>> “MIssissippi Delta” and a strange slash from Virginia (the Shenendoah Valley?) <<
Good observation about a couple of famous agricultural areas!
Also striking is the crescent sweeping from mid-Alabama up thru northeastern Mississippi, all the way to the Tennessee line. It’s an old cotton-producing area that was a stronghold of the slave-holding plantation aristocracy before the Civil War.
This latter region is often called the “Black Belt” in Alabama (mainly for its rich soil, but also for its black-majority population) and the “Prairie” in northeastern Mississippi. Fascinating how such land-using and demographic patterns have been maintained over nearly 200 years!