The Nadigangri Group of the Geladandong area in the source region of Yangtze River is composed of basic and intermediate-felsic volcanic rocks and/or volcaniclastic-sedimentary rocks.  It is separated from the overlying Middle Jurassic Quemocuo Group by an angular unconformity, and is underlain conformably by the Late Triassic Bagong Group. U-Pb isotopic geochronologic analysis yielded an age of (212 ± 1.7) Ma. The Naganri Group is considered to be late Norian and Rhaetian, and the Norangri volcanic rocks are interpreted to have formed through arc magmatism triggered by southward subduction of Lazhulong-Jingshajiang ocean crust.