Looks like a good way to grow seldom irrigated agaves in the low desert. Have you seen any among the indian ruins you've found in search of agaves in habitat?"

Difficult to say. There are typically a lot of rocks around all the areas in which we've found domesticate Agaves. I couldn't say whether some were placed there as an agricultural feature.

As an aside, I believe this technique could prove quite valuable in regard to growing any xeric plants in our landscapes.