Defty emigrated to the United States from England, and assisted his father, Henry Defty, and his uncle, Jacob Defty, in the procurement and sale of real estate to English investors. All of the Deftys were involved in mining activities in the San Bernadino Mountains during the late 1880s and early 1890s.
By 1891, he worked as a mining engineer, geologist and mining consultant, with offices in Phoenix. For the next thirty-five years, Mr. Defty operated this business, specializing in detailed mining reports, the acquisition and sale of small mining properties, the formation of joint-stock mining companies, and the management of mining properties. While the majority of his work was done in Arizona, Defty also inspected properties in Alabama, California, Colorado, Idaho, Montana, Nevada, New Mexico, South Carolina, Jamaica and Mexico.
Between 1890 and 1910, Defty was extensively involved with a series of mining ventures in Sonora, Mexico as a mining engineer, mine broker and mine manager. His most notable tenure in Sonora was as general manager and part-owner of the La Gran Proveedora de Cobre, an American-owned copper mining company with properties in the Altar Mining District.
Most of the personal and family papers consist of clippings and invitations relating to the Deftys' musical interests, but also include a few family photographs and two diaries. The diary entries generally contain very brief statements.
The business records which include correspondence, field notebooks, mining reports, other non-mining business reports and maps and blueprints are the bulk of this collection. These records relate to Defty's business activities which consisted largely of preparing detailed mining reports pertaining to mining sites in Arizona and Sonora, Mexico. Other business records relate to his involvement with several irrigation companies engaged in developing lands for agricultural purposes in Arizona and California. The mining reports can be specifically tied into the field notebooks and the diaries. For a given mining report with a date, the researcher can refer to the same date in a field notebook and diary and find additional information on an individual mine. The field notebooks contain the most detailed information since they have all of the basic field data from which Defty wrote his reports for clients. For a more detailed description of each series, see below.