dissected upland of complex geologic structure in north-central Laos. The plateau constitutes a western extension of the northern Annamite Chain; it is drained principally by the Ngum and Ngiap (Nhiêp) rivers to the south and the Khan River to the north, all of which are Mekong River tributaries. Once the upland's limestone and sandstone hills were covered with tropical monsoon rain forest, but shifting cultivation practiced by mountain Hmong (Miao, or Meo) and Lao-Theung (Mon-Khmer) peoples have left only scattered remnants of oak and pine, principally along the stream courses. Around Xiangkhoang town are workable deposits of alluvial gold, antimony, copper, lead, zinc, and silver.