The exercise is complicated by the fact that populations in borderland areas are often mixed within a single county, although segregation might still remain very distinct. For instance, in Xunhua Salar Autonomous County of the Haidong District in Qinghai, the birthplace of the 10th Panchen Lama, Tibetans account for about one-fifth of the population. However, this Tibetan population remains very homogeneous in the higher-altitude townships of the county to this day, while Salar Muslims dominate the lower-altitude townships and towns, and this pattern of segregation pre-dates the twentieth century.