Forest fires are a natural part of the cycle. In fact, it's forest fire "prevention" that causes even bigger forest fires than normal. If they simply let fires burn, it would naturally cleanse the forests of brush and dead trees and create much smaller forest fires.
It's more that the specific type of forests that John Muir was so fond of were the result of intensive agroforestry by the tribes of California. They used fire as part of a fairly large toolbox, and you don't get that sort of forest without it.
