Rebun Island lies in the Sea of Japan off the northwestern tip of Hokkaido and is part of the Rishiri-Rebun-Sarobetsu National Park. Momoiwa ("Peach Rock") was created in a relatively new era of Rebun Island's strata when underground magma pushed the earth's surface upward where it cooled into a huge spherical rock formation. Spheroidal joints (plate-shaped joints on the surface) peeled away like the skin of an onion, revealing the scree, which cooled at a slower rate than the surface, creating the columnar jointing that can be seen.