Wiebelt, Frank J.; Sanborn, W. C.; Trengove, R. R. & Ricker, Spangler. Investigation of West Belt Copper-Zinc Mines, El Dorado, Amador, Calaveras, and Mariposa Counties, California, report, February 1951; (https://digital.library.unt.edu/ark:/67531/metadc38555/m1/4/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, digital.library.unt.edu; .