Washington State Park

The carvings, or petroglyphs, carved in dolomite rock, are believed to have been made around 1000 to 1600 C.E. and to give clues to the lives of the prehistoric Native Americans who once inhabited this part of Missouri. It is also believed that the park served as ceremonial grounds for these Middle Mississippi people who were related to the builders of the Cahokia Mounds in Illinois.

• http://en.wikipedia.org/wiki/Washington State Park