The rock, named the Glenwood Erratic, is located in a field near the village of Glenwood, about 100 kilometres southwest of Lethbridge.
A media report said old pictographs and petroglyphs had been destroyed, possibly with acid, a pressure-washer and an electric hammer drill.
RCMP investigated the reports this week with the help of the Alberta Archeological Survey and the Royal Alberta Museum.
Inspector Joe McGeough said Friday there was no wilful damage to the rock and there is no record of there being any native pictographs or petraglyphs at the site.
Police say their investigation is over and they have no idea what prompted the report.
"We are very pleased that there was no known wilful damage to a historical site in our area," McGeough said.
"The RCMP takes very seriously the history and heritage of Alberta, especially when one considers that it ties so closely to our own."
Police also consulted with archeological experts familiar with nearby Writing On Stone Provincial Park, which contains dozens of ancient aboriginal rock carvings.
(CJOC, The Canadian Press)
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