The monolith appears to be completely rectangular and there is speculation as to whether it is an artificial construct or not.
The camera which took the photo of the monolith is more than 300 kilometers above the ground when it took the shot. This means that at this height, it is possible for a round surface to appear straight to the viewer. The monolith may in fact just be a squarish boulder.
The fact that it is at the bottom of a cliff supports this theory but there is currently no way to verify the object’s structure.