I used to live in the Bay Area for a while, so naturally I tried to find out about its pre-colonial language group, Ohlone. This turned out to have been a set of fairly closely related dialects/languages stretching from San Francisco down beyond Monterey, plus the coast of the East Bay. Their only reasonably close relative is Miwok, another small language family spoken to its north and west, although wider relations with languages further north along the Pacific coast are likely. Among the more noteworthy features of Ohlone are regular metathesis processes - for example, the plural suffix can be either -mak or -kma, depending on whether it's preceded by a consonant or a vowel.
Dave Kaufman has just posted some interesting Ruminations on Rumsien, one of the southern dialects; or, if you speak Spanish, you can read a grammar of Mutsun, a southeastern dialect. Wikipedia has a map.