A publication released last year by the U.S. Forest Service titled Wildfire, Wildlands, and People: Understanding and Preparing for Wildfire in the Wildland-Urban Interface has some interesting charts. The one above shows where in the United States structures have burned in wildfires.
The other chart shows that while the often-heard statement that “humans cause most wildfires” is true, that is not the case in all areas. In the Great Basin lightning is the primary cause of fires, and there are almost as many lighting fires as human caused fires in the Northwest, Southwest, and Rocky Mountains.
(Click on the charts to see larger versions.)