Why did income growth vary across states during the Great Depression?

"State per capita incomes became more disperse during the contraction phase of the Great Depression, and less disperse during the recovery phase. We investigate the effects of geography, industry structure, bank failures and fiscal policies on state income growth during each phase. We find that industrial composition and spatial interdependencies contributed to negative state income growth during the contraction, whereas New Deal spending and spatial interdependencies contributed to positive state income growth during the expansion phase. We find no evidence that banking conditions or state government expenditures influenced state income growth during the Great Depression"--Federal Reserve Bank of St. Louis web site.