I respectively submit that all of the available information indicates that the 26 rock structures on your property likely represent some activity of Euroamericans (i.e., since 1820) rather than prehistoric Indians, whetherthat be field clearing or stockpiling for construction of mills, fences,outbuildings, or some other odd reason. For example, I grew up on a farm in the 1960s and 70s and my father would make my brothers and me do odd jobs such as clearing a field just to keep us busy for a small fee (.50-.75/hr).
Prehistoric rock cairns in MO typically occur alone on bluffs overlooking perennial streams, although occasionally 2 rock cairns may occur on a ridge and rarely in small groups of 3 or 4 (never 20 or more). Working in the Ozarks for more than 30 years, I have never heard of more than 4 prehistoric rock cairns on any one site. Additionally, as I understand it, there is no soil mixed with the sandstone rocks, only decayed leaf litter. Most prehistoric burial mounds have at least some soil mixed with the rocks.
As for other sites, I suspect that prehistoric sites occur all along (redacted) Creek (ridge summits and stream terraces). This is not at all uncommon along perennial streams in the Ozarks, since during the past 12,000 or so years of prehistory, Native Americans traversed and occasionally camped on nearly every level spot. The problem, however, would be linking these sites to your cairns. Just because they are present in the valley doesn't mean that they are associated with the cairns. Even if you find Scallorn arrow points (and apparently you have....they are the most common arrow point type in the Ozarks...they are found practically everywhere) in the general vicinity, it is not necessarily supportive evidence that Late Woodland peoples constructed those rock piles....just that they lived in the area. If, on the other hand, you were to find Scallorn and other artifacts within and beneath the rock piles, you can make a better case that they indeed are prehistoric. As I understand it, no artifacts have been found directly associated with any of the rock piles.
Although Jack has not yet visited the site, his experience in the Ozarks weighs heavily in finding the truth of the subject rock features. An excavation of one or two of the cairns is now a real possibility, if the owner's ancient body can stand the strain and pain!
Standby for a decision...