He was with the initial group of Dominican missionaries who took over responsibility for the Baja California missions in 1773 from the Franciscans, who in turn had replaced the expelled Jesuits in 1768.
Sales wrote three letters to an anonymous friend in Valencia while he was serving at San Miguel and during his voyage home.
The first provided a brief geographical description of the peninsula and then discussed in detail the customs and character of the Indians on its northwestern frontier, particularly regarding the Kiliwa and Paipai.
The second letter continued the discussion of ethnography and related the history of Spanish involvement, including a lengthy digression on the Nootka Crisis.
Sales' view of the native peoples was often strongly negative, recalling the acerbity of the Jesuit Johann Jakob Baegert.