I recommend clicking "search inside this book" for a closeup on the ancestral ranges of the Tribes and then "first pages" for what is excellent contemporary scholarship.
Karuk was once considered Hokan but is now classified as a language isolate.
The adjacent Hupa and Yurok Tribes originally spoke languages in the Athabascan and Alaquonkin (sp?) linguistic families and came after the Karuk but adopted Karuk spiritual and material cultures. Some native speakers survived until relatively recent times and there are dictionaries / lexicons recorded by cataloguing anthropologists.
Edit to add:
Now You're Speaking Karuk! (Arar'ahih - the People's Language)