A US Forest Service worker has been given a six-year jail sentence for starting the worst wildfire in Colorado’s history.

Terry Barton pleaded guilty to igniting the fire which burned 133 homes and 138,000 acres of forest last summer, causing US$13m damage. She also admitted making false statements to federal investigators.

She said she was burning a letter from her estranged husband in a campfire ring when the blaze got out of control.