Scientific American: High in the Rocky Mountains, snowmelt fills a stream that trickles down into Ohio Creek and then onward toward the Upper Gunnison River. From there, it tumbles through the chasms of the Black Canyon, joining the Colorado River, filling the giant Lake Powell reservoir, and, one day, flowing to Los Angeles.
But before the water gets more than a few miles off the mountain, much of this stream is diverted into dirt ditches used by ranchers along the Ohio Creek Valley. Standing astride one of those...