Question: The Pahute Mesa's southeast region lies in what was formerly known as what?

Context paragraphs:
Western High Plateau: The Western High Plateau, Western Highlands or Bamenda Grassfields is a region of Cameroon characterised by high relief, cool temperatures, heavy rainfall and savanna vegetation.  The region lies along the Cameroon line and consists of mountain ranges and volcanoes made of crystalline and igneous rock.  The region borders the South Cameroon Plateau to the southeast, the Adamawa Plateau to the northeast and the Cameroon coastal plain to the south.

Kawich Range: The Kawich Range is a mountain range in Nye County in southern Nevada in the United States, just south of the Hot Creek Range.  The southern part of the range lies on the Nellis Air Force Range.  The mountains cover an area of about 250 sqmi and contain Kawich Peak, at 9399 ft above sea level.  U.S. Route 6 crosses the pass between The Kawich and the Hot Creek ranges and meets State Route 375 at Warm Springs just north of the range.  To the east lies the Reveille and Kawich valleys with the Reveille Range to the east of the northern portion and the Belted Range east of Quartzite Mountain at the southern end.  The broad Pahute Mesa and Gold Flat lie to the south with Cactus Flat and the Cactus Range to the southwest.  To the northwest across Stone Cabin Valley lies the Monitor Range.

Penstemon pahutensis: Penstemon pahutensis is a species of penstemon known by the common name Pahute Mesa beardtongue, or simply Pahute beardtongue.  It is native to the desert hills and mountains of southern Nevada, including the Pahute Mesa for which it is named.  It can also be found in a few areas over the border in California.  It is a perennial herb growing up to 35 cm tall.  The paired, narrow leaves are linear to lance-shaped and up to 10 cm long.  The inflorescence bears blue-purple flowers up to 3 cm long.  The inside of the wide mouth of the flower is lined with white or yellow hairs, and the staminode is coated in yellow hairs.

Nevada Test Site: The Nevada National Security Site (N2S2),(though the abbreviation NNSS is still used), previously the Nevada Test Site (NTS), is a United States Department of Energy reservation located in southeastern Nye County, Nevada, about 65 miles (105 km) northwest of the city of Las Vegas.  Formerly known as the Nevada Proving Grounds, the site was established on 11 January 1951 for the testing of nuclear devices, covering approximately 1,360 square miles (3,500 km) of desert and mountainous terrain.  Nuclear weapons testing at the Nevada Test Site began with a 1-kiloton-of-TNT (4.2 TJ) bomb dropped on Frenchman Flat on 27 January 1951.  Many of the iconic images of the nuclear era come from the NTS.  NNSS is operated by National Security Technologies, LLC, a joint venture of Northrop Grumman, AECOM, CH2M Hill, and Babcock & Wilcox.

Mount Lunxhëri: Mount Lunxhëri is a mountain in southern Albania in the geographical region of Southern Albanian Highlands.  Its highest elevation is 2,156 m. Its orientation is northwest to southeast.  The valley of the river Drino, with the city Gjirokastër, lies to its southwest.  The Zagori region lies to its east.  It is part of the mountain chain Shëndelli-Lunxhëri-Bureto chain, which goes parallel to the Trebeshinë-Dhembel-Nemërçkë chain.  The mount has the same name of the region of Lunxhëri.

Nochiya Region: The Nochiya Region, which is different from Nochiya (a sub-district located in the Nochiya Region), is the area which consists of five districts and many sub-districts.  The Nochiya Region lies in three countries: western Iran, northeastern Iraq and southeast Turkey.  The districts that make up parts of the Nochiya Region are Shamizdin, north eastern half of the Shaqlawa District, Soran District, Mergasur District and the western part of Urmia District.

Pahute Mesa (landform): The Pahute Mesa (landform) is a large, 60 mi long mesa in southern Nye County, Nevada.  The mesa's southeast region lies in the Nevada Test Site which is southeast; the region in the test site is called Pahute Mesa, one of the major test site sub-regions.

Turan Depression: The Turan Depression, Turan Lowland or Turanian Basin is a low-lying desert basin region stretching from southern Turkmenistan through Uzbekistan to Kazakhstan.  The lowland region lies to the east of the Caspian Sea and southeast of the Aral Sea in the vast Aral–Caspian Depression but extends to parts above sea level as well.  It is one of the largest expanses of sand in the world.  On average, the region receives less than 15 inches (381mm) of rainfall per year.  The Kara Kum desert lies at the southern portion of the Turan Lowlands.

Pahute Mesa: Pahute Mesa is one of four major nuclear test regions within the Nevada National Security Site (NNSS).  It occupies 243 sqmi in the northwest corner of the NNSS in Nevada.  The eastern section is known as Area 19 and the western section as Area 20.

Cactus Range: The Cactus Range is a small mountain range in Nye County, Nevada.  The range lies southwest of Cactus Flat and north of Pahute Mesa.  Goldfield lies 23 mi to the west in Esmeralda County.  The range lies within the restricted area of the Tonopah Test Range.

Supporting paragraphs: Pahute Mesa (landform) Nevada Test Site
Answer: Nevada Proving Grounds