Language.

The dunes below are similar to some sort of alphabet. The original poster of this image can be seen here.

Compare this to another shape nearby:

and these discovered under the face:

This shape: is similar to

This: is similar to:

This: is similar to: or perhaps this:

Just south of the top photo is the KK face made out of dunes.

One has then the KK face made of dunes. The approximately north of it ones has possible language symbols. Then north of that one has Cydonia with similar possible language symbols. The also in Cydonia one has the theta symbol.