I'll begin with some simple history. Using the WiFire map, I looked at the last twenty years of wildfires in the San Gabriels. It appears that roughly 80-85% of the range now has burned in the last two decades. (Note that the map has not been updated for the recent Ranch2 Fire in Roberts Canyon.)
1. Sand Fire
2. Station Fire
3. Bobcat Fire
4. Curve Fire
5. Williams Fire
6. Grand Prix Fire
7. Blue Cut Fire
I labelled some of the largest fires based on memory and a bit of googling. Let me know if I made any mistakes.
The majority of Eaton Canyon and Little Santa Anita have not burned in some time, as well as much of the high country around Mt. Baldy.
Historically forests in the western USA grow, burn, and regrow. They don't require human intervention to burn, but sometimes we help the process along on purpose or by accident. Some say that wildfire is good for the forests, yet it is too often the cause of tragedy for humans and other animals living in or near the mountains.
Another basic, historical point is that even though a whole wilderness burns, this does not mean that everything was destroyed. Large and healthy trees often survive and live for centuries, and the wetter canyon bottoms often don't burn very much. Treeless slopes and ridges might be completely barren immediately after the fire, but new plants should appear soon, and after a few years the place will start looking nice again.
