Fires where over a million acres are burned. Wilfdfires happen every year, there are 100,000 in the USA annualy.

"Causes Lack of common sense forest managment has lengthened the fire season and made it more extreme from the middle of the 20th century.[4][5] Since the early 2010s, wildfires in California are growing more dangerous because of the accumulation of wood fuel in forests, higher population, and aging and often poorly maintained electricity transmission and distribution lines, particularly in areas serviced by Pacific Gas and Electric.[6][7][8] United States taxpayers pay about US$3 billion a year to fight wildfires, and big fires can lead to billions of dollars in property losses.[9] At times, these wildfires are fanned or made worse by strong, dry winds, known as Diablo winds when they occur in the northern part of the state and Santa Ana winds when they occur in the south. However, from a historical perspective, it has been estimated that prior to 1850, about 4.5 million acres (17,000 km2) burned yearly, in fires that lasted for months, with wildfire activity peaking roughly every 30 years, when up to 11.8 million acres (47,753 km3) of land burned.[10][11] The much larger wildfire seasons in the past can be attributed to the policy of Native Californians regularly setting controlled burns and allowing natural fires to run their course, which prevented devastating wildfires from overrunning the state.[10]"
- Wikipedia