Oboke and Koboke Gorges — Marble Rock Canyons

The Yoshino River has carved two dramatic gorges through western Tokushima: Oboke (大歩危, 'big steps danger') and Koboke (小歩危, 'small steps danger'), named for the treacherous cliffs that threatened Edo-period travelers. The gorge walls rise 100–200 meters, composed of crystalline schist rock streaked with white and green mineral bands, resembling marble. Sightseeing boats navigate the river between towering rock formations, with autumn foliage reflecting in the emerald water.

The gorges mark the gateway to the Iya Valley — most visitors combine gorge boat tours with vine bridge visits in a full-day excursion.