조몬 시대
The Sannai-Maruyama settlement was occupied from the middle of the Early Jōmon period to the end of the Middle Jōmon period (3900 – 2200 BC), and is the largest the Jōmon settlement yet discovered in Japan. It is located on a 20 meter high fluvial terrace on the right bank of the Okidate River, at the tip of a ridge extending southwest from the Hakkōda Mountains.