The materials making up the mountainous circle surrounding the region, plus those forming the substrate where the Tertiary and Quaternary materials are found, apart from the carboniferous soils of La hoya , are very old.
We could situate them in the first half of the Primary Era with an age going from 570 to 390 million years.  They are located Northwest-Southeast in the period from the mid-Cambrian to the Lower Ordovician, within the Primary era.

On top of these materials, and due to the effect of successive and deep transformations of orogenic activity, other materials have deposited in the centre of the Region, namely:

• Carboniferous sediments:  in the area of the high Sil, in the Carboniferous period (prior to the Secondary Era) and in a surface of around 325 sq. km., there are carboniferous materials deposited in a disorderly manner, creating the coal mines in the Bierzo region.
• Tertiary Era sediments:  different movements and orogenic activities of the Neogene, together with the mild and humid climate, produce block areas which tend to rise (easily eroded) and others (within the mountains) where these sediments are deposited.
• Quaternary Era activities:  Different movements produced by faults in the Pliocene permits a  re-youth and the formation (in the Pleistocene) of vast plains with different terraces, apart from the formation of the present hydrography in the Bierzo Region.

Ordovician: slate and sandstone
Neogene: undifferentiated
Carboniferous: conglomerates, sandstone, slate and carbon
Cambrian: limestone and spar
Precambrian: metamorphic