(Karlstad, MN)  --  Investigators say arson is the probable cause of a major wildfire in Kittson and Marshall Counties in northwestern Minnesota and a reward is being offered.  The "County 27" fire burned 44-hundred acres, led to the partial evacuation of Karlstad, destroyed 11 homes and damaged dozens of other structures.  The D-N-R, Kittson and Marshall County sheriff's offices are offering a six-thousand-dollar reward for information leading to the identity of the arsonist.  Anyone with information is asked to contact local authorities or the Arson Tip Line at 800-723-2020.