A 4 km diameter ring complex occupies part of Chazzi Hill and extends north of the hill as a negative topographic feature. The outermost ring is a coarse nepheline-biotite syenite inside which is a mesocratic nepheline syenite. The core is a deeply weathered coarse, porphyritic nepheline syenite. There are a number of trachytic plugs. The complex intrudes basement gneisses which to the south are overlain by sandstones that are tilted close to the syenite intrusion. West of Chazzi Hill is Gara Dresa which is a 12x7 km intrusion of porphyritic leucocratic syenite cut by dykes of microsyenite. The main syenite is also cut by nepheline syenite and syenite breccia. Chazzi Hill East lies some 20 km northeast of Chazzi Hill but no details of the petrology have been found.