The source of the River Gualija lies in the vicinity of the village of Navatrasierra in the heart of the Guadarranque syncline; it runs northwest until it meets the River Tajo at what is today the Valdecañas Reservoir, very near the Roman ruins of the city of Augustobriga.
It owes its name (Río de Alija) to the presence on its right-hand bank on a steep granite hill of the ruins of the Arab castle of Alija (Hisn Alixa), a bastion of the Tajo frontier during the Reconquest.
The San Román chapel and its Roman ruins, the olive grove, and the adjacent mine are located some three kilometres south of the town of Peraleda de San Román. Access to the mine is by means of a road that runs directly from the town towards the banks of the River Gualija on its right-hand side. Above the old olive grove the outcropping of a wide dike of quartz can be seen with the abandoned mine workings.
From a geological point of view the Marialina mine is located on the join of the Guadarranque-Gualija syncline and the granite outcrops of the Valdelacasa anticline. It is a quartz lode that crosses both the granites and the metamorphic slates that border it (a lode is formed in a fracture of the crust that has been filled with mineralised fluids, which rise from the magma and have subsequently solidified). The mineral association consists of quartz, barite, galena, lead ore, sphalerite, chalcopyrite, and malachite, with lead, zinc, and copper being obtained. The lode runs approximately N45ºE, is vertical, and spreads horizontally for nearly one kilometre. The whole deposit and the encasing rocks have been affected by a considerable tectonic deformation and the resultant alteration by meteorisation, which facilitates mining activity.
It can be observed how this quartz lode with metallic minerals of interest to industry has crossed other types of rock, such as granites and metamorphic slates. Likewise it is possible to recognise the appearance of lead and copper ore mineral in this type of deposit, in which it is shown that the rocks are also deformed in a ductile and brittle manner; this phenomenon is known as a shear zone.
The industrial exploitation of the Marialina mine was begun in about 1871 by an English company with a shaft 80 metres deep and two underground galleries at a depth of 30 and 50 m and with a length of 500 m. The last mining concession dates from 1917.
On the fertile soils of the banks of the Gualija the Romans established the neighbouring city of Augustobriga, an extensive settlement with its remains being found around the ruined medieval chapel of San Román. This building was mentioned by Alfonso XI in 1345 in the Libro de la Montería when he hunted bears in this country; its current surroundings are centenary olive trees. Very near this Roman city there is abundant iron slag from old ironworks and also a limestone quarry that produced the necessary lime for the building of the temples, the city walls, and other buildings of Roman Augustobriga.