The Resident Agent's Office Records contain the bulk of St. Mary's early records. In addition to land records, correspondence, and financial records, this subseries includes the diaries of the St. Mary's explorers.

The diaries, covering 1862-1866, provide detailed accounts of the explorers' surveying efforts and contain correspondence and sketches. As well as surveying, the explorers often visited nearby copper mines and gave brief reports on the progress of the mines.