A lava field is found beneath Aracar volcano. It is constructed by lava flows that range in composition from basaltic andesite bordering on trachyandesite over dacite and smaller flows of partially silicic magma. Basal lava flows are heavily eroded and reach of length in the south and width decreasing from to . They have cancelled out the prior landscape. These lower lava flows reach the Salar de Taca Taca and extend south-southeast. The main andesitic cone is high and wide and formed on top of older dacitic lava flows. The dacite flows which form the bulk of the edifice are covered with debris and have flow fronts high. The lava field formed over a north-south slope.