See my post The Ascent of the Second World for international examples. In 1929, the U.S. South (as well as North Dakota and surrounding states) was very relatively poor, while the U.S. North (especially New York and Illinois) was very relatively rich. The four richest states in the country were New York, Illinois, Delaware, and California, with the exception of Delaware, all home to the largest cities of America. Today, things are very different. Due to greater mobility of labor and capital and institutional convergence of the U.S. South and North (at least partly due to Federal legislation), the U.S. is a much more regionally equal country than it was in 1929, or even 1979. As I discussed in the Ascent of the Second World post, Puerto Rico is also much closer to U.S. income levels than it was in 1950.

Lighter states are richer. In 1929, regional inequality in the United States was at a point unimaginable today. South Carolina and Mississippi, the poorest states in the Union, had less than 40% of the U.S. average per capita income. Today, no state has a per capita income of less than 70% of the U.S. average.

PNGs (bummer WordPress does not allow SVGs):

Animated GIF:

I did not enter the data I used to make the maps into a spreadsheet (I got it all from FRED2), but might do so a few days from now.