A basin below the sea
In the arid plains of Patagonia lies a basin so deep its floor is 105 meters (344 feet) below sea level. This makes Laguna del Carbón, a salt lake within the Gran Bajo de San Julián depression, the lowest point in both the Western and Southern Hemispheres. It is the seventh-lowest terrestrial point on Earth. The depression is an endorheic basin, a closed drainage system with no outlet to the sea. Any water that flows in can only escape through evaporation, a process that concentrates salts and minerals over millennia.
The formation of the Gran Bajo de San Julián was formed by erosion and deflation acting over the last 5 million years. The Patagonian wind, a relentless force, stripped away softer, friable marine sediments from the Paleogene and Neogene periods. This erosion exposed a harder volcanic basement rock from the Jurassic period. The process gradually carved out the vast depression we see today, which is approximately 54 kilometers from the town of Puerto San Julián. The lake itself, whose name means "Coal Lagoon," is named for the visible deposits of lignite and sub-bituminous coal in the area, remnants of ancient swampy environments.