The records of the Portland Mining Company span the years 1912 to 1947, with the bulk of the material covering the years 1940 to 1943. Included are minutes of meetings, financial statements, correspondence with suppliers and stockholders, annual statements and reports to state agencies, stock ledgers and journals, financial ledgers and journals, vouchers, voucher registers, and tax returns.

Related materials can be found in the records of the Monitor Mining Company and the West Sunset Mining Company.