It is not clear to me that the hydroplate theory can be connected to the Grand Canyon. Even if it can it might be a bit too big to fit into this thread and there have been a number on it.
If it can be connected I'd like to see that connection made very well before it is discussed and then I think the discussion should be elsewhere.
During the Flood, the sedimentary layers (along with fossils) were laid down. Then, when the Flood ended, the huge lake broke, carving out the Grand Canyon out of previously formed layers (with fossils). Just because both were created by the flood, doesn't mean they were created at the same time. The flood did last for 150 years....
That has nothing at all to do with hydroplate theory. Please do not mention it again in this thread.