(CNN) Here's a look at Area 51, a highly classified United States Air Force facility located at Groom Lake in southern Nevada.
The US government's official name for Area 51 is the Nevada Test and Training Range, which is a unit of the Nellis Air Force Base. Today it is used as an open training range for the US Air Force.
According to the CIA, the name Area 51 comes from its map designation. It was also previously referred to as "Paradise Ranch" in order to make the facility sound more attractive to those that would be working there. "Paradise Ranch" was then shortened to "the Ranch." Other nicknames include "Watertown" and "Dreamland."
In 1958, under Public Land Order 1662, the 38,400-acre land area was "withdrawn from public use by the US Atomic Energy Commission, a predecessor to the US Department of Energy."
It is located more than 120 miles northwest of Las Vegas.
It is restricted to the public and has armed guards patrolling the perimeter. It's also impossible to enter the airspace above without permission from air traffic control.
Area 51 has long been a topic of fascination for conspiracy theorists and paranormal enthusiasts who believe it to be the location where the US government stores and hides alien bodies and UFOs.
One popular UFO conspiracy is that in 1947 in Roswell, New Mexico, remains from a flying saucer that supposedly crashed were brought to Area 51 for reverse engineering experiments in order to replicate the extraterrestrial spacecraft.
In June 2019, a poll conducted by YouGov found that 54% of US adults think it is likely the government knows more than it's telling about UFOs.
April 12, 1955 - CIA officer Richard Bissell, who is overseeing the development of the U-2 plane, first sees the site that would become known as Area 51 while on an "aerial scouting mission." Bissell, along with three others, including Col. Osmund Ritland and Kelly Johnson, Director of the Lockheed Corporation's Skunk Works, agree that the area would "make an ideal site for testing the U-2 training pilots" and request the Atomic Energy Commission add the area to its real estate holdings in Nevada.
July 1955 - The CIA begins using Area 51 to develop the high-altitude U-2 reconnaissance plane. Other aircrafts are also tested at the site later, including the OXCART (a supersonic reconnaissance A-12 aircraft) and the F-117 stealth ground attack jet.
November 1959 - A radar test facility is established at Area 51.
October 13, 1961 - In a letter to Bissell, now the CIA's Deputy Director of Plans, CIA Inspector General Lyman Kirkpatrick writes that Area 51 appears to be "extremely vulnerable in its present security provisions against unauthorized observation."
December 22, 1961 - The first A-12 arrives at Area 51.
1974 - Skylab astronauts inadvertently take photographs of Area 51. The images are reviewed by the National Photographic Interpretation Center and then removed from the rolls of film and stored in a vault.
August 26, 1976 - In a memo from the Deputy Director of Central Intelligence E.H. Knoche to General David C. Jones, the Air Force chief of staff, the National Security Council's Committee on Foreign Intelligence approves the recommendation "that management of Area 51 be transferred from CIA to Air Force by fiscal year 1978."
May 13, 1989 - KLAS (CBS affiliate in Las Vegas) reporter George Knapp interviews Bob Lazar, who exposes details about Area 51. Lazar claims to be working with physicists trying to "back-engineer a downed alien spacecraft." The interview generates public interest in the base.
September 8, 1994 - The US Air Force issues a report stating that the wreckage recovered in Roswell, New Mexico, in July 1947, often referred to as the "Roswell Incident," consisted of a smashed part of the balloons, sensors and radar reflectors from a classified government project called Project Mogul.
January 30, 1996 - US President Bill Clinton signs a presidential determination exempting the "Air Force's operating location near Groom Lake, Nevada, from any federal, state, interstate, or local hazardous or solid waste laws that might require disclosure of classified information concerning that location to unauthorized persons."
March 6, 1996 - A citizen suit between former employees at Area 51 and the Department of Defense is filed. The plaintiffs (former employees) allege violations of Resource Conservation and Recovery Act "in the storage, treatment, and disposal of hazardous waste at the operating location near Groom Lake."
July 23, 1996 - A citizen suit between former employees at Area 51 and the Environmental Protection Agency is filed. The court determines that the administrator of the EPA "completed her statutory duties with regard to the inspection and inventory of the operating location near Groom Lake.
April 2000 - A Russian-built satellite reveals views of Area 51.
September 2003 - US President George W. Bush signs a memorandum to the Environmental Protection Agency. The memorandum to the Administrator states, "I find that it is in the paramount interest of the United States to exempt the United States Air Force's operating location near Groom Lake, Nevada, the subject of litigation, from any applicable requirement for the disclosure to unauthorized persons of classified information concerning that operating location."
2005 - A Freedom of Information Act request is filed by Dr. Jeffrey T. Richelson, a senior fellow at the George Washington University National Security Archive. The FOIA request is for information on the CIA's "Lockheed U-2 plane reconnaissance program."
May 17, 2011 - Journalist Annie Jacobsen's book, "Area 51: An Uncensored History of America's Top Secret Military Base," is published.
2012 - Funding for the Advanced Aerospace Threat Identification Program, the Pentagon's secret UFO office, ends. The office spent $22 million over five years collecting and analyzing what they considered "anomalous aerospace threats."
August 15, 2013 - The CIA publishes declassified documents which officially acknowledge for the first time that Area 51 is a secret US military site, following the FOIA request filed in 2005. The declassified documents concern the history of the U-2 and A-12 OXCART aerial surveillance programs that were constructed and tested at Area 51. The documents claim the site's secret status was a way to keep information from the Soviets, rather than to cover-up an alien encounter.
December 8, 2013 - At the 36th Annual Kennedy Center Honors, US President Barack Obama becomes the first president to use the phrase "Area 51" in public, while honoring the actress Shirley MacLaine, who has long been vocal about her interest and belief in UFOs and the extraterrestrial.
April 2, 2014 - In an appearance on ABC's "Jimmy Kimmel Live," Clinton jokes that while he was president, he asked aides to investigate what the government knew about UFOs and Area 51. He says, "First I had people go look at the records on Area 51, to make sure there was no alien down there."
March 24, 2016 - On "Jimmy Kimmel Live," presidential candidate Hillary Clinton says if elected, she would open government files on any unexplained aerial phenomenon barring any threats to national security.
July 11, 2019 - More than 1.5 million people say they will attend a Facebook event titled "Storm Area 51, They Can't Stop All of Us," pledging to raid Area 51 in a quest to "see them aliens." The post suggests that people run onto the site on September 20, 2019 at 3:00am.
July 12, 2019 - Laura McAndrews, an Air Force spokesperson, says government officials are aware of the Facebook event. She says "(Area 51) is an open training range for the US Air Force, and we would discourage anyone from trying to come into the area where we train American armed forces. The US Air Force always stands ready to protect America and its assets."
August 9, 2019 - The Alienstock Festival, a festival celebrating aliens that's set to take place September 19-22 in Rachel, Nevada, is announced. "We're aiming to establish something unique here, a meeting place for all the believers. Come out to the desert to dive into a world full of live music, arts, and camping under the stars," the festival's website says.
August 20, 2019 - Officials in Lincoln County, Nevada vote to pre-sign an emergency declaration in preparation for the influx of visitors.
September 10, 2019 - Organizers cancel Alienstock saying, "critical infrastructure needed was not provided for this festival." Instead, people are encouraged to attend the Area 51 Celebration in Las Vegas.
September 10, 2019 - Two Dutch men are arrested in the Nevada National Security Site near Area 51. The men tell police that they saw the 'No Trespassing' signs, but wanted to take a look at the facility. They later plead guilty to trespassing and illegal parking.
September 20, 2019 - Approximately 200 people show up outside the gates of Area 51 for the "raid" on the facility. Two people are arrested, according to the Lincoln County Sheriff. There is one alcohol-related arrest and a Canadian citizen is arrested for indecent exposure. One woman comes close to crossing and is briefly detained and released at the scene.