In geologic time if the Flood really did happen, it happened like a blink of an eye ago. So if there's any evidence in the rocks of the Flood, it should still be there, and it should be pretty clear. There's enough water on the earth (more than a billion cubic kms) to cover it all under 2km of water, if the earth's crust was uniformly thick, but it's not, we have deep ocean trenches and tall mountains.
The Bible says the tallest mountains were covered by 15 cubits of water at the Flood's height. A cubit is over a foot in length, so this is over 15 feet over the tallest mountain peaks. That height of water corresponds to the 2km depth aforementioned. Which means the tallest mountains before the Flood were no more than 2km tall, whereas today Mount Everest for example is like 9km tall.
The waters of the Flood wouldn't just stay up at a high level for any longer than gravity would permit, so something changed in order to allow both the level to drop down, but also for mountains like Everest to rise up.
If the surface of the earth was separated from the crust by water, then the Flood could have occurred through the collapse of this structure. That would fairly quickly submerge the entire surface under 2km of water.
So now the question is, what happened so that the total height from the earth's mantle of rock is now between like 7km and 20km (Mariana trench Challenger Deep being like 7kms and Everest's summit being like 20kms from the mantle directly underneath them), which is a range of like 13km of rock. For the Flood's water to cover a 2km mountain means that even if 7km thickness at Mariana trench didn't change, the tallest mountain's summit was no more than 13kms from the mantle.
What causes rock to rise up 7km toward the sky?