Area 51 is a rectangle in Nevada, North-West from Las Vegas. The designation "Area 51" is somewhat contentious, appearing on older maps of the NTS but not newer ones, but the same naming scheme is used for other parts of the Nevada Test Site. It is included in the Nellis Air Force Range. These facilities is actually located near the bed of a dry lake.
South-West of the lake (bottom of the picture on the left), there is an airport with several concrete runways, one of them continuing on the lake. There are also four beaten earth runways, set as a V.
[Quoting Wikipedia]
Groom Lake is not a conventional airbase, and frontline units are not normally deployed there. It appears, rather, to be used during the development, test, and training phases for new aircraft. Once those aircraft have been accepted by the United States Air Force, operation of that aircraft is generally shifted to a normal air force base. Groom is reported, however, to be the permanent home for a small number of aircraft of Soviet design (obtained by various means). These are reportedly analyzed and used for training purposes.
Soviet spy satellites obtained photographes of the Groom Lake area during the height of the Cold War, but these support only modest conclusions about the base. They depict a nondescript base, airstrip, hangars, and so forth, but nothing that supports some of the wilder claims about underground facilities. Later, commercial satellite images show that the base has grown, but remains superficially unexceptional.
[…]
In 1997 the US Government declassified the existence of Area 51. Unlike much of the Nellis range, the area surrounding the lake is permanently off-limits both to civilians and normal military air traffic. The area is protected by radar stations, and uninvited guests are met by helicopters and armed guards. Even military pilots training in the NAFR are reportedly interrogated extensively by military intelligence agents when they accidentally stray into the exclusionary "box" surrounding Groom's airspace.
[…]
The base does not appear on public US government maps; the USGS topological map for the area only shows the long-disused Groom Mine, and the civil aviation chart for Nevada shows a large restricted area, but defines it as part of the Nellis restricted airspace. Similarly the National Atlas page showing federal lands in Nevada does not distinguish between the Groom block and other parts of the Nellis range.
[End quoting]
