The California Wildfires: How Experts Track A Blaze to Its Origin

One huge fire was caused by a spark set off by a man with a hammer, working on a fence post in a field of dry vegetation. Another began at a backyard barbecue. A 2007 fire on Santa Catalina Island was ignited by workers cutting metal wires with a torch. As investigators try to determine what started the most devastating wildfire in California history, which killed at least 56 people, the beginning premise is that human beings — through their mistakes, or their toys, tools and technologies — were probably behind it. But looking into the cause of a fire, which can take months of painstaking work, also means rolling back the clock to a moment and to a spot that, like most of the town of Paradise, has been reduced to ash.