 The magma erupted by the Galán system was likewise channelled along such fault systems, and neighbouring volcanoes were similarly influenced by them; the fault systems at Galán proper are known as the Diablillos-Galán faults.Another major lineament in the area is the Archibarca lineament, which is formed by a strike-slip fault that extends from the northwest to the southeast in the region and which intersects the Diablillos-Galán faults at the location of the caldera.Galán has erupted mainly potassium-rich dacitic to rhyolitic rocks that are often called rhyodacitic, and which reflect a calc-alkaline suite.