New York Times: WEDGED between Arizona and Utah, less than 20 miles upriver from the Grand Canyon, a soaring concrete wall nearly the height of two football fields blocks the flow of the Colorado River. There, at Glen Canyon Dam, the river is turned back on itself, drowning more than 200 miles of plasma-red gorges and replacing the Colorados free-spirited rapids with an immense lake of flat, still water called Lake Powell, the nations second-largest reserve. When Glen Canyon Dam was built in the middle of the...