Which, in the greater context of the actual age of the planet, is but a blip. There are thousands of years of undocumented history. What was the climate then? They don't know. What caused the Grand Canyon to happen without man-made pollutants around? You telling me there were no fires and droughts and floods and hurricanes before "documented history"?
Why did the tribes in Arizona leave?
The grand canyon happened because Paul Bunyan was tired after chopping down the nevada/ colorado forrest and dragged his axe on the ground as he was heading back up north for more work. Granma told me so.