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.
Most tributary creeks in the Napa River watershed form alluvial fans where they exit mountainous canyons and spread out onto the valley floor.
Alluvial fans are typically composed of cobble, gravel, and sand deposited in a cone-shaped or fan formation when streamflow exits the canyon, slows down, and spreads out onto the valley floor.
Alluvial fans have multiple-thread channel systems which can rapidly fill or erode in storms. Water percolates rapidly through the porous rock and sand; connected surface flow may be limited to short periods.
Percolated water exits the base of the fan where fine sediments typically deposit and create wetland and lake habitats.
In the Napa drainage, alluvial fans had oak savannah vegetation: live and valley oaks widely dispersed over a grassland cover. This pattern of alluvial fans and wetlands dominated the Napa Valley prior to development. Currently most of the fans have a single-thread channel which has been created to maintain a single location for the streamflow and to allow the fan to be farmed. As storms deposit cobble and gravel in this single channel, floods may occur and require removal of the deposited material.
The Napa River, like the Russian River, has entrenched or downcut into its floodplain or valley. The causes of the entrenchment are numerous. Four large municipal on-stream reservoirs impound water and sediment, creating an imbalance downstream.
Zinfandel Lane bridge shows the effect of river channel entrenchment. The bridge piers show the original position of the riverbed.
The river replaces the impounded sediment by eroding the bed and banks of its channel and deepening the channel.
In addition, the Napa River historically had a multi-thread channel system distributed over its floodplain. As the floodplain was developed, many of these channels were modified, and in most locations the Napa River now has a single channel, instead of 3-6 separate channels. Confining a majority of flood flows to one channel results in erosion of the channel. Other causes of the river's entrenchment include gravel mining, channel clearing and straightening, urbanization, construction of agricultural reservoirs on tributaries, and construction of levees along the river channel.
Despite all of these changes, the Napa River supports a variety of wildlife species: migratory and resident songbirds, wading birds, and raptors; many species of reptiles and amphibians; small mammals such as meadow voles and larger species such as raccoons and river otters. A run of Chinook salmon inhabits the river and steelhead trout use both the river and tributary creeks.
Native Americans of three tribes—Patwin, Coast Miwok, and Wappo—lived in the Napa Valley for thousands of years. The first Spanish settlement in the region was the Mission in San Francisco, founded in 1776. The Native Americans were forcibly relocated from their villages to the missions, and thousands died from European illnesses.
In 1822, the Mexican government took over California and divided Napa into 12 ranchos. Cattle ranching and wheat growing were the primary land uses. General Mariano Vallejo was the Mexican military commander and major landowner near Petaluma. Nathan Coombs, who arrived in 1842. Coombs purchased property from the rancho owners and established the town of Napa in 1847 where Napa Creek and Napa River meet.
With statehood in 1849, Napa became an early supplier of food to miners of the Gold Rush, as goods could be readily moved by water from Napa to the Sierra foothills. Grain, meat, eggs, prunes, and other foodstuffs were exported. Quicksilver mining in the northeast corner of the watershed was also a major industry from the 1880s.
During the 1870s and 1880s, Napa had a number of mineral and hot springs resorts which drew tourists to the valley. Visitors would travel by ferry, railroad, and stage. These resorts included the hot springs of Calistoga at the terminus of the rail and stage lines as well as the White Sulphur Springs and Napa Soda Springs. Beyond Napa, visitors could take the stage to the geysers.
Joseph Schram planted the first hillside vineyard in 1852. The first wineries to be established in the Napa Valley were Charles Krug in 1861, Beringer Brothers in 1876, Inglenook in 1879, and Christian Brothers in 1882. These and other wineries survived Prohibition and have contributed to the recognition of Napa Valley as a premier wine region.