Majorville Medicine Wheel
The Majorville Medicine Wheel near Brooks, Alberta is the oldest known medicine wheel in North America.  Excavation of the central cairn in 1971 gave evidence it was constructed around 2500 B.C.  There is also evidence that Majorville was constructed in stages.  A long period of inactivity (1000 B.C. to 200 A.D.)
gives reason for speculation that the purpose for the wheel may have changed over time.  For many cultures, the reason for sacred sites change, but not the location. 
A map of known medicine wheels. 
Note the preponderance in Alberta.
Erosion and vandalism has
taken it's toll, but it is now protected by a fence. 

The central cairn is 9 meters
in diameter. The central cairn is surrounded by a stone circle 27 meters across. The circle is
linked with the central cairn by
28 spokes. 

Small cairns on nearby hills
may have been constructed for solar alignments with this medicine wheel.
1