The territory covered by the present treatise is that laying between the Coast range and the sea from San Francisco to the northern boundary of the state. Those languages sketched are, in order from south to north, Miwok, Pomo, Yuki, Wiyot, Yurok, Karok. It must be clearly understood that while languages may be spoken of, it is really linguistic families that are dealt with. Where several languages are unquestionably kindred, one of the group has been selected for grammatical investigation.
Thus the Pomo family comprises seven dialects or languages, as evinced by comparison of the vocabularies. As a comparative grammatical study of seven languages is a larger task than was feasible for a preliminary investigation, the Eastern dialect has been chosen to represent the six others, which it undoubtedly does approximately typify in all essentials. In the same way the descriptions of Yuki and Miwok apply each primarily to one language selected from several constituting the family. So far everything shows that kindred languages in California are very similar in structure, however much they differ in a large proportion of their vocabulary (from the introduction)