The main goal of this project, to begin in August 2013, is to compare Mason’s documentation of Tepecano (1911-1912), and Southern Tepehuan (1948), dating from the 20th century, with my own research on Southeastern Tepehuan (SET), a more recent contribution to the field of endangered language documentation (2010-2011). During my staying at the American Philosophical Society Library, I will use the Mason collection there to analyze the similarities and differences found for the Tepehuan language over a period of sixty-three years.