Oboke & Koboke Gorges

Oboke and Koboke Gorges stretch for approximately 8 kilometers along the Yoshino River in western Tokushima Prefecture, Shikoku Island. These dramatic gorges were carved over millions of years as the river cut through layers of crystalline schist rock formations twisted and folded by tectonic activity. The exposed rock faces display remarkable blue-green hues from chlorite minerals, with distinctive striations revealing the violent geological forces that created Shikoku's mountainous interior.

The names 'Oboke' (big danger) and 'Koboke' (small danger) reference the historical difficulty of navigating this treacherous river section. Before modern roads, river transport was essential for moving goods between Shikoku's interior and coastal areas. The narrow gorges with swift currents and hidden rocks claimed many boats and lives, earning their ominous names. The completion of Route 32 in 1935 finally provided safe overland passage, though remnants of the old river-following path remain visible.

The gorges gained geological significance when researchers identified the exposed schist formations as part of the Sambagawa Metamorphic Belt, dating 60-80 million years. These ancient rocks, formed deep underground under extreme pressure and temperature before being uplifted and exposed by erosion, provide valuable insights into plate tectonic processes. The area has been designated a National Natural Monument for its geological importance and scenic beauty.

Tourism development began in earnest during the 1970s-80s with the introduction of Oboke Pleasure Boats offering scenic cruises through the gorge's calmest sections. More recently, whitewater rafting companies established operations taking advantage of the river's exciting rapids. The area now balances adventure tourism with geological education, featuring the Lapis Oboke museum dedicated to stone and mineral exhibitions. Despite modern developments, the gorges retain their wild, primeval character, with towering rock walls and rushing waters creating an atmosphere of ancient, elemental power.