The Napa River watershed encompasses 426 square miles of mountains and creeks draining into the broad Napa Valley and south into northern San Francisco Bay. The eastern mountains are much drier than the western side of the valley. Blue oaks, one of the most drought-tolerant of all California oaks, cover the rolling eastern hills. Coniferous forest blankets the wetter western ridges.
We have divided the Napa River watershed into upper, middle, and lower areas.