The 65-mile long Centennial Valley in southwest Montana is largely desolate except for grazing cattle and abandoned homesteads. However, 100 years ago it was home to nearly 500 people, who moved there in the belief that they could make the area agriculturally productive. During the 1860s and ?70s a series of unusually wet years coincided with the population expansion into the West, and gave rise to the belief that ?the rain would follow the plow? ? that by tilling the soil and planting crops, moisture from the ground would be released into the atmosphere and return as rain. When homesteading laws opened the Centennial Valley to settlers in the 1890s, more than 100 families moved in. After three years of hot dry summers and brutally harsh winters, most had left with what possessions they could carry, leaving behind a valley that today feels largely unspoiled, where cattle graze at a stocking rate of one cow to every 40 acres. Throughout the history of American agriculture, well-intentioned mistakes have been made, not only in climatology but through the introduction of a myriad of non-native plant species that have turned out to be invasive weeds, and miracle chemicals that have had negative long-term consequences..