There's an engine somewhere inside Andrew Skurka, a quiet, relentless drive that never quits—and there would have to be. On the day I caught up with him, Skurka, 26, was about two-thirds into a 6,875-mile (11,064-kilometer) hike, an epic, first-of-its-kind journey that in one fell swoop passed through five major mountain ranges, 12 National Parks, and 75 Wilderness Areas. He calls it the Great Western Loop.

Skurka set out from the Grand Canyon on April 9, 2007, and quickly hit an average pace of around 35 miles (56 kilometers) a day. Over the next two weeks or so, he walked 675 miles (1,086 kilometers) west across the Sonoran and Mojave Deserts. Near Palm Springs he turned right onto thePacific Crest Trail and walked north 2,415 miles (3,887 kilometers), blitzing through the early spring snowpack of the Sierra and past the looming volcanoes of the Cascade Range. Close to the Canadian border, he turned east onto the Pacific Northwest Trail and followed that for 675 miles (1,086 kilometers) until he hit the Continental Divide Trail in northern Montana. By the time I went looking for him in mid-September, he was in the middle of that leg: a 2,400-mile (3,862-kilometer) shot south along the spine of the Rockies, back toward the Grand Canyon.