Each spring, when I drive north from Jackson Hole to fish the Firehole River in Yellowstone National Park, I cross the Continental Divide at three places. There is nothing spectacular about these low mountains west of Yellowstone Lake; nonetheless, each crossing brings a thrill, the sheer dimension of being on the spine of a continent. The melting snowpack in this lodgepole forest will become both the Columbia River, entering the Pacific near Portland, Oregon, and the Mississippi, reaching the Gulf of Mexico at New Orleans. One can wander about on the wet pine needles and watch these journeys begin. Doing so rekindles a desire for my own journey: to walk the Continental Divide, all 3,100 miles it, from Canada to Mexico.

Spanning five ecological zones, with diverse flora and fauna—from grizzly bears and dwarf shrews to whitebark pine and mesquite—the Continental Divide Trail (CDT) offers a glimpse of the West as it was when Lewis and Clark tra-versed its wild tracts. It enables us to know the Rockies with the soles of our feet.

The problem is, the trail is only half finished.

In 1978, Congress designated the CDT as part of the National Trails System Act, joining America's other great footpaths, the Appalachian and Pacific Crest trails. But it failed to allocate funds for the CDT's completion, and though you can now hike beautiful sections through Montana, Wyoming, Colorado, and New Mexico, 1,400 miles of the proposed route remain incomplete. The challenge now is to stitch together existing routes with new trails through a patchwork of federal, state, and private ranchland—an effort that depends increasingly on volunteer labor and private donations. (Mariah Media, the company that owns Outside, is a sponsor.) The Continental Divide Trail Alliance has a plan to finish the path by 2008.

If the CDT is completed on time, I intend, one early-spring day, to skip the Firehole River and stand on the Mexico border at a point just south of the Big Hatchet Mountains and face north. Then I will take a 3,100-mile walk through the heart of the American West.