This is Secretary Harold Ickes' September 30, 1941 letter of introduction to the "Officers and Employees [of the] Department of the Interior." With it, Adams is granted entrée to "reclamation projects, Indian reservations, national parks, and" (my personal favorite) "other places under the jurisdiction of this Department."
I wonder if he ever had to present it to anyone. Or, was his experience a bit more like buying beer on your 21st birthday and having no one ID you?