North America and nature can present some mysterious structures of question, that if combined with the structures that are clearly UN-Natural become a question upon themselfs.
There are many mysterious structures around all major waterways within North America that clearly show they are man-made and had a purpose to either create that waterway or expand it. They can vary in many forms that I have tried to cover through most post's and easy to recognize as man-made , but these I show here were a little questionable towards being natural at first , until I managed to see a better presentation of similar markings being shown in other areas, where you can see its UN-natural.
The first image shows the UN-Natural man-made area where large areas of land were once marked then cleared away to create a waterway, that is the image to use as a reference towards all other images where you can only see the markings on the land but not much else to give an idea of use . Many areas are marked like this and once you realize that a lot of land around North America near a lot of shore lines and within is all man-made... Some areas just have the markings left from a time not fully marked in history...