Cerro Pachón, Astronomical observatory in Vicuña, Chile

Cerro Pachón is a 2,682 m peak in the Coquimbo Region, east of La Serena, whose summit holds three observatories: the 8.1 m Gemini South telescope, the 4.1 m SOAR telescope and the Vera C. Rubin Observatory on El Peñón, its southernmost summit. The mountain lies within the El Totoral Reserve owned by AURA and rises about 500 m above neighbouring Cerro Tololo.

Scientists first began observing from this mountain location in the 1960s as part of international research efforts. Advanced telescopes were constructed in later decades to take advantage of the excellent conditions and continue making astronomical discoveries.

Cerro Pachón lies within the El Totoral Reserve, owned by the Association of Universities for Research in Astronomy, and its summit holds a rock art site attributed to the El Molle culture, dated 300 BC to 800 AD. The mountain also hosts the Andes Lidar Observatory, built by the University of Illinois, which studies the upper atmosphere between 80 and 110 km altitude.

Cerro Pachón lies east of La Serena in the Coquimbo Region, about 10 km southeast of Cerro Tololo, and is reached by road from the El Totoral Reserve area. The summit stands at 2,682 m, so allow time to adjust to the altitude. The site is an active research facility, not a public visitor attraction, so access to the telescopes is not open to tourists.

The 8.4 m Vera C. Rubin Observatory stands on El Peñón, the southernmost summit of Cerro Pachón; it was chosen for the Large Synoptic Survey Telescope in May 2006 over Sierra de San Pedro Mártir, and its first light images were released on 23 June 2025. The mountain also hosts the 8.1 m Gemini South telescope, which saw first light on 18 January 2002.