extinct volcano on the Kenya-Uganda boundary. Its crater, about 5 miles (8 km) in diameter, contains several peaks, of which Wagagai (14,178 feet 【4,321 m】) is the highest. Its extrusions cover about 1,250 square miles (3,200 square km) and consist largely of fragmental rocks and only a smattering of lavas. The mountain slope is gentle and the outline unimpressive. On the east and southeast at about 6,200 feet (1,890 m) its relief merges with the Uasin Gishu Plateau, but in the west and northwest spectacular cliffs dominate the 3,600-foot (1,100-metre) plains of eastern Uganda. In the summit zone, moraines provide ample evidence of former glaciation. On the caldera's uneven floor there are considerable swamps, tapped by the Suam and Turkwel rivers. Other streams furrow the slopes. The moorland zone, containing tree heaths, giant groundsels, and lobelias, extends down to 10,000 feet (3,050 m), where it is succeeded by bamboo forest. Below 8,300 feet (2,550 m) is a temperate deciduous forest.

The Bantu-speaking Gishu (Gisu), cultivators of coffee, bananas, millet, and corn (maize), occupy the western slopes. Elgonyi was the Masai name for the mountain. The Scottish explorer Joseph Thomson (Thomson, Joseph) visited the southern side of Elgon in 1883; in 1890 Frederick (later Sir Frederick) Jackson and Ernest Gedge traversed the caldera from north to south.