a mountain massif in northwestern Vietnam; part of the Hoang Lien Son Range. The massif rises to a maximum elevation of 3,143 m. It is composed primarily of quartzites, granites, and gneisses. The steep slopes are deeply cut by gorges, and the crests are pointed. The slopes have evergreen forests and, above 1,700–1,800 m, deciduous and coniferous forests.