Just east of the Weyto horst is an extensive cluster of phonolite plugs that may be related to phonolite lavas occurring west of the horst. These rocks contain zoned nepheline phenocrysts. There are also plugs of quartz trachyte amongst the phonolite plugs.
DAVIDSON, A. 1983. The Omo River project. Reconnaissance geology and geochemistry of parts of Ilubabor, Kefa, Gemu Gofa and Sidamo, Ethiopia. Bulletin, Ethiopian Institute of Geological Surveys, 2: 1-89.