If you go out looking for "rock pile", "stone mound", "stone pile", "cairn", "rock stack", or whatever, on Google, you will find lots of stuff about fishing [apparently underwater rock piles create a favorable fish ecosystem], terriers, monster trucks, etc. You will also find discussions of two kinds of Indian rock piles: Donation piles and Bison drive piles. Donation piles are described as piles located where a person fell in battle, or a where a person is buried, or where a memorial is erected. Each person in passing is supposed to place a stone donation on the pile. This is a worldwide idea and piles like this are described in Israel, Nepal, and probably many other places. Also, when cornered, New England academic archeologists acknowledge that - yes - it is known that Indians created such piles. For example there is a famous donation pile on "Monument Mountain" in Stockbridge Massachusetts (thanks N.M. for the info).
BUT here is why the idea is a problem for the study of rock piles: it trivializes the location of the pile and it trivializes the structure of the pile. If the location is, by coincidence, where someone happened to die in battle or was buried, this is not a location that is special in itself. Rather the location is special because of the events that occurred there. By contrast, most of the rock pile sites I see are located in a very specific topography and, I have come to believe, these spots are places of natural energy and aesthetics. So the location is not special because of the rock pile but because it already was special before the pile was built. It is a working hypothesis that the pile was built only in this location for a very good reason. The site layout is complex and needs to be studied not dismissed. This is exactly the opposite conclusion to the one arrived at from assuming "donation piles". It is also sometimes said that donation piles will tend to occur along trails (see that pdf link from earlier). So the structure of the "rock pile site" will be the structure of the trail that passes bye - of no particular interest. I find that rock piles are usually grouped - not strung out along a trail.
Also the shape of a donation pile is dictated by people randomly tossing rocks onto it, so the pile will have no structure worth speaking of. It will tend to be conical with sloping sides at the angle of repose for the materials.
Well these things are simply not true for the majority of piles that we study. They are usually grouped, the location is special, and they are either low or stacked but rarely conical - except when they have been vandalized. So if you hear someone talking about donation piles - check you wallet because they are implying that the location and the structure of the pile are of no interest. I think the opposite should be assumed until proven otherwise. The locations are special and the structures are special and usually matched to the location in some way. People who are so confident to talk about donation piles seem to be pretendeding to wisdom - another reason to check you wallet.
We should always beware of assumptions which block the study of the details. These assumptions are an impediment.
On the positive side, if you keep looking in Google you might eventually come across Turtle Mountain and Bannock Point. I'll go look for the links and put them in the list to the right if I can find them.
[later]My Point is: donation piles exist but are not the interesting part of the subject. They represent a small minority of the sites.