Several miles from Phantom Ranch, Grand Canyon, Arizona, April 2013 – Down here, at the bottom of the continent’s most spectacular canyon, the Colorado River growls past our sandy beach in a wet monotone. Our group of 24 is one week into a 225-mile, 18-day voyage on inflatable rafts from Lees Ferry to Diamond Creek. We settle in for the night. Above us, the canyon walls part like a pair of maloccluded jaws, and moonlight streams between them, bright enough to read by.

One remarkable feature of the modern Colorado, the great whitewater rollercoaster that carved the Grand Canyon, is that it is a tidal river. Before heading for our sleeping bags, we need to retie our six boats to allow for the ebb.

These days, the tides of the Colorado are not lunar but Phoenician. Yes, I’m talking about Phoenix, Arizona. On this April night, when the air conditioners in America’s least sustainable city merely hum, Glen Canyon Dam, immediately upstream from the canyon, will run about 6,500 cubic feet of water through its turbines every second.

Tomorrow, as the sun begins its daily broiling of Phoenix, Scottsdale, Mesa, Tempe, and the rest of central Arizona, the engineers at Glen Canyon […]