Earth Glide (Ex)
A burrowing earth elemental can pass through stone, dirt, or almost any other sort of earth except metal as easily as a fish swims through water. If protected against fire damage, it can even glide through lava. Its burrowing leaves behind no tunnel or hole, nor does it create any ripple or other sign of its presence. A move earth spell cast on an area containing a burrowing earth elemental flings the elemental back 30 feet, stunning the creature for 1 round unless it succeeds on a DC 15 Fortitude save.
For more ideas on what it can do, look at sandman from spiderman. Plenty of things make sandform awesome.
I think it also works with this section of the monster write up.
"Stealthy and unpredictable, the sandman is a terror to all travelers in the desert, whether they be traders, messengers, or adventurers. When at rest, sandmen resemble ordinary piles of sand, blending in perfectly with barren surroundings or ancient tombs. They rely on their soporific powers in most situations, putting their enemies to sleep and killing their unconscious opponents or dragging them back to their summoner."
It seems to be used as a pre combat strategy where they lie in wait somewhere where terrain attracts people (like an oasis) or funnels traffic like a gateway into a ancient tomb and let it's sleep aura catch a few unsuspecting victims letting it start combat hopefully with an advantage.
Additionally with Cubic Prism's observation if their Sleep Aura fails pre fight and they're spotted they can always then earth glide away and try again hoping for better results.
A well-crafted desert encounter with one or more of these guys could last days. It could be an entire session/adventure, especially if they start attacking small settlements or caravans.