Question: In what year did the agency that maintains the Presidential Library system become independent?

full_context: Document 1: National Archives and Records Administration: NARA also maintains the Presidential Library system, a nationwide network of libraries for preserving and making available the documents of U.S. presidents since Herbert Hoover. The Presidential Libraries include:
Document 2: National Archives and Records Administration: The first Archivist, R.D.W. Connor, began serving in 1934, when the National Archives was established by Congress. As a result of a first Hoover Commission recommendation, in 1949 the National Archives was placed within the newly formed General Services Administration (GSA). The Archivist served as a subordinate official to the GSA Administrator until the National Archives and Records Administration became an independent agency on April 1, 1985.
Document 3: National Archives and Records Administration: The National Archives Building, known informally as Archives I, located north of the National Mall on Constitution Avenue in Washington, D.C., opened as its original headquarters in 1935. It holds the original copies of the three main formative documents of the United States and its government: the Declaration of Independence, the Constitution, and the Bill of Rights. It also hosts a copy of the 1297 Magna Carta confirmed by Edward I. These are displayed to the public in the main chamber of the National Archives, which is called the Rotunda for the Charters of Freedom. The National Archives Building also exhibits other important American historical documents such as the Louisiana Purchase Treaty, the Emancipation Proclamation, and collections of photography and other historically and culturally significant American artifacts.
Document 4: Hoover Institution Library and Archives: The Hoover Institution Library and Archives is a research center and archival repository located at Stanford University, near Palo Alto, California in the United States of America. Built around a collection amassed by Stanford graduate Herbert Hoover prior to his becoming President of the United States, the Hoover Library and Archives is largely dedicated to the world history of the 20th and 21st centuries. It includes one of the largest collections of political posters in the world.
Document 5: National Archives and Records Administration: In 2010, Executive Order 13526 created the National Declassification Center to coordinate declassification practices across agencies, provide secure document services to other agencies, and review records in NARA custody for declassification.
Document 6: National Archives and Records Administration: The National Archives and Records Administration (NARA) is an independent agency of the United States government charged with preserving and documenting government and historical records and with increasing public access to those documents, which comprise the National Archives. NARA is officially responsible for maintaining and publishing the legally authentic and authoritative copies of acts of Congress, presidential proclamations and executive orders, and federal regulations. The NARA also transmits votes of the Electoral College to Congress.
Document 7: National Archives and Records Administration: In May 2008, the National Archives announced a five-year agreement to digitize selected records including the complete U.S. Federal Census Collection, 1790–1930, passenger lists from 1820–1960 and WWI and WWII draft registration cards. The partnership agreement allows for exclusive use of the digitized records by Ancestry.com for a 5-year embargo period at which point the digital records will be turned over to the National Archives.
Document 8: National Archives and Records Administration: The National Historical Publications and Records Commission (NHPRC)—the agency's grant-making arm—awards funds to state and local governments, public and private archives, colleges and universities, and other nonprofit organizations to preserve and publish historical records. Since 1964, the NHPRC has awarded some 4,500 grants.
Document 9: National Archives and Records Administration: Originally, each branch and agency of the U.S. government was responsible for maintaining its own documents, which often resulted in records loss and destruction. Congress established the National Archives Establishment in 1934 to centralize federal record keeping, with the Archivist of the United States as chief administrator. The National Archives was incorporated with GSA in 1949; in 1985 it became an independent agency as NARA (National Archives and Records Administration).
Document 10: State Archive Service of Ukraine: The State Archive Service of Ukraine or Ukrderzharkhiv is a Ukrainian government agency that realizes state policy in spheres of keeping of archives, record, function of state system of documentation security fund as well as an inter-trade coordination on matters within its competence. As part of administrative reorganization initiated by the President of Ukraine Viktor Yanukovych in 2010, the service was created out the State Committee of Archives (DerzhKomArchiv). The agency is part of the Ministry of Justice of Ukraine since 1999.
Document 11: National Archives and Records Administration: Libraries and museums have been established for other presidents, but they are not part of the NARA presidential library system, and are operated by private foundations, historical societies, or state governments, including the Abraham Lincoln, Rutherford B. Hayes, William McKinley, Woodrow Wilson and Calvin Coolidge libraries. For example, the Abraham Lincoln Presidential Library and Museum is owned and operated by the state of Illinois.
Document 12: National Archives and Records Administration: In 2011 the National Archives initiated a Wikiproject on the English Wikipedia to expand collaboration in making its holdings widely available through Wikimedia.
Document 13: National Personnel Records Center fire: The National Personnel Records Center fire of 1973, also referred to as the 1973 National Archives fire was a fire that occurred at the United States National Personnel Records Center (NPRC) in Overland, Missouri, a suburb of St. Louis, on July 12, 1973, striking a severe blow to the National Archives and Records Administration of the United States. NPRC, the custodian of military service records, lost approximately 16 -- 18 million official military personnel records as a result of the fire.
Document 14: National Archives of Guyana: The National Archives of Guyana (also known as the Walter Rodney Archives) is the legal depository for official records and local newspaper publications in Guyana. Established in 1958, the National Archives are situated in D'Urban Park on Homestretch Avenue in Central Georgetown. In 1972 it was made a Department of the Ministry of Culture, Youth and Sport in the Government of Guyana.
Document 15: National Archives and Records Administration: Most records at NARA are in the public domain, as works of the federal government are excluded from copyright protection. However, records from other sources may still be protected by copyright or donor agreements. Executive Order 13526 directs originating agencies to declassify documents if possible before shipment to NARA for long-term storage, but NARA also stores some classified documents until they can be declassified. Its Information Security Oversight Office monitors and sets policy for the U.S. government's security classification system.
ground_truth: 1985
sub_queries: What agency maintains the Presidential Library system? Answer: NARA
In what year did NARA become an independent agency? Answer: 1985