An outcrop is visible on the upward slope to the Samani Dam parking lot. The light-colored lenticular part in the middle of the precipitous mudstone bed is sandstone. Such a mixture of different rocks without continuous bedding is known as a mélange (like a meringue in culinary parlance ).

The Japanese archipelago is an aggregation of accretionary prisms. These are formed from the surface layer of an oceanic plate that is scraped off and accreted onto a continental plate when the two collide and the former subducts below the latter in a trench on the ocean floor. They form the foundation of the Japanese archipelago, in which different rocks are mixed to form a mélange structure. The accretionary prism in this area is known to have formed in a trench 70 to 80 million years ago.