This collection is arranged into four subgroups. The largest portion of the collection contains Frank L. Sizer's incoming and outgoing correspondence, school notebooks, diary, reports, legal documents, scrapbook, and miscellaneous financial records, all of which serve to document his various activities and associations (1878-1909). The remaining materials in this collection are organized by three of the mining companies for which Sizer served as general manager: Rosario Mines, Limited; Whitlatch Mining Company; and Spring Hill Mining Company. The letterpress book for 1882-1884 has been microfilmed (Microfilm 140). An additional letterpress book containing the letters of Frank L. Sizer for the period of February 13-June 17, 1905 has also been microfilmed (Microfilm 287). The original 1905 letterpress book is privately owned, and is not contained in this collection.