Nomads of the North

Nomads of the North is a 1920 American film featuring Lon Chaney and Lewis Stone. A Canadian Mountie allows an innocent fugitive to escape with the woman he loves. The film is based on the 1919 novel of the same name by American author James Oliver Curwood.

Betty Blythe and Lon Chaney were burned while filming the forest fire scene when a blaze that popped up unexpectedly blocked their escape. They were rescued through a tunnel that had been previously built for just such an occurrence, but filming was stopped for ten days while the actors recovered in a local hospital.The crew erected a phony forest on the Universal lot, with fake trees,trimmed with natural foliage, planted in the ground,barked and painted. The forest fire was filmed withcameras. ........

Source: Wikipedia