The Pomo were bordered on the north by the three Yukian groups—Coast Yuki, Yuki, Huchnom—on the northeast by the Patwin, on the southeast by the Wappo and Lake Miwok, and on the south by the Coast Miwok. The diversity of Languages in a compact area suggests that the Pomo have lived somewhere in their present territory, developing their unique speech forms, for a very long time, on the order of fifteen hundred years. The Salt Pomo have a legend of migrating from a place next to other Pomo across the Inner Coast Range to their present location in recent prehistoric times. If this is so, they must have already possessed a distinct language, as its divergence from the other Pomoan languages is so great as normally to have taken a millennium or so.
The destruction of the Pomo began with the founding of the San Rafael Mission in 1817 and the Sonoma Mission in 1823, with the Southern Pomo the first to be severely affected. In the Russian River and Clear Lake regions, Mexican land grants, rapid settlement, and conversion of the land to grazing and farming deprived the Indians of their former livelihood. In 1833, an epidemic, possibly cholera, took many; in 1838-1839, many more died of smallpox. From 1834 to 1847, thousands died from these causes and from Mexican military campaigns. Survivors were pressed into forced labor, both locally and, later, in distant gold mines. Two White settlers particularly abusive of the Clear Lake Indians were killed in 1849; a U.S. cavalry punitive force swept through the area, northward along the lake and westward to the Russian River valleys, massacring along the way Southeastern, Eastern, Northern, and Central Pomo, most of whom had nothing to do with the killing of the pair of men. Especially infamous was the slaughter of an innocent fishing party at a place known since as Bloody Island. In the next few years, the surviving Pomo were rounded up and forced onto the Mendocino Indian Reserve and the Round Valley Reservation (considerably north of Porno territory and mixed with non-Pomo groups). Some escaped to return to their ancestral homes, and the Mendocino Reserve was disbanded. These Indians could not renew their earlier life and became agricultural workers.
The Kashaya have a unique history among the Pomo. Their first contact with Europeans was not with Hispanic or Anglo-Americans but with Russians at the Fort Ross colony, 1811-1842. Because of their relative freedom from forced removal to missions and reservations and their isolation from the regions of densest settlement, they are now the culturally best preserved of the Pomo groups, with more speakers of their language (perhaps sixty) than all the rest of the Pomo combined.