Campbell, Russell H. & Schafer, Max. A Systematic Radioactivity Reconnaissance of Part of the North Gilpin County Mining District, Colorado, report, September 1953; (https://digital.library.unt.edu/ark:/67531/metadc304729/m1/1/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .