Blaauboschkraal Stone Ruins are a provincial heritage site in Waterval Boven in the Mpumalanga province of South Africa. The site was originally declared a national monument on 18 April 1975.
The ruins are thought to be the remains of structures created by Bokoni people who settled the region in the 16th century and who altered the landscape to increase agricultural yields in high-altitude grasslands. The stone rings were probably used as enclosures for cattle (kraals).
The Blaauboskraal stone ruins are among a number of stone circle ruins located in the Mpumalanga escarpment over an area of approximately 150 km2, a number of which are facing threats to conservation. Information about the people who created these stone circles and terraces was often omitted from South African historical sources.
Pseudoarchaeological alternative explanations have been put forward for the Blaauboschkraal stone ruins, attributing alien and/or ancient origins. The most prominent proponent is Michael Tellinger, a politician whom Hammer and Swartz characterize as a promoter of conspiracy theories, influenced by Zecharia Sitchin's ideas of ancient astronauts. He calls the site "Adam's Calendar", and claims it is the remains of an alien-made construction built 300,000 years ago as an ancient calendar.