“These fires aren’t even in forests,” said Max Moritz, a wildfire specialist at the University of California, Santa Barbara.

Rather, the Camp and Woolsey fires, which are ripping through Northern and Southern California, began in areas known as the wildland-urban interface: places where communities are close to undeveloped areas , making it easier for fire to move from forests or grasslands into neighborhoods.

[Why does California have so many wildfires? There are four key ingredients.]

A 2015 report by the United States Department of Agriculture found that between 2000 and 2010 (the last year for which data was available), the number of people moving into the wildland-urban interface had increased by 5 percent . According to the report, 44 million houses, equivalent to one in every three houses in the country, are in the wildland-urban interface. The highest concentrations are in Florida, Texas and, yes, California.

It is true that California wildfires are getting larger and that most of the state’s largest wildfires have happened this century. The Mendocino Complex Fire, earlier this year, was the biggest California fire on record, as measured by acres burned. The Camp Fire is already the most destructive in state history, having razed more than 6,000 homes.