Leadville, Colorado is the highest incorporated city in the United States at elevation 10,152 feet above sea level. That means it will probably be pretty chilly there on January 23, 2010, for the first of a series of winter snow mountain bike races.
The temperatures generally range from the single digits to low 30s Fahrenheit in January, which isn't too bad when you're exerting yourself.
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Props to UltraRob and 303 Cycling.