Within this national park are two of the highest mountains in the coastal range: Cerro El Roble (2200m); and Cerro La Campana (1890m), which Charles Darwin climbed in 1834. Visitor numbers have risen since then, but the park remains relatively uncrowded despite its proximity to Santiago. It's subdivided into three sectors: Conaf's main administration station is at Granizo, near Olmué. There are also rangers at the nearby entrance of Cajón Grande and at Ocoa, in the north of the park.
Most of the park's 80 sq km resemble the dry, jagged scrubland of the mountains of Southern California. The park protects around 100 animal species, and several endemic plant species. There's excellent hiking to be had here. Paved access roads lead to the three entrances, but there are no roads within the park. Spring is the best time to visit.