White earth: kaolin in Alto Tajo

Earth for painting

Beside Peñalén, the Utrillas sands reach the surface: white, yellow and reddish layers laid down in the Cretaceous. They yielded two very different riches. The first was colour. In Santa Engracia mine, miners followed horizontal galleries with rails and carts to find the clays richest in iron. They ground and roasted them to make ochre for paint. The mine operated until 1936. The white sands from those same layers were used at home to scrub and whiten wood.

White gold

The second richness was kaolin, a fine white clay needed in large quantities by the ceramics industry. Modern mechanised open-pit mining began in 1965, at María José mine, in the catchments of the Tajuelo and Merdero streams between Poveda de la Sierra and Peñalén. Over the years, these mines came to produce around 60% of Spain’s kaolin. By the late 20th century they provided an important share of local jobs, in villages whose populations were dwindling.

Photographs from 1974 and 1975 preserved on Wikimedia Commons already show the white pits beside Poveda and the erosion gullies cut into Peñalén’s kaolin.

The price on the river

Kaolin is fine and light. During storms, water strips sand and clay from natural gullies, but also from unprotected waste heaps and pits, and carries it into the Tagus. This was studied closely for years: in a single winter, 2009–2010, the check dams in the Peñalén stream catchment trapped 6,200 tonnes of sediment in less than two months. That mud covers the gravel where trout spawn, which is why projects were undertaken to restore their spawning grounds.

The mining concessions predate the Natural Park and were left outside its boundaries, but lie within the same catchments: everything flowing down from them ends up in the Tagus.

A restoration laboratory

The story does not end with the problem. Since 2007, Complutense University, the mining company and the Park have worked together to measure erosion and address it. Some mines were restored by imitating natural terrain, with slopes and hollows that channel water without stripping away soil. Studies indicate that they retain soil much better than sites without these measures.

In 2020 the European LIFE RIBERMINE project began, with almost €3 million, to restore the old Santa Engracia mine. First the waste heaps were reshaped into natural forms; then seeds of local grasses were sown, with organic erosion-control blankets protecting the soil on the steepest slopes. Work in Alto Tajo began in July 2020. The mine that started by bringing colour to walls is now a lesson in how to heal a landscape.

Looking with new eyes

The white patches on the hillsides are still visible from the road between Peñalén and Poveda. They belong to Alto Tajo’s memory as much as a shepherd’s hut or a saltworks: the memory of a territory that, when timber and resin ran out, kept looking to its earth for a living.