Mount Tarn is a small mountain located on the southernmost part of the Strait of Magellan, in Brunswick Peninsula, about 70 km south of Punta Arenas, Chile. It is in the southern extreme of continental Chile very close to Cape Froward, surrounded by historic places such as Fort Bulnes and Puerto del Hambre (Port Famine).
From the summit it is possible to see the Strait of Magellan, Dawson and Tierra del Fuego islands, and many other smaller ones; the Darwin Mountain Range, Mount Sarmiento, and most of the Brunswick Peninsula.
On 6 February 1834 a group from the second Beagle survey expedition, including Charles Darwin, ascended Mount Tarn by forcing their way up through dense woodland to the bare ridge which took them to the summit. He recounted the story in his Journal and Remarks. In his ascent the young naturalist found the first ammonites ever known in South America.