[pepsi_junkie]

They are only like 6-12 inches high.

[txhurl]

OK, uh, Scarab beetle pens, then. :)

[ZOOKER]

On the internet, everyone can be an expert, so here's my expert opinion:

These used to be corrals for keeping livestock penned up at night, when the desert was grassland (not that long ago, as some have pointed out).

Over the years, most of the stone was stolen to make other structures, except for the lowest layers that were underground at that time. Now it's desert and the topsoil has blown away, leaving a low wall.