Thanks Sirous for the info on the Gutians. They've been a personal interest to me for quite some time. I understand they've just recently found a settlement that they believe was there's.
Back of the boat's got a good plan! You might also survey the area, from above, with a drone. Likely as not, if this was setting open, the grave was looted. This could also be a air vent for another chamber below. Are there any local legends referring to this landmark. What do the locals call it? What can you learn from the glyphs above the hole? Have you checked around with a metal detector? Perhaps you could try dowsing. It works well here but I don't know about an arid climate. If you found water it might be treasure enough!
I can only imagine the personal risk of investigating sites like this on your own, Best wishes and go safe!