What started as a mine railway to operate iron and coal-rich mines late 19thcentury, led to the discovery of a set of palaeoanthropological sites right in the mountains, a place unique in chronology and importance. The main sites in the railway cuts are three.
SIMA del ELEFANTE. The lower levels date back more than 1,200,000 years. The most ancient hominid remains in Western Europe were found here.
COMPLEJO GALERÍA. Vertical hole which functioned as a natural trap for animals nearly 400.000 years ago. Humans groups (HOMO HEIDELBERGENSIS) went in through a more accessible entrance to make use of the meat from dead animals.
GRAN DOLINA. Of all the numerous remains found here, the most outstanding are the 150 fossils dating back 850,000 years found on level TD6. This discovery meant the origin of a new species: Homo ancestors.