Etymology and distribution of 古田原.

Kotahara 【古田原】^{レベル2
About 20}  The Japanese surnames etymology dictionary.

Kagoshima-ken , Fukuoka-ken , Oosaka-fu . Terrain . In fact , "Oka" was added, which is the surname of Amagi archipelago of Kagoshima-ken . Estimated at the time of returning to Japan in 1953. 実 Sane reference.