William F. Witherell was a mining engineer and businessman. His collection contains correspondence, financial records, and miscellaneous papers relating to mining investments in Pima County dating 1870-1886. Includes letters from mining investors regarding their investments, chiefly from Pelican Mining Co. and Arizona Gold and Silver Mining Co. Also includes a check register dating from May 1878 to May 1879, and a financial journal from May 1878 to March 1880 for the Arivaca Milling, Mining and Commercial Co.