The 76.49-square-kilometre (29.53 sq mi) area was declared a natural park by the Andalusian Autonomous Government, primarily for its geology and landscape, but also for its notable flora and fauna.

It has historically been much used by humans as a natural pass through the Sierra Morena, constituting a principal path of connection between Andalusia and the Meseta Central, Castile-La Mancha, and the rest of Spain.

The walls are composed of extremely hard "Armorican" quartzite, formed in the ocean 500 million years ago in the Paleozoic, which were later covered by more recent materials.

In the strata of Armorican quartzite some spectacular ripples or crinkles are visible, fossil effects of waves, similar to those that can be observed in any deep, sandy sea, which reveals their origin.

[1] Among the formations visible in Despeñaperros are several that have been given names of their own: El Salto del Fraile ("Friar's Leap"), Las Correderas ("The Slides"), or Los Órganos ("The Organs").

[3] During the Peninsular War, especially during the first weeks of June 1808, Napoleon's troops had great difficulty in maintaining fluid communications between Madrid and Andalusia, mainly due to the activity of guerrilleros in the Sierra Morena.

[4] On 19 June General Vedel was ordered to head south from Toledo with a division of 6,000 men, 700 horses and 12 guns to force a passage over the Sierra Morena, hold the mountains from the guerrillas and link up with Dupont, pacifying Castile-La Mancha along the way.

On 26 June 1808 Vedel's column defeated Lieutenant-Colonel Valdecaños' detachment of Spanish regulars and guerrillas with six guns blocking the mountain pass of Puerta del Rey and the following day met up with Dupont at La Carolina, reestablishing military communications with Madrid after a month of disruption.