Obviously we have our own thoughts on what it would take to make the stones. But just to be clear, when I wrote "to make", I was not writing about the actual process of carving a stone. I was describing everything (skill set, education, profession, ect.) that would be needed to even attempt such a project. That list is actually quite long.
The best analogy I can offer is something like trying to understand/ID the man who constructed the Loretto staircase. Without a name, researchers must build a profile of the man base on what is known and the results of his work. Above average intelligence, classically trained in carpentry, familiar with math... with a little effort, this list can become substantial. (Ellie... it has 33 stairs).
Well, the stones were not lost to history. Remember, one was protruding from the earth when found. Amazing when you try to reason how something buried intentionally can make its way to the surface. Here, where it gets very cold, stones are forced to the surface with the freeze and eventual thawing. Knowing the climate and composition of the earth where the stones were discovered, I wonder if this process is even possible in that location. I honestly do not know.
Planting the stones at a highway construction site was, when one thinks about it, a perfect approach. So, that is another thing to add to the list. Someone familiar with Arizona's highway expansion project.