Hi Tom128, I agree, it's very difficult to tell. The sun is coming from the left and is lighting up the left side of the image more than the right, suggesting a slope. It may be that the dark area is at the top of a raised landscape feature. It does have the appearance of some kind of venting but then it does have the appearance of shadows. I would love to see an oblique shot of this area.
Thanks again for looking out and posting this one.