Volcanism in the southwestern Marra mountains took place between 4.35 million years ago and 60,000 years ago, subdivided into an Old Series and a New Series which is younger than 2 million years ago. After an initial stage, during which olivine basalt and small amounts of pyroclastic material were erupted, trachyte were emplaced. The Deriba caldera probably formed either 60,000 or 3,520 ± 100 years before present (BP), but activity continued with the volcanic cone inside of the caldera and peripheral vents, possibly into historical time.