The collection consists primarily of property records, including records relating to property in Tillamook County in which Joseph McMahon invested, such as Camelot Estates. There are some records relating to McMahon's mother, Catherine, and receipts for family plots and gravestones at Mt. Calvary Cemetery. The collection also includes title abstracts for a number of properties in Portland, Oregon; Oberlin, Oregon; and Marion County, Oregon; as well as records and correspondence relating to people outside of the McMahon family, particularly real estate dealer Patrick Holland.