Like most other large mountains in East Africa, Mt. Elgon is an extinct volcano, a relic of the volcanic activity that formed the Rift Valley several million years ago. The volcano first exploded roughly 24 million years ago and is thought to have remained active for 14 million years. At its peak of activity, Elgon was almost certainly higher than Kilimanjaro is today. The caldera is 7 km width and one of the largest in the world. The base of the mountain has a diameter of up to 80 km.
