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
Black Tern Bog State Natural Area in southwest Vilas County, approximately northwest of Arbor Vitae. Access is via an unnamed dirt road off US Highway 51, north of the bog. The road wraps around the northern and eastern portions of the bog. It is also possible to park on the shoulder of US Highway 51, which passes along the western edge of the bog. Black Tern Bog State Natural Area Black Tern Bog State Natural Area is a Wisconsin Department of Natural Resources-designated State Natural Area featuring 20 acres (8 ha) of quaking sphagnum bog surrounding two small seepage lakes situated in a pitted outwash plain.