How do you know a rock pile is man made? By the company it keeps.

People are often puzzled about how do you know a rock pile is man-made? And how do you know it is Native American and ceremonial or something boring, practical and Anglo? Both questions are related to how random the rock pile is versus how well built it is, but it is almost never a matter of a single isolated rock pile. They must be examined in a collection.

How does my eye know when a cluster of rocks is too clusered to be natural? Well I have trained my eye to recognize that degree of clustering. I could try to prove this in a statistical setting but that does not clarify the basic point: a rock pile that looks pretty random, found next to a more organized rock pile, gets the credibility of its better-formed neighbor. You look at lots of clusters of rocks, natural clusters such as when frost has broken up a larger rock, or where cobbles have accumulated somehow. And you learn that those are natural. But the exact same collection of accumulated cobbles, found next to a better rock pile would be seen as man-made.

More generally the sites can have more or less structure. Particularly when the piles are equally sized and spaced evenly within the area. Or spaced regularly in the area. The piles are not random but also the site structure is not random. Structured sites tend to be considered ceremonial.

So one bit of non-randomness builds on the next. Yes those are piles, yes this is a structured site, yes it is ceremonial. And it is much more common than you think.