Three million years ago, this volcano erupted with such force that it blew off its top, creating a crater 5km across – one of the largest in the Americas. In the eons that followed, the crater gradually filled with rainwater to create a large lake. However, through erosion or collapse, a breach opened at the present site of Chorro de Las Mozas and the entire lake drained. The resulting flood created an extensive network of waterways, which attracted indigenous populations to the valley. Today, their early petroglyphs can still be seen throughout the valley.