A mountain range turned to Swiss cheese in Andalusia, the limestone peaks of the Sierras de Cazorla, Segura y Las Villas Natural Park hide a vast secret.%%CITE_1%%%%CITE_2%% This entire mountain range, composed largely of Jurassic and Cretaceous carbonate rocks, is being steadily dissolved by water.%%CITE_3%%%%CITE_4%% Rainwater, made slightly acidic by atmospheric carbon dioxide, seeps into fractures in the stone. Over millions of years, this acidic water has etched away the soluble limestone and dolomite, creating a complex underground drainage system known as a karst aquifer.
The surface landscape reveals clues to the world below. You can see features like dolines (sinkholes), deep chasms, and vast, rocky plateaus called lapiaces, where the limestone bedrock is exposed and fluted by water. This process has created a rugged terrain, with towering peaks that exceed 2,000 meters. The park itself is the largest protected area in Spain, covering over 200,000 hectares. This entire area acts as a massive sponge, absorbing rainfall and channeling it into a subterranean conduits and caves.
The birthplace of the great river
The "giant" born from this hidden system is the Guadalquivir River, the second-longest river entirely within Spain. Its headwaters are located deep within the park at a site called Cañada de las Fuentes. Here, water that has traveled for years or even decades through the underground limestone network emerges from numerous springs. This is the discharge point for the aquifer, where the invisible, underground river becomes one of Andalusia's most important surface waterways.
The Guadalquivir begins its 657-kilometer journey to the Atlantic Ocean from this spot. The water flowing from the springs is high in dissolved calcium bicarbonate, a chemical signature of its path through the limestone. The dissolution process has created magnificent geological formations, including caves like La Cueva del Agua and dramatic waterfalls. The park's unique geology supports an incredible biodiversity, with over 2,200 plant species, including 35 that are found nowhere else on Earth. One of the most famous is the Cazorla violet (Viola cazorlensis), a rare flower adapted to life in the limestone rock crevices.