Course
The Napa River rises in northwestern Napa County just south of the summit of Mt. St. Helena in the Mayacamas Mountains of the California Coast Ranges. The source begins as seasonal Kimball Canyon Creek in Robert Louis Stevenson State Park at an elevation of 3,745 feet (1,141 m) which descends the southern slope of Mt. St. Helena to Kimball Canyon Dam. It flows south for 4 miles (6 km), entering the head of the slender Napa Valley north of Calistoga. In the valley, it flows southeast past Calistoga, St Helena, Rutherford, Oakville and through Napa, its head of navigation. Downstream from Napa, it forms a tidal estuary, entering Mare Island Strait, a narrow channel on the north end of San Pablo Bay. It discharges into San Pablo Bay through the Napa Sonoma Marsh.
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