It burned so fiercely because it has been dry as a bone for a few years now. Plus it has been windy. Fires can cover a lot of territory when the wind gets going. The trees were pretty dense in that area and Ponderosa Pine forests are prone to periodic fires. In a natural Ponderosa forest, fires every 3-5 years clear out the smaller trees and a lot of the dry fuels. You can’t really do controlled burns in subdivisions on private property so the fuels collect. I have witnessed several wildfires in Colorado including one that came pretty close to my house. I could see flames from my front porch. Years and years of fire suppression mean that many areas are primed for a big, crowning fire. I just spent the weekend in an area of Colorado where whole mountains for miles are completely dead from bark beetles. All it will take is a lightning strike to set them off.
It is a bit scary to think that sop far, neither last year’s big fires (waldo, RMNP) nor this year’s v(Royal Gorge, Black Forest) occurred in the “dangerous”, i.e. beetle killed, NW part of the state. when one of those hitsm, it may be Peshtigo redux.