Not that I have any sympathy for smokers, but there are a lot of anthropogenic sources of ignition. Cars dragging metal, and hot catalytic converters are a couple. Electric lines that frequently run along roads are another. And campfires and ordinary cooking fires can spark a wildfire; homeless people tend to live near roads and overpasses.

The fact that we don't have more arsonists in California is one thing that gives me faith in humanity.