After earning her Ph.D., Zhang joined the faculty of environmental archeology at Lanzhou University. Zhang changed her research direction from the Loess Plateau to the Tibetan Plateau and began to study the Xiahe mandible, together with her former advisor Chen Fahu. The Xiahe mandible is a fossilized jawbone found in 1980 by a monk in the Baishiya Karst Cave, which is located in Xiahe County on the northeastern edge of the Tibetan Plateau, from the Denisova Cave where the only other known Denisovan remains have been found. It was donated to Lanzhou University. According to Zhang, the mandible was so weird that Lanzhou researchers could not classify it, and it was overlooked for thirty years.