Here's a view with the shaders stripped off, just using Base Colors to see the displacement.
For those of you following the construction process, this illustrates why I originally used two separate displacements, one for terrain and one for potholes and other small-scale pavement detail and why I'm going back to that method. There are ditches and other features that don't require much detail, and there is the parking lot, which not only is the focal point, but has a lot of very shallow but highly varied displacement. A 256 bit depth map is fine when (black through greys up to white) stretched over 1 meter, the approximate depth of the ditches. 256 colors divided by 100 centimeters for main features. For the shallow detailed parking lot paving and potholes though, by compressing a 256 color map down to a tenth of a meter, the result is a far more fine resolution for that 10 centimeter cross-section.
So it's back to the drawing board to recreate something I figured out a long time ago but forgot why I did it that way (until early this morning when I saw the rendered result of what yesterday I thought was a better simpler way to do it).