The ruling Tuesday means an 11-member bipartisan commission has until Dec. 6 to modify and resubmit the maps. The court heard arguments against the maps last week from some of the state's largest counties, including Arapahoe, Jefferson, Weld, Douglas and El Paso counties.
Representatives from the counties told the court many counties were unnecessarily split.
The maps the commission submitted seek to make a third of state Legislature races competitive next year. Democrats control the Senate and Republicans the House.
The once-a-decade process to redraw legislative districts to account for population changes impacts the Legislature's balance of power for years.
(Copyright 2011 by The Associated Press. All Rights Reserved.)