In the Eastern US, many Paleo and Early Archaic sites now are covered by ocean, which moved in as glacial melting increased the sea level. The East Coast in Paleo and Early Archaic times was miles out from where it is now. Very few artifacts on these sites ever will be recovered.
The effect may be more pronounced than one might think. I recall a museum on Mt. Desert Island I visited many years ago, which displayed late Archaic relics recovered from an island off the coast of Maine. Pollen studies showed that the site was a winter camp, not a summer camp, and the reason is that even cold seas can warm land in their immediate proximity above normal New England winter temperatures. Mt. Desert Island, for examply, today has noticeably milder winters than points only ten miles in from the coast. Particularly in Paleo times, I suspect that many groups tended to gravitate toward the coast during the winter. If that suspicion is correct, those winter sites now are all in the drink.
My understanding is that the line of the West Coast was as dramatically affected by the post-Ice Age rise in the sea level.
atorius