evidence: Bhutan’s northern and western boundary with the Tibet Autonomous Region (part of China), although undefined, generally follows the crest of the Great Himalayas. In the Duars Plain to the south of the Himalayan range lies Bhutan’s boundary with the Indian states of West Bengal and Assam. Bhutan borders the Indian states of Arunachal Pradesh to the east and Sikkim to the southwest. [...] Bhutan’s mountainous territory is dissected by numerous rivers. The main rivers from west to east are the Torsa (Amo), Wong (Raidak), Sankosh (Mo), and Manas. All the rivers flow southward from the Great Himalayas and join the Brahmaputra River in India.