Click Here>The FBI has released 69 pages of formerly classified "GUS Survey" documents.<Click Here
The "GUS Survey" was an investigative snooping technique that the FBI employed by which postal mail coming into specific zip codes would be "examined". The "GUS Survey" was employed during the early 1960's.
The San Francisco FBI office had estimated that they "examined" 662,560 pieces of mail during a 19 day period from, 10/30/61 -to- 11/17/61.