Tsurukawa Conglomerate Formation below Uenohara High School

The Tsurukawa Conglomerate Formation (deposited approximately 6 to 4 million years ago) is exposed on the riverbed of the Tsurukawa River in this area. The gravel consists mainly of sandstone, mudstone, and chert, with a small amount of volcanic rock. The gravel diameter ranges from 3 to 20 cm, and it is composed of subangular to subrounded pebbles. Overall, sorting is poor, and the poorly sorted areas have a particularly high proportion of angular pebbles, suggesting that debris flow deposits were transformed into conglomerate.

Furthermore, the Tsurukawa Conglomerate Formation in this area is interspersed with softer sandstone layers, and the continuity along the strike direction tends to be poor. Occasionally, blackened, carbonized plant fragments are also found. Therefore, it is thought that the Tsurukawa Conglomerate Formation in this area was deposited in an unstable environment, such as a braided riverbed, where debris flows occasionally surged.