Mount Elgon (4,321 m) is a giant, free-standing mountain located on the Western Rift Platform of the Gregory Rift Valley. Large parts of the mountain are protected in two national parks, one located in Uganda and one in Kenya. Elgon is an extinct dome-shaped shield volcanic cone with an extensive summit plateau. The latter is disrupted by a near-circular depression which has been interpreted as the eroded remnants of a caldera. The Early Miocene age (22 Ma), which makes Elgon one of the oldest volcanoes in the region has resulted in the cone being deeply eroded. The cone is built directly on Basement terranes, an unusual feature as most of the volcanoes associated with the Gregory Rift are constructed on older plateau-style volcanics. The average composition of the Elgon Volcano is nephelinite, typical of the group of magmas associated with the pre-rift stage of the East African Rift System (EARS). Details of the eruptive history are sparse although the cone is probably dominated by tephra and agglomerate with only very minor lava flows. This is typical of a volcano with an extremely high explosive index. The presence of hot springs is indicative of minor geothermal activity. Possibly the most interesting feature of Elgon is the occurrence of small caves, including the famous Kitum Cave, which are regularly accessed by large game including elephant, seeking deposits of salt. The caves are erosional features, rather than lava tubes. The central slopes of Mount Elgon are thickly forested and the mountain supports a remarkable ecosystem that includes numerous endemic species of plants and flowers. The volcanic rocks are deeply weathered and severe landslides are a major hazard, notably on the Ugandan side where human encroachment onto the lower slopes and the removal of forest has caused considerable problems.