@djsumdog In the last few years I keep hearing of archeologist discoveries that push back when various species of humans started, or when they left Africa, so it would not be impossible to cram in somewhere a new undiscovered civilization. The difficulty is, where are the artifacts left by the civilization? Clay figures, pots, writing in clay tablets, various tools, these are the traditional signs of civilization.
Even with massive floods, at some point you'll find something scattered somewhere because archeologists and geologists have been able to identify when and where flooding took place. So if you assume a flood wiped across a valley, you'll just go downstream, where the water would have settled everything it carried, and start digging for signs of the wiped civilization.
We could of course also be dealing with tribes that for one reason or another have their "technology" based mostly around biodegradable material. Less usage of stone, mud, clay, and more wood and plant matter, that would decompose and leave nothing to find for archeologists. They could still have had language, stories with basic philosophical concepts behind them, but expressed orally. You could have had civilizations that were intellectually advanced, but at the same time, you wouldn't be able to find evidence for it. At which point it would be like believing in Santa, with no evidence.
I've heard of Göbekli Tepe only in passing, and I just know that there's some fringe ideas about it being something, with little evidence to prove it. A geographical feature that looks as if it could be man made, but no human artifacts discovered.
I don't think I've heard of the Richat Structure.
I'm open to the idea, but ultimately it's important that we find conclusive evidence of human settlement. Even with cave men we've been able to find wall art and ash remains of fires lit by humans.