The Trans-Himalayan region refers to the area north of the Himalayan ranges, including the Tibetan Plateau. Rivers like Sutlej, Indus (Sindh), and Brahmaputra originate in this region (near Mansarovar/Kailash). The Ganga, however, originates from the Gangotri glacier in the Greater Himalayas (Garhwal region), not in the Trans-Himalayan zone.