The Costanoan languages are considered by most linguists to be part of the Penutian family
of languages, most closely related to Miwok.
There were once several distinct Costanoan languages, including Mutsun, Rumsen, Karkin, and Cholon.
These languages were as different from one another as the Romance languages of Europe (French, Spanish, Italian, and Portuguese.)
Language loss in California has been especially severe--the legacy of the Gold Rush days, in which massacres
and Indian slavery, while technically illegal, were not actively discouraged--and none of the Costanoan languages has been spoken in more than fifty years.
However, some Ohlone Indian people are working to revive their ancestral language again.