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GRAND COUNTY, Colo. (KDVR) — A fire burning near the East Troublesome burn scar was started on Aug. 29 by a lightning strike, fire investigators determined.

The cause of the Black Mountain Fire was discovered by using photos and video of the fire along with mapping technology to locate the tree that was struck by lightning sparking the blaze. 

The fire covers 416 acres and is 35% contained but has been a threat in the Grand County area due to dry conditions and wind creating a possible quick spread.

According to a tweet from the Medicine Bow-Routt National Forests and Thunder Basin National Grassland: “Along the path of a tree struck by lightning, sap boils, steam is generated and cells explode in the wood, leading to the physical damage and in many case, ignition of fire.”

Warmer, windier weather on Saturday is expected to increase fire activity. Aerial and ground crews of 180 personnel will continue to battle the fire with water drops and line containment.

This story was edited to reflect an increased containment of the fire.