The caldera was formed during a series of rhyolitic explosive eruptions from a group of stratovolcanoes between about 72,000 and 57,000 years ago.

The youngest dome, Cerro Pacho, formed after 8000 BC.

It is in Coatepeque municipality, Santa Ana, El Salvador.

At 26 square kilometres (10 sq mi), it is one of the largest lakes in El Salvador.

In the lake is the island of Teopan, which was a Mayan site of some importance.