[e_engineer]

They really should have found a way to get some sonar equipment to locate promising sites first. Even some USGS low resolution sonar images like this would be better than nothing:

[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.

[Citizen Tom Paine]

I was thinking of EG&G high resolution sonar (250KC as I recall). Towing this along the banks of submerged rivers which ran out to the continetal shelf break should turn up any sites that are still there. Plan your survey lines on existing bathymetric charts.