The rock, named the Glenwood Erratic, is located in a field near the village of Glenwood, about 100 kilometres southwest of Lethbridge.
Stan Knowlton, a historian with the Head-Smashed-In Buffalo Jump heritage site, wrote in a local online newspaper that he had visited the rock several times to document the pictographs and petroglyphs.
On the morning of Sept. 9, he discovered the images had been destroyed.
"This was a deliberate act to erase history and definitely not accidental," Knowlton wrote in a report published by the Pincher Creek Voice.
"The world has been deprived of the ancient knowledge contained within these artifacts."
Knowlton said the apparent vandalism was well planned and resourced. It appears acid or detergent, a pressure-washer and an electric hammer drill were used to remove the markings.
He said the culprits would have also needed a large ladder, since the rock is about five metres high.
He spotted tire tracks leading to the rock and talked to members of the nearby Hutterite colony that owns the land. They had seen a white pickup truck in the field a few days earlier.
RCMP officers from Cardston have visited the site and are looking into what happened.
Insp. Joe McGeough said investigators will be co-ordinating with government agencies such as Alberta Environment and Parks Canada.
"The RCMP is a proud part of Alberta's history and takes these matters very seriously," he said.
Chris Davis, a reporter with the Pincher Creek Voice, toured the site with Knowlton after he discovered the destruction.
"To see the damage was just mind-boggling. We just sat there for half an hour not knowing what to say.
Davis said readers have reacted with shock and sadness. "There seems to be a real hope that this isn't some white people coming along and wiping out native history."
Knowlton said the rock is well-known as a "magnificent giant of the plains," but not many people knew of the aboriginal images on it because they were covered by lichens. The thick, hardened fungus began disappearing this year due to warm, dry weather.
Knowlton said he's certain the markings were syllabic writings and ochre paintings dating back hundreds if not thousands of years.
He planned to take a high-definition camera to the site to record the images but never got the chance.