2014 USA Pro Challenge Climbs
The peloton climbs up through the Garden of the Gods on Stage 4 of the 2012 USA Pro Challenge.

Colorado’s USA Pro Challenge climbs nearly 40,000 feet over seven days of racing. That’s the equivalent of scaling Denali twice — from sea level. The feat would already make it America’s hardest bike race, but most of the course also sits well over a mile above sea level. The 2014 edition adds a new uphill finish at Monarch Mountain resort (elevation 10,820), but that won’t even be the high point of the stage race or the cruelest climb. Here are the five toughest, lung-busting ascents the pros must tackle.

The Climb: Kebler Pass
Highest Point: 9,980 Feet
Why It Will Ruin Riders: Stage 2 offers General Classification contenders their first uphill finish in Crested Butte, but first they have to survive Kelber. The pass tops out just below 10,000 feet as it grinds toward Crested Butte, climbing 1,157 feet over 4.6 miles on Gunnison County Road 12. The seasonal road consists largely of packed gravel, save for a few miles of pavement on both sides of the peak.

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The Climb: Monarch Pass
Highest Point: 11,312 Feet
Why It Will Ruin Riders: Stage 3 takes racers to the south approach of the climb from Sargents before the course turns around in Salida for the north climb to Monarch Mountain ski resort. The race the to ski lodge stops 500 feet (vertically) below the summit, but neither side offers respite. The Sargents route climbs 2,750 feet over 10 miles for a 5.2-percent grade, and the north route begins in Maysville, gaining 3,000 feet over 11.5 miles with a 4.9-percent grade.

The Climb: Hoosier Pass
Highest Point: 11,542 Feet
Why It Will Ruin Riders: The highest point of the 2014 Pro Challenge sits 3,800 feet above that of the Col d'Izoard, the highest point at this year’s Tour de France. The road begins to point up from the town of Fairplay (elevation 9,953), gaining 1,600 feet over 10 miles. Don’t be fooled by the average 2.6 percent grade; the bulk of the climbing comes in the final three miles as the pass hits 7 percent and the oxygen thins out to 65 percent of the concentration at sea level.

The Climb: Garden of the Gods
Highest Point: 6,409 Feet
Why It Will Ruin Riders: The race’s Stage 4 circuit through Colorado Springs’ Garden of the Gods features a relatively measly 6,409-feet climb summit, but the journey through the breathtaking — and aptly named — park hits a maximum grade of 17 percent. The sharp, roughly 400-foot gain via Ridge Road seems easy by comparison to the mountain passes, but the pros tackle it four times.

The Climb: Vail Pass
Highest Point: 9,663 Feet
Why It Will Ruin Riders: The Stage 6 time trial in Vail consists of a single, no-reprieve ascent of Vail Pass. The course has been a fixture of American racing for more than 30 years with roots in Colorado’s first major stage race, the Coors Classic. Though it averages just a 3-percent gradient, the 10-mile, 1,513-foot climb breaks riders that push too hard on the flatter first half. In 2013, overall Pro Challenge winner Tejay van Garderen set a course record of 25:01.