1. Timberline Trail



Mt. Hood, OR



Score: 95 Miles: 41 Elevation Change: 12,000 feet X Factor: Insane mileage

This legendary path deserves top honors for its mileage alone: Most sane hikers take 4 days-not 1-to conquer the Timberline, which circles the base of 11,239-foot Mt. Hood. But these are Oregon's Cascades, so the challenge goes well beyond trekking more than a marathon and a half's worth of miles. Numerous climbs and descents hamper your progress. From Cloud Cap Saddle, for example, you'll lurch 1,500 feet up in less than 3 miles, then drop more than 1,800 feet in the next 2. There are dicey river crossings-glacier-fed streams rise in the afternoon-and the wind, rain, even blizzards can kick up at any time. In a typical incident in 2003, five climbers had to be rescued in unexpected whiteout conditions. The good news: It's tough to get lost; hike clockwise and keep the volcano on your right. And meadows awash in flowers, waterfalls, and towering glaciers distract you from the pain. Start and finish at the great Timberline Lodge on Hood's south side. Contact: Mt. Hood National Forest, (503) 668-1700; www.fs.fed.us/r6/mthood

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2. Pemi Loop



White Mountains, NH



Score: 92 Miles: 32 Elevation Change: 18,000 feet X Factor: Knee-hammering rocks

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Extreme types hardened on the Whites' granite staircases obsess over the better-known Presidential Range Traverse, but we consider that so-called Death March a mere training jaunt for this classic in the rugged Pemigewasset Wilderness. From Lincoln Woods trailhead on the Kancamagus Highway (NH 112), this circuit chugs up and over eight craggy 4,000-footers: the four peaks of Franconia Ridge (Flume, Liberty, Lincoln, and Lafayette), and Mts. Garfield, South Twin, and the Bonds. The long stretches of abusively rocky trail never seem more demoralizing than on the South Twin ascent, a straight-uphill section that ascends 1,150 feet in less than a mile, midway through. Be ready for dazzling views and pitiless winds above treeline-and go hard; even if you've lucked into a tailwind, this is likely a 16-hour trek, with miles of jouncing descent on shaky legs in the dark, even on summer's longest days. The Appalachian Mountain Club's Galehead Hut, near the halfway point, provides the logistical advantage of a water resupply and leftover pancakes-but tempts you to linger so long you may never get up again. Which might not be a bad idea, if you're not truly ready for this. The state's 6-year-old "reckless hiker" law means that if you try something hairball and need to be rescued, you reimburse the costs. Contact: White Mountain National Forest, (603) 528- 8721; www.fs.fed.us/r9/white

3. Great Range Traverse



Adirondacks, NY



Score: 90 Miles: 25 Elevation Change: 17,600 feet X Factor: Endless ups and downs

There's no small irony in the fact that New York's tallest peak is merely the last challenge on this classic loop-and far from the toughest. The route scales nine peaks, including six 4,000-footers and the aforementioned 5,344-foot Mt. Marcy. But numerous cols and false summits, plus heinously eroded trail beds, wear you down physically and psychologically. From Keene Valley, the murderer's row of peaks includes Rooster Comb, Hedgehog, Lower Wolf Jaw, Upper Wolf Jaw, Armstrong, Gothics, Saddleback, Haystack, and Marcy, from which you descend the Phelps Trail. Gut-check moments include a half-mile of teetering above a 700-foot drop on a knife-edge between the Wolf Jaws-inevitably followed by a steep climb-and the southeast face of Gothics, a scary-steep, exposed descent over open slab rock. (The face used to have cables to aid hikers, but, fittingly, they've been removed.) There are long stretches of scrambling and ladder-climbing, and you'll need to carry enough water for the day. Contact: Adirondack Mountain Club, (518) 668-4447; www.adk.org

4. Windom Peak



San Juan Mountains, CO



Score: 85 Miles: 20 Elevation Change: 11,600 feet X Factor: Violent thunderstorms

Once you commit to Windom, there's no dawdling over views: In summer, the lightning risk is so great that climbers should top out by 11 a.m. That isn't easy, given the 10-mile, 5,800-foot hump through increasingly thin air to the precarious 14,082-foot summit. You'll likely hear the clock ticking as you maneuver through a talus field halfway up, solve off-trail scrambling and route-finding problems, and tackle the crux: a brutal ascent from Chicago Basin to the summit that climbs 2,900 feet in just under 2 miles. Wind, hail, and snow often enter the picture, even in summer, and then there are the daunting logistics. Windom lies deep in the heart of the San Juans, part of the aptly named Needle Mountains, so it's tougher than most 14ers to bag in a day. In fact, you'll need to catch an 1880s steam locomotive that follows the Animas River Canyon just to get to the trailhead, then camp nearby (no hardship-it's lovely aspen country) for the compulsory alpine start. Contact: San Juan National Forest, (970) 247-4874; www.fs.fed.us/-r2/sanjuan; Durango & Silverton Narrow Gauge Railroad, (970) 247-2733; www.durangotrain.com

5. Cactus to Clouds Trail



Mt., San Jacinto from Palm Springs, CA



Score: 80 Miles: 23 Elevation Change: 13,400 feet X Factor: Broiling temps

Sure, it's a big deal to climb Mt. Whitney-but on the highest peak in the lower 48, you begin at 8,360 feet. To conquer Cactus to Clouds, you start on the desert floor and ascend 10,700 feet-a vertical half-mile more than Whitney. Two fun ways to put your pain in perspective as you churn up the unmaintained trail: The trek to San Jacinto's 10,804-foot, boulder-strewn crown is only 800 vertical feet shorter than the climb from Everest basecamp to summit-and comparable to doing more than a thousand flights of stairs. Start before dawn, because temps hit triple digits more than 100 days a year, and there's no water below 8,500 feet. But come prepared for wild temperature inversions and possible rain and hail up high; the worst scenario is to be forced to descend waterless in the ruthless afternoon heat. From the top, where you'll see every major peak in Southern California and all the way to the coast, most people hike down 2,300 feet and take the tram back to town; the hike's tough enough without adding another 8,000 feet of downhill. Contact: Long Valley Ranger Station, Mt. San Jacinto State Park, (951) 659-2607; www.sanjac.statepark.org. Palm Springs Aerial Tram, (760) 325-1391; www.pstramway.com

6. Great Smoky Mountains End-to-End



TN/NC



Score: 78 Miles: 32 Elevation Change: 12,300 feet X Factor: Mud, bugs, humidity

It's a safe bet that leisurely Bill Bryson won't ever wax poetic about doing this one-day walk in the woods. The Appalachian Trail's infamous switchback-free section from Newfound Gap to TN 32 at the national park's northeast corner breaks you down mentally and physically, rising 4,600 feet and dropping (perhaps literally) a staggering 7,678. The Smokies' famed low clouds and chronically wet ground (Bryson writes of rain falling there "with an endless, typewriter pattern) lend the incessant downhill a distinctly Appalachian flavor-you'll churn through slick mud, rocks, and roots. When it's clear, the views from ridgelines along one of the AT's highest stretches are the best in the Southeast. Contact: Great Smoky Mountains National Park, (865) 436-1297; www.nps.gov/grsm

7. Grand Canyon South Rim to North Rim



AZ



Score: 74 Miles: 21 Elevation Change: 10,500 feet X Factor: Dehydrating heat

For sheer majesty, this beauty takes the cake. But there's nothing pretty about the prospect of a 5,800-foot climb out in the afternoon sun, which can bring triple-digit temps as early as May. So strap on a headlamp and head for the depths of Bright Angel Canyon before dawn; you'll be perfectly positioned for one of the world's most colorful sunrises-and for a midmorning river crossing to start up the other side. Your best bet is to go in early spring or mid-autumn; there may be snow on the rims and temp swings of up to 40 degrees, but you'll avoid the scalding heat that makes dehydration a real risk here. The South Kaibab Trail drops 7 stunning miles and 4,700 feet from the South Rim to the Colorado River; the 14 miles up the North Kaibab Trail are less steep (and less crowded) but beyond epic in duration. Locals ID dayhikers who pull off this feat by their gimpy gait; they call it the "Grand Canyon Shuffle."Contact: Grand Canyon National Park, (928) 638-7888; www.nps.gov/grca

8. Enchantment Lakes Traverse



Cascade Range, WA



Score: 71 Miles: 18 Elevation Change: 11,000 feet X Factor: Sketchy footing up high

When you eyeball the route over 7,800-foot Aasgard Pass into the massive cliffs hemming in Colchuck Lake, you'll know why this hike made the list: The loose, primitive footpath climbs a ridiculously steep 2,200 feet in three-quarters of a mile. (Try not to contemplate just how far you'd tumble if you slipped.) And after the 4,600-foot climb from the Colchuck Lake-Stuart Lake trailhead beats you silly, the 6,500-foot drop to the Snow Creek trailhead delivers a knee-jarring coup de gráce. Focus instead on the Eden of wildflowers, gnarled trees, glaciers, and mountain goats. Contact: Wenatchee National Forest, (509) 548-6977; www.fs.fed.us/r6/wenatchee

9. Paintbrush Canyon-Cascade Canyon Loop



Grand Teton National Park, WY



Score: 66 Miles: 19 Elevation Change: 8,000 feet X Factor: The occasional ultramarathoner passing you

Why does the 4,000-foot climb from String Lake up Paintbrush Canyon seem to last longer than Paris Hilton's overextended 15 minutes of fame? There's no shade, and the climb stretches endlessly out over 8 miles. Start before dawn to beat the high-altitude sun-and to get over 10,700-foot Paintbrush Divide before early afternoon, the witching hour for the Tetons' infamous thunderstorms. At the pass, drink in views up and down the range, but don't celebrate yet: 11 long miles down Cascade Canyon await. Contact: Grand Teton National Park, (307) 739-3300; www.nps.gov/grte

10. Bigelow Range Traverse



ME



Score: 64 Miles: 17 Elevation Change: 10,000 feet X Factor: Black flies with attitude

You'll be tempted to run this northbound traverse of the AT from ME 27/16-not because you're feeling jaunty, but to escape the Maine woods' infamous black flies. But the relentlessly steep and rocky trail along long, forested ridges discourages any such fantasies. The trail gets ruthless on the fierce half-mile climb to 3,331-foot South Horn, the ridges are waterless, and the summits windy and exposed. But the wild-north panoramas stretch all the way to Mt. Washington. Contact: Appalachian Trail Conference, (304) 535-6331; www.appalachiantrail.org