The Yamagata prefectural tourism site gives the usual peak here as late October to early November. Mogami-kyo is the middle stretch of the Mogami river, sixteen kilometres of gorge running from the Furukuchi district of Tozawa village down to Kiyokawa in Shonai. Mountains close in from both banks, and the water carries the colour of the slopes on its surface.

There are two ways to see it. Route 47 follows the river the whole way, so the gorge can be driven, and most people do. The older way is to go down on the water. Boats leave from the landing at Furukuchi, and the boatmen sing as they steer, with commentary in the Mogami accent that belongs to this valley rather than to the guidebooks. From the boat the trees are above you rather than beside you, which changes what you notice: less the shape of the gorge than the light coming through it.

The river gathers the water of the whole prefecture on its way to the Sea of Japan, and this is the reach where the mountains come closest to it. Wild cherry marks the slopes in spring, summer fills the walls with a single green, and winter empties the colour out again. Autumn is the short window when the number of colours goes up rather than down.

Allow an hour on the boat and rather less if you drive. The gorge sits between the rice country of the Shonai plain and the mountains inland, so it works as one stop on a longer day.