This archipelago is part of a submerged mountain range, with the four islands representing the peaks of volcanoes emerging above sea level. The islands provide critical habitat for a range of wildlife and are of particular importance for seabirds.

The 714,566 hectare site comprises two distinct parts: the dormant volcanic Pinacate Shield of black and red lava flows and desert pavements to the east, and, in the west, the Gran Altar Desert with its ever changing and varied sand dunes that can reach a height of 200 metres.

The 56,259 ha biosphere lies within rugged forested mountains about 100 km northwest of Mexico City. Every autumn, millions butterflies from wide areas of North America return to the site and cluster on small areas of the forest reserve, colouring its trees orange and bending their branches under their collective weight.

The site comprises 244 islands, islets and coastal areas that are located in the Gulf of California in north-eastern Mexico. The site is home to 695 plant species and 891 of fish; has a striking natural beauty in a dramatic setting formed by rugged islands with high cliffs and sandy beaches, which contrast with the brilliant reflection from the desert and the surrounding turquoise waters.

In the language of the Mayan peoples who once inhabited this region, Sian Ka'an means 'Origin of the Sky'. Located on the east coast of the Yucatán peninsula, this biosphere reserve contains tropical forests, mangroves and marshes, as well as a large marine section intersected by a barrier reef.