Marmolejo, Pleistocene stratovolcano in San José de Maipo, Chile.

Marmolejo is a Pleistocene stratovolcano on the border between San José de Maipo and Argentine territory. The mountain rises to about 6,100 meters and displays a wide collapsed crater at its summit with clearly visible volcanic features.

The peak was first climbed in 1928 by German mountaineers, marking the start of documented exploration of this mountain range. The route across the pass later became a known pathway for expeditions in this section of the high Cordillera.

The name honours Alonso de Góngora Marmolejo, considered Chile's first historian, who reached Chile in 1549 with an expedition led by Pedro de Valdivia. The peak stands in the San José volcanic complex beside San José, La Engorda, Plantat and Espíritu Santo, and is known for its large glacier and its north wall.

The route involves river crossings and follows unmarked paths in places, so GPS and map skills are needed. Waterproof gear and solid physical fitness are important since conditions are demanding and can change quickly.

Marmolejo's first ascent, on 1 October 1928, was made by Hermann Sattler, Sebastian Krückel and Albrecht Maass of the German Andean Club, via the eastern slope. In 1943 Bachmann, Krahl and Araneda, from the same club, completed the first ascent by the Estero Marmolejo. In November 2023 three Argentine mountaineers died after reaching the summit from the Chilean side.