Dozens of the world's best cyclists are racing across the state of Colorado this week.The 2012 Pro Cycling Challenge started in Durango on Monday morning. During the weeklong race, cyclists will cross nine mountain passes, climb 42,000 feet in elevation gain and race 683 miles. The race ends in Denver on Sunday.This is the second year for the race.Four new cities are on the race route in 2012 -- Durango, Telluride, Montrose and Boulder.In 2011, the race prologue was held in Colorado Springs with a time trial. In 2012, the prologue is a 125-mile road race from Durango to Telluride that includes Lizard Head Pass at 10,222 feet.Stage 2 starts in Montrose and challenges riders with a sprint line in Gunnison, a second sprint line in Crested Butte, then what race officials call "a nasty 2 mile climb to the dramatic finish on Mt. Crested Butte."Stage 3 is considered one of the toughest days of racing in the U.S. -- the epic Gunnison to Aspen stage will again feature two of the highest climbs in professional racing. The 131-mile Queen Stage includes a sprint line in Almont, a 14-mile dirt climb to the 12,126-foot summit of Cottonwood Pass, a sprint line in Buena Vista, followed by another monster 12,000 foot summit on the famed Independence Pass before a wild descent into Aspen.Stage 4 takes riders back over Independence Pass to Leadville, over Tennessee Pass (10,424 feet) to Minturn. Then riders will be faced by a stiff 2.5 mile climb that rises almost 1,000 feet to the ski resort of Beaver Creek.Stage 5 includes what race officials call a daunting 10-mile climb up Hoosier Pass to 11,500 feet to Fairplay and eventually down to Colorado Springs with a technical uphill run through Garden of the Gods Park.For Stage 6, riders return to Golden, which hosted one of the races largest crowds during the 2011 race. Day 6's ride takes the cyclists from Golden to Boulder, then on a circle tour of the mountains starting with a 15 mile climb up Boulder Canyon to the town of Nederland, a ride along Peak to Peak Highway to a sprint line in Lyons. Then riders will climb up Left Hand Canyon and Lee Hill Road, back to Boulder. The race will end with a final 3.5 mile climb to the historic Sunrise Amphitheater on Flagstaff Mountain.The final day is a flat and fast time trial course in downtown Denver.The 2011 race made $83.5 million in economic impact, according to an analysis by race organizer Medalist Sports.