I was gonna mention the catastrophic flood that resulted when the ice dam holding lake Missoula broke. (the last time) It's a subject that's pretty close to home considering I'm sitting in Missoula MT right now haha. In certain spots you can still see where waterlines once were on the sides of mountains, and there are other geological features that indicate this area was once underwater.
In the mid 2000s I flew commercial from Seattle to Spokane over the Washington desert/Badlands. It was obvious that a massive amount of water had rushed over that area at one point. I saw huge ripples probably a mile from peak to peak in the terrain like you would find on a sandy beach, and Delta type formations.
These features were pretty clearly defined and that (last) flood was supposed to have happened 10,000 - 14,000 years ago.
If the whole earth had been flooded a measley 4000 years ago, it would be blaringly apparent everywhere on the planet.