The shell mounds built in the early Jomon period (about 6,000 years ago) were discovered on the plateau, which is 20 m above sea level, in the Bibi district in Chitose City, Hokkaido. They were discovered when the railroad construction work was being done at the end of the Taisho period (1912-1926).

A shell mound is comprised mainly of sea shells of shellfish such as common fresh water clams and short-necked clams, which were thrown away at the same place for a long time until it formed a mound. This indicates that the area around a shell mound as right beside the sea when it was formed.

The Bibi Shell Mounds are considered important evidence that proves the level of the sea was much higher in the Jomon period than the present time because of the warm temperature trend in those days.

They are large mounds with a height of 1.2 m and a diameter of 4 m. They are the shell mounds discovered in the innermost land in Hokkaido. The shells of 14 species of shellfish including Corbicula japonica and short-necked clam together with earthen ware have been unearthed at the site. This is a huge time capsule in which the life of the people living 6,000 years ago is bottles up.