Different discussions on the causes of the 1856 Xiaonanhai, Chongqing earthquake disaster are available, and different understandings of the earthquake's origin, magnitude, and epicentral intensity exist. This work analyzed historical earthquake records and the extant traces of the Xiaonanhai earthquake site in reference to previous investigations and studies. It also calculated the magnitudes of earthquakes in the Xiaonanhai area in accordance with the calculated gravitational collapse potential of several large landslides. The earthquake disaster in Xiaonanhai area may have resulted from the superposition of multiple tectonic earthquakes because four earthquakes with M ≥ 5 were located near the Qianjiang Fault Zone. Satellite images revealed the active tectonic features of the fault zone. In addition, numerous earthquakes were distributed near the fault zone. Several possible causes of seismogeological disasters were discussed, and other potential predisposing factors were presented. The Xiaonanhai earthquake may have resulted from the superposition of multiple tectonic earthquakes or from a pure mountain collapse, but other causes cannot be completely ruled out. The further development of scientific practice is needed to uncover and further discuss the mystery of the geological disaster of the Xiaonanhai earthquake.