The Oonitan site sits at the entrance to the Daimongawa Valley where the Daimon River passes through the obsidian mountains and flows out from the south-western foot of Mt. Yatsugadake. The site was a large village with buildings dating back predominantly to the middle Jomon period, and featured a facility in the center for holding festivals. This village operated the obsidian mine in Hoshikuso Pass and flourished as a center for distributing the obsidian mined there. Various kinds of Jomon pottery seen in many other areas north, south, east, and west have been excavated from this site, telling us that cultural exchanges were also taking place along with the distribution of obsidian resources. This site has been fully preserved and serves as an important site typical of this area.