A rugged and mountainous terrain makes up Robinson Crusoe, Santa Clara and Alejandro Selkirk, the three islands located 667 kilometers west of Chile's mainland, which are collectively known as the Juan Fernández Archipelago. The geological makeup here comes from volcanic origins, a submarine mountain range that sits below, and emerges out of, the Pacific Ocean and South American continent. Starting at sea level, the range rises up 4,327 feet (1319 m) to the highest point, Cerro de Los Inocentes, a peak found on Isla Alejando Selkirk. Though the landmass is small, the islands concentrated, uneven topography lends to erratic rainfall dispersed across the archipelago. Year round there is far more precipitation at high altitudes, though rain increases everywhere during the winter months. The areas of the islands with elevations above 1,640 feet (500 m) experience rainfall almost daily, while lower parts of Robinson Crusoe and Santa Clara are as dry as the Atacama Desert.

The islands are host to temperatures ranging from 37.5 - 93ºF (3 – 34ºC), and, naturally, it's the higher elevations on the archipelago that have the cooler temps. Its mean temperature of 15ºC, however, is attributed to the cold Humboldt Current which runs northwestward along the coast, from the south of Chile to the north of Peru. As the islands are far enough west of the mainland, they do escape some of the subantarctic waters, and over all enjoy rather Mediterranean climate, with normally chilly, wet winters, and warm, dry summers. While this a generalized understanding of climate in the archipelago, per usual, it all depends on El Niño.