The gravels of the Okui Formation of the Komoro Group are derived from the mountains on the west and east sides of the basin. According to deep drilling data, the basement of the Komoro Group is considered to be middle Miocene formations consisting of altered volcanic rocks, and its maximum depth reaches 1,000 m. Approximately 60% of the sediments of the Komoro Group are ejected from the Kita-Yatsugatake Volcano. The Komoro Collapse Basin is a graben-like depression forming under the tensional stress field during Pliocene to early Pleistocene in age.