Proponents of the measure say that marijuana should be regulated like alcohol and taxed to raise money for school construction. Opponents say the pot measure would increase youth drug use and wouldn't raise that much money.
Former Republican Senate candidate Ken Buck will argue against legalization.
Colorado is one of three states considering ballot measures this fall to defy federal law and legalize marijuana without a doctor's recommendation.
Colorado and 16 other states already buck federal drug law for so-called "medical marijuana," or allowing people with certain medical conditions to use the drug.
(Copyright 2012 by The Associated Press. All Rights Reserved.)