Camelback High School librarian Georgette Bordine says the two Audubon Society books checked out in 1959 and the money order were sent by someone who wanted to remain anonymous.
Bordine says the letter explained that the borrower's family moved to another state and the books were mistakenly packed.
The letter said the money order was to cover fines of 2 cents per day for each book. That would total about $745. The letter says the extra money was added in case the rates had changed.
Bordine says the money will buy more books, and the overdue books will be returned to the shelves.
Information from: KPHO-TV, http://www.kpho.com