The photo below is of a boulder that tumbled off a cliff and landed alongside the Upper Iowa River.
Seven is a sacred number for some of the tribes that lived in the area over the millenia.
Years ago when natives were still visiting the area, a clam shell was found behind the stone by a child. She put it in the trunk of the car when they headed home from a stop to see the rock. This was in the 40's and car springs on bumpy roads was entertainment for children in the back seat. One road a few miles away is called Roller Coaster Road. My kids always insisted to use that transportation link when we went from the hill tops down the Mississippi Valley.
When the girl reached home she took out the clamshell and the clay that had held it together and come loose, and inside it were 7 arrows, all the same made of white chert, and at one time were called "bird points". We know many of these were used in burials and were for hunting in a different world.
Two of the arrows were sent by the amateur archologists of the county to the state but they never returned. One of the libraries has the other five. As a group they were ritual objects
There is a plaque on the rock that some recent thief tried to gather for scarp, but was chased of my the senior old woman who was getting her mail about 50 yards down the road at the end of her farm driveway. The plaques says it is the home of a spirit and many left tobacco bundles tied in ribbon there over the last two hundred years.
The circle may be of the rising sun. Several miles down the road is an earthen mound that is in a circular shape with a lineal mound separating it in to two halves. When the Sun rises on the Spring Equinox it is lined up with that central mound in the 60 meter circle.
Archeologists R. Clark Mallam had his students clear off the brush and used a transit and measuring poles to check this one year when I was a photographer for him. One could go use up the stores from the winter as spring approached. Gardens could be planted and people returned to their summer villages from the narrow valleys in the area which some call coolies, from the French,
Ancient Waterways Society