Area 51 the base extends further east. After leaving the restricted area, Groom Lake Road descends eastward to the floor of the Tikaboo Valley, passing the dirt-road entrances to several small ranches, before converging with State Route 375, the "Extraterrestrial Highway", south of Rachel. Area 51 shares a border with the Yucca Flat region of the Nevada Test Site, the location of 739 of the 928 nuclear tests conducted by the United States Department of Energy at NTS. The Yucca Mountain nuclear waste repository is southwest of Groom Lake. Groom Lake is a salt flat in Nevada used for runways of the
U.S. Route 51 in Louisiana neighborhood in Jefferson Parish remained in the state highway system as a disconnected part of Route 33 until the 1955 Louisiana Highway renumbering. The remainder of US 51 carried no state route designation after the renumbering, which eliminated unnecessary concurrencies between U.S. and state routes. Paving projects during the late 1920s and early 1930s led to the early realignment of two portions of US 51 in Tangipahoa Parish. The original route between Independence and Amite City followed what is now known as Old US 51 and remained for a time in the pre-1955 state highway system as State Route 1094.