This photograph in the Mission Operations Centre (MOC) series appears to show a forest and what appears to be a lake.
Take a look at the artificial looking structures on the western shore of the lake. The objects are virtually in a line and spaced equally apart.
Original NASA source: http://asimov.msss.com/moc_gallery/m07_m12/images/M09/M0901354.html
Watch the video by Will Farrar from WhatsUpInTheSky below for a lot more details and analysis:
I doubt this type of layout is produced naturally. What the heck? You decide.