The Richat Structure

[Pimander]

The Mars one looks like it has a dry lake bed surrounding it.

Examples on Earth:


http://en.wikipedia.org/wiki/File:Edwards_AFB_satellite_photo.jpg


http://fellowshipoftheminds.com/2013/08/16/cia-admits-mysterious-area-51-exists/

[ArMaP]

An even bigger version (at 27.2 cm per pixel) can be seen here, along with an anaglyph that shows that that whole area is not as flat as it looks at first.