The basement consists mainly of Precambrian-Paleozoic metamorphic rocks with intruded granitic, mafic and ultramafic rocks of Paleozoic age; these metamorphic rocks are also known as the Puncoviscana Formation. There are Paleogene-Neogene continental sequences. It is mostly buried beneath Quaternary sediments; outcrops have characteristic dark colours. The Quaternary sediments in turn contain both aeolian, colluvium and alluvium-derived sediments. A major regional tectonic lineament known as Culampaja passes through Pasto Ventura and the Vicuña Pampa volcanic complex lies east of the area.