Calabozos lies in an area between thick and thin continental crust, and its eruptions are probably fed from a pool of andesitic and rhyolitic magma that sits just under its caldera. The caldera is underlain by a layer of volcaniclastic sedimentary rock from the Mesozoic era coalesced with intrusive and volcanic rocks of Tertiary age, over a layer of Precambrian-Triassic sedimentary and metamorphic rock formed from later plutons (magma intrusions). Under its northeast edge, Calabozos is cut by a north-south trending segment of sedimentary rock that includes gypsiferous and carbonates.