In 1878, the American geologist and explorer John Wesley Powell drew an invisible line in the dirt-a very long line. It was the 100th meridian west, the longitude he identified as the boundary between the humid eastern United States and the arid Western plains. Running south to north, the meridian cuts northward through the eastern states of Mexico, and on to Texas, Oklahoma, Kansas, Nebraska, the Dakotas, and the Canadian province of Manitoba on its way to the pole. Powell, best known for exploring the Grand Canyon and other parts of the West, was wary of large-scale settlement in that often harsh region, and tried convincing Congress to lay out water- and land-management districts crossing state lines to deal with environmental constraints. Western political leaders hated the idea-they feared this might limit development, and their own power-and it never went anywhere. It was not the first time that politicians would ignore the advice of scientists.