Are you in a "landscaped" development (one of many of the past 5-40
years), where the lay of the land was moved around by bulldozers and
turnapulls, houses built, and then maybe six inches of black dirt
dropped on
top?

Actually no, I'm out in the country, on 10 acres in former farmland.

The area with the soil I described earlier is out front by the road,
and may have been bulldozed as you describe, although from the looks of
it, it seems to match the contour of the undisturbed areas all around
it.

Folks who have lived in this area longer than I have tell me that there
used to be a stand of large mature trees lining the road in this area,
but they destroyed them all when they put in the power poles.
Sickening. So maybe the area was bulldozed and just happens to match
the surrounding areas because they pushed the dirt back into place
after they were done.

The strange thing is, there's hardpan in various degrees all over the
place, even in areas well away from the road and house. I read the
other day where excessive tilling can destroy the "soil structure" and
then when the land is no longer tilled, hardpan can form. I wonder if
maybe this is what happened here. The land hasn't been farmed for
maybe 20 years or so.