Hellinghausen, F. A. [Report to W. P. Gannaway by F. A. Hellinghausen, January 28, 1964 #1], report, January 28, 1964; (https://texashistory.unt.edu/ark:/67531/metapth337791/m1/1/: accessed June 23, 2024), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu.; .