The website Jomon Japan has more on this site:
This site featuring stone circles from the early to the middle phases of the Late Jomon period (approx. 2,000 – 1,500 BC) is located on a plateau at an altitude of approximately 180 m on the left bank of the Oyu River (a tributary of the Yoneshiro River) in the upper Yoneshiro River basin of northeastern Akita Prefecture.
The form of the stone circles is thought to be based on the shape of circular settlements that developed with the establishment of the era’s permanent settlements. The site features the two stone circles of Manza and Nonakado, each of which is surrounded by the remains of pillar-supported buildings, pits, storage pits and dumping grounds containing relics arranged concentrically. Along with these remains, clayware and stoneware (including everyday pottery and stone tools), clay figurines, clay tablets, bell-like clay objects, stone rods and stone swords have been excavated.
More from the site:
The center of the two circle stones and the sundial-like collection of stones form a line that points toward the sunset on the summer solstice, suggesting that Jomon people were aware of the summer/winter solstice, the vernal equinox and the sun’s movements. These typical Jomon stone circles were constructed in consideration of their positioning and the sun’s movements, and their formation would have been highly labor-intensive and required a strong spirit. These forms are very important in studies of the period’s spiritual culture.
Compare with other standing stones: