That dark area in South Dakota is the Pine Ridge reservation, the poorest single community in the United States. It's absolutely disgusting how we have not only allowed people to live, but actively caused them to live in such abject poverty. If I dropped you in the middle of that reservation with no context you'd think you'd landed in a 3rd world country.
Unemployment on the reservation hovers between 80% and 85%, and 49% of the population live below the federal poverty level. Many of the families have no electricity, telephone, running water, or sewage systems; and many use wood stoves to heat their homes, depleting limited wood resources.
Then again, why don't they just pull themselves up by the moccasin straps? Look at them. I bet some of them even have refrigerators! /s
I'm curious how this correlates to things like counties with vacation hotspots and the like, as Cape Cod is marked as less than 10% but I know for a fact that that county has the highest rates of drug addiction and homelessness in the state and I can only conclude that that isn't really showing because of how much of the county is vacation homes and how the average working poor are outpriced from the area.
Same with Garrett County in Western Maryland; lots of multi-million dollar vacation houses that border Maryland's largest lake, despite there being few job opportunities in the county as a whole.