Ryuo Valley

The Ryuokyo Valley runs for approximately 6 kilometers along the Kinugawa River, with the hot-spring resorts of Kawaji Onsen and Kinugawa Onsen at either end. The mountains here were formed in an undersea volcanic eruption roughly 22 million years ago. Over the millennia, the force of the river’s currents and cascading stones chiseled away at the landscape, sculpting the gorge into its present configuration. The characters for ryu-o mean “dragon king,” a name given the valley in 1950 because its winding course is said to resemble the auspicious image of an ascending dragon.

Rocks visible from the nature trail that follows the river through the gorge tell the story of three distinct geological phenomena that contributed to its creation. The rocks of Shiryu, the upriver section, are mostly purplish andesite created in the early stages of the eruption. In the middle section, Seiryu, the rocks are primarily green tuff, which is formed when ash and other rock fragments are ejected from a volcanic vent. The extreme heat of the ash fuses it with the rock fragments, and the presence of copper in the mix stains the rock a bluish green. The rocks of Hakuryu, the downriver section, are predominantly rhyolite, a silica-rich volcanic rock characterized by its fine grain and a white appearance.

Each of the three sections showcases unusual formations shaped by erosion and the collapse of rocks as the river makes its way through the gorge. Although its flow may seem peaceful much of the time, the Kinugawa River earned its name—meaning “angry oni” (a mythical demon)—from the turbulence of the water and the noise of tumbling stones following heavy rainfalls.