That is an interesting article, I hadn't seen it before. We're just east of the Guadalupe, across the river from the article's stated limit of range. I guess the natives crossed the river. Our area is loaded with flint nodules. I could never understand how they were all broken and shattered since there is virtually no freezing here, and flint is not porous, anyway. We finally realized that the early people must have broken them.
We're on the Balcones escarpment in Hill Country, which has virtually no topsoil. It all runs down hill into the coastal plains in the article. There is no backhoe digging here, only jack hammers and drilling.