The Camp dels Ninots palaeontological site was discovered inside the crater of a volcano that erupted five million years ago. A lake was formed in this crater which 3.5 million years ago became gradually filled with deposits. Due to these optimal and highly unusual conditions, animal and plant remains were trapped there and have remained in an excellent state of preservation.

Through the excavations, fossils of large animals have been recovered (bovids, rhinos, tapirs), along with those of other smaller animals, such as tortoises, frogs, rodents and fish. The plant fossils reveal that the climate was in a period of transition from tropical forests to the Mediterranean forests we see today.