Arayashiki Shell Mound, Archaeological site in Wakaba ward, Chiba City, Japan.

The Arayashiki Shell Mound is a Jōmon-period shell midden and settlement site in the Kaizuka neighborhood of Wakaba ward, Chiba, at an elevation of 31 meters near where the Yoshi River meets the Miyakogawa River. Its shell layer forms a near-complete horseshoe ring about 150 meters north-to-south and 160 meters east-to-west, and within the site are pits interpreted as storage pits and the traces of pit dwellings.

The site was discovered in 1872 when workers found it during lime mining operations. The remains date to the middle Jomon period, roughly 5500 to 3500 years ago.

The midden's shells come mainly from tidal flats of Tokyo Bay: hamaguri clams, asari, kesago and especially large numbers of ibusago. Fish bones such as sardines show active fishing. Excavated artifacts are kept at the Chiba Prefectural Bōsōmura no Fudoki no Oka Museum.

The mound lies near where the Yoshi River meets the Miyakogawa River, in the Kaizuka neighborhood of Wakaba ward. From JR Chiba Station, take a Keisei bus and get off at the "Totsubashi" stop; the site is about 10 minutes on foot from there. Excavated artifacts are kept and shown at the Chiba Prefectural Bōsōmura no Fudoki no Oka Museum.

When plans threatened to destroy the mound in 1964, engineers built a tunnel underneath it for a road extension instead. This clever solution saved the site from disappearing entirely.