La Jarosa Reservoir

La Jarosa reservoir is located in the Jarosa valley and it belongs to the municipality of Guadarrama, Madrid, Spain. It is the smallest reservoir of the Sierra de Guadarrama mountain range. Its total capacity reaches 7’2 cubic hectometres and its total surface area is 55 hectares. La Jarosa, does not only include the main swamp but also the meadows surrounding the body of water, several recreational zones and vast pine forest areas. The Nuestra Señora de la Jarosa hermitage and the Altar Mayor hermitage are also found in this vast terrain. La Jarosa would be included in the proposed Guadarrama National Park project, once it is finally realized. The lower zone, which contains the marsh, would belong to the "pre-park" area for consideration for the Regional Park but the highest part of La Jarosa, adjacent to the Puerto de Guadarrama, would be included in the National Park itself.HistoryLa Jarosa reservoir was built in 1968 as a part of General Franco's economic policies on water reservoirs. It was decided that its location would be the Herrería Village, deserted two centuries earlier. Even today the remains of the tower of the St. Macarius chapel are still visible, lodged in the meadows around the swamp. When the water level permits, it is possible to wander among the remains of the old houses of the village which remain flooded beneath the swamp waters.Description of the environmentGeologyIn the areas surrounding the marsh, the most abundant rocks are granite, gneiss and quartz, but biotite, muscovite, mica and plagioclase can also be found. There is sedimentary material on the river beds, as a result of erosion by the water flow.