The roaring Strontia Springs Dam in Douglas County, Colorado, diverts water from a giant reservoir into a 3.4-mile-long tunnel under the mountains to the Foothills Water Treatment Plant near Denver. Completed in 1983, this dam towers 243 feet above the South Platte River streambed, forming a 1.7-mile-long lake with 98 surface acres. Most of this takes place in plain sight of one of metropolitan Denver's favorite workout venues -- the 6.2-mile Waterton Canyon Trail that crosses from Jefferson County into Douglas County -- where bicylists, hikers, walkers, and horseback riders exercise in a beautiful, invigorating, patrolled environment managed by Denver Water -- the city's public water utility -- and the U.S. Forest Service. Photo by Carol Highsmith, 2016.