The Magellan Strait joins the Atlantic and Pacific Oceans, separating Tierra del Fuego from southernmost continental South America. The strait cuts both the Andean Cordillera and the Magellan foreland basin. Other arms of the sea intrude the axial zone of the Magellan basin. These depressions have long been interpreted as glacial valleys. On the basis of Landsat images, digital topography, and field data, we interpret the depressions as rifts or half-rifts. In general, active rifts developed within foreland basins are unusual, but in Patagonia they are consistent with regional deformation and its plate-tectonic setting during the Neogene.