• D4: Taisho Tunnel

Hidaka Yabakei Area

Geological Site


Taisho Tunnel

Taisho Tunnel

Visitors can park near the private house on the left after the tunnel on the former national highway (Yamanaka No. 2 Tunnel). The house is used as a kelp shed, and on the shore in front of it is a gravel-covered kelp drying ground.

The old tunnel next to Yamanaka No. 2 Tunnel (dug in the 1960s) dates back to the 1920s. There is also another tunnel, excavated in the 1880s, behind an ocean-side lodge there. These three tunnels from different times run parallel.

Geologically, the area is part of the Hidaka Mountains (technically known as the Hidaka Metamorphic Belt). On the other side of the Taisho Tunnel, green-gray rock is found intruding into brown rock. The brown type is gneiss, which metamorphosed from mudstone and other rocks due to heat and pressure, whereas the green-gray rock is tonalite consisting of cooled and solidified magma.

Visitors viewing Ohonai Waterfall behind the private house can also go down the former national highway to the tunnel, and will see another geosite ahead.