From what I have read, the theory is that there was a massive lake, referred to as “grand lake“ that was formed as a result of the great flood, which eventually washed out one of its natural dams and flooded downhill, creating the Grand Canyon. There’s some good resource material to support the theory.
Just looking at the walls of the canyon, it looks like a sudden even, not a million years of slow formation.
Steep, no vegetation or remains of vegetation, and it’s so wide. A wide river flows slowly...........