Folded Rock Layers on the Banks of the Jinzu River
The Inotani Anticline and Syncline (猪谷の背斜向斜, Inotani no Haisha Kosha) is an exposure of folded rock strata on the left bank of the Jinzu River at Inotani, Toyama City, Toyama Prefecture, which in 1941 was designated a Natural Monument.
The Agency for Cultural Affairs lists it under the criteria for the occurrence of rocks, minerals and fossils, and for folding and thrusting of strata. Toyama Prefecture's cultural heritage site gives the address as 3 Kawara, Inotani, with Toyama City as owner and manager.
The designation text describes the Inotani beds of the Tetori Group, alternating sandstone and shale, forming a typical anticline and syncline well exposed on the Jinzu's left bank.
Anticline and Syncline
Toyama Prefecture explains that folding is the bending of rock layers: where the strata arch upward is called an anticline, and where they sag downward a syncline. At the Inotani Anticline and Syncline, both appear in a single cliff.
The rock is the Inotani alternating beds of the Tetori Group, laid down in the early Cretaceous, with sandstone about 1 metre thick alternating with shale about 30 centimetres thick. The prefecture values the fine exposure in a river-terrace cliff as an important scientific resource.
Because sandstone and shale differ in hardness and colour, the alternating layers show as stripes. As the stripes curve into arcs, they make visible how the strata were squeezed from the side and deformed.
The Site Today and Visiting
Toyama Prefecture notes that the finest part of the designated fold now lies under a dam reservoir and cannot be seen. Part of it can still be viewed from the opposite bank to Hokuriku Electric Power's Inotani power station.
The fold is best seen from across the river. As a Natural Monument, the rock must not be struck or chipped. The riverbanks are rough and water levels can change with releases from the dam, so take great care near the water.
Q&A
- When was the Inotani Anticline and Syncline designated?
- It was designated a Natural Monument on 3 October 1941.
- What are an anticline and a syncline?
- Folds in rock layers: an anticline arches upward and a syncline sags downward.
- How old are the rocks of the Inotani Anticline and Syncline?
- They are the Inotani beds of the Tetori Group, laid down in the early Cretaceous.
- Can I still see the Inotani Anticline and Syncline?
- Most of the designated fold is under a dam reservoir, but part can be seen from across the river from the Inotani power station.
- Where is the Inotani Anticline and Syncline?
- On the left bank of the Jinzu River at Inotani, Toyama City.
Basic Information
| Name | Inotani Anticline and Syncline (猪谷の背斜向斜) |
|---|---|
| Location | 3 Kawara, Inotani, Toyama City, Toyama Prefecture |
| Designation | Natural Monument |
| Year Designated | Designated 1941/10/3 (Showa 16) |
| Quantity | Not recorded in the Agency for Cultural Affairs database |
| Dimensions | Sandstone beds about 1 metre thick, shale beds about 30 centimetres thick |
| Owner | Toyama City (owner and manager) |
| Public Access | Mostly submerged in a reservoir; part visible from the opposite bank |
References
- Agency for Cultural Affairs Database: Inotani Anticline and Syncline (Japanese)
- https://kunishitei.bunka.go.jp/bsys/maindetails/401/956
- Cultural Heritage Online: Inotani Anticline and Syncline (Japanese)
- https://online.bunka.go.jp/heritages/detail/205203
- Toyama Cultural Heritage: Inotani Anticline and Syncline (Japanese)
- https://toyama-bunkaisan.jp/search/2183/
Last verified: 2026.09.27