Structure Found In Mars Opportunity Rover Photo

I was looking for structures on Mars and came across this photo posted around the web.  Some are calling it a pyramid or a metronome.  To me it looks like a shelter or some sort of entry way maybe to underground tunnels and such.  This structure which was taken by the Mars Opportunity Rover SOL 1402 is very detailed.  It may have some sort of object on the top right of it possibly a handle or button of some sort.  

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Here is the ORIGINAL NASA Link for those interested Click Here