The USA Pro Challenge kicks off today in Aspen, Colorado, with a 66-mile circuit race. From there the route gets progressively harder, as it takes riders on a challenging journey through the Rocky Mountains. The race will visit eight host cities for the starts and finishes of each stage, ranging from Aspen and Steamboat Sprints, to the state capitol of Denver. All told the race will cover nearly 600 miles. Here's a stage-by-stage look at this year's testing race:

Stage 1: Aspen Circuit Race - Monday, Aug. 19
The new for 2013 Aspen/Snowmass Circuit may be short on distance, but it packs a punch that will welcome the riders to Colorado. Consisting of three 22-mile laps, 66 miles total, Stage 1 includes 3,080 feet of climbing per lap with minimal recovery. Each lap will see the racers fight for position onto the narrow, but beautiful Maroon Creek Bridge, then grind up to Snowmass Village. A quick descent leads to two short, but steep climbs and a quick loop through downtown before doing it all again. Pair that with a starting elevation of 7,900 feet and you have one tough opening day.

Stage 2: Aspen to Breckenridge - Tuesday, Aug. 20
The familiar battleground of Independence Pass will be anything but easy as riders ascend the 12,000 feet climb, the highest point reached in any professional cycling race. Then they'll continue on through some familiar spots as the race zooms through Buena Vista, Fairplay and Alma, before tackling Hoosier Pass from the south this year. But before crossing the finish, riders will have to conquer the nasty 15 percent grade of Moonstone Road in the heart of Breckenridge, before bombing down Boreas Pass to the waiting crowd.

Stage 3: Breckenridge to Steamboat Springs - Wednesday, Aug. 21
Stage 3 of this year's USA Pro Challenge is wide open for the taking. After leaving Breckenridge, Swan Mountain Road provides a great launch pad for breakaways as the riders weave north to Kremmling, but it's all just a prelude to the day's main showdown on Rabbit Ears Pass. Climbing the challenging eastern slope will give the climbers a chance, but they will have to hold off the sprinters for 20 miles after cresting the top as they head downtown Steamboat Springs.

Stage 4: Steamboat Springs to Beaver Creek - Thursday, Aug. 22
Stage 4 is the Queen Stage of the 2013 USA Pro Challenge. It features some previously used terrain, but with some added spice. One thing is for sure, the road to the final podium in Denver goes straight over Bachelor Gulch. A new start in Steamboat will send the race off onto new country roads around Routt County. This roller coaster of small hills gives way to a gentle route south until the racers have to climb up from the river bottom at State Bridge. That's just the beginning, as the new approach to Beaver Creek will now send the racers up the new climb of Bachelors Gulch. The relentless grade with pitches up to 18 percent will do real damage. After Bachelor Gulch, the leaders still have to race down a technical descent and power up the final 2 km climb to Beaver Creek Village.

Stage 5: Vail Individual Time Trial - Friday, Aug. 23
The last time the USA Pro Challenge visited Vail, the Time Trial was decided by 58 hundredths of a second. Competition will be equally fierce this time around, but the names may change a bit. The course's roots are in Colorado racing lore and trace back to the Coors Classic. The route starts in Vail and climbs most of the way up Vail Pass. The gentle grades of the first half of the course give way to a steady climb for the last three miles.

Stage 6: Loveland to Feet Collins - Saturday, Aug. 24
With a flat speed-fest scheduled for Sunday in Denver, any contenders for the Leader Jersey will have only this stage left to make a move. The outskirts of Loveland will see the racers off as they spend some early miles on the flat windswept plains passing through Windsor and back to Loveland. Then it's up Big Thompson Canyon where things will heat up. Split north onto Devils Gulch, the race's last King of the Mountains competition, before hitting Estes Park and back down Big Thompson. Horsetooth Reservoir provides one last chance for aggression on its steep rollers. If no one gets away here, look for the sprinters to have their day.

Stage 7: Denver Circuit Race - Sunday, Aug. 25
After six days of fighting over mountains trying to stay with racers 20 or more pounds lighter, the sprinters will have their day in Denver. The Denver Circuit takes the best parts of the 2011 and 2012 Denver stages and combines them into a new circuit. It still hits all the Denver highlights - LoDo, City Park, Civic Center Park. There isn't a bad viewing spot. Watch for early breakaways, and then watch the teams cue up and try to set up their sprinters for the final push to the finish line.