Well I assume that area that is now where the Grand Canyon is now was under an ancient sea that hosted prehistoric species. Over time, possibly over a billion years sediment, rocks, volcanic activity piled in layers which can clearly be seen in the rock face. That’s why there are some different species of fossils at the bottom of the canyon than the ones found closer to the rim.I don't take a stand one way or the other. Either could have been God's plan.
But, let me ask a question that is prompted by Dennis' comment. How did fossils of sea creatures end up on mountains that are around 8000 feet (or perhaps even higher) up on the mountain?
Over time the sea receded. Leaving a landscape that would possibly be eroded over millions of years to for the canyon we see today revealing the different layers of sediment, rocks, including volcanic that we see today. In the course of this, it slowly revealed the fossils we see today. That was the thought when I was a Geology major at OSU when I dropped out to take care of a wife and unexpected baby 28 years ago.
Who knows I wasn’t there and probably forgot more about geology than I wanted to.
Whether a massive dump of water created the canyon I don’t know. Doesn’t really sound real plausible but I guess possible if a earthquake created a fissure to help aid in erosion at such s quick rate. Especially since the canyon in its entirety is close to 200 miles long and 15-20 miles wide. Sorry that’s the best I can do with my limited knowledge. None of this certainly occurred over a 6k year timeline. It just doesn’t seem to be possible in my not so educated opinion