It is believed that two unconformities are developed in the Miocene sequence of the Yuki-Oyama district of North-Kanto area. The younger one, the Yuki unconformity, divides the upper Miocene and the middle, and the older one, the Oyama unconformity divides the middle and the lower. These unconformities are likely to develop over a rather wide area, covering from north to south in the Kanto Region.
Natural gas indications are found in the middle Miocene and also in the lower in the survey wells of the Yuki-Oyama area.