Nakama River Bog Rock Formation of Wamigawa River

The Nakama River Megabloc Formation, a simultaneous anomaly in the upper part of the Tsurukawa Conglomerate Formation of the Iwadonoyama Formation, can be observed. This formation is characterized by a large amount of subangular pyroxene andesite breccia, with maximum breccia diameters reaching nearly 2 meters. Other breccia types include sandstone, shale, and chert, primarily consisting of poorly sorted angular breccia. Due to the tuffaceous matrix and high degree of consolidation, numerous small waterfalls can be seen on the riverbed.

From this, it is thought that the Nakama River Megabloc Formation was formed by the deposition and formation of volcanic mudflows generated by nearby volcanic activity in a localized depression.