Such mountain ranges have a complex structure, which is usually the result of folding and faulting accompanied by volcanic activity. In South America, the ranges include numerous volcanic peaks. The Andes cordillera has Ojos del Salado, the highest active volcano in the world and second-highest point in the Western Hemisphere. (Though not itself a volcano, Argentina's Mount Aconcagua, at 6,960 m, at (22,834 ft), is the highest point in the Western Hemisphere.) Some of the volcanoes have been active in historical times.