United States. Bureau of Economic Analysis. "Region 4 : Plains, Volume 7" in 1980 OBERS BEA Regional Projections : Economic Activity in the United States by State, Economic Area, SMSA and State Portions of the Areas, Historical and Projected, 1969-2030
(July 1981).
https://fraser.stlouisfed.org/title/9324/item/682153, accessed on January 22, 2026.