One of the most impressive sights in South America is a tropical forest growing upon a glacial moraine. In many places in eastern Bolivia and Peru the glaciers of the Ice Age were from 5 to 10 miles long—almost the size of the Mer de Glace or the famous Rhone glacier. In the Juntas Valley in eastern Bolivia the tree line is at 10,000 feet (3,050 m.), but the terminal moraines lie several thousand feet lower. In eastern Peru the glaciers in many places extended down nearly to the tree line and in a few places well below it. In the Cordillera Vilcapampa vast snowfields and glacier systems were spread out over a summit area as broad as the Southern Appalachians. The snowfields have since shrunk to the higher mountain recesses; the glaciers have retreated for the most part to the valley heads or the cirque floors; and the lower limit of perpetual snow has been raised to 15,500 feet.
Fig. 132—Recessed volcanoes in the right background and eroded tuffs, ash beds, and lava flows on the left. Maritime Cordillera above Cotahuasi.
Fig. 133—The summit of the great lava plateau above Cotahuasi on the trail to Antabamba. The lavas are a mile and a half in thickness. The elevation is 16,000 feet. Hence the volcanoes in the background, 17,000 feet above sea level, are mere hills on the surface of the lofty plateau.