The image below was taken on a hike. Circular patterns at bottom (it is flatter on this face and round otherwise) appear either man-made or possibly it is a fossil.
Any idea what this could be?
The face of the rock with the round center portion looks strongly like a Rugosa or Horn Coral. I suggest it is a Rugosa coral because of the center with the radial lines out from the center and the clear edge surrounding the radial lines. See https://en.wikipedia.org/wiki/Rugosa.