In the past twenty years, previously borderless valleys and mountains on the Tibetan Plateau have been carved up into small plots of private land, which have made herding and subsistence farming increasingly difficult. As a result, many rural Tibetans are moving to cities both large (like Beijing and Chengdu) and small (like Yushu) in search of work. In fact, the rate of urbanization in China is so high that the exodus has been recognized by the World Bank as one of the largest rural-to-urban migrations in human history.