[RightWhale]

If you had a sonar scan like that, where would you start digging? One thing is they would probably put a camp along the banks of sunken riverways. Another place would be high points where hunting lookout camps might have been.

[e_engineer]

In many places around the world submerged beaches and ancient tree stumps have been found that provide an indication of where the sea level once was. I would try to find a submerged beach, then focus my efforts on the river valleys upstream from the submerged beach.