Topper Site was just exactly what I had in mind. Have to love the last of the Wiki article, which corroborates what I said:
Until the recent challenges to the Clovis theory, it was unusual for archaeologists to dig deeper than the layer of the Clovis culture, on the grounds that no human artifacts would be found older than Clovis.We won't dig, because we won't find anything, because we believe there is nothing to find, so there is no reason to dig to try to find what we don't believe exists....
Same thing with the centuries of 'no pre-Columbus New World visitation' on the part of historians.