The Takashozu fault system, running NE-SW direction, is located at the northwestern foot of the Takashozu Mountains, Toyama Prefecture, and separates the Tonami Plain from the high mountains. Along the fault line, several kinds of fault topographies have developed, such as terminal facets, kern cols, kern buts and valleys flowing parallel to the strike of the fault.
At Inami and Akasobu, the Miocene andesitic rock has thrusted up from south to north onto the terrace gravels of the middle and upper Pleistocene ages. The Takashozu fault has dislocated vertically the several levels of terrace surfaces here and there along the fault line. The higher the terraces are, the larger the amount of displacement is. In the drainage basin of the Sho River, it is inferred that not only Pleistocene terraces but also Holocene terrace gravel beds have been cut by the fault activities.
In the southwestern part of the Tonami Plain, the gradient of the terrace surface is steeper in the older terraces. The valley dissecting the higher terrace surfaces shows an asymmetric form, i.e., the valley walls of the northern side are generally steeper than those of the southern side. It would be considered that the principal factor forming this asymmetric valley topography is the continuous upheaval of the mountains located to the south of the plain.
