The USGS offers data on more than 20 years of wildfires handled by the federal government. I’ve mapped these data in two ways. The upper map simply shows the kernel density of wildfire occurrences. In this unweighted version, yellow regions correspond to areas that have experienced fewer wildfires, while blue areas have experienced frequent wildfires. The lower map is weighted by the number of acres burned by each fire. In this case, the blue shading highlights regions that have experienced the most geographically widespread fires.

Data source: http://wildfire.cr.usgs.gov/firehistory/data.html