The Tsugawa Basin in Niigata Prefecture has different levels of river terraces along the Agano and Tokonami Rivers. The terraces are categorized into higher, middle, and lower groups, with gravel beds covering their surfaces. The river course shows a distinct pattern, with an uneven distribution of terraces due to geological influences. The terraces along the Agano River are also divided into higher, middle, and lower groups, with the lower surfaces containing pumice materials from the Numazawa Volcano. These materials were carried by the Tadami and Agano Rivers and accumulated on old river floors, forming lower surfaces after being dissected.