High Quality Content by WIKIPEDIA articles! The Bay Miwok were a cultural and linguistic group of Miwok, a Native American people in Northern California who lived in Contra Costa County. They joined the Franciscan mission system during the early nineteenth century, suffered a devastating population decline, and lost their language as they intermarried with other native California ethnic groups and learned the Spanish language. The Bay Miwok were not recognized by modern anthropologists or linguists until the mid-twentieth century. In fact, A.L. Kroeber, father of California anthropology, who knew of one of their constituent local groups, the Saclan (his Saklan), from nineteenth century manuscript sources, presumed that they spoke a Ohlone (aka Costanoan) language. In 1955 linguist Madison Beeler recognized an 1821 vocabulary taken from a Saclan man at Mission San Francisco as representative of a Miwok language. The language was christened Bay Miwok and its territorial extent was rediscovered during the 1960s (see Landholding Groups or Local Tribes section below).