Mount Elgon’s highest peaks are formed by high points around a jagged rim enclosing one of the world’s largest calderas, at 40km long and 8km wide. The tallest peak is the 4,321m Wagagi, followed by Sudek (4,303m), Koitobos (4,222m) and Mubiyi (4,210m).

The Caldera was formed as a result of magma being drained from the chamber. When it could no longer support the overlying volcanic cone, it collapsed into a depression-like shape. In the eastern corner of the caldera, hot springs are found at the start of the deep Suam Gorge.

In the northwest, Simu Gorge was formed by the sheer weight of the water in the caldera cutting two stream beds out of the weak volcanic ash and agglomerate walls.