Ulan Moron in the context of "Tongtian River"

The Tanggula (Chinese: 唐古拉山, p Tánggǔlāshān, or 唐古拉山脉, p Tánggǔlāshānmài), Tangla, Tanglha, or Dangla Mountains (Tibetan: གདང་ལ་།, w Gdang La, z Dang La) is a mountain range in the central part of the Qinghai-Tibet Plateau in Tibet. Administratively, the range is in the Nagqu Prefecture of the Tibet Autonomous Region, with the central section extending into the Tanggula Town and the eastern section entering the Yushu Tibetan Autonomous Prefecture of Qinghai province.

Tanggula is the source of the Ulan Moron and Dam Qu Rivers, the geographic headwaters of the Yangtze River. It functions as a dividing range between the basin of the Yangtze in the north and the endorheic basin of northeastern Tibet in the south.

The Dangqu, Dam Qu (Chinese: 当曲, p Dāngqū) or Dam Chu (Tibetan: འདམ་ཆུ, w 'Dam Chu, lit. "Marshy River") is the longest source of the Yangtze River, with a total length of 365.7 km (227.2 mi) located in the Qinghai province of the People's Republic of China. It runs from its source in an eastern offshoot of the Tanggula Mountains (唐古拉山), receives its main tributary the Buqu-Gar Qu River (布曲), and has a confluence with the Ulan Moron, where the Tongtian River is formed. The Dangqu has been discovered to be the actual and the longest headwater of the Yangtze River under modern criteria, although the nearby Ulan Moron or Tuotuo was traditionally regarded as the primary river of the two.