There is a layer of Sanuki-gan stone (Sanukaite) (a kind of bronzite andesite), of which stone tools can be made, in the ground under the Nijo-zan mountain range, and therefore, it is believed that people had lived around there since ancient times.
二上山には石器の素材となる讃岐岩（サヌカイト）の層があり、古くから周辺に人が住んでいたものとみられる。