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
Utah State Route 51 of the oldest grade separated interchanges in Utah still in use. Although portions of Interstate 15 were constructed in 1955, the Beck Street interchange (I-15/US-89) is the only original structure from 1955 still in use. Utah State Route 51 State Route 51 is a short highway completely within Utah County in northern Utah that connects SR-147 to US-89. The highway runs for three miles (5 km) and is an old routing of U.S. Route 91. The route begins at the intersection of 400 North (SR-147) and Childs Road in Spanish Fork, SR-51 heading northeast as a two-lane undivided highway on