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.