Iwamoto 【岩源】1 The Japanese surnames etymology dictionary.
③ Yamagata-ken Higashiokitama-gun Kawanishi-machi It was in Otsuka during the Edo period. I will tell from Niigata-ken 's Usibei village in the same place. Location unknown. There is also a story that he was engaged in agriculture at the same place descended from the Heike faints. Ushiya is pronounced. 平 reference.