Unprecedented departure for the Spanish tour. The streets of Arroyomolinos tell the story of our Arab and Roman past, though it wasn't until the 14th century, during the reign of the Catholic Kings, that the Madrid municipality built the fortified tower that is now the city's emblem and that, from its privileged vantage point, will preside over the final stage of this edition of the Vuelta.
Autonomous Community of Madrid
Las Rozas -> Madrid
In cities and their surroundings, in Madrid as in Nimes, there is geodiversity. You need to be a trained observer, however, as the infrastructures hide the substrata they stand on. But all the rocks, structures and reliefs are there, waiting to be found.
When the Central System, the Iberian Mountain Range and Montes de Toledo were formed, a depression also formed where all the materials that eroded from the mountains ended up. This depression, known as the Madrid Basin, eventually filled up with conglomerate rocks, sand, clay and salts in the centre. When the Tajo River opened the way towards the Atlantic Ocean, all the rivers began dragging these sediments towards the sea.
The result is a landscape made up of valleys that are separated by small hills. The first part of the stage, between Arroyomolinos and Alcorcón, rises and descends through the Guadarrama River Valley (from the Arab for “river of sand”) and its tributaries. Then it goes to the Manzanares Basin and the Paseo del Prado-Paseo de la Castellana axis, passing through the borderline between the Manzanares and the Arroyo de la Paz. Almost the entire route takes place on sands and conglomerate rocks, although Madrid's South also has clay and gypsum, a testimony to the large lakes that existed around 30 million years ago, where antelopes grazed or lions hunted.
In Madrid, the rocks seem to have disappeared beneath the asphalt and the pavements. This is not true, below the city of Madrid is 30 million years old sandstone that is soaked with water. This sand plays a vital role in Madrid, because it is essential for the construction of streets and buildings. A city cannot grow if it does not possess construction materials, because transporting sand is very expensive. And, if that was not enough, without that sand and underground water that feeds the wells, it would be impossible to have a large city like Madrid with such little rainfall. Nowadays, water is transported to Madrid from the Central System, but the birth of Madrid would not have happened without its sand and aquifers.
It is true that everything is hidden, but there is also geo-diversity in plain view. Every building in a city is an opportunity to remember that many aspects of our daily life depend on geology. The city is full of brick buildings, impossible to create without the clay from the tertiary basins. The most luxurious buildings, like the Royal Palace, are built using marble or granite. Today, the majority of rocks are used to coat and embellish already-existing structures. Even the most modern buildings, covered in glass, hide a lesson; because all the glass comes from silica, from quartz, that mineral that is so common we almost forget it exists.
The stage and La Vuelta come to an end in front of the Cibeles Fountain, in front of the Palacio de Comunicaciones, current headquarters of the Madrid Town Hall, built in 1919 using limestone from Novelda (Alicante).
Stage Term: Madrid Tertiary Basin.
It is one of the large depressions that formed between the Iberian Peninsula mountain ranges. All these basins are full of sediments that formed during the Tertiary Period, in the last 50 million years.
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