From the ArcaMax Publishing, The Culinary World, with Chef James Newsletter:
http://www.arcamax.com/news/chefjames/s-323903-396315
Barley is grown by the Aymara people on the highest cultivated plot of
land in the world at 15,420 feet near Lake Titicaca. The lake is the
border between Peru and Bolivia at 12,500 feet, and the area was home
to one of the oldest civilizations in the Americas. The Aymara people
that live there still practice ancient methods of agriculture.
Potatoes and quinoa are also grown there at slightly lower elevations.
Courtesy of FoodReference.com.