https://phys.org/news/2018-08-firefighters-major-california-blazes.html > And when they can't take that direct approach, firefighters retreat to a ridge, wide road or stream where they use bulldozers to cut a "fire line." There they'll wait for the blaze to come to them while lighting "backfires" to clear vegetation between the fire line and the approaching blaze. > Experts say whichever approach Cal Fire takes, California firefighters are often more aggressive in trying to extinguish wildfires than those in other less-populated states. That's because California wildfires are increasingly threatening sprawling urban areas.