The chance that this occurs in this particular spot is indeed small. The chance that a natural face-like feature occurs somewhere on the earth's hundreds of millions of square miles of land area is virtually guaranteed. Even if the chance of natural face formation in an area this size is one in a billion, it's utterly unsurprising to find a few faces scattered around the globe.
I don't think you'll be able to model the geological and pattern recognition processes to generate a probabilistic estimate that's more precise than one part in a billion. There isn't any evidence to suggest that this formation is anything but natural, and unless your geological model can accurately state that the likelihood of such a face in such an area is less than 0.0000001%, we should not be surprised to find a formation that looks like a face when looking at hundreds of millions of square miles of land area. At that level of precision, variability due to your choice of assumptions for the modeling are likely to dwarf any meaningful output of the model.
Pareidolia is the phenomenon of perceiving meaningful patterns where there are none. It's extremely common to see meaningful shapes in natural formations like clouds and rocks, even though the formations are natural and random. With nothing to suggest any kind of active sculpting of this formation (nothing to suggest by whom, or how, or when, or for what purpose it was sculpted), the most likely explanation is natural formation and pareidolia.