Hi steveh and welcome to the GEC. Looks like a poorly captured geological feature to me, but since you're obviously ruling out logical explanations in favor of a buried object, I doubt you'll accept any answer that doesn't fit your pre-conceived notion. No offense meant, just an observation on how you worded your question. Have fun!  Gregg _________________________ "Other job markets may lay claim to the title, but astronomy is actually the world's oldest profession." - Phil Plait My Musical Tours . Hubble Showcase Musical Tour . Monument Valley Musical Tour |