Wikipedia. Guidestones website - https://www.georgiaguidestones.org/about - see the History entry there.
Nobody knows who commissioned a local quarry to erect the stones; the pseudonym R. C. Christian having been used. Nobody knows who exploded things.
If intended to exist for eternity, the actual lifetime of the monument was less.
UPDATE: If you want news coverage of the story - there is not much - but try this websearch:
https://duckduckgo.com/?q=georgia+guidestones&iar=news&ia=news
The roadside attraction received renewed attention during Georgia's May 24 gubernatorial primary when third-place Republican candidate Kandiss Taylor claimed the guidestones are satanic and made demolishing them part of her platform.
One may wonder - what parts of the guidestones remained intact after the explosion but were removed as a safety precaution, who took custody of those, where are they now, and what will be their future? In private hands at a private place?
Who would assert a right to seize custody? The State of Georgia, the local county?
Will the public continue to have some manner of access to intact remains?
BOTTOM LINE: The history of how they got there is mainly mystery. The future the remains hold should be an open book public record; from dismemberment of the monument remains from on site, onward. Who contracted for removal, who got that contract? Who took final jurisdiction? On what basis?
Keep a memorial, same site or elsewhere? Break it all up into paving rock? Sink all remains at sea? Who decides?
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Guradian. YouTube: here, here and here.
Auto parked at, then leaving the site soon before the blast.
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In light of the first policy guideline of the Guidestones, suggesting a safe and stable sane worldwide diverse and fit population be half a billion people, this AP item opens -
World population to reach 8 billion by November even as growth slows
New projections from the United Nations’ Department of Social and Economic Affairs show that the global population is expected to reach 8 billion on Nov. 15 — though population growth is at its slowest in decades, with rates dipping under 1% in 2020.
Released Monday, the agency’s “World Population Prospects” report projects that India will surpass China as the most populous country in the world by 2023 — a change, in part, because of China’s aging population and history of restricting births.
According to India’s local census, the country’s population was 1.21 billion in 2011. The government had deferred the 2021 census because of the coronavirus pandemic.
Population trends outlined in the report show that, in most parts of the world, death is outpacing life.
That is sixteen times as great as the Guidestones monument envisioned. Population cannot grow without limit, on a finite planet. Food scarcity with continuing growth will become more of an issue as time passes. Anger will rise. Demonstrations will be put down with greater official brutality, as time passes. Those in power will not relinquish it, nor do they have an answer to growing worldwide population on a finite planet. A fix is needed, long term, if not sooner.