Well data including geological columns and resistivity curves from 34 water wells was examined to demonstrate subsurface geology of Tokorozawa city. The base of the Imokubo Formation dips gently to the northeast and two SW-NE trending highs in the southwestern part are harmony with surface distribution of the Formation. Two pumice-bearing layers (A and B layers in descending order) indicating same time horizons are recognized, but these distributions in cuttings are not extensive and changeable in adjacent wells. The thickness between the A and B layers is the thickest in the West plant. As the thickness increases, the percentage of sand and gravel beds tends to increase. The distributional extent of marine intervals which are shell-bearing reduces from the B layer to the A layer, and the area of sea around Tokorozawa city was spread at the deposition of the B layer (ca.1.6 Ma).

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The Miocene is widely distributed in the Chichibu Basin located in the northwestern part of Saitama Prefecture. The lowest layer is distributed from the north to the west edge of the basin, and these are important strata for elucidation of the structural development history of the sedimentary basin. In the northwestern rim of the basin, there are conglomerate layers with a thickness of 200 m or more. In addition to the conglomerate layers mainly composed of angular to sub-angular gravel what seems to be cliff cones, there are conglomerate layers mainly composed of rounded to sub-rounded gravel. I conducted a sedimentological study on the Miocene of the northwestern margin of the basin and attempted to restore the sedimentary process of the lowest layer of the Miocene. The conglomerate layer distributed along the northwestern edge of the basin contains fan-like sediments including debris flow sediments, and it is possible that the sea did not enter the sedimentary basin at the beginning of the sedimentary period. It is thought that the formation of sedimentary basins began when the sedimentary basins generated by the depression were buried by fan-like sediments.

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Chichibu tonalitic body, which is distributed in the northwestern Saitama Prefecture, is composed of magnetite series (Main body MT) and ilmenite series (Main body IL) as part of the main body, and the ilmenite series (Satellite IL) as the satellite body. Rocks of both series are tonalite to granodiorite, but the Main body IL and Satellite IL are richer in quartz and mafic minerals than the Main body MT, and Mg/(Fe+Mn+Mg) values of biotite and amphibole contained in the former are smaller than those contained in the latter. The Main body IL is richer in SiO₂ than the Main body MT, and has different compositions of MnO, Cr, Pb, Sr, Th, Y, Zn, and Zr. Furthermore, the Main body IL has a slightly high A.S.I. (alumina saturation index), but no reaction with pelitic sedimentary rocks can be confirmed. In addition, there is a clear difference in the composition of the rare earth element patterns of the dark inclusions in both series. These differences in petrological features suggest that the Chichibu tonalitic body may have been formed from multiple magmas, but this has not been confirmed, and further investigation is required.

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As a result of surveys conducted from 2014 to 2022 in the Chichibu area, we found Oberonia japonica, listed as Extinct (EX) in the Red Data Book of Saitama Prefecture, at five sites along three valleys. This is the first record of the species in Saitama since 1973, and the rediscovery in about 40 years. All the populations located in riparian forests near streams, therefore it is inferred the high aerial humidity and the stable natural forest of the surroundings are important factors for the habitat of this species. O. japonica is thought to have a limited distribution in Saitama and a hard-to-detect epiphytic orchid, thus the extinction assessment of the species was considered to be an underestimate of surviving probability. Based on the objective data obtained from the current survey, such as the threats, the number of individuals, and the rate of decline, we evaluated the extinction risk and conservation status of the species.

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The distribution and habitats of Libelloides ramburi were researched in Saitama Prefecture. The earliest record in Saitama was from 1981. However, records of neighboring regions suggested that L. ramburi may have been distributed in Saitama prior to 1980. Most of the record sites belonged to seven regions included in one of the zonal classifications used in the Saitama Red Data Book: Animal Edition 2018: low mountain area, hilly area and lowland area adjacent to hilly area. L. ramburi existed in all these regions in 2022. Therefore, it is suggested that there are many sites with adequate environments for the species at least within these seven areas, and that these sites have been used frequently by the species in recent years. Because most of the record sites were located along riverbeds, riverbeds were considered to be an important habitat for the species in the prefecture. The sites where large numbers of individuals were recorded were not significantly biased toward any particular environmental type. Therefore, the environmental types classified in this study were not considered to be significant factors affecting the population of L. ramburi.

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