I know there are rational explanations for this, know that an engineer with a computer and a couple of calibrators could calculate the exact angle and intersection of repose. But that’s beside the point.
This looks cool, but must require a lot of patience.
Update: They have a page about my name, Cairns:
The simplest cairns are often a single stack of rocks intended to mark a path, a territory, or a specific site. The intent is utility and meaning, rather than art. Those who place them are thinking of those who will come after. Those who find and follow them are trusting travelers who went before.