This collection contains biographical materials (undated) McKay and Hansen family geneaology; incoming correspondence (1875-1919) concerning mining and realestate business dealings; outgoing correspondence (1887, 1901, 1908); court papers (1857-1922) court cases dealing mostly with mining properties and water rights; financial records (1865-1919) dealing with daily expenses and various financial enterprises including Mill Creek Mill, mining and realestate; legal documents (1872-1912) primarily regarding mining claims and deeds; and miscellaneous certificates and programs, and clippings.

The Elling, Baker and McKay subgroup relates to mining holdings controlled jointedly by Henry Elling, William Baker and Alex McKay. The records include financial records (1887-1911) mainly assay, banking and tax records.

The Mill Creek Mills subgroup contains financial records (1887-1898) including ledgers; financial statements on grain milled, daily expenses and account activities; receipts and miscellaneous work forms.

The Caroline Hanson McKay subgroup consists of incoming correspondence (1877-1910) divided equally between family issues and mining and realestate business; legal documents (1860-1911) primarily related to family estates and land holdings; and calling cards.

The Mary McKay Herhold Bothwell Swanze subgroup consists of incoming correspondence (1876-1910) mainly from McKay family; financial records (1897, 1925) includes deposit clips an receipts; legal documents (1897, 1905) regarding mining leases and patents; and calling cards and miscellaneous notes. [For materials on Flora McKay McNulty see MC 261.]