The basement of the volcano is formed by Precambrian rocks, which are overlaid by various sediments and volcanic formations of Mesozoic and Cenozoic age. Especially during the Neogene, the supply of volcanic material was high and dominated the region, forming a volcanic foot; the present volcanoes are constructed on this volcanic foot. This foot is made out of an ignimbrite plateau that drops down south. The foot beneath Ampato, Hualca Hualca and Sabancaya has been dated 2.2 ±0.15 million years ago, while a lava flow beneath the first and the last of these is about 0.8 ±0.04 million years old.