Hamke, J. R.; Marchant, L. C. & Cupps, C. Q. Oilfields in the Williston Basin in Montana, North Dakota, and South Dakota, report, Date Unknown; (https://digital.library.unt.edu/ark:/67531/metadc12781/m1/1/: accessed December 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .