Something like trillions and trillions of gallons of water carved out the Grand Canyon, and very quickly.
A a flood of melting ice sheet from a comet impact would fit the bill...............
The geology reports I’ve read are that there was repeated massive flooding in the pacific northwest as ice dams broke and then reformed again repeatedly. That happened in only the last 12 thousand years.
The grand canyon was something different. It was created starting about 4 million years ago as the land rose. Then over several million years—in pretty much the same fashion as the niagra falls is creating the falls canyon there—the falling water wore backwards creating the grand canyon.