Mt Elgon (4321 m) is an extinct solitary shield volcano from the Miocene on the border between Uganda and Kenya. The top is an 8 km wide crater. The slopes are generally gentle until 2800–
3000 m, with characteristic steep cliffs dropping down to the plains in the north, and some steeper slopes in the south-west. The mountain’s slopes are cut by river and stream valleys that
run down the mountain from the caldera (Fig. 1). A 20 km long ridge extends towards the west (Fig. 1). Dry north-easterly and moist south-westerly winds determine the climate. Rain falls
year-round but peaks in April–May and September–November. Annual precipitation is between 1500 and 2000 mm. Rainfall is higher on the southern and western slopes than on the northern and eastern slopes and most rain falls at between 2000 and 3000 m above sea level (Dale, 1940; IUCN, 2005).