The ocean was as low as it goes. Humans, as usual, lived on the flood planes of the slow flowing rivers, or near the shoreline ~ and that was about 400 ft deep in the present ocean.
With a small population they had no reason whatsoever to advance inland or uphill so whatever it was they did is little known ~ as yet.
Besides the inland areas were filled to the brim with giant elephants and enormous saber toothed tigers and dire wolves.
A guy could get et!
I suppose ANTIDILUVIAN is as good a name for it as any.
Wow...you mean everybody got free beach-front property and no property taxes, to boot? Man, what a time to live!