For sled dog-racing fans worldwide, the most important calendar day is the first Saturday in March, when teams convene for the start of mushing's Superbowl--the Iditarod Trail Sled Dog Race(r). Every year, as it has since 1973, this ultimate challenge begins in the state's most populated city, Anchorage, and then dives into the Alaska Bush on a historic trail that wends over mountain ranges, along frozen rivers, and onto the Bering Sea ice. The finish line lies 1,000-plus miles away in Nome, beneath a giant, burled archway. There, dogs and their drivers are greeted by masses of locals,...