does not, though a warming climate is nudging that line eastward. Beneath much of the region lies the Ogallala Aquifer, fossil water that irrigation is drawing down far faster than rain recharges it. The land tops out near 1,830 meters where it meets the mountain front. Trees grow almost nowhere except along rivers such as the Platte and the Missouri, and the wind is relentless.
Comanche, Lakota, Cheyenne and other nations built a mounted bison-hunting culture here once Spanish horses reached the grass, and the deliberate slaughter of the herds in the nineteenth century — from perhaps 30 million animals to a few hundred — was the instrument that broke it. Homesteaders followed, plowed the sod, and in the 1930s watched it blow away in the Dust Bowl, the largest man-made ecological disaster in American history. The plains today grow wheat, corn and cattle at industrial scale, host enormous wind farms, and steadily lose rural population. A quiet countermovement is buying land back for bison and native grass, betting the prairie held this ground better than anything that replaced it.