One authority identifies Mount Chilalo as a late Trap Series volcano. The geologist Erik Nilsson claimed to have identified traces of glaciation on Chilalo, as well as on its neighbor Mount Kaka down to about 3400 meters, which he dated to the Last Pluvial Period. Although this mountain is located south of the East African Rift, along with Mount Gugu to the north and Mount Kaka to the south, it is considered, geologically speaking, part of the Ethiopian Highlands.