FYI, I did consider the possibility of cloud shadow, but for a cloud to produce a shoadow anywhere near that dark, the cloud would have to be extremely dense (a very tall cumulonimbus) and very close to the ground, And from the satellite altitude, such a low lying cloud would be visible in the image, In fact, it would have obscured the subject.
If anyone can show me an lmage of an isolated (no visible cloud) cloud shadow on Google Earth that produces that same low albedo and high opacity -- I will reconsider my analysis.
That leaves two alternatives: a dark, dusty deposit -- or Photoshop trickery. I'll see if I can fake the effect on the "before" photo...
Very good,...Excellent work!