Up in the Altiplan at 4000 meters there is not much in the way of natural fuel. This is because there are relatively few trees. The only sources of fuel are little gas cylinders. However, if you are a farmer that practices mixed agriculture then a free source of fuel is collecting dry cow dung of the fields and burning that. This is exactly what the farmers do to heat their stoves for cooking!
Here is a video inside Gladys' kitchen showing us exactly that.