On the basis of a space-time substitution, rates of cliff retreat and talus development over the past tens of thousands of years were quantified for valley-side slopes along the Shomyo River with a known rate of waterfall recession. Detailed
profiles of the valley-side slopes were obtained at 19 sites along the river by map reading and field survey, and the morphologic characteristics of the slopes were then measured. By combining the locations of the slopes with the recession rate of Shomyo