Gushri Khan's Tartars take Shigatse fortress
Editorial contextDas summarises Sumpa's account of how the Khoshut Mongol ruler Gushri Khan invaded Tibet, besieged the fortress of Samdruptse (Shigatse), took thirteen district forts and captured the king of Tsang, who was thrown into the Tsangpo river. Gushri was then proclaimed king of all Tibet and handed religious authority to the Dalai Lama's church. The 'Tartars' here are Oirat Mongols from Kokonor.
The seige of Sam-dub-tse (now fort Shi-ga-tse) by the Tartars and the capture of thirteen Jong by them under the lead of Gucri Khan … The king of Tsang surrendered himself. He was thrown into the river Tsang-po
About Khoshut Mongols ('Tartars') under Gushri Khan
Keep in mind
Das adds that the king was packed into something before being drowned, but that word is garbled in the OCR.