The southern foot of Mount Yatsugatake was prone to heavy rainfalls, and whenever such rainfalls occurred, a landslide swept away large rocks that mowed down trees, bridges and houses in their path. Records indicate that such flood disasters have occurred every twenty to eighty years since 1485.
Large floods continued to occur in the early modern period, and a large rock that was dislodged by a flood in 1943 remains in Sanbuichi Yusui Park as a monument called “Oare no Hi” (literally, “disaster monument”). It reminds people of the disaster that buried Sanbuichi Spring in dirt and sand, swept away homes and fields, and took the lives of many people.