Those two lines of evidence (though the one is anecdotal) plus the fact that it seems hard to imagine the rock could have lithified enough during the receding stages have convinced me, at this time, that the canyon formed centuries after the Flood.
However, I will not say that it did NOT happen that way.
This is interesting. I didn't know that some influential creationist organizations had started to give up on the flood as the cause for the grand canyon.
It is also interesting that again a creationist won't actually come down firmly on something. That is very common.
You do understand that the believers in the genesis stories were the original researchers in the geology. They have had more time than the "non-genesis" side but still haven't gotten a coherent idea of what they think happened.