The mountain not only has one of the largest surface areas of any ancient extinct volcano in the world but is also peppered with cliffs, caves, gorges and water falls with the most notable being the romantic Sipi falls. The caldera covers some 40 square km at the top of the mountain. The mountain is named after the Elgeyo tribe, who once lived in huge caves on the south side of the mountain.

It was known as "Ol Doinyo Ilgoon" (Breast Mountain) by the Maasai of Kenya and as "Masaba" by the Ugandans.