A large village dating to the Middle Jomon Period (c. 3,500?2,500 BC), Onitan was settled at the entrance to Daimon river valley, where the river passes through obsidian mines to the south-western foot of Mt. Yatsugatake. The location indicates that the people were mining at the Hoshikuso Pass and that the site flourished as a hub for the distribution of obsidian. These interactions are seen in the discoveries of various styles of pottery vessels at this site. This site has been well-preserved after conducting minimal excavation.