Regarding the 1st image in post #1811...
I can see what you are saying about a “slab on a sub-slab”, but
I have trouble understanding how that has dropped down vertically
six to ten feet from its original position, and now appears to sit on bedrock.
Unless that is just the perspective of the photo and confusing/deceptive to the eye.
The slab by the wall has the same arrangement, a facing slab atop one, maybe two, sub-slabs.