B y the Numbers The percentage of wildfires on the Olympic National Forest last year that were caused by people. Overall, nearly half of all fires reported on national forests in Washington and Oregon were human-caused. Often unintentional, fires commonly are caused by abandoned campfires, cigarette butts or poorly disposed hot charcoal, according to a news release from the U.S. Forest Service. While not as prone to fires as national forests in arid regions, the Olympic forest has a history of wildfires. Steep slopes and natural fuel conditions — soil that has thick layers of material, plus moss and lichens that easily combust when dry — can provide opportunities for wildfires to grow and spread, the release said.