Having been to Chaco several times and having read anything I can find on it and the Anasazi, I've always been curious why there don't seem to be middens of a size and quantity that might be expected if a large population lived there over several hundred years. Theories which suggest the many rooms in the Great Houses were mostly ceremonial, never meant to be occupied meaning a much smaller population would be more consistent. Why, then, would they have gone to the significant effort building them? One of the more fascinating questions which may never be answered.