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They do the burns, but not everywhere, all the time. I usually see them done on grasslands; I honestly don't know if they do them in the mountain forests. We don't have forests east of the mountains (where Denver is, where I live). Sorry I said that kinda weird. Maybe it depends on who is managing the land. I've seen it done on Trail Ridge Road in the mountains, which is federal land, but again, on the grass.

I can imagine how fast fire can spread through grass, watching the local farmers burn clear their maize paddocks after harvest gives great respect to fire, and that is only in stubble.
Denver is too high for trees, but I liked the main street bus idea that was running about 2007. and catching a train underground to change airport terminals, mind-boggling for us country kids

Nah, we're not too high for trees. Treeline is like twice as high as Denver's altitude. It's just that we're considered high desert, so besides the planted trees, and the ones that run alongside creek beds, it's just too dry. But the mountains have snowpack, so they get aspens and evergreens. The SW desert technically stops around Fort Collins, which is about an hour north and just this side of Wyoming.
Thinking on it, I bet they use burning on the prairie because it's easier to control on the flatter areas, and are less likely to burn the forests on the more steep terrain because it could more easily get out of hand, but that's a guess.
The DIA train was one of those construction things that take way longer than planned, and so people have this conspiracy theory that they were building secret tunnels going to the Brown Palace (old hotel downtown) where Satanic baby sacrifices take place. I wish I was kidding, but that conspiracy theory still lives on the internet... 😂 I guess it doesn't help that we now have a statue at the airport affectionately called Bluecifer of a blue horse with glowing red eyes that killed its sculptor by falling on him.