The Colorado Court of Appeals also said state District Judge Edward Colt, who presided over Barton's case, had at least ``the appearance of prejudice'' because smoke from the wildfire forced him to leave his own home for a night.
The court ordered a new sentencing hearing before a new judge.
The appeals court said Colt acted improperly when he gave Barton twice the normal prison term after finding ``extraordinarily aggravating'' circumstances without a jury trial.
The appeals court said such a finding should have been made by a jury, not the judge. Barton had waived her right to a jury trial, but the appeals court said that did not affect the requirement.
Barton pleaded guilty to state arson charges for setting 2002 fire that eventually blackened 138,000 acres, destroyed 300 buildings and caused property damage in excess of $29 million.
The state appeals court ruling does not affect a separate, six-year prison sentence Barton received in U.S. District Court after pleading guilty to federal charges for the same fire.
In court testimony and interviews with investigators, Barton said the fire started when she burned a letter from her estranged husband in a campfire ring on June 8, 2002, despite a ban on outdoor fires because of a severe drought.
She worked for the U.S. Forest Service at the time.
Colt had cited Barton's work for the Forest Service and her specialized knowledge of wildfires as one of the aggravating circumstances. He also cited the catastrophic results of the fire.
``Any fact that increases the penalty for a crime beyond the prescribed statutory maximum must be submitted to a jury, and proved beyond a reasonable doubt,'' the appeals court said.
The court also noted that Colt had been in a ``state of panic'' when he helped a court clerk evacuate her home because of the fire, that he had helped serve food to people displaced by the blaze and that the operation of his court had been disrupted by the fire.
``We also note of further concern that, during the sentencing hearing, the judge injected comments about his personal experience into his findings,'' the appeals court said.
