sentences:  Writing Rock State Historical Site
  
  Writing Rock State Historical Site, located twelve miles (19 km) northeast of Grenora, North Dakota in Divide County near the Montana border, is the site of two large granite boulders, carved with petroglyphs featuring thunderbirds, mythological creatures that are of importance in the culture of Plains Indian tribes.The age of the carvings has not been determined, but they could date from 1000 to about 1700, according to the North Dakota Historical Society.