The Nevada National Security Site (NNSS), previously the Nevada Test Site (NTS), is a United States Department of Energy reservation located in southeastern Nye County, Nevada. Formerly known as the Nevada Proving Grounds, the site was established on January 11,1951 for the testing of nuclear devices, covering approximately 1,360 square miles of desert and mountainous terrain. During the 1950s, the mushroom clouds from the 100 atmospheric tests could be seen for almost 100 miles. The Nevada Test Site contains 28 areas, 1,100 buildings, 400 miles of paved roads, 300 miles of unpaved roads, ten heliports, and two airstrips. The vast majority of nuclear tests, 828 in all, were underground. Aerial view of preparations for an underground atomic bomb test. Craters caused by subsidence after previous underground nuclear explosions lie around the test site. The craters vary is depth and diameter, depending upon the weapon's size and burial depth, as well as the geology of the area immediately around it. Undated.