This is the most extensive of the volcanic fields of southwestern Uganda, extending from the northern shores of Lake Edward for 30 km to the foothills of Ruwenzori, all of it being within the Western Rift.
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The Bunyaruguru volcanic field, referred to in some publications as Kichwamba, lies along the eastern side of the rift valley south of Lake George and extends over an area of 33x7 km.
This isolated volcano stands nearly 200 m above the surrounding valley floor but the lowermost 60-70 m are of Karagwe Ankolean schists. The slopes of the volcano proper are steep and rise to a rim within which is a 230 m-diameter crater.
Bufumbira is the name given to the part of the Virunga volcanic field (see Congo No. 6) lying within Uganda. It covers about 380 km2, but this is only some 10% of the total Virunga field.
Agoro is an intrusion of eudialyte phonolite lying close to the border with Sudan (P. Nixon, pers.comm., 1990) No other details have been traced.
Lotukei is shown by Nixon and Clark (1967, Fig. 1) as an alkaline rock occurrence lying on the border with Sudan immediately to the west of Zulia (No. 11). Do details have been traced.
Zulia is a syenite intrusion forming a hill close to the international boundary ‘triple point’ with Sudan and Kenya. Smith (1938) describes a loose boulder from the foot of the hill as a ‘hornblendic quartz syenite rich in microperthite’, which does not sound particularly alkaline.
Close to the Kenya border in northeastern Uganda four plugs/vents have been mapped, three of which are of trachyte and one of phonolite (MacGregor, 1962). The Loyapat vent is circular and about 500 m in diameter. It consists of trachytic tuffs that cut sharply across the basement gneisses.
Along the Kenya border an area of lavas of about 11x5 km is distributed around a plug centred on Yelele Mountain. Dykes cut both the lavas and basement granulites and gneisses west of the lavas.
The Toror Hills comprise a central carbonatite complex around which are a number of trachyte and phonolite intrusions. The central complex consists of a partial ring of carbonatite, which cuts and fenitizes the Precambrian country rocks, and is itself invaded by a mass of phonolitic breccia.