The Jinmentong Cliff is one of the largest collapsed lands in Taiwan. It is also a classic example of headward river erosion as well as river capture. It is an excellent location for geologic research and exemplification of cliff, fault, watershed, and collapsed land. The Jinmentong Cliff is divided into the following three areas based on the characteristics of collapse, stratigraphy and the nature of the rock: (1) Area C Lushan terrane (slate) area; (2) Area D Jinmentong fault rubble belt; (3) Area E Jiayang terrane (metamorphic sandstone interspersed slate.) Wooden posts were sunken into the ground at the crest of the collapsed cliff in order to measure the rate of headward erosion. Aside from conducting field research and photographic records at fixed intervals, measurements were made also at unspecified time during the typhoon, heavy rain, and spring rain seasons. These were accompanied by discontinuity survey research, geographic information systems analysis, as well as aerial photography analysis to explore the development mechanism of the cliff. Also, these were collated with previous studies and textual evidence about the Yushan area left by others. Finally, the study estimates the future evolution of the collapsed cliff.