 Mafic volcanism occurred south and west of Galán both before its large eruption and afterwards, in the valley of Antofagasta de la Sierra and may have continued to less than ten thousand years ago.The positions of the exact vents are controlled by recent fault systems in the region.Since about 10 million years ago, the area has been subject to reverse faulting which has disrupted the basement along north-south lines, forming a rift valley that also stretches from north to south.