The Gallocanta lagoon is in the middle of the Iberian Mountain Range, on a plateau 1,000 metres above sea level.

It is a large endorheic steppe depression which began to form at the end of the Tertiary Age (about 2 million years ago), and continued to develop throughout the Quaternary Age.

The system of lagoons which used to extend over the entire basin is today limited to a few active areas the most important of which are the Gallocanta and Zaida lagoons, the Guialguerrero lagoon plus two small lagoons in Santed, one with freshwater and the other with salt water.

The Gallocanta lagoon covers an area of 14.4 km². Its maximum width is 2.8 km and it is 7.7 km long. Its maximum capacity is 5 hm³ and its waters are usually 45-50 cm deep, although during period of heavy rainfall they may rise to 2 m.