The authors previously reported the Quaternary stratigraphy of the northern part of the Uonuma hills (MASAI and TAKAHAMA, 1981). In the present paper, the authors described the geological structures and investigated the tectonic movement of this area, which are summarized as follows; 1. The surveyed region can be subdivided into three tectonic domains, namely I-the folded area, the Uonuma sedimentary basin proper, II-the stable area, least subsiding part of the basin and III-the fractured area along the Shibata-Koide tectonic line, especially the Aburuma-gawa fault angle basin. 2. The Uonuma sedimentary basin was generated when the basal unconformity of the Uonuma group was formed and developed at the early Pleistocene due to great subsidence with deposition of thick sediments of the middle member of the Uonuma group. The sub-siding center of the (Uonuma sedimentary) basin might have migrated to the north at the stage before sedimentation of the upper member of the Uonuma group, inferred from the marginal unconformity, facies change from middle to upper member and isopach map (MIYASHITA et al., 1972) of the Uonuma group. This change was caused by local upheaval movement. The basin up to this stage is called the "Uonuma sedimentary basin in a narrow sense." The basin was completely disappeared in the middle Pleistocene owing to the rapid regional upheaval movement. The whole basin from the Pliocene to the middle Pleistocene is called the "Uonuma sedimentary basin in a broad sense." 3. The Shibata-Koide tectonic line, the eastern marginal tectonic boundary zone of the Niigata Cenozoic sedimentary basin, was developed by large-scale faulting accompanied with volcanic activity at the end of Miocene epoch. It was still active at the Pliocene and early Pleistocene, and acted to bound the eastern margin of the Uonuma sedimentary basin in the southern part. 4. Faulting, folding and volcanic activity was active in the middle Pleistocene. The Aburuma-gawa fault angle basin along the river Aburuma was formed in the terrace-forming stage by the upheaval movement which also affected to deform the terrace II surface at the northern part of the tectonic zone I.

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