A boundary section of the Hidakagawa Group of accretionary prism which accomplishes a foundation in Kii Peninsula and Kumano Group of a forearc basin deposits who accumulated on it exposes. There is time difference of 50 million years in accumulation of a two layer group, and such relation is called clinounconformity. I accumulated in the Cretaceous period when Hidakagawa Group had a dinosaur by the oldest stratum group in the geopark plan area. Rotten spot (pothole) is seen and also produces a fossil seashell in whole sandstone bed of Kumano Group in an upstream riverbed right now.
The V shape-like canyon where I come to vertical drop 600m was formed by sudden protuberance in the earth which consists of stratum of accretionary prism mainly and downward erosion on Kitayama-gawa River. The accretionary prism in this area was the oldest Hidakagawa Group in the geopark plan area and was accumulated in 70 million years bago. To carry a wood to Shingu before, a raft sink was performed. Wood transportation is switched over to a land route in now, and sightseeing raft descent is performed.
Otonori was a dangerous place in a raft sink, and the oar judgment by which the one by which heir’s eldest son didn’t take it and gave my younger brother a ride weathers the etymology, a historical origin and here was said to be a flower of a raft teacher.
There is an inscription which commemorates excavation job completion of the channel of stream carved on a rock surface in a dangerous place in Kitayama-kyo Gorge raft sink in Jigo. The stratum of the accretionary prism distributed over a ravine was alternation of sandstone and mudstone of the oldest Hidakagawa Group in the geopark plan area and was accumulated 70 million years ago. The folding structure is also seen.
Former riverbed face was left in downward erosion, and it was formed. A river terrace with pellet beds is distributed over altitude 120m-130m more expensive than the present riverbed and 160-170m at Kitayama-gawa River basin. Shimooi remains (mountain remains of highlands of the Jomon period) is on the terrace, and it’s the place where a person was living more than ancient times.