Thewo Tibetan is a Tibetic language of China spoken along the Bailong River in Northern Sichuan Province and Southern Gansu Province. Although typically listed as a dialect of Choni Tibetan (ISO 639-3 cda), Thewo is reported to have a high degree of internal variation (Renzengwangmu 2013). The goal of this paper is to examine whether or not this internal variation can be explained in part by Chamberlain’s (2015) hypothesis of linguistic watersheds. Chamberlain (2015) argues that the distribution of watersheds on the Qinghai-Tibet Plateau provides a spatial model through which we can predict the geographical spread of language variation. This paper’s research reveals some spatial correlation between the distribution of the watersheds and dialectal variation in the Thewo speaking region of Diebu County. These results can neither disprove Chamberlain’s hypothesis nor fully explain the spatial distribution of language variation in Thewo Tibetan. However, the results do demonstrate how watersheds could be a useful model for predicting the location of language documentation needs on the Qinghai-Tibet Plateau.