The Mixedwood Plains ecozone, as we know it today, is a result of ongoing geologic processes and climatic changes that have happened over millions of years. It's not tied to a specific geologic era like the Paleozoic or Mesozoic.

Here's a breakdown of how the Mixedwood Plains came to be:

* The Precambrian: The bedrock of the Mixedwood Plains was formed billions of years ago during the Precambrian era. This bedrock, consisting of granite, gneiss, and other metamorphic rocks, laid the foundation for the landscape.

* The Paleozoic and Mesozoic: During these eras, the area experienced periods of sedimentation and erosion, building up layers of sedimentary rock.

* The Cenozoic Era: This era, which started about 66 million years ago, saw the rise of the modern landscape. The glaciers of the Pleistocene Epoch (about 2.6 million to 11,700 years ago) significantly shaped the topography of the Mixedwood Plains, leaving behind glacial deposits and depressions that filled with water, forming lakes and wetlands.

* Holocene: This current epoch, starting about 11,700 years ago, saw the retreat of the glaciers and the establishment of forests. The Mixedwood Plains gradually evolved its unique mix of deciduous and coniferous trees, shaping the characteristic vegetation we see today.

So, while the Mixedwood Plains' bedrock formed in the Precambrian, the ecozone as we know it is a product of ongoing geological and climatic changes spanning several geological eras and epochs.