Frank Sizer was a Helena and Butte, Montana, mining engineer. He managed the Whitlach-Union, Spring Hill, Eclipse-Argo, and Gould mines; worked for Canoll and Martin; and served as a consultant to William A. Clark in his Colusa Parrott law suit and his purchase of the Rosario Mine in Mexico. Collection (1878-1909) includes correspondence, financial records, legal documents, diaries, scrapbooks, clippings, and notebooks.