Interpreting old weathered rocks

I was walking on Hathaway Rd in Freetown State Forest and was amazed at how many of the pieces of gravel show signs of percussive organized flaking. This sort of thing is typical:

(That looks like a modern scratch.)

Here is a honking big example:

See the flakes?

Perhaps such a tool is not worth putting in anyone's collection but it's a tool nonetheless. What is interesting is the sheer number of such things. They were on the order of every fifth rock along the entire road. I am not going to bother to argue with someone who does not recognize this as a stone tool but, aside from that, I do want to discuss how is it possible for there to be such a high density of tools over the entire road? I am not talking about little clusters of tools here and there but rather a geological layer of gravel that contains numerous stone tools in every sample examined.

There are two things that stand out. First, it takes a long time to use so many rocks that you run out of material. Second, those rock must be exposed in order to be used. Putting such statements to work interpreting what we see in the Freetown gravel, I conclude that there must have been a long period of time when these gravels were exposed, as an entire surface of gravel. The best candidate for this is the period of time after the gravel was deposited (~19K years ago) and before there were significant additional soil buildup - quite a while later.

To tell the truth I am often puzzled by larger rocks that come out of the glacial till showing signs of having been used or flaked. A reasonable possibility is that there was a long post-glacial period of high population density.