Rocks of the Kailimerlim volcano extend over an area of about 20x20 km in the northwestern corner of the Maralal area (No. 085-00-011) but are extensively mantled by alluvial deposits. The volcano forms a low shield with a thickness in the central area of about 600 m where there is a foyaite plug some 2 km in diameter that may occupy the original vent. The volcano consists essentially of feldspar-phyric trachyte lavas that dip away from the foyaite plug. These are overlain by welded tuffs, phonolitic trachytes and phonolites, the last three units being confined to the northwestern part of the volcano. The whole sequence is overlain unconformably by Nathelot basalts, a widespread series that erupted from dykes over a large area on the western shoulder of the rift. The foyaite plug intrudes the trachyte lavas and contains alkali feldspar and nepheline phenocrysts.