In 1992, NASA did a satellite comparison of the Mt Hood National Forest and a state in the central Amazon in Brazil.  Mt. Hood was more fragmented.

In the coast range, maybe one percent of the old growth remains and a lot of that is in the small "Wilderness" zones.  In the Cascades, maybe ten percent is still left, much of that in "Wilderness."  In both areas, the very biggest trees are long gone.   Areas large enough for evolution are mostly gone, too.  I realize not everyone believes that evolution is real.

As for oak savannah, pristine examples of that are more rare than 500 year old Doug firs.

The Kalapuya did burn but they didn't remove the biomass, compact the soil with fellerbunchers or spray poisons.  

We are changing the climate faster than trees migrate.