evidence: The word pamir in the language of the region denotes the high undulating grasslands of the eastern portion of the mountains, especially where they abut Afghanistan and China. Deep river valleys mark the boundaries of the Pamirs in the north beyond the ridges of the Trans-Alai Range, and the valleys of the Vākhān region (Wakhan Corridor) of Afghanistan form the southern limit. The Sarykol pamir in the Uygur Autonomous Region of Xinjiang in western China bounds the eastern margin, and a series of southwestern-aligned valleys that eventually drain into the Vakhsh and Panj rivers serrate the western boundary. The Pamirs are a combination of east-west and north-south ranges, with the former predominating. The east-west Trans-Alai Range, which forms the northern frame of the Pamirs, falls steeply to the intermontane Alai Valley. The high central part of the Trans-Alai, between the Tersagar Pass on the west and Kyzylart on the east, averages between 19,000 and 20,000 feet (5,800 and 6,100 metres), reaching its highest point at Lenin (Ibn Sīnā) Peak, 23,405 feet (7,134 metres). South from the Trans-Alai extend three north-south ranges. Of these the western, the Akademii (Akademiya) Nauk Range, and the central, Zulumart, are relatively short; the eastern, the Sarykol Range, forms the border between Tajikistan and China. The mountains east of the Sarykol Range are sometimes called the Chinese Pamirs.