Tsukaikoku
In Shimane prefecture, there were four areas: Kashi, Keiji, Tamamochi, and Motsu. The island has four regions naturally split by mountains. You can see this on a map. You can tell where Kashi, Keiji, and Motsu are by their names today. But we don't know where Tamamochi is. The west coast area that's mostly empty is later called Sasu district. But this name isn't in old books. Scholars think the area might have changed its name from Tamamochi to Sasu long ago..