The volcanic deposits are fresh and dip uniformly towards the south at approximately 30°. The sequence is divided into three formations which are, from base to top, the Kebobutak, Semilir and Nglanggran Formations (note that Kebobutak Formation is not a same eruption event with Semilir and Nglanggran). The top part of Kebobutak Formation are intensely bioturbated by a Cruziana-type assemblage. The formation is interpreted to be air-fall deposits reworked in a shallow marine sublittoral setting. Above the Kebobutak Formation lies at least of dacitic pumice, volcanic lithic and crystal-rich tuffs and breccias assigned to the Semilir Formation.