Ordos Plateau  The Ordos Plateau or the Ordos is the land enclosed by the Ordos Loop, a large rectangular bend of the Yellow River in northern China. The Great Wall of China cuts across the center, roughly separating the sparsely populated north—considered the Ordos proper—from the agricultural south, known as the Loess Plateau. The Wei River valley, which cuts horizontally across the south of the loop, was one of the cradles of Chinese civilization and remains densely populated, including Xi'an, which long served as the capital of China. The Ordos Desert in the north is administered by Inner Mongolia. The area is of high archaeological interest. Skeletal remains and artifacts show the Ordosian culture occupied the area in the Upper Paleolithic. The late Neolithic saw the development or introduction of the Zhukaigou culture, which was followed by the iron-wielding Ordos culture. The Yellow River flows from its source in the Sanjiangyuan National Nature Reserve on the Tibetan Plateau in a roughly eastern course before turning northwest after its confluence with the Bai He ("White River") in Maqu County, Gansu. After reversing course back towards the east, it begins the massive Ordos Loop by turning northwards at Zhongning County in Ningxia. It runs northwards about , leaving the Loess Plateau—whose eroded silt produces the river's yellow color—for the Ordos proper before turning east in Inner Mongolia. It continues this course for about before Shaanxi's Lüliang Mountains force it sharply southwards. The eastern side of the loop runs about , reëntering the Loess Plateau before reaching its confluence with the Wei River at Tongguan in Shaanxi and again turning sharply eastward. It then flows through Henan's Hangu Pass to enter the North China Plain. The Wei River largely forms a southern side of the imperfect rectangle formed by these curves of the Yellow River, flowing about through the Loess Plateau from a source not far from its southwestern corner to a confluence at the southeastern corner. The Qin Mountains—including the famous Mount Hua—separate its watershed from that of the Han River, which flows south to a confluence with the Yangtze at Wuhan. Underlying the loess plateau is one of the largest coal beds in China. Rainfall and therefore population decreases rapidly as one moves north. The Wei River valley on the south is densely populated and is one of the ancient centers of Chinese civilization.