The western side of the Andes goes from one of the worlds highest rainfall zones over the icecaps of Patagonia, to the world's driest desert in the Atacama of northern Chile and southern Peru. On the east side of the Andes, there is a rain shadow which keeps most of the area semi-arid, until changing rain patterns in northernmost Argentina and Bolivia leads into the Amazon Basin. Throughout the southern sector of the area treated, glaciers descending in both directions during the ice ages gouged basins adjacent to the mountains, which now contain some very large and beautiful lakes. Farther north the lakes are largely in alpine cirques. Then it is mainly artificial reservoirs and saline ponds in the Altiplano, until the tectonic basin that holds Lake Titicaca in Bolivia and Peru.
As one might expect with high ranges so close to the Pacific Ocean, the rivers come down large and fast in Southern Chile, but what little falls in the Altiplano adjacent to the Atacama Desert tends to end up in salt lakes and pans known as salitres. In Peru, however, there are rivers from the mountains that are famous for sending flash floods through the deserts, and have cut some spectacular canyons in their history.
This sector of Terrain is divided into three pages, as follows: