Above photo from Whiteshell Provincial Park in Manitoba. More nice photos to be found at: www.manitobaphotos.com/petroforms.htm and a search of google images will turn up many more.
Think about how similar are some of the things we "rock pile people" post up here and elsewhere.
Why are they petroforms there but not here??
Then think about the Ojibwe People most closely associated with the Petroforms: "The Ojibwe language... belongs to the Algonquian linguistic group, and is descended from Proto-Algonquian. According to their tradition, and from recordings in birch bark scrolls, many Ojibwe came from the eastern areas of North America, or Turtle Island, and from along the east coast. They traded widely across the continent for thousands of years and knew of the canoe routes west and a land route to the west coast...The use of petroforms, petroglyphs, and pictographs was common throughout the Ojibwe traditional territories. Petroforms and medicine wheels were a way to teach the important concepts of four directions and astronomical observations about the seasons, and to use as a memorizing tool for certain stories and beliefs...Birch bark scrolls and petroforms were used to pass along knowledge and information, as well as for ceremonies..."
From Wiki's Ojibwe entry ( http://en.wikipedia.org/wiki/Ojibwe)
Petroforms video: petroforms