I remember reading or hearing once that nobody seems to really know who built that thing, but one of the strongest candidates from what I remember was Ted Turner and some friends. Him and Hanoi Jane have some strange views about things.
Man Behind the Georgia Guidestones Speaks Out
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https://americasvoice.news/man-behind-the-georgia-guidestones-speaks-out/
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https://www.liberalforum.org/topic/236628-truth-revealed-ted-turner-was-behind-the-georgia-guidestones/