This stone is grey in color, as big as an adult's head with weird raised portions almost like a harder substance wasn't worn away and it now appears like rings around Saturn but in a rock.
Another backyard find, only rock I ever saw with ridges like this
It looks to me like it once was part of an ocean or river that kept eroding it down as the water levels lowered. Best quess I have. Good luck.
I think there would be fossils on a sea floor.