The basement of Ubinas consists of volcanic and sedimentary rocks. The sedimentary rocks include the Jurassic Chocholate Formation, the Socosani Formation and the Yura Group. The oldest volcanic rocks of the Matalaque Volcanics date to the Late Cretaceous and crop out east and southeast of Ubinas, far away from the volcano. Most of the volcanics in proximity to Ubinas are the younger, Eocene-to-Oligocene Tacaza Group and the more restricted Miocene-Pliocene Barroso Group, which directly underlies the Ubinas mountain. Even older basement rocks include Paleoproterozoic plutons and the sedimentary Yura Group of Jurassic to Cretaceous age. A depression, whose margin is cut by landslide scars, cuts into the basement southeast of Ubinas and contains the Ubinas valley. Faults cut across the volcano and create unstable areas, especially in its southern sector, and NNW-SSE trending geological lineaments have influenced the stability and the hydrothermal system of Ubinas.