[blam]

"Shell middens deposited by humans typically contain shells of a very few selected (human food) species. Geophysical (tsunami) deposits generally contain a very wide -- and mixed -- assortment of shells of diverse species. "

Shouldn't be that difficult.

[geopyg]

I think it was near the four corners in Colorado that their is “Black Ridge” or something that has a thick deposit of black obsidian all along the top. Nearest outcrop for the stuff is hundreds of miles away. Seems the indians sat on this ridge making flint arrows and spears while waiting for the buffalo to appear.